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This paper summarized recent research progress on the influencing factors and the enhancement methods of heat and mass transfer in falling film absorbers. In terms of influencing factors, this paper discussed tube spacing and diameter, solution inlet flow rate, temperature and concentration, coverage ratio of heat transfer surface, cooling water temperature and flow rate and water vapor pressure. In terms of enhancement methods, this paper summarized the methods of using additives in absorbent and optimizing the heat transfer surface of falling film absorbers. The research direction of the next stage will be to explain the influence mechanism of additives on heat and mass transfer through molecular dynamics simulation and enhance heat and mass transfer by integrating various methods. [ABSTRACT FROM AUTHOR]

The parallel dual-evaporator system has energy-saving potential in frost-free refrigerator-freezers, since it can provide proper evaporating temperature difference for the refrigerator and the freezer, respectively. However, energy loss is generated during the transition period of switches between refrigerating (R-) and freezing (F-) cycles in actual use. In this article, switch loss of a frost-free refrigerator-freezer with parallel dual-evaporator refrigeration system is studied experimentally. Results show that the transition process after F- to R-cycle switch takes 7.17 min and consists of three stages according to R-evaporator's feeding: short feeding (1.83 min), no feeding (2 min), and continuous feeding (3.34 min). The starvation in R-evaporator during the first two stages leads to switch loss for the refrigerator-freezer, by consuming 23.3% electric energy but yielding only 6.9% capacity for an entire R-cycle. The pump-down (P/D) action before R-cycles accelerates refrigerant's pumping from F-evaporator and feeding to R-evaporator, thus recovering part of the capacity loss. However, the introduction of P/D is not necessarily energy-efficient because P/D itself consumes considerable electric energy. By contrast, R- to F-cycle switch has little effect on refrigerator-freezer performance due to instant feeding. Dynamic simulation on the transition process will be provided in the future. [ABSTRACT FROM AUTHOR]

Periodical defrost actions are essential for the frost-free refrigerator–freezer to remove frost on the evaporator and recover its heat transfer performance. However, defrost heat could leak into the freezer and raise its temperature during defrost cycles. In this article, the effect of defrost heat leakage on freezer temperature rise of a frost-free refrigerator–freezer using an electric defrost heater was experimentally investigated. The defrost cycle was subdivided into three stages: heating, melting, and draining. Results show that in the heating stage, little warm air leaked into the freezer due to the obstruction of the frosted evaporator, so freezer temperature hardly rose (by less than 0.1°C/min). In the melting stage, flow area between adjacent fins gradually enlarged with frost melting from the bottom to the top of the evaporator; thus, warm air leaked into the freezer, raising its temperature by 0.6°C/min in average. In the draining stage, the adjacent-fin flow area reached maximum as nearly all the frost had been removed throughout the evaporator; hence, large amount of warm air entered the freezer and raised its temperature by 1.0°C/min. To the best of the author's knowledge, the stage-based acceleration in freezer temperature rise during defrost cycles was covered for the first time. [ABSTRACT FROM PUBLISHER]