Local evaporative heat transfer coefficient in turbulent free-falling liquid films

1988 ◽  
Vol 31 (4) ◽  
pp. 731-742 ◽  
Author(s):  
J.A. Shmerler ◽  
I. Mudawwar
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Liquid Films ◽  
Evaporative Heat Transfer ◽  
Evaporative Heat Transfer Coefficient ◽  
Falling Liquid Films ◽  
Free Falling

Heat Transfer Analysis of Local Evaporative Turbulent Falling Liquid Films

1992 ◽  
Vol 114 (3) ◽  
pp. 688-694 ◽  
Author(s):  
N. M. Al-Najem ◽  
K. Y. Ezuddin ◽  
M. A. Darwish
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Homogeneous Problem ◽  
Interfacial Shear Stress ◽  
Liquid Films ◽  
Heat Transfer Analysis ◽  
Tube Length ◽  
Prandtl Numbers ◽  
Falling Liquid Films

A theoretical study has been conducted for evaporative heating of turbulent free-falling liquid films inside long vertical tubes. The methodology of the present work is based on splitting the energy equation into homogeneous and nonhomogeneous problems. Solving these simple problems yields a rapidly converging solution, which is convenient for computational purposes. The eigenvalues associated with the homogeneous problem can be computed efficiently, without missing any one of them, by the sign-count algorithm. A new correlation for the local evaporative heat transfer coefficient along the tube length is developed over wide ranges of Reynolds and Prandtl numbers. Furthermore, the average heat transfer coefficient is correlated as a function of Reynolds and Prandtl numbers as well as the interfacial shear stress. A correlation for the heat transfer coefficient in the fully developed region is also presented in terms of Reynolds and Prandtl numbers. Typical numerical results showed excellent agreement of the present approach with the available data in the literature. Moreover, a parametric study is made to illustrate the general effects of various variables on the velocity and temperature profiles.

Evaporative Heat Transfer Analysis of a Heat Pipe With Hybrid Axial Groove

2013 ◽  
Vol 135 (3) ◽  
Author(s):  
Lizhan Bai ◽  
Guiping Lin ◽  
G. P. Peterson
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Liquid Film ◽  
Transfer Coefficient ◽  
Flow Resistance ◽  
Heat Pipes ◽  
Low Flow ◽  
Circular Channel ◽  
Evaporative Heat Transfer ◽  
Evaporative Heat Transfer Coefficient

Through the application of thin film evaporation theory and the fundamental operating principles of heat pipes, a hybrid axial groove has been developed that can greatly enhance the performance characteristics of conventional heat pipes. This hybrid axial groove is composed of a V-shaped channel connected with a circular channel through a very narrow longitudinal slot. During the operation, the V-shaped channel can provide high capillary pressure to drive the fluid flow and still maintain a large evaporative heat transfer coefficient. The large circular channel serves as the main path for the condensate return from the condenser to the evaporator and results in a very low flow resistance. The combination of a high evaporative heat transfer coefficient and a low flow resistance results in considerable enhancement in the heat transport capability of conventional heat pipes. In the present work, a detailed mathematical model for the evaporative heat transfer of a single groove has been established based on the conservation principles for mass, momentum and energy, and the modeling results quantitatively verify that this particular configuration has an enhanced evaporative heat transfer performance compared with that of conventional rectangular groove, due to the considerable reduction in the liquid film thickness and a corresponding increase in the evaporative heat transfer area in both the evaporating liquid film region and the meniscus region.

scholarly journals FORCED CONVECTION DRYING OF INDIAN GROUNDNUT: AN EXPERIMENTAL STUDY

2017 ◽  
Vol 15 (3) ◽  
pp. 467
Author(s):  
Ravinder Kumar Sahdev ◽  
Mahesh Kumar ◽  
Ashwani Kumar Dhingra
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Forced Convection ◽  
Experimental Error ◽  
Linear Regression Analysis ◽  
Convective Heat Transfer Coefficient ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
Evaporative Heat Transfer

In this paper, convective and evaporative heat transfer coefficients of the Indian groundnut were computed under indoor forced convection drying (IFCD) mode. The groundnuts were dried as a single thin layer with the help of a laboratory dryer till the optimum safe moisture storage level of 8 – 10%. The experimental data were used to determine the values of experimental constants C and n in the Nusselt number expression by a simple linear regression analysis and consequently, the convective heat transfer coefficient (CHTC) was determined. The values of CHTC were used to calculate the evaporative heat transfer coefficient (EHTC). The average values of CHTC and EHTC were found to be 2.48 W/m2 oC and 35.08 W/m2 oC, respectively. The experimental error in terms of percent uncertainty was also estimated. The experimental error in terms of percent uncertainty was found to be 42.55%. The error bars for convective and evaporative heat transfer coefficients are also shown for the groundnut drying under IFCD condition.

Experiments on Hydrodynamic and Thermal Behaviors of Thin Liquid Films

2003 ◽  
Author(s):  
B. Ozar ◽  
B. M. Cetegen ◽  
A. Faghri
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Liquid Flow ◽  
Local Heat Transfer ◽  
Disk Surface ◽  
Local Heat ◽  
Liquid Films ◽  
Local Heat Transfer Coefficient ◽  
Flow Rates

An experimental study of heat transfer into a thin film of liquid water on a rotating disk is described. The film was introduced from a flow collar at the center of a heated, horizontal disk at a fixed initial film thickness with a uniform radial velocity. Radial distribution of the disk surface temperatures was measured using a thermocouple / slip ring arrangement. Experiments were performed for a range of liquid flow rates between 3.0 lpm and 15.0 lpm corresponding to Reynolds numbers (based on the liquid inlet gap height and velocity) between 238 and 1188. The angular speed of the disk was varied from 0 rpm to 500 rpm. The local heat transfer coefficient was determined based on the heat flux supplied to the disk and the temperature difference between the measured disk surface temperature and the entrance temperature of the liquid onto the disk. The local heat transfer coefficient was seen to increase with increasing flow rate as well as increasing angular velocity of the disk. Effect of rotation on heat transfer was largest for the lower liquid flow rates with the effect gradually decreasing with increasing liquid flow rates. Semi-empirical correlations are presented in this study for the local and average Nusselt numbers. In addition to the heat transfer characterization, the thickness of the liquid film on the disk surface was measured by an optical method, including the characteristics of the hydraulic jump and the subcritical and supercritical flow regions.

Numerical Simulation of Upward Two-Phase Flow in Narrow Channel Between Two Flat Plates With Bilateral Heating

2008 ◽  
Author(s):  
Lei Li ◽  
Zhijian Zhang ◽  
Jiange Liu
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Liquid Film ◽  
Transfer Coefficient ◽  
Narrow Channel ◽  
Liquid Films ◽  
Phase Flow ◽  
Two Phase ◽  
Narrow Channels ◽  
Bilateral Heating

The convection heat transfer characteristic in narrow channel is superior. Therefore, narrow channels are suitable for being manufactured into compact heat transfer components with high heat transfer performance. This new technology of heat transfer enhancement with no source is widely applied to various fields such as microelectronic heat sink, cryogenic industry, chemical industry, aeronautic & astronautic industry and nuclear engineering. In integrated reactor, the coolant channels between the plate fuels are narrow channels. As to the investigation of two-phase flow and heat transfer in narrow channels, reports are focused on experimental research with low pressure, at home and abroad, but reports on numerical simulation research are relatively small. Based on separated flow, a theoretical two-fluid model predicting for upward flow in a rectangular narrow channel with bilateral heating has been developed in this paper. The theoretical model is based on fundamental conservation principles: the mass, momentum and energy conservation equations of liquid films and the momentum conservation equation of vapor core. The model assumed that liquid film covers the surface of the channel while the vapor with entrained droplets flows in the central core. And there exists the mass transfer between the liquid droplets in the vapor core and the liquid films. Through numerically solving these equations, liquid film thickness, radial velocity and temperature distribution in liquid films and heat transfer coefficient are obtained. The calculated results shows that the width of the narrow channel, heat pattern, heat flux have great influences on heat transfer coefficient and the thickness of liquid film. The heat transfer coefficient will increase with the decrease of the channel width. That is, the heat transfer may be enhanced with small rectangular narrow channel. But when the channel width is less than a certain value, the model may not be proper anymore. So the further research should be necessary. As the applications of the present model, the critical heat flux and critical quality are calculated.

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