scholarly journals WEDM of Copper for the Fabrication of Large Surface-Area Micro-Channels: A Prerequisite for the High Heat-Transfer Rate

Micromachines ◽  
2020 ◽  
Vol 11 (2) ◽  
pp. 173 ◽  
Author(s):  
Naveed Ahmed ◽  
Mohammad Pervez Mughal ◽  
Waqar Shoaib ◽  
Syed Farhan Raza ◽  
Abdulrhman M. Alahmari
Keyword(s):  
Heat Transfer ◽  
Surface Area ◽  
Electrical Discharge ◽  
Electrical Discharge Machining ◽  
High Heat ◽  
Critical Feature ◽  
Maximum Heat ◽  
High Heat Transfer ◽  
Maximum Heat Transfer ◽  
Micro Channels

To get the maximum heat transfer in real applications, the surface area of the micro-features (micro-channels) needs to be large as possible. It can be achieved by producing a maximum number of micro-channels per unit area. Since each successive pair of the micro-channels contain an inter-channels fin, therefore the inter-channels fin thickness (IFT) plays a pivotal role in determining the number of micro-channels to be produced in the given area. During machining, the fabrication of deep micro-channels is a challenge. Wire-cut electrical discharge machining (EDM) could be a viable alternative to fabricate deep micro-channels with thin inter-channels fins (higher aspect ratio) resulting in larger surface area. In this research, minimum IFT and the corresponding machining conditions have been sought for producing micro-channels in copper. The other attributes associated with the micro-channels have also been deeply investigated including the inter-channels fin height (IFH), inter-channels fin radius (IFR) and the micro-channels width (MCW). The results reveal that the inter-channels fin is the most critical feature to control during the wire electrical discharge machining (WEDM) of copper. Four types of fin shapes have been experienced, including the fins: broken at the top end, deflected at the top end, curled bend at the top, and straight with no/negligible deflection.

Heat Transfer Enhancement by Sinusoidal Motion of a Water-Based Nanofluid

2019 ◽  
Vol 11 (4) ◽  
Author(s):  
Omer F. Guler ◽  
Oguz Guven ◽  
Murat K. Aktas
Keyword(s):  
Heat Transfer ◽  
Capillary Tube ◽  
Tube Bundle ◽  
Measured Temperature ◽  
Maximum Displacement ◽  
Maximum Heat ◽  
Transfer Rates ◽  
High Heat Transfer ◽  
Maximum Heat Transfer ◽  
Experimental Apparatus

The oscillatory flows are often utilized in order to augment heat transfer rates in various industrial processes. It is also a well-known fact that nanofluids provide significant enhancement in heat transfer at certain conditions. In this research, heat transfer in an oscillatory pipe flow of both water and water–alumina nanofluid was studied experimentally under low frequency regime laminar flow conditions. The experimental apparatus consists of a capillary tube bundle connecting two reservoirs, which are placed at the top and the bottom ends of the capillary tube bundle. The upper reservoir is filled with the hot fluid while the lower reservoir and the capillary tube bundle are filled with the cold fluid. The oscillatory flow in the tube bundle is driven by the periodic vibrations of a surface mounted on the bottom end of the cold reservoir. The effects of the frequency and the maximum displacement amplitude of the vibrations on thermal convection were quantified based on the measured temperature and acceleration data. It is found that the instantaneous heat transfer rate between de-ionized (DI) water (or the nanofluid)-filled reservoirs is proportional to the exciter displacement. Significantly reduced maximum heat transfer rates and effective thermal diffusivities are obtained for larger capillary tubes. The nanofluid utilized oscillation control heat transport tubes achieve high heat transfer rates. However, heat transfer effectiveness of such systems is relatively lower compared to DI water filled tubes.

scholarly journals Wettability and nanostructure effect on oscillating heat pipes

2015 ◽  
Author(s):  
◽  
Feng Zhao Zhang
Keyword(s):  
Heat Transfer ◽  
High Heat ◽  
High Heat Flux ◽  
Maximum Heat ◽  
Oscillating Heat Pipe ◽  
Maximum Heat Transfer ◽  
Heat Transfer Limit ◽  
Efficient Heat Transfer ◽  
Oscillating Motion ◽  
Transfer Device

As electronics technologies rapidly develop with a demand for more power and miniaturization, effective thermal management of these systems becomes much more important. The oscillating heat pipe (OHP) is a promising highly efficient heat transfer device that is great for high heat flux applications common in the electronics industry. In the current investigation, the wettability effect on the heat transfer performance of OHPs has been conducted. 1). The overall performance of configuration of hydrophilic evaporator/ hydrophobic condenser and hydrophobic evaporator/ hydrophilic condenser was worse than the nontreated OHP, however; the oscillations were much damper when comparing the amplitudes. 2). High oscillating motion occurs in the OHP with the hydrophilic surface while low oscillating motion occurs in the untreated OHP. 3). A mathematical model shows that contact angle increases the oscillating motion decreases. 4). A theoretical model predicting operating limit is developed. Results show that radius and charging ratio has a large effect on the maximum heat transfer limit. Working fluids changes the operating limit.

Computational Development of a Gas to Liquid Heat Exchanger With a Breathing Operation

2010 ◽  
Author(s):  
Richard N. Jorgenson ◽  
James D. Van de Ven
Keyword(s):  
Heat Transfer ◽  
Surface Area ◽  
Fitness Function ◽  
Liquid Bath ◽  
Nsga Ii ◽  
Maximum Heat ◽  
Pressure Drops ◽  
Maximum Heat Transfer ◽  
Compression And Expansion ◽  
3D Elements

Thermal conditioning of a gas during compression and expansion processes requires rapid transfer of heat. Proposed is a thin flexible membrane with a biologically-inspired, lung-like structure characterized by branching tubes, massive surface area, and low overall pressure drops. By forcing the working gas into contact with the large surface area of a thin membrane, rapid heat transfer may be achieved across the membrane and into a liquid bath. Inspiration and expiration of the gas is driven by volume changes in the liquid bath. A computational approach is taken to the design of the lung-like structure. First, Non-dominated Sorting Genetic Algorithm II (NSGA-II) is run to optimize elemental geometries for minimum pressure drop and maximum heat transfer. In the initial case, 2D elements are passed through Gambit and Fluent to evaluate the fitness function. Here, we present the results of the elemental optimization. In the future, 3D elements will be analyzed and connected in an optimal way to generate a 3D lung-like structure.

Guidelines for Designing Micropillar Structures for Enhanced Evaporative Heat Transfer

2021 ◽  
Author(s):  
Kidus Guye ◽  
De Dong ◽  
Yunseo Kim ◽  
Hyoungsoon Lee ◽  
Baris Dogruoz ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Interfacial Area ◽  
High Heat ◽  
Heat Fluxes ◽  
Air Cooling ◽  
Transfer Coefficients ◽  
Two Phase ◽  
Maximum Heat ◽  
Maximum Heat Transfer ◽  
Evaporation Heat

Abstract Over the last several decades, cooling technologies have been developed to address the growing thermal challenges associated with high-powered electronics. However, within the next several years, the heat generated by these devices is predicted to exceed 1 kW/cm2, and traditional methods, such as air cooling, are limited in their capacities to dissipate such high heat fluxes. In contrast, two-phase cooling methods, such as microdroplet evaporation, are very promising due to the large latent heat of vaporization associated with the phase change process. Previous studies have shown non-axisymmetric droplets exhibit different evaporation characteristics than spherical droplets. For a droplet pinned atop a micropillar, the solid-liquid and liquid-vapor interfacial area, the volume, and thickness of the droplet are the major factors that govern the evaporation heat transport process. In this work, we develop a shape optimization tool using the particle swarm optimization algorithm to maximize evaporation from a droplet confined atop a micropillar. The tool is used to optimize the shape of a nonaxisymmetric droplet. Compared to droplets atop circular and regular equilateral triangular micropillar structures, we find that droplets confined on pseudo-triangular micropillar structures have 23.7% and 5.7% higher heat transfer coefficients, respectively. The results of this work will advance the design of microstructures that support droplets with maximum heat transfer performance.

Enhanced Pool Boiling Performance on Micro-, Nano-, and Hybrid-Structured Surfaces

2011 ◽  
Author(s):  
Qian Li ◽  
Wei Wang ◽  
Chris Oshman ◽  
Benoit Latour ◽  
Chen Li ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Thermal Management ◽  
Pool Boiling ◽  
High Heat ◽  
High Heat Flux ◽  
Maximum Heat ◽  
Structured Surfaces ◽  
Maximum Heat Transfer ◽  
Functional Components

Thermal management plays an important role in both high power electronics and energy conversion systems. A key issue in thermal management is the dissipation of the high heat flux generated by functional components. In this paper, various microstructures, nanostructures and hybrid micro/nano-structures were successfully fabricated on copper (Cu) surfaces, and the corresponding pool boiling heat transfer performance was systematically studied. It is found that the critical heat flux (CHF) of hybrid structured surfaces is about 15% higher than that of the surfaces with nanowires only and micro-pillars only. More importantly, the superheat at CHF for the hybrid structured surface is much smaller than that of the micro-pillared surface (about 35%), and a maximum heat transfer coefficient (HTC) of about 90,000W/m2K is obtained. Compared with the known best pool boiling performance on biporous media, a much larger HTC and much lower superheat at a heat flux of 250W/cm2 have been obtained on the novel hybrid-structured surfaces.

Determination of Optimal Row Spacing for a Staggered Cross-Pin Array in a Turbine Blade Cooling Passage

1998 ◽  
Author(s):  
E. E. Donahoo ◽  
A. K. Kulkarni ◽  
A. D. Belegundu ◽  
C. Camci
Keyword(s):  
Heat Transfer ◽  
Turbine Blade ◽  
Total Pressure ◽  
Reynolds Numbers ◽  
Steady Increase ◽  
Maximum Heat ◽  
High Heat Transfer ◽  
Maximum Heat Transfer ◽  
Wide Range ◽  
Cooling Passage

Crosspin configurations are of interest in turbine blade design due to the enhanced cooling they provide. In addition, crosspins which extend from the walls of hollow blades provide structural integrity and stiffness to the blade itself. Numerous crosspin shapes and arrangements are possible, but only certain combinations offer high heat transfer capability while maintaining low overall total pressure loss. This study presents results from 2-D numerical simulations of coolant airflow through a turbine blade internal cooling passage. The simulations model viscous flow and heat transfer over circular pins in a staggered arrangement of varying pin spacing. Preliminary analysis over a wide range of Reynolds numbers indicates existence of an optimal spacing for which maximum heat transfer and minimum total pressure drop occurs. Pareto plots, which graphically identify the optimum data points with multiple optimization parameters, were obtained for a range of Reynolds numbers and streamwise soarings in a staggered crosspin arrangement. There is a steady increase in crosspin heat transfer up to a certain number of rows, then a gradual decrease in heat transfer in subsequent rows. Knowledge obtained from such findings can be used to determine the number of crosspins used, as well as the ultimate pin arrangement.

Development of Heat Sinks for Air Cooling and Water Cooling Using Lotus-Type Porous Metals

2011 ◽  
Author(s):  
H. Chiba ◽  
T. Ogushi ◽  
H. Nakajima
Keyword(s):  
Heat Transfer ◽  
Porous Materials ◽  
Heat Sink ◽  
High Heat ◽  
Heat Sinks ◽  
Air Cooling ◽  
Water Cooling ◽  
Cooling Performance ◽  
High Heat Transfer ◽  
Micro Channels

In recent years, since heat dissipation rates and high frequency electronic devices have been increasing, a heat sink with high heat transfer performance is required to cool these devices. Heat sink utilizing micro-channels with several ten microns are expected to provide an excellent cooling performance because of their high heat transfer capacities due to small channel. Therefore, various porous materials such as cellular metals have been investigated for heat sink applications. However, heat sink using conventional porous materials has a high pressure drop because the cooling fluid flow through the pores is complex. Among the described porous materials, a lotus-type porous metal with straight pores is preferable for heat sinks due to the small pressured drop. In present work, cooling performance of the lotus copper heat sink for air cooling and water cooling is introduced. The experimental data for air cooling show 13.2 times higher than that for the conventional groove fins. And, the data for the water cooling show 1.7 times higher than that for the micro-channels. It is concluded that lotus copper heat sink is the most prospective candidate for high power electronics devices.

scholarly journals Numerical Investigation of Heat Transfer and Friction Factor Characteristics in a Circular Tube Fitted with V-Cut Twisted Tape Inserts

2013 ◽  
Vol 2013 ◽  
pp. 1-8 ◽  
Author(s):  
Sami D. Salman ◽  
Abdul Amir H. Kadhum ◽  
Mohd S. Takriff ◽  
Abu Bakar Mohamad
Keyword(s):  
Heat Transfer ◽  
Friction Factor ◽  
Numerical Investigation ◽  
Heat Transfer Rate ◽  
Transfer Rate ◽  
Twisted Tape ◽  
Maximum Heat ◽  
High Heat Transfer ◽  
Maximum Heat Transfer ◽  
Twist Ratio

Numerical investigation of the heat transfer and friction factor characteristics of a circular fitted with V-cut twisted tape (VCT) insert with twist ratio (y=2.93) and different cut depths (w=0.5, 1, and 1.5 cm) were studied for laminar flow using CFD package (FLUENT-6.3.26). The data obtained from plain tube were verified with the literature correlation to ensure the validation of simulation results. Classical twisted tape (CTT) with different twist ratios (y=2.93, 3.91, 4.89) were also studied for comparison. The results show that the enhancement of heat transfer rate induced by the classical and V-cut twisted tape inserts increases with the Reynolds number and decreases with twist ratio. The results also revealed that the V-cut twisted tape with twist ratioy=2.93and cut depthw=0.5 cm offered higher heat transfer rate with significant increases in friction factor than other tapes. In addition the results of V-cut twist tape compared with experimental and simulated data of right-left helical tape inserts (RLT), it is found that the V-cut twist tape offered better thermal contact between the surface and the fluid which ultimately leads to a high heat transfer coefficient. Consequently, 107% of maximum heat transfer was obtained by using this configuration.

High Efficiency Heat Sinks from Polycrystalline Diamond Grown by CVD Method

2006 ◽  
Vol 956 ◽  
Author(s):  
Oleg A. Voronov ◽  
Gary S. Tompa ◽  
Veronika Veress
Keyword(s):  
Heat Transfer ◽  
Semiconductor Lasers ◽  
High Efficiency ◽  
Heat Removal ◽  
High Heat ◽  
Heat Fluxes ◽  
Heat Sinks ◽  
Measuring System ◽  
High Heat Transfer ◽  
Micro Channels

ABSTRACTWhile absolute power levels in microelectronic devices are relatively modest (a few tens to a few hundred watts), heat fluxes can be significant (through 50 W/cm2 in current electronic chips and up to 2000 W/cm2 in semiconductor lasers). Diamond heat sinks enable heat transfer rates well above what is possible with standard thermal management devices. We have fabricated heat sinks using diamond, which has the highest temperature thermal conductivity of any known material. Polycrystalline diamonds manufactured by chemical vapor deposition (CVD) are machined by laser and combined with metallic or ceramic tiles. Cooling by fluid flow through micro-channels enhances heat removal. These unique attributes make diamond based heat sinks prime contenders for the next generation of high heat load sinks. Such devices could be utilized for efficient cooling in a variety of applications requiring high heat transfer capability, including semiconductor lasers, microprocessors, multi-chip modules in computers, laser-diode arrays, radar systems, and high-flux optics, among other applications. This paper will review test designs, heat flux measuring system, and measured heat removal values.

Numerical Prediction of Flow and Heat Transfer Rates in Metal Based Microchannels Using Lattice Boltzmann Method

2008 ◽  
Author(s):  
Pritish R. Parida ◽  
Srinath V. Ekkad
Keyword(s):  
Heat Transfer ◽  
Lattice Boltzmann ◽  
Heat Dissipation ◽  
Transfer Problem ◽  
High Heat ◽  
Lattice Boltzmann Model ◽  
Channel Height ◽  
High Heat Transfer ◽  
Viscous Heat ◽  
Micro Channels

Metal-based Microchannel Heat Exchangers (MHEs) are of current interest due to the combination of high heat transfer performance and improved mechanical integrity. In the present work, a simple two-dimensional thermal lattice Boltzmann model without viscous heat dissipation and pressure compressible work has been developed to simulate the heat transfer phenomenon in Cu- and Al-based micro-channels. A 2D fluid-solid conjugate heat transfer problem is solved using LBM and Fluent. For the Cu specimen, the height of the channel considered was 204 μm and the top and bottom wall thickness was taken to be same as the channel height. The LBM results were compared with 3D and 2D fluent models. The study also compares the numerically computed velocity profile with the analytical results and compares the Nusselt number values predicted by LBM and Fluent with the experimental data. Owing to the simplicity of the thermal LB model, promising results were obtained from the LBM predictions.

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