DEVELOPMENT OF HFC-134a ABSORBENTS FOR THE CHEMICAL/MECHANICAL HEAT PUMP

This paper will describe the screening and development of absorbents for HFC-134a in the chemical/mechanical heat pump. The absorbents must have low volatility, low melting point, high solubility for HFC-134a vapor, high heat of mixing with HFC-134a, suitable vapor pressure/temperature concentration characteristics when mixed with HFC-134a, low toxicity, low flammability, and thermal stability. A screening procedure was used to select approximately 15 absorbents for experimental evaluation. Measurement of the key physical and thermodynamic properties of the absorbent/HFC-134a mixtures, such as vapor pressure/temperature/concentration properties, materials compatibility, and thermal stability, is described. From these measurements, activity coefficients, enthalpy of mixing, and entropy of mixing of the liquid solution were determined. This physical and thermodynamic property information was then used to calculate the theoretical performance of the absorbent/HFC-134a pairs in a chemical/mechanical heat pump computer simulation. This simulation allowed for the evaluation of the effects of different absorbent/refrigerant mixtures, different mixture concentrations, and different temperature lifts on calculated performance. Recommendations of the most suitable absorbent/HFC-134a pairs for use in a breadboard demonstration unit are made.