Temperature Drops and Liquid Film Heat Transfer Coefficient in Vertical Tubes

1937 ◽  
Vol 29 (8) ◽  
pp. 912-918 ◽  
Author(s):  
R. M. Boarts ◽  
W. L. Badger ◽  
S. J. Meisenburg
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Liquid Film ◽  
Transfer Coefficient ◽  
Film Heat Transfer ◽  
Vertical Tubes

scholarly journals Experimental investigation of heat transfer of flowing liquid film with inserted metal foam layer subjected to air jet impingement

2019 ◽  
Vol 23 (5 Part B) ◽  
pp. 3093-3104
Author(s):  
Yunsong Zhang ◽  
Wei Chen ◽  
Wei Li ◽  
Xiao Zhu
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Liquid Film ◽  
Transfer Coefficient ◽  
Porous Layer ◽  
Metal Foam ◽  
Jet Impingement ◽  
Heated Wall ◽  
Flowing Liquid ◽  
Air Jet

In this paper, coupling the air jet impingement and the copper metal foam above flowing liquid film were employed to enhance the heat transfer. The thickness of flowing liquid film can be controlled owing to the application of the metal foam above the film, and its solid matrix extends the air-liquid-solid interface of heating surface. The evaporated water can be supplied by the capillary force in the porous layer. The experiments were conducted to investigate the performances of the flowing liquid film with inserted porous layer subjected to impinging jet air. The air jet velocity, the flow rate and thicknesses of the liquid film as well as the porosity of metal foam influence the surface temperature of heated wall and the corresponding local heat transfer coefficient greatly. The change ratios of heat transfer coefficient due to the above factors were presented. More cooling can be obtained on the heated wall in the flowing liquid film with inserted porous layer subjected to impinging jet air while the higher liquid film velocity and air jet velocity, the thinner liquid film and the lower porosity of metal foam occur.

Analysis of Passive Tube Condensation With Non-Condensable Gas Using Heat and Mass Analogy Model

2021 ◽  
Author(s):  
Ugur Cotul ◽  
Shripad T. Revankar
Keyword(s):  
Heat Transfer ◽  
Boundary Layer ◽  
Heat Transfer Coefficient ◽  
Liquid Film ◽  
Transfer Coefficient ◽  
Condensation Heat Transfer ◽  
Vapor Flow ◽  
Vapor Mixture ◽  
Condenser Tube ◽  
Numerical Predictions

Abstract In this study, we used the heat and mass analogy model to be able to predict the heat transfer properties of a condenser tube operating in passive mode. The most important advantage of analogy model comparing boundary layer model is simplicity and fast computation, that’s why it can be applied to various engineering problems for many cases. The heat and mass analogy model is based on the heat transfer balance between liquid film and gas mixture area. The main problem for the liquid film region is the heat transfer coefficient (HTC) which is affected negatively in the presence of non-condensable gas. Therefore, our main goal is to increase the HTC and condensation heat transfer rate by updating the analogy code. In the gas-vapor mixture region, heat transfer mainly occurred as latent condensation and sensible heat transfer. In order to maintain this balance between the mixture and liquid film, the interface temperature is iterated. After defining a specified tolerance value of the heat and mass analogy model codes, this iteration process was started to be used at the entrance of a condenser tube. The gas and vapor mixture is considered to be saturated at the liquid/gas interface in the heat and mass transfer analogy model. Via boundary layer study of species concentration and energy balance, the non-condensable gas effect on condensation is added into the equation. For the condensation heat transfer coefficient of turbulent vapor flow associated with laminar condensate, numerical predictions were made and they were satisfactory. The predictions were compared with the experimental data from the literature to be able to test the model. Non-condensable gas mass fraction and vapor-non-condensable mixture temperature were presented in the form of radial and axial profiles.

Simulation of Sweating/Evaporation Boosted Convective Heat Transfer Under Laminar Flow Condition

2017 ◽  
Author(s):  
Sudipta Saha ◽  
Rajib Mahamud ◽  
Jamil Khan ◽  
Tanvir Farouk
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Reynolds Number ◽  
Heat Transfer Coefficient ◽  
Laminar Flow ◽  
Film Thickness ◽  
Liquid Film ◽  
Transfer Coefficient ◽  
Water Film ◽  
The Heat Transfer Coefficient

Phase change driven heat transfer has been the topic of interest for a significantly long time. However, in recent years on demand sweating boosted evaporation which requires substantially less amount of the liquid medium has drawn attention as a possible way of increasing/supplementing heat transfer under convective conditions where the convective heat transfer coefficient has already reached its maximum value as well as where dry cooling is a desired objective. In this study, a numerical study is conducted to obtain insight into the ‘hybrid’ system where evaporation and convection both contribute to the heat transfer effect. The system modeled consists of evaporation of thin liquid (water) film under a laminar flow condition. The mathematical model employed consists of coupled conservation equations of mass, species, momentum and energy for the convection-evaporation domain (gaseous), with only mass and energy conservation being resolved in the liquid film domain. The evaporative mass flux is obtained from a modified Hertz-Knudsen relation which is a function of liquid-vapor interface temperature and pressure. A two-dimensional rectangular domain with a pre-prescribed thin liquid water film representative of an experiment is simulated with the developed model. The thin rectangular liquid film is heated by uniform heat flux and is placed in the convection-evaporation domain with an unheated starting length. A moving boundary mesh is applied via the“Arbitrary Lagrangian-Eulerian” technique to resolve the receding liquid interface resulting from evaporation. The prescribed relative displacement of the moving interface is calculated from the net mass flux due to evaporation and is governed by the principle of mass conservation. Simulations were conducted over a range of Reynolds number, heat flux conditions and liquid film thickness. The numerical predictions indicate that under convective-evaporative conditions the overall heat transfer coefficient increases significantly (∼factor of a five) in comparison to the purely forced convection scenario. An increase in the heat transfer coefficient is observed with Reynolds number and vice versa for film thickness. A critical Reynolds number is identified beyond which the heat transfer coefficient does not continue to increase significantly rather tends to plateau out.

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