Transient cooling of petroleum by natural convection in cylindrical storage tanks—II. Effect of heat transfer coefficient, aspect ratio and temperature-dependent viscosity

Abstract

The transient natural convection of a warm crude oil contained in a large vertical cylindrical storage tank located in a cold environment is investigated numerically. The effect of the external heat transfer coefficient is examined by using four different values. Increasing this parameter is found to increase the rate of heat loss as expected, but only a minor effect on the resulting fluid flow is found. The effect of the tank aspect ratio (height to radius) on the natural convection process is investigated by using four different aspect ratios ranging from 0.25 to 2.0, and is found to affect the flow patterns that develop. Two recirculating cells arise for the aspect ratios of 0.25, 0.5 and 1.0, while a single cell arises in the case of aspect ratio of 2.0. The effect of the fluid viscosity is examined for a tank of aspect ratio 0.5 by using five different apparent viscosity-temperature relationships. The increase in fluid viscosity concomitant with cooling is found to significantly slow down the rate of heat loss from the tank compared to the constant viscosity case.