A comparative study of plain and enhanced helical microfin evaporator tube with drift flux-based entropy generation model for R32 and R410A refrigerants

Abstract

In the present paper, a comparative study is carried out to assess the relative thermodynamic performance of plain and helical microfin evaporator tubes with two new emergent refrigerants, R32 and R410A. An entropy generation analysis is performed based on the drift flux model for two-phase forced convective boiling flow, and the comparison of the enhanced tube to the plain one is done quantitatively. A critical value of relevant parameters, i.e., mass flux, tube diameter, length, heat flux, inlet quality, and operating pressure, are identified, below or above which the enhanced tube is observed to be thermodynamically more favourable than the plain tube. The study reveals that by increasing the tube diameter from 8 mm to 14 mm, the critical mass flux increases from 335 kg/m2s to 495 kg/m2s for R32 and 394 kg/m2s to 565 kg/m2s for R410A, respectively, below which the enhanced tube performs better. The helical microfin tube exhibits a better performance below a critical mass flux from 412 kg/m2s to 374 kg/m2s for R32 and 492 kg/m2s to 443 kg/m2s for R410A when tube length increases from 1 m to 5 m. The critical inlet quality, below which the enhanced tube is observed to be superior, shifts to a lower value (0.29 to 0.16 for R32 and 0.44 to 0.26 for R410A), increasing the mass flux from 400 kg/m2s to 500 kg/m2s. However, the enhanced tube shows a better performance above a critical operating pressure, which increases from 11.4 bar to 16.9 bar for R32 and 9.3 bar to 13.4 bar for R410A, with increasing the mass flux from 400 kg/m2s to 500 kg/m2s. The enhanced tube performs better below a critical mass flux which increases from 336 kg/m2s to 461 kg/m2s for R32 and 399 kg/m2s to 489 kg/m2s for R410A when the heat flux is increased from 8 kW/m2 to 15 kW/m2. The overall parametric study with two emergent refrigerants enables one for effective selection of the helical microfin evaporator tube for a suitable range of relevant parameters.