Swirl flow heat transfer and pressure drop with twisted-tape inserts (original) (raw)
Related papers
Simulation of heat transfer enhancement in tube flow with twisted tape insert
Progress in Computational Fluid Dynamics, An International Journal, 2017
Heat transfer behaviour in a tube with inserted twisted tape swirl generator is investigated numerically, for different values of the twist ratio and diameter ratio and for Reynolds numbers within the range 100-20,000. The transition-SST model is used as the turbulence model. The computational model is validated, first, on a plain tube, where a good agreement is achieved with the correlations. The subsequent analysis of the tube with twisted tape indicates that the use of twist tape enhances heat transfer generally, which is accompanied by a higher pressure drop. It is observed that an improvement of the thermal-hydraulic performance can only be observed for certain configurations and Reynolds numbers.
Symmetry, 2020
This paper investigates the convective heat transfer in a heat exchanger equipped with twisted tape elements to examine effects of the twisted tape truncation percentage, pitch value, position and Reynolds number using 3D numerical simulation. A symmetric heat flux is applied around the tube as the studied heat exchanger. Based on the influences in both heat transfer enhancement and pressure drop, the performance evaluation criterion (PEC) is utilized. Inserting twisted tape elements and reducing the pitch value significantly augment the Nusselt number, friction coefficient and PEC number compared to the plain tube. For the best case with a Reynolds number of 1000, the average Nusselt number increases by almost 151%, which is the case of fully fitted twisted tape at a pitch value of L/4. Moreover, increasing the twisted tape truncation percentage reduces both heat transfer and pressure drop. Furthermore, the highest heat transfer rate is achieved when the truncated twisted tape is l...
Applied Thermal Engineering, 2017
Twisted tapes are known to enhance convection heat transfer with an accompanying rise in pressure drop where the enhancement is essentially attributed to the secondary swirl flow. The heat transfer enhancement attributed to twisted-tape inserts in a laminar counter-flow concentric tube heat exchanger is investigated experimentally. The twisted tapes are characterized by different twist ratios. Empirically, the twisted tapes increase the friction factor by ten folds and the Nusselt number by three folds. The performance evaluation of the twisted-tape inserts is scrutinized based on various performance criteria such as the pumping power ratio, flow resistance ratio, heat transfer augmentation efficiency, Nusselt number ratio, heat duty ratio, and effectiveness ratio. The performance evaluation is based on two different conditions-variable and constant pumping power. An analysis on the dominance between free convection and swirl-flow-induced convection is performed through the buoyancy force and centrifugal force balance. This provides a sound explanation of the distinct heat transfer characteristics for different ranges of Reynolds number. This comprehensive analysis of performance evaluation provides interesting insights into the role played by the twisted tape insert in the contribution of energy transport in laminar forced convection.
Turbulent heat transfer enhancement in tubular heat exchangers with different twisted tape inserts
Journal of Mechanical Engineering and Sciences
Experimental and numerical analyses are carried out to investigate the influence of twisted tape inserts on the heat transfer and the flow behavior in double tube heat exchangers. First, all the performance factors, namely the Nusselt number, friction factor, and thermal performance factor, were studied for a basic heat exchanger (BHE). Afterwards, twisted tapes with three different twist ratios (7.5, 6, and 4.5) were inserted inside the inner tube of the BHE, which resulted in three different modified heat exchangers (MHEs). For the numerical study, a 3D numerical model is developed with the k-ε RNG turbulent model to visualize the flow and the heat transfer behavior inside the heat exchangers. In both studies, turbulent flow field is maintained, ranging Reynolds number from 15000 to 50000. From the experimental result, an enhanced heat transfer, characterized by the performance factors, is found for all the MHEs compared to the BHE. The most enhanced thermal performance factor is...
2013
The swirl flow devices like twisted tape, winglet, groove, conical ring, wire coil etc. have been used as passive heat transfer augmentation technique. Especially, twisted tape devices have been applied in thermal engineering systems such as boilers, heat exchangers, water heater. Many researches using swirl flow devices particularly twisted tape with different geometries for heat transfer enhancement have been published. In this paper, different modified twisted tapes which had examined in previous studies were compared with each other with regard to heat transfer augmentation. Heat transfer, friction factor and thermal-hydraulic performance factor characteristics were investigated separately under the same conditions such as same twisted ratios and same Reynolds number values. Twisted tape which gives best heat transfer and friction factor results was determined. Derived empirical correlations which had been found by researchers were used for comparison between twisted tapes. ayri...
Energy and Power Engineering, 2019
The heat transfer augmentation of plain twisted tape inserts for different twist ratios has been studied in this study. The data are conducted using the plain twisted tape insert with five different twist ratios respectively. The range of Reynolds number is considered under a uniform heat flux condition. In the case of simulation, the tapes are made from a stainless steel strip with a thickness of 2 mm. A tubular pipe with 850 mm U-loop length and twist length of 800 mm each is considered in our study for simulation. Water is used as working fluids inside the tube for our simulation. The simulation results demonstrate that the important heat transfer parameters including Nusselt number (Nu), friction factor (f) and thermal performance index (η) are gradually increased with the increment of the twist ratio and reached at the saturated level while twist ratio is 3.5, afterward the thermal properties are decreased.
In the present work heat transfer and friction factor properties were experimentally investigated by using copper wavy (corrugated) twisted tape inserts. The turbulent flow was created by inserting the wavy twisted tape inserts into the inner tube of heat exchanger creating high rate of turbulence in pipe, which results in increasing heat transfer enhancement and pressure drop. The tape consists of the corrugations and the twisting with various twist ratios (TR=10.7, 8.5, 7.1). The length and width of insert was 1 meter and 14 mm respectively. The outer tube of heat exchanger is made up of mild steel with outside diameter 0.0198 m & 0.0142 m inside diameter and the inner tube is made up of copper with 0.038 m outside diameter and 0.032 m inside diameter. The length of pipe in pipe heat exchanger is 1.4 m. The bulk mean temperatures at various positions are used for different flow rate of water. From the obtained results the new Correlations for Nusselt number and friction factor are developed for twisted tape inserts. The Reynolds number is varied from 5000 to 17000. The results of varying twists in wavy twisted tape inserts with different pitches have been compared with the values for the smooth tube. It showed that the highest heat transfer rate was achieved for the wavy twisted tape with twist ration 7.1. The Nusselt number value increased by 172 % and friction factor value increased by 32.11% as compared to the smooth tube values.
Case Studies in Thermal Engineering, 2019
Twisted tubes and twisted tapes are swirl flow generators utilized for increasing thermal performance. The combined effects of twisted tubes and twisted tapes on heat transfer, pressure drop and thermal performance were experimentally investigated. Experiments were performed using a trapezoidal shaped twisted tube and twisted tapes having various twist ratios (y/w = 2.0, 3.0, 4.0 and 5.0). Water was used as the test fluid in a turbulent regime (4,500<Re<16,000). A simulation of velocity, temperature contours and local Nusselt number plots was also performed to gain information about fluid flow and heat transfer. The results of the combined devices are studied along with those of a smooth circular tube and a twisted tube alone, for comparison. The experimental results show that at a given Re, the Nusselt number (Nu), friction factor (f) and thermal performance of a
ICMIEE 18-164 Study of Heat Transfer Enhancement in Tubular Heat Exchanger with Twisted Tape Inserts
2018
In the present work an experimental investigation has been carried out to study the convective heat transfer augmentation in a double pipe counter flow heat exchanger (HE) with twisted tape insert. Also, the results are compared with a basic heat exchanger (BHE) of similar length, diameter and flow rate. The HE consists of a 140 inches long copper tube with diameter of 1inch which is concentered in a PVC pipe having a diameter of 2inch. Hot fluid is allowed to flow through the inner copper tube and the cold fluid was allowed to flow through the annular passage between copper tube and the PVC pipe. Experiments were conducted at different mass flow rates of the hot fluid for both the BHE and MHEs. The effects of inserted twisted tapes and twist ratio on heat transfer rate, pressure drop and thermal performance factor characteristics have been investigated extensively. A twist ratio is defined as the ratio of twist length (y) to twisted tape width at the large end (W). The experiments ...
Applied Thermal Engineering, 2018
The present 3D numerical study was performed to show the effects of the length of central cut twisting tape (CCTT) on the characteristics of thermodynamic and hydrodynamic fields when this tape is inserted inside a tube in which, air is flows in turbulent pattern. Central cut twisting tapes of the same cut ratio (c = C/D) of 0.4 and four different length ratio (LR = l/L) of 0.25, 0.5, 0.75 and 1 were inserted in the tested tube that subjected to a uniform heat flux. The range of Reynolds number of air flow was 10000 ≤ Re ≤ 40000. Fluent in ANSYS 15 was used for problem designing, formulation and results obtaining in the present study. Finite volume method was the discretization method and tetrahedral type of mesh element was used. RNG k-ɛ was chosen as the turbulent model. The obtained results showed that the increasing in Reynolds number leads to an increasing in Nusselt number and a decreasing in both friction factor and thermal performance factor. Also, these results cleared that the increasing in the length ratio of the studied type of twisting tape gives higher Nessult number, friction factors and thermal performance factor of 171.172, 0.0932 and 1.432 respectively.