Heat Transfer During Drop Impact Onto Wetted Heated Smooth and Structured Substrates: Experimental and Theoretical Study

2010 ◽  
Author(s):  
Tatiana Gambaryan-Roisman ◽  
Mete Budakli ◽  
Ilia V. Roisman ◽  
Peter Stephan
Keyword(s):  
Heat Transfer ◽  
Temperature Distribution ◽  
Film Thickness ◽  
Spray Cooling ◽  
Drop Impact ◽  
Interface Temperature ◽  
Heated Plate ◽  
Initial Film ◽  
Impact Parameters ◽  
Heated Plates

Spray cooling is a very effective means of heat removal from hot surfaces. Its efficiency can be further improved using structured wall surfaces. One of the fundamental processes governing spray cooling is an impact of a single cold droplet onto a heated wetted wall. The hydrodynamics of drop impact governs the transient heat transport in the film and in the wall. We study hydrodynamics and heat transfer during impact of a single drop onto heated smooth and structured heated plates. The temperature distribution in the heated plates has been measured with seven thermocouples. The splash dynamics and the evolution of interface temperature distribution have been visualized using high-speed infrared thermography. The film thickness evolution in the inner region has been measured using chromatic confocal imaging technique. Initial film thickness and drop impact parameters have been varied in the experiments. The evolution of the temperature distribution at the liquid-gas interface and the instationary temperature distribution in the heated plate depend on the initial film thickness, impact parameters and the plate topography. A self-similar analytical solution of the full Navier-Stokes equations and of the energy equation is obtained for the velocity and temperature fields in the spreading film. The theory allows prediction of the contact temperature and the residual film thickness.

Quasi-Steady-State Temperature Distribution in Periodically Contacting Finite Regions

1981 ◽  
Vol 103 (4) ◽  
pp. 739-744 ◽  
Author(s):  
B. Vick ◽  
M. N. O¨zis¸ik
Keyword(s):  
Heat Transfer ◽  
Thermal Conductivity ◽  
Steady State ◽  
Temperature Distribution ◽  
Interface Temperature ◽  
Quasi Steady State ◽  
Exact Analytical Solutions ◽  
One Dimensional ◽  
Steady State Temperature ◽  
Regular Cycle

Heat transfer across two surfaces which make and break contact periodically according to a continuous regular cycle is investigated theoretically and exact analytical solutions are developed for the quasi-steady-state temperature distribution for a two-region, one-dimensional, periodically contacting model. The effects of the Biot number, the thermal conductivity and thermal diffusivity of the materials and the duration of contact and break periods on the interface temperature and the temperature distribution within the solids are illustrated with representative temperature charts.

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.

scholarly journals Establishment of the falling film evaporation model and correlation of the overall heat transfer coefficient

2019 ◽  
Vol 6 (5) ◽  
pp. 190135 ◽  
Author(s):  
Jing Fang ◽  
Kaixuan Li ◽  
Mengyu Diao
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Temperature Distribution ◽  
Film Thickness ◽  
Liquid Film ◽  
Velocity Distribution ◽  
Transfer Coefficient ◽  
Falling Film ◽  
Overall Heat Transfer Coefficient ◽  
Proposed Model

In order to study the heat transfer of the falling film evaporator with phase change on both sides, in this paper we built the mathematical model and the physical model where the liquid film inside the tube is laminar and turbulent. The film thickness of the condensate at different axial positions, total condensate volume and velocity distribution, and temperature distribution of condensate outside the tube can be obtained by calculating the proposed model. Meanwhile, the liquid film thickness, velocity distribution and temperature distribution inside the tube were obtained by numerical simulation by considering the influence of the liquid film with different compositions on the heat transfer during fluid flow. With ethanol–water as the system, the overall heat transfer coefficient and heat transfer quantity of the falling film evaporator were obtained by the calculation of the model. The accuracy of the proposed model was confirmed by experiments. The model and the calculation of heat transfer proposed in this paper have enormous significance for the basic data and theoretical guidance of the heat transfer performance prediction and operational optimization of the evaporator.

Multiple Droplet Impingements on Nanostructured Surfaces for Enhanced Spray Cooling

2011 ◽  
Author(s):  
Jorge L. Alvarado ◽  
Yen-Po Lin
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Contact Angle ◽  
Film Thickness ◽  
Tangential Velocity ◽  
Spray Cooling ◽  
High Heat ◽  
Nanostructured Surface ◽  
Velocity Gradients ◽  
Crown Morphology

Spray cooling has been studied thoroughly over the years in an effort to understand its unique heat transfer potential. Spray cooling is characterized by its ability to dissipate high heat transfer rates while maintaining relatively uniform surface temperatures. Despite of all the recent developments, liquid-surface properties such as contact angle and surface tension have been shown to limit the ability of spray cooling to dissipate high heat flux. Recent high-speed images of multiple droplet impingent events have revealed that liquid film thickness, impact crown morphology, and tangential velocity gradients tend to dominate the overall heat transfer process. All these aspects are intrinsically linked to surface morphology. Therefore, enhancement of heat transfer should be preceded by the design, fabrication and use of surfaces that reduce film thickness, promote constructive impact crown morphology, and facilitate greater tangential velocity gradients. Recently, a new type of nanostructured surface has been designed, fabricated, and tested that reduces film thickness and contact angle by at least 30%. The nanostructured surface consists of nanopillars of 100 nm in height and 200 nm in diameter. The combination of spacing and nanopillar size has resulted in a thinner liquid film. The nanostructured surface was fabricated using the Step and Flash Imprinting Lithography (S-FIL) technique. Current work also includes the study of the relationship between the effective thermal diameter and heat flux when using nanostructured and bare surfaces.

Experimental Study on Heat Transfer of Pressurized Spray Cooling on the Heated Plate by Using 45° Full Cone Nozzles

2014 ◽  
Vol 535 ◽  
pp. 32-36 ◽  
Author(s):  
Peng Jiang ◽  
Qian Wang ◽  
I. Sabariman ◽  
Eckehard Specht
Keyword(s):  
Heat Transfer ◽  
Heat Removal ◽  
Infrared Camera ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Spray Cooling ◽  
Material Surface ◽  
Transient Temperature ◽  
Heated Plate ◽  
Water Spray Cooling

Water spray cooling is widely used in many industrial processes to control heat removal from a hot material surface. In this work, pressurized spray nozzle was applied to break film boiling immediately once the quenching process is started. For this purpose, a circular disc made of non-ferrous metals is heated to approximately 850 °C and sprayed on one side by hydraulic nozzle and the temperature distribution with respect to time and space is measured by using Infrared camera. On the other side, the measured surface was coated with graphite paint in order to achieve a high emissivity. By this IR thermography, transient temperature measurement can be carried out within the window of 320 × 80 pixels. The heat transfer was analyzed through 1D method. In this method, the temperature difference between both sides neglected. The local heat transfer can then be calculated from a simple differential energy balance.

scholarly journals Single and Double Drop Impingement on a Heated Plate CFD and Experimental Investigation

2021 ◽  
Vol 06 (04) ◽  
Author(s):  
Ruaa Basim Namaa ◽  
Keyword(s):  
Heat Transfer ◽  
Temperature Distribution ◽  
Water Drop ◽  
Flow Behavior ◽  
Central Zone ◽  
Heated Plate ◽  
Single Drop ◽  
Transfer Coefficients ◽  
High Tendency ◽  
Heat Transfer Coefficients

A drop impingement on a hot surface is known as an effective way for heat removal. The present work uses a VOF (volume of fluid) model to simulate the flow behavior and temperature distribution on a 50 °C heated plate while relatively cold water drop is impinging. The temperature distribution at the impingement zone is used to examine the transient heat transfer coefficients using a single drop and double drops conditions. The spreading factor is tested in both cases. A test rig is built to verify the temperature distribution and a heat balance method is introduced to find the experimental heat coefficients on the heated. The CFD solution and its flow results gives a good agreement for single drop previous results. The results for the double drop condition show a high tendency for rebound and splash of the drop leaving the central zone without water drop coverage which way causes a burn out in case of high heat fluxes. The single drop condition show a symmetrical temperature and heat transfer coefficients distribution while the double drop impingement gives lower value of coefficients with non-uniform and unsymmetrical distribution specially at the bigger drop to plate distances. The experimental average heat coefficients gives relatively low error of only 5% in case of double drop when compared to the single drop values.

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.

scholarly journals Transient evolution of the heat transfer and the vapor film thickness at the drop impact in the regime of film boiling

2018 ◽  
Vol 30 (12) ◽  
pp. 122109 ◽  
Author(s):  
G. Castanet ◽  
W. Chaze ◽  
O. Caballina ◽  
R. Collignon ◽  
F. Lemoine
Keyword(s):  
Heat Transfer ◽  
Film Thickness ◽  
Drop Impact ◽  
Film Boiling ◽  
Vapor Film
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