Experimental analysis of a novel helical air gap membrane distillation system

Abstract

Membrane distillation presents one of the feasible solutions to fresh water problems. The present study aims to develop an innovative Helical Air Gap Membrane Distillation (HAGMD) system and to analyze its behavior under different operating conditions. In this design the condenser is made up of a cylindrical copper tube with continuous helical fins over it, that increases the total available condensation area by almost 45% and enhances the overall heat transfer throughout the module. The presence of fins in the gap also reduces the total air gap width by almost 64%and therefore improves the flux production. A detailed experimental analysis is carried out for a better understanding of the underlying phenomenon. The effect of feed water temperature, feed flow rate, cold flow rate, coolant temperature and feed salinity on the performance of HAGMD is investigated experimentally. The analysis shows that the finned condenser results in very high flux. The maximum flux obtained from the system was 20 kg/m2 hr with feed of 5gm/liter salinity and a diving force temperature difference of 45 °C.

Theoretical analysis and parametric investigation of an innovative helical air gap membrane desalination system

“…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). The complete details of the components and the assembly are shown in a three-dimensional Fig.…”

“…The flowing condensate may also develop a centrifugal inertial suction force as it flows in a helical manner, sweeping the condensate diffusing through the membrane surface (Video 1, Annexure 1), and this way the vaporization may be accelerated at the feed-membrane interface. However, this effect may be minor but may help in the vaporization and therefore in increased the permeate production (Shahu and Thombre 2021).…”

“…The fins and the condenser tube are made up of copper as the thermal conductivity of this metal is very high that will facilitate the heat transfer through them. The copper was selected as the fin material because the inclusion of copper in the potable water helps in adding important nutrients and makes it more beneficial for the health (Shahu and Thombre 2021).…”

“…With the increased number of fins, the condensation surface area increases and therefore the heat transfer rate of the latent heat of condensation to the condenser is increased (Shahu and Thombre 2021). And hence, the permeate flux for 35 fins is more than that with 1 fin.…”

Comparison of the Effect of Air and Permeate Gap Regions on Highly Saline Water Desalination Using Hollow Fiber Membrane Distillation Modules

“…The sources of lowtemperature such as waste heat and solar energy could be utilized efficiently by MD technology to warm the inlet feed saline solution. Compared with other MD technologies such as sweeping gas (SGMD) (Ajdar et al 2020), vacuum (VMD) (Shahu & Thombre, 2019), and direct contact membrane distillation (DCMD) (Damtie et al 2019), the air gap membrane distillation (AGMD) is deemed the best one in terms of having low heat loss and high thermal efficiency (Gao et al 2019;Abu-Zeid & ElMasry, 2020;Shahu & Thombre, 2020, 2021. However, the air gap region sandwiched between the membrane and cooling (condensing) plate decreased notably the productivity of pure drinkable water.…”