Film condensation experiments of R1233zd(E) over horizontal tubes and high-temperature condensation predictions for high-temperature heat pump

In the context of carbon neutrality goals, the heating process, which contributes to half of energy consumptions, is urgent to achieve electrification under the trend of growing renewable electricity. To replace fossil fuel-fired boilers, the high-temperature heat pump (HTHP) is preferable for industrial heating decarbonization. However, the high-temperature and large-scale challenges propose requirements for critical component development, including the shell-and-tube condenser. The design principle of enhanced structure, which is unique for high-temperature condensation and low-global warming potential (GWP) refrigerant characteristics, still needs to be improved. This paper conducted R1233zd(E) condensing experiments over horizontal tubes and modified the condensation Nusselt formulas based on different structures. The modified models are applied to predict high-temperature film condensation performance. 2D tube with ε = 1.0 (the ration of rib height and pitch) yields the best heat transfer performance among the ε structures of 0.6–1.2. The 3D structure with ε = 1.0 design yields better enhancement performance under condensation temperature lower than 100 °C; when the condensation temperature is over 100 °C, the 2D tube of ε = 1.0 shows similar heat transfer coefficients (HTCs). Characteristics analysis of high-temperature condensation are conducted to prove the optimal rib structure. Due to surface tension decay, gravity gradually dominates as the main driving force for condensate film flowing above 100 °C saturation temperature, resulting in the limited effect of 3D structures. Further, 2D tubes with different rib pitches and heights are analyzed from flooding ratio and effective area enhancement, proving ε = 1.0 and 1 mm rib pitch as the preferable structure for R1233zd(E) high-temperature condensation.