Heat transfer enhancement of falling film evaporation of HFO-1233zd(e) and HFC-134a on a horizontal tube by thermal spray coating

Number: 2223

Author(s) : UBARA T., SUGIMOTO K.


A falling film evaporator can reduce the amount of refrigerant compared with a flooded evaporator. Required functions for the heat transfer surface in falling liquid film evaporation are thin liquid film formation without breaking at low heat flux, nucleate boiling promotion in liquid film, and suppression of liquid entrainment at high heat flux. In this study, a porous thermal spray coating using copper as the coating material was made on a copper cylinder. The heat transfer performance of falling film evaporation and pool boiling was evaluated using HFO- 1233zd(E) as the refrigerant, and the obtained results were compared with those for HFC-134a. The test cylinder was heated by a cartridge heater inserted at the center. Falling film evaporation experiments had been conducted with a film mass flow rate of 3.3×10-2 kg/(m·s), heat flux of 10 to 85 kW/m2, and a saturation temperature at 20 ºC. The effects of the thermal spray coating, heat flux and thermo-physical properties of the refrigerants on heat transfer performance were investigated. The heat transfer coefficient increased with increasing heat flux. For the thermal spray coating, a large hysteresis effect according to the heating procedure with increasing or decreasing heat flux was observed in the characteristics of the heat transfer coefficient. The heat transfer enhancement factor by the thermal spray coating was up to 4.8. The value was higher than that for HFC-134a, especially under high heat flux condition. In the comparison between pool boiling and falling film evaporation heat transfer, falling film produced higher heat transfer coefficients for the thermal spray coating while the heat transfer on the smooth surface deteriorated due to partial dryout. The fine porous structure enhanced liquid spreading by the capillary force and evaporation from the liquid film surface by vapor bubble agitation.

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  • Original title: Heat transfer enhancement of falling film evaporation of HFO-1233zd(e) and HFC-134a on a horizontal tube by thermal spray coating
  • Record ID : 30028443
  • Languages: English
  • Subject: Technology
  • Source: 2021 Purdue Conferences. 18th International Refrigeration and Air-Conditioning Conference at Purdue.
  • Publication date: 2021/05
  • Document available for consultation in the library of the IIR headquarters only.


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