Experimental Study of Nanofluids for Droplet Cooling Applications Using Temperature Microsensors

2006 ◽  
Author(s):  
John E. Guinn ◽  
Debjyoti Banerjee
Keyword(s):  
Experimental Study ◽  
Heat Flux ◽  
Surface Temperature ◽  
Heated Surface ◽  
Temperature Fluctuations ◽  
Spray Cooling ◽  
Nano Particles ◽  
Test Fluid ◽  
Spray Parameters ◽  
Nano Fluid

The use of nano-fluids in droplet cooling (boiling) was explored parametrically in this experimental study. The experimental parameters are: nanofluid composition, superheat, liquid subcooling, and spray parameters (nozzle diameter, injection distance, size of droplets, injection pressure, mass flow rate, etc.). Two test fluids were used in the experiments: de-ionized (DI) water and nanofluid. The nano-fluid consists of silica nano-particles with a nominal diameter of 10nm dissolved in water at 2% concentration by weight. An experimental apparatus was fabricated to measure the surface temperature fluctuations during spray cooling of a heated surface. An array of microthermocouples (Thin Film Thermocouples or "TFT") was micro-fabricated on a heated surface to measure the surface temperature fluctuations during spray cooling. The TFT are capable of measuring temperature fluctuations up to a speed of 100 MHz. In the experiments, the exit of the single droplet spray was set a distance of 10 mm away from the surface and was aligned with the location of the TFT array. The spray was produced by pumping test fluid using a syringe pump into a traversing spray head. Silicon wafers with surface micromachined TFT array were clamped on the top of the heater apparatus for measuring temperature changes on the surface of the heater. Wire bead K-Type thermocouples were embedded in the heater apparatus and were used to measure heat flux. The transient temperature data from the TFT were recorded by a data acquisition system connected to a computer. The nano-fluid spray was found to cause fouling of the heater surface due to precipitation of the constituent nano-particles during boiling. This caused the overall heat flux to decrease drastically when compared to spray cooling using water. The nano-fluid spray was found to enhance heat flux by 300% compared to the base heat flux without the spray.

Imaging Measurements in Nano-Particle Enhanced Spray Cooling

2010 ◽  
Author(s):  
J. Torres ◽  
A. Perdones ◽  
A. Garcia ◽  
F. J. Diez
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
High Speed ◽  
Heated Surface ◽  
Heat Removal ◽  
Thermal Control ◽  
Spray Cooling ◽  
Nano Particles ◽  
Copper Block ◽  
Alumina Oxide

Thermal control is a major constraint in spacecraft development as increased demand on electronics performance requires large heat dissipation from smaller surfaces which has led to increased challenges for thermal control. Spray cooling has a great amount of application in industrial processes as a heat removal method. It is thought to be the future in thermal management systems in space because of its capability for ‘close’ and accurate control of heat removal. Spray cooling is based on phase change heat transfer generating high heat transfer rates for low superheats. This last term is used to describe the difference in temperature between the heated surface and the cooling fluid. When the temperature of the surface to be cooled rises above the saturation temperature of the fluid splashed to the surface, a phase change occurs at the solid liquid interface during the boiling regime. However, the most interesting phase (regime) is the nucleating boiling where the critical heat flux, CHF, is reached. The CHF is then achieved due to the vapor generation is such as great that the liquid cannot still be in contact with the surface. Thus the heat is transferred through the vapor if there is not enough cold fluid. The thermal conductivity of vapor is lower and so the efficient of the cooling process. This turns out in a decrease on heat flux. Nowadays it is being taken more into account nanofluids as a technique capable of enhancing heat transfer. Nanofluids, a mix of nano-size particles in a base fluid, have been found to have a very high thermal conductivity as compared to the base fluid. In You et al., 2003; Kim et al., 2004a; Moreno et al., 2005 water was used with various Al2O3 particle concentration in a flat plate nucleate pool boiling system. They came across with no change in the heat transfer coefficient but a dramatic enhancement in CHF. They also found that high concentrations can degrade nucleate boiling. The aim of this project is study the effects of spray cooling with suspended nano-particles as an enhanced method for heat transfer removal. The working fluid was water with different concentrations of alumina-oxide particles added. The alumina oxide particles were supplied by Nanophase Technologies (Nano Tek® Alumina Oxide AL-01000-003-025) which had a mean diameter of 60 nm. Three different concentrations were used and the following: .5 g/L, 1 g/L, 2 g/L. Since clumping of particles can affect the heat transfer properties of the droplets, the solution was placed on inside an ultrasonic bath and left there for at least 24 hrs and immediately used in the experiments. Two nozzles were used in this experiment to study a wide range of sauter diameter of droplets. The experiment was carried out using three experimental techniques which looked into different characteristics of spray cooling. In the first mode, the fluid was sprayed onto a copper block heater surface while it was imaged with a high speed camera and synchronized with a high speed Nd-YAG laser. 9 thermocouples were positioned inside the copper block heater, as seen on Figure 1, to measure critical heat flux, while a camera was used to record different impact properties and the influence of nano-particles. Some of these properties were pool buildup size, spread, and duration of pool. For the second imaging technique, the spray on the heated surface was also considered to be an impinging jet, so to visualize the flow of this jet and how the heated surface affected it, PIV (Particle Image Velocimetry) was used in the study. A third imaging technique was used to study the droplet behavior when in contact with a heated surface. A transparent glass heater made of aluminum silicate glass and coated with an ITO (indium tin oxide) film was used as the heater. The size of the drops had an average diameter of 2.38 mm. When compared to the copper block study, this method allows images to be taken from directly below the clear glass heater. Furthermore, these images allow for a clear edge detection of drops as they spread on the surface and what characteristics they develop when the droplets have different concentrations of nanoparticles, as seen on Figure 2. The experiment used a pulsed laser to provide the background illumination. This project is a continuing research project.

Development of a Transparent Heater to Measure Surface Temperature Fluctuations Under Spray Cooling Conditions

2008 ◽  
Vol 130 (11) ◽  
Author(s):  
A. R. Griffin ◽  
A. Vijayakumar ◽  
R.-H. Chen ◽  
K. B. Sundaram ◽  
L. C. Chow
Keyword(s):  
Surface Temperature ◽  
Indium Tin Oxide ◽  
High Speed ◽  
Quartz Substrate ◽  
Sampling Rate ◽  
Temperature Fluctuations ◽  
Spray Cooling ◽  
Fused Silica ◽  
Measure Surface Temperature ◽  
Lift Off

A heater designed to monitor surface temperature fluctuations during pool boiling and spray cooling experiments while the bubbles are simultaneously being observed has been fabricated and tested. The heat source was a transparent indium tin oxide (ITO) layer commercially deposited on a fused quartz substrate. Four copper-nickel thin film thermocouples (TFTCs) on the heater surface measured the surface temperature, while a thin layer of sapphire or synthetic fused silica provided electrical insulation between the TFTCs and the ITO. The TFTCs were microfabricated using the lift-off process to deposit the nickel and copper metal films. The TFTC elements were 50μm wide and overlapped to form a 25×25μm2 junction. A DAQ program recorded the TFTC voltages at a sampling rate of 50kHz and sent a trigger to a high-speed camera to synchronize bubble images with the surface temperature data. As the bubbles and their contact rings grew over the TFTC junction, correlations between bubble behavior and surface temperature changes were demonstrated.

Experimental Investigation to Boiling Heat Transfer on a Heated Surface with Multiple Impinging Jets

2013 ◽  
Vol 663 ◽  
pp. 477-482
Author(s):  
Bin Ni ◽  
Jie Wen ◽  
Jun Liao ◽  
Hong Wu Deng
Keyword(s):  
Heat Transfer ◽  
Experimental Study ◽  
Heat Flux ◽  
Atmospheric Pressure ◽  
Boiling Heat Transfer ◽  
Heated Surface ◽  
Impinging Jets ◽  
Boiling Regime ◽  
Multiple Jets ◽  
Jet Velocity

On the condition of water multiple jet impingements, a steady-state experimental study had been conducted for boiling heat transfer in an atmospheric pressure. The jet velocity was 0.95~1.59m/s and the sub-cooling degrees of jet fluid were 30~83°C.The results revealed that increasing either jet velocity or sub-cooling degrees would promote the heat flux through heated surface, and the effect was more pronounced in partial boiling regime than fully-developed boiling regime. The heat transfer with multiple jets is enhanced due to disturbance of different impingements. With modification of the factor which related to flow distance of fluid on heated surface, correlation which is applicable to one single impinging jet boiling, can also be used to calculate critical heat flux(CHF) in boiling heat transfer with multiple impinging jets.

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.

scholarly journals Experimental Study of Interfacial Heat Flux and Surface Temperature by Inverse Analysis with Thermocouple (Fully Embedded) during Hot Steel Strip Rolling

2012 ◽  
Vol 452-453 ◽  
pp. 959-963 ◽  
Author(s):  
Daniel Weisz-Patrault ◽  
Alain Ehrlacher ◽  
Nicolas Legrand ◽  
Nathalie Labbe ◽  
Jaroslav Horsky ◽  
...  
Keyword(s):  
Experimental Study ◽  
Heat Flux ◽  
Surface Temperature ◽  
Inverse Analysis ◽  
Steel Strip ◽  
Strip Rolling ◽  
Interfacial Heat Flux

A Heat Flux Correlation for Spray Cooling in the Nucleate Boiling Regime

2000 ◽  
Author(s):  
E. Cabrera ◽  
J. E. Gonzalez
Keyword(s):  
Heat Flux ◽  
Surface Roughness ◽  
Mass Flow Rate ◽  
Mass Flow ◽  
Flow Rate ◽  
Ambient Pressure ◽  
Heated Surface ◽  
Nucleate Boiling ◽  
Spray Cooling ◽  
Boiling Regime

Abstract In this work an experimental study of spray cooling using monodispersed droplet sprays impinging on a flat and heated surface is reported. The aim of the work was to formulate an empirical model describing the heat flux (HF) for the nucleate boiling regime. Monodispersed water droplets with a known diameter and velocity, produced by a droplet generator, were directed toward a heated surface and the heat transfer was registered using a data acquisition system. The resulting high heat flux was investigated as function of the droplets’ diameter and velocity, mass flow rate, ambient pressure, subcooling degree and surface roughness. The resulting matrix of variables investigated in the experiments included; mass flux rate (340 < ṁ″ < 750 kg/m2s), subcooling degree (25 < Tsub < 78 °C), ambient pressure (1 < P < 1.8 bar), and surface roughness (79 < Rt < 5 μm). A generalized correlation was developed for the dimensionless HF as function of the dimensionless mass flow rate, temperature, surface roughness and pressure, along with the Jacob number. The form of the correlation is q ˙ ″ ρ V h f g = 0.245 ( Ja ) 1.038 ( Δ T sub Δ T sat ) 0.491 ( ρ σ m ˙ μ 3 ) 0.133 ( R t D ) 0.0213 ( P P 0 ) 0.291 having a confidence level greater than 95%, the differences between predicted and experimental HF were less than ±19%.

Application of Inverse Heat Conduction Method and Method of Lines in Spray Cooling of Heated Surface

2016 ◽  
Author(s):  
Ramin Soujoudi
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Heat Transfer Coefficient ◽  
Heat Conduction ◽  
Transfer Coefficient ◽  
Heated Surface ◽  
Method Of Lines ◽  
Spray Cooling ◽  
Approximation Technique ◽  
Inverse Heat Conduction

This paper investigates application of Method of Lines (MOL) and Inverse Heat Conduction techniques in spray cooling process. A flat face of a heated cylinder is cooled by using a nozzle spray and using room temperature water as a cooling fluid. The numerical analysis is done using MOL to estimate exposed surface temperature, surface heat flux, and convection heat transfer coefficient [3],[4]. Since there is no exact solution to verify the approximation result, for the verification purpose and accuracy of the result, the numerical result from this study is compared to other approximation results with experimental research done by Chen-Lee and Qiao-Chandra [1]. The results illustrate that disparity between the outcome of MOL and the one generated by Chen and Lee’s raw data is very insignificant throughout the whole time domain. This discrepancy between these two estimated results proves that MOL is a very reliable approximation technique compared to other finite element methods which require a finer mesh size and significant amount of calculations[2],[5]. However, comparing the results obtained through MOL with Qiao and Chandra shows that the difference between the estimated heat transfer coefficient and estimated heat flux converges rapidly for the short times of 0 < t < 60, but as the time passes, the MOL approximation results diverge slowly until it reaches its maximum value at ninety seconds, and the variance remains almost constant for the rest of the time period.

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