CFD simulation to investigate heat and mass transfer processes in a membrane-based absorber for water-LiBr absorption cooling systems

Absorption cooling systems employing membrane based components provide an interesting opportunity to use the technology for small scale applications. Steady-state heat and mass transfer analyses of a water-lithium bromide membrane based absorber are performed. CFD (computational fluid dynamics) tool ANSYS/FLUENT 14.0 is used to perform the simulation and investigate the behaviour of the heat and mass transfer mechanisms at local levels in the channels. Results show that the solution film thickness is an important parameter which significantly affects the mass transfer mechanism. It was observed that the absorption rate increased by a factor of 3 when the solution channel thickness was reduced from 2 mm to 0.5 mm. In addition, the absorption rate was increased by a factor of 2.5 when the solution inlet flow velocity was increased from 0.00118 m/s to 0.00472 m/s. The solution film thickness and velocity can be independently controlled in plate-and-frame membrane based absorbers. Therefore to design a compact and efficient plate-and-frame membrane absorber with water as a refrigerant, an optimum value of 0.5 mm for the solution channel thickness is suggested and a solution inlet velocity of about 0.005 m/s is recommended to achieve high absorption rates with acceptable pressure drop along the solution channel.