An Experimental Study on the Transient Spray-cooling of Hot Surface at Different Angles of Inclination PDF Download

Author: Abdul-Rahman Bleik
Publisher:
ISBN:
Category :
Languages : en
Pages : 154

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Author: Raymond Emil Gaugler
Publisher:
ISBN:
Category :
Languages : en
Pages : 83

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Author: H. Dawson
Publisher:
ISBN:
Category : Cooling
Languages : en
Pages : 208

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Techniques of infrared thermography were used to conduct an experimental study of the evaporative cooling of a hot, low thermal conductivity, non-metallic surface heated by radiation and subject to a random array of impinging water droplets. A droplet generating and distributing apparatus and a data acquisition system employing digital image analysis devices were also developed and implemented. Real time infrared images of the heated surface were recorded and digitized using computer resident frame grabbing hardware and analyzed on a pixel by pixel basis, giving a high degree of thermal and spatial resolution. From these analyses, the instantaneous surface temperature distribution and transient surface temperature profile were obtained for a range of initial temperatures and impinging mass fluxes. The surface temperature was found to decay exponentially with time to a steady state value for the fluxes used. Three dimensional plots of the temperature distribution on the surface also showed the significant lowering of the average surface temperature, and provided a qualitative description of the cooling phenomena at various stages during the transient. Results obtained will be used in the future validation of a computer model of the phenomena.

Author:
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ISBN:
Category :
Languages : en
Pages : 14

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An analytical and experimental study was conducted for the application of spray cooling in a micro gravity and high-g environment. Experiments were carried out aboard the NASA KC-135 reduced gravity aircraft, which provided both the microgravity and high-g environments. In reduced gravity, surface tension flow was observed around the spray nozzle, due to unconstrained liquid in the test chamber and flow reversal at the heat source. A transient analytical model was developed to predict the temperature and the spray heat transfer coefficient within the heated region. Comparison of the experimental transient temperature variation with analytical results showed good agreement for low heat input values. The transient analysis also verified that thermal equilibrium within the heated region could be reached during the 20-25s reduced gravity portion of the flight profile.

Author: Alex M. Tulchinsky
Publisher:
ISBN:
Category : Electronic apparatus and appliances
Languages : en
Pages : 306

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Spray impingement cooling has been shown to be a leading candidate for future high heat flux cooling applications. In general, spray cooling curves consist of three heat flux regimes; single-phase, two-phase and critical heat flux (CHF). CHF is considered the design limit for almost all two-phase cooling applications, as a rapid increase in temperature and decrease in heat flux occurs beyond this point. Recent studies have shown that the addition of micro-structures on the impingement surface can enhance heat transfer relative to a smooth surface. In the present study, spray cooling curves are obtained for two micro-structured surfaces and are compared to smooth surface results. Micro-structured surfaces consisted of bio-inspired fractal-like geometries, denoted as grooves and fins, extending in a radial direction from the center to the periphery of a 37.8 mm circular disc. Depending on the location on the surface, dimensions of groove widths and heights varied from 100 to 500 um, and 30 to 60 um, respectively. Fin width and height dimension remained constant throughout the surface at 127 and 60 um, respectively. Heat flux and wall temperature at the impingement surface were calculated from temperature data measured at multiple locations below the impingement surface. Results are presented as heat flux, q" , versus the wall-to-spray temperature difference, deltaT[subscript w], at each of 5 volume flux, Q", conditions ranging from 0.54 to 2.04 x 10−3 m3/m2s. Convection coefficients, h[subscript cv], and spray efficiencies, n, are also presented for each case as a function of q" and deltaT[subscript w] , respectively. Results of the study indicate that at low and high volume fluxes, an improvement in heat transfer occurs in the single-phase regime for the fin geometry. Enhancement in the single-phase regime did not occur at the intermediate volume flux condition of 1.37 x 10−3 m3/m2s. At all volume flux states tested, significant enhancements, as high as 50% in some cases, were observed in the two-phase regime for the fin structure, whereas the groove structure performed identically to the flat surface in the single-phase regime and exhibited a large degradation in the two-phase and critical heat flux regimes (~50%). Critical heat flux for the fin surface compared to the flat surface was slightly lower at low volume flux conditions, equivalent at the intermediate volume flux, and slightly greater at high volume flux conditions. Further investigations into the underlying mechanisms responsible for these results are needed.

Author: Tony Tung-Ming Man
Publisher:
ISBN:
Category : Integrated circuits
Languages : en
Pages : 194

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Author: M. Pohanka
Publisher:
ISBN:
Category : Coolants
Languages : en
Pages : 13

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An experimental technique for the measurements of heat transfer distribution at spray cooled surfaces is described. The measurements were done at moving surfaces up to a velocity of 12 m/s. The samples of different cross sections (flat, profile, rail, etc.) can move linearly. Different approaches are used for the measurements of heat transfer coefficient (HTC) distribution or heat flux distribution at rotating cylindrical body. An inverse task for the computation of surface temperature, HTC, and heat flux distribution obtained from the measurements conducted for internal transient temperature is described. The paper describes necessary demands on experiment configuration and temperature measurements when studying highly transient processes (fast moving objects under spraying nozzles or high circumferential velocities of rotating surface). The results of HTC distribution for spray cooling are shown and are compared to water impingement density. Influence of water impingement density, water pressure, spray configuration, and surface velocity is studied. Examples for water nozzles and for mist nozzles (water-air) are given. Emulsions and oils are beneficial for some industrial applications of spray cooling. The cooling experiments performed with these liquids provide information about decrease of cooling intensity even for a low concentration of the oils in water. The results comparing the cooling properties of these liquids and their comparison to water are presented.

Author: Hamed Muhammed A. Al-Ahamdi
Publisher:
ISBN:
Category :
Languages : en
Pages : 0

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Author: Andrea C. Ashwood
Publisher:
ISBN:
Category :
Languages : en
Pages : 144

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Author: James B. Fillius
Publisher:
ISBN: 9781423521440
Category : Cooling
Languages : en
Pages : 79

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Book Description
Spray cooling is a promising means of dissipating large steady state heat fluxes in high density power and electronic systems, such as thermophotovoltaic systems. The present study reports on the effectiveness of spray cooling in removing heat fluxes as high as 220 W/cm2. An experiment was designed to determine how the parameters of spray volumetric flow rate and droplet size influence the heat removal capacity of such a system. A series of commercially available nozzles were used to generate full cone water spray patterns encompassing a range of volumetric flow rates (3.79 to 42.32 L/h) and droplet Sauter mean diameters (17.4 to 35.5 micrometers). The non-flooded regime of spray cooling was studied, in which liquid spreading on the heater surface following droplet impact is the key phenomenon that determines the heat transfer rate. The experimental data established a direct proportionality of the heat flux with spray flow rate, and an inverse dependence on the droplet diameter. A correlation of the data was developed to predict heat flux as a function of the studied parameters over the range of values tested in this experiment.