Convegni ATI - Accesso riservato soci CTI

Autore: V. Soldo, M. Grozdek, T. Curko

Collana: CA - 61 - Perugia 2006

Note:
The paper presents the calculation of heat transfer in a tube of the solar collector (evaporator) where the refrigerant R134a evaporates. The test system used consists of a compressor, a freon-water compact plate condenser, an electronic expansion valve and two parallel unglazed solar collectors. The solar-assisted heat pump with direct expansion of the refrigerant in the solar collector uses the solar irradiation and the ambient temperature as a heat source on the evaporator.
The heat transfer in the two-phase flow of the refrigerant in a horizontal tube is expressed by the expressions taken over from the VDI Wärmeatlas. The effect of the mass velocity G (kg/(m2 s)), the heat flux based on the inner surface of the tube q (W/m2) and the vapour quality x on the heat transfer coefficient in the heat pump solar collector is recorded.
Results of calculation have shown that the nucleate boiling is dominant in the first part of the evaporator-collector, while in the second part of the evaporator, with the increase in vapour quality, the convective evaporation prevails.