A numerical study on the effect of the heat sink as condenser on the performance of passive solar still
A theoretical work is presented to study the effect of using heat sink as condenser on the performance of passive solar still. Single acting solar still facing the south with pure saline water is used in this work. During this study, a heat sink of a tip fin is used as a condenser instead of vertical glass plate of the conventional passive solar still. The theoretical model of the energy balance equations for each component: the basin water, the cover glass, the basin base and the condenser of the solar still were presented. The theoretical model was numerically solved by using MATLAB to assess the temperatures of the various components, the desalinated water productivity, and the system performance. To examine the validity of the model, the numerical results were compared with the available experimental data in the literature. It is found that the numerical results were in close agreement with the experimental data for both the components' temperatures and output productivity. A comparison of the performance of the studied solar still and the conventional solar still is presented. The results showed that the maximum productivity and efficiency of the solar still with heat sink as condenser are 0.8756 kg/m2.hr and 61.72 %, respectively comparing with 0.4305 kg/m2.hr and 30.35% for conventional solar still at the same conditions. Additionally, heat sink as condenser increases also the performance of the solar still compared to conventional solar still.
Assessment of convective heat transfer coefficient and mass of water evaporated from a single-slope passive solar still by different thermal models: an experimental validation
Abstract In this paper, an effort has been made to evaluate the convective heat transfer coefficient and mass of water evaporated from a single-slope passive solar still for different water depths (0.01, 0.015, 0.02 and 0.025 m) by various thermal models, namely Dunkle’s model, Chen et al.’s model, Clark’s model, Adhikari et al.’s model, Kumar and Tiwari’s model, Zheng Hongfei et al.’s model and Tsilingiris’s model. These models were studied and compared with our experimental work. Also, the energy and exergy efficiency were calculated and the percentage deviation between experimental and theoretical prediction is also listed out. The experimental validation of energy and exergy efficiency of single slope passive solar still using different thermal models was carried out at Chennai, Tamil Nadu, India. By comparing the theoretical values of the hourly yield with the experimental data it was found that Dunkle’s, Chen et al.’s and Tsilingiris’s models gave better conformity between the forecasted and experimental results. Kumar and Tiwari’s model yield is very high, whereas Clark’s model, Adhikari et al.’s model and Zheng Hongfei et al.’s model predict lower values as compared with our experimental results.
Techno-economic analysis of solar thermal power plants using liquid sodium as heat transfer fluid
Abstract Solar thermal power plants with central receiver and thermal storage are expected to be one key technology in future electricity generation, because they are renewable and due to the thermal storage independent of the current solar radiation. State-of-the-art solar power plants often use molten nitrate salts as heat transfer fluid. The use of liquid sodium instead leads to lower electricity generation costs. Sodium has a high thermal conductivity and thus large heat transfer rates are possible. Hence, a smaller absorber surface is sufficient for the same thermal power. As a result, the sodium receiver achieves a higher efficiency at lower investment cost. Additionally, the aiming strategy, which reduces the peak heat flux on molten salt receivers isn’t necessary for sodium. Even at high heat flux densities, the absorber tubes will be cooled sufficiently due to the high heat transfer coefficients. Therefore, the sodium receiver in this analysis is designed for one single aim point, resulting in a heat flux density of q mean = 1.06 MW / m 2 and q peak = 2.99 MW / m 2 . The state-of-the-art system with molten salt considers q mean = 0.51 MW / m 2 and q peak = 1.0 MW / m 2 . The presented techno-economic analysis of two sodium based concepts compared to a reference system with molten salt results in up to 16% lower electricity generation costs.