scholarly journals Phase Change Heat Exchangers Made of Pin-Fins for Boiling Enhancement

2019 ◽  
Vol 1 (1) ◽  
pp. 433-439
Author(s):  
Łukasz J. Orman ◽  
Norbert Radek ◽  
Jacek Pietraszek ◽  
Dariusz Gontarski
Keyword(s):  
Heat Flux ◽  
Heat Exchangers ◽  
Boiling Heat Transfer ◽  
Smooth Surface ◽  
Mechanical Treatment ◽  
Heat Fluxes ◽  
Heater Surface ◽  
Transfer Enhancement ◽  
Boiling Enhancement ◽  
Pin Fins

Abstract The paper deals with the important issue of boiling heat transfer enhancement using mechanical treatment of the heater surface. The surface has been modified in such a way that microfins have been produced. The application of such a structure leads to highly increased heat fluxes in relation to the smooth surface as has been presented and discussed in the paper. The experiments including distilled water and ethyl alcohol on the horizontal copper samples of 3 cm diameter have been considered. The heat flux value of microfinned surface was even nine times higher than the heat flux dissipated from the smooth surface without any coating. It proves a considerable enhancement of boiling with the application of the mechanically treated surfaces of heat exchangers.

HEAT TRANSFER ENHANCEMENT IN PHASE-CHANGE HEAT EXCHANGERS

Aviation ◽  
2014 ◽  
Vol 18 (1) ◽  
pp. 40-43 ◽  
Author(s):  
Rafał Chatys ◽  
Milan Malcho ◽  
Łukasz J. Orman
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Enhancement ◽  
Atmospheric Pressure ◽  
Heat Exchangers ◽  
Boiling Heat Transfer ◽  
Smooth Surface ◽  
Transfer Enhancement ◽  
Mesh Structure ◽  
Heat Exchanger Surface ◽  
Copper Mesh

The paper presents the results of boiling heat transfer enhancement due to the application of additional mesh on the heat exchanger surface. The copper mesh of porosity of 75% was sintered to the copper heater producing strong bonds between the elements. The results indicate a possibility of significant improvement of heat transfer conditions in comparison to the smooth surface. The heat flux was found to be almost six times higher for the same superheat if the mesh structure was applied. Distilled water and ethanol were the working fluids. The investigations were performed under atmospheric pressure.

Pool Boiling Characteristics of Metallic Nanofluids

2011 ◽  
Vol 133 (11) ◽  
Author(s):  
K. Hari Krishna ◽  
Harish Ganapathy ◽  
G. Sateesh ◽  
Sarit K. Das
Keyword(s):  
Heat Transfer ◽  
Thermal Conductivity ◽  
Boiling Heat Transfer ◽  
Volume Fraction ◽  
Pool Boiling ◽  
Heat Fluxes ◽  
Solid Particles ◽  
Heater Surface ◽  
Heat Transfer Characteristics ◽  
Transfer Characteristics

Nanofluids, solid-liquid suspensions with solid particles of size of the order of few nanometers, have created interest in many researchers because of their enhancement in thermal conductivity and convective heat transfer characteristics. Many studies have been done on the pool boiling characteristics of nanofluids, most of which have been with nanofluids containing oxide nanoparticles owing to the ease in their preparation. Deterioration in boiling heat transfer was observed in some studies. Metallic nanofluids having metal nanoparticles, which are known for their good heat transfer characteristics in bulk regime, reported drastic enhancement in thermal conductivity. The present paper investigates into the pool boiling characteristics of metallic nanofluids, in particular of Cu-H2O nanofluids, on flat copper heater surface. The results indicate that at comparatively low heat fluxes, there is deterioration in boiling heat transfer with very low particle volume fraction of 0.01%, and it increases with volume fraction and shows enhancement with 0.1%. However, the behavior is the other way around at high heat fluxes. The enhancement at low heat fluxes is due to the fact that the effect of formation of thin sorption layer of nanoparticles on heater surface, which causes deterioration by trapping the nucleation sites, is overshadowed by the increase in microlayer evaporation, which is due to enhancement in thermal conductivity. Same trend has been observed with variation in the surface roughness of the heater as well.

Stability and Enhancement of Boiling in Microchannels

2011 ◽  
Author(s):  
A. E. Bergles
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Critical Heat Flux ◽  
High Heat ◽  
Heat Fluxes ◽  
Transfer Enhancement ◽  
The Past ◽  
The Stability ◽  
Saturated Boiling ◽  
Microelectronic Components

During the past 20 years, there has been intense worldwide interest in microchannel heat exchangers, particularly for cooling of microelectronic components. Saturated boiling of the coolant is usually indicated in order to accommodate high heat fluxes and to have uniformity of temperature. However, boiling is accompanied by several instabilities, the most severe of which can sharply limit the maximum, or critical, heat flux. These stability phenomena are reviewed, and recent studies will be discussed. Elevation of the critical heat flux will be discussed within the context of heat transfer enhancement. Means to improve the stability of boiling and the enhancement of boiling heat transfer, in general, are discussed.

Growth of Micro Bubbles on Micro-Configured Metal-Graphite Composite Surfaces and Boiling Enhancement

2008 ◽  
Author(s):  
David Chao ◽  
Nengli Zhang ◽  
Wen-Jie Yang
Keyword(s):  
Heat Transfer ◽  
Boiling Heat Transfer ◽  
Active Sites ◽  
Nucleate Boiling ◽  
Transfer Enhancement ◽  
Growth Processes ◽  
Graphite Composite ◽  
Boiling Enhancement ◽  
Structure Of Metal ◽  
Graphite Fibers

A series of studies in nucleate boiling phenomena on metal-graphite composite surfaces has been investigated by Prof. Wen-Jei Yang and their associates. It has been discovered that the unique micro-configured construction of the composite surfaces plays a crucial role in the enhancement of boiling heat transfer. The present paper focuses on the formation and growth processes of micro bubbles and the micro/nano scale boiling behavior to reveal the mechanism of boiling heat transfer enhancement on the unique surfaces. The growth processes of the micro and macro bubbles are analyzed and formulated followed by an analysis of bubble departure. Based on these analyses, the enhancement mechanism of the pool boiling heat transfer on the composite surfaces is clearly revealed. The micro-configured composite surfaces provide more even distribution of a great number of stable boiling active sites through the graphite fibers. Consequently, the heat conduction through the layers is increased, which provides the power of phase change at the interfaces on bubble bottoms. Experimental results convincingly demonstrate the enhancement effects of the unique structure of metal-graphite composite surfaces on boiling heat transfer.

Boiling Heat Transfer With Freon 11 (R11) in Brazed Aluminum, Plate-Fin Heat Exchangers

1983 ◽  
Vol 105 (3) ◽  
pp. 605-610 ◽  
Author(s):  
J. M. Robertson ◽  
P. C. Lovegrove
Keyword(s):  
Heat Transfer ◽  
Test Section ◽  
Heat Exchangers ◽  
Boiling Heat Transfer ◽  
Industrial Process ◽  
Heat Fluxes ◽  
Test Fluid ◽  
Transfer Coefficients ◽  
Simple Method ◽  
Wide Range

The results of laboratory experiments with Freon 11 (R11) flowing in an electrically heated, serrated-fin test section to measure local boiling coefficients over a wide range of vapor quality, with mass fluxes up to 150 kg/m2 s, heat fluxes to 4 kW/m2, and pressure from 3–7 bar, are reported. These low mass and heat fluxes reflect the industrial process application of these heat exchangers where exceedingly small temperature differences may exist between streams. Results are compared with the very similar boiling characteristics previously reported elsewhere for the same test section, with liquid nitrogen as a test fluid under comparable flow conditions. A simple method using the Reynolds number of the total flow regarded as a liquid has been used to correlate boiling heat transfer coefficients with quality for both fluids. The use of a liquid-film flow model to produce a nondimensional correlation connecting the Nusselt, Reynolds, and Prandtl numbers of the film is discussed.

Enhancement of Critical Heat Flux From High Power Microelectronic Heat Sources in a Flow Channel

1990 ◽  
Vol 112 (3) ◽  
pp. 241-248 ◽  
Author(s):  
Issam Mudawar ◽  
Douglas E. Maddox
Keyword(s):  
Heat Flux ◽  
Critical Heat Flux ◽  
Vertical Channel ◽  
Heat Fluxes ◽  
Semiempirical Model ◽  
High Profile ◽  
Low Profile ◽  
Pin Fins ◽  
Augmentation Techniques ◽  
Discrete Heat Source

Several surface augmentation techniques were examined in an investigation of enhancement of critical heat flux (CHF) from a simulated electronic chip to a fluorocarbon (FC-72) liquid in a vertical channel. A parametric comparison of boiling performances is presented for a smooth surface and for surfaces with low-profile microgrooves, low-profile microstuds, and high-profile pin fins. Critical heat fluxes as high as 361 W/cm2 were achieved using a combination of moderate flow velocity, high subcooling and surface enhancement. A semiempirical model constructed previously for CHF from a smooth discrete heat source to saturated or subcooled liquid flow, was found successful in correlating CHF data for the three enhanced surfaces.

Effect of Heat Flux on Pool Boiling Heat Transfer Enhancement (Numerical Investigation Approach)

2020 ◽  
Author(s):  
T. S. Mogaji ◽  
O. A. Sogbesan ◽  
Tien-Chien Jen
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Heat Transfer Enhancement ◽  
Numerical Investigation ◽  
Boiling Heat Transfer ◽  
Pool Boiling ◽  
Nucleate Boiling ◽  
Transfer Enhancement

Abstract This study presents numerical investigation results of heat flux effect on pool boiling heat transfer enhancement during nucleate boiling heat transfer of water. The simulation was performed for five different heated surfaces such as: brass, copper, mild steel, stainless steel and aluminum using ANSYS simulation software at 1 atmospheric pressure. The samples were heated in a domain developed for bubble growth during nucleate boiling process under the same operational condition of applied heat flux ranged from 100 to 1000 kW/m2 and their corresponding heat transfer coefficient was obtained numerically. Obtained experimental data of other authors from the open literature result is in close agreement with the simulated data, thus confirming the validity of the CFD simulation method used in this study. It is found that heat transfer coefficient increases with increasing heat flux. The results revealed that in comparison to other materials tested, better heat transfer performance up to 38.5% and 7.11% is observed for aluminum and brass at lower superheated temperature difference conditions of 6.96K and 14.01K respectively. This behavior indicates better bubble development and detachment capability of these heating surface materials and could be used in improving the performance of thermal devices toward producing compact and miniaturized equipment.

Mechanism of Nucleate Boiling Heat Transfer Enhancement From Microporous Surfaces in Saturated FC-72

2002 ◽  
Vol 124 (3) ◽  
pp. 500-506 ◽  
Author(s):  
J. H. Kim ◽  
K. N. Rainey ◽  
S. M. You ◽  
J. Y. Pak
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Heat Transfer Enhancement ◽  
Latent Heat ◽  
Boiling Heat Transfer ◽  
Nucleate Boiling ◽  
Direct Result ◽  
Vapor Flow ◽  
High Heat Flux ◽  
Transfer Enhancement

The present study is an experimental investigation of the nucleate pool boiling heat transfer enhancement mechanism of microporous surfaces immersed in saturated FC-72. Measurements of bubble size, frequency, and vapor flow rate from a plain and microporous coated 390 μm diameter platinum wire using the consecutive-photo method were taken to determine the effects of the coating on the convective and latent heat transfer mechanisms. Results of the study showed that the microporous coating augments nucleate boiling performance through increased latent heat transfer in the low heat flux region and through increased convection heat transfer in the high heat flux region. The critical heat flux for the microporous coated surface is significantly enhanced over the plain surface due to decreased latent heat transfer (decreased vapor generation rate) and/or increased hydrodynamic stability from increased vapor inertia; both of which are a direct result of increased nucleation site density.

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