Experimental Study of the Heat Transfer Characteristic in Vertical Rectangular Capillary Microgrooves Heat Sink Under an Electric Field

2013 ◽  
Author(s):  
Xiazhen Fang ◽  
Xuegong Hu ◽  
Dong Yu ◽  
Cong Guo
Keyword(s):  
Heat Transfer ◽  
Threshold Voltage ◽  
Heat Sink ◽  
High Speed ◽  
Temperature Drop ◽  
Nucleate Boiling ◽  
Absolute Temperature ◽  
Heat Fluxes ◽  
Maximum Speed ◽  
The Absolute

In this study, the EHD (electrohydrodynamic) enhancement of heat transfer in open vertical rectangular capillary microgrooves heat sink was studied, and with the help of a high-speed digital camera with maximum speed of 100,000 frames per second, the nucleate boiling phenomena in microgrooves were also visually investigated. The tests results have shown: (1) the input heat flux has no influences on the threshold voltage basically, while the absolute temperature drop ΔT of the lower or higher input heat fluxes were smaller than that of the midrange ones. (2) the threshold voltage was getting small with the decreasing distance between the electrodes, meanwhile the absolute temperature drop ΔT was growing larger and larger. (3) the threshold voltages of NO. 1 microgrooves (the dimensions are listed in Table 1) were lower than that of NO. 2, and ΔT of NO. 1 microgrooves was larger than that of NO. 2. (4) the bubble growth process was becoming longer with the increasing applied voltage.

Nucleate Boiling From Micro-Machined Surfaces

2003 ◽  
Author(s):  
Adrian M. Holland ◽  
Colin P. Garner
Keyword(s):  
Heat Transfer ◽  
High Speed ◽  
Imaging System ◽  
Laser System ◽  
Ccd Camera ◽  
Nucleate Boiling ◽  
Heat Fluxes ◽  
Frame Rate ◽  
High Speed Imaging ◽  
Machined Surfaces

This paper discusses the production and use of laser-machined surfaces that provide enhanced nucleate boiling and heat transfer characteristics. The surface features of heated plates are known to have a significant effect on nucleate boiling heat transfer and bubble growth dynamics. Nucleate boiling starts from discrete bubbles that form on surface imperfections, such as cavities or scratches. The gas or vapours trapped in these imperfections serve as nuclei for the bubbles. After inception, the bubbles grow to a certain size and depart from the surface. In this work, special heated surfaces were manufactured by laser machining cavities into polished aluminium plates. This was accomplished with a Nd:YAG laser system, which allowed drilling of cavities of a known diameter. The size range of cavities was 20 to 250 micrometers. The resulting nucleate pool boiling was analysed using a novel high-speed imaging system comprising an infrared laser and high resolution CCD camera. This system was operated up to a 2 kHz frame rate and digital image processing allowed bubbles to be analysed statistically in terms of departure diameter, departure frequency, growth rate, shape and velocity. Data was obtained for heat fluxes up to 60 kW.m−2. Bubble measurements were obtained working with water at atmospheric pressure. The surface cavity diameters were selected to control the temperature at which vapour bubbles started to grow on the surface. The selected size and spacing of the cavities was also explored to provide optimal heat transfer.

scholarly journals The Simultaneous Analysis of Droplets’ Impacts and Heat Transfer during Water Spray Cooling Using a Transparent Heater

Water ◽  
2021 ◽  
Vol 13 (19) ◽  
pp. 2730
Author(s):  
Vladimir Serdyukov ◽  
Nikolay Miskiv ◽  
Anton Surtaev
Keyword(s):  
Heat Transfer ◽  
High Speed ◽  
Heating Surface ◽  
Nucleate Boiling ◽  
Spray Cooling ◽  
Capillary Waves ◽  
Heat Fluxes ◽  
Small Scale ◽  
Unsteady Temperature ◽  
The Impact

This paper demonstrates the advantages and prospects of transparent design of the heating surface for the simultaneous study of the hydrodynamic and thermal characteristics of spray cooling. It was shown that the high-speed recording from the reverse side of such heater allows to identify individual droplets before their impact on the forming liquid film, which makes it possible to measure their sizes with high spatial resolution. In addition, such format enables one to estimate the number of droplets falling onto the impact surface and to study the features of the interface evolution during the droplets’ impacts. In particular, the experiments showed various possible scenarios for this interaction, such as the formation of small-scale capillary waves during impacts of small droplets, as well as the appearance of “craters” and splashing crowns in the case of large ones. Moreover, the unsteady temperature field during spray cooling in regimes without boiling was investigated using high-speed infrared thermography. Based on the obtained data, the intensity of heat transfer during spray cooling for various liquid flow rates and heat fluxes was analyzed. It was shown that, for the studied regimes, the heat transfer coefficient weakly depends on the heat flux density and is primarily determined by the flow rate. In addition, the comparison of the processes of spray cooling and nucleate boiling was made, and an analogy was shown in the mechanisms that determine their intensity of heat transfer.

Boiling Heat Transfer Performance in a Spiraling Radial Inflow Microchannel Cold Plate

2015 ◽  
Author(s):  
Maritza Ruiz ◽  
Claire M. Kunkle ◽  
Jorge Padilla ◽  
Van P. Carey
Keyword(s):  
Heat Transfer ◽  
Heat Sink ◽  
Boiling Heat Transfer ◽  
Flow Boiling ◽  
Nucleate Boiling ◽  
Contact Angles ◽  
Heat Fluxes ◽  
Working Fluid ◽  
Maximum Heat ◽  
Flow Boiling Heat Transfer

This study presents an experimental exploration of flow boiling heat transfer in a spiraling radial inflow microchannel heat sink. The effect of surface wettability, fluid subcooling levels, and mass fluxes are considered in this type of heat sink for use in applications with high fluxes up to 300 W/cm2. The design of the heat sink provides an inward radial swirl flow between parallel, coaxial disks that form a microchannel of 300 μm and 1 cm radius with a single inlet and a single outlet. The channel is heated on one side through a copper conducting surface, while the opposite side is essentially adiabatic to simulate a heat sink scenario for electronics cooling. Flow boiling heat transfer and pressure drop data were obtained for this heat sink device using water at near atmospheric pressure as the working fluid for inlet subcooling levels from 20 to 81°C and mean mass flux levels ranging from 184 to 716 kg/m2s. To explore the effects of varying surface wetting, experiments were conducted with two different heated surfaces. One was a clean, machined copper surface with water equilibrium contact angles in the range of 14–40°, typical of common metal surfaces. The other was a surface coated with zinc oxide nanostructures that are superhydrophilic with equilibrium contact angles measured below 10°. During boiling, increased wettability resulted in quicker rewetting and smaller bubble departure diameter as indicated by reduced temperature oscillations during boiling and achieving higher maximum heat flux without dryout. Reducing inlet subcooling levels was also found to reduce the magnitude of oscillations in the oscillatory boiling regime. The highest heat transfer coefficients were seen in fully developed boiling with low subcooling levels as a result of heat transfer being dominated by nucleate boiling. The highest heat fluxes achieved were during partial subcooled flow boiling at 300 W/cm2 with an average surface temperature of 134 °C and requiring a pumping power to heat rate ratio of 0.01%. The hydrophilic surface retained wettability after a series of boiling tests. Recommendations for use of this heat sink design in high flux applications is also discussed.

An Experimental Investigation of Sub-Cooled Flow Boiling in Hypervapotron Cooling Configuration

2004 ◽  
Author(s):  
Peipei Chen ◽  
Barclay G. Jones ◽  
Ty A. Newell
Keyword(s):  
Heat Transfer ◽  
High Speed ◽  
Flow Boiling ◽  
Experimental Studies ◽  
Nucleate Boiling ◽  
High Heat ◽  
Heat Fluxes ◽  
High Heat Flux ◽  
Subcooled Boiling ◽  
Reduced Pressure

This work reports on experimental studies to visualize nucleate boiling on the enhanced heat transfer surface of the hypervapotron for with application in the International Thermonuclear Experiment Reactor [ITER]. This research uses the simulant fluid Freon (R134A) instead of prototypic water to model the system performance. This results in much lower thermophysical conditions to represent the prototypic phenomena. By using reduced pressure, temperatures, etc, based on the critical physical properties of both working fluids, Freon and water, the dramatic drop in the level of these quantities with Freon allows the use of modest test conditions. The experiment was conducted for both saturated and subcooled boiling with different heat fluxes (from 50 to 300 kW/m2). A comparison of the heat transfer performance of finned structures and flat surfaces were examined under particular fluid conditions. The uniqueness of this work is the visualization method that allows direct observation of the subcooled boiling process of the Hypervapotron surfaces. Working with a high speed (12,000 frames per second), high fidelity digital camera with variable magnifications (from 1×–25×), the sub-cooled boiling phenomena was observed in detail. A major conclusion of this work is the existence of two separate zones linked to different energy removal efficiency in hypervapotron. Under high heat flux condition, enhanced boiling heat transfer (about 20–30% higher than flat surface) was observed for hypervapotron effect, while saturated boiling happened in the cavity, and a large portion of the region was vapor filled. The process of vapor bubble rotation in the slot appeared to be helpful to enhance energy transfer, as evidenced by an improved wetting condition on the heating surfaces.

An Experimental Investigation of a High Flux Heat Pipe Heat Sink

2004 ◽  
Author(s):  
H. B. Ma ◽  
K. P. Lofgreen ◽  
G. P. Peterson
Keyword(s):  
Heat Transfer ◽  
Experimental Investigation ◽  
Heat Pipe ◽  
Heat Sink ◽  
Temperature Drop ◽  
High Heat ◽  
Heat Fluxes ◽  
High Heat Flux ◽  
Forced Air ◽  
Pipe Heat

An experimental investigation on a highly efficient heat pipe heat sink was investigated, in which the interline region was optimized using sintered particles. The effects of condenser size, sintered particles, and forced air flow on the heat transfer performance were investigated experimentally. The experimental results indicated that the thin film evaporation could significantly increase the evaporating heat transfer coefficient and remove heat fluxes up to 800 kW/m2. In addition, a theoretical model capable of predicting the temperature drop occurring in the device was developed. The predicted performance was in good agreement with the experimental data. The resulting model can be used to assist in the design of high heat flux, heat pipe heat sinks for applications to both ground based and spacecraft applications.

An Experimental Investigation of a High Flux Heat Pipe Heat Sink

2005 ◽  
Vol 128 (1) ◽  
pp. 18-22 ◽  
Author(s):  
H. B. Ma ◽  
K. P. Lofgreen ◽  
G. P. Peterson
Keyword(s):  
Heat Transfer ◽  
Experimental Investigation ◽  
Heat Pipe ◽  
Heat Sink ◽  
Temperature Drop ◽  
High Heat ◽  
Heat Fluxes ◽  
High Heat Flux ◽  
Forced Air ◽  
Pipe Heat

An experimental investigation of a highly efficient heat pipe heat sink was investigated, in which the interline region was optimized using sintered particles. The effects of condenser size, sintered particles, and forced air flow on the heat transfer performance were investigated experimentally. The experimental results indicated that the thin film evaporation could significantly increase the evaporating heat transfer coefficient and remove heat fluxes up to 800kW∕m2. In addition, a theoretical model capable of predicting the temperature drop occurring in this device was developed. The predicted performance was in good agreement with the experimental data and the resulting model can be used to assist in the design of high heat flux, heat pipe heat sinks.

scholarly journals COMPARATIVE ANALYSES OF THE THERMAL PERFORMANCE OF REFRIGERANTS R134A, R245fa, R407C AND R600a DURING FLOW BOILING IN A MICROCHANNELS HEAT SINK

2018 ◽  
Vol 17 (2) ◽  
pp. 57
Author(s):  
H. L. S. L. Leão ◽  
D. B. Marchetto ◽  
G. Ribatski
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Heat Sink ◽  
Flow Boiling ◽  
Saturation Temperature ◽  
Nucleate Boiling ◽  
Heat Fluxes ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients

A comparative study of the performance of of refrigerants R134a, R407C, R245fa and R600a during flow boiling was performed for a 123x494 µm2 heat sink composed of 50 parallel rectangular microchannels. Heat transfer experimental results for heat fluxes up to 310 kW/m2, mass velocities from 300 to 800 kg/(m2 s), liquid subcoolings of 5 and 10 °C and saturation temperature close to 30 ºC were obtained. Global heat transfer coefficients (footprint) up to 10 kW/(m2 °C) were found. The liquid superheating necessary for the onset of nucleate boiling (ONB) was also characterized, and the fluids R245fa and R407C presented the highest and lowest, respectively, superheating to trigger the boiling process. Moreover, for a fixed averaged vapor quality, the average effective heat transfer coefficient increases with increasing mass velocity and liquid subcooling. The refrigerants R600a and R407C presented the highest and the lowest heat transfer coefficients, respectively. Five heat transfer predictive methods from literature provided accurate predictions of the data for R134a, R245fa and R600a, capturing most of the data trends. No one method provided accurate predictions of the heat transfer coefficient data of R407C.

Experimental Investigation of Effect of Pore Diameter on Nucleate Boiling Heat Transfer in Reentrant Tunnel Structured Surfaces

2017 ◽  
Author(s):  
Ali Can Ispir ◽  
Tugce Karatas ◽  
Eren Dikec ◽  
Seyhan Onbasioglu
Keyword(s):  
Heat Transfer ◽  
Boiling Heat Transfer ◽  
High Speed ◽  
Pore Diameter ◽  
Experimental Studies ◽  
Nucleate Boiling ◽  
High Heat ◽  
Heat Fluxes ◽  
Vapor Bubbles ◽  
Structured Surfaces

This paper focuses on experimental studies of boiling heat transfer on surfaces with reentrant tunnels and pores. Three structured surface which have same tunnel width and height but different pore diameter, have been developed for enhancement boiling heat transfer. The experimental studies were carried out for the structured surfaces using distilled water at atmospheric pressure. The narrow reentrant tunnels are parallel to each other and have 3 mm width, 4 mm height. A number of pores whose diameter 1.5 and 2.0 mm were machined on lateral surfaces of tunnels. The surfaces were termed according to their geometric specifications as 3.0W-30-30, 1.5D-3.0W-30-30, 2.0D-3.0W-30-30. D and W capitals represent pore diameter and tunnel width, respectively. 30-30 part of name shows the dimension of square surface. The tunnels were used to increase area of heat transfer and active nucleation sites of vapor bubbles. In addition, sufficient amount of liquid must be supplied and vapor bubbles should be released fast from the boiling surface before they merge on the surfaces under conditions especially with high heat fluxes. Therefore, it was considered that pore structures would help for fluid transition hence the bubble frequency will increase. Pool boiling experiments were held to determine the performance of surfaces in different range of heat fluxes. Besides, high-speed visualization studies were conducted with high speed camera to observe behavior of nucleation of vapor bubbles. Amongst different geometry sizes the surface which has 1.5 mm of pore diameter (1.5D-3.0W-30-30) demonstrated the best nucleate boiling performance at high heat fluxes. However, the pored ones without pores has higher augmentation than pored structures at low heat fluxes. Thus, it is concluded that pored structures caused active nucleation sites to decrease under low heat fluxes.

An Experimental Study on Flow Boiling Characteristics of pHEMA Nano-Coated Surfaces in a Microchannel

2016 ◽  
Author(s):  
Abdolali Khalili Sadaghiani ◽  
Yağmur Şişman ◽  
Gözde Özaydın İnce ◽  
Ali Koşar
Keyword(s):  
Heat Transfer ◽  
High Speed ◽  
Flow Boiling ◽  
Nucleate Boiling ◽  
Heat Fluxes ◽  
Working Fluid ◽  
Transfer Coefficients ◽  
Rectangular Microchannel ◽  
Camera System ◽  
Coated Surfaces

In this study, the effect of pHEMA (Polyhydroxyethylmethacrylate) nanostructure coated surfaces on flow boiling was investigated in a rectangular microchannel. Experiments were conducted using deionized water as the working fluid to investigate flow boiling in a microchannel with dimensions of 14 cm length, 1.5 cm width, and 500 μm depth. The effect of pHEMA coatings (coated on 1.5 × 1.5 cm2 silicon plates) on heat transfer coefficients and flow patterns was assessed and supported using a high speed camera system. Although the contact angle decreases on nano-coated surfaces, due to surface porosity, boiling heat transfer coefficient increases. Furthermore, visualization results indicated that uncoated surfaces experienced a smaller nucleate boiling region. It was also observed that dryout occurs at higher heat fluxes for coated surfaces.

Flow Boiling Heat Transfer of R134a in a Microchannel Heat Sink

2012 ◽  
Author(s):  
Francisco J. do Nascimento ◽  
Hugo L. S. L. Leão ◽  
Gherhardt Ribatski
Keyword(s):  
Heat Transfer ◽  
Heat Sink ◽  
Mass Velocity ◽  
Flow Boiling ◽  
Nucleate Boiling ◽  
Heat Fluxes ◽  
Transfer Coefficients ◽  
Heat Spreader ◽  
Heat Transfer Coefficients ◽  
The Difference

In the present study, the thermal performance of a micro heat spreader based on flow boiling mechanism was evaluated. The heat spreader under study has a foot print area of 15 × 15 mm2 and is composed by 50 channels with width of 100 μm and depth of 500 μm. Experiments were performed for R134a, heat fluxes up to 310 kW/m2 (based on the foot print area), mass velocities from 400 to 1500 kg/m2s, saturation temperatures of approximately 25°C and liquid subcoolings of 5 and 15°C. Heat-sink averaged heat transfer coefficients based on the effective heat transfer area up to 9 kW/m2K were obtained. From the analyses of the experimental results, for a fixed heat-spreader averaged wall superheating, it was found that the dissipated heat flux increases with decreasing the mass velocity and liquid subcooling. Moreover, the trend with varying mass velocity of the difference between the heat spreader averaged superheating for the onset of nucleate boiling (ONB) and the respective value under boiling conditions is not clear, however it seems that its value increases with increasing the liquid subcooling. The wall superheating excess necessary for the onset of nucleate boiling becomes negligible for mass velocities higher than 1000 kg/m2s.

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