Numerical study on heat and mass transfer behavior of pool boiling in LiBr/H2O absorption chiller generator considering different tube surfaces

Abstract

Investigating the pool boiling process in the absorption chiller generator by studying the valid parameters may enhance the chiller's coefficient of performance (COP). In the present study, the transient two-dimensional numerical modeling of LiBr/H2O solution pool boiling in the generator of the absorption chiller was carried out using the two-phase Eulerian- Eulerian approach, extended Rensselaer Polytechnic Institute (RPI) boiling model and renormalization group (RNG) K-? turbulence model. The numerical model was applied on three types of the bare, notched fin, and low fin tubes to investigate the effect of using fin on the boiling heat transfer rate in the generator of the absorption chiller and comparing it with the bare tube. Moreover, the numerical results were compared with the data obtained from the previous experimental studies to validate numerical modeling. A good agreement was achieved between numerical and experimental results. The results showed the evaporation mechanisms in the microlayer, evaporation in the three-phase (liquid-vapor-solid) contact line, and transient conduction to the superheat layer for constant thermal heat flux and the three surfaces of the copper tube within a specific period from the boiling point of LiBr/H2O solution. The results also showed that the use of a notched fin-tube and low fin tube increases the non-homogeneous nucleation rate, causes the solution to boil earlier than the bare tube, and reduces the required thermal energy in the generator of an absorption chiller.

Thermo-economic analysis and optimization of the steam absorption chiller network plant

“…The mechanical compressor of a compression chiller is indeed substituted by a thermal compressor, where the refrigerant vapor at the outlet of the evaporator is first absorbed in an absorbent solution, pumped to the higher-pressure level, and then desorbed again in the generator [4,5]. To drive this process, a low temperature heat source is necessary at the generator [6][7][8][9]. The absorption refrigeration cycle is gaining considerable attention because it can make fair use of low grade waste heat for cooling demand and employ eco-friendly refrigerant [10,11].…”