Thermal characteristics of an underground cold-water reservoir: Analytical and experimental studies

The thermal characteristics of an underground cold-water reservoir are investigated analytically and experimentally. An analytical solution is developed for the temperature distribution in the reservoir by assuming a linearized boundary condition at the water surface. The results are compared with the experimental measurements which have been conducted in a cistern located in the city of Yazd. Very good agreements between the analytical and the experimental results at various times during the withdrawal cycle are observed, ensuring the accuracy of the analytical solution obtained for the linearized boundary condition. The results show that a stable thermal stratification is preserved in the reservoir throughout the entire course of the withdrawal cycle. During this period, the outside temperature reaches as high as 42 °C, while cool water with the temperature varying from 12 to 13 °C is easily available from the underground water reservoir under investigation.