Heat Transfer and Pressure Drop of R1234yf Boiling in Helically Coiled Tubes

In the present study, the boiling flow of R1234yf refrigerant in a horizontal helically coiled tube is investigated to experimentally measure the heat transfer coefficient and pressure drop. A well-instrumented apparatus consisting of the test evaporator and other necessary equipment is used in this investigation. A preheater and a post-evaporator are used to achieve the required vapor qualities and test conditions. Experimental investigations are carried out for a straight tube of 8.7 mm inner diameter and 1,200 mm length as well as helically coiled tubes with three different coil diameters of 10.95, 13.45, and 15.95 cm. For each experiment, different characteristic parameters such as refrigerant flow rate, outside tube surface temperature at various locations, heat flux, and pressure drop within the test section are measured. The results reveal that under the flow conditions studied in this work, heat transfer coefficient is increased up to 299% for the helically coiled tube compared to the horizontal straight tube. In addition, it is observed that for a constant coil pitch, pressure drop increases up to 227% occurring at the minimum coil diameter of 10.95 cm. Moreover, it is found that among the available models, Gungor and Winterton correlation predicts the experimental data with the least error.