HEAT TRANSFER IN THIN LIQUID FILMS FLOWING DOWN HEATED INCLINED GROOVED PLATES

2010 ◽  
Vol 2 (5) ◽  
pp. 455-468 ◽  
Author(s):  
Hongyi Yu ◽  
Karsten Loffler ◽  
Tatiana Gambaryan-Roisman ◽  
Peter Stephan
Keyword(s):  
Heat Transfer ◽  
Liquid Films ◽  
Thin Liquid Films

Study of the Fluid Dynamics of Thin Liquid Films Flowing Down a Vertical String With Counterflow of Gas

2015 ◽  
Author(s):  
Zezhi Zeng ◽  
Gopinath Warrier ◽  
Y. Sungtaek Ju
Keyword(s):  
Heat Transfer ◽  
Fluid Dynamics ◽  
Film Thickness ◽  
Liquid Film ◽  
Direct Contact ◽  
High Speed ◽  
Small Diameter ◽  
Liquid Films ◽  
Thin Liquid Films ◽  
Liquid Coolant

Direct-contact heat transfer between a falling liquid film and a gas stream yield high heat transfer rates and as such it is routinely used in several industrial applications. This concept has been incorporated by us into the proposed design of a novel heat exchanger for indirect cooling of steam in power plants. The DILSHE (Direct-contact Liquid-on-String Heat Exchangers) module consists of an array of small diameter (∼ 1 mm) vertical strings with hot liquid coolant flowing down them due to gravity. A low- or near-zero vapor pressure liquid coolant is essential to minimize/eliminate coolant loss. Consequently, liquids such as Ionic Liquids and Silicone oils are ideal candidates for the coolant. The liquid film thickness is of the order of 1 mm. Gas (ambient air) flowing upwards cools the hot liquid coolant. Onset of fluid instabilities (Rayleigh-Plateau and/or Kapitza instabilities) result in the formation of a liquid beads, which enhance heat transfer due to additional mixing. The key to successfully designing and operating DILSHE is understanding the fundamentals of the liquid film fluid dynamics and heat transfer and developing an operational performance map. As a first step towards achieving these goals, we have undertaken a parametric experimental and numerical study to investigate the fluid dynamics of thin liquid films flowing down small diameter strings. Silicone oil and air are the working fluids in the experiments. The experiments were performed with a single nylon sting (fishing line) of diameter = 0.61 mm and height = 1.6 m. The inlet temperature of both liquid and air were constant (∼ 20 °C). In the present set of experiments the variables that were parametrically varied were: (i) liquid mass flow rate (0.05 to 0.23 g/s) and (ii) average air velocity (0 to 2.7 m/s). Visualization of the liquid flow was performed using a high-speed camera. Parameters such as base liquid film thickness, liquid bead shape and size, velocity (and hence frequency) of beads were measured from the high-speed video recordings. The effect of gas velocity on the dynamics of the liquid beads was compared to data available in the open literature. Within the range of gas velocities used in the experiments, the occurrence of liquid hold up and/or liquid blow over, if any, were also identified. Numerical simulations of the two-phase flow are currently being performed. The experimental results will be invaluable in validation/refinement of the numerical simulations and development of the operational map.

Review of Microscale Heat Transfer

1994 ◽  
Vol 47 (9) ◽  
pp. 397-428 ◽  
Author(s):  
A. B. Duncan ◽  
G. P. Peterson
Keyword(s):  
Heat Transfer ◽  
Final Section ◽  
Radiative Heat ◽  
Heat Pipes ◽  
Liquid Films ◽  
Thin Liquid Films ◽  
Review Of The Literature ◽  
Conduction Heat Transfer ◽  
Microscale Heat Transfer ◽  
Micro Heat Pipes

A review of the literature in the area of microscale heat transfer is presented to provide a concise overview of the recent advances in this field of study. The review is divided into three major sections with each subdivided into subsections. The first section deals with the effects of size reductions in conduction heat transfer, and includes subsections on laser induced heating on the microscale and conduction in thin films. The second section addresses microscale forced convection and includes subsections on micro heat pipes, microscale boiling, and thin liquid films near the contact line. The final section examines the effects of small length scales on radiative heat transfer. The three major sections are followed by a summary that identifies, consolidates, and summarizes the most important advances in each of these three areas.

Heat Transfer in Thin Liquid Films Utilizing Binary Fluid Mixtures

2003 ◽  
Vol 30 (5) ◽  
pp. 473-484
Author(s):  
Rama Subba Reddy Gorla ◽  
Santosh Viswanadham ◽  
Asad Salem ◽  
Larry W. Byrd
Keyword(s):  
Heat Transfer ◽  
Liquid Films ◽  
Thin Liquid Films ◽  
Binary Fluid ◽  
Fluid Mixtures ◽  
Binary Fluid Mixtures

Heat Transfer During Evaporation on Capillary-Grooved Structures of Heat Pipes

1995 ◽  
Vol 117 (3) ◽  
pp. 740-747 ◽  
Author(s):  
D. Khrustalev ◽  
A. Faghri
Keyword(s):  
Heat Transfer ◽  
Experimental Data ◽  
Surface Roughness ◽  
Thermal Resistance ◽  
Heat Pipes ◽  
Liquid Films ◽  
Thin Liquid Films ◽  
Interfacial Thermal Resistance ◽  
Interfacial Resistance ◽  
The Heat Transfer Coefficient

A detailed mathematical model is developed that describes heat transfer through thin liquid films in the evaporator of heat pipes with capillary grooves. The model accounts for the effects of interfacial thermal resistance, disjoining pressure, and surface roughness for a given meniscus contact angle. The free surface temperature of the liquid film is determined using the extended Kelvin equation and the expression for interfacial resistance given by the kinetic theory. The numerical results obtained are compared to existing experimental data. The importance of the surface roughness and interfacial thermal resistance in predicting the heat transfer coefficient in the grooved evaporator is demonstrated.

Flow Patterns and Heat Transfer in Thin Liquid Films on Walls With Straight, Meandering and Zigzag Mini-Grooves

2008 ◽  
Author(s):  
Karsten Lo¨ffler ◽  
Hongyi Yu ◽  
Tatiana Gambaryan-Roisman ◽  
Peter Stephan
Keyword(s):  
Heat Transfer ◽  
High Speed ◽  
Flow Patterns ◽  
Liquid Films ◽  
Thin Liquid Films ◽  
Transport Processes ◽  
Temperature Fields ◽  
Film Stability ◽  
Falling Films ◽  
Falling Liquid Films

Thin liquid films flowing along solid walls are widely used in technological applications in which high rates of heat and mass transport are required. The transport processes can be further intensified by using structured walls. In the present work hydrodynamics and heat transfer in falling liquid films on heated vertical and inclined walls with mini-grooves are studied experimentally and theoretically/numerically. The experiments are performed with straight, meandering and zigzag mini-grooves. The film dynamics is investigated using a confocal chromatic sensoring (CHR) technique. The flow patterns and the temperature of the liquid-gas interface are visualized using the high-speed infrared thermography. The wall temperature distribution is measured with thermocouples. A numerical model for description of the velocity and temperature fields in the thermal entrance region of the falling films on smooth and structured walls is developed. This model is based on the solution of the Graetz-Nusselt problem for falling films on grooved plates. We show that the mini-grooves significantly affect the flow patterns, film stability and heat transfer in falling liquid films. Using grooved walls leads to the increase of the maximal attainable heat transfer rate.

Boiling Heat Transfer for Freon R21 in Rectangular Minichannel

2006 ◽  
Author(s):  
V. V. Kuznetsov ◽  
A. S. Shamirzaev
Keyword(s):  
Heat Transfer ◽  
Boiling Heat Transfer ◽  
Flow Patterns ◽  
Liquid Films ◽  
Thin Liquid Films ◽  
Modified Model ◽  
Wide Range ◽  
Nucleation Boiling ◽  
The Heat Transfer Coefficient ◽  
Transfer Mechanisms

In this paper we study the boiling heat transfer of upward flow of R21 in a vertical mini-channel with size 1.6×6.3 mm. The heat transfer coefficient was measured as a function of heat flux for a wide range of vapor quality and for two levels of mass flow rate, G = 215 kg/m2s and G = 50 kg/m2s. The temperature dispersions over channel perimeter and in time were calculated. Different heat transfer mechanisms were revealed for different flow patterns. We distinguish the dominant nucleation boiling and the joint mode of nucleation boiling and convective evaporation. We also found the modes when the evaporation of thin liquid films makes the main contribution to heat transfer. The modified model of Liu and Winterton describes the experimental data for the flow patterns when the nucleation boiling and convective transfer make the most contribution to the heat transfer.

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