Impact of micromixing on performance of a membrane-based absorber

Abstract

a b s t r a c tIn this study, microstructures are employed to manipulate thermohydraulic characteristics of the lithium bromide (LiBr) solution flow in a membrane-based absorber in order to enhance the absorption rate. In a membrane-based absorber, the liquid absorbent is constrained between a solid wall and a highly permeable membrane, thus facilitating manipulation of the flow properties. Recent numerical studies have shown that transport mode in a laminar flow can be changed from diffusive to advective via the implementation of surface microstructures on the flow channel walls. Here, we experimentally evaluate the enhancement in absorption rate caused by the introduction of microstructures on the solution flow channel wall of a membrane-based absorber. The experiments are conducted in a fully instrumented membrane-based absorption refrigeration system. The geometry and dimensions of the microstructures are based on the optimal values determined in our previous numerical studies. Absorption rates as high as that of a 100-mm-thick solution film (in the absence of wall features) is achieved but at two orders of magnitude less pressure drop. The achievement of a high absorption rate at a relatively low solution pressure drop in the proposed approach enhances the prospect of developing large-scale membranebased absorbers.

Role of Membrane Technology in Absorption Heat Pumps: A Comprehensive Review

“…According to the authors, the reduced size of the membrane absorbers could help develop new absorption cooling systems for small scale applications. Isfahani et al [ 111 ] studied the performance of a membrane absorber with microstructures on the solution flow channel to promote vortex generation and to improve the mass transfer process. The microchannels were 0.5 mm deep, 1 mm wide, and 195 mm long, while the microstructures were 0.2 mm deep and were in a 30° herringbone arrangement.…”

Experimental performance comparison of three flat sheet membranes operating in an adiabatic microchannel absorber

“…It was also higher than the value reported by Ali and Shwerdt [1] in their plate absorber. Later, Isfahani et al [13] employed micro protrusions on the solution channel wall to enhance the absorption rate.…”

Efficiency analysis of semi-open sorption heat pump systems

“…This challenge can be addressed by implementing a thermal barrier like a membrane [9]- [13], which allows mass transfer of vapor but impedes heat transfer from the interface to the air side. Membrane technology can also enable absorption enhancement techniques like micromixing (demonstrated numerically by Bigham et al [14] and experimentally by Nasr Isfahani et al [15]) or can be combined with a finned structure as demonstrated in Mortazavi et al [16].…”

“…The unknowns are α, T interface , and . Note that T interface appears as an argument in an equilibrium EOS for vapor pressure in Equation (15). Since this EOS does not have a simple analytical form, a solution of this system of three equations must be pursued using a numerical solver.…”

“…In this work, Engineering Equation Solver, which includes a built-in equilibrium vapor pressure EOS for water/LiBr, was used to generate the results shown in Sections 3 and 4. 13; (14) ; (15) .…”