Flow and thermal characteristics of airflow inside a refrigerated container

Abstract

Paper presented to the 10th International Conference on Heat Transfer, Fluid Mechanics and Thermodynamics, Florida, 14-16 July 2014.

This study mainly focuses on parametric investigation of ceiling-slot ventilated enclosures for determining the airflow and thermal characteristics. In the analyses, the container cross-sectional area is kept constant. However, the container length assumes values of 6.13 m, 8.33 m, and 13.3 m, and the aspect ratio of the container varies accordingly. Besides, the effect of injection slot width on the flow distribution is also studied by taking two different slot widths at a particular aspect ratio. The air velocity at the slot exit is varied in such a way that the Reynolds number of injection is in the range of 20 and 2x10^5. The numerical analyses are carried out by using ANSYS-FLUENT software which is based on control volume approach. Reynolds Stress Model is applied for modeling the 3D turbulent flow inside the enclosure. In discretization of convective terms, QUICK scheme is adopted, and SIMPLE algorithm is applied for solution of momentum and continuity equations. For evaluating the turbulent stresses near the wall, “log-law” function is used. In heat transfer analysis, for the top, lateral and rear surfaces of the container, the combine effect of solar radiation, convection and surface emission is simultaneously considered. In doing so, 3D flow of air around the truck surface, and the related heat transfer problem is studied by generating thirty-two million of non-uniform grids around the truck. To capture the velocity, pressure and temperature gradients along the boundary layer, special type grids are generated in regions close to the solid surface. Convergence criteria for all flow and temperature parameters are taken to be 10-5. For flows with Re>200, if the container aspect ratio is H/L<0.2, the flow separates from the upper surface of the container at a length ratio of z/L.≈0.85 Otherwise a cone-like vertical vortex occurs and causes uneven flow distribution in the container. The thermal performance of ventilation in the container is measured by a non-dimensional temperature distribution, θx at a particular cross-section. Generally, uniformity in temperature is provided at high Reynolds numbers. However, for02H/L.<, temperature disturbance takes place at the rare surface and can be avoided by full-size injection slot.