Promotion of uniform radial temperature distribution using buoyancy effect in inclination pipes

摘要

A model case was formulated to examine the buoyancy effect on radial temperature distribution in the heating section of thermal sterilization for high water content juices. Computational Fluid Dynamics (CFD) was employed in the short isothermal pipe to study the effect of Reynolds numbers (50, 300, and 2000), Rayleigh numbers (1 x 10(6) and 4.29 x 10(6)), and pipe inclined angles (0 = theta = 60 degrees). The simulation results were validated with the experimental and numerical data obtained from literature. When the buoyancy effect was dominant, the velocity and temperature were found to be unevenly distributed in the horizontal pipe. Besides, the coldest spot fluid reached maximum velocity, which does not allow adequate thermal sterilization. However, the significant effect of the inclined pipe angle was observed upon the enhancement of radial temperature uniformity. Moreover, the local Nusselt number increased with escalating pipe angles when compared with the horizontal pipe.Practical applications Radial temperature uniformity is important in continuous thermal sterilization for safety and retention of nutritional properties. When the fluid enters the heating section of thermal sterilization, it operates in a laminar or low turbulent region and gets heated up. Hence, the buoyancy effect may be dominant in this part. A method is proposed to exploit the buoyancy effect for promoting the radial mixing in the heating section of thermal sterilization. The present study asserts that the use of an upward inclined pipe can provide uniform radial temperature distribution and a high heat transfer coefficient. This approach may be applicable for fruit juices of low-to-moderate viscosity.