No abstract

No abstract

The heat transfer of supercritical fluids is a vastly growing field, specifically to find suitable alternatives to replace conventional R134a, which can be beneficial for climate change. Most of the experimental and numerical investigations have been conducted to explore supercritical water, carbon dioxide and R134a as heat transfer working fluids. Hydrofluoroolefin (HFO) and refrigerants blends have been considered the most environment-friendly refrigerants to replace Chlorofluorocarbons (CFCs), Hydrochlorofluoro-carbons (HCFCs) and Hydrofluorocarbons (HFCs). Their main advantage of zero Ozone Depletion Potential (ODP) and comparatively lower Global Warming Potential (GWP) have attracted growing amount of attention to mitigate environmental issues. This work adopts the computational method and takes the environmentally friendly refrigerants to investigate the heat transfer characteristics under widely used shear-stress transport (SST) model. A comprehensive comparison was performed at reduced pressure of 1.10 for supercritical fluids R515A, R1234ze(E) and R134a. The peaks of heat transfer coefficient occurred in the vicinity of pseudo critical temperature for all of these considered fluids; however, R134a resulted in higher heat transfer coefficient, Reynolds number and Prandtl number in comparison with R515A and R1234ze(E). The higher heat transfer coefficient of supercritical fluid R134a is owing to its thermophysical properties and the specific heat plays crucial role in the heat transfer of supercritical fluids. Owing to environmental issues, R515A can be a considerable replacement of R134a. R1234ze(E) is also promising alternative to R134a; however, safety issues should thoroughly concern its mild flammable characteristics.

The major reason behind failure of electronic components is the rise in temperature. To optimize design of naturally cooled electronic equipment enclosure, a detailed experimental study and a computational fluid dynamics (CFD) analysis were performed. Commercially available software, ANSYS Fluent, was used for CFD analysis. The three-dimensional form of Navier-Stokes equations was used to solve the problem computationally. Aluminium enclosure having dimensions of 40 cm × 40 cm × 21 cm and thermal conductivity of 210 W/m·K were manufactured for experimentation in this research study.Electronic components were modelled as constant heat flux body during experimentation and CFD analysis. Effect of heat source vertical and horizontal position, inlet height, and buoyancy effect on mean rise in temperature inside the aluminium enclosure was studied. Mean temperature inside the casing was increased by increasing either heat source height or inlet height. At the end, computational results were compared with experimental results in order to check the validity of results. Computational results were highly in accordance with experimental results, because maximum percentage difference between experimental and CFD results was less than 6%. On the basis of results obtained from experiments and simulations, the best configuration of heat source and inlet was proposed, which will provide optimum thermal performance.Numerical results of velocity and temperature inside the enclosure were plotted in the form of streamlines and isotherms. This study can be used as a fundamental step prior to designing electronic equipment enclosure. KEYWORDS computational fluid dynamics (CFD), electronic equipment cooling, heat transfer experimentation, natural convection, three-dimensional analysis, ventilated enclosure Nomenclature: T ∞ , Ambient temperature (K); h, Enthalpy value per unit volume (kJ/kg·m 3 ); g, Gravitational constant (m/s 2 ); Ra, Rayleigh number; c p , Specific heat of fluid (kJ/kg·K); Ρ, Static pressure of air (N/m 2 ); T o , Temperature of the flow (K); u i , Velocity component in the ith direction (m/s); S h , Volumetric heat generation rate (W/m 3 ); K, Wall thermal conductivity (W/m·K); , Greek symbols; β, Coefficient of thermal expansion (1/K); ρ, Density of fluid (kg/m 3 ); μ, Dynamic viscosity of fluid (kg/m·s); α, Thermal diffusivity fluid (m 2 /s); , Subscripts; ∞, Indicating the conditions at infinity; o, Indicating the operating conditions

No abstract