Experimental Study on CaCO3 Fouling Characteristics during Falling Film Evaporation

2021 ◽  
pp. 1-27
Author(s):  
Zhikou Ding ◽  
Wei Li ◽  
Lei Wang ◽  
Limin Zhao ◽  
S.A. Sherif ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Stainless Steel ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Falling Film ◽  
Steel Tubes ◽  
Film Evaporation ◽  
Falling Film Evaporation ◽  
Teflon Coating ◽  
The Heat Transfer Coefficient

Abstract Falling film evaporation is widely used in solar desalination systems. Fouling is an important problem to be addressed in many applications involving heat transfer including processes involving the utilization of solar energy in desalination applications. In the research upon which this paper partly reports, an experimental investigation was carried out on a vertical tube in falling film evaporation to determine the effects of temperature, velocity, the use of a porous-sintered tube, and the use of Teflon coating on calcium carbonate deposition characteristics. During the fouling experiments, the pressure inside the test tubes was maintained constant at 101.3kPa, and the inlet temperature was maintained at 373K, while allowing the water mass velocity to vary from 0.42-1.05kg m−1s−1. Results show that the fouling in the test tube becomes more serious as the temperature increases and the flow rate decreases. Compared with stainless steel tubes, porous-sintered tubes can significantly reduce fouling resistance, but at the same time they bring about a decrease in the heat transfer coefficient. The Teflon coating also has anti-fouling performance, but does not affect the heat transfer coefficient in stainless steel tubes. Through the weighing of local fouling deposits, it has been found that the mass of the fouling deposits in the lower part of the tested tubes is greater than that in the upper part.

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.

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.

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]

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.

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.

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%.

A New Model for Predicting Falling Film Evaporation Heat Transfer Coefficients

2016 ◽  
Author(s):  
Apurva Baruah ◽  
Sunil Mehendale
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Thermal Design ◽  
Falling Film ◽  
Transfer Coefficients ◽  
New Model ◽  
Heat Transfer Coefficients ◽  
Film Evaporation ◽  
Falling Film Evaporation

For falling film evaporation, the most important considerations from a thermal design standpoint are the onset of film dryout and the local heat transfer coefficients in partially and fully wet conditions. Previous methods developed for the prediction of (i) pool boiling heat transfer coefficient (HTCs), (ii) the onset of dryout, and (iii) falling film heat transfer coefficient consist of empirical, tube-specific constants which are quite difficult, if not impossible, to determine, and hence have limited utility. New methods to predict these parameters have been developed in the present study, which eliminate the special constants by incorporating dimensionless parameters that capture the effect of refrigerant properties and macro-level tube-geometry. The predictions of the new model have been found to be better than or comparable to those of the best available existing models.

Falling Film Evaporation of HFO-1233zd(E) in Vertical Rectangular Minichannels Consisting of Serrated-Fins

2019 ◽  
Author(s):  
Junichi Ohara
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Mass Velocity ◽  
Thin Liquid Film ◽  
Vapor Flow ◽  
Falling Film ◽  
Film Evaporation ◽  
Downstream Region ◽  
Falling Film Evaporation

Abstract In the present study, the characteristics of heat transfer are experimentally investigated on the falling film evaporation of alternative pure refrigerant HFO-1233zd(E) in a plate-fin heat exchanger having a vertical rectangular minichannels of 2.11 mm hydraulic diameter consisting of serrated-fins. The refrigerant liquid is supplied to the channel through 37 holes of a liquid distributor. The liquid flowing down vertically is heated electrically from the rear wall of the channel and evaporated. The experimental parameters are as follows: the mass velocities are varied 7.4∼55.1 [kg/(m2s)], the heat fluxes are varied 8.7∼50 [kW/m2] and the pressures are about 100 [kPa]. In the case of small mass velocity being smaller than 20 [kg/(m2s)], heat transfer coefficient decreases monotonously and gradually with increase of quality and take value of 5∼1[kW/m2K]. It is thought that the cause of lower value of heat transfer coefficient is occurring dry patch and aria enlargement of dry area in the downstream region. In the case of large mass velocity being larger than 41 [kg/(m2s)], the value of heat transfer coefficient becomes larger with increase of quality except for the case of mass velocity being 41 [kg/(m2s)] and heat flux being 50[kW/m2]. Improved heat transfer is to be thinkable that the liquid and vapor flow becomes dripping in the middle-stream region, and turns into mist flow with thin liquid film on the fin surface in the downstream region of quality being larger than 0.4.

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