scholarly journals Droplet Impact Sub-cavity Histories and PDPA Spray Experiments for Spray Cooling Modeling

2013 ◽  
Author(s):  
Nicholas Lee Hillen
Keyword(s):  
Spray Cooling ◽  
Droplet Impact

Experimental Characterization of Single and Multiple Droplet Impingement on Surfaces Subject to Constant Heat Flux Conditions

2010 ◽  
Author(s):  
Guillermo Soriano ◽  
Jorge L. Alvarado ◽  
Yen Po Lin
Keyword(s):  
Heat Flux ◽  
Heat Removal ◽  
Spray Cooling ◽  
Constant Heat Flux ◽  
Droplet Impact ◽  
Fluid Temperature ◽  
Impact Zone ◽  
Constant Heat ◽  
Droplet Impingement ◽  
The Impact

Spray cooling is one of the most promising technologies in applications which require large heat removal capacity in very small areas. Previous experimental studies have suggested that one of the main mechanisms of heat removal in spray cooling is forced convection with strong mixing due to droplet impingement. These mechanisms have not been completely understood mainly due to the large number of physical variables, and the inability to modulate and control variables such as droplet frequency and size. Our approach consists of minimizing the number of experimental variables by controlling variables such as droplet direction, velocity and diameter. An experimental study of single and multiple droplet impingements using HFE 7100 as the cooling fluid under constant heat flux conditions is presented. A monosized droplet train is produced using a piezoelectric droplet generator with the ability to adjust droplet frequency, diameter and velocity. In this study, heaters consisting of a layer of Indium Tin Oxide (ITO) as heating element, and silicon substrates are used. Film morphology was characterized using a Laser Induced Fluorescence (LIF) technique with a focus on the droplet impact zone by measuring variables such as film thickness and diameter of the impact zone. Infrared thermography was used to measure surface temperature at the liquid-solid interface. The IR thermography technique was also used to characterize temperature gradients at the droplet impact zone. The results and effects of droplet frequency, fluid flow rate, and fluid temperature on heat flux are also presented.

3-D Multiphase Flow Modeling of Bubble Growth and Burst in Spray Cooling Using Parallel Computing

2007 ◽  
Author(s):  
R. Panneer Selvam ◽  
Joseph Johnston ◽  
Suranjan Sarkar
Keyword(s):  
Heat Transfer ◽  
Parallel Computing ◽  
Multiphase Flow ◽  
Liquid Film ◽  
Convective Flow ◽  
Bubble Dynamics ◽  
Thin Liquid Film ◽  
Spray Cooling ◽  
Droplet Impact ◽  
Multiphase Model

In this paper, we present an extension of the level set method from 2D into 3D for solving multiphase flow problems using distributed parallel computing. The model solves the incompressible Navier-Stokes equations to study the behavior of a bubble immersed in a thin liquid film at microscale as found in a spray cooling environment. Since modeling all aspects of spray cooling, including nucleation, bubble dynamics, droplet impact, convection and thin film evaporation is very difficult at this time; these phenomena have been divided and studied separately in order to study the heat transfer behavior of each phenomenon individually. We studied the droplet impact effect as seen in spray cooling by our 3D multiphase model in earlier studies. Through the 3D multiphase model this study simulates the dynamics of a nucleating bubble in a thin liquid film that merges with the ambient atmosphere above the film. In this study we did not consider the droplet impact effect to concentrate on the vapor bubble dynamics in thin liquid film and its effect on heat transfer. The effect of convective flow is not considered to keep the 3-D model simple. However the 2D model was modified to simulate the effect that a horizontal flow of constant velocity has on the growth and detachment of a nucleating bubble and discussed in the second part of the paper. This study illustrates the importance of considering the convective flow effect in our 3-D multiphase flow model in future with droplet impact for spray cooling modeling studies.

Droplet impact time histories for a range of Weber numbers and liquid film thicknesses for spray cooling application

2013 ◽  
Author(s):  
Nicholas L. Hillen ◽  
Jon Stephen Taylor ◽  
Christopher Menchini ◽  
Gary Morris ◽  
Murat Dinc ◽  
...  
Keyword(s):  
Liquid Film ◽  
Spray Cooling ◽  
Droplet Impact ◽  
Impact Time ◽  
Time Histories

Computer Modeling of Liquid Droplet Impact on Heat Transfer During Spray Cooling

2005 ◽  
Author(s):  
R. Panneer Selvam ◽  
Sandya Bhaskara ◽  
Juan C. Balda ◽  
Fred Barlow ◽  
Aicha Elshabini
Keyword(s):  
Heat Transfer ◽  
Liquid Film ◽  
Vapor Bubble ◽  
Liquid Droplet ◽  
Heat Removal ◽  
Spray Cooling ◽  
Droplet Impact ◽  
System Level ◽  
High Heat Flux ◽  
Micro Level

Spray cooling is a high flux heat removal technique considered for systems dissipating high power within small areas such as advanced lasers. Recently Selvam and Ponnappan (2004 & 2005) identified the importance of modeling heat transfer in a thin liquid film on a hot surface at the micro level and illustrated how this micro level modeling could help to improve the macro level spray cooling. The goal of this research is to advance the theoretical understanding of spray cooling to enable efficient system level hardware designs. Two-phase flow modeling is done using the level set method to identify the interface of vapor and liquid. The modifications made to the incompressible Navier-Stokes equations to consider surface tension and phase change are presented. The equations are solved using the finite difference method. The effect of liquid droplet impact on a 40 μm thick liquid film containing vapor bubble and the consequent heat removal is explained with a sequence of temperature vs. time contours. From that, the importance of fast transient conduction in the liquid film leading to high heat flux in a short time is illustrated. The optimum positioning of the droplet with respect to the vapor bubble for effective heat removal is also systematically investigated. This information is expected to help in proper positioning of the droplet in three-dimensional modeling.

scholarly journals Investigation of Dynamic Characteristics of Liquid Nitrogen Droplet Impact on Solid Surface

2022 ◽  
Vol 14 (2) ◽  
pp. 710
Author(s):  
Ke Zhao ◽  
Yang Ding
Keyword(s):  
Liquid Nitrogen ◽  
Solid Surface ◽  
Dynamic Characteristics ◽  
Wall Temperature ◽  
Spray Cooling ◽  
Droplet Impact ◽  
Spreading Factor ◽  
Normal Medium ◽  
The Common ◽  
Cooling Technology

Liquid nitrogen spray cooling technology exhibits excellent heat transfer efficiency and environmental protection performance. The promotion of this technology plays an important role in improving the sustainable development of the refrigeration industry. In order to clarify its complex microscale behavior, the coupled Level Set-VOF method was adopted to study the dynamic characteristics of liquid nitrogen droplet impact on solid surface in this paper. The spreading behaviors under various factors (initial velocity, initial diameter, wall temperature, and We number) were systematically analyzed. The results show that the spreading behaviors of liquid nitrogen droplet share the same process with the normal medium, which are rebound, retraction, and splashing. For the droplet with smaller velocity and diameter, Rebound is the common phenomenon due to the smaller kinetic energy. With the increase of droplet diameter (0.2 mm to 0.5 mm) and velocity (0.1 m/s to 5 m/s), the spreading factor increases rapidly and the spreading behaviors evolve into retraction and splashing. The increase of wall temperature accelerates the droplets spreading, and the spreading factor increases accordingly. For the liquid nitrogen droplets hit the wall, the dynamic behaviors of rebound (We < 0.2), retraction (0.2 < We < 4.9), and splashing (We > 4.9) will occur with the droplet weber number increased, which are consistent with the common medium. However, due to liquid nitrogen having lower viscosity and surface tension, the conditions of morphological transformations are different from the common media. The maximum spreading diameter has a power correlation with We, the power index of We is 0.306 for liquid nitrogen, lager than common medium (0.25). The reasons are: (1) the better wettability of liquid nitrogen, and (2) the vapor generated by the violent phase change ejects along the axial direction. The article will provide a certain theoretical basis for liquid nitrogen spray cooling technology, and can also enrich the flow dynamics of cryogenic fluids.

Controlling the Contact Times of Bouncing Droplets: Droplet Impact on Vibrating Surfaces

2018 ◽  
Vol 140 (3) ◽  
Author(s):  
Patricia Weisensee ◽  
Jingcheng Ma ◽  
William King ◽  
Nenad Miljkovic
Keyword(s):  
Heat Transfer ◽  
Vibration Frequency ◽  
Contact Time ◽  
High Speed ◽  
Rational Design ◽  
Turbine Blades ◽  
Spray Cooling ◽  
Industrial Applications ◽  
Droplet Impact ◽  
Impact Phase

Droplet impact on vibrating solids is ubiquitous in nature and industrial applications, including impact on turbine blades, insect wings, or during spray cooling of electronic systems and steel manufacturing processes. Using high speed imaging, we demonstrate that through substrate vibration (60 – 320 Hz), droplet contact times tc, which are independent of impact speed on rigid stationary substrates, can be actively manipulated and controlled. We show that droplet dynamics and contact times are most sensitive to impact phase, followed by vibration frequency, with vibration amplitude having negligible effects (Figure 1, Figure 2b). We determine a critical impact phase φc at which contact times transition rapidly from a minimum (tc ≈ 0.5tc,th) to a maximum (tc ≈ 1.6tc,th), where tc,th is the theoretical contact time on a stationary rigid substrate (insert Figure 2a). Averaging contact times over all impact phases, we show that for low frequencies (< 80 Hz) average contact times increase relative to impact on stationary substrates, while contact times decrease for impact at higher vibration frequencies (> 100 Hz) (Figure 2a). The present findings provide guidelines for the rational design of applications where the contact time influences heat transfer. During spray cooling, for example, the per droplet heat transfer rates increase (decrease) for longer (shorter) contact times. Thus, by tailoring the vibration frequency of the substrate, the average contact time, and consequently the average heat transfer, can be actively controlled.

Direct Simulation of Spray Cooling: Effect of Multiple Droplet Impact and Latent Heat of Vaporization of Coolant Liquid on Heat Transfer

2008 ◽  
Author(s):  
Mita Sarkar ◽  
R. Panneer Selvam ◽  
Rengasamy Ponnappan
Keyword(s):  
Heat Transfer ◽  
Liquid Film ◽  
Latent Heat ◽  
Stokes Equations ◽  
Thin Liquid Film ◽  
Spray Cooling ◽  
Droplet Impact ◽  
Vapor Bubbles ◽  
Heat Of Vaporization ◽  
Latent Heat Of Vaporization

Spray cooling is a way of efficiently removing the heat from a hot surface and considered for high power system such as advanced lasers. The heat transfer phenomenon in spray cooling is complex in nature because it occurs due to conduction, convection and phase change. The numerical model of spray cooling is done by solving the set of incompressible Navier-Stokes equations using finite difference method. Level set method is used to capture the liquid vapor interface in our multiphase flow model. Our previous 2D model which included single droplet impact on single growing vapor bubble is modified to introduce multiple droplets impact on thin liquid film with multiple growing vapor bubbles. Though the previous model was effective so far to predict the spray cooling phenomena and also the parameters for high heat removal, but the actual spray cooling phenomena consists of multiple droplets impact on multiple growing vapor bubbles at different time instances. To understand the spray cooling further and to represent it more realistically the inclusion of multiple droplets and multiple vapor bubbles is essential. In the present work, an investigation on the effect of latent heat of vaporization of coolant is conducted for the case of a thin liquid film of 44 μm in removing the heat and bubble growth when a liquid spray droplet is impacting. The flow and heat transfer details are presented for multiple droplet impacts on thin liquid film with multiple growing vapor bubbles.

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