scholarly journals Interferometric Study of the Heat Transfer Phenomena Induced by Rapid Heating of Nickel Sheet

2020 ◽  
Vol 10 (13) ◽  
pp. 4658
Author(s):  
Hyeon-Seok Seo ◽  
In-Ju Hwang ◽  
Youn-Jea Kim
Keyword(s):  
Heat Transfer ◽  
High Speed ◽  
Rapid Heating ◽  
Compressive Force ◽  
Heating Surface ◽  
Fringe Analysis ◽  
Thermodynamic Critical Point ◽  
Secondary Function ◽  
In The Beginning ◽  
Relationship Of

Visualization of the heat transfer phenomena induced by the rapid heating of nickel sheets was carried out using a Mach–Zehnder interferometer (MZI) and a high-speed camera. This phenomenon may be an important factor in heat transfer phenomena when the working fluids reach the thermodynamic critical point. The effect of heat transfer on the heating conditions of a nickel sheet was quantified by finite fringe analysis. The results show that isotherms near the heating surface with rapid heating are generated, and the induced isotherms are moved upward with similar patterns for different heating conditions. In addition, it is confirmed that the local Nusselt number decreases to the relationship of a secondary function if the thickness of the metal specimen is very thin and the time to reach the highest temperature is very short. Moreover, it decreased according to the increase of heating energy because the heat transfer mainly occurred by conduction and radiation rather than by convection, because the expansive force and compressive force between the fluid layers on the wall increased due to an increase in the heating energy in the beginning.

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.

Heat Transfer Between Particulates and Surface in a Vibrofluidized Layer

2003 ◽  
Author(s):  
Vladimir Sheyman ◽  
Mulchand S. Rathod
Keyword(s):  
Heat Transfer ◽  
Mass Transfer ◽  
Experimental Research ◽  
Heating Surface ◽  
Mass Transfer Process ◽  
Fine Particulates ◽  
Significant Difference ◽  
Heterogeneous Processes ◽  
Upward Direction ◽  
Relationship Of

The apparatus, in which fluidization of the particulates is obtained by filtration of the gas in the upward direction through the layer of the particulates, is widely used in the industry for various types of processes. This gas serves as source of fluidized agent and the heat transfer carrier. In particular, the fluidized bed creates a favorable condition to carry out numerous heterogeneous processes. In spite of a significant advantage of this hydrodynamics regime, there are some drawbacks. The fluidization occurs only when sufficient filtration velocity of gases is achieved. In some cases when there is a significant difference in particulate sizes, this condition is not acceptable, and for a layer of fine particulates, such type of fluidization cannot be obtained at all. In the latter case, a combination of vibration and filtration of very small amount of gas through the layer is used, and the heat transfer to the solids occurs by conduction from the heating surface. In this paper, a set of differential equations for the heat and mass transfer are formulate and solved for variable and constant temperature of the heating surface. As a result, a relationship of the solid temperatures as a function of time is established. An experimental research also was performed. A comparison of the experimental research data and theoretical analysis shows that the deviation does not exceed 10%. The experimental research also shows that the main influence on the intensity of the mass transfer process has the amplitude of vibration and to the lesser extent the effects of frequency of vibration.

Dynamics of a Leidenfrost Droplet Modulated by Electrowetting

2017 ◽  
Vol 139 (8) ◽  
Author(s):  
Yi Lu ◽  
Hui Fang ◽  
Jiming Bao ◽  
Dong Liu
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Electric Fields ◽  
High Speed ◽  
Water Drop ◽  
Heating Surface ◽  
Interfacial Instabilities ◽  
Ac Electric Fields ◽  
Instantaneous Temperature ◽  
Reduced Surface

Leidenfrost phenomenon is closely related to film boiling and the critical heat flux (CHF) limit of boiling heat transfer. Understanding the mechanisms of Leidenfrost phenomenon and devising effective ways to suppress it is of great interest to the heat transfer enhancement community. In this work, a synchronized high-speed optical imaging and infrared (IR) thermography approach was employed to investigate the dynamics of a Leidenfrost droplet under the influence of electrowetting (EW). The Leidenfrost droplet was produced by dispensing a water drop on a Teflon-coated silicon wafer maintained at a wall temperature of Twall = 200 °C. Both direct-current (DC) and alternating-current (AC) electric fields were applied to induce EW effect to suppress the Leidenfrost state. The interfacial instabilities of the Leidenfrost droplet were observed, and the instantaneous temperature and heat flux distributions on the heating surface were measured. The results suggest that the electrical forces destabilize the liquid-vapor interface and cause the vapor film that insulates the heating surface from the droplet to collapse. Re-establishment of the liquid-solid contact helps to drastically improve the heat transfer, as evidenced by the reduced surface temperature and the enhanced heat flux.

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.

THE MECHANISM OF RAISING AND QUANTIFICATION OF SPECIFIC HEAT FLUX AT BOILING OF NANOFLUIDS IN FREE CONVECTION CONDITIONS

2017 ◽  
pp. 25-34
Author(s):  
V.N. Moraru
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Heat Capacity ◽  
Specific Heat ◽  
Chemical Properties ◽  
Heating Surface ◽  
Physical Models ◽  
Superheated Liquid ◽  
Two Phase ◽  
Boiling Process

The results of our work and a number of foreign studies indicate that the sharp increase in the heat transfer parameters (specific heat flux q and heat transfer coefficient _) at the boiling of nanofluids as compared to the base liquid (water) is due not only and not so much to the increase of the thermal conductivity of the nanofluids, but an intensification of the boiling process caused by a change in the state of the heating surface, its topological and chemical properties (porosity, roughness, wettability). The latter leads to a change in the internal characteristics of the boiling process and the average temperature of the superheated liquid layer. This circumstance makes it possible, on the basis of physical models of the liquids boiling and taking into account the parameters of the surface state (temperature, pressure) and properties of the coolant (the density and heat capacity of the liquid, the specific heat of vaporization and the heat capacity of the vapor), and also the internal characteristics of the boiling of liquids, to calculate the value of specific heat flux q. In this paper, the difference in the mechanisms of heat transfer during the boiling of single-phase (water) and two-phase nanofluids has been studied and a quantitative estimate of the q values for the boiling of the nanofluid is carried out based on the internal characteristics of the boiling process. The satisfactory agreement of the calculated values with the experimental data is a confirmation that the key factor in the growth of the heat transfer intensity at the boiling of nanofluids is indeed a change in the nature and microrelief of the heating surface. Bibl. 20, Fig. 9, Tab. 2.

Experimental investigation of wall heat transfer due to spray combustion in a high-pressure/high-temperature vessel

2021 ◽  
pp. 146808742110072
Author(s):  
Karri Keskinen ◽  
Walter Vera-Tudela ◽  
Yuri M Wright ◽  
Konstantinos Boulouchos
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
High Pressure ◽  
High Temperature ◽  
High Speed ◽  
Transfer Problem ◽  
Wall Heat Transfer ◽  
Gas Temperature ◽  
Reference Case ◽  
High Pressure High Temperature

Combustion chamber wall heat transfer is a major contributor to efficiency losses in diesel engines. In this context, thermal swing materials (adapting to the surrounding gas temperature) have been pinpointed as a promising mitigative solution. In this study, experiments are carried out in a high-pressure/high-temperature vessel to (a) characterise the wall heat transfer process ensuing from wall impingement of a combusting fuel spray, and (b) evaluate insulative improvements provided by a coating that promotes thermal swing. The baseline experimental condition resembles that of Spray A from the Engine Combustion Network, while additional variations are generated by modifying the ambient temperature as well as the injection pressure and duration. Wall heat transfer and wall temperature measurements are time-resolved and accompanied by concurrent high-speed imaging of natural luminosity. An investigation with an uncoated wall is carried out with several sensor locations around the stagnation point, elucidating sensor-to-sensor variability and setup symmetry. Surface heat flux follows three phases: (i) an initial peak, (ii) a slightly lower plateau dependent on the injection duration, and (iii) a slow decline. In addition to the uncoated reference case, the investigation involves a coating made of porous zirconia, an established thermal swing material. With a coated setup, the projection of surface quantities (heat flux and temperature) from the immersed measurement location requires additional numerical analysis of conjugate heat transfer. Starting from the traces measured beneath the coating, the surface quantities are obtained by solving a one-dimensional inverse heat transfer problem. The present measurements are complemented by CFD simulations supplemented with recent rough-wall models. The surface roughness of the coated specimen is indicated to have a significant impact on the wall heat flux, offsetting the expected benefit from the thermal swing material.

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