scholarly journals Subcooled Flow Boiling Heat Flux Enhancement Using High Porosity Sintered Fiber

2021 ◽  
Vol 11 (13) ◽  
pp. 5883
Author(s):  
Edgar Santiago Galicia ◽  
Yusuke Otomo ◽  
Toshihiko Saiwai ◽  
Kenji Takita ◽  
Kenji Orito ◽  
...  
Keyword(s):  
Heat Flux ◽  
Porous Body ◽  
Flow Boiling ◽  
Heating Surface ◽  
Working Fluid ◽  
High Porosity ◽  
Subcooled Flow Boiling ◽  
Wall Superheat ◽  
Subcooled Flow ◽  
Bare Surface

Passive methods to increase the heat flux on the subcooled flow boiling are extremely needed on modern cooling systems. Many methods, including treated surfaces and extended surfaces, have been investigated. Experimental research to enhance the subcooled flow boiling using high sintered fiber attached to the surface was conducted. One bare surface (0 mm) and four porous thickness (0.2, 0.5, 1.0, 2.0 mm) were compared under three different mass fluxes (200, 400, and 600 kg·m−2·s−1) and three different inlet subcooling temperature (70, 50, 30). Deionized water under atmospheric pressure was used as the working fluid. The results confirmed that the porous body can enhance the heat flux and reduce the wall superheat temperature. However, higher porous thickness presented a reduction in the heat flux in comparison with the bare surface. Bubble formation and pattern flow were recorded using a high-speed camera. The bubble size and formation are generally smaller at higher inlet subcooling temperatures. The enhancement in the heat flux and the reduction on the wall superheat is attributed to the increment on the nucleation sites, the increment on the heating surface area, water supply ability through the porous body, and the vapor trap ability.

scholarly journals Enhancement of Subcooled Flow Boiling Heat Transfer with High Porosity Sintered Fiber Metal

2021 ◽  
Vol 11 (3) ◽  
pp. 1237
Author(s):  
Yusuke Otomo ◽  
Edgar Santiago Galicia ◽  
Koji Enoki
Keyword(s):  
Heat Flux ◽  
Mass Flux ◽  
High Speed ◽  
Flow Boiling ◽  
Rectangular Channel ◽  
Working Fluid ◽  
High Porosity ◽  
Subcooled Flow Boiling ◽  
Subcooled Flow ◽  
Porous Surfaces

We conducted experimental research using high-porosity sintered fiber attached on the surface, as a passive method to increase the heat flux for subcooled flow boiling. Two different porous thicknesses (1 and 0.5 mm) and one bare surface (0 mm) were compared under three different inlet subcooling temperatures (30, 50 and 70 K) and low mass flux (150–600 kg·m−2·s−1) using deionized water as the working fluid under atmospheric pressure. The test section was a rectangular channel, and the hydraulic diameter was 10 mm. The results showed that the heat flux on porous surfaces with a thickness of 1 and 0.5 mm increased by 60% and 40%, respectively, compared to bare surfaces at ΔTsat = 40 K at a subcooled temperature of 50 K and mass flux of 300 kg·m−2·s−1. An abrupt increase in the wall superheat was avoided, and critical heat flux (CHF) was not reached on the porous surfaces. The flow pattern and bubble were recorded with a high-speed camera, and the bubble dynamics are discussed.

Heat Transfer Characteristics and Flow Pattern Visualization for Flow Boiling in a Vertical Narrow Microchannel

2018 ◽  
Author(s):  
Kan Zhou ◽  
Junye Li ◽  
Zhao-zan Feng ◽  
Wei Li ◽  
Hua Zhu ◽  
...  
Keyword(s):  
Heat Flux ◽  
Flow Pattern ◽  
Flow Boiling ◽  
Nucleate Boiling ◽  
Working Fluid ◽  
Inlet Temperature ◽  
Lower Mass ◽  
Subcooled Flow Boiling ◽  
Mass Fluxes ◽  
Subcooled Flow

For improving the functionality and signal speed of electronic devices, electronic components have been miniaturized and an increasing number of elements have been packaged in the device. As a result there has been a steady rise in the amount of heat necessitated to be dissipated from the electronic device. Recently microchannel heat sinks have been emerged as a kind of high performance cooling scheme to meet the heat dissipation requirement of electronics packaging, In the present study an experimental study of subcooled flow boiling in a high-aspect-ratio, one-sided heating rectangular microchannel with gap depth of 0.52 mm and width of 5 mm was conducted with deionized water as the working fluid. In the experimental operations, the mass flux was varied from 200 to 400 kg/m2s and imposed heat flux from 3 to 20 W/cm2 while the fluid inlet temperature was regulated constantly at 90 °C. The boiling curves, flow pattern and onset of nucleate boiling of subcooled flow boiling were investigated through instrumental measurements and a high speed camera. It was found that the slope of the boiling curves increased sharply once the superheat needed to initiate the onset of nucleate boiling was attained, and the slope was greater for lower mass fluxes, with lower superheat required for boiling incipience. As for the visualization images, for relatively lower mass fluxes the bubbles generated were larger and not easy to depart from the vertical upward placed narrow microchannel wall, giving elongated bubbly flow and reverse backflow. The thin film evaporation mechanism dominated the entire test section due to the elongated bubbles and transient local dryout as well as rewetting occurred. Meanwhile the initiative superheat and heat flux of onset of nucleate boiling were compared with existing correlations in the literature with good agreement.

Subcooled Flow Boiling in Mini and Micro Channel: Contribution Toward High Heat Flux Cooling Technology for Electronics

2009 ◽  
Author(s):  
Tomoyuki Nomura ◽  
Michael V. Shustov ◽  
Koichi Suzuki ◽  
Chungpyo Hong ◽  
Yury A. Kuzma-Kichta
Keyword(s):  
Heat Flux ◽  
Liquid Velocity ◽  
Flow Boiling ◽  
Heating Surface ◽  
Heat Fluxes ◽  
High Heat Flux ◽  
Subcooled Flow Boiling ◽  
Maximum Heat ◽  
Subcooled Flow ◽  
Micro Channels

Subcooled flow boiling has been investigated for horizontal mini and micro channels of which hydraulic diameters are 1mm and 150μm, respectively for high heat flux cooling in electronics. The heating surface is 1mm in width and 10mm in length for the mini channel. Eleven micro grooving are made on the copper heating block of 5.25mm×5.25mm. Aqueous solutions of ethanol, 10% and 50% in mass concentration, are used as boiling liquid for the micro channel. Microbubble emission boiling (MEB) of water is generated at liquid subcooling of 40K in the mini channel as same cases of conventional macro channels and the maximum heat flux obtained is a 10MW/m2 at liquid velocity of 1m/s (1000kg/m2s). However, the boiling turns to film boiling at low liquid velocity, 0.3m/s (300kg/m2s) for an example. In subcooled boiling of aqueous solutions, the heat flux becomes small for the lower ethanol concentration. The critical heat fluxes are well agreed with the existing theories and the maximum heat fluxes are higher than CHF. However, no micro bubble emission boiling is observed in subcooled flow boiling of mini channels and the CHF is considerably smaller than the existing theories. It is difficult to generate MEB for micro channels with heating surface of large thermal capacity because the coalescing bubbles formed on the heating surface are filled up in the channel and the liquid vapor exchange is disturbed.

Subcooled Flow Boiling in a Minichannel

2009 ◽  
Author(s):  
Akira Oshima ◽  
Koichi Suzuki ◽  
Chungpyo Hong ◽  
Masataka Mochizuki
Keyword(s):  
Heat Flux ◽  
High Speed ◽  
Flow Boiling ◽  
Heating Surface ◽  
Nucleate Boiling ◽  
High Heat Flux ◽  
Subcooled Flow Boiling ◽  
Maximum Heat ◽  
High Speed Video ◽  
Subcooled Flow

It has been considered that the dry-out is easy to occur in boiling heat transfer for a small channel, a mini or microchannel because the channel was easily filled with coalescing vapor bubbles. In the present study, the experiments of subcooled flow boiling of water were performed under atmospheric condition for a horizontal rectangular channel of which size is 1mm in height and 1mm in width with a flat heating surface of 10mm in length and 1mm in width placed on the bottom of the channel. The heating surface is a top of copper heating block and heated by ceramics heaters. In the high heat flux region of nucleate boiling, about 70 ∼ 80 percent of heating surface was covered with a large coalescing bubble and the boiling reached critical heat flux (CHF) by a high speed video observation. In the beginning of transition boiling, coalescing bubbles were collapsed to many fine bubbles and microbubble emission boiling was observed at higher liquid subcooling than 30K. The maximum heat flux obtained was 8MW/m2 (800W/cm2) at liquid subcooling of higher than 40K and the liquid velocity of 0.5m/s. However, the surface temperature was extremely higher than that of centimeter scale channel. The high speed video photographs indicated that microbubble emission boiling occurs in the deep transition boiling region.

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.

scholarly journals Convective flow boiling heat transfer in an annular space: N-heptane/water case in a bubbly sub-cooled flow

2020 ◽  
Vol 3 (2) ◽  
pp. 33
Author(s):  
M. M. Sarafraz ◽  
H. Arya
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Flow Rate ◽  
Boiling Heat Transfer ◽  
Flow Boiling ◽  
Heating Surface ◽  
Nucleate Boiling ◽  
Subcooled Flow Boiling ◽  
Subcooled Flow ◽  
Flow Boiling Heat Transfer

The subcooled flow boiling heat transfer characteristics of n-heptane and water is conducted for an upward flow inside the vertical annulus with an inner gap of 30 mm, in different heat fluxes up to 132kW.m-2, subcooling max.:30C, flow rate: 1.5 to 3.5lit.min-1 under the atmospheric pressure. The measured data indicate that the subcooled flow boiling heat transfer coefficient significantly increases with increasing liquid flow rate and heat flux and slightly decreases with decreasing the subcooling level. Although results demonstrate that subcooling is the most effective operation parameter on onset of nucleate boiling such that with decreasing the subcooling level, the inception heat flux significantly decreases. Besides, recorded results from the visualization of flow show that the mean diameter of the bubbles departing from the heating surface decreases slightly with increasing the flow rate and slightly decreases with decreasing the subcooling level. Meanwhile, comparisons of the present heat transfer data for n-heptane and water in the same annulus and with some existing correlations are investigated. Results of comparisons reveal an excellent agreement between experimental data and those of calculated by Chen Type model and Gungor–Winterton predicting correlation.

Wall Heat Flux Partitioning During Subcooled Flow Boiling: Part 1—Model Development

2005 ◽  
Vol 127 (2) ◽  
pp. 131-140 ◽  
Author(s):  
Nilanjana Basu ◽  
Gopinath R. Warrier ◽  
Vijay K. Dhir
Keyword(s):  
Heat Flux ◽  
Flow Boiling ◽  
Model Development ◽  
Wall Heat Flux ◽  
Vapor Generation ◽  
Subcooled Flow Boiling ◽  
Wall Superheat ◽  
Subcooled Flow ◽  
Flux Partitioning ◽  
Transient Conduction

In this work a mechanistic model has been developed for the wall heat flux partitioning during subcooled flow boiling. The premise of the proposed model is that the entire energy from the wall is first transferred to the superheated liquid layer adjacent to the wall. A fraction of this energy is then utilized for vapor generation, while the rest of the energy is utilized for sensible heating of the bulk liquid. The contribution of each of the mechanisms for transfer of heat to the liquid—forced convection and transient conduction, as well as the energy transport associated with vapor generation has been quantified in terms of nucleation site densities, bubble departure and lift-off diameters, bubble release frequency, flow parameters like velocity, inlet subcooling, wall superheat, and fluid and surface properties including system pressure. To support the model development, subcooled flow boiling experiments were conducted at pressures of 1.03–3.2 bar for a wide range of mass fluxes 124-926kg/m2 s, heat fluxes 2.5-90W/cm2 and for contact angles varying from 30° to 90°. The model developed shows that the transient conduction component can become the dominant mode of heat transfer at very high superheats and, hence, velocity does not have much effect at high superheats. This is particularly true when boiling approaches fully developed nucleate boiling. Also, the model developed allows prediction of the wall superheat as a function of the applied heat flux or axial distance along the flow direction.

Heat Transfer Characteristics and Flow Pattern Visualization for Flow Boiling in a Vertical Narrow Microchannel

2019 ◽  
Vol 141 (3) ◽  
Author(s):  
Kan Zhou ◽  
Hua Zhu ◽  
Wei Li ◽  
Junye Li ◽  
Kuang Sheng ◽  
...  
Keyword(s):  
Heat Flux ◽  
High Speed ◽  
Heat Dissipation ◽  
Flow Boiling ◽  
Nucleate Boiling ◽  
Working Fluid ◽  
Inlet Temperature ◽  
Rectangular Microchannel ◽  
Subcooled Flow Boiling ◽  
Subcooled Flow

Recently, microchannel heat sinks have been emerged as a kind of high performance cooling scheme to meet the heat dissipation requirement of electronics packaging and integration. In this study, an experimental investigation of subcooled flow boiling in a high-aspect-ratio rectangular microchannel was conducted with de-ionized water as the working fluid. In the experimental operations, the mass flux was varied from 200 to 400 kg/m2s and the imposed heat flux from 3 to 20 W/cm2 while the fluid inlet temperature was regulated constantly at 90 °C. The boiling curves, onset of nucleate boiling (ONB), and flow patterns of subcooled flow boiling were investigated with the aid of instrumental measurements and a high-speed camera. The slope of the boiling curves increased sharply once the superheat needed to initiate the onset of nucleate boiling was attained, with lower superheat required of boiling incipience for lower mass fluxes. Meanwhile, the initiative superheat and heat flux of onset of nucleate boiling were compared with the existing correlations in the literature with good agreement. As for the flow visualization images, slug flow and reverse backflow were observed, where transient local dryout as well as rewetting occurred. A facile image processing tool was developed to profile the transient development and progression of the liquid–vapor interface and partial dryout patches in microchannels, which proved that the physical quantities of bubble dynamics for the elongation period during subcooled boiling could be well detected and calculated.

Subcooled Flow Boiling With Sintered Porous Coatings in Small Channel

2010 ◽  
Author(s):  
Yan Sun ◽  
Li Zhang ◽  
Hong Xu ◽  
Dongmei Ji
Keyword(s):  
Heat Transfer ◽  
Flow Boiling ◽  
Heating Surface ◽  
Nucleate Boiling ◽  
Working Fluid ◽  
Polished Surface ◽  
Subcooled Flow Boiling ◽  
Porous Coatings ◽  
Small Channel ◽  
Subcooled Flow

Heat transfer characteristics from sintered microporous coating surfaces are experimentally investigated for subcooled flow boiling in the horizontal, rectangular small channel with the low aspect ratio. The channel has a hydraulic diameter of 1.98 mm and a heated length of 150 mm. Experiments are conducted at atmospheric pressure with fully-degassed deionized water as the working fluid. The liquid mass flux ranges from 93.6 to 187.1 kg/m2s, and the inlet subcooling ranges from 30 to 70 K. The heating surface of the channel is covered with the copper microporous coatings to enhance the nucleate boiling heat transfer. Four coatings sintered with differently sized particles are tested to reveal influences of microporous parameters and identify the optimum structure. A smooth (highly polished) surface is also tested as reference. Although few studies have been performed to quantify the heat transfer enhancement contributed by combining internal porous coatings and small channels, this combination has promising applications in many areas such as air conditioning, chip cooling, refrigeration systems, and many others involving compact heat exchangers.

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