Conduction through Droplets during Dropwise Condensation

1973 ◽  
Vol 95 (1) ◽  
pp. 12-19 ◽  
Author(s):  
Charles J. Hurst ◽  
Donald R. Olson
Keyword(s):  
Heat Transfer ◽  
Finite Element Analysis ◽  
Experimental Investigation ◽  
High Heat ◽  
Dropwise Condensation ◽  
Lower Side ◽  
Element Analysis ◽  
High Heat Transfer ◽  
Very High ◽  
Good Agreement

An experimental investigation was undertaken in which dropwise condensation was caused to occur on the upper side of a 0.001-in-thick horizontal copper condensing surface. The lower side of the condensing wall was convectively cooled, and the cooled-side temperatures under growing droplets were measured using infrared-radiation techniques. Temperature measurements showed good agreement with the results of a finite-element analysis of the droplet and condensing surface. Both experimental and analytical results pointed to the existence of an area of very high heat transfer right around the droplet perimeter, and to the importance of the condensing wall as a heat-diffusing mechanism in dropwise condensation.

Spatial and Temporal Wall Temperature Fluctuations in Two-Phase Flow in Microgap Coolers

2010 ◽  
Author(s):  
Jessica Sheehan ◽  
Avram Bar-Cohen
Keyword(s):  
Heat Transfer ◽  
High Heat ◽  
Heat Fluxes ◽  
Operating Conditions ◽  
Transfer Coefficients ◽  
Two Phase ◽  
Heat Transfer Coefficients ◽  
High Heat Transfer ◽  
Volumetric Cooling ◽  
Very High

Heat transfer to an evaporating refrigerant and/or dielectric liquid in a microgap channel can provide very high heat transfer coefficients and volumetric cooling rates. Recent studies at Maryland have established the dominance of the annular flow regime in such microgap channels and related the observed high-quality peak of an M-shaped heat transfer coefficient curve to the onset of local dryout. The present study utilizes infrared thermography to locate such nascent dryout regions and operating conditions. Data obtained with a 210 micron microgap channel, operated with a mass flux of 195.2 kg/m2-s and heat fluxes of 10.3 to 26 W/cm2 are presented and discussed.

Microchannels and Minichannels: History, Terminology, Classification and Current Research Needs

2003 ◽  
Author(s):  
Satish G. Kandlikar
Keyword(s):  
Heat Transfer ◽  
Historical Perspective ◽  
High Heat ◽  
High Flux ◽  
Research Needs ◽  
Transfer Rates ◽  
High Heat Transfer ◽  
Liver And Kidney ◽  
The Brain ◽  
Very High

Microchannels and Minichannels are found in many biological systems providing very high heat and mass transfer rates in organs such as the brain, lung, liver and kidney. Many high flux cooling applications are effectively utilizing their high heat transfer capabilities of these channels. A brief overview of the historical perspective and some of the issues that need to be addressed with microchannels and Minichannels are presented in this paper.

scholarly journals A Review of Research on Dropwise Condensation Heat Transfer

2021 ◽  
Vol 11 (4) ◽  
pp. 1553
Author(s):  
Xuechao Hu ◽  
Qiujie Yi ◽  
Xiangqiang Kong ◽  
Jianwei Wang
Keyword(s):  
Heat Transfer ◽  
Theoretical Models ◽  
High Heat ◽  
Condensation Heat Transfer ◽  
Formation Mechanisms ◽  
Transfer Model ◽  
Dropwise Condensation ◽  
High Heat Transfer ◽  
Nucleation Sites ◽  
Enhancing Heat Transfer

Dropwise condensation is considered to be an effective method of enhancing heat transfer due to its high heat transfer performance. However, because the effect of dropwise condensation is affected by many complex factors, there is no systematic review summarized on the law of dropwise condensation heat transfer by scholars. In this paper, the main methods and problems of promoting dropwise condensation were reviewed based on the dropwise condensation mechanism and theoretical model. The three different hypotheses about the mechanism of dropwise condensation and the heat transfer model of dropwise condensation based on the hypothesis of nucleation sites were summarized. The methods for promoting dropwise condensation and the problems that influence dropwise condensation heat transfer are introduced in this paper. The research showed that many researchers focused on how the surface fabricated forms dropwise condensation rather than whether it enhances heat transfer. In this paper, we point out that the droplet shedding rate is the key to enhancing dropwise condensation heat transfer. Much more research on droplet formation mechanisms and theoretical models of different surfaces is supposed to be carried out in the future.

Effect of Geometrical Parameters on Flow Mal-Distribution in a Wavy Microchannel

2015 ◽  
Vol 813-814 ◽  
pp. 674-678
Author(s):  
M. Satheeshkumar ◽  
M.R. Thansekhar ◽  
C. Anbumeenakshi ◽  
S. Suresh
Keyword(s):  
Heat Transfer ◽  
Fluid Flow ◽  
Flow Distribution ◽  
High Heat ◽  
Geometrical Parameters ◽  
Transfer Coefficients ◽  
Geometrical Properties ◽  
Heat Transfer Coefficients ◽  
High Heat Transfer ◽  
Very High

Microchannels are of current interest for use in heat exchangers, where very high heat transfer performance is desired. Microchannels provide very high heat transfer coefficients because of their small hydraulic diameters. In this study, a numerical investigation of fluid flow in microchannels with varying hydraulic diameters is presented. Six channels with wavy shape are considered. Header is the major part in the microchannel, which supplies fluid into different channels. A CFD model was created to simulate the fluid flow in the header and microchannels. In this work, five different shapes of the header were considered namely circular, frustum conical, rectangular, triangular and trapezoidal. The results from these simulations are presented, and it is observed that the flow distribution is significantly affected by geometrical properties of the channel and the header.

scholarly journals Enhanced condensation heat transfer using porous silica inverse opal coatings on copper tubes

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Solomon Adera ◽  
Lauren Naworski ◽  
Alana Davitt ◽  
Nikolaj K. Mandsberg ◽  
Anna V. Shneidman ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Porous Silica ◽  
High Heat ◽  
Condensation Heat Transfer ◽  
Inverse Opal ◽  
Dropwise Condensation ◽  
High Heat Transfer ◽  
The Heat Transfer Coefficient

AbstractPhase-change condensation is commonplace in nature and industry. Since the 1930s, it is well understood that vapor condenses in filmwise mode on clean metallic surfaces whereas it condenses by forming discrete droplets on surfaces coated with a promoter material. In both filmwise and dropwise modes, the condensate is removed when gravity overcomes pinning forces. In this work, we show rapid condensate transport through cracks that formed due to material shrinkage when a copper tube is coated with silica inverse opal structures. Importantly, the high hydraulic conductivity of the cracks promote axial condensate transport that is beneficial for condensation heat transfer. In our experiments, the cracks improved the heat transfer coefficient from ≈ 12 kW/m2 K for laminar filmwise condensation on smooth clean copper tubes to ≈ 80 kW/m2 K for inverse opal coated copper tubes; nearly a sevenfold increase from filmwise condensation and identical enhancement with state-of-the-art dropwise condensation. Furthermore, our results show that impregnating the porous structure with oil further improves the heat transfer coefficient by an additional 30% to ≈ 103 kW/m2 K. Importantly, compared to the fast-degrading dropwise condensation, the inverse opal coated copper tubes maintained high heat transfer rates when the experiments were repeated > 20 times; each experiment lasting 3–4 h. In addition to the new coating approach, the insights gained from this work present a strategy to minimize oil depletion during condensation from lubricated surfaces.

Finite Element Analysis of Printed Circuit Heat Exchanger Core for Creep and Creep-Fatigue Responses

2019 ◽  
Author(s):  
Heramb P. Mahajan ◽  
Tasnim Hassan
Keyword(s):  
Finite Element Analysis ◽  
Finite Element ◽  
Interaction Analysis ◽  
High Heat ◽  
Element Analysis ◽  
Printed Circuit ◽  
High Heat Transfer ◽  
Creep Fatigue ◽  
Section Viii ◽  
Nuclear Applications

Abstract Printed circuit heat exchangers (PCHEs) have a high heat transfer coefficient which makes them a suitable option for very high temperature reactors (VHTRs). ASME Section VIII design code provide PCHE design rules for non-nuclear applications. The PCHE design methodology for nuclear applications is yet to be established. Towards developing the ASME Section III code rules, this study started with the PCHE design as per section VIII. An experimental set up is developed to evaluate the designed PCHE for creep and creep-fatigue performances. This study performed pretest finite element analysis to estimate experimental responses and failure loads for setting up the experiments. Three dimensional isothermal analyses of the PCHE’s were conducted by using an advanced unified constitutive model to simulate the creep-fatigue interaction. The sub-modeling technique was used to analyze the channel scale response of the PCHE. Analysis results indicate that the failure may be governed by the channel corner responses, which is influenced by the creep-fatigue interaction. Analysis based creep-fatigue damage curve is plotted as per ASME code to evaluate the design of PCHEs for nuclear application.

Boiling of Water at Sub-Atmospheric Conditions With Enhanced Structures

2005 ◽  
Author(s):  
Aniruddha Pal ◽  
Yogendra Joshi
Keyword(s):  
Heat Transfer ◽  
Electronics Cooling ◽  
High Heat ◽  
Maximum Temperature ◽  
Working Fluid ◽  
Atmospheric Conditions ◽  
Liquid Cooling ◽  
High Heat Transfer ◽  
Heat Loads ◽  
Very High

Liquid cooling with phase change is a very attractive option for thermal management of electronics because of the very high heat transfer coefficients achievable. Two-phase liquid cooling can be implemented in a thermosyphon loop, which has an evaporator, where heat is absorbed from the source during boiling of the working fluid, and a condenser, where the absorbed heat is rejected. Water is a preferred working fluid for boiling heat transfer due to its excellent thermal properties. Using water at sub-atmospheric conditions helps in initiation of boiling at low temperatures, which is necessary for electronics cooling applications, often limiting the maximum temperature to 85°C for silicon devices. Past studies have also shown that using boiling enhancement structures improve heat transfer by lowering the incipience overshoot, increasing heat flux and reducing evaporator volume. However, detailed study on the effects of enhancement structures and sub-atmospheric saturation conditions on the boiling of water in a compact thermosyphon loop is lacking in the literature. The objective of this study is to understand the boiling phenomena under the above-mentioned conditions and to investigate their effectiveness in electronics cooling applications. Experiments were carried out in a thermosyphon setup at 9.7, 15 and 21 kPa saturation pressures for two different enhancement structure geometries at varying heat loads (1–170 W). The experimental investigation showed that very high heat fluxes (≥ 80 W/cm2) can be achieved by boiling at sub-atmospheric pressures with enhancement structures. It is observed that with decreasing system pressure, the surface temperature also decreased for all the heat loads. The surface temperatures attained were well below the acceptable value of 85° C for all the cases.

Computer Modeling of a Tire under Cornering Loads

1989 ◽  
Vol 17 (2) ◽  
pp. 86-99 ◽  
Author(s):  
I. Gardner ◽  
M. Theves
Keyword(s):  
Finite Element Analysis ◽  
Geometric Approach ◽  
Lateral Force ◽  
Slip Angle ◽  
Element Analysis ◽  
Pressure Distributions ◽  
Slip Effects ◽  
Improved Accuracy ◽  
Nonlinear Geometric ◽  
Good Agreement

Abstract During a cornering maneuver by a vehicle, high forces are exerted on the tire's footprint and in the contact zone between the tire and the rim. To optimize the design of these components, a method is presented whereby the forces at the tire-rim interface and between the tire and roadway may be predicted using finite element analysis. The cornering tire is modeled quasi-statically using a nonlinear geometric approach, with a lateral force and a slip angle applied to the spindle of the wheel to simulate the cornering loads. These values were obtained experimentally from a force and moment machine. This procedure avoids the need for a costly dynamic analysis. Good agreement was obtained with experimental results for self-aligning torque, giving confidence in the results obtained in the tire footprint and at the rim. The model allows prediction of the geometry and of the pressure distributions in the footprint, since friction and slip effects in this area were considered. The model lends itself to further refinement for improved accuracy and additional applications.

Sign in / Sign up

Export Citation Format

Share Document