Numerical and Experimental Investigation Into the Effects of Nanoparticle Mass Fraction and Bubble Size on Boiling Heat Transfer of TiO2–Water Nanofluid

2016 ◽  
Vol 138 (8) ◽  
Author(s):  
Cong Qi ◽  
Yongliang Wan ◽  
Lin Liang ◽  
Zhonghao Rao ◽  
Yimin Li
Keyword(s):  
Heat Transfer ◽  
Bubble Size ◽  
Boiling Heat Transfer ◽  
Mass Fraction ◽  
Experimental Methods ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
Mass Fractions ◽  
Boiling Heat Transfer Coefficient ◽  
Bubble Sizes

Considering mass transfer and energy transfer between liquid phase and vapor phase, a mixture model for boiling heat transfer of nanofluid is established. In addition, an experimental installation of boiling heat transfer is built. The boiling heat transfer of TiO2–water nanofluid is investigated by numerical and experimental methods, respectively. Thermal conductivity, viscosity, and boiling bubble size of TiO2–water nanofluid are experimentally investigated, and the effects of different nanoparticle mass fractions, bubble sizes and superheat on boiling heat transfer are also discussed. It is found that the boiling bubble size in TiO2–water nanofluid is only one-third of that in de-ionized water. It is also found that there is a critical nanoparticle mass fraction (wt.% = 2%) between enhancement and degradation for TiO2–water nanofluid. Compared with water, nanofluid enhances the boiling heat transfer coefficient by 77.7% when the nanoparticle mass fraction is lower than 2%, while it reduces the boiling heat transfer by 30.3% when the nanoparticle mass fraction is higher than 2%. The boiling heat transfer coefficients increase with the superheat for water and nanofluid. A mathematic correlation between heat flux and superheat is obtained in this paper.

Convective Boiling Heat Transfer Enhancement by Microgrooves in Plate Evaporator

2011 ◽  
Author(s):  
Hirofumi Arima ◽  
Nobuhiko Matsuo ◽  
Keita Shigyou ◽  
Akio Okamoto ◽  
Yasuyuki Ikegami
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Boiling Heat Transfer ◽  
Flat Surface ◽  
Saturation Pressure ◽  
Transfer Coefficients ◽  
Convective Boiling ◽  
Heat Transfer Coefficients ◽  
Boiling Heat Transfer Coefficient

In this experimental study, we investigate the enhancement of heat transfer in ammonia on a new plate evaporator whose surface is configured with microgrooves. The microgrooves have a depth of 30 μm and a width of 200 μm. The local boiling heat transfer coefficients were measured on the evaporator. To compare the heat transfer characteristics of the evaporator, the local boiling heat transfer coefficient on a flat surface and on two microgrooved surfaces—one vertical and one horizontal to the direction of the ammonia flow—were measured at different ranges of mass flux (2–7.5 kg/m2s), heat flux (10–20 kW/m2), and saturation pressure (0.7–0.9 MPa). The results show that the local boiling heat transfer coefficient of the horizontal and vertical microgrooved surfaces was larger than that of a flat surface. In particular, the horizontal microgrooved surface had the best heat transfer coefficient.

Nucleate Pool Boiling Heat Transfer of R134a and R134a-PVE Lubricant Mixtures on Smooth and Five Enhanced Tubes

2010 ◽  
Vol 132 (11) ◽  
Author(s):  
Wen-Tao Ji ◽  
Ding-Cai Zhang ◽  
Nan Feng ◽  
Jian-Fei Guo ◽  
Mitsuharu Numata ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Boiling Heat Transfer ◽  
Pool Boiling ◽  
Saturation Temperature ◽  
Transfer Coefficients ◽  
Pool Boiling Heat Transfer ◽  
Heat Transfer Coefficients ◽  
Enhanced Tubes ◽  
Mass Fractions

Pool boiling heat transfer coefficients of R134a with different lubricant mass fractions for one smooth tube and five enhanced tubes were tested at a saturation temperature of 6°C. The lubricant used was polyvinyl ether. The lubrication mass fractions were 0.25%, 0.5%, 1.0%, 2.0%, 3.0%, 5.0%, 7.0%, and 10.0%, respectively. Within the tested heat flux range, from 9000 W/m2 to 90,000 W/m2, the lubricant generally has a different influence on pool boiling heat transfer of these six tubes.

The Effects of Rolling Motion Upon the Coefficient of Flow Boiling Heat Transfer

2014 ◽  
Author(s):  
Chong Chen ◽  
Pu-zhen Gao
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Test Section ◽  
Boiling Heat Transfer ◽  
Narrow Channel ◽  
Rolling Motion ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
Boiling Heat Transfer Coefficient ◽  
Time Average

Experimental investigations on boiling heat transfer coefficients of boiling flows in rectangular narrow channel under rolling motion condition are performed. The cross section of the testing rectangular narrow channel is 2×40 mm, and the mechanical rolling thermal-hydraulic experimental facility is used in the experimental research of boiling heat transfer characteristics. Deionized water is used as the working fluid. The results show that the amplitude of boiling heat transfer coefficients of rectangular narrow channel increases with increasing rolling amplitude and rolling period of the rolling platform, the time average boiling heat transfer coefficients of test section in rolling motion are equal to the coefficients of the test section at equilibrium position, and with the increase of rolling amplitude and rolling period the time average boiling heat transfer coefficient almost unchanged. The amplitude of boiling heat transfer coefficients increases with increasing heat flux and flow rate, while decreases with the increase of system pressure. The curve of boiling heat transfer coefficient fluctuations of rectangular narrow channel is close to sine or cosine curve when the rolling period less than 15 seconds.

Latent and Sensible Heat-Transfer Rates in the Boiling of Binary Mixtures

1982 ◽  
Vol 104 (3) ◽  
pp. 474-478 ◽  
Author(s):  
J. R. Thome
Keyword(s):  
Heat Transfer ◽  
Heat Transport ◽  
Binary Mixtures ◽  
Boiling Heat Transfer ◽  
Constant Heat Flux ◽  
Absolute Pressure ◽  
Sensible Heat ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
Boiling Heat Transfer Coefficient

Nucleate pool boiling bubble departure data were obtained for the liquid nitrogen-argon cryogenic binary mixture system at 1.3 atmospheres absolute pressure. The latent and sensible heat transport rates at individual boiling sites were calculated from the data to deduce their effect on the degradation in the boiling heat-transfer coefficient in binary mixtures. The latent heat-transfer rate is a result of the bubble evaporation mechanism and the sensible heat-transport rate is due to cyclic thermal boundary layer stripping by departing bubbles. The latent and sensible heat-transport rates at individual boiling sites were found to decrease to a minimum at the maximum vapor-liquid mole fraction difference for both constant heat flux and wall superheating conditions. The large decrease in binary boiling heat-transfer coefficients was thus partially explained by the retardation of these two mechanisms and should be included in any model for predicting boiling heat-transfer coefficients in binary and multicomponent mixtures.

Enhancement of Pool Boiling and Critical Heat Flux in Self-Rewetting Fluids at Above Atmospheric Pressures

2011 ◽  
Author(s):  
Mostafa Morovati ◽  
Hitesh Bindra ◽  
Shuji Esaki ◽  
Masahiro Kawaji
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Critical Heat Flux ◽  
Boiling Heat Transfer ◽  
Pool Boiling ◽  
Heat Pipes ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
Bubble Sizes ◽  
Butanol Solution

Pool boiling experiments have been conducted with a self-rewetting fluid consisting of an aqueous butanol solution to study the boiling heat transfer enhancement at pressures of 1 ∼ 4 bars. Although self-rewetting fluids have been used to enhance the performance of heat pipes, boiling heat transfer characteristics are yet to be fully understood especially at pressures above atmospheric. Pool boiling experiments with aqueous butanol solutions were performed using an electrically heated platinum wire to obtain pool boiling heat transfer data up to the Critical Heat Flux (CHF). Aqueous butanol solutions with butanol concentrations 2–7% showed enhanced heat transfer coefficients and CHF data at various pressure levels. In comparison to water, aqueous butanol solutions showed 20–270% higher values of CHF at pressures up to 4 bars. The bubble sizes were also observed to be significantly smaller in self-rewetting fluids compared to those in water at the same pressure. This observation was consistent even at higher pressures. However, for the highest butanol concentration tested (7%), the CHF enhancement was diminished at higher pressures.

Heat Transfer Coefficients During Condensation of the Zeotropic Refrigerant Mixture HCFC-22/HCFC-142b

2002 ◽  
Vol 124 (6) ◽  
pp. 1137-1146 ◽  
Author(s):  
F. J. Smit ◽  
J. R. Thome ◽  
J. P. Meyer
Keyword(s):  
Heat Transfer ◽  
Flow Regime ◽  
Mass Fraction ◽  
Saturation Pressure ◽  
High Mass ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
Mass Fluxes ◽  
Mass Fractions ◽  
Hcfc 142B

Heat transfer coefficients during condensation of zeotropic refrigerant mixtures were obtained at mass fractions of 90 percent/10 percent, 80 percent/20 percent, 70 percent/30 percent, 60 percent/40 percent, and 50 percent/50 percent for HCFC-22/HCFC-142b and for pure HCFC-22 in a horizontal smooth tube at a high saturation pressure of 2.43 MPa. The measurements were taken in a series of eight 8.11 mm inner diameter smooth tubes with lengths of 1 603 mm. At low mass fluxes, from 40 kg/m2s to 350 kg/m2s where the flow regime is predominately stratified wavy, the refrigerant mass fraction influenced the heat transfer coefficient by up to a factor of two, decreasing as the mass fraction of HCFC-142b is increased. At high mass fluxes of 350 kg/m2s and more, the flow regime was predominately annular and the heat transfer coefficients were not strongly influenced by the refrigerant mass fraction, decreasing only by 7 percent as the refrigerant mass fraction changed from 100 percent HCFC-22 to 50 percent/50 percent HCFC-22/HCFC-142b. The results also indicated that of three methods tested to predict heat transfer coefficients, the flow pattern correlation of Dobson and Chato (1998) gave the best results for pure HCFC-22 and for the mixtures utilizing the Silver-Bell-Ghaly method (1964).

scholarly journals Pool Boiling Heat Transfer Coefficients in Mixtures of Water and Glycerin

Processes ◽  
2021 ◽  
Vol 9 (5) ◽  
pp. 830
Author(s):  
Viktor Vajc ◽  
Radek Šulc ◽  
Martin Dostál
Keyword(s):  
Heat Transfer ◽  
Dynamic Method ◽  
Water Mass ◽  
Heat Fluxes ◽  
Static Method ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
Mean Relative Error ◽  
Mixture Effects ◽  
Mass Fractions

Heat transfer coefficients were investigated for saturated nucleate pool boiling of binary mixtures of water and glycerin at atmospheric pressure in a wide range of concentrations and heat fluxes. Mixtures with water mass fractions from 100% to 40% were boiled on a horizontal flat copper surface at heat fluxes from about 25 up to 270kWm−2. Experiments were carried out by static and dynamic method of measurement. Results of the static method show that the impact of mixture effects on heat transfer coefficient cannot be neglected and ideal heat transfer coefficient has to be corrected for all investigated concentrations and heat fluxes. Experimental data are correlated with the empirical correlation α=0.59q0.714+0.130ωw with mean relative error of 6%. Taking mixture effects into account, data are also successfully correlated with the combination of Stephan and Abdelsalam (1980) and Schlünder (1982) correlations with mean relative error of about 15%. Recommended coefficients of Schlünder correlation C0=1 and βL=2×10−4ms−1 were found to be acceptable for all investigated mixtures. The dynamic method was developed for fast measurement of heat transfer coefficients at continuous change of composition of boiling mixture. The dynamic method was tested for water–glycerin mixtures with water mass fractions from 70% down to 35%. Results of the dynamic method were found to be comparable with the static method. For water–glycerin mixtures with higher water mass fractions, precise temperature measurements are needed.

Effect of Surface Roughness on Pool Boiling Heat Transfer of Water on a Superhydrophilic Aluminum Surface

2017 ◽  
Vol 139 (10) ◽  
Author(s):  
Jinsub Kim ◽  
Seongchul Jun ◽  
Jungho Lee ◽  
Juan Godinez ◽  
Seung M. You
Keyword(s):  
Heat Transfer ◽  
Surface Roughness ◽  
Boiling Heat Transfer ◽  
Aluminum Surface ◽  
Transfer Coefficients ◽  
Copper Surfaces ◽  
Heat Transfer Coefficients ◽  
Superhydrophilic Surface ◽  
Aluminum Surfaces ◽  
Effect Of Surface

The effect of surface roughness on the pool boiling heat transfer of water was investigated on superhydrophilic aluminum surfaces. The formation of nanoscale protrusions on the aluminum surface was confirmed after immersing it in boiling water, which modified surface wettability to form a superhydrophilic surface. The effect of surface roughness was examined at different average roughness (Ra) values ranging from 0.11 to 2.93 μm. The boiling heat transfer coefficients increased with an increase in roughness owing to the increased number of cavities. However, the superhydrophilic aluminum surfaces exhibited degradation of the heat transfer coefficients when compared with copper surfaces owing to the flooding of promising cavities. The superhydrophilic aluminum surfaces exhibited a higher critical heat flux (CHF) than the copper surfaces. The CHF was 1650 kW/m2 for Ra = 0.11 μm, and it increased to 2150 kW/m2 for Ra = 0.35 μm. Surface roughness is considered to affect CHF as it improves the capillary wicking on the superhydrophilic surface. However, further increase in surface roughness above 0.35 μm did not augment the CHF, even at Ra = 2.93 μm. This upper limit of the CHF appears to result from the hydrodynamic limit on the superhydrophilic surface, because the roughest surface with Ra = 2.93 μm still showed a faster liquid spreading speed.

High Heat Flux Boiling Heat Transfer for Laser Diode Arrays

2016 ◽  
Author(s):  
Todd M. Bandhauer ◽  
Taylor A. Bevis
Keyword(s):  
Heat Transfer ◽  
Thermal Management ◽  
Laser Diode ◽  
Boiling Heat Transfer ◽  
Single Phase ◽  
Laser Diodes ◽  
Heat Fluxes ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
Laser Diode Arrays

The principle limit for achieving higher brightness of laser diode arrays is thermal management. State of the art laser diodes generate heat at fluxes in excess of 1 kW cm−2 on a plane parallel to the light emitting edge. As the laser diode bars are packed closer together, it becomes increasingly difficult to remove large amounts of heat in the diminishing space between neighboring diode bars. Thermal management of these diode arrays using conduction and natural convection is practically impossible, and, therefore, some form of forced convective cooling must be utilized. Cooling large arrays of laser diodes using single-phase convection heat transfer has been investigated for more than two decades by multiple investigators. Unfortunately, either large fluid temperature increases or very high flow velocities must be utilized to reject heat to a single phase fluid, and the practical threshold for single phase convective cooling of laser diodes appears to have been reached. In contrast, liquid-vapor phase change heat transport can occur with a negligible increase in temperature and, due to a high enthalpy of vaporization, at comparatively low mass flow rates. However, there have been no prior investigations at the conditions required for high brightness edge emitting laser diode arrays: >1 kW cm−2 and >10 kW cm−3. In the current investigation, flow boiling heat transfer at heat fluxes up to 1.1 kW cm−2 was studied in a microchannel heat sink with plurality of very small channels (45 × 200 microns) using R134a as the phase change fluid. The high aspect ratio channels (4.4:1) were manufactured using MEMS fabrication techniques, which yielded a large heat transfer surface area to volume ratio in the vicinity of the laser diode. To characterize the heat transfer performance, a test facility was constructed that enabled testing over a range of fluid saturation temperatures (15°C to 25°C). Due to the very small geometric features, significant heat spreading was observed, necessitating numerical methods to determine the average heat transfer coefficient from test data. This technique is crucial to accurately calculate the heat transfer coefficients for the current investigation, and it is shown that the analytical approach used by many previous investigations requires assumptions that are inadequate for the very small dimensions and heat fluxes observed in the present study. During the tests, the calculated outlet vapor quality exceeded 0.6 and the base heat flux reached a maximum of 1.1 kW cm−2. The resulting experimental heat transfer coefficients are found to be as large a 58.1 kW m−2 K−1 with an average uncertainty of ±11.1%, which includes uncertainty from all measured and calculated values, required assumptions, and geometric discretization error from meshing.

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