Abstract
A novel system for recovering waste heat is investigated, consisting of an auto-cascade cell and working fluids of tetrafluoro-ethane (R134a)/trifluoro-methane (R23)/dimethylformamide (DMF). For the novel system, reliable models are developed by applying thermodynamic principles and the Peng–Robinson equation of state. The main factors are discussed from broader insights that affect the performance of the novel system. It is found that there is an optimal generating pressure and composition of R134a/R23 mixtures to obtain a maximum coefficient of performance (COP), which are affected, not only by generating, condensing, and evaporating temperatures, but also by absorption temperatures. Under general operational conditions, the maximum COP ranges from 0.048 to 0.1093, and the optimal mole ratio of R23 to R134a ranges from 0.29 to 0.41. Moreover, the experimental refrigeration temperature reaches −62.3 °C and the COP is 0.023, with an enhancement of 30%, which corresponds to an optimal generating pressure of 1130 kPa and a mole ratio of 0.3. Through the theoretical and experimental results, it is demonstrated that mass and energy coupling of refrigerants in the auto-cascade cell has key effects on the performance. It also shows that refrigeration temperatures could be lowered, and that COP is improved by staged double absorbers.
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