Performance of a Compression-absorption Heat pump System Driven by Low-temperature Geothermal Water

Abstract

This paper analyzes the performance of a compression-absorption heat pump (CAHP) system driven by low-temperature geothermal water. Two models, respectively, for the generator and whole system using ammonia-water as the working fluid are proposed. The results show that there is an optimum concentration around 65% for the system. The maximum of overall heat transfer coefficient can be obtained with optimum spray density between 0.13 and 0.19 kg•m•s of ammonia water solution. Operating with a high heat sink temperature between 70 and 85°C, and a low heat source temperature from 25 to 40°C, the COP of the system is above 4. KeywordsCAHP; COP; vertical out-tube falling film; generator; ammonia-water NOMENCLATURE COP the electrical coefficient of performance h enthalpy J/kg δ film thickness mm v velocity of y direction m/s u velocity of x direction m/s ξ solution concentration λ coefficient of heat conductivity ΔH enthalpy difference J/kg ρ density kg/m3 m mass kg m& mass transfer of ammonia vapor kg e compression ratio Ug heat transfer coefficient of generator w/(m2•k) V volume flow m/s ηis isentropic efficiency f cycle ratio Dm mass transfer coefficient mm Do outside diameter mm Di inner diameter mm Subscripts 1~12 condition points of Fig .1 0 initial state a absorber g generator w water