Abstract
Wet ammonia-water compression-resorption heat pumps constitute an attractive alternative to the commonly known heat pumps based on Osenbrück cycle because they eliminate the necessity of oil-liquid refrigerant separation. In this respect, a special designed oil-free compressor operating under wet (two-phase) conditions equips the heat pump. The compressor is lubricated by the liquid refrigerant which is carried-out while compressing the vapor. The thermodynamic cycle is located completely inside the two-phase region. In this paper are demonstrated two procedures to optimize the design for COP maximization. It is shown that there is: (i) an optimal choice of the vapor quality at suction, and (ii) an optimal distribution of heat transfer surface between the resorber and the desorber (the total amount of heat transfer surface, being an expression of investment cost, is fixed). The circulating concentration of ammonia has to be chosen such that the minimum pressure in the system is over one bar (to avoid air penetration from the atmosphere) and the maximum pressure is bounded by a technical-economical maximal limit. A general procedure for calculation of the optimal cycle parameters is presented and exemplified for a case with practical relevance. The paper presents only the trends and rough quantitative estimations because the analyzed case is restricted to the ideal isentropic compression. Further research is needed to quantify in detail the effect of compression irreversibility.
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