scholarly journals Nanofluids Characterization for Spray Cooling Applications

Symmetry ◽  
2021 ◽  
Vol 13 (5) ◽  
pp. 788
Author(s):  
Miguel Sanches ◽  
Guido Marseglia ◽  
Ana P. C. Ribeiro ◽  
António L. N. Moreira ◽  
Ana S. Moita
Keyword(s):  
Heat Transfer ◽  
Thermophysical Properties ◽  
High Speed ◽  
Lower Surface ◽  
Spray Cooling ◽  
Heat Fluxes ◽  
Structure Evolution ◽  
Transfer Coefficients ◽  
Systematic Analysis ◽  
Nanoparticles Concentration

In this paper the mathematical and physical correlation between fundamental thermophysical properties of materials, with their structure, for nanofluid thermal performance in spray cooling applications is presented. The present work aims at clarifying the nanofluid characteristics, especially the geometry of their nanoparticles, leading to heat transfer enhancement at low particle concentration. The base fluid considered is distilled water with the surfactant cetyltrimethylammonium bromide (CTAB). Alumina and silver are used as nanoparticles. A systematic analysis addresses the effect of nanoparticles concentration and shape in spray hydrodynamics and heat transfer. Spray dynamics is mainly characterized using phase Doppler interferometry. Then, an extensive processing procedure is performed to thermal and spacetime symmetry images obtained with a high-speed thermographic camera to analyze the spray impact on a heated, smooth stainless-steel foil. There is some effect on the nanoparticles’ shape, which is nevertheless minor when compared to the effect of the nanoparticles concentration and to the change in the fluid properties caused by the addition of the surfactant. Hence, increasing the nanoparticles concentration results in lower surface temperatures and high removed heat fluxes. In terms of the effect of the resulting thermophysical properties, increasing the nanofluids concentration resulted in the increase in the thermal conductivity and dynamic viscosity of the nanofluids, which in turn led to a decrease in the heat transfer coefficients. On the other hand, nanofluids specific heat capacity is increased which correlates positively with the spray cooling capacity. The analysis of the parameters that determine the structure, evolution, physics and both spatial and temporal symmetry of the spray is interesting and fundamental to shed light to the fact that only knowledge based in experimental data can guarantee a correct setting of the model numbers.

Experiments and Modeling of a Liquid Droplet Transported by a Gas Stream Impinging on a Heated Surface: Evaporative Regime

2009 ◽  
Author(s):  
Ryan P. Anderson ◽  
Alfonso Ortega
Keyword(s):  
Heat Transfer ◽  
High Speed ◽  
Single Phase ◽  
Heat Dissipation ◽  
Liquid Droplet ◽  
Heated Surface ◽  
Thin Liquid Film ◽  
Spray Cooling ◽  
High Speed Photography ◽  
Transfer Coefficients

Understanding the transport mechanisms involved in a single droplet impinging on a heated surface is imperative to the complete understanding of droplet and spray cooling. Evidence in the literature suggests that gas assisted sprays and mist flows are more efficient than sprays consisting only of liquid droplets. There has been few if any fundamental studies on gas-assisted droplets or spray cooling, in which a carrier gas or vapor stream propels the droplet to the target surface. The current work extends previous studies of a droplet impinging on a heated surface conducted by the same group from the single phase regime into the evaporative regime. For both regimes, understanding the transport physics due to the heat transfer from the heated surface to the droplet and then by convection and evaporation to the airflow is of fundamental importance. High-speed photography was used to capture the spreading process and yielded results that correlated well with previously published isothermal and single-phase results. The heat transfer was measured with a fitting approach by which the instantaneous temperature profile was matched to an analytic solution to determine the instantaneous value of the centerline heat transfer coefficient. A very large increase in the heat dissipation was observed when compared to previously published single-phase results. Heat transfer was optimized at Reynolds numbers that produced an optimally thin liquid film and high heat and mass transfer coefficients on the surface of the film.

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.

Film Thickness and Heat Transfer Measurements in a Spray Cooling System With R134a

2011 ◽  
Vol 133 (1) ◽  
Author(s):  
Eduardo Martínez-Galván ◽  
Juan Carlos Ramos ◽  
Raúl Antón ◽  
Rahmatollah Khodabandeh
Keyword(s):  
Heat Transfer ◽  
Nusselt Number ◽  
Film Thickness ◽  
High Speed ◽  
Average Nusselt Number ◽  
Cooling System ◽  
Spray Cooling ◽  
Heat Fluxes ◽  
Long Distance ◽  
Thickness Measurements

Experimental measurements in a spray cooling test rig have been carried out for several heat fluxes in the heater and different spray volumetric fluxes with the dielectric refrigerant R134a. Results of the heat transfer and the sprayed refrigerant film thickness measurements are presented. The film thickness measurements have been made with a high speed camera equipped with a long distance microscope. It has been found that there is a relation between the variation in the average Nusselt number and the film thickness along the spray cooling boiling curve. The heat transfer regimes along that curve are related not only with a variation in the average Nusselt number but also with changes in the film thickness. The qualitative analysis of those variations has served to understand better the heat transfer mechanisms occurring during the spray cooling.

An Experimental Study on the Effects of Nozzle and Surface Geometry in FC-72 Jet Cooling

2012 ◽  
Vol 28 (1) ◽  
pp. 53-61
Author(s):  
L.-H. Chien ◽  
T.-L. Wu
Keyword(s):  
Heat Transfer ◽  
Flow Rate ◽  
Smooth Surface ◽  
Volume Flow Rate ◽  
Nucleate Boiling ◽  
Spray Cooling ◽  
Heat Fluxes ◽  
Transfer Coefficients ◽  
Surface Geometry ◽  
Heat Transfer Coefficients

ABSTRACTIn this study, a spray cooling device for electronic components was investigated. Dielectric fuid (FC-72) was sprayed at 50°C through five nozzles (4.243mm spacing). The nozzles are of diameters 0.17, 0.23 or 0.41mm. Volume flow rate varied from 24.5 to 99.1ml/min. Two grooved surfaces and a smooth surface were tested, and the heated area was 12 × 12mm2. The larger nozzles yielded greater heat transfer coefficients at high heat fluxes (300 ∼ 600kW/m2). However, smaller nozzles result in greater dry-out heat fluxes and greater heat transfer coefficients at heat flux < 300kW/m2. The C4 surface, having parallel grooves of 0.4mm depth, improved the spray cooling performance by up to 80% as compared with the smooth suface. Its thermal resistance is 0.11 ∼ 0.12K/W at 99.1ml/min flow rate, in the range of 85 ∼ 130W heat input. A new correlation of spray cooling, accounting for the contributions of nucleate boiling and spray convection, is proposed. For data of FC-72 in the range of Re = 856 ∼ 6188, Bo = 0.19 ∼ 5.70, We = 25.2 ∼ 3541.3, the predicted h-values agree with experimental data of the smooth surface within ±25%.

scholarly journals Thermofluid Characterization of Nanofluid Spray Cooling Combining Phase Doppler Interferometry with High-Speed Visualization and Time-Resolved IR Thermography

Energies ◽  
2020 ◽  
Vol 13 (22) ◽  
pp. 5864 ◽  
Author(s):  
Miguel Figueiredo ◽  
Guido Marseglia ◽  
Ana S. Moita ◽  
Miguel R. O. Panão ◽  
Ana P. C. Ribeiro ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Surface Tension ◽  
High Speed ◽  
Lower Surface ◽  
Spray Cooling ◽  
Time Resolved ◽  
Maximum Heat ◽  
Phase Doppler Interferometry ◽  
Wetted Area

Spray impingement on smooth and heated surfaces is a highly complex thermofluid phenomenon present in several engineering applications. The combination of phase Doppler interferometry, high-speed visualization, and time-resolved infrared thermography allows characterizing the heat transfer and fluid dynamics involved. Particular emphasis is given to the use of nanofluids in sprays due to their potential to enhance the heat transfer mechanisms. The results for low nanoparticle concentrations (up to 1 wt.%) show that the surfactant added to water, required to stabilize the nanofluids and minimize particle clustering, affects the spray’s main characteristics. Namely, the surfactant decreases the liquid surface tension leading to a larger wetted area and wettability, promoting heat transfer between the surface and the liquid film. However, since lower surface tension also tends to enhance splash near the edges of the wetted area, the gold nanospheres act to lessen such disturbances due to an increase of the solutions’ viscosity, thus increasing the heat flux removed from the spray slightly. The experimental results obtained from this work demonstrate that the maximum heat convection coefficients evaluated for the nanofluids can be 9.8% to 21.9% higher than those obtained with the base fluid and 11.5% to 38.8% higher when compared with those obtained with DI water.

Heat Transfer Characteristics of a Train of Droplets Impinging Over a Hot Surface: From Film Evaporation to Leidenfrost Point

2021 ◽  
Author(s):  
Ganesh Guggilla ◽  
Ramesh Narayanaswamy ◽  
Peter Stephan ◽  
Arvind Pattamatta
Keyword(s):  
Heat Transfer ◽  
High Speed ◽  
Heated Surface ◽  
Contact Angle Hysteresis ◽  
Electronics Cooling ◽  
Spray Cooling ◽  
Heat Fluxes ◽  
High Speed Photography ◽  
Heat Transfer Characteristics ◽  
Transfer Characteristics

Abstract High-performance computing systems are needed in advanced computing services such as machine learning and artificial intelligence. Consequently, the increase in electron chip density results in high heat fluxes and requires good thermal management to maintain the servers. Spray cooling using liquid offers higher heat transfer rates and is efficient when implemented in electronics cooling. Detailed studies of fundamental mechanisms involved in spray cooling, such as single droplet and multiple droplet interactions, are required to enhance the process's knowledge. The present work focuses on studying a train of two FC-72 droplets impinging over a heated surface. Experimental investigation using high-speed photography and infrared thermography is conducted. Simultaneously, numerical simulations using opensource CFD package, OpenFOAM are carried out, emphasizing the significance of contact angle hysteresis. The surface temperature is chosen as a parameter, and different boiling regimes along with Dynamic Leidenfrost point (DLP) for the present impact conditions are identified. Spreading hydrodynamics and heat transfer characteristics of these consecutively impinging droplets till the Leidenfrost temperature, are studied and compared.

Correlation of Heat Transfer Data to Film Thickness Data of the Thin Film Found in Spray Cooling

2004 ◽  
Author(s):  
Adam G. Pautsch ◽  
Timothy A. Shedd
Keyword(s):  
Thin Film ◽  
Heat Transfer ◽  
Film Thickness ◽  
Heated Surface ◽  
Spray Cooling ◽  
Heat Fluxes ◽  
Experimental Measurements ◽  
Transfer Coefficients ◽  
Two Phase ◽  
Heat Transfer Coefficients

As electronic circuit design and packaging technology progresses, the density and power levels of electronic components is increasing at a nearly exponential rate. The higher heat loads dissipated by these devices are nearing the limits of traditional cooling techniques. One method capable of removing heat fluxes as high as 100 W/cm2 is spray cooling. This process involves the impingement of liquid droplets onto a heated surface, forming a thin two-phase film. In order to create reliable models of the heat transfer during spray cooling, the behavior of the film must be understood. This paper presents an investigation into the behavior of the thin film found in spray cooling. A study was performed to relate experimental measurements of the heat transfer coefficients to experimental measurements of film thickness as they vary spatially over a die surface. Both a single nozzle and a multi-nozzle array were investigated. Measured heat transfer coefficients ranged from 0.2 to 1.2 W/m2K and film thicknesses ranged from 90 to 300 μm.

Pool Boiling Heat Transfer of Water on Finned Surfaces at Near Vacuum Pressures

2009 ◽  
Vol 132 (3) ◽  
Author(s):  
Mark Aaron Chan ◽  
Christopher R. Yap ◽  
Kim Choon Ng
Keyword(s):  
Heat Transfer ◽  
Boiling Heat Transfer ◽  
High Speed ◽  
Heat Fluxes ◽  
Vapor Pressures ◽  
Transfer Coefficients ◽  
Factors Affecting ◽  
Thin Film Evaporation ◽  
Heat Transfer Coefficients ◽  
Fin Thickness

This research paper presents a study of boiling heat transfer from longitudinal rectangular-finned surfaces immersed in saturated water at low vapor pressures. Finned surfaces with assorted fin spacing, fin thicknesses, and fin heights on a copper based surface have been investigated. All the finned surfaces were found to increase both boiling heat transfer coefficients and critical heat fluxes. An optimal fin thickness was found for a configuration, and heat transfer coefficients have been obtained at the pressures. Factors affecting the boiling characteristics have been identified and the optimal enhancement requires a balance of the active nucleation sites, bubble flow resistance, natural convection, thin film evaporation, liquid superheating, heat transfer area, bubble coalescence, and liquid reflux resistance. High speed visualization of vapor plug and vapor film generation on the boiling surfaces has revealed significant insights into the boiling mechanisms at low saturation pressures.

A Novel CFD Method to Estimate Heat Transfer Coefficient for High Speed Flows

2016 ◽  
Vol 66 (3) ◽  
pp. 203 ◽  
Author(s):  
A. Bhandarkar ◽  
Malsur Dharavath ◽  
M.S.R. Chandra Murty ◽  
P. Manna ◽  
Debasis Chakraborty
Keyword(s):  
Heat Transfer ◽  
High Speed ◽  
Isothermal Condition ◽  
Heat Fluxes ◽  
Aerodynamic Heating ◽  
Transfer Coefficients ◽  
Adiabatic Wall ◽  
Speed Test ◽  
The Difference ◽  
Cfd Method

<p>Accurate prediction of surface temperature of high speed aerospace vehicle is very necessary for the selection of material and determination of wall thickness. For aerothermal characterisation of any high speed vehicle in its full trajectory, it requires number of detailed computational fluid dynamics (CFD) calculations with different isothermal calculations. From the detailed CFD calculations for different flow conditions and geometries, it is observed that heat transfer coefficients scale with the difference of adiabatic wall temperature and skin temperature. A simple ‘isothermal method’, is proposed to calculate heat flux data with only two CFD simulations one on adiabatic condition and other on isothermal condition. The proposed methodology is validated for number of high speed test cases involving external aerodynamic heating as well as high speed combusting flow. The computed heat fluxes and surface temperatures matches well with experimental and flight measured values.</p>

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.

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