Study on the temperature distribution of heated falling liquid films

Zhang, Feng; Tang, Dongming; Geng, Jiao; Wang, Zhixiang; Zhang, Zhibing

doi:10.1016/j.physd.2007.10.018

Cited by 22 publications

(6 citation statements)

References 26 publications

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“…There have been a number of attempts to investigate the liquid film flow by both practical and theoretical approaches in the past few years [1][2][3][4][5][6]. Yang and Shen [7] carried out an experimental study of falling film heat transfer in order to show how the heat transfer coefficient was affected by different parameters.…”

Section: Abbreviationsmentioning

confidence: 99%

Numerical study of heat and mass transfer of ammonia-water in falling film evaporator

Huang

2011

Heat Mass Transfer

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To investigate the performance of the heat and mass transfer of ammonia water during the process of falling film evaporation in vertical tube evaporator, a mathematical model of evaporation process was developed and solved based on stream function. Then an experimental study of falling film evaporation was carried out in order to validate the mathematical model. A series of parameters, such as velocity, film thickness and concentration, etc., were obtained from the mathematical model. The calculated results show that the average velocity and the film thickness change sharp at the entrance region when x \ 100 mm, while they vary slightly in the fully developed region when x [ 100 mm. The film thickness depends largely on the flow rate of solution. It is observed that the heating power and mass flow of solution significantly affect the concentration difference between the inlet and outlet of evaporation tube. The calculated results reveal that the tube length has a significant impact on the amounts of ammonia vapor evaporated. It is suggested that the roll-worked enhanced tube should be used in order to decrease the concentration gradient in the film thickness direction and enhance the heat and mass transfer rate. Furthermore, the experimental and calculated results indicate that the inlet solution concentration has a great influence on the heat exchange capacity, the amounts of ammonia vapor evaporated and the evaporation pressure. AbbreviationsC P Specific heat, J kg -1 K -1 D Tube diameter, m D m Diffusion coefficient, m 2 /s H Specific enthalpy, J/kg L Tube length, m m Solution mass flow, kg/h mE The amount of evaporated ammonia vapor, kg/h _ m Evaporation rate, kg/s/m 2 N Sequence number of experiment P Evaporating pressure, kPa PE Percent of evaporated ammonia vapor, % Q Heat exchange capacity between hot water and solution, kW T Temperature,°C u Film velocity of x direction, m/s v Film velocity of y direction, m/s V Volumetric flow of water, L/h DH Enthalpy difference, J/kgGreek symbols n Mass concentration of solution, kg/kg d Film thickness, m U Spray density, kg m -1 s -1 l Dynamic viscosity, N s/m 2 q Density, kg/m 3 k Thermal conductivity, W m -1 K -1

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Section: Abbreviationsmentioning

confidence: 99%

Numerical study of heat and mass transfer of ammonia-water in falling film evaporator

Huang

2011

Heat Mass Transfer

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“…The falling film flow of low‐viscosity liquid quickly evolves into wave flow driven by inertial force and gravity, [ 13 ] while the primary flow pattern of high‐viscosity fluid is peristaltic laminar flow due to the sizeable viscous resistance. Additionally, specific operating conditions may cause irregular fluctuations in falling film flow, such as non‐isothermal walls [ 14 ] and the presence of airflow in the liquid film and at the gas–liquid interface. [ 15 ] In early reports, cylindrical tubes, plates, wires, and fibres were the most extensively used as the substrate structure for the hydrodynamic characteristics of falling film flow.…”

Section: Introductionmentioning

confidence: 99%

The velocity field characteristics of high‐viscosity fluids falling film flow down clamped channels

Wang

Chen

et al. 2023

Can J Chem Eng

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The complexity of falling film flow has been studied in many industrial applications. In this work, the velocity field of high-viscosity fluids falling film flow down clamped channels was investigated numerically and experimentally.The results show that the numerical simulation results are consistent with the experimental results, and the characteristics of the velocity field are related to the fluid properties, operating conditions, and structure of the clamped channels. When the fluid viscosity is greater than or equal to 10 Pa Á s, the type of velocity field changes into I shape, U shape, and V shape. While the fluid viscosity drops to 0.89 Pa Á s, the viscous force cannot resist the inertial force and gravity, resulting in a cardioid velocity field. By adjusting the structure of the clamped channels and operating conditions, the tension of the liquid film can be changed, and the velocity distribution of the liquid film can be manipulated.Significantly, under the fluctuating curtain flow, the liquid film coalesces and breaks frequently, which enlarges the surface area of the liquid film and strengthens the surface renewal frequency. Hence, this form of falling film flow can be applied to process intensification of high-viscosity materials.clamped channels, falling film flow, high-viscosity fluids, velocity field | INTRODUCTIONAs an energy-efficient process for intensifying heat and mass transfer, falling film flows have been widely used in chemical engineering, [1] refrigeration, [2] and seawater desalination. [3] Various flow patterns of falling film flows based on fluid properties, the geometric structure of the supporting wall, the working environment, and other factors have been described in the literature. Many reports found that the flow patterns of liquid film flow down vertical geometric structures could be categorized as drop-like flows, inertially driven flows, gravity-driven flows, solitary wave-like flows, and disturbance flows. [4][5][6][7] Liquid viscosities can vary from low (0.001$1 Pa Á s), [8,9] such as water, glycerin, and aqueous lithium bromide solution, to high (thousands of times higher than the viscosity of low-viscosity fluids), [10][11][12] such as silicone oil, syrup, and melt polymer. The hydrodynamic mechanism of the falling film is strongly dependent on fluid viscosity. The falling film flow of low-viscosity liquid quickly evolves into wave flow driven by inertial force and gravity, [13] while the primary flow pattern of highviscosity fluid is peristaltic laminar flow due to the sizeable viscous resistance. Additionally, specific operating conditions may cause irregular fluctuations in falling film Abbreviations: CFD, computational fluid dynamics; LDA, laser doppler analysis; VOF, volume of fluids.

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“…In practical falling film systems, the uncompleted wetting condition has been reported in many previous researches [10][11][12][13][14]. Zhang et al [15,16] developed a theoretical model to evaluate the water film area, and indicated that the contact angle of water on the working surface was indispensable for calculating the area. Recently, Qi et al [17] developed a theoretical model for calculating film deformation during the liquid desiccant regeneration, and found that small contact angle may benefit the film wetted area.…”

Section: Introductionmentioning

confidence: 99%

Investigation on the liquid contact angle and its influence for liquid desiccant dehumidification system

Jiang

2015

International Journal of Heat and Mass Transfer

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Study on the temperature distribution of heated falling liquid films

Cited by 22 publications

References 26 publications

Numerical study of heat and mass transfer of ammonia-water in falling film evaporator

Numerical study of heat and mass transfer of ammonia-water in falling film evaporator

The velocity field characteristics of high‐viscosity fluids falling film flow down clamped channels

Investigation on the liquid contact angle and its influence for liquid desiccant dehumidification system

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