Heat transfer enhancement Research Papers (original) (raw)

2025, Thermal Engineering

Al 2 O 3 /water nanofluid flow in thermally developing region of a circular tube is the subject of present numerical study. In order to consider the hydrodynamically fully developed condition in the tube, a fully developed velocity profile is defined in the inlet section of tube. Three-dimensional computations are performed for a wide variety of nanoparticle concentrations (1 ≤ γ ≤ 10%). On the other hand, for examination of nanoparticle size, effects on the thermal characteristics, two different particle sizes of d p = 25 and 75 nm are applied. The resulting governing equations are solved numerically by means of the finite volume method. For enhanced visualization, different results are presented in thermally developing region. It is obtained that suspending the Al 2 O 3 nanoparticles in pure water increases the thermal boundary layer growing rate. In addition, an increase on the heat transfer rate is observed in thermal boundary layer using the Al 2 O 3 nanoparticles in which this enhancement varies as a function of nanoparticle size and nanoparticle volume concentration. However, it is found that the role of nanoparticle volume concentration on the thermal characteristics such as thermal boundary layer growing rate, temperature gradient, and heat transfer enhancement is significantly important comparing to the nanoparticle size.

2025, Applied Thermal Engineering

In this paper, the moment and heat transfers of a non-Newtonian fluid flowing in steady laminar regime through a circular tube with a twisted tape at constant wall temperature is studied using CFD. The effect of different twist ratios of the tape on the convective heat transfer and the pressure drop are investigated over the Reynolds number range of 0.2-600. It was found that a twisted tape induces a swirling flow, which increases the velocity gradient at the tube wall and consequently generates an enhancement in heat transfer. Data reduction is applied to CFD data; and it is found a good agreement between the calculated Reynolds and Fanning friction numbers and the theoretical relationship (f = 16/Re). A novel formulation for evaluating the thermo-hydraulic performance was developed. The results indicate that the thermo-hydraulic performance increases when the twist ratio decreases and the Reynolds number increases.

2025, Journal of Mechanical Science and Technology

The effect of winglet height on the thermal-hydraulic performance of finned tube heat exchanger (FTHE) is investigated numerically. The rectangular winglet pairs (RWPs) having 5° attack angle are placed in common flow up (CFU) manner adjacent to the tubes for analysis. The air-side performance evaluation has been done based on the area goodness factor (j/f). The working fluid (air) is considered as incompressible fluid. Additionally, MOORA (multi objective optimization on the basis of ratio analysis) method is employed to get the best performance order of various configurations by taking Nusselt number (Nu) and area goodness factor (j/f) as beneficial attributes and friction factor (f) as a non-beneficial attribute having equal significances. The present study reveals that the rectangular vortex generators having 60 % of the channel height provides the better thermal hydraulic performance compared to the other considered cases.

2025, International Journal of Exergy

This paper presents the results of an experimental investigation of transient forced convective heat transfer for turbulent flow of nine circular tubes with baffle plate inserts using different pitch to tube inlet diameter ratios and baffle orientation angles in the range of Reynolds number 3000 Re 20000 in the case of constant heat flux. The characteristic parameters of the tubes are: pitch to tube inlet diameter ratio HaD 1, 2 and 3; baffle orientation angle 45, 90 and 180 degree. Air, having a Prandtl number of 0.71 was used as the working fluid, while stainless steel was considered as the pipe material. The data show that unsteady entropy generation numbers for the baffled tubes are higher than those from the steady one. A generalised correlation for the unsteady entropy generation number relative to the steady dimensional entropy generation number for the baffle inserted tubes has been developed.

2025, International Journal of Heat and Mass Transfer

Pin fin heat exchangers represent a common, viable means of keeping components cool and are widely used for electronics cooling and turbine airfoil cooling. Advancements in manufacturing technology will allow these heat exchangers to be built using new methods, such as laser powder bed fusion, a form of additive manufacturing. New manufacturing approaches, however, render a direct comparison between newly and conventionally manufactured parts meaningless without a good understanding of the difference in the performance. This research study investigated microchannel pin fin arrays that were manufactured using Laser Powder Bed Fusion and compared them to studies of pin fin arrays from the literature, which are representative of traditionallymanufactured pin fin arrays, where the pin and endwall surfaces exhibited much lower surface roughness. Pin fin arrays with four different spacings were manufactured and tested over a range of Reynolds numbers; pressure loss and heat transfer measurements were taken. Additionally, the test coupons were evaluated nondestructively and the asbuilt geometric features were analyzed. Measured surface roughness was found to be extremely high in each one of the microchannel pin fin arrays and was found to be a function of the pin spacing in the array, as was the shape of the pin itself; with more pins in the array came higher surface roughness and more distorted pin shapes. Comparisons between the smooth pin fin arrays from literature and the rough pin fin arrays from the current study showed that the high surface roughness more strongly affected the friction factor augmentation than it did the heat transfer augmentation relative to the smooth pin fin arrays.

2025, Materials Today: Proceedings

Corrosion in refinery assets is complex which involves multi factors contributing to damage mechanisms. The present study aims to evaluate the damage mechanism which caused the heat exchanger (HEX) to leak in parallel sequence. In this sense, experiments were conducted to investigate the correlation between convective heat transfer coefficients and reveals the correlation with material degradation in the heat exchanger. Failure analysis was concluded HEX was attacked by naphthenic acid corrosion (NAC) due to sharp-edged, crater-like holes to sharp-edged streamlined grooves with corrosion product consist of sulphide. Material behaviour analysis assisted by computerized fluid dynamics (CFD) software strongly suggested that the inhibitor is not well distributed at the location of 356 mm because the velocity distribution at the specific location of the corrosive tubes was not uniform. Parallel failure initiated in the distribution of inhibitor and heat in HEX using CFD. From the results of the research, it can be concluded that the selection of material needs to be upgraded to at least 9% molybdate alloying content. CFD results reveal the optimum temperature and pressure of heat exchanger to control NAC attack as well as failure associated with the impact of stream detachment inside the bay to a few tubes. Overall results reveal the CFD method is suitable in predicting the fluid flow and thermal condition at the location of the corrosion failure in the shell tube heat exchanger. The location of corrosion can also be identified and the streamline of flow can be visualized by other materials failure analysis techniques.

2025

In this study, temperature distribution and heat flux through various fin surfaces have been investigated. Here only steady state heat transfer was discussed. The temperature distribution has been estimated by taking the assistance of finite element method. In order to do so, automatic meshing method has been used. The meshing process was done by using ANSYS meshing utility. Later these results were compared to find out the relatively more efficient fin profile. Finally, the success of this simulation based experiment was mainly dependent on the refinement of generated mesh as well as its quality. Both hexahedral and tetrahedral mesh element were utilized but considering the capability of the available device (processing unit), available time, complexity and accuracy, finally automatic method was chosen. For this experiment, flared and rectangular fin arrays were considered. Based on the variations in fin profiles, different temperature distribution as well as heat flux have been found.

2025, Heat and Mass Transfer

Cross sectional area of test section (m 2 ) C p Specific heat at constant pressure (J/kg K) D i Tube inside diameter (m) D o Tube outer diameter (m) f Friction factor, dimensionless f p Predicted friction factor, dimensionless h Convective heat transfer coefficient (W/m 2 K) h x Local convective heat transfer co-efficient (W/m 2 K) I Current [ampere] k Thermal conductivity (W/m K) L Tube length (m) ṁ Mass flow rate (kg/s) P Pitch length (m) ΔP Pressure drop along the length of the tube (N/m 2 ) Q Heat rate absorbed by the fluid (W) q Heat flux (W/m 2 ) Q tloss Total heat rate loss (W) Q t Generated total heat rate (W) Q a Actual heat rate supplied (W) T i Inlet temperature (K) T o Outlet temperature (K) T b Mean bulk temperature (K) T w Mean wall temperature (K) T bx Local bulk fluid temperature (K) T wx Local wall temperature (K) V Mean velocity in the test section (m/s) dimensionless V Mass flow flux (kg/s.m 2 ) V i Mean velocity at inlet section (m/s) V v Voltage (volt) W Wetted perimeter (m) W d Tape width (m) X Axial distance (m)

2025, International Communications in Heat and Mass Transfer

The augmentation of heat transfer for turbulent fluid flow through a tube by using double helical tape inserts was investigated experimentally in the present work. The effects of insertion of the helical tape turbulators with different helix angles (9°, 15°, 21°and 28°) on heat transfer and pressure drop in the tube for Reynolds number ranging from 22,000 to 51,000 were examined. Experimental results showed that the heat transfer and thermal performance of the inserted tube were significantly increased compared to those of the plain tube. The study showed the Nussselt number, friction factor as well as thermal enhancement efficiency were increased with decreasing helix angles under the same operating conditions. The results indicated that the Nusselt number and friction factor were increased up to 305% and 170%, respectively, than those over the plain tube while the maximum thermal performance was found to be 215% for using the double helical tape insert with helix angle 9°at high Reynolds number. Furthermore, correlations of the Nusselt number and friction factor were developed in terms of the helix angle (α), Reynolds number (Re) and Prandtl number (Pr) based on the experimental data.

2025, International Communications in Heat and Mass Transfer

In the present study, the heat transfer performance and friction factor characteristics in a circular tube fitted with twisted wire brush inserts were investigated experimentally. The twisted wire brush inserts were fabricated with four different twisted wire densities of 100, 150, 200, and 250 wires per centimeter by winding a 1 mm diameter of the copper wire over a 5 mm diameter of two twisted iron core-rods. Heat transfer and friction factor data in tubes were examined for Reynolds number ranging from 7,200 to 50,200. The results indicated that the presence of twisted wire brush inserts led to a large effect on the enhancement of heat transfer with corresponding increase in friction factor over the plain tube. The Nusselt number and friction factor of using the twisted wire brush inserts were found to be increased up to 2.15 and 2.0 times, respectively, than those over the plain tube values. Furthermore, the heat transfer performance was evaluated to assess the real benefits of using those type of inserts and the performance was achieved 1.85 times higher compared to the plain tube based on the constant blower power. Finally, correlations were developed based on the data generated from this work to predict the heat transfer, friction factor, and thermal performance factor for turbulent flow through a circular tube fitted with the twisted wire brush inserts in terms of wire density (y), Reynolds number (Re), and Prandtl number (Pr).

2025, International Communications in Heat and Mass Transfer

Influence of triple helical tapes inserted for turbulent flow through a tube on heat transfer enhancement was studied experimentally. The triple helical tapes made of mild steel with different helix angles, α = 9°, 13°, 17°, and 21°were examined for Reynolds number ranging from 22,000 to 51,000. The experiment showed that the Nusselt number, effectiveness and friction factor for the inserts were found to be up to 4.5, 3.45 and 3.0 times, respectively, over the plain tube. The highest enhancement efficiency achieved was 3.7 for the inserts based on constant blower power. Finally, new correlations for predicting heat transfer and friction factor for turbulent flow through a circular tube fitted with the inserts were proposed.

2025, Energy

Abatrart-Enhanced heat-transfer surfaces have been successfully used in the heatexchanger industry to obtain compact and low-cost units. The heat-transfer is higher than for standard surfaces and flow configurations. There are numerous ways for heat-transfer augmentation which have been marketed or tested in the laboratory. In this paper, we review major studies. Among the most promising heat-transfer enhancement techniques is the compound augmentation method, in which different enhancement techniques are used simultaneously.

2025, Progress in Computational Fluid Dynamics

The present paper deals with the Buongiorno's model for nanofluids with a novel TVD 1 Hybrid Lattice Boltzmann technique. It is well known that when the diffusion fluxes (with Dissipation behaviors) own negligible values regarding convective fluxes, almost all classical methods suffer serious instability errors. The Lattice Boltzmann method also is not an exception to this rule. In order to resolve this issue, many novel techniques and methods (e. g. MRT-LBM) are developed. Here we propose a novel TVD Hybrid LB method to solve Buongiorno's model for Al2O3-Water nanofluid in the presence of an elliptic cold obstacle. The Model naturally possesses small values of diffusion coefficients and thereby, explicit methods are not considered as primitive choices to be applied in the simulation of this model. But the TVD characteristics of the following Hybrid LB method made it a valuable asset in resolving these kinds of problems. Moreover, the heat transfer and entropy generation of a square cavity with sinusoidal temperature and concentration boundary conditions were numerically examined and different aspect ratio combinations, as well as different obstacle locations, were tested. The results indicated that for a moderate Ra number like Ra=10 5 , total entropy generation of the system and the heat transfer rate from the walls are reduced with an increment in the obstacle size. In addition, it was found that site 4 presents the highest rate of entropy generation amongst all, yet still, the average Be number is not remarkably raised for this location.

2025, Heat Transfer Engineering

The transport phenomena in microchannel are significant in designing MEMS devices. The current study investigates numerically the simultaneously developing unsteady laminar flow and heat transfer inside a twisted sinusoidal wavy microchannel. At the inlet sinusoidal varying velocity component is applied. Varying pulsating amplitude and frequency represented by the Strouhal number was studied for Reynolds numbers ranging from 1 to 100. The governing equations are solved with a finite volume based numerical method. In comparison with steady flow, it was found that imposed sinusoidal velocity at the inlet can provide improved heat transfer performance at different amplitudes and frequencies while keeping the pressure drop within acceptable limits. The friction factor, convective heat transfer coefficient and the effects of inner wall surface roughness for laminar and turbulent flow in micro tubes

2025, Applied Thermal Engineering

In the present study, the heat transfer rate through a shell and helical tube heat exchanger with alumina nanofluid as current flow was investigated and the obtained results were compared to those of the distilled water. Effects of alumina concentration in the nanofluid (0-0.5 vol.%) and the temperature of hot fluid (40-70 °C) were evaluated at different flow rates (2-3.5 L/min). Heat transfer coefficients were determined using Wilson method. The overall heat transfer rate decreased with Dean number at low Dean numbers and increased after passing through a minimum at higher dean numbers due to simultaneous and competitive effects of convective heat transfer coefficient and temperature difference on heat transfer rate. At low Dean numbers, the effect of temperature difference dominated the effect of convective heat transfer coefficient and at high Dean numbers, the convective heat transfer coefficient effect was more determining. Higher temperature of the hot fluid led to higher convective heat transfer coefficient due to increased thermal conductivity of the fluid at higher temperatures. Compared to the distilled water, higher convective heat transfer coefficient was obtained for nanofluid as the current flow at low volume fractions of the nanofluid. The maximum heat transfer rate (9505.6 W) was obtained at a volume fraction of 0.016, flow rate of 3.5 L/min, and temperature of 70 °C.

2025, International Communications in Heat and Mass Transfer

The two-dimensional flow and convective heat transfer over a rectangular bluff plate are numerically simulated with the incoming pulsating flow. For low Reynolds number, variations of the frequency and amplitude of the pulsating flow will introduce instability and force the flow to become unsteady with the formation of shedding vortices. The separation bubble is decreased and the heat transfer rate is enhanced. At moderate Reynolds number, the shedding vortices characteristic is controlled by the pulsating frequency. The optimal pulsating frequency which produces a maximum overall heat transfer rate, is found at f = 0.3 for A = 0.1. Increasing the pulsating frequency in this regime leads to a temperature concentration downstream.

2025, Fluid Dynamics & Materials Processing

This study includes an experimental and numerical analysis of the performances of a parabolic trough collector (PTC) with and without cylindrical turbulators. The PTC is designed with dimensions of 2.00 m in length and 1.00 m in width. The related reflector is made of lined sheets of aluminum, and the tubes are made of stainless steel used for the absorption of heat. They have an outer diameter of 0.051 m and a wall thickness of 0.002 m. Water, used as a heat transfer fluid (HTF), flows through the absorber tube at a mass flow rate of 0.7 kg/s. The dimensions of cylindrical turbulators are 0.04 m in length and 0.047 m in diameter. Simulations are performed using the ANSYS Fluent 2020 R2 software. The PTC performance is evaluated by comparing the experimental and numerical outcomes, namely, the outlet temperature, useful heat, and thermal efficiency for a modified tube (MT) (tube with novel cylindrical turbulators) and a plain tube (PT) (tube without novel cylindrical turbulators). According to the results, the experimental outlet temperatures recorded 63.2°C and 50.5°C for the MT and PT, respectively. The heat gain reaches 1137.5 W in the MT and 685.8 W in the PT. Compared to the PT collector, the PTC exhibited a (1.64 times) higher efficiency.

2025, International Journal of Heat and Technology

The thermal performance of a parabolic trough receiver (PTR) with hollow cylindrical inserts (HCIs) is numerically investigated. The HCIs are coupled in an axial manner and also radially joined to the interior of the PTR. Totally, eleven different internally hollow cylindrical receivers are examined and compared with the plain tube (PT). The lengths, thicknesses, and numbers of HCIs are tested at varied values, and all these tubes are examined under a constant inlet temperature of 300 K and mass flow rates in the range of 0.6-1.0 kg/s. ANSYS Fluent is the simulation software in this work. The developed model is validated with experimental correlations for PT case. The simulation findings demonstrated that the addition of HCIs may greatly enhance the uniformity of the temperature gradient between the wall of the PTR and the water. The optimum case of the HCIs has a length of 40 mm, a thickness of 2 mm, and a number of 15 inserts. This model recoded the higher ranges of Nusselt number (132-296), fraction factor (0.301-0.064), and thermal efficiency (41-79%). Also, the outlet temperatures of the PT and modified tube are increased from 300 K to 325.5 K and 339.7 K, respectively. As a result, this approach provides advantages over the utilization of interior fins, as it can be applied on the parabolic trough collector (PTC) without requiring any modifications to the PTR, which are associated with numerous operational challenges.

2025, MDPI

This study numerically investigates unsteady natural convection (NC) heat transfer (HT) and entropy generation (E gen) in trapezoidal cavities filled with two thermally stratified fluids. Both air-filled and water-filled configurations are analyzed to evaluate and compare their thermal performance under varying conditions. The cavities are characterized by a heated base, thermally stratified sloped walls, and a cooled top wall. The governing equations are numerically solved using the finite volume (FV) approach. The study considers a Prandtl number (Pr) of 0.71 for air and 7.01 for water, Rayleigh numbers (Ra) ranging from 10 3 to 5 × 10 7 , and an aspect ratio (AR) of 0.5. Flow behavior is examined through various parameters, including temperature time series (TTS), average Nusselt number (Nu), average entropy generation (E avg), average Bejan number (Be avg), and ecological coefficient of performance (ECOP). Three bifurcations are identified during the transition from steady to chaotic flow for both fluids. The first is a pitchfork bifurcation, occurring between Ra = 10 5 and 2 × 10 5 for air, and between Ra = 9 × 10 4 and 10 5 for water. The second, a Hopf bifurcation, is observed between Ra = 4.7 × 10 5 and 4.8 × 10 5 for air, and between Ra = 10 5 and 2 × 10 5 for water. The third bifurcation marks the onset of chaotic flow, occurring between Ra = 3 × 10 7 and 4 × 10 7 for air, and between Ra = 4 × 10 5 and 5 × 10 5 for water. At Ra = 10 6 , the average HT in the air-filled cavity is 85.35% higher than in the water-filled cavity, while E avg is 94.54% greater in the air-filled cavity compared to water-filled cavity. At Ra = 10 6 , the thermal performance of the cavity filled with water is 4.96% better than that of the air-filled cavity. These findings provide valuable insights for optimizing thermal systems using trapezoidal cavities and varying working fluids.

2025, American Journal of Nano Research and Applications

The presented paper reports the analysis of the flows characteristic of TiO 2 -water nanofluid flowing inside a horizontal microchannel with circular cross section area. The flow is investigated by CFD techniques using a finite volume method. A recently introduced viscosity correlation was used to model the effective viscosity of the nanofluid. A range of Re number is tested in the present study. Various temperature ranges were used as constant temperature boundary conditions. The increase of the nanoparticle volume fraction was found to increase the heat transfer rate; water showed less enhancement in heat transfer compared to the nanofluid. The increase in Re number promoted Nu number. The effect of the temperature on the effective viscosity in the channel was also reported. The change of the velocity in the entrance region was studied and discussed. The velocity gradient in the microchannel is calculated, and the results are shown and discussed.

2025, International Journal of Engineering Research and

The present study presents a three-dimensional analysis for a co-current heat exchanger with inclined baffles where Magnesium Oxide-copper Oxide-water hyper nanofluid is the cooling fluid. A recently introduced viscosity correlation was used to model the effective viscosity of the hyper nanofluid. The governing equations, continuity equation, momentum equation and energy equation were solved along with the boundary conditions by finite volume method. The aim of the study is to enhance the heat transfer rate using the hybrid nanofluid as a working fluid, enhancing the heat transfer can lead to a minimal cost. Various volume fractions were tested in the present study (0% to 4%). It was found that the heat transfer improved noticeably with the increase in the volume fraction of the hybrid nanoparticle. The heat performance was also promoted with the increase in Re number.

2025, Engineering Research Express

This study investigates thermal performance improvements in smooth duct solar air heaters (SAHs) using artificial roughness-rectangular ribs (ARRRs) with various cutoff corner (CC) designs. The goal is to optimize the thermal efficiency of SAHs by exploring different CC configurations on the absorber plate's bottom wall, while keeping other surfaces smooth. Four configurations are tested: rectangular (R) with CC = 0.0, type 1 (T1) with CC = l/6, type 2 (T2) with CC = l/3, and type 3 (T3) with CC = l/2. Parameters such as Nusselt number (Nu), thermal enhancement factor (TEF), friction factor (f), entropy generation (Sgen), and Bejan number (Be) are analyzed over a range of Reynolds numbers (Re = 4000 to 18000) and rib pitches (P = 10 to 25). Results show that ribbed SAHs significantly improve heat transfer (HT) over smooth ducts, with the T2 configuration achieving the highest thermal enhancement factor (TEF = 1.87) at a smaller rib pitch (P = 10). However, the smooth duct SAH exhibited the lowest friction and entropy generation. This study provides new insights into designing artificial roughness ribs to enhance SAH thermal performance.

2025

In many engineering applications, the relevance of heat transfer improvement has grown, and a lot of work has gone into using various ways to enhance the hydraulic thermal performance of fluids running through pipes. This study uses numerical analysis to examine the thermal performance of turbulent flow properties and heat transfer under a uniform 30000 W/m 2 heat flux in dimpled pipes. For several designs of dimpled pipes, the friction factor, heat transfer rate, and performance assessment criterion were calculated and compared with smooth pipes. The examples under consideration are within the range of 8000 to 14,000 Reynolds numbers. For this, the ANSYS Fluent 2023 R2 is employed. The governing flow equations are modeled using the Reynolds-averaged Navier-Stokes equations (RANS). To simulate turbulent flow next to the inner wall surface, the realizable k-ε turbulence model is applied with increased wall conditions. The results of the current study showed the presence of dimples on the surface of the pipe significantly enhances the rate of heat transfer represented by the Nusselt number compared to the normal smooth pipe. Also, the analyzed models indicated by the results of the numerical investigation have high average Nusselt counts, low pressure, overall performance criterion, and low average thermal resistance due to the increase in the Reynolds number. The dimpled pipe with different radii (2,3, and 4 mm) has an increased percentage of enhanced heat transfer (79.91, 86.77, and 94.47%) compared to the smooth pipe.

2025, International Journal of Hydrogen Energy

Metal hydrides can be used for a variety of applications. The thermal conductivity of metal hydride powders and the heat transfer coe cient between metal hydride powder beds and the walls of reaction beds are usually low. Heat transfer enhancement techniques have to be applied, when metal hydride powders are used. Here, expanded natural graphite/metal hydride compacts are described, possessing a high e ective thermal conductivity ( e ≈ 19 W m -1 K -1 ). Reaction kinetics of these compacts have been measured and compared to those of metal hydride beds employing Al-foams as heat transfer matrices. It was found that hydrogen absorption rates were only slightly decreased by the expanded natural graphite/metal hydride compacts, thus providing an e cient, cost-e ective and simple solution.

2025, International Journal of Hydrogen Energy

The thermal conductivity of metal hydride powders and the heat transfer coe cients between metal hydride powder beds and the walls of reaction beds are usually low. When metal hydride powders are used in practical applications, heat transfer enhancement techniques have to be generally applied. Here, expanded natural graphite/metal hydride compacts are described, possessing a high-e ective thermal conductivity. Furthermore, the heat transfer coe cient between expanded natural graphite pellets and the inner surface of the surrounding steel tube has been investigated.

2025, Experimental Thermal and Fluid Science

Experimental investigations of pool boiling from novel tubular heat transfer surfaces (structured tubes with re-entrant cavities) are carried out with the hydrocarbon propane as working fluid operating under moderate heat fluxes (<100 W/m 2 ) and saturation conditions. The heat transfer coefficients determined by thermocouple measurements are presented. The evaporation phenomena are visualized by a high speed video system and by means of digital image processing techniques (e.g. Fourier-analyses, correlationtechniques). The bubble departure diameter at the surface, the bubble generation frequency at corresponding nucleation sites and the bubble upward flow velocity are quantitatively determined. This work has been partly funded by the European Union within the frame of the JOULE programme (project no. JOE3-CT97-0061).

2025, Rodriko Atthaariq

This paper aims to understand the basic phenomena of heat transfer through forced convection mechanisms, especially in cross flow against a single cylinder. Heat transfer is a natural process that occurs from high-temperature substances to lower-temperature substances, which can take place by conduction, convection, or radiation. In the context of forced convection, the rate of heat transfer is strongly influenced by the velocity of the fluid flowing around the surface of the object. This practicum illustrates that airflow given to a high-temperature object, such as a glass filled with hot coffee, can accelerate its temperature drop compared to conditions without airflow. Through observation and measurement, data is obtained that can be used to calculate the convection heat transfer coefficient (h) and determine the Reynolds and Nusselt numbers as important parameters in thermal analysis. The results of this practicum are expected to provide a basic understanding in the application of forced convection, especially in cooling systems such as radiators and air coolers.

2025, Thermal Science

Nanofluids are colloidal mixtures of nanometric metallic or ceramic particles in a base fluid, such as water, ethylene glycol or oil. Nanofluids possess immense potential to enhance the heat transfer character of the original fluid due to improved thermal transport properties. In this article, a brief overview has been presented to address the unique features of nanofluids, such as their preparation, heat transfer mechanisms, conduction and convection heat transfer enhancement, etc. In addition, the article summarizes the experimental and theoretical work on pool boiling in nanofluids and their applications.

2025, International Journal of Innovation in Mechanical Engineering and Advanced Materials

This study presents a comprehensive Computational Fluid Dynamics (CFD) analysis of heat transfer enhancement in microchannels with varying geometries, specifically focusing on wavy microchannels with trapezoidal and rectangular cross-sections. Water is used as the working fluid, and silicon is selected as the solid wall material. A three-dimensional conjugate heat transfer model is developed by solving the steady-state Navier-Stokes and energy equations using the finite volume method in ANSYS Fluent, with the SIMPLEC algorithm employed for pressure-velocity coupling. The analysis examines the influence of cross-sectional shape and wall waviness on thermal performance, while maintaining a constant hydraulic diameter across all configurations. Eight different geometries, including straight and wavy versions of rectangular and trapezoidal cross-sections with varying top-to-bottom width ratios (0.075-0.055 mm), are evaluated over a Reynolds number range corresponding to inlet velocities of 0.5-4.0 m/s. Results show that wavy microchannels significantly enhance heat transfer compared to their straight counterparts. For instance, at 4 m/s, the Nusselt number for the wavy rectangular microchannel reaches 9.48, compared to 7.19 for the straight rectangular configuration, representing a 32% enhancement. Similarly, the wavy trapezoidal channel with a top width of 0.18 mm achieves a maximum Nusselt number of 9.25, compared to 7.19 for its straight equivalent, indicating a 29% improvement. Additionally, the Nu/Nu₀ versus Re plots reveal a consistent trend of increased heat transfer due to wall waviness across all geometries, with negligible influence from cross-sectional shape when hydraulic diameter is kept constant. The study demonstrates that incorporating wavy structures into microchannel designs significantly improves thermal performance with minimal increases in pressure drop, and that the effect is driven more by wall geometry than by cross-sectional shape. These findings provide valuable insights for the development of compact and efficient microchannel heat sinks for electronic cooling applications.

2025, Journal of Thermal Analysis and Calorimetry

A numerical analysis is performed to investigate the thermal performance of turbulent fluid flow and heat transfer through a circular tube equipped with curved twisted tapes. The considered geometrical parameters are the pitch ratio, height and curvature of the curved twisted tape. Three-dimensional simulations are validated by experimental data available in the literature. The governing equations of turbulent flow are solved by using kε model for range of Reynolds number between 2500 and 20,000. Due to swirl flow, the effect of two regions, including near wall region and core region, on heat transfer and pressure drop are discussed. The presence of curved profile twisted tape leads to better heat transfer rate. The results show that case with height of curved twisted tape equal to 7 mm has around 35% higher thermal performance than the base case. Also, case with height of curved twisted tape equal to 5 mm has 30% higher thermal performance than the base case. Cases with pitch ratio between 5 and 15 have better thermal performance than normal pipe, but generally case with pitch ratio equal to unity has lower average thermal performance than the normal pipe. The maximum and minimum thermal performance improvement belongs to pitch ratio equal to 5 at Re = 10,000 (around 26%) and pitch ratio equal to unity at Re = 2500 (-14%). The maximum and minimum thermal performance belongs to curve of curved twisted tape equal to 5 mm and 1.5 mm with 28% (at Re = 20,000) and -4% (at Re = 2500), respectively.

2025

This study explores the Fluid-Structure Interaction (FSI) and heat transfer dynamics in a wavy L-shaped enclosure with a flexible baffle simulated using COMSOL Multiphysics. The analysis focuses on the maximum von Mises stress, streamlines, isotherms, mean Nusselt number, and scaled temperature under varying elasticity modulus (1 GPa ≤ E ≤ 50 GPa), Rayleigh number (10 3 ≤ Ra ≤ 10 6), baffle length (0.05 m ≤ B ≤ 0.25 m), and Prandtl number (0.71 ≤ Pr ≤ 13.2). The results demonstrate that the presence of a flexible baffle within the wavy L-shaped enclosure significantly alters fluid dynamics and heat transfer characteristics. The baffle acts as an obstruction, disrupting natural convection currents, yet its flexibility enables it to conform to fluid motion, thereby reducing drag while maintaining an extended surface area crucial for efficient heat transfer. Comparative analyses reveal that the inclusion of the baffle enhances heat transfer rates by approximately 74.9 % and 82.5 % for Rayleigh numbers of 10 5 and 10 6 , respectively, by optimizing flow dynamics and improving heat exchange efficiency. Furthermore, increasing the Rayleigh and Prandtl numbers enhances heat transfer efficiency, with mean Nusselt numbers increasing by up to 60 % for higher parameter values. Longer baffle lengths improve heat transfer but result in increased mechanical stress, with the maximum von Mises stress rising by up to 45 % when B = 0.25 m. These findings underscore the importance of optimizing material properties and geometric configurations to balance thermal performance and structural integrity in fluid-structure interaction applications.

2025, WSEAS TRANSACTIONS ON HEAT AND MASS TRANSFER

The numerical study on the improvement of the cooling of a microprocessor by the use of Nanofluids has been made. Natural convection is analyzed in a box fence with a temperature source encountered at its lower border and loaded with an Ethylene Glycol-Copper nanoparticle. This article explores the influences of relevant aspects such as thermal Rayleigh number, solid volume fraction, and enclosure dimensions on the thermal efficacy of the box fence, which are enhanced with an enlargement in thermal Rayleigh number and solid volume fraction. The results also illustrate that the change of the warmth transfer rate concerning the box dimensions of the enclosure is unlike at inferior and elevated thermal Rayleigh numbers. A simile is offered between the upshots got and the literature. Results were presented in terms of heat transfer rate depending on thermal Rayleigh number (Rat = 10^3 , and 10^6 ), nanoparticle solid volume fraction (0 ≤ φ < 5%), and box dimensions. The results show ...

2025, Chemical Engineering and Processing - Process Intensification

 A novel semi-active microchannel is designed to gain a better convective heat transfer.  Using magnetic nanoparticles (MNPs) and rotating magnetic field (RMF) as an effective method for heat transfer enhancement.  The influence of RMF on improvement of heat transfer characteristics compared with those results by static magnetic field (SMF).  RMF shows higher enhancement effect on average heat transfer coefficient (have) compared to SMF.  In RMF, the effect of rotational speed (ω) of magnet is investigated and an optional value is proposed.

2025, Journal of Engineering

Heat transfer around a flat plate fin integrated with piezoelectric actuator used as oscillated fin in laminar flow has been studied experimentally utilizing thermal image camera. This study is performedfor fixed and oscillated single and triple fins. Different substrate-fin models have been tested, using fins of (35mm and 50mm) height, two sets of triple fins of (3mm and 6mm) spacing and three frequenciesapplied to piezoelectric actuator (5, 30 and 50HZ). All tests are carried out for (0.5 m/s and 3m/s) in subsonic open type wind tunnel to evaluate temperature distribution, local and average Nusselt number (Nu) along the fin. It is observed, that the heat transfer enhancement with oscillation is significant compared to without oscillation for low air inlet velocity. Higher thermal performance of triple fins is obtained compared to the single rectangular fin, also triple fins with (height=50mm and finspacing=3mm) gives better enhancement as compared to other cases. This work shows t...

2025

Article history: Received 11 November 2018 Received in revised form 21 February 2019 Accepted 13 March 2019 Available online 13 April 2019 This paper reports the recent researches of carbon nanotube application in solar collectors. The efficiency of different stationary solar collectors (Flat plate collector FPC, Evacuated tube solar collector ETSC and Direct absorber solar collector DASC) was found to improve with the use of single wall carbon nanotube (SWCNT) and multiwall carbon nanotube (MWCNT) respectively. From literatures many comparisons were reported with other nanoparticles, it has shown that carbon nanotube display higher thermal conductivity compared to other solid nanoparticles. Effect of thermal conductivity, stability and production cost of SWCNT and MWCNT was thoroughly reviewed and investigated for application in stationary solar collectors.

2025, Investigation of solar air heater optimization with spherical Rib

One clean and environmentally beneficial energy source is solar power. Transparent collector solar air heaters (SAH) are a prime example of the technology currently being researched for use in warming homes and offices. Spherical ribs with three groups of diameters (2, 2.5, and 3 mm) and a relative pitch P/e = 12 for each one. Heat flux from solar energy is 1000 W/m2 for both shapes if a smooth absorbent plate and roughened rib are used. The flow rate at the inlet is determined from the range of values for the Reynolds number (5000-15000). A k-ɛ turbulence model and ANSYS Fluent have been used for the numerical simulation. The Nusselt number, friction factor, and heat transfer coefficient values have all been determined. The velocity vector and temperature contour give the flow behavior inside the collector. For the Reynolds number range of 5000-15000, the thermohydraulic factor performance (THPF) can be enhanced up to 2.3. Including spherical ribs across the absorber plate improves the SAH's thermal performance. The suggested artificially roughened surface is advantageous for low domain Reynolds numbers because the maximum enhancement of the THPF value has been found in a region of low Reynolds numbers.

2025, Zenodo (CERN European Organization for Nuclear Research)

Due to the higher requirement for energy in recent times, the most important industry for power generation is the thermal power plant. Due to the higher requirement of heat transfer without any loss from one fluid to another fluid counter-flow heat exchangers play a very important role. In past decades, many researchers attempted to find an effective way to increase the transfer rate from one fluid to another. In this study, we are more focused toward increase the heat transfer rate in the counter-flow heat exchanger (CFHX). In addition, the summary is provided information related to the increased heat transfer rate in counter flow HX.

2025, Thermal Science

In this investigation, deionized water was used as base fluid. Two different types of nanoparticles, namely Al2O3 and Cu were used with 0.251% and 0.11% volumetric concentrations in the base fluid, respectively. Nanofluids cooling rate for flat heat sink used to cool a microprocessor was observed and compared with the cooling rate of pure water. An equivalent microprocessor heat generator i. e. a heated Cu cylinder was used for controlled experimentation. Two surface heaters, each of 130 W power, were responsible for heat generation. The experiment was performed at the flow rates of 0.45, 0.55, 0.65, 0.75, and 0.85 liter per minute. The main focus of this research was to minimize the base temperature and to increase the overall heat transfer coefficient. The lowest base temperature achieved was 79.45 oC by Al2O3 nanofluid at Reynolds number of 751. Although, Al2O3-water nanofluid showed superior performance in overall heat transfer coefficient enhancement and thermal resistance redu...

2025, Energy engineering

Heat augmentation techniques play a vital role in the heating and cooling processes in industries, including solar collectors and many applications that utilize heat exchangers. Several studies are based on inserting fillers inside the tubes to enhance heat transfer. This investigation considered the effects of twisted tapes with large holes on a tubular heat exchanger's (HX) heat transmission, pressure drop, and thermal boosting factor. In the experimental section, counter-swirl flow generators used twisted tapes with pairs of 1.0 cm-diameter holes and changes in porosity (R p ) at 1.30% and 2.70%. In the experiments, air was utilized as a working fluid in a tube with a circular cross-section. The turbulent flow was considered, with Reynolds numbers (Re) domain from 4800 to 9500, and a boundary condition with a uniform wall heat flux was constructed. The findings expound that when the number of holes rose, the Nusselt number (Nu), the factor of friction (f ), and the thermal enhancement factor (η) all increased as well. Additionally, as the friction factor increased, the Nusselt number of the tape-equipped tube was noticeably higher. Additionally, it was discovered that the friction factor was between 70% and 94% lower than the values of the tube without tape, while the (Nu) was between 87% and 97% higher than the conventional tube values. The maximum value of η is 89%. According to the experimental results, empirical correlations for Nu, f, and η were also generated.

2025, Elsevier

The thermal conductivity of nanofluid has been measured using an ultrasonic interferometer with the help of Bridgman's equation. Due to the strong dependency of the thermal conductivity of nanofluid on base fluid, we have taken different combinations of water and ethylene glycol. An equal proportion of both fluids gives the highest thermal conductivity. The thermal conductivity of nanofluid with concentrations of 0.05%, 0.1%, and 0.2% have been measured within the temperature range of 30 O C to 80 O C. Measured thermal conductivity of the prepared nanofluids is increased up to 288% (CuO), 272% (MgO), and 234% (Fe 2 O 3) and found better increment in comparison to the results reported by earlier researchers. Observed increment in the thermal conductivity of metal oxide nanofluids can be explained on the basis of static and dynamic parameters of the nanofluid. The high thermal conductivity of such nanofluids suggests it as a potential candidate for systems where heat transfer is required.

2025

As a result of significant scaling challenges and complex engineering, there has been considerable academic interest in recent years in the use of porous materials to improve forced convection heat transfer. The current work involves computational fluid dynamics (CFD) numerical simulation using three types of porous material (glass, steel and ceramics) with different diameters (0.004, 0.006 and 0.005 m), respectively to optimize heat transfer for a concentric single-tube heat exchanger with a length (1 m) and a diameter (0.03 m) exposed uniform heat flux on the outer wall (60kW/m 2). The governing equations of steady singlephase turbulent flow were solved using the commercial program (Ansys Fluent) for the Reynolds number range (10000-19000). Under the same operating conditions, the four cases of the heat exchanger tests were carried out, namely the three cases of the porous medium plus the exchanger without the porous medium. The numerical results showed the heat transfer rate (Nusselt number) improved by (92.563%) when using the porous material ceramic type compared to the empty pipe, while using the porous material (glass and steel) percentage increased (91.44 and 87.86%), respectively. Moreover, the friction factor may be affected by the inclusion of the porous material, and by increasing the Reynolds number gradually decreases. The current study proposes the inclusion of nanomaterials as a composite technology with porous material to improve the heat transfer properties and the flow of various fluids through the heat pipe.

2025

Increasing electronic product manufacturing volumes and cooling requirements necessitate the use of new materials and innovative techniques to meet the thermal management challenges and to contribute towards sustainable development in the electronic industry. Thermally conductive polymer composites, using high thermal conductivity fillers such as carbon fibers, are becoming commercially available and provide favorable attributes for electronic heat sinks, such as low density and fabrication energy requirements. These polymer composites are inherently anisotropic but can be designed to provide high thermal conductivity values in particular directions to address application-specific thermal requirements. This Thesis presents a systematic approach to the characterization, analysis, design, and optimization of orthotropic polymer composite fins used in electronic heat sinks. of thermally conductive Poly-Phenylene Sulphide composites are used to determine the significant directional thermal conductivity in such composites. An axisymmetric orthotropic thermal conductivity pin fin equation is derived to study the orthotropic thermal conductivity effects on pin fin heat transfer rate and temperature distribution. FEM simulation and water cooled experiments, focusing on the radial temperature variations in single pin fins, are used to validate the analytical model. Theoretical models, CFD modeling, and experiments are used to characterize the thermal performance of heat sinks, fabricated of PPS composite pin fins, in air natural convection and forced convection modes. Simplified solutions, for the orthotropic fin It has been a privilege to work closely with Professor Avram Bar-Cohen. I would like to sincerely thank him for providing direction and support that enabled me complete this important milestone in my life. His passion for creative research is a constant source of inspiration. My research work is built on the solid foundation of several previous researchers. Most significantly among them is Dr. Allan Kraus whose least material optimization is the principal inspiring element in this work. Dr. Madhu Iyengar's previous research work under Professor Avram Bar-Cohen, on resource constrained optimization of heat sinks, provides a foundation for this work. I would like to thank Dr. Peter Rodgers for helping me with the Laser Flash test facility and for his insightful suggestions and guidance in writing this thesis report. My sincere thanks to Professor Gregory Jackson for letting me use his TGA facility. Thanks to Professor Michael Ohadi for providing me opportunity to present my work in several consortium meetings. Thanks to CALCE center for extending its resources including laser flash test facility and ESEM. Special thanks to Sony Corporation for funding initial phase of my research activities. Thanks to Coolpolymer Inc for generously providing samples of their thermally conductive Poly-Phenylene composite. Many thank to Dr. Gary Solbrekken for his help in the initial hardware instrumentation.

2025

A three-dimensional numerical analysis has been performed to investigate the thermohydraulic performance of innovative designs of double-layer microchannel heat sinks (DL-MCHS). The conventional DL-MCHS design has been altered by integrating intermediate fins with rectangular and sinusoidal shapes, the latter featuring varying amplitudes (A) and wave numbers (t). These fins are strategically placed along the flow paths within the channel. A comparative evaluation of heat transfer efficiency and pressure drop characteristics between the traditional and modified DL-MCHS designs has been conducted for Reynolds numbers ranging from 100 to 400, and heat flux levels between 500 and 2000 kW/m 2. Single-phase liquid water serves as the cooling medium. The results indicate that the modified designs can enhance heat dissipation by 50-70 % compared to the conventional DL-MCHS. But owing to higher obstructions encountered by coolant in the flow passage, pressure drop penalty also increases in such configurations. Among all the analyzed configurations, the modified DL-MCHS incorporating sinusoidal intermediate fins with an amplitude (A) of 10 μm and a wave number (t) of 5 mm-1 demonstrated consistently better thermal performance, achieving approximately 5-10 % higher thermal performance factor compared to the conventional DL-MCHS. Flow visualization of the coolant indicates that the presence of sinusoidal fins promotes improved fluid mixing, which in turn enhances heat transfer. Furthermore, a time-efficient optimization study on DL-MCHS with sinusoidal intermediate fin discloses that heat sink with A = 10 μm, and t = 15.303 mm-1 achieves average Nusselt number (Nu‾) ≈ 60-70 % higher than the conventional DL-MCHS.

2025, Applied Thermal Engineering

< We develop a method for designing an effective finned heat exchanger. < This new design characterize by smaller dimensions of the heat exchanger. < The tubes bend in a zigzag shape. Consequently, the fin block forms a zigzag shape. <... more

2025, International Journal of Heat and Technology

This work investigates the potential of hybrid nanoparticles suspended in pure water to enhance the thermal performance of heat exchangers at minimal weight fractions. A hybrid nanofluid consisting of 50% ZnO and 50% Al2O3 nanoparticles dispersed in pure water at weight fractions of 0.1%, 0.3%, and 0.5% was prepared. An experimental rig, featuring a straight horizontal tube with a constant wall heat flux, was equipped with eight thermocouples positioned at the inlet, outlet, and along the tube's surface. The study focuses on the impact of the hybrid nanofluid on the friction factors and heat transfer coefficients within a Reynolds number range of 5000 to 20000. Observations indicate that the Nusselt number escalates with an increase in the Reynolds number through the horizontal tube, while the friction factor exhibits a converse relationship. The peak Nusselt number and friction factor were observed at a 5% mass fraction of the hybrid nanofluid. Specifically, enhancements in the Nusselt number were recorded at 9%, 11.8%, and 16.7% for the weight fractions of 0.1%, 0.3%, and 0.5% respectively. Additionally, the deviation in the friction factor was noted at 2.3%, 3.6%, and 4.1% in comparison to pure water. This study thus provides critical insights into the role of hybrid nanofluids in optimizing heat transfer in heat exchangers.

2025, Journal of Radiation Research and Applied Sciences

The increasing prevalence of cardiovascular disorders necessitates advanced computational approaches to investigate blood flow dynamics in stenotic arteries. This examination studies the combined influence of electroosmotic forces and nanoparticles on the blood flowing via a tapered, porous-saturated artery featuring stenosis, with the influences of magnetized fields and body acceleration. A key innovation lies in the novel integration of tetra-hybrid nanoparticles (Tetra-HNFs) with the Bingham-Papanastasiou rheological framework to simulate the non-Newtonian performance of blood. This extends the conventional Tiwari and Das tetra-hybrid nanofluid framework to accommodate the tetra-HNF case, incorporating various shapes of nanoparticles for detailed analysis. The electrical phenomena induced by the applied electric field are described using the Poisson-Boltzmann equation, linearizing via the Debye-Hückel approximation because of the assumption of low zeta potential at the arterial walls. This results in a closed-form solution for the electric potential. The arterial vessel displays the penetrability impact, with an outside magnetized force used radially to the flowing. The mild stenosis approximation is applied to simplify the governing equations. The study employs a finite difference methodology to numerically resolve the governing equations, analyzing the effects of electro-osmotic forces, nanoparticle configurations, magnetic fields, and body acceleration on key hemodynamic factors. The results presented graphically highlight the impact on velocity profiles, temperature outline, surface shearing stress, flowing rate, and confrontation. This exploration runs new perceptions into the interaction of electro-osmosis, nanoparticle dynamics, and non-Newtonian blood behavior in complex arterial geometries. By leveraging computational biomedical simulations, the study contributes to the advancement of diagnostic and therapeutic strategies for cardiovascular conditions, paving the way for improved clinical outcomes.

2025, Applied Fluid Mechanics (JAFM)

In comparison to a plain fin, the addition of dimples or protrusions to the fins of a finned tube heat exchanger significantly affects the promotion of heat transfer. The impact of the number of dimples or protrusions and the arrangement of inline and staggered configurations on pressure drop and heat transfer is examined numerically in this research. The outcomes demonstrate that increasing the number of dimples and protrusions significantly affects heat transfer magnitude and pressure drop. Increasing the number of dimples and protrusions within the Reynolds number range of 150-1200 enhances the friction coefficient and heat transfer by 108%-163% and 16%-112%, respectively, in contrast to the plain fin. In evaluating the result of the arrangement of inline and staggered configurations, the heat transfer amounts of these two models are almost the same, and the friction coefficient is higher in the model that uses the arrangement of inline. In the inline arrangement model utilizing dimplesprotrusions, the resultant heat transfer and friction coefficient increase 11%-92% and 64%-113% within the Reynolds number range of 150-1200, respectively, compared to the plain fin.

2025, Thermal Science and Engineering Progress

With the availability of advanced manufacturing techniques, non-conventional shapes and bio-inspired/biomorphic designs have shown to provide more efficient heat transfer. Consequently, this research investigates the heat transfer performance and fluid flow characteristics of novel biomorphic scutoid pin fins with varying volumes and top geometries. Numerical simulations were conducted using four hybrid designs for Reynolds Number 5500–13500. The impact of pin fin 'top' geometrical features on the heat transfer coefficient (HTC) was evaluated by combining computational fluid dynamics (CFD), experimental data, and machine learning. The results highlighted that the new pin fins saved 6.3 % to 14.3 % volume/material usage but produced around 1.5 to 1.7 times more heat transfer than conventional square/rectangular fins. Also, manipulating pin fins via the top geometrical properties can lead to more uniform velocity and temperature distributions while demonstrating the potential for increased thermal efficiency with reduced thermal resistance. Furthermore, six machine learning models accurately predict HTC using volume and surface area as key variables, achieving less than 5 % mean absolute percentage error (MAPE). Overall, this research introduces innovative biomorphic designs with unconventional geometries, emphasising resource optimisation and efficient HTC prediction using machine learning. It simplifies design processes, supports agile product development, calls for re-evaluation of conventional heat sink geometries, and provides promising directions for future research.