Turbulence model assessment and heat transfer phenomena inside a rectangular channel under forced and mixed convection

In recent years Computational Fluid Dynamics (CFD) simulations are increasingly used to model the air circulation and temperature environment inside the rooms of residential and office buildings to gain insight into the relative energy consumptions of various HVAC systems for cooling/heating for climate control and thermal comfort. This requires accurate simulation of turbulent flow and heat transfer for various types of ventilation systems using the Reynolds-Averaged Navier-Stokes (RANS) equations of fluid dynamics. Large Eddy Simulation (LES) or Direct Numerical Simulation (DNS) of Navier-Stokes equations is computationally intensive and expensive for simulations of this kind. As a result, vast majority of CFD simulations employ RANS equations in conjunction with a turbulence model. In order to assess the modeling requirements (mesh, numerical algorithm, turbulence model etc.) for accurate simulations, it is critical to validate the calculations against the experimental data. For this purpose, we use three well known benchmark validation cases, one for natural convection in 2D closed vertical cavity, second for forced convection in a 2D rectangular cavity and the third for mixed convection in a 2D square cavity. The simulations are performed on a number of meshes of different density using a number of turbulence models. It is found that k-epsilon two-equation turbulence model with a second-order algorithm on a reasonable mesh gives the best results. This information is then used to determine the modeling requirements (mesh, numerical algorithm, turbulence model etc.) for flows in 3D enclosures with different ventilation systems. In particular two cases are considered for which the experimental data is available. These cases are (1) air flow and heat transfer in a naturally ventilated room and (2) airflow and temperature distribution in an atrium. Good agreement with the experimental data and computations of other investigators is obtained.

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Computer Simulation of Mixed Convection of Alumina-Deionized Water Nanofluid Over Four In-Line Electronic Chips Embedded in One Wall of a Vertical Rectangular Channel

Journal of Thermal Science and Engineering Applications ◽

10.1115/1.4045696 ◽

2019 ◽

Vol 12 (4) ◽

Author(s):

Nalla Ramu ◽

P. S. Ghoshdastidar

Keyword(s):

Heat Transfer ◽

Reynolds Number ◽

Heat Transfer Coefficient ◽

Mixed Convection ◽

Transfer Coefficient ◽

Base Fluid ◽

Rectangular Channel ◽

Working Fluid ◽

Al2o3 Nanoparticles ◽

Enhancement Factors

Abstract This paper presents a computational study of mixed convection cooling of four in-line electronic chips by alumina-deionized (DI) water nanofluid. The chips are flush-mounted in the substrate of one wall of a vertical rectangular channel. The working fluid enters from the bottom with uniform velocity and temperature and exits from the top after becoming fully developed. The nanofluid properties are obtained from the past experimental studies. The nanofluid performance is estimated by computing the enhancement factor which is the ratio of chips averaged heat transfer coefficient in nanofluid to that in base fluid. An exhaustive parametric study is performed to evaluate the dependence of nanoparticle volume fraction, diameter of Al2O3 nanoparticles in the range of 13–87.5 nm, Reynolds number, inlet velocity, chip heat flux, and mass flowrate on enhancement in heat transfer coefficient. It is found that nanofluids with smaller particle diameters have higher enhancement factors. It is also observed that enhancement factors are higher when the nanofluid Reynolds number is kept equal to that of the base fluid as compared with the cases of equal inlet velocities and equal mass flowrates. The linear variation in mean pressure along the channel is observed and is higher for smaller nanoparticle diameters.

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MEASUREMENT OF MIXED-CONVECTION HEAT TRANSFER FROM AN ARRAY OF DISCRETE SOURCES IN A HORIZONTAL RECTANGULAR CHANNEL WITH AND WITHOUT SURFACE AUGMENTATION

Experimental Heat Transfer ◽

10.1080/08916159008946387 ◽

1990 ◽

Vol 3 (3) ◽

pp. 215-237 ◽

Cited By ~ 2

Author(s):

H. V. MAHANEY ◽

F. P. INCROPERA ◽

S. RAMADHYANI

Keyword(s):

Heat Transfer ◽

Mixed Convection ◽

Rectangular Channel ◽

Convection Heat Transfer ◽

Convection Heat ◽

Mixed Convection Heat Transfer

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Mixed Convective Heat Transfer From a Simulated Microchip to Liquid Flows in a Horizontal Rectangular Channel

Journal of Electronic Packaging ◽

10.1115/1.2905411 ◽

1991 ◽

Vol 113 (3) ◽

pp. 309-312 ◽

Cited By ~ 1

Author(s):

Y. Chin ◽

C. F. Ma ◽

X. Q. Gu ◽

L. Xu

Keyword(s):

Heat Transfer ◽

Reynolds Number ◽

Rayleigh Number ◽

Mixed Convection ◽

Transfer Process ◽

Rectangular Channel ◽

Heat Transfer Process ◽

Flow Directions ◽

Liquid Flows ◽

Hot Surface

Mixed convection from a small heater (5mm × 5mm) to liquid flows in a horizontal rectangular channel is investigated experimentally. The results of three cases in which the buoyancy is normal to the liquid flow directions — hot surface facing upward, facing downward and vertically attached to one wall of the channel — are presented. Correlations are also provided to predict the mixed convective effects in the range 100 < ReL < 4000. The results demonstrated that both the Reynolds number ReL and the modified Rayleigh number RaL* pronouncedly dominate the heat transfer process. In all of the above cases, heat transfer was enhanced over that of forced convection.

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