scholarly journals Analysis of Wetting Characteristics on Microstructured Hydrophobic Surfaces for the Passive Containment Cooling System

2015 ◽  
Vol 2015 ◽  
pp. 1-6 ◽  
Author(s):  
Wei Zhao ◽  
Xiang Zhang ◽  
Chunlai Tian ◽  
Zhan Gao
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Performance ◽  
Cooling System ◽  
Heat Removal ◽  
Interface State ◽  
Transfer Performance ◽  
Hydrophobic Property ◽  
High Mechanical Strength ◽  
Feasible Solutions ◽  
Baxter Model

As the heat transfer surface in the passive containment cooling system, the anticorrosion coating (AC) of steel containment vessel (CV) must meet the requirements on heat transfer performance. One of the wall surface ACs with simple structure, high mechanical strength, and well hydrophobic characteristics, which is conductive to form dropwise condensation, is significant for the heat removal of the CV. In this paper, the grooved structures on silicon wafers by lithographic methods are systematically prepared to investigate the effects of microstructures on the hydrophobic property of the surfaces. The results show that the hydrophobicity is dramatically improved in comparison with the conventional Wenzel and Cassie-Baxter model. In addition, the experimental results are successfully explained by the interface state effect. As a consequence, it is indicated that favorable hydrophobicity can be obtained even if the surface is with lower roughness and without any chemical modifications, which provides feasible solutions for improving the heat transfer performance of CV.

scholarly journals Enhanced heat transfer characteristics of conjugated air jet impingement on a finned heat sink

2017 ◽  
Vol 21 (1 Part A) ◽  
pp. 279-288 ◽  
Author(s):  
Shuxia Qiu ◽  
Peng Xu ◽  
Liping Geng ◽  
Arun Mujumdar ◽  
Zhouting Jiang ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Enhancement ◽  
Heat Sink ◽  
Heat Transfer Performance ◽  
Cooling System ◽  
Flow Characteristics ◽  
Jet Impingement ◽  
Transfer Performance ◽  
Transfer Enhancement ◽  
Air Jet

Air jet impingement is one of the effective cooling techniques employed in micro-electronic industry. To enhance the heat transfer performance, a cooling system with air jet impingement on a finned heat sink is evaluated via the computational fluid dynamics method. A two-dimensional confined slot air impinging on a finned flat plate is modeled. The numerical model is validated by comparison of the computed Nusselt number distribution on the impingement target with published experimental results. The flow characteristics and heat transfer performance of jet impingement on both of smooth and finned heat sinks are compared. It is observed that jet impingement over finned target plate improves the cooling performance significantly. A dimensionless heat transfer enhancement factor is introduced to quantify the effect of jet flow Reynolds number on the finned surface. The effect of rectangular fin dimensions on impingement heat transfer rate is discussed in order to optimize the cooling system. Also, the computed flow and thermal fields of the air impingement system are examined to explore the physical mechanisms for heat transfer enhancement.

The Effect of Initial Cross Flow on the Cooling Performance of a Narrow Impingement Channel

2005 ◽  
Vol 127 (4) ◽  
pp. 358-365 ◽  
Author(s):  
Andrew C. Chambers ◽  
David R. H. Gillespie ◽  
Peter T. Ireland ◽  
Geoffrey M. Dailey
Keyword(s):  
Heat Transfer ◽  
Large Scale ◽  
Heat Transfer Performance ◽  
Cooling System ◽  
Cross Flow ◽  
Scale Model ◽  
Transfer Performance ◽  
Test Technique ◽  
Turbine Blade Cooling ◽  
Turbine Cooling

Impingement channels are often used in turbine blade cooling configurations. This paper examines the heat transfer performance of a typical integrally cast impingement channel. Detailed heat transfer coefficient distributions on all heat transfer surfaces were obtained in a series of low temperature experiments carried out in a large-scale model of a turbine cooling system using liquid crystal techniques. All experiments were performed on a model of a 19-hole, low aspect ratio impingement channel. The effect of flow introduced at the inlet to the channel on the impingement heat transfer within the channel was investigated. A novel test technique has been applied to determine the effect of the initial cross flow on jet penetration. The experiments were performed at an engine representative Reynolds number of 20,000 and examined the effect of additional initial cross flow up to 10 percent of the total mass flow. It was shown that initial cross flow strongly influenced the heat transfer performance with just 10 percent initial cross flow able to reduce the mean target plate jet effectiveness by 57 percent.

Effect of Protuberances in the Heat Transfer Enhancement in Mini-Channels

2021 ◽  
Author(s):  
Ariel Cruz Diaz ◽  
Gerardo Carbajal
Keyword(s):  
Heat Transfer ◽  
Numerical Simulation ◽  
Pressure Drop ◽  
Heat Transfer Enhancement ◽  
Heat Transfer Performance ◽  
Heat Removal ◽  
Working Fluid ◽  
Transfer Performance ◽  
Transfer Enhancement ◽  
Mini Channels

Abstract This study presents the effects of adding an array of protrusions in a microchannel for heat transfer enhancement. The presence of mini-channels increases the overall heat transfer area and boosts the mixing development near the solid-fluid interaction; therefore, it can remove more heat than conventional mini-channels without protuberances. A numerical study proved that protuberances in a mini-channel increase the heat transfer performance by disturbing the relative fluid motion near the solid wall. The numerical simulation was performed with three different protuberances arrays: aligned, staggered, and angular. Each array consists of a thin flat plate with a hemispherical shape; the working fluid and the solid materials were water and copper. The study also includes the effect of different Reynolds numbers: 1,000, 1,500, and 2,000. Three heat inputs were applied in the numerical simulation; these were 1W, 3W, and 5W. The study was compared with a simple microchannel with non-protuberances to analyze the microchannel performance regarding heat removal and pressure drop. For heat transfer performance, the best array was the staggering array with a maximum heat removal increase of 5.26 percent. In terms of pressure drop performance, the best array was the aligned array, with a maximum increase of 34.73 percent.

Design Optimization of Magnetic Fluid Cooling System

2012 ◽  
Author(s):  
J. Lee ◽  
T. Nomura ◽  
E. M. Dede
Keyword(s):  
Magnetic Field ◽  
Heat Transfer ◽  
Design Optimization ◽  
Magnetic Fluid ◽  
Heat Transfer Performance ◽  
Cooling System ◽  
Maximum Temperature ◽  
Transfer Performance ◽  
Field Source ◽  
The Magnetic Field

This paper introduces topology design optimization for a magnetically controlled convective heat transfer cooling system. It is well known that a stationary magnetic field subjected to a temperature gradient generates fluid motion in a magnetic fluid (e.g. ferrofluid). This physical phenomenon may be exploited to drive convective motion in the cooling system to maximize the heat transfer performance. Here, the magnetic field source layout of the system is designed to enhance the heat transfer performance. More specifically, the distribution and magnetization direction of the permanent magnet (PM) field source is optimized to minimize the maximum temperature of a closed loop heat transfer system. The design optimization is performed using a gradient-based topology optimization method with a fully coupled non-linear analysis for magnetic-thermal-fluid systems. Interestingly, magnet designs similar to Halbach arrays are obtained as the optimal PM layout. The magnetic field distribution generated by the designed layout affects the body force that the fluid is subjected to and results in unique fluid flow patterns for maximum cooling performance of the system. Thus, this paper will provide an explanation of the design optimization procedure and provide the design result.

Effect of Materials’ Wettability on the Heat Transfer Performance of Fluid Flowing through Microchannel by Lattice Boltzmann Method

2011 ◽  
Vol 320 ◽  
pp. 347-352
Author(s):  
Jing Cui ◽  
Wei Zhong Li ◽  
Yang Liu
Keyword(s):  
Heat Transfer ◽  
Lattice Boltzmann Method ◽  
Lattice Boltzmann ◽  
Heat Transfer Performance ◽  
Numerical Approach ◽  
Transfer Performance ◽  
Hydrophobic Property ◽  
Cold Walls ◽  
Boltzmann Method

The material’s wettability plays an important role in the field of micro-fluid flow. In this paper, the effect of material’s wettiability on heat transer performance of fluid flowing through the microchannel has been investigated by numerical approach. The process of the hot liquid flowing through a microchannel with cold walls, whose materials possess different wettabilities, is simulated by lattice Boltzmann method (LBM). The results indicate the heat transfer performance is deteriorated with surface hydrophobic property becomes better. It is because that, for thehydrophobic material, the attractive force of the fluid/solid interaction is small and the flow velocity will be larger which will lead to heat exchang become insufficient. Especially, for the ideal-hydrophobic material, the heat transfer coefficient will be reduced notably. In this case, a gas formed between liquid and soild surface will play a role of the heat insulating layer since the thermal conductivity of the gas is relatively small compared to that of liquid.

Formation of Nano-Adsorption Layer and Its Effects on Nanofluid Spray Heat Transfer Performance

2015 ◽  
Vol 137 (2) ◽  
Author(s):  
Tong-Bou Chang
Keyword(s):  
Heat Transfer ◽  
Layer Thickness ◽  
Adsorption Layer ◽  
Heat Transfer Performance ◽  
Cooling System ◽  
Heated Surface ◽  
Spray Cooling ◽  
Working Fluid ◽  
Transfer Performance ◽  
Test Pieces

For spray cooling using nanofluid as the working fluid, a nano-adsorption layer is formed on the heated surface and affects the heat transfer performance of the cooling system. This study performs an experimental investigation into the formation of this nano-adsorption layer and its subsequent effects on the spray heat transfer performance of a cooling system using Al2O3–water nanofluid as the working fluid. The experiments consider four different nanoparticle volume fractions (i.e., 0 vol. %, 0.001 vol. %, 0.025 vol. %, and 0.05 vol. %) and two different surface roughnesses (i.e., 0.1 μm and 1.0 μm). The experimental results show that the 0.001 vol. % nanofluid yields the optimal heat transfer performance since most of the nanoparticles rebound from the heated surface directly on impact or are washed away by subsequently arriving droplets. The surface compositions of the spray-cooled specimens are examined using scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDS). The results reveal that for all of the nanofluids, a nano-adsorption layer is formed on the surface of the spray-cooled test pieces. Moreover, the layer thickness increases with an increasing nanoparticle concentration. A greater nano-adsorption layer thickness not only results in a higher thermal resistance but also reduces the effect of the surface roughness in enhancing the heat transfer performance. In addition, the nano-adsorption layer absorbs the nanofluid droplets under the effects of capillary forces, and therefore reduces the contact angle, which induces a hydrophilic surface property.

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