Experimental investigation of phase change in a multitube heat exchanger

TLDR: In this paper, the melting and solidification processes in a multitube heat exchanger were investigated and the thermal characteristics of the units involving melting front, heat transfer rate and Nusselt number were also analyzed.

Abstract: The present paper investigates melting and solidification processes in a multitube heat exchanger. The shell side is filled with paraffin (RT35) while water flows through the tube passes as the heat transfer fluid (HTF). The arrangements of one, two, three and four inner tubes cases are studied for HTF inlet temperatures of 70 °C, 75 °C and 80 °C. The thermal characteristics of the units involving melting front, heat transfer rate and Nusselt number are also analyzed. Results indicate that increasing the number of inner tubes results in a faster pace of melting and solidification. The effect is so pronounced that, when the HTF inlet temperature is 80 °C, application of 4-tube heat exchanger reduces the duration required for complete melting and solidification up to 43 and 50 percent, respectively as compared to the corresponding single-HTF-tube case. The results also show that by increasing the number of tubes, the surface-averaged Nusselt number decreases. This can be attributed to the inhibition of upper pipes against PCM melt movement. Also a correlation is proposed to calculate Nusselt number of tubes. Comparing the temperatures recorded by the thermocouples in rotational direction, it is indicated that the variation of the inner tube arrangement affects solidification process more than melting.