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.

scholarly journals The usage of infrared thermography to investigate spatial variations of heat transfer at spray cooling

2019 ◽  
Vol 196 ◽  
pp. 00055
Author(s):  
Anton Surtaev ◽  
Aleksandr Nazarov ◽  
Anatoliy Serov ◽  
Nikolay Miskiv ◽  
Vladimir Serdyukov
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Infrared Thermography ◽  
High Speed ◽  
Heating Surface ◽  
Spray Cooling ◽  
Spray Parameters ◽  
Maximum Heat ◽  
Maximum Heat Transfer

In present paper new approach to study heat transfer at spray cooling, based on the using of high-speed infrared thermography with high spatial resolution is proposed. Also in the paper new data on basic spray parameters, including sizes and velocities of droplets at different pressure at the nozzle inlet were obtained with the use of shadow technique and high-speed video camera. It is found, that heat transfer coefficient is unequally spatially distributed value and essentially depends on flow rate in the stationary irrigation mode. The dependence of heat transfer coefficient on a distance between spray source and heat exchange surface is obtained and an optimal distance corresponding to the maximum heat transfer intensity at present configuration of irrigation points relatively to the heating surface is determined.

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.

Phase-Change Heat Transfer Measurements Using Temperature-Sensitive Paints

2017 ◽  
Vol 140 (3) ◽  
Author(s):  
Husain Al Hashimi ◽  
Caleb F. Hammer ◽  
Michel T. Lebon ◽  
Dan Zhang ◽  
Jungho Kim
Keyword(s):  
Heat Transfer ◽  
High Speed ◽  
Uv Light ◽  
Flow Boiling ◽  
Low Cost ◽  
Data Interpretation ◽  
Temperature Sensitive ◽  
Time Resolved ◽  
Light Emitting ◽  
Phase Change Heat Transfer

Techniques based on temperature-sensitive paints (TSP) to measure time-resolved temperature and heat transfer distributions at the interface between a wall and fluid during pool and flow boiling are described. The paints are excited using ultraviolet (UV) light emitting diodes (LEDs), and changes in fluorescence intensity are used to infer local temperature differences across a thin insulator from which heat flux distribution is obtained. Advantages over infrared (IR) thermometry include the ability to use substrates that are opaque to IR (e.g., glass, plexiglass and plastic films), use of low-cost optical cameras, no self-emission from substrates to complicate data interpretation, high speed, and high spatial resolution. TSP-based methods to measure wall heat transfer distributions are validated and then demonstrated for pool and flow boiling.

Phenomenon and Mechanism of Spray Cooling on Nanowire Arrayed and Hybrid Micro/Nanostructured Surfaces

2018 ◽  
Vol 140 (11) ◽  
Author(s):  
Jian-nan Chen ◽  
Rui-na Xu ◽  
Zhen Zhang ◽  
Xue Chen ◽  
Xiao-long Ouyang ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Enhancement ◽  
High Speed ◽  
Spray Cooling ◽  
High Heat ◽  
High Heat Flux ◽  
Transfer Enhancement ◽  
Nanostructured Surfaces ◽  
New Energy ◽  
Dry Out

Enhancing spray cooling with surface structures is a common, effective approach for high heat flux thermal management to guarantee the reliability of many high-power, high-speed electronics and to improve the efficiency of new energy systems. However, the fundamental heat transfer enhancement mechanisms are not well understood especially for nanostructures. Here, we fabricated six groups of nanowire arrayed surfaces with various structures and sizes that show for the first time how these nanostructures enhance the spray cooling by improving the surface wettability and the liquid transport to quickly rewet the surface and avoid dry out. These insights into the nanostructure spray cooling heat transfer enhancement mechanisms are combined with microstructure heat transfer mechanism in integrated microstructure and nanostructure hybrid surface that further enhances the spray cooling heat transfer.

Electrical Impedance Based Characterization of Wettability During Electrostatic Suppression of the Leidenfrost State

2019 ◽  
Author(s):  
Onur Ozkan ◽  
Vaibhav Bahadur
Keyword(s):  
Heat Transfer ◽  
Electrical Impedance ◽  
Statistical Nature ◽  
Impedance Measurements ◽  
Threshold Voltages ◽  
Different Temperatures ◽  
Order Of Magnitude ◽  
Wetted Area ◽  
Impedance Characterization

Abstract An electric field can suppress the Leidenfrost state by electrostatically attracting liquid to the surface, which results in significantly higher heat transfer. This study highlights and quantifies the statistical nature of wetting during electrostatic suppression via electrical impedance characterization of Leidenfrost pools. Firstly, electrical impedance characterization is used to study the onset of suppression of the Leidenfrost state. Two different threshold voltages are defined and measured. The first threshold voltage corresponds to the onset of transient (intermittent) wetting and the second threshold corresponds to the onset of continuous wetting. The effect of the temperature and the applied AC waveform frequency on the threshold voltages is studied. Next, the wetted area is measured for different temperatures and voltages. The statistical nature of wetting during electrostatic suppression of the Leidenfrost state is characterized. The measured wetting enhancement indicates that heat transfer can be enhanced by an order of magnitude via electrostatic suppression. Together, these results provide an in-depth understanding of electrostatic suppression, and highlight electrical impedance measurements as a powerful diagnostic tool for this field.

Experimental Investigation of Droplet Dynamics on Solid Surfaces: Spreading and Recoil Effects

2006 ◽  
Author(s):  
Kalpak P. Gatne ◽  
Milind A. Jog ◽  
Raj M. Manglik
Keyword(s):  
Surface Tension ◽  
High Speed ◽  
Lower Surface ◽  
Video Camera ◽  
Temporal Variations ◽  
Liquid Viscosity ◽  
Viscous Effects ◽  
Droplet Dynamics ◽  
Digital Video Camera ◽  
The Impact

A study of the normal impact of liquid droplets on a dry horizontal substrate is presented in this paper. The impact dynamics, spreading and recoil behavior are captured using a high-speed digital video camera at 2000 frames per second. A digital image processing software was used to determine the drop spread and height of the liquid on the surface from each frame. To ascertain the effects of liquid viscosity and surface tension, experiments were conducted with four liquids (water, ethanol, propylene glycol and glycerin) that have vastly different fluid properties. Three different Weber numbers (20, 40, and 80) were considered by altering the height from which the drop is released. The high-speed photographs of impact, spreading and recoil are shown and the temporal variations of dimensionless drop spread and height are provided in the paper. The results show that changes in liquid viscosity and surface tension significantly affect the spreading and recoil behavior. For a fixed Weber number, lower surface tension promotes greater spreading and higher viscosity dampens spreading and recoil. Using a simple scale analysis of energy balance, it was found that the maximum spread factor varies as Re1/5 when liquid viscosity is high and viscous effects govern the spreading behavior.

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.

Experimental Investigation of Micro-Scale Heat Transfer at an Evaporating Moving 3-Phase Contact Line

2010 ◽  
Author(s):  
K. Ibrahem ◽  
M. F. Abd Rabbo ◽  
T. Gambaryan-Roisman ◽  
P. Stephan
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Contact Line ◽  
High Speed ◽  
Local Maximum ◽  
Back Side ◽  
Phase Contact ◽  
Flat Plates ◽  
Maximum Heat ◽  
Micro Scale

An experimental study is conducted to investigate the micro-scale heat transfer at an evaporating moving 3-phase contact line. The moving evaporating meniscus is formed by pushing or sucking a liquid column of HFE7100 in a vertical channel of 600 μm width using a syringe pump. The gas atmosphere is pure HFE7100 vapor. This channel is built using two parallel flat plates. A 10 μm thick stainless steel heating foil forms a part of one of the flat plates. Two-dimensional micro-scale temperature field at the back side of the heating foil is observed with a high speed infrared camera with a spatial resolution of 14.8 μm × 14.8 μm and an in-situ calibration procedure is used at each pixel element. A high speed CMOS camera is used to capture the shape of the moving meniscus, the images are post-processed to track the free surface of the meniscus. Local heat fluxes from the heater to the evaporating meniscus are calculated from the measured transient wall temperature distributions using an energy balance for each pixel element. In the vicinity of the 3-phase contact line the heat flux distribution shows a local maximum due to high evaporation rates at this small region. The local maximum heat flux at the 3-phase contact line area is found to be dependent on the input heat flux, the velocity and the direction of the meniscus movement. The results give detailed insight into the specific dynamic micro-scale heat and fluid transport process.

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.

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