Experimental Study of Heat Transfer Characteristics for Horizontal-Tube Falling Film Evaporation

2012 ◽  
Author(s):  
Xingsen Mu ◽  
Yong Yang ◽  
Shengqiang Shen ◽  
Gangtao Liang ◽  
Luyuan Gong
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Fresh Water ◽  
Horizontal Tube ◽  
Falling Film ◽  
Heat Transfer Characteristics ◽  
Film Evaporation ◽  
Transfer Characteristics ◽  
Falling Film Evaporation

The horizontal-tube falling film evaporation is a widely adopted technique in multiple-effect distillation (MED) desalination plant due to the higher heat transfer coefficient under quite small temperature differences. In the present study, an experimental platform for horizontal-tube falling film evaporation was set up to measure its heat transfer characteristics. Results indicate that heat transfer coefficient (h) for both fresh water and seawater are almost independent with heat flux. The h increases firstly and then decreases with growth of Re. Along the tube circumference, the h increases after decreasing. In addition, the distribution of h for fresh water and seawater at the different evaporation temperatures and Reynolds number (Re) are also provided.

Heat Transfer and Fouling Performance During Falling Film Evaporation in Vertical Porous Tubes

2020 ◽  
Author(s):  
Lei Wang ◽  
Weiyu Tang ◽  
Limin Zhao ◽  
Wei Li
Keyword(s):  
Heat Transfer ◽  
Stainless Steel ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Smooth Tube ◽  
Outer Diameter ◽  
Falling Film ◽  
Film Evaporation ◽  
Falling Film Evaporation ◽  
The Heat Transfer Coefficient

Abstract An experimental investigation was conducted on falling film evaporation along two porous tubes, which were sintered by stainless-steel powder with a diameter of 0.45 and 1 um, respectively. The test section is a 2 m long sintered tube with an outer diameter of 25 mm and a wall thickness of 2 mm. During the experiment, the pressure inside the tube was maintained at 1 atm, the inlet temperature was 373 K, and mass flux ranged from 0.51 to 1.36 kg/ (m s). Conditions of the steam outside the pipe, which was the heat source, were fixed, while the fouling tests were carried out at a constant mass flow of 0.74 kg/ (m s) using high-concentration brine as work fluid. The overall heat transfer coefficient under different working conditions was tested and compared with the stainless steel smooth tube of the same dimensions. The heat transfer coefficient of the two porous stainless tubes are about 35% and 20% lower than that of the smooth one, showing an inferior effect because the steam in the pores of the pipe wall during the infiltration process will reduce the heat conductivity. The heat transfer coefficient of the smooth tube deteriorated severely due to the deposition of calcium carbonate, which had little effect on the sintered tubes. Besides, the fouling weight of porous tubes is 2.01 g and 0 g compared with 5.52 g of the smooth tube.

Falling Film Evaporation of Binary Refrigerant Mixture in Vertical Rectangular Minichannels Consisting of Serrated-Fins

2014 ◽  
Author(s):  
Junichi Ohara ◽  
Shigeru Koyama
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Mass Fraction ◽  
Mass Velocity ◽  
Falling Film ◽  
Film Evaporation ◽  
Refrigerant Mixture ◽  
Falling Film Evaporation ◽  
Binary Refrigerant

The characteristics of heat transfer are investigated experimentally for the vertical falling film evaporation of binary refrigerant mixture HFC134a/HCFC123 in a rectangular minichannels consisting of offset strip fins. The refrigerant liquid is uniformly supplied to the channel through 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, the small circular window is set at the center of every section on the front wall. The experimental parameters are as follows: the mass velocity G = 28∼70 kg/(m2s), the heat flux q = 30∼50 kW/m2 and the pressure P ≈ 100∼260 kPa. In the case of large mass velocity G ≥ 55 kg/(m2s), the value of heat transfer coefficient becomes lower with increase of mass fraction of low-boiling component HFC134a wb in the region of x ≥ 0.3. The main reason for this inclination of α is considered that shearing force acts on the liquid-vapor interface becomes smaller because of vapor velocity suppressed by higher pressure in the test evaporator in the case of larger mass fraction of low-boiling component. Additionally, mass diffusion resistances formed on each side of vapor and liquid phase along the liquid-vapor interface are considered as a possible cause of reduction in the heat transfer coefficient α with increase of mass fraction wb. In the region of x ≥ 0.8, α descend rapidly despite the difference in the value of wb. It can be attributed to dry-out state of heat transfer area. Heat transfer coefficient derived from experiments is compared with that calculated from empirical correlation equation for heat transfer coefficient of pure refrigerant in a vertical falling film plate-fin evaporator.

Vertical Falling Film Evaporation of Pure Refrigerant HCFC123 in a Plate-Fin Heat Exchanger

2013 ◽  
Author(s):  
Junichi Ohara ◽  
Shigeru Koyama
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Flow Patterns ◽  
Falling Film ◽  
Fin Efficiency ◽  
Film Evaporation ◽  
Evaporation Heat ◽  
Falling Film Evaporation ◽  
The Heat Transfer Coefficient

The characteristics of heat transfer and flow patterns are investigated experimentally for the vertical falling film evaporation of pure refrigerant HCFC123 in a rectangular minichannels consisting of offset strip fins. The refrigerant liquid is uniformly supplied to the channel through 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 types. Then the empirical correlation equations for evaporation heat transfer coefficient on a vertical falling film plate fin evaporator with minichannels are proposed. From the physical model to evaluate the heat transfer coefficient of the minichannel surface with fins, the characteristics of fin efficiency is clarified that the average value of fin efficiency is about 0.6 and the distributive characteristics of fin efficiency is roughly inverse of heat transfer coefficient characteristics.

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