Enhancing Thermal Stratification in Liquid Storage Tanks During Relaxation Periods

Hamed Mahmoud, Mohammed; Kadhem Abdulsada, Ghanim

	Enhancing Thermal Stratification in Liquid Storage Tanks During Relaxation Periods
Journal of Engineering and Sustainable Development
Article 1, Volume 12, Issue 1, 2008, Pages 161-177
Authors
Mohammed Hamed Mahmoud; Ghanim Kadhem Abdulsada
Abstract
To date, the majority of previous numerical models of the decay of thermal stratification during relaxation time in liquid tanks have ignored the effects of the wall of the storage tank. In this study, a one-dimensional, time dependent mathematical model to predict the degradation of heat in stratified thermocline liquid tank during relaxation periods (i.e. in the absence of external flow) for both cold and hot storage has been developed and tested. The model analyzes the interaction between the liquid inside the tank with its walls by including the effects of heat transfer by convection and conduction through the tank wall. The numerical simulations have been compared with experimental measurements of water tank. Data were taken on tank fitted with various horizontal porous baffles configuration (including location, number and materials of the porous baffles) and for various initial temperature distributions (stratified and isothermal conditions). The predicated profiles have been found close to those obtained experimentally especially at the top of the tank. It is found that the walls of the container can have a strong effect in destroying the thermocline. Temperature variation is found to be negligible in the horizontal direction except in the regions very near to the tank wall. Experiments show that better thermal stratification can be obtained by using horizontal porous baffles. The gravel baffles is found to be more effective for enhancing thermal stratification than other two types that have been tested. Experiments indicate that thermal stratification improves with increasing number of baffles and then flattens. The optimum number of baffles is found to be two baffles. The initial temperature distribution is found to be very important in the subsequent decay of stratification. The natural cooling of an isothermal tank is found to be remaining isothermal and thermal stratification moves forward in the direction to the top of tank.

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