Energy and exergy analysis of a liquid desiccant heat and mass transfer loop with natural convection: The effect of heat sink and heat source temperature

Desiccant systems, as a promising air conditioning technology have opened new aspects as a
replacement for vapor compression systems. The liquid desiccant energy exchanger system with
natural convection flow is proposed here; the system is a loop with two hollow fiber membrane
air-desiccant exchanger of shell-and-tube type that works as the humidifier and regenerator. The
LiCl aqueous solution as desiccant directed over the fibers and the air is inside the fibers; the
water stream flows outside the modules to provide the required heat exchange. The heat sink and
source as merged subparts of the exchangers have a major influence on system performance. The
system is examined from the energetic and exergetic viewpoints at different heat sink and heat
source temperatures. Keeping the fixed air flow rate and using the standard air properties, the
cold and hot water temperatures of 15–25 ◦C and 50–70 were employed and the effectiveness
coefficients including the latent, sensible and total and 2nd law efficiency evaluated. It was shown
that the values of NTU and Cr* depend on each other and attenuating effect of NTU reduction is
higher than enhancing effect of Cr* increase on effectiveness values. The prominent factor on
exergy performance which hinders the effect of the other parameters is the solution flow rate.
Also, the highest and lowest values of 2 nd law efficiency are 81% and 5% which are for tem-
perature pairs of (52, 20) and (65,25), respectively.

Keywords:
Natural convection energy exchanger loop
Latent effectiveness
Heat sink temperature
Heat source temperature
Sensible effectiveness
2nd law Efficiency
Total effectiveness

https://doi.org/10.1016/j.csite.2023.102833