Experimental Study of Critical Heat Flux and Heat Transfer Coefficient Enhancements in Pool Boiling Heat Transfer With Nanostructure Modified Active Nucleation Site and Contact Angle

2012 ◽  
Author(s):  
Eric Nolan ◽  
Russell Rioux ◽  
Calvin Hong Li
Keyword(s):  
Heat Transfer ◽  
Experimental Study ◽  
Heat Flux ◽  
Contact Angle ◽  
Heat Transfer Coefficient ◽  
Boiling Heat Transfer ◽  
Nucleation Site ◽  
Copper Surfaces ◽  
Site Density ◽  
Nucleation Site Density

An experimental study of nanostructure modified nucleation site density and contact angle that significantly enhances the Heat Transfer Coefficient (HTC) and the Critical Heat Flux (CHF) in pool boiling heat transfer of water on copper surfaces has been conducted. The nanostructures on copper surfaces have been created by an electrodeposition technique. It has been found that the nanostructured copper surfaces show an increase in CHF of up to 142% and an increase in HTC of 33% over that of a mirror-finished plain copper surface. Calculations for nucleation site density and active nucleation site diameter reveal a direct correlation between these factors and the HTC, as well as the CHF. More interestingly, a contact angle study on the tested surfaces shows that there is a connection between the contact angle reduction and CHF enhancement, which confirms the contact angle mechanism of CHF with experimental evidence.

scholarly journals Enhancement of the pool boiling heat transfer coefficient using the gas injection into the water

2012 ◽  
Vol 14 (4) ◽  
pp. 100-109 ◽  
Author(s):  
M.M. Sarafraz ◽  
S.M. Peyghambarzadeh ◽  
S.A. Alavi Fazel
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Boiling Heat Transfer ◽  
Pool Boiling ◽  
Nucleation Site ◽  
Pool Boiling Heat Transfer ◽  
Site Density ◽  
Boiling Heat Transfer Coefficient ◽  
Nucleation Site Density

Abstract In this paper, a new method for enhancing the pool boiling heat transfer coefficient of pure liquid, based on the gas injection through the liquids has been introduced. Hence, the effect of gas dissolved in a stagnant liquid on pool boiling heat transfer coefficient, nucleation site density, and bubble departure diameter has experimentally been investigated for different mole fractions of SO2 and various heat fluxes up to 114 kW/ m2. The presence of SO2 in captured vapor inside the bubbles, particularly around the heat transfer surface increases the pool boiling heat transfer coefficient. The available predicted correlations are unable to obtain the reasonable values for pool boiling heat transfer coefficient in this particular case. Therefore, to predict the pool boiling heat transfer coefficient accurately, a new modified correlation based on Stephan-Körner relation has been proposed. Also, during the experiments, it is found that nucleation site density is a strictly exponential function of heat flux. Accordingly, a new correlation has been obtained to predict the nucleation site density. The major application of the nucleation site density is in the estimating of mean bubble diameters as well as local agitation due to the rate of bubble frequency.

Creation of Nano-Scaled Surface Structure for the Enhancement of Boiling Heat Transfer

2004 ◽  
Author(s):  
Sho Ngai ◽  
A. I. Leontiev ◽  
John R. Lloyd ◽  
S. P. Malyshenko
Keyword(s):  
Heat Transfer ◽  
Boiling Heat Transfer ◽  
Nucleation Site ◽  
Glancing Angle Deposition ◽  
Surface Structures ◽  
Transfer Enhancement ◽  
Site Density ◽  
Glancing Angle ◽  
Angle Deposition ◽  
Nucleation Site Density

The present research is an experimental investigation of nucleate pool boiling heat transfer enhancement on a surface with micro/nano-scaled surface structures. Glancing Angle Deposition (GLAD) was employed to fabricate porous surfaces in this study. The thin film microstructure consists of closely packed columns oriented in the plane of incidence formed due to a self-shadowing mechanism. Boiling heat transfer from the nano-structured surface was compared to that of a smooth reference surface and the commercial High Flux surface. The results of this study have shown that nano-structured films created by the GLAD process increase the nucleation site density as compared to the smooth surface. This research has opened up new areas in the field of heat transfer, which motivate new surface coating concepts to enhance the understanding of boiling heat transfer on nano-structured films.

Saturated Nucleate Pool Boiling of Ethanol-Water Binary Mixtures on Smooth and Enhanced Laser Processed Metal Surfaces

2018 ◽  
Author(s):  
Matevž Zupančič ◽  
Jure Voglar ◽  
Peter Gregorčič ◽  
Iztok Golobič ◽  
Peter Zakšek
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Binary Mixtures ◽  
Pure Water ◽  
Pool Boiling ◽  
Nucleation Site ◽  
Site Density ◽  
Nucleation Frequency ◽  
Nucleation Site Density

Pool boiling experiments of water and ethanol-water binary mixtures were conducted on smooth and laser textured stainless steel foils. High-speed IR thermography was used to measure transient temperature field during boiling in order to determine nucleation frequencies, nucleation site densities, bubble activation temperatures, wall-temperature distributions and average superheats as well as heat transfer coefficients. Saturated pool boiling experiments were conducted at atmospheric pressure over a heat flux range of 5–250 kW m−2 for pure water and ethanol-water mixtures (1% and 10% m/m). For both mixtures and both types of surfaces we measured significant decrease in average heat transfer coefficient and increase in bubble activation temperatures in comparison to pure water. However, laser textured surface in average provided around 60% higher nucleation frequency and more than 100% higher nucleation site density compared to smooth surface for both of the tested binary mixtures. Consequentially, heat transfer coefficient was enhanced for more than 30%. Our results show that laser textured surfaces can improve boiling performance for water and ethanol-water mixtures, but at the same time the addition of ethanol reduces heat transfer coefficient despite the enhancement of nucleation site density and nucleation frequency. This is also in agreement with available experimental data and existing theoretical models.

Onset of Nucleate Boiling and Active Nucleation Site Density During Subcooled Flow Boiling

2002 ◽  
Vol 124 (4) ◽  
pp. 717-728 ◽  
Author(s):  
Nilanjana Basu ◽  
Gopinath R. Warrier ◽  
Vijay K. Dhir
Keyword(s):  
Heat Flux ◽  
Contact Angle ◽  
Flow Boiling ◽  
Nucleate Boiling ◽  
Nucleation Site ◽  
Subcooled Flow Boiling ◽  
Site Density ◽  
Wall Superheat ◽  
Subcooled Flow ◽  
Nucleation Site Density

The partitioning of the heat flux supplied at the wall is one of the key issues that needs to be resolved if one is to model subcooled flow boiling accurately. The first step in studying wall heat flux partitioning is to account for the various heat transfer mechanisms involved and to know the location at which the onset of nucleate boiling (ONB) occurs. Active nucleation site density data is required to account for the energy carried away by the bubbles departing from the wall. Subcooled flow boiling experiments were conducted using a flat plate copper surface and a nine-rod (zircalloy-4) bundle. The location of ONB during the experiments was determined from visual observations as well as from the thermocouple output. From the data obtained it is found that the heat flux and wall superheat required for inception are dependent on flow rate, liquid subcooling, and contact angle. The existing correlations for ONB underpredict the wall superheat at ONB in most cases. A correlation for predicting the wall superheat and wall heat flux at ONB has been developed from the data obtained in this study and that reported in the literature. Experimental data are within ±30 percent of that predicted from the correlation. Active nucleation site density was determined by manually counting the individual sites in pictures obtained using a CCD camera. Correlations for nucleation site density, which are independent of flow rate and liquid subcooling, but dependent on contact angle have been developed for two ranges of wall superheat—one below 15°C and another above 15°C.

Towards an Explanation of the Mechanism of Boiling Critical Heat Flux Enhancement in Nanofluids

2007 ◽  
Author(s):  
Jacopo Buongiorno ◽  
Lin-Wen Hu ◽  
In Cheol Bang
Keyword(s):  
Heat Flux ◽  
Contact Angle ◽  
Critical Heat Flux ◽  
Hot Spot ◽  
Heated Surface ◽  
Nucleation Site ◽  
Nanoparticle Layer ◽  
Site Density ◽  
Static Contact ◽  
Nucleation Site Density

Nanofluids exhibit a very significant enhancement of the boiling Critical Heat Flux (CHF) at low nanoparticle concentrations. This paper reviews the nanofluid boiling database in a quest for the CHF enhancement mechanism. Briefly, buildup of a nanoparticle layer on the heated surface occurs upon boiling of nanofluids. This layer changes the surface roughness and the nucleation site density and, remarkably, can improve the surface wettability, as shown by a reduction of the static contact angle on the nanofluid-boiled surfaces. Significant differences are also observed in the dynamic behavior of the hot spot at CHF.

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