Effect of ground heat extraction on stability and thermal performance of solar ponds considering imperfect heat transfer. (1st March 2020)

• Record Type: Journal Article
• Authors: Verma, Sunirmit; Das, Ranjan
• Is Part Of: Solar energy. Volume 198(2020)
• Page Start: 596
• Page End: 604
• Publication Date: 2020-03-01
• Subjects: Solar pond -- Ground heat recovery -- Analytical solution -- Imperfect heat transfer -- Stability -- Entropy generation; Solar energy -- Periodicals; Solar engines -- Periodicals; 621.47
• DOI: 10.1016/j.solener.2020.01.085
• Languages: English
• ISSNs: 0038-092X

Abstract

Highlights: Improved model to assess ground heat recovery in solar ponds is developed. Considerable deviations with respect to the conventional assumption are observed. Ground heat extraction considerably affects the pond stability. Present model reveals larger optimal NCZ thickness against prevailing assumptions. Entropy generation is underestimated by the assumption of present literature. Abstract: This work revisits the idea of ground heat extraction in solar ponds by addressing various limitations associated with the conventional assumption of perfect heat transfer. For this, an overall heat transfer coefficient, U has been introduced to analyse the heat extraction taking place from the ground beneath the pond. The pond's thermal performance is analysed for different values of U using closed form solutions and significant departure is seen with respect to the conventional assumption of an infinite U . Temperature distributions across various zones are obtained which exhibit deviation from the ideal distributions. It is also observed that the optimum size of non-convective zone yielding maximum efficiency depends on the effectiveness of ground heat extraction. Further, calculations are made for the minimum salt diffusion rate required to sustain stable pond operation. It is observed that the idealized exchanger performance assumption underestimates this critical value and a design based on it may initiate instability. Finally, calculations are made for the net entropy production rate which is also seen to be under-predicted with the existing theory. The present work can therefore prove useful for making an accurate assessment of the performance and stability of solar ponds involving ground heat extraction.