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 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 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 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.

Pseudo-turbulent heat flux and average gas–phase conduction during gas–solid heat transfer: flow past random fixed particle assemblies

2016 ◽  
Vol 798 ◽  
pp. 299-349 ◽  
Author(s):  
Bo Sun ◽  
Sudheer Tenneti ◽  
Shankar Subramaniam ◽  
Donald L. Koch
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Gas Phase ◽  
Volume Fraction ◽  
Turbulent Heat Flux ◽  
Turbulent Heat ◽  
Fluid Temperature ◽  
Bulk Fluid ◽  
The Mean ◽  
Temperature Equation

Fluctuations in the gas-phase velocity can contribute significantly to the total gas-phase kinetic energy even in laminar gas–solid flows as shown by Mehrabadi et al. (J. Fluid Mech., vol. 770, 2015, pp. 210–246), and these pseudo-turbulent fluctuations can also enhance heat transfer in gas–solid flow. In this work, the pseudo-turbulent heat flux arising from temperature–velocity covariance, and average fluid-phase conduction during convective heat transfer in a gas–solid flow are quantified and modelled over a wide range of mean slip Reynolds number and solid volume fraction using particle-resolved direct numerical simulations (PR-DNS) of steady flow through a random assembly of fixed isothermal monodisperse spherical particles. A thermal self-similarity condition on the local excess temperature developed by Tenneti et al. (Intl J. Heat Mass Transfer, vol. 58, 2013, pp. 471–479) is used to guarantee thermally fully developed flow. The average gas–solid heat transfer rate for this flow has been reported elsewhere by Sun et al. (Intl J. Heat Mass Transfer, vol. 86, 2015, pp. 898–913). Although the mean velocity field is homogeneous, the mean temperature field in this thermally fully developed flow is inhomogeneous in the streamwise coordinate. An exponential decay model for the average bulk fluid temperature is proposed. The pseudo-turbulent heat flux that is usually neglected in two-fluid models of the average fluid temperature equation is computed using PR-DNS data. It is found that the transport term in the average fluid temperature equation corresponding to the pseudo-turbulent heat flux is significant when compared to the average gas–solid heat transfer over a significant range of solid volume fraction and mean slip Reynolds number that was simulated. For this flow set-up a gradient-diffusion model for the pseudo-turbulent heat flux is found to perform well. The Péclet number dependence of the effective thermal diffusivity implied by this model is explained using a scaling analysis. Axial conduction in the fluid phase, which is often neglected in existing one-dimensional models, is also quantified. As expected, it is found to be important only for low Péclet number flows. Using the exponential decay model for the average bulk fluid temperature, a model for average axial conduction is developed that verifies standard assumptions in the literature. These models can be used in two-fluid simulations of heat transfer in fixed beds. A budget analysis of the mean fluid temperature equation provides insight into the variation of the relative magnitude of the various terms over the parameter space.

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.

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.

scholarly journals Validation of Heat Transfer between Theoretical and Experimental from the Internal Surface of Vertical Tubes with Internal Rings Heated by Electrical Heating Coils

2019 ◽  
Vol 1 (1) ◽  
Author(s):  
Ramesh Chandra Nayak ◽  
Manmatha K. Roul ◽  
Ipsita Jena ◽  
Ipsita Dash ◽  
Ashish Ku. Patra
Keyword(s):  
Heat Transfer ◽  
Experimental Data ◽  
Heat Flux ◽  
Internal Surface ◽  
Constant Heat Flux ◽  
Separation Distance ◽  
Electrical Heating ◽  
Experimental Result ◽  
Fluid Temperature ◽  
Theoretical Results

The comparison between experimental and theoretical heat transfer inside heated vertical channels that dissipate heat from the internal surface with and without internal rings  is studied. The experimental setup consists of a circular pipe which is heated electrically by providing constant heat flux on the wall. The theoretical and experimental analysis is conducted in several pipes of same diameter but different lengths. The length of the pipe varies from 450 mm to 850 mm. The length to diameter ratios are taken as L/D = 10, 12.22, 15.56, and 18.89. The value of imposed heat flux varies from 250 to 3340 W/m2. The internal ring thickness varies from 4 mm to 8 mm. separation distance between the internal rings varies from 75mm to 300 mm. The theoretical results are compared with experimental data to ascertain numerical accuracy of the method. The effects of L/D ratio, thickness of internal rings and separation distance on the heat transfer performance are studied. The experimental result is compared with theoretical, theoretical results are found by using ANSYS. In this study theoretical result for wall temperature along the height of tube, fluid temperature at exit of tube are compared with experimental data.

Simulation on the Flow and Heat Transfer Characteristics of Confined Bubbles in Micro-Channels

2012 ◽  
Author(s):  
Qingming Liu ◽  
Björn Palm ◽  
Henryk Anglart
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Mass Flux ◽  
Phase Interface ◽  
Working Fluid ◽  
Initial Shape ◽  
Thin Film Evaporation ◽  
Flow And Heat Transfer ◽  
Vof Model ◽  
Micro Channels

3D simulations on confined bubbles in micro-channels with diameter of 1.24 mm were conducted. The working fluid is R134a with a mass flux range from 125kg/m2s to 375kg/m2s. The VOF model is chosen to capture the 2 phase interface while the geo-construction method was used to re-construct the 2-phase interface. A heated boundary wall with heat flux varying from 15kW/m2 to 102kW/m2 is supplied. The wall temperature was calculated. The effects of mass flux and heat flux are studied. The shape of the bubble was predicted by the simulation successfully and the results show that they are independent of the initial shape. Both thin film evaporation and micro convection enhance the heat transfer. However, the micro convection which is caused by bubble motion has greater contribution to the total heat transfer at the stage of bubble growth studied.

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