Condensation of Hydrocarbons in Compact Smooth and Microfinned Tubes

Abstract

A database for flowing condensation of three hydrocarbons, namely propane (R290), isobutane (R600a), and propylene (R1270), is extended by experimental tests in a smooth tube and two microfinned tubes with an increase of heat exchange area of 1.51 and 2.63, respectively. The outer diameter for all of the test tubes was 5 mm. Heat transfer coefficient and pressure drop are compared between the fluids and tubes. Tests were conducted at saturation temperatures of 35 °C and mass fluxes between 200 to 500 kgm−2s−1. Results show that isobutane (R600a) has a higher heat transfer coefficient and pressure drop while propylene (R1270) and propane (R290) present very similar characteristics. Both microfinned tubes increase the heat transfer coefficient compared to the smooth tube, but with different magnitude and tendencies and almost independently of the fluid tested. The maximum increase of heat transfer coefficient reached values of up to 1.8 while the maximum increase in pressure drop was by a factor of 1.7. Data have been compared with predictive methods exhibiting accurate correlation for smooth tube, while the accuracy of results for the microfinned are dependent on the type of tube and fluid used.

Numerical Study of Hydrocarbon Charge Reduction Methods in HVAC Heat Exchangers

“…These problems are explained by the inability of the correlations to predict HTC of microfinned tubes with a high number of fins. This was expected and it is well documented in Allymehr et al [10,11]. It can be seen in Table 5 where the δ30% value for MF2 tube is significantly lower than MF1 tube.…”

“…The correlations for microfinned tubes are specially developed to consider specific geometrical characteristics of the tubes that can significantly affect HTC and pressure drop values. The prediction methods considered in the current study are based on the best performing correlations shown in [10][11][12], they are summarized in Table 5 where δ30% presents the number of experimental data points that the correlation can predict with less than 30% error. The correlation from Granryd [27] was used for the airside heat transfer and pressure drop.…”

“…Different studies have shown the possibility to run specially designed low charge heat pumps with capacities up to 8 kW with a maximum charge of 150 g to fulfill regulations and provide maximum safety by minimizing inner volume, especially for components containing liquid refrigerant [7][8][9]. Studies have shown that hydrocarbons' heat transfer coefficient can be increased substantially by using microfinned tubes with minimum penalization in pressure drop [10][11][12], which could be utilized to reduce refrigerant charge of heat pumps. Moreover, brazed plate heat exchangers (BPHE) are favorable for condensation and evaporation due to their low inner volume at high thermal capacity.…”