Electrohydrodynamic Enhancement of Falling Film Evaporation Heat Transfer and its Long-Term Effect on Heat Exchangers

1997 ◽  
Vol 119 (2) ◽  
pp. 339-347 ◽  
Author(s):  
K. Yamashita ◽  
A. Yabe
Keyword(s):  
Heat Transfer ◽  
Electric Field ◽  
Heat Exchangers ◽  
Industrial Applications ◽  
Falling Film ◽  
Film Evaporation ◽  
Evaporation Heat ◽  
Falling Film Evaporation ◽  
Evaporation Heat Transfer

Electrohydrodynamic (EHD) enhancement of vertical falling film evaporation heat transfer has been experimentally studied using HCFC123, which is an alternative working fluid for CFCs. This research verified that EHD enhancement of HCFC123 condensation was as effective as that of conventional working fluids. The electrodes used for EHD enhancement of vertical falling film evaporation utilized the following two EHD phenomena: extracting the liquid by a nonuniform electric field, and surface granulation by a nearly uniform electric field. As a result, an electrode with vertically arrayed offset-slits that is suitable for industrial applications has been developed that showed a six-fold enhancement of evaporation heat transfer over that for a smooth tube. The long-term effects of the high voltages associated with EHD on heat exchanger performance have been evaluated. Operation of EHD heat exchangers for 1000 hours indicates they do not sustain serious damage, and are, therefore, suitable for industrial applications.

Effects of Inclination Angle on Falling Film Evaporation Using R-134a

2005 ◽  
Author(s):  
Liang-Han Chien ◽  
Hung-Ta Lin
Keyword(s):  
Heat Transfer ◽  
Inclination Angle ◽  
Falling Film ◽  
Film Evaporation ◽  
Evaporation Heat ◽  
Finned Surface ◽  
Falling Film Evaporation ◽  
Plain Surface ◽  
Evaporation Heat Transfer ◽  
R 134A

This manuscript discusses the effect of inclination angle and surface geometries on the falling film evaporation performance. Falling film evaporation experiments were conducted on a smooth plate and finned plates using refrigerant R-134a at 18 °C system temperature. The plate was inclined with angles between 10° and 40°, and the heat fluxes are between 36 and 73.5kW/m2. The local heat transfer coefficients are measured, and the falling film flow distribution is observed through a sight glass. The test results showed that the falling film evaporation heat transfer coefficient increases as the inclination angle increases or the heat flux increases. The finned surface yields better falling film evaporation heat transfer performance than the smooth surface. The ratio of the heat transfer coefficient of the finned surface versus the plain surface is between 2.5 and 12.4 folds. This ratio increases as the inclination angle increases. The visualization observation showed that bubble nucleation is more pronounced on the finned surface than the plain surface. The effect of boiling on falling film evaporation is discussed.

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.

An Experimental Study of Falling Film Evaporation on Horizontal Tubes Using R-134a

2012 ◽  
Vol 28 (2) ◽  
pp. 319-327 ◽  
Author(s):  
L.-H. Chien ◽  
R.-H. Chen
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Smooth Tube ◽  
Fluid Temperature ◽  
Falling Film ◽  
Film Evaporation ◽  
Evaporation Heat ◽  
Falling Film Evaporation ◽  
Fin Tube

AbstractThis study investigates evaporation heat transfer performance of refrigerant R-134a falling film on three horizontal copper tubes in a vertical column. Experiments were performed at saturation temperatures of 10 and 26.7°C. The liquid flows through a liquid feeder with a row of circular holes at a rate of 0.0075 ∼ 0.0363kg/ms, while heat fluxes varied from 4.5 to 48.5kW/m2. A smooth tube, a fin tube of 0.4mm fin height, 60FPI (Fins Per Inch), and a new boiling enhanced tube (mesh tube) were tested. The test results show that heat transfer coefficient of the smooth tube increases with increasing heat flux and fluid temperature, and increases slightly with increasing flow rate before dry-out occurs. At low flow rates (less than 0.015kg/ms) or when Ref (≤ 255), the fin tube is in thin film evaporation mode and results in a large heat transfer coefficient. At high flow rates (0.0225, 0.03, and 0.0375kg/ms) the falling film evaporation curves are similar to those in pool boiling. For all tubes, the fluid temperature and the flow rate have only minor influences on heat transfer coefficient before dry-out occurs. The 60 FPI tube and the mesh tube enhance the falling film evaporation heat transfer coefficient 6.3 ∼ 8.29 fold and 1.9 ∼ 5.0 fold, respectively, as compared with the smooth tube. A new correlation of falling film evaporation, accounting for contributions of nucleate boiling and spray convection, is proposed. It predicts h-values of the falling film evaporation data of the smooth surface within ±30%.

scholarly journals Heat Exchangers for Condensation and Evaporation Applications Operating in a Low Pressure Atmosphere

10.14311/1550 ◽  
2012 ◽  
Vol 52 (3) ◽  
Author(s):  
Petr Kracík ◽  
Jiří Pospíšil ◽  
Ladislav Šnajdárek
Keyword(s):  
Heat Transfer ◽  
Heat Exchangers ◽  
Horizontal Tube ◽  
Heat Transfer Process ◽  
Falling Film ◽  
Evaporation And Condensation ◽  
Film Evaporation ◽  
Condensation Mode ◽  
Falling Film Evaporation ◽  
The Heat Transfer Coefficient

This paper presents a state-of-the-art study of a heat transfer process in liquid spraying heat exchangers placed in a vacuum chamber. The experimental case studied here describes the behavior of a falling film evaporation and condensation mode on horizontal tube bundles. The study aims to obtain the heat transfer coefficient and its correlations by means of a mathematical model.

Augmentation of Thin Falling-Film Evaporation on Horizontal Tubes Using an Applied Electric Field

1999 ◽  
Vol 122 (2) ◽  
pp. 391-398 ◽  
Author(s):  
J. Darabi ◽  
M. M. Ohadi ◽  
S. V. Dessiatoun
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Electric Field ◽  
Transfer Coefficient ◽  
Applied Electric Field ◽  
Falling Film ◽  
Film Evaporation ◽  
Horizontal Tubes ◽  
Falling Film Evaporation ◽  
The Heat Transfer Coefficient

Heat transfer enhancement of falling-film evaporation on commercially available horizontal tubes using an applied electric field was studied experimentally. The tube surfaces tested included: smooth, 19 fins per inch (19 fpi) low-fin type, and Turbo BIII which is a state-of-the-art commercially available boiling tube. The nominal outside diameters of all the tubes were 19 mm. Experiments were performed with R-134a at a saturation pressure of 550 kPa. Effects of heat flux, film flow rate, applied electric field potential, and heat transfer surface on the heat transfer coefficient were investigated. In addition, the effect of Poloyl-ester oil on the heat transfer coefficients was also investigated. Experiments were conducted for oil concentrations ranging from 0.5 percent to 5 percent on a mass basis. Small concentrations of a poloyl-ester lubricant were found to improve the heat transfer performance, while large concentrations reduced the heat transfer coefficient. [S0022-1481(00)00702-7]

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