Investigation of Heat Transfer and Pressure Drop for R744 in a Horizontal Smooth Tube of R744/R404A Hybrid Cascade Refrigeration System—Part 2: Low-Temperature Region

This paper studies the evaporative heat transfer characteristics of R744 at low temperatures in a horizontal smooth tube as cascade refrigeration system (CRS) among hybrid systems (HCRSs). There is lack research on low-temperature under operating conditions evaporators used actual CRSs supermarkets. Therefore, this study aims to provide basic data refrigerators The evaporation experiment conducted herein was copper with an inner diameter and length 11.46 mm 8000 mm, respectively. experimental parameters were follows: fluxes 11.8–21.3 kW/m2, mass 76.3–175.1 kg/(m2·s), saturation −49.8–−30.2 °C. main results are summarized coefficient can be predicted well by using correlation formula Chen temperature −40 °C CRS.