Numerical Investigation of the Flow Characteristics of Liquid Film in the Process of Falling Film Evaporation

2016 ◽  
Author(s):  
Lin Zhang ◽  
Xuecheng Fan ◽  
Weigang Xu ◽  
Feng Jiang ◽  
Yang Wang ◽  
...  
Keyword(s):  
Liquid Film ◽  
Numerical Investigation ◽  
Flow Characteristics ◽  
Falling Film ◽  
Film Evaporation ◽  
Falling Film Evaporation

Falling Film Evaporation of Pure Refrigerant HCFC123 in a Vertical Rectangular Minichannel Consisting of Offset Strip Fins

2005 ◽  
Author(s):  
Junichi Ohara ◽  
Shigeru Koyama ◽  
Ken Kuwahara
Keyword(s):  
Heat Transfer ◽  
Liquid Film ◽  
High Speed ◽  
Video Camera ◽  
Flow Patterns ◽  
Front Wall ◽  
Falling Film ◽  
Film Evaporation ◽  
High Speed Video Camera ◽  
Falling Film Evaporation

In the present study, the characteristics of heat transfer and flow patterns are experimentally investigated on the falling film evaporation of pure refrigerant HCFC123 in a vertical rectangular minichannel consisting of offset strop fins. The refrigerant liquid is supplied to the channel through 37 holes of a distributor. The liquid flowing down vertically is heated electrically from the rear wall of the channel and evaporated. To observe the flow patterns during the evaporation process directly, a transparent vinyl chloride resin plate is placed as the front wall. The experimental parameters are as follows: the mass velocity G = 28∼70 kg/(m2s), the heat flux q = 20∼50 kW/m2 and the pressure P≈ 100 kPa. It is clarified that the heat transfer coefficient α depends on G and q in the region of vapor quality x ≥ 0.3 while there is little influence of G and q in the region x ≤ 0.3. From the direct observation using a high speed video camera and a digital still camera, flow patterns are classified into five typical ones: plane liquid film, wavy liquid film, liquid film accompanied with dry patch, liquid film accompanied with dripping and liquid film accompanied with mist. Then the relation between heat transfer and flow pattern is clarified. The results of heat transfer characteristics are also compared with some previous correlation equations.

NUMERICAL INVESTIGATION OF FILM DISTRIBUTION IN HORIZONTAL-TUBE FALLING FILM EVAPORATOR

2011 ◽  
Vol 19 (03) ◽  
pp. 177-183 ◽  
Author(s):  
JIN-BO CHEN ◽  
QING-GANG QIU
Keyword(s):  
Numerical Simulation ◽  
Fluid Flow ◽  
Film Thickness ◽  
Liquid Film ◽  
Numerical Investigation ◽  
Horizontal Tube ◽  
Flow Density ◽  
Falling Film ◽  
Film Distribution ◽  
Simulation Results

The technique of horizontal-tube falling film has been used in the cooling and heating industries such as refrigeration systems, heating systems and ocean thermal energy conversion systems. The comprehensive performance of evaporator is directly affected by the film distribution characteristics outside tubes. In this paper, numerical investigation was performed to predict the film characteristics outside the tubes in horizontal-tube falling film evaporator. The effects of liquid flow rate, tube diameter and the circular degree of tube on the film thickness were presented. The numerical simulation results were compared with that of the empirical equations for calculating the falling film thickness, and agreements between them were reasonable. Numerical simulation results show that, at the fixed fluid flow density, the liquid film is thicker on the upper and lower tube and the thinnest liquid film appears at angle of about 120°. The results also indicate that, when the fluid flow density decreases to a certain value, the local dryout spot on the surface of the tube would occur. In addition, the film thickness decreases with the increases of the tube diameter at the fixed fluid flow density.

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