Contents lists available at ScienceDirect Applied Thermal Engineering journal homepage: www.elsevier.com/locate/apthermeng Research Paper Augmented heat and mass transfer effect on performance of a solar still using porous absorber: Experimental investigation and exergetic analysis A.F. Mohamed a , A.A. Hegazi a , G.I. Sultan a , Emad M.S. El-Said b, ⁎ a Mechanical Power Engineering Department, Faculty of Engineering, Mansoura University, Mansoura, Egypt b Mechanical Engineering Department, Faculty of Engineering, Fayoum University, Fayoum, Egypt HIGHLIGHTS • The influence of enhanced heat and mass processes on the performance of a SS using porous absorber was investigated. • The Nusselt, Sherwood numbers and exergy efficiency were studied and discussed. • The average Nusselt and Sherwood numbers were enhanced by about 115% and 51.95% respectively. • The exergy efficiency was enhanced by about 123%. ARTICLE INFO Keywords: Solar still Porous absorber Exergy Nusselt number Sherwood number ABSTRACT In this paper, an experimental study is performed to investigate the influence of heat and mass transfer en- hancement on the solar still thermodynamic performance by using porous absorber. This study used two identical solar stills with the basin area of 1 m 2 : one is conventional and the other has a layer of fine basalt stones in the base of the still as a porous absorber with different particle size (1 cm, 1.5 cm and 2 cm). The experimental results showed that the average Nusselt and Sherwood numbers inside the solar still cavity by using porous bed with different porosity based on stone particle size were enhanced by about 115% and 51.95% respectively. Also, The exergy efficiency of the solar still with the 1 cm, 1.5 cm and 2 cm fine stone particle size was enhanced by about 65%, 104.4% and 123% respectively compared to solar still without stones. In addition, the empirical correlations to estimate the Nusselt and Sherwood numbers inside the solar still cavity were obtained. The agreement between these correlations and experimental results was fairly good. 1. Introduction Solar still (SS) has been considered as an alternative desalination device for utilizing solar thermal energy to provide the isolated or re- mote areas by fresh water [1,2]. The performance of SS depends on climatic, design and operational parameters such as ambient tempera- ture, solar radiation intensity, weather condition, inclination angle and brine water depth [3]. To enhance the SS performance, it is important to improve the heat and mass transfer processes inside the still cavity by changing the flow treatment by using two main methods; active and passive [4]. A lot of research has been carried out to improve the SS performance by using heat storage materials as a passive method. Deshmukh and Thombre [5] investigated the performance of a single slope single basin SS with sand and servotherm medium oil as storage material beneath the basin liner. They studied the influence of different depth of storage material. Their results showed that the overnight productivity was enhanced while daylight productivity lowered. Kabeel et al. [6] investigated a single basin SS with high thermal conductivity sensible storage material (graphite) to study the effect of high thermal conductivity sensible storage materials (graphite) on the thermal per- formance. They found that the yield of a single basin SS with graphite was 7.73 L/m 2 with enhancement about 74.89-80.05% compared to a traditional one. Also, their results showed that the daily thermal effi- ciency for the single-basin still with graphite was between 33.41 and 34.6% with about improvement 200% compared to SS without gra- phite. Bait and Ameur [7] presented a comprehensive review about the role of nanofluids in enhancement of heat and mass transfer in SSs. Sarray et al. [8] studied the heat transfer, mass transfer, and entropy rate of humid air for a single SS to evaluate the influences of humid air temperature and pressure on heat and mass transfer and on the entropy rate on SS performance. They found that the increase of water vapor partial pressure and humid air temperature are the best conditions for https://doi.org/10.1016/j.applthermaleng.2019.01.070 Received 31 October 2018; Received in revised form 18 January 2019; Accepted 19 January 2019 ⁎ Corresponding author. E-mail address: emadsaad@fayoum.edu.eg (E.M.S. El-Said). Applied Thermal Engineering 150 (2019) 1206–1215 Available online 29 January 2019 1359-4311/ © 2019 Elsevier Ltd. All rights reserved. T