Experimental and numerical study of the thermal and hydrodynamic characteristics of laminar natural convective flow inside a rectangular cavity with water, ethylene glycol–water and air (original) (raw)
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Study of Natural Convection Heat Transfer in a Closed Wall with Thermal Conditions
Lecture Notes in Mechanical Engineering, 2021
In this study, conjugate natural convection in a square cavity filled with fluids under steady-state condition is numerically investigated with the finite element method. The left side wall is considered as hot wall, and the right wall is considered to be cold. The top and bottom walls are assumed to be adiabatic. Different boundary conditions are introduced on the walls, and a thorough investigation is done in the present study. Numerical simulations have been done for different parameters of Grashof number (10 3-10 7) and Prandtl number. The graph of Nusselt number versus Grashof number and Nusselt number versus Prandtl number is plotted. It is observed that the buoyant forces developed in the cavity due to thermally induced density gradients vary as the value of acceleration due to gravity (g) differs, due to the change in temperature and stream function. Keywords Conjugate natural convection heat transfer Á Square cavity Nomenclature AR aspect ratio (H/L) g acceleration due to gravity (m s −2) H height of square cavity (m) K thermal conductivity (W m −1 K −1) L length of the square cavity (m)
A steady state and two-dimensional laminar free convection heat transfer in a partitioned cavity with horizontal adiabatic and isothermal side walls is investigated using both experimental and numerical approaches. The experiments and numerical simulations are carried out using a Mach-Zehnder interferometer and a finite volume code, respectively. A horizontal and adiabatic partition, with angle of θ is adjusted such that it separates the cavity into two identical parts. Effects of this angel as well as Rayleigh number on the heat transfer from the side-heated walls are investigated in this study. The results are performed for the various Rayleigh numbers over the cavity side length, and partition angles ranging from 1.5 × 10 5 to 4.5 × 10 5 , and 0 ° to 90 ° , respectively. The experimental verification of natural convective flow physics has been done by using FLUENT software. For a given adiabatic partition angle, the results show that the average Nusselt number and consequently the heat transfer enhance as the Rayleigh number increases. However, for a given Rayleigh number the maximum and the minimum heat transfer occurs at θ = 45 ° and θ = 90 ° , respectively. Two responsible mechanisms for this behavior, namely blockage ratio and partition orientation, are identified. These effects are explained by numerical velocity vectors and experimental temperatures contours. Based on the experimental data, a new correlation that fairly represents the average Nusselt number of the heated walls as functions of Rayleigh number and the angel of θ for the aforementioned ranges of data is proposed.
IJERT-Numerical Investigation of Natural Convection Heat Transfer in a Square Cavity
International Journal of Engineering Research and Technology (IJERT), 2015
https://www.ijert.org/numerical-investigation-of-natural-convection-heat-transfer-in-a-square-cavity https://www.ijert.org/research/numerical-investigation-of-natural-convection-heat-transfer-in-a-square-cavity-IJERTV4IS070206.pdf Natural convection heat transfer in enclosures find many applications such as heating and cooling of building spaces, solar energy utilization, thermal energy storage, cooling of electrical and electronic components etc. In the present study, Numerical Investigation is conducted in a square cavity with one vertical wall maintained at a high temperature and with the opposing vertical wall at a low temperature. The influence of Grashof numbers ranging from 20000 to 200000 for Prandtl number 0.7 (air) is studied. The governing vorticity and energy equations are solved by finite difference methods including Alternating Direction Implicit (ADI) and Successive Over Relaxation (SOR) techniques with C coding. Steady state isothermal lines and streamlines are obtained for all the Grashof numbers considered. In addition, the average Nusselt number, over the hot wall for the range of Grashof numbers is calculated. The contours of streamlines and isothermal lines are presented for all the parameters investigated. Changes in the streamline and isothermal line patterns are observed with the change in Grashof numbers. The results obtained in this study are useful for the design of devices with enclosures subjected to high temperature differences.
Double Diffusive Natural Convective Flow Characteristics in a Cavity
Procedia Engineering, 2013
The influences of Soret and Dufour coefficients on free convection flow phenomena in a partially heated square cavity filled with water-Al 2 O 3 nanofluid is studied numerically. The top surface has constant temperature T c , while bottom surface is partially heated T h , with T h > T c . The concentration in top wall is maintained higher than bottom wall (C c < C h ). The remaining bottom wall and the two vertical walls are considered adiabatic. Water is considered as the base fluid. By Penalty Finite Element Method the governing equations are solved. The effect of the Soret and Dufour coefficients on the flow pattern and heat and mass transfer has been depicted. Comprehensive average Nusselt and Sherwood numbers, average temperature and concentration and mid-height horizontal and vertical velocities inside the cavity are presented as a function of the governing parameters. Results shows that both heat and mass transfer increased by Soret and Dufour coefficients.
IJERT-Effects Of Heat Source Location On Natural Convection In A Square Cavity
International Journal of Engineering Research and Technology (IJERT), 2014
https://www.ijert.org/effects-of-heat-source-location-on-natural-convection-in-a-square-cavity https://www.ijert.org/research/effects-of-heat-source-location-on-natural-convection-in-a-square-cavity-IJERTV1IS6332.pdf Natural convection in a closed square cavity has occupied the centre stage in many fundamental heat transfer analysis which is of prime importance in certain technological applications. Infact buoyancy driven convection in a sealed cavity with differentially heated isothermal walls is a prototype of many industrial applications such as energy efficient buildings, operation and safety of nuclear reactor and convective heat transfer associated with electronic cooling equipment. The internal flow problems are considerably more complex than external ones. In electronic systems normally the heat generating bodies exist within the cavity. The effect of the presence of heat source on the mass flow rate and heat transfer is considered in present case for investigation. In order to verify the methodology of using fluent, the commercial software, the available problem in the literature is verified for parametric study on the location of heat source and its strength is considered for study. In present work, the given source is split into two parts and its effect on the flow rate and heat transfer is studied. An attempt is made for the best location of the heat source in the cavity so that it can be used in the electronic equipment generating heat. Nomenclatures AR = Aspect ratios, H/L, Gr = Grashoff Number g = Acceleration due to gravity (m/s 2), Ra = Rayleigh number H = Height of the cavity (m), Pr = Prandtl number h = Convective heat transfer coefficient (W/m 2 K) k = Thermal conductivity (W/m.K), Nu = Nusselt number L = Length of the cavity (m), T = Temperature (K) q = Heat flux (W/m 2) Greek Symbols α = Thermal diffusivity (m 2 /s) β = Volume expansion coefficient (K-1) ρ = Fluid Density (kg/m 3) ν = Kinematic viscosity (m 2 /s) θ = Dimensionless temperature Subscript b = Bottom wall s = Side wall
Analysis of mixed convection flows within a square cavity with linearly heated side wall(s)
International Journal of Heat and Mass Transfer, 2009
Finite element simulations have been performed to investigate the influence of linearly heated side wall(s) or cooled right wall on mixed convection lid-driven flows in a square cavity. It is interesting to note that multiple circulation cells appear inside the cavity with the increase of Pr for Re ¼ 10 and Gr ¼ 10 5 in the case of linearly heated side walls. For Pr ¼ 0:015, only two circulation cells are formed inside the cavity. As Pr increases to 0.7, three circulation cells are formed inside the cavity. Further increase in Pr to 10, leads to the formation of four circulation cells inside the cavity. On the other hand, only two circulation cells are formed inside the cavity for the case of cooled right wall. A detailed analysis of flow pattern shows that as the value of Re increases from 1 to 10 2 , there occurs a transition from natural convection to forced convection depending on the value of Gr irrespective of Pr. It is observed that the secondary vortex at the top left corner disappears for Re ¼ 10 2 and Gr ¼ 10 5 due to enhanced motion of the upper lid in the case of cooled right wall while a small secondary vortex exist at the bottom right corner in the case of linearly heated side walls. The local Nusselt number (Nu b ) plot shows that heat transfer rate is equal to 1 at the edges for the case of linearly heated side walls case and that is zero at the left edge and thereafter that increases for the case of cooled right wall. It is interesting to observe that Nu b is large within 0:4 6 X 6 0:6 due to compression of isotherms for Pr ¼ 0:7 and 10 in the case of linearly heated side wall. It is also observed that Nu r or Nu l exhibits oscillations especially for Pr ¼ 10 at higher Gr due to the presence of multiple circulations. It is also observed that Nu r or Nu l vs Gr plots show oscillation for two case studies. Average Nusselt numbers at the bottom and right walls are strong functions of Grashof number at larger Prandtl numbers whereas average Nusselt number at the left wall at a specific Pr is a weaker function of Gr.
International Communications in Heat and Mass Transfer, 2013
Heat transfer and fluid flow characteristics of laminar flow past an open cavity with 2 heating from below ☆ 3 Y. Q1 Stiriba ⁎, J.A. Ferré, F.X. Grau 4 Universitat Rovira i Virgili, ETSEQ, Dpt. Mechanical Engineering, Av. Paisos Catalans 26, 43007 Tarragona, Spain 5 6 a b s t r a c t a r t i c l e i n f o 7 8 Available online xxxx 9 10 11 12 Keywords: 13 Mixed convection 14 Direct numerical simulation 15 Open-ended cavity 16 Stability 17 Laminar mixed convective flow over a three-dimensional open cavity with heating from below at constant tem-18 perature was numerically simulated using direct numerical simulation and the most hydrodynamic and thermal 19 aspects of the flow are presented. The effects over the velocity and temperature distribution of the buoyancy 20 forces acting perpendicular to the mainstream flow are studied for a range of Reynolds numbers between 100 21 and 1500, and Richardson numbers from 0.001 to 10 to obtain a phenomenological description of the convective 22 air flowing through the channel and the cavity. At low Reynolds and Richardson numbers the flow becomes 23 steady and the heat diffusion is predominant, whereas at high Richardson number the heat transfer by convec-24 tion becomes important and the flow experiences unsteady behavior with a significant interaction between the 25 external flow and the recirculating flow inside the cavity, and exhibits a three-dimensional nature. 26 27 28 29 30 31 33 siderable attention due to its wide range of application in engineering 34 and science, for example, cooling of electronic components, finned 35 heat exchangers, cavity of solar central receivers, evaporative cooling 36 and fire control in buildings. The presence of open cavity geometry gen-37 erates a vortex motion whose axis is parallel to the transverse direction 38 (z-direction) as well as unsteady velocity and pressure fluctuations 39 which may extend downstream the cavity. 40 In the literature, it is possible to find many numerical simulations and 41 experimental studies on the flow over open-ended cavity, see for instance 42 [1,11,18,8,14,15] and references therein. Most of the flow studies have 43 dealt with the steady flow regime, effects of the Reynolds and Richardson 44 numbers, and aspect ratio on the mixed convection. 45 Examples of these studies include the work [11] where the authors 46 studied numerically the transport process due to the interaction of air 47 ICHMT-02742; No of Pages 8
The International Conference on Applied Mechanics and Mechanical Engineering
Two-dimensional steady laminar natural convection in a differentially heated cavity filled with water and has various aspect ratios due to buoyancy force effect is analyzed numerically. The governing mass, momentum and energy equations are considered and a finite volume algorithm is used to capture the numerical solution. The left vertical side wall of the cavity is linearly heated while the right vertical one is maintained at constant cold temperature. The bottom wall is maintained at constant hot temperature while the top wall is considered thermally insulated. The Rayleigh number is varied from 10 3 to 10 6 , while the cavity aspect ratio (W/H) is varied as 0.5, 1.0 and 2.0 respectively. Results are presented in the form of streamline and isotherm contours. The results of the present work explain that the natural convection phenomenon is significantly influenced by changing the cavity aspect ratio, so that when the aspect ratio is high the convection effect is week and vice versa. Also, it is found that non-uniform heating in the left vertical sidewall of the cavity plays a major role to improve the heat transfer rates. For uniform and nonuniform heating of the bottom wall and left vertical sidewall respectively, the local Nusselt number at these walls increases from its minimum value at the left edge of these walls toward maximum value at the right edge. While, the average Nusselt number for both left side and bottom walls increases with increasing of Rayleigh number.
International Journal of Heat and Fluid Flow, 2011
Results of an experimental study of flow structure formation and heat transport in turbulent forced and mixed convection are presented. The experiments were conducted in a rectangular cavity with a square cross section, which has an aspect ratio between length and height of C xz = 5. Air at atmospheric pressure was used as working fluid. The air inflow was supplied through a slot below the ceiling, while exhausting was provided by another slot, which is located directly above the floor. Both vents extend over the whole length of the cell. In order to induce thermal convection the bottom of the cell is heated while the ceiling is maintained at a constant temperature. This configuration allows to generate and study mixed convection under well defined conditions. Results of forced convection at Re = 1.07 Â 10 4 as well as mixed convection at 1.01 Â 10 4 6 Re 6 3.4 Â 10 4 and Ra = 2.4 Â 10 8 (3.3 P Ar P 0.3), which were obtained by means of Particle Image Velocimetry and local temperature measurements, are presented. For purely forced convection a 2D mean wind, which can be approximated by a solid body rotation, is found. With increasing Archimedes number this structure becomes unstable, leading to a transition of the solid body rotation into additional smaller convection rolls. Proper orthogonal decomposition of the instantaneous velocity fields has been performed for further analysis of these coherent large-scale structures. Their fingerprint is found in the spatial temperature distribution of the out flowing air at the end of the outlet channel, which reveals a temporally stable profile with two maxima over the length of the outlet. Moreover a maximum in the global enthalpy transport by the fluid is found at Ar % 0.6.