Heat and mass transfer in a quasi-counter flow parallel-plate membrane-based absorption heat pump (QPMAHP)

• A quasi-counter flow parallel-plate membrane absorption heat pump (QPMAHP) is proposed.
• Heat and mass transfer in QPMAHP for heating are investigated.
• The QPMAHP with small entrance ratio and aspect ratio have better performances.

A quasi-counter flow parallel-plate membrane-based absorption heat pump (QPMAHP) is proposed and used for fluid heating. The concept is like a combined counter/cross-flow parallel-plate membrane contactor, where the refrigerant (water) and the absorbent (salt solution) flows are separated by the semi-permeable membranes, which only guarantee the permeation of water vapor. The solution stream attracts the water vapor from the water stream across the membranes. Latent and mixing heats are then released on the solution side for upgrading low-temperature heat to high temperature useable heat. A mathematical model is established in a unit cell, containing two membranes with an air-gap in between and two neighboring channels, to study the coupled heat and mass transports in the QPMAHP. A finite difference method is employed to solve the normalized equations governing momentum, heat and mass transports. The solution temperature lift and efficiency are then obtained. A heat pump system based on the QPMAHP is designed and set up to validate the results. It can be found that the solution temperature lift and efficiency increase about 9.1% when the entrance ratio and aspect ratio are equal to 0.1 compared to those of a cross-flow one.