scholarly journals Spray Cooling Trajectory Angle Impact Upon Heat Flux Using a Straight Finned Enhanced Surface

2005 ◽  
Author(s):  
Eric A. Silk ◽  
Jungho Kim ◽  
Ken Kiger
Keyword(s):  
Heat Flux ◽  
Flat Surface ◽  
Spray Cooling ◽  
Technical Conference ◽  
Chamber Pressure ◽  
Working Fluid ◽  
Electronic Systems ◽  
Cross Sectional ◽  
Enhanced Surface ◽  
Trajectory Angle

Experiments were conducted to study the effects of spray trajectory angles on heat flux for flat and enhanced surface spray cooling. The surface enhancement consisted of straight fins machined on the top surface of a copper heater block. Spray cooling curves were obtained with the straight fin surface aligned both parallel (axial) and perpendicular (transverse) to the spray axis. Measurements were also obtained on a flat surface heater block for comparison purposes. Each copper block had a cross-sectional area of 2.0 cm2. A 2×2 nozzle array was used with PF-5060 as the working fluid. Thermal performance data was obtained under nominally degassed (chamber pressure of 41.4 kPa) conditions. Results show that the highest CHF in all cases was attained for a trajectory angle of 30° from the surface normal. Also, straight finned surfaces can enhance critical heat flux (CHF) as much as 75% (heat flux value of 140 W/cm2) relative to the vertical spray orientation for the analogous flat surface case.   This paper was also originally published as part of the Proceedings of the ASME 2005 Pacific Rim Technical Conference and Exhibition on Integration and Packaging of MEMS, NEMS, and Electronic Systems.

scholarly journals Investigation of Enhanced Surface Spray Cooling

2004 ◽  
Author(s):  
Eric A. Silk ◽  
Jungho Kim ◽  
Ken Kiger
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Flat Surface ◽  
Spray Cooling ◽  
Chamber Pressure ◽  
Working Fluid ◽  
Sectional Area ◽  
Cross Sectional ◽  
Pin Fins ◽  
Enhanced Surface

Experiments were conducted to study the effects of enhanced surfaces on heat transfer during spray cooling. The surface enhancements consisted of cubic pin fins, pyramids, and straight fins (uniform cross sectional straight fins) machined on the top surface of copper heater blocks. Each had a cross-sectional area of 2.0 cm2. Measurements were also obtained on a heater block with a flat surface for baseline comparison purposes. A 2×2 nozzle array was used with PF-5060 as the working fluid. Thermal performance data was obtained under nominally degassed (chamber pressure of 41.4 kPa) and gassy conditions (chamber with N2 gas at 101 kPa). The results show that the straight fins had the largest enhancement in heat flux. Critical heat flux (CHF) for this surface showed an increase of 55% in comparison to the flat surface for the nominally degassed condition. The cubic pin finned and pyramid surfaces provided slightly more than half the heat flux enhancement (30%–40% greater than the flat surface) of the straight fins. The gassy case showed that the straight fins again provided the largest enhancement (48%) in CHF relative to the flat surface. This was followed by the cubic pin fins, and pyramids which had increases of 31% and 18% respectively. No significant effect was observed in the surface temperature at which CHF occurs for either portion of the study.

scholarly journals Impact of Cubic Pin Finned Surface Structure Geometry Upon Spray Cooling Heat Transfer

2005 ◽  
Author(s):  
Eric A. Silk ◽  
Jungho Kim ◽  
Ken Kiger
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Flat Surface ◽  
Spray Cooling ◽  
Separation Distance ◽  
Chamber Pressure ◽  
Working Fluid ◽  
Fluid Temperature ◽  
Cross Sectional ◽  
Bulk Fluid

Experiments were conducted to study the effects of enhanced surface structures on heat flux using spray cooling. The surface enhancements consisted of cubic pin fins machined on the top surface of copper heater blocks. The structure height, pitch, and width were parametrically varied. Each copper block had a projected cross-sectional area of 2.0 cm2. Measurements were also obtained on a heater block with a flat surface for baseline comparison purposes. A 2×2 nozzle array was used with PF-5060 as the working fluid. Thermal performance data was obtained under nominally degassed (chamber pressure of 41.4 kPa) and gassy conditions (chamber with N2 gas at 101 kPa) with a bulk fluid temperature of 20.5°C. Results for both the degassed and gassy cases show that structure width and separation distance have a dominant effect upon the heat transfer for the size ranges used. Cubic pin fin height had little impact upon heat flux. The highest critical heat flux (CHF) attained for any of the surfaces was 121 W/cm2, giving an enhancement of 51% relative to the flat surface case under nominally degassed conditions. The highest CHF in the gassy case was 149 W/cm2, giving an enhancement of 38% relative to the flat surface case.

scholarly journals Heat transfer performance and influences of spray cooling under quenching

2020 ◽  
pp. 349-349
Author(s):  
Nianyong Zhou ◽  
Hao Feng ◽  
Muhao Xu ◽  
Enhai Liu
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Critical Heat Flux ◽  
Cooling System ◽  
Temperature Drop ◽  
Spray Cooling ◽  
Cooling Curve ◽  
Chamber Pressure ◽  
Working Fluid ◽  
Vapor Film

In this study, a closed-loop spray cooling system using R134a as the working fluid was established. The heat transfer characteristics and influencing mechanism of transient spray cooling were studied. The transient spray cooling curve under quenching was built accurately. The results show that the vapor film suppressed time tsup is the main period that the spray cooling must pass through. The flow rate and the sub-cooling of R134a have little effect on the cooling rate but the critical heat flux, which are mainly affected by chamber pressure. The transient Jacob number Ja+ decreases with the increases of chamber pressure. As Ja+ decreases, the growth of vapor film is inhibited, then the tsup reduces in consequence. The surface temperature drop point and critical heat flux increases with the rise of chamber pressure. The maximum critical heat flux is 70.08 W/cm2in this experiment.

Analysis and Mitigation of Sample Heating in Thermoreflectance Microscopy

2005 ◽  
Author(s):  
Andrew C. Miner ◽  
Uttam Ghoshal
Keyword(s):  
Heat Flux ◽  
Temperature Field ◽  
Temperature Rise ◽  
Technical Conference ◽  
Electronic Systems ◽  
Sample Heating ◽  
Large Measurement ◽  
Reflectance Microscopy ◽  
Analytical Expressions ◽  
Thermoreflectance Microscopy

The illumination of a sample when imaged by thermoreflectance thermal microscopy may cause significant heating of the surface. Nonlinearities in the performance of the system being imaged may lead to large measurement induced errors in the observed temperature field. Analytical expressions are presented to estimate the temperature rise and heat flux in a sample. Spatially filtered thermo-reflectance microscopy is introduced as a technique to significantly reduce the incident heat flux without loss of spatial resolution.   This paper was also originally published as part of the Proceedings of the ASME 2005 Pacific Rim Technical Conference and Exhibition on Integration and Packaging of MEMS, NEMS, and Electronic Systems.

Experimental Study of Inclination on Non-Boiling Regime Spray Cooling

2008 ◽  
Author(s):  
Yongxian Guo ◽  
Jianyuan Jia ◽  
Weidong Wang ◽  
Shaorong Zhou
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Heated Surface ◽  
Spray Cooling ◽  
Copper Surface ◽  
Experimental Results ◽  
Working Fluid ◽  
Distilled Water ◽  
Optimal Heat ◽  
Inclination Angles

Based on the maximum CHF (critical heat flux) criterion, an optimal heat transfer criterion, which is called H criterion, was proposed. Experimental apparatuses were conducted. Distilled water was used as the working fluid. Three different DANFOSS nozzles with cone angles being 54°, 50° and 54° respectively were used. A 30×30mm2 square copper surface was used as the heated surface. Experimental results indicated that the volumetric fluxes were proportioned to P0.5, where P is the pressure drop across the nozzles. The optimal distance between the nozzles and the heated surface were derived. The results indicated that the optimal heat transfer appeared while the outside of the impellent thin spray film inscribed in the square heated surface. Based on the H criterion aforementioned, two DANFOSS nozzles of the three, with cone angles being 54° and 50° respectively, were used to study the temperature distribution of the heated surface while there were spray inclination angles during spray cooling experiments. Distilled water was also used impacting on the 30×30mm2 square copper surface aforementioned and a circular heated copper surface with diameters being 30mm respectively. The heat flux of the surface was kept in constant (about 26–35W/cm2). The inclination angles were 0°, 10°, 20°, 30°, 40° and 50° respectively. Three thermocouples imbedded in the heated surface were used to predict the grads of the temperature of the surface. Experimental results indicated that the temperature and the grads of the temperature of the surface increases first and then decreases with the increase of the inclination angle.

Effect of Microgrooved Surface and Surface Orientation on Spray Cooling Heat Transfer

2009 ◽  
Author(s):  
Dong-Fang Chen ◽  
Da-Wei Tang ◽  
Xue-Gong Hu
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Thermal Performance ◽  
High Speed ◽  
Heat Transfer Performance ◽  
Flat Surface ◽  
Spray Cooling ◽  
Surface Orientation ◽  
Microgrooved Surface ◽  
Water Spray Cooling

Experiments were performed to investigate the flow structure and boiling heat transfer characteristics of water spray cooling on flat and microgrooved surfaces using a high-speed camera and a microscope. The heaters were made of cooper, with surface size of 2.0cm×7.4cm. Three orientations of the heater surfaces were selected: horizontal upward-facing, vertical, and horizontal downward-facing. A full-cone spray nozzle was placed normal to these heated surfaces. The heat transfer was directly measured using thermocouples within the heater. The experimental results show the bubble’s growth, coalescence along/between microgrooves, and break-up as wall heat flux reaches some higher values. It was found that the heat transfer for microgrooved surface is generally higher than that of flat surface at a given flow rate with the same surface orientation. The thermal performance of vertical microgrooved surface was highest at low temperatures; the thermal performance of the horizontal upward-facing was highest at higher wall temperature. The heat transfer performance for the horizontal downward-facing microgrooved surface had the highest critical heat flux (CHF).

Two-Phase Spray Cooling With Water/2-Propanol Binary Mixture: Investigation of Mass Diffusion Resistance

2016 ◽  
Author(s):  
Sai Sujith Obuladinne ◽  
Huseyin Bostanci
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Heat Transfer Performance ◽  
Pure Water ◽  
Spray Cooling ◽  
High Heat ◽  
Working Fluid ◽  
High Heat Flux ◽  
Two Phase ◽  
High Heat Transfer

Two-phase spray cooling has been an emerging thermal management technique offering high heat transfer coefficients (HTCs) and critical heat flux (CHF) levels, near-uniform surface temperatures, and efficient coolant usage that enables to design of compact and lightweight systems. Due to these capabilities, spray cooling is a promising approach for high heat flux applications in computing, power electronics, and optics. The two-phase spray cooling inherently depends on saturation temperature-pressure relationships of the working fluid to take advantage of high heat transfer rates associated with liquid-vapor phase change. When a certain application requires strict temperature and/or pressure conditions, thermophysical properties of the working fluid play a critical role in attaining proper efficiency, reliability, or packaging structure. However, some of the commonly used working fluids today, including refrigerants and dielectric liquids, have relatively poor properties and heat transfer performance. In such cases, utilizing binary mixtures to tune working fluid properties becomes an alternative approach. This study aimed to conduct an initial investigation on the spray cooling characteristics of practically important binary mixtures and demonstrate their capability for challenging high heat flux applications. The working fluid, water/2-propanol binary mixture at various concentration levels, specifically at x1 (liquid mass fraction of 2-proponal in water) of 0.0 (pure water), 0.25, 0.50, 0.879 (azeotropic mixture) and 1.0, represented both non-azeotropic and azeotropic cases. Tests were performed on a closed loop spray cooling system using a pressure atomized spray nozzle with a constant liquid flow rate at corresponding 20°C subcooling conditions and 1 Atm pressure. A copper test section measuring 10 mm × 10 mm × 2 mm with a plain, smooth surface simulated high heat flux source. Experimental procedure involved controlling the heat flux in increasing steps, and recording the steady-state temperatures to obtain cooling curves in the form of surface superheat vs heat flux. The obtained results showed that pure water (x1 = 0.0) and 2-propanol (x1 = 1.0) provide the highest and lowest heat transfer performance, respectively. At a given heat flux level, the HTC values indicated strong dependence on x1, where the HTCs depress proportional to the concentration difference between the liquid and vapor phases. The CHF values sharply decreased at x1≥ 0.25.

Role of Random Roughness on Thermal Performance of Micro-Fins

2005 ◽  
Author(s):  
M. Bahrami ◽  
M. M. Yovanovich ◽  
J. R. Culham
Keyword(s):  
Heat Transfer ◽  
Thermal Performance ◽  
Technical Conference ◽  
Electronic Systems ◽  
Cross Sectional ◽  
Random Roughness ◽  
Surface Areas ◽  
Isotropic Distribution ◽  
Developed Surface

Heat transfer in rough circular cylinder microfins is studied and a novel analytical model is developed. Surface roughness is assumed to posses a Gaussian isotropic distribution. It is shown that, as a result of roughness, both cross-sectional and surface areas are increased. As a result, an enhancement is observed in the heat transfer rate and thus the thermal performance of microfins. The present model can be implemented to analyze other geometries such as rectangular and tapered microfins.   This paper was also originally published as part of the Proceedings of the ASME 2005 Pacific Rim Technical Conference and Exhibition on Integration and Packaging of MEMS, NEMS, and Electronic Systems.

Critical Heat Flux of Multi-Nozzle Spray Cooling

2004 ◽  
Vol 126 (3) ◽  
pp. 482-485 ◽  
Author(s):  
Lanchao Lin ◽  
Rengasamy Ponnappan
Keyword(s):  
Heat Flux ◽  
Critical Heat Flux ◽  
Flat Surface ◽  
Swirling Flow ◽  
Spray Cooling ◽  
High Heat ◽  
High Heat Flux ◽  
Pressure Drops ◽  
Nozzle Pressure ◽  
Nozzle Plate

Tiny nozzles are developed that are capable of creating the swirling flow necessary to generate a full cone spray. Eight miniature nozzles are embedded in a multi-nozzle plate used to generate a spray array for the cooling of high heat flux laser diodes. The target spray cooling area is a 1×2 cm2 flat surface of a copper heater plate. A closed loop spray cooling test setup is established. FC-87, FC-72 and methanol are used as the working fluids. Critical heat flux (CHF) is experimentally investigated at various spray saturation temperatures and nozzle pressure drops (from 0.690 bar to 3.10 bar). It is demonstrated that the spray cooler can reach the CHF levels up to 91.5 W/cm2 with FC-87 and 490 W/cm2 with methanol.

Spray Cooling Performance of Single and Multi-Jet Spray Nozzles Using Subcooled FC-72

2007 ◽  
Author(s):  
Gilberto Moreno ◽  
Seung M. You ◽  
Erlendur Steinthorsson
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Critical Heat Flux ◽  
Flow Rate ◽  
Spray Cooling ◽  
Working Fluid ◽  
Spray Nozzle ◽  
Cooling Performance ◽  
Transfer Rates ◽  
Jet Array

In this study experiments were performed to evaluate the spray cooling performance of three different spray nozzles using gassy-subcooled (∼Tsub = 31°C) FC-72 as the working fluid. The three different nozzles tested can be characterized as a single hollow cone spray nozzle (Nozzle A), 2×2 jet array spray nozzle (Nozzle B) and a 4×4 jet array spray nozzle (Nozzle C). For all tests, a 10×10 mm polished (600 grit) copper surface was utilized as the heater and tests were carried out at near atmospheric pressure conditions. All three nozzles were tested at various flow rates and nozzle-to-heater distances and the results were compared. Results show that changing the nozzle-to-heater distance affects heat transfer rates more than critical heat flux (CHF). The spray boiling curves for all three nozzles were similar with Nozzle C, for some cases, demonstrating the highest heat transfer rates. The disparity in CHF values between the various nozzles was more apparent. Compared at an equivalent flow rate, Nozzle C consistently produced CHF values which were higher than those of the other nozzles. Some common trends observed for all nozzles are, increasing flow rate increases heat transfer rates and critical heat flux (CHF) but decreases nozzle efficiency.

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