Phase-Change Heat Transfer in Microsystems

2006 ◽  
Vol 129 (2) ◽  
pp. 101-108 ◽  
Author(s):  
Ping Cheng ◽  
Hui-Ying Wu ◽  
Fang-Jun Hong
Keyword(s):  
Heat Transfer ◽  
Phase Change ◽  
Mass Flux ◽  
Annular Flow ◽  
Pulse Heating ◽  
Flow Boiling ◽  
Mist Flow ◽  
Flow Condensation ◽  
Phase Change Heat Transfer ◽  
Condensation Flow

Recent work on miscroscale phase-change heat transfer, including flow boiling and flow condensation in microchannnels (with applications to microchannel heat sinks and microheat exchangers) as well as bubble growth and collapse on microheaters under pulse heating (with applications to micropumps and thermal inkjet printerheads), is reviewed. It has been found that isolated bubbles, confined elongated bubbles, annular flow, and mist flow can exist in microchannels during flow boiling. Stable and unstable flow boiling modes may occur in microchannels, depending on the heat to mass flux ratio and inlet subcooling of the liquid. Heat transfer and pressure drop data in flow boiling in microchannels are shown to deviate greatly from correlations for flow boiling in macrochannels. For flow condensation in microchannels, mist flow, annular flow, injection flow, plug-slug flow, and bubbly flows can exist in the microchannels, depending on mass flux and quality. Effects of the dimensionless condensation heat flux and the Reynolds number of saturated steam on transition from annular two-phase flow to slug/plug flow during condensation in microchannels are discussed. Heat transfer and pressured drop data in condensation flow in microchannels, at low mass flux are shown to be higher and lower than those predicted by correlations for condensation flow in macrochannels, respectively. Effects of pulse heating width and heater size on microbubble growth and collapse and its nucleation temperature on a microheater under pulse heating are summarized.

Investigation of the Effects of Simultaneous Internal Flow Boiling and External Condensation on the Heat Transfer Performance

2019 ◽  
Author(s):  
M. M. Kabir ◽  
Sangsoo Lee
Keyword(s):  
Heat Transfer ◽  
Heat Exchanger ◽  
Phase Change ◽  
Single Phase ◽  
Heat Transfer Performance ◽  
Flow Boiling ◽  
Internal Flow ◽  
Transfer Performance ◽  
Test Rig ◽  
Phase Change Heat Transfer

Abstract Recent leaps in heat dissipation make it difficult for typical heat exchangers to meet the requirements of the advanced applications even with the maximally obtainable heat transfer performance associated with a single-phase process. Especially high heat flux applications such as thermal management in microelectronics, advanced material processing, and nuclear fusion reactors require extreme heat transfer methods to overcome the current limits. In this study, a heat exchanger adopting simultaneously two-opposite, phase-change heat transfer processes (internal flow boiling and external condensation) was proposed and analytically investigated. The phase-change heat transfer analyses were conducted for internal flow boiling and external condensation at a test section and the heat transfer performances were compared with that of a system with an internal single-phase, liquid flow process. It is found that the proposed heat exchanger configuration with an internal flow boiling can substantially enhance the heat transfer performances and provide better methods to manage the temperature difference comparing to those with an internal single-phase heat transfer due to its significant increase in a heat transfer coefficients and constant temperatures during phase-change processes. Additionally, this study also explains the design for a test rig to evaluate and validate the results in detail. The test rig consists of an internal flow boiling loop with a test section, an external condensation loop, sensors, auxiliary monitoring parts, and controlling and data acquisition systems. Thermodynamic cycle, pressure drop, and heat transfer analyses were conducted to determine the conditions and the specifications of components and sensors for the test rig.

scholarly journals Comparative study of flow condensation in conventional and small diameter tubes

2012 ◽  
Vol 33 (2) ◽  
pp. 67-83 ◽  
Author(s):  
Dariusz Mikielewicz ◽  
Rafał Andrzejczyk
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Flow Structure ◽  
Annular Flow ◽  
Flow Boiling ◽  
Small Diameter ◽  
Bubble Generation ◽  
Flow Condensation ◽  
The Heat Transfer Coefficient

Abstract Flow boiling and flow condensation are often regarded as two opposite or symmetrical phenomena. Their description however with a single correlation has yet to be suggested. In the case of flow boiling in minichannels there is mostly encountered the annular flow structure, where the bubble generation is not present. Similar picture holds for the case of inside tube condensation, where annular flow structure predominates. In such case the heat transfer coefficient is primarily dependent on the convective mechanism. In the paper a method developed earlier by the first author is applied to calculations of heat transfer coefficient for inside tube condensation. The method has been verified using experimental data from literature on several fluids in different microchannels and compared to three well established correlations for calculations of heat transfer coefficient in flow condensation. It clearly stems from the results presented here that the flow condensation can be modeled in terms of appropriately devised pressure drop.

Biotemplated Nanostructured Surfaces for Enhanced Phase Change Heat Transfer

2012 ◽  
Author(s):  
S. M. King ◽  
Md. M. Rahman ◽  
A. K. Krick ◽  
L. D. Branco ◽  
E. Olceroglu ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Tobacco Mosaic Virus ◽  
Phase Change ◽  
Mosaic Virus ◽  
Self Assembly ◽  
High Speed ◽  
Flow Boiling ◽  
Structured Surfaces ◽  
Nanostructured Surfaces ◽  
Phase Change Heat Transfer

The fabrication and characterization of biotemplated nanostructured coatings based on the Tobacco mosaic virus for enhanced phase-change heat transfer is reported. A simple room temperature nanofabrication process, using the self-assembly and mineralization of the Tobacco mosaic virus (TMV), has been implemented to create superhydrophilic surfaces. Using this technique, a variety of structured surfaces have been fabricated and characterized showing enhanced surface wettability and heat transfer characteristics. High-speed images of droplet impact evaporation on flat and hierarchical samples have been recorded, showing increased wetting and evaporation for the nanostructured surfaces. The addition of nanostructures increases the heat transfer rate by more than a factor of three as compared to the flat surfaces, and hierarchical surfaces exhibit heat transfer rates more than an order of magnitude larger than flat non-structured surfaces. Additionally, an increase in Leidenfrost temperature of 100°C as compared to flat samples has been recorded. TMV nanostructures were also assembled onto the walls of heated minichannels, promoting continuous bubble detachment as well as reduced slug formation and instabilities during flow boiling. While bare minichannel exhibits nearly complete dry-out, the nanostructured channels maintain annular flow at similar loadings. This work demonstrates the feasibility of enhancing phase-change heat transfer using TMV structured coatings.

Numerical Investigation of Transition of Flow Condensation in Microchannel

2018 ◽  
Author(s):  
Il Seouk Park ◽  
Jong Hyeon Son
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Phase Change ◽  
Transfer Coefficient ◽  
Mass Flux ◽  
Channel Wall ◽  
Change Model ◽  
Micro Channel ◽  
Flow Condensation ◽  
The Heat Transfer Coefficient

Due to the miniaturization of electronic devices and advanced machines, the micro-channel phase change heat transfer is used for heat removal on limited surfaces. However, since the complexity of the phase change phenomenon, it is difficult to numerically analyze the phase change phenomenon inside the microchannel. In this study, the flow condensation problem of FC-72 fluid in a microchannel is numerically analyzed with the phase change model. SST k-omega turbulence model is used and Volume of Fluid method is used for tracking the gas-liquid interface inside micro-channels. The condensation phenomenon is analyzed by applying the phase change model based on the difference of the phase interface and saturated temperature. The transition of two-phase flow pattern, cross-sectional velocity profiles in a micro-channel are studied according to the inlet mass flux and the heat flux at the channel wall surface. The heat transfer coefficient was compared with the experimental results and it is confirmed that the heat transfer coefficient at the wall increase when the inlet mass flux increase. Also, the channel wall side surface temperature profiles, changes of isotherms, and velocity vector field inside channel due to liquid-phase creation are presented.

scholarly journals Comparative study of heat transfer and pressure drop during flow boiling and flow condensation in minichannels

2014 ◽  
Vol 35 (3) ◽  
pp. 17-37 ◽  
Author(s):  
Dariusz Mikielewicz ◽  
Rafał Andrzejczyk ◽  
Blanka Jakubowska ◽  
Jarosław Mikielewicz
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Shear Stress ◽  
Pressure Drop ◽  
Flow Structure ◽  
Annular Flow ◽  
Flow Boiling ◽  
Bubble Nucleation ◽  
Shear Stresses ◽  
Flow Condensation

Abstract In the paper a method developed earlier by authors is applied to calculations of pressure drop and heat transfer coefficient for flow boiling and also flow condensation for some recent data collected from literature for such fluids as R404a, R600a, R290, R32,R134a, R1234yf and other. The modification of interface shear stresses between flow boiling and flow condensation in annular flow structure are considered through incorporation of the so called blowing parameter. The shear stress between vapor phase and liquid phase is generally a function of nonisothermal effects. The mechanism of modification of shear stresses at the vapor-liquid interface has been presented in detail. In case of annular flow it contributes to thickening and thinning of the liquid film, which corresponds to condensation and boiling respectively. There is also a different influence of heat flux on the modification of shear stress in the bubbly flow structure, where it affects bubble nucleation. In that case the effect of applied heat flux is considered. As a result a modified form of the two-phase flow multiplier is obtained, in which the nonadiabatic effect is clearly pronounced.

scholarly journals Flow Pattern Map of Flow Boiling in a Rectangular Channel Filled with Porous Media

Energies ◽  
2021 ◽  
Vol 14 (9) ◽  
pp. 2440
Author(s):  
Youngwoo Kim ◽  
Dae Yeon Kim ◽  
Kyung Chun Kim
Keyword(s):  
Porous Media ◽  
Flow Pattern ◽  
Flow Regime ◽  
Annular Flow ◽  
Flow Boiling ◽  
Rectangular Channel ◽  
Flow Patterns ◽  
Flow Pattern Map ◽  
Mist Flow ◽  
Churn Flow

A flow visualization study was carried out for flow boiling in a rectangular channel filled with and without metallic random porous media. Four main flow patterns are observed as intermittent slug-churn flow, churn-annular flow, annular-mist flow, and mist flow regimes. These flow patterns are clearly classified based on the high-speed images of the channel flow. The results of the flow pattern map according to the mass flow rate were presented using saturation temperatures and the materials of porous media as variables. As the saturation temperatures increased, the annular-mist flow regime occupied a larger area than the lower saturation temperatures condition. Therefore, the churn flow regime is narrower, and the slug flow more quickly turns to annular flow with the increasing vapor quality. The pattern map is not significantly affected by the materials of porous media.

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