Liquid recirculation, evaporator performance, heat transfer measurements, numerical model
In the present work, the performance of a segmentally baffled shell-and-tube evaporator working with liquid overfeeding is investigated. The refrigerant is R134a that flows inside the tubes, while water flows on the shell side. A single shell pass has been adopted for the water with one tube pass for the evaporating fluid. The test rig used for the experimental measurements consists of a primary refrigerant loop plus the condenser and the evaporator water auxiliary loops. The evaporator can be fed with two-phase mixture from the expansion valve or with saturated liquid coming from the liquid-vapor separator (in this case a variable speed recirculation pump is used). Inlet and outlet temperatures have been measured for both fluids together with the flow rate allowing the determination of the overall heat transfer coefficient. In addition, pressure drop have been measured on the refrigerant side. Tests have been performed both without overfeeding and with overfeeding at different values of recirculation ratio. The recirculation ratio is defined as the ratio between refrigerant flow rate at the evaporator and the vaporized refrigerant flow rate. Furthermore, measurements have been taken at fixed water outlet temperature and varying the heat duty. In order to study the evaporator behavior, a computational procedure has been developed. Finally, the numerical model of the heat exchanger has been validated against experimental data.