Numerical Study of Evaporation Heat Transfer From the Liquid-Vapor Interface in Wick Microstructures

2009 ◽  
Author(s):  
Ram Ranjan ◽  
Jayathi Y. Murthy ◽  
Suresh V. Garimella
Keyword(s):  
Heat Transfer ◽  
Numerical Study ◽  
Saturated Vapor ◽  
Wire Mesh ◽  
Liquid Meniscus ◽  
Vapor Interface ◽  
Evaporation Heat ◽  
Evaporation Heat Transfer ◽  
Solid Liquid ◽  
Liquid Vapor

A numerical model of the evaporating liquid meniscus under saturated vapor conditions in wick microstructures has been developed. Four different wick geometries representing the common wicks used in heat pipes, viz., wire mesh, rectangular grooves, sintered wicks and vertical microwires, are modeled and compared for evaporative performance. The solid-liquid combination considered is copper-water. Steady evaporation is modeled and the liquid-vapor interface shape is assumed to be static during evaporation. Liquid-vapor interface shapes in different geometries are obtained by solving the Young-Laplace equation using Surface Evolver. Mass, momentum and energy equations are solved numerically in the liquid domain, with the vapor assumed to be saturated. Evaporation at the interface is modeled by using appropriate heat and mass transfer rates obtained from kinetic theory. Thermo-capillary convection due to non-isothermal conditions at the interface is modeled for all geometries and its role in heat transfer enhancement from the interface is quantified for both low and high superheats. More than 80% of the evaporation heat transfer is noted to occur from the thin-film region of the liquid meniscus. Very small Capillary and Weber numbers arising due to small fluid velocities near the interface for low superheats validate the assumption of static liquid meniscus shape during evaporation. Solid-liquid contact angle, wick porosity, solid-vapor superheat and liquid level in the wick pore are varied to study their effects on evaporation from the liquid meniscus.

Numerical study of seed bubble-triggered evaporation heat transfer in a single microtube

2013 ◽  
Vol 16 (1-2) ◽  
pp. 347-360 ◽  
Author(s):  
Luxiang Zong ◽  
Dongliang Sun ◽  
Jinliang Xu ◽  
Xiaodong Wang
Keyword(s):  
Heat Transfer ◽  
Numerical Study ◽  
Evaporation Heat ◽  
Evaporation Heat Transfer ◽  
Seed Bubble

Investigation of Thin Film Evaporation Limit in Single Screen Mesh Layer

2002 ◽  
Author(s):  
Y. X. Wang ◽  
G. P. Peterson
Keyword(s):  
Thin Film ◽  
Heat Transfer ◽  
Heat Pipes ◽  
Liquid Meniscus ◽  
Thin Film Evaporation ◽  
Film Evaporation ◽  
Evaporation Heat ◽  
Heat Transfer Limit ◽  
Evaporation Heat Transfer ◽  
Screen Mesh

Thin film evaporation heat transfer plays an extremely important role in capillary microstructures of the type used extensively in micro heat pipes, loop heat pipes and high-flux film heat spreaders. Because the formation of the liquid meniscus in the pore cell has a significant effect on the evaporation process occurring at the interface of the liquid meniscus, it is necessary to investigate the mechanisms and limitations of the phase-change phenomena occurring in the thin layer. In the current study, an analytical model, which combines the heat conduction in the wick layer with bubble formation mechanisms in the capillary structure, has been developed to determine the evaporation heat transfer limit. Temperature distribution, superheat, and heat flux distribution in the liquid meniscus area are investigated for a single layer of metal screen mesh. The wire diameter, the space between the wires and the contact conditions between the solid wall and mesh layer is shown to have a significant effect on the evaporation limit and capillary force. Results indicated that evaporation takes place mainly in the thin film region, and the heat transfer coefficient is much higher in this area than in the intrinsic region. The evaporation limit is restrained by the formation of the liquid meniscus, and the higher the capillary pressure, the lower the evaporation heat transfer limit.

A Numerical Study of Single Bubble Dynamics During Flow Boiling

2004 ◽  
Author(s):  
Ding Li ◽  
Vijay K. Dhir
Keyword(s):  
Heat Transfer ◽  
Bubble Dynamics ◽  
Numerical Study ◽  
Flow Boiling ◽  
Forced Flow ◽  
Single Bubble ◽  
Horizontal Line ◽  
Vapor Interface ◽  
Single Bubble Dynamics ◽  
Liquid Vapor

Nucleate flow boiling is a liquid-vapor phase-change process associated with high heat transfer rates. A complete 3D numerical simulation of single bubble dynamics on surfaces inclined at 90°, 45° and 30° to the horizontal line and subjected to forced flow parallel to the surface is performed in this work. The continuity, momentum and energy equations are solved with finite difference method and the level-set method is used to capture the liquid-vapor interface. The heat transfer contribution of the micro-layer between the solid wall and evolving liquid-vapor interface is included in this numerical analysis. The effect of dynamic contact angle is also included. The numerical result of bubble growth and sliding distance have been compared with experimental data.

Evaporation Heat Transfer Characteristics on the Outside of Horizontal Smooth, Herringbone and Enhanced Surface 1EHT Tubes

2015 ◽  
Author(s):  
Jian-jun Sun ◽  
Jing-xiang Chen ◽  
David J. Kukulka ◽  
Kan Zhou ◽  
Wei Li ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Pressure Drop ◽  
Smooth Tube ◽  
External Diameter ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
Mass Fluxes ◽  
Evaporation Heat ◽  
Evaporation Heat Transfer ◽  
Enhanced Surface

An experiment investigation was performed using R410A in order to determine the single-phase and evaporation heat transfer coefficients on the outside of (i) a smooth tube; (ii) herringbone tube; and (iii) the newly developed Vipertex enhanced surface 1EHT tube; all with the same external diameter (12.7 mm). The nominal evaporation temperature is 279 K, with inlet and outlet qualities of 0.1 and 0.8. Mass fluxes ranged from 10 to 40 kg m−2s−1. Results suggest that the 1EHT tube has excellent heat transfer performance but a higher pressure drop when compared to a smooth tube. Evaporation heat transfer coefficient for the 1EHT is lower than the herringbone tube and the pressure drop is almost the same.

Experimental Study of Evaporation Heat Transfer Characteristics and Pressure Drops of R410A and R134a in a Multiport Mini-Channel

2009 ◽  
Author(s):  
Jatuporn Kaew-On ◽  
Somchai Wongwises
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Pressure Drop ◽  
Transfer Coefficient ◽  
Transfer Coefficients ◽  
Pressure Drops ◽  
Heat Transfer Coefficients ◽  
Evaporation Heat ◽  
Evaporation Heat Transfer ◽  
R 134A

The evaporation heat transfer coefficients and pressure drops of R-410A and R-134a flowing through a horizontal-aluminium rectangular multiport mini-channel having a hydraulic diameter of 3.48 mm are experimentally investigated. The test runs are done at refrigerant mass fluxes ranging between 200 and 400 kg/m2s. The heat fluxes are between 5 and 14.25 kW/m2, and refrigerant saturation temperatures are between 10 and 30 °C. The effects of the refrigerant vapour quality, mass flux, saturation temperature and imposed heat flux on the measured heat transfer coefficient and pressure drop are investigated. The experimental data show that in the same conditions, the heat transfer coefficients of R-410A are about 20–50% higher than those of R-134a, whereas the pressure drops of R-410A are around 50–100% lower than those of R-134a. The new correlations for the evaporation heat transfer coefficient and pressure drop of R-410A and R-134a in a multiport mini-channel are proposed for practical applications.

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