Near-zero shear stress experiments with heat flux effects on falling film evaporation inside a vertical tube

2014 ◽  
Vol 76 ◽  
pp. 137-146 ◽  
Author(s):  
T. Storch ◽  
Ch. Philipp ◽  
A. Doeg ◽  
U. Gross
Keyword(s):  
Heat Flux ◽  
Shear Stress ◽  
Vertical Tube ◽  
Falling Film ◽  
Film Evaporation ◽  
Falling Film Evaporation

Horizontal-Tube Falling-Film Evaporation With Structured Surfaces

1989 ◽  
Vol 111 (2) ◽  
pp. 518-524 ◽  
Author(s):  
M.-C. Chyu ◽  
A. E. Bergles
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Pool Boiling ◽  
Nucleate Boiling ◽  
High Heat ◽  
High Flux ◽  
Falling Film ◽  
Structured Surfaces ◽  
Film Evaporation ◽  
Falling Film Evaporation

Extensive experimental tests for tubes with commercial structured surfaces in a horizontal single-tube falling-film evaporator were conducted. The test sections were hollow copper cylinders with GEWA-T, Thermoexcel-E, or High Flux surfaces electrically heated by inserted cartridge heaters. A smooth surface cylinder was also tested for reference. All tubes were tested in both pool boiling and falling-film evaporation with water. The results reveal that falling-film evaporation provides much higher heat transfer coefficients than pool boiling in the low heat flux, convective region. The GEWA-T surface enhances heat transfer through its increased and accessible area, while Thermoexcel-E and High Flux demonstrate high heat transfer performances because of enhanced nucleate boiling. The falling-film evaporation data for the structured surfaces either merge or show a tendency to merge with the respective pool boiling curves at high heat fluxes. Unusual incipient boiling behavior of Thermoexcel-E and the effects of factors such as surface aging, surface subcooling, film flow rate, liquid feed height, and rate of heat flux change, are described.

scholarly journals Heat Transfer Enhancement of Falling Film Evaporation on a Horizontal Tube by Thermal Spray Coating

2020 ◽  
Vol 10 (5) ◽  
pp. 1632 ◽  
Author(s):  
Tsutomu Ubara ◽  
Hitoshi Asano ◽  
Katsumi Sugimoto
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Heat Transfer Enhancement ◽  
Spray Coating ◽  
Horizontal Tube ◽  
Thermal Spray Coating ◽  
Falling Film ◽  
Transfer Enhancement ◽  
Film Evaporation ◽  
Falling Film Evaporation

Falling film evaporators are gaining popularity as substitutes to typical flooded evaporators because of their low refrigerant charge. It is important to form and keep a thin liquid film on the heat transfer surface to ensure their high heat transfer performance. In this study, as a heat transfer enhancement surface, a fine porous surface processed using thermal spray coating was applied to a smooth copper tube with an outer diameter of 19.05 mm. Heat transfer coefficients of falling film evaporation on a single horizontal tube were experimentally evaluated using the HFC-134a refrigerant. The experiments were performed at a saturation temperature of 20 °C with the heat flux ranging from 10 to 85 kW·m−2 and for film Reynolds numbers up to 673. The study aimed to clarify the effect of the coating on the heat transfer characteristics of falling film evaporation. The results revealed that the coating could suppress partial dry out and enhance nucleate boiling in the falling film. The maximum heat transfer enhancement factor was 5.2 in the experimental range. It was further noted that the effect of the coating was especially strong under a low heat flux condition.

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