Abstract
A helical air gap membrane desalination (HAGMD) system is designed in the present study. The condenser is designed as a cylindrical shape with helical fins machined on the outer surface of a hollow copper condenser. A detailed theoretical model, studying heat and mass transfer in the HAGMD module, was developed. The theoretical model for a cylindrical system with fins is developed for the first time and is unique in the MD literature. Experimentation was carried out to examine the behavior of the HAGMD module under diverse design and operating conditions. The effect of cold flow rate, feed flow rate, feed temperature, the height of fins, the number of fins, and the length of the module is determined on the performance of the HAGMD system. Permeate flux and gained output ratio (GOR) were considered as the performance indicators of the system. Results showed that permeate flux increases with cold flow rate, feed temperature, feed flow rate, as well as number of fins, while the increase in height of fins negatively affects the flux. Theoretical model and experimental results are found to be in excellent agreement with only 6.7% of error which shows that the present theoretical model is excellent to predict the performance of any HAGMD system. For similar design parameters, the average flux increased by 135% for the finned HAGMD module, with 35 fins over the one with that only for 1 fin. Maximum experimental distillate flux is found to be 20 kg/m2 hr, and GOR is found to be 0.75.
Highlights
Out of all, the most important element for life is water
Air gap membrane distillation (AGMD) methods are favorable over other Membrane distillation (MD) configurations due to their ability to be used even with very high salinity solutions (Swaminathan et al 2018), allow internal heat recovery (Khayet and Matsuura 2011a), and higher thermal efficiency (Khayet and Cojocaru 2012)
A helical air gap membrane distillation module is a cylindrical AGMD module with helical fins machined on the outer surface of a conductive copper tube (Shahu and Thombre 2021)
Summary
The most important element for life is water. About 71% of the earth’s surface is covered with water, and still, we are facing water scarcity just because of mismanaged use of water resources. Alkhudhiri et al (2017) presented a detailed AGMD study to analyze the effect of different salts of NaCl, MgCl2, Na2CO3, and Na2SO4 with a high concentration on the permeate flux production and rejection factor They used three membranes with different pore sizes to check the influence of pore size on the performance. Summers et al presented a novel idea of direct solar heating of membrane to result in an increased thermal efficiency (Summers and Lienhard 2013) They included reduced pressure for lower diffusion resistance in the air gap. A double-pipe AGMD module was designed with PVDF hollow fiber membranes and capillary copper tube for heat exchange by Liu et al (2016) They introduced a term as equivalent distillation
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