Sintered Copper Powder Research Articles

Anti-Gravity Loop-shaped heat pipe with graded pore-size wick

Abstract An Anti-Gravity Loop-Shaped Heat Pipe (AGLSHP) with a Continuous Graded Pore-Size Wick (CGPSW) was developed for the cooling of electronic devices at the anti-gravity orientation on the ground. At this orientation, heat is transferred toward the direction of the gravitational field. The AGLSHP consists of an evaporator, a condenser, a vapor line and a liquid line. The CGPSW is formed by sintered copper powders and it is filled inside the evaporator and the liquid line. The corresponding test system was developed to investigate the start-up characteristics and heat transfer performance of the AGLSHP at the anti-gravity orientation. The experimental result shows that, the AGLSHP has the capability to start-up reliably without any temperature overshoot or oscillation at the test heat loads. And the AGLSHP is able to keep the temperature of the evaporator below 105 °C and the overall thermal resistance below 0.24 °C/W at the heat load of 100 W. It is also found that the ideal heat load range of the AGLSHP at the anti-gravity orientation is from 30 W to 90 W. In this power range the overall thermal resistance stabilizes at about 0.15 °C/W, and the maximum temperature of the evaporator is lower than 84 °C at the heat load of 90 W.

Experimental investigation on temperature oscillation in a miniature loop heat pipe with flat evaporator

In this work, a series of experiments were conducted to investigate the effect of temperature oscillation on startup behavior and operating performance in a miniature LHP with flat evaporator of 8 mm thick. The evaporator with sintered copper powder wick is in series structure with compensation chamber and made of copper. Water is the working fluid. It is found that the LHP is able to start up at heat load of 15 W with temperature oscillation. And the oscillating frequency of temperature rises and amplitude decreases with increasing heat load. For the LHP in the present work, temperature oscillation is caused by insufficient driving force and phase distribution of working fluid in the compensation chamber under different heat load. The development of unstable operation in the LHP is the reflection of the re-distribution of working fluid in the loop while the hydrodynamic and thermal equilibrium of the loop is broken and re-built repeatedly. For specific heat load, high operating temperature can improve the operating stability of LHP due to large capillary force.

Fabrication and testing of phase change heat sink for high power LED

A novel phase change heat sink was fabricated for packaging cooling of high power light emitting diode (LED). 3D structures as enhanced boiling structure in the evaporation surface were composed of a spiral micro-groove along circumferential direction and radial micro-grooves which were processed by ploughing-extrusion (P-E) and stamping, respectively. Meanwhile, the cycle power of refrigerant was supplied by wick of sintered copper powder on internal surface of phase change heat sink. Operational characteristics were tested under different heat loads and refrigerants. The experimental results show that phase change heat sink is provided with a good heat transfer capability and the temperature of phase change heat sink reaches 86.8 °C under input power of 10 W LED at ambient temperature of 20 °C.

Pool Boiling Performance Comparison of Smooth and Sintered Copper Surfaces with and Without Carbon Nanotubes

Pool boiling heat transfer is measured with two individual working fluids on copper surfaces enhanced with sintered copper powder and carbon nanotubes. The working fluids are a segregated hydrofluoroether, HFE-7300 (3M Electronic Markets Materials Division, St. Paul, MN), and deionized water. The surfaces considered in the experiments include smooth copper, copper with sintered copper particles, smooth copper with copper-coated carbon nanotubes (CNT), and copper with sintered copper particles and copper-coated carbon nanotubes. Characteristics of the resulting boiling curves are discussed and analyzed. Lower wall superheats resulted from both the sintered particles and the CNT array for both working fluids. For water, there was no additional benefit from the addition of CNTs on the sintered particle substrate. For HFE-7300, however, the hybrid (sintered with CNTs) surface achieved the lowest wall superheat at high heat fluxes. Critical heat flux for HFE-7300 increased by more than 45% for the hybrid surface relative to the smooth copper surface.

A Novel Heat Sink for High Power Light Emitting Diode-Phase Change Heat Sink

A novel heat sink was fabricated for packaging cooling of high power LED. Enhanced boiling structures in the evaporation surface were processed by ploughing-extrusion (P-E) and stamping methods, respectively. The cycle power of refrigerant was supplied by wick of sintered copper powder on internal surface of phase change heat sink. The experimental results showed that phase change heat sink was provided with a good heat transfer capability and the temperature of phase change heat sink reached 86.8°C under input power of 10W LED at ambient temperature of 20°C.

Characterization of evaporation and boiling from sintered powder wicks fed by capillary action

The thermal resistance to heat transfer into the evaporator section of heat pipes and vapor chambers plays a dominant role in governing their overall performance. It is therefore critical to quantify this resistance for commonly used sintered copper powder wick surfaces, both under evaporation and boiling conditions. The objective of the current study is to measure the dependence of thermal resistance on the thickness and particle size of such surfaces. A novel test facility is developed which feeds the test fluid, water, to the wick by capillary action. This simulates the feeding mechanism within an actual heat pipe, referred to as wicked evaporation or boiling. Experiments with multiple samples, with thicknesses ranging from 600 to 1200 μm and particle sizes from 45 to 355 μm, demonstrate that for a given wick thickness, an optimum particle size exists which maximizes the boiling heat transfer coefficient. The tests also show that monoporous sintered wicks are able to support local heat fluxes of greater than 500 W cm −2 without the occurrence of dryout. Additionally, in situ visualization of the wick surfaces during evaporation and boiling allows the thermal performance to be correlated with the observed regimes. It is seen that nucleate boiling from the wick substrate leads to substantially increased performance as compared to evaporation from the liquid free surface at the top of the wick layer. The sharp reduction in overall thermal resistance upon transition to a boiling regime is primarily attributable to the conductive resistance through the saturated wick material being bypassed.

Investigation on transient behaviors of flat plate heat pipes

By means of both experimental and theoretical approaches, this paper is aimed to study performance and mechanism of a flat plate heat pipe (FPHP) in which a layer of sintered copper powder is applied to the heated surface of the heat pipe to enhance evaporation process. The performance of the FPHP is experimentally measured under different heat fluxes, orientations and amount of the working fluid in order to investigate the effects of charge amount of the working fluid, thickness of the sintered layer, and orientation of the heat pipe on the performance of the FPHP. On basis of some assumptions, a theoretical model is proposed to simulate dynamic behavior and steady-state performance of the FPHP. The model and simulation method developed in this article are verified by the experimental results. Simulation shows that dynamic behavior of a FPHP is affected by geometrical parameters, charge amount of the working fluid and installation orientation. The porous sintered layer on the heated surface can enhance evaporation process and improve performance of the FPHP. Such a technique ensures proper operation of the heat pipe at high heat flux in arbitrary orientation. With regard to the potential application to electronic cooling, comparison between the FPHP and conventional solid heat sink is provided. Compared with the solid heat sink, the FPHP has great potential for electronic elements with high power consumption because of its unique performance of high response, efficiency, isothermal and lightweight feature.

Experimental Study of Evaporative Heat Transfer in Sintered Copper Bidispersed Wick Structures

An experiment has been carried out on evaporative heat transfer in rectangular bidispersed wick structures heatedbya groovedblock from thetop. Threebidispersedwick structures,havinglarge/smallpore-diameterratios of 200/80, 400/80, and 800/80 πm, were formed by sintering copper powder. For comparison, two monodispersed wick structures having pore diameters of 80 and 800 πm, respectively, were also tested. It was found that the heat transfer coefe cient and the critical heat e ux of a bidispersed wick are much higher than that of a monodispersed wick having its pore diameter equal to the smaller pore diameter of the bidispersed wick. It is also found that for bidispersed wicks with the same small-pore diameter there exists an optimal large-pore diameter that gives both the highest heat transfer coefe cient and the highest critical heat e ux. Finally, the effect of the adverse hydrostatic head on the heat transfer performance in the wick is shown. Nomenclature Ah = heating surface area, m 2 a = length of heating block, m h = heat transfer coefe cient, W/m 2 K K = permeability, m 2 P m = mass e ow rate, kg/m 2 s Q = heat power, W Tl = temperature of the subcooled liquid water, ± C Ts = saturation temperature, ± C Tv = temperature of the exhaust vapor, ± C TW = temperature of the heating block, ± C 1H = adverse hydrostatic head, mm = porosity Subscripts l = liquid s = saturation v = vapor w = wall

Investigations into the high-speed forging of sintered copper powder strips

The present paper reports on an investigation into the various technological aspects of the high-speed forging of sintered copper powder strips. Experiments were conducted and measurements were made in the development of barrelling, the strain variations at the free surface and densification during the high-speed forging of sintered copper powder strips at room temperature under dry and lubricated conditions. The theoretical relationship between the frictional stress at the interface and other process variables is also discussed and the results are analysed critically to illustrate the inter-action of various processing parameters involved during the high-speed forging of sintered copper powder strips, these results being presented graphically.

放電焼結における通電経路とモールド内部の温度分布

In spark sintering copper powder and alumina one with a graphite and insulated dies under a constant pressure and a constant electric current, electric voltage between electrodes and temperature distributions of die, punch and specimen were measured. And, we considered effect of the electric current paths on the spark sintering.In the first case of sintering the copper powder with the graphite die, during initial electricity, almost all the electric current went through the specimen. During sequential electricity, the electric current went through both the graphite die and the specimen. Therefore, fluctuation of temperature distribution in the specimen was decreased as the discharged time was spent.In the second case of sintering the copper powder with the insulated die, the electric current went through the graphite punch and the specimen. The fluctuation of temperature distribution in the specimen was larger than that of the case which the graphite die was used, for the specimen was not heated by the graphite die.In the third case of sintering of alumina powder with the graphite die, the electric current went through the graphite punch and the graphite die. Therefore, the temperature distribution of both the graphite mold and the specimen was considerably different from that of the case of the copper powder with the graphite die.

Dynamic effects during a high-speed sinter-forging process

The paper reports on an investigation into the various technological aspects of a high-speed sinter-forging process. Experiments were conducted and measurements were made in the development of barrelling, strain variations at the free surface and densilication during dry and lubricated high-speed cold forging of sintered copper powder discs. The relationship between the frictional stress at the interface and other process variables is discussed and an analysis is given for the calculation of pressure distribution and die load by the solution of the equations of equilibrium taking barrelling into consideration for axial symmetry and plane strain sinter-forging conditions. Results are discussed critically to illustrate the interaction of various processing parameters involved during high-speed sinter-forging process and are presented graphically.

Acoustic and dynamic properties of two-phase media with non-spherical inclusions

Abstract The propagation and attenuation of ultrasonic waves in sintered copper powder with air saturated pores is studied experimentally and theoretically in the long-wavelength approximation using the self-consistent single scattering theory. The overall dynamic and propagation properties of such an example of a two-phase composite are analysed computationally, the properties of the pure matrix material being, in the first step, determined by extrapolation from suitable ultrasonic measurements carried out at low porosities. The results presented confirm the ultrasound to be extremely useful in estimating the influence of the volume concentration and shape of the inclusions on the overall dynamic properties of multi-phase composites.

Obtaining extremely high vacuum using sintered fine copper powder as a cryosorbent

Fine copper powder (FCP), sintered to the cryopanels of cryopumps, was evaluated as a cryosorbent for H2. A Gifford–McMahon refrigerator cooled the tested cryopanel of a two‐stage cryopump. The third stage of a three‐stage cryopump that was tested was cooled by Joule–Thomson expansion of He. 30 g of FCP were sintered to the second stage panel (20 K) of the two‐stage bakeable cryopump, whereas 10 g of FCP were sintered to the third stage panel (4.3 K) of the three‐stage bakeable cryopump. Hydrogen pumping speed, capacity, and base pressure measurements are given as a function of temperature. Cryopanel preparation and system bakeout procedures, reliably leading to pressures <10−9 Pa, are given. Hydrogen thermal desorption peaks for the FCP sintered cryopanel are also reported.

Critical heat flux in pool boiling of aqueous surfactant solutions as determined by the quenching method

Pool boiling heat transfer of a copper microporous coating was experimentally studied in borated water with a concentration of boric acid from 0.0 to 5.0 vol percent (vol%) to determine the effect of boric acid on boiling heat transfer in water. A high-temperature, thermally conductive microporous coating (HTCMC) was created by sintering copper powder with an average particle size of 67 μm onto a 1 cm × 1 cm plain copper surface with a coating thickness of ~300 μm within a furnace in a vacuum environment. The tests showed that the nucleate boiling heat transfer coefficient (NBHT) of HTCMC became slightly less enhanced as the concentration of boric acid increased but the NBHT coefficient values were still significantly higher than those of the plain surface. The critical heat flux (CHF) values from 0 to 1.0 vol% were maintained at ~2,000 kW/m2, and then, they gradually decreased down to ~1,700 kW/m2 as the concentration increased further to 5.0 vol%. It is believed that the micro-scale pores of the HTCMC were partially blocked by the high boric acid concentration during the nucleate boiling such that the small bubbles were not effectively created using the HTCMC reentrant cavities as the boric acid concentration increased.

Heat Pipes for Cooling High Flux/High Power Semiconductor Chips

Results of an experimental study are reported which demonstrate the ability of heat pipes to simultaneously dissipate high heat fluxes and high total power at low surface temperatures. The application is to cooling high power density (and high total power) semiconductor chip modules. The two designs studied incorporate air or liquid cooling in the condenser sections. The air-cooled design consisted of a manifold base plate with a series of holes drilled in it each of which was lined with sintered copper powder which served as the wick. An array of wick lined tubes was attached normal to the plate and served as the condenser section. The other heat pipe was disk shaped and also had a sintered wick structure. Cooling water channels were placed over the entire periphery of the housing except in the region of heat input. Reported steady heat fluxes are up to 31 W/cm2 corresponding to total power dissipation of up to 1400 W for the water cooled heat pipe and up to 47 W/cm2 (900 W total power) for the air cooled heat pipe with surface temperatures under 100°C.

Particulates in laser-deposited copper oxide films

We have studied the particulates formed on single-phase copper oxide thin films obtained by laser deposition in a variable oxygen atmosphere. Two different targets have been used: a thick copper foil and a sintered copper powder. We conclude that there are two very different kinds of particulates. The first have very irregular morphology and very similar average size. They are due to solid debris coming from the surface target. The second kind of particulate observed has a round perimeter and is formed in the liquid phase. The morphology of the latter round particulates, which varies considerably, is dependent on the substrate and the oxygen content. Thus, we have been able to determine the conditions for growing particulate-free single-phase copper oxides.

Degree of pore-grain boundary contact during sintering

The stereological method of Aigeltinger and Exner[5] for quantifying the degree of pore-grain boundary contact by second phases has been modified to correct a bias in the computation of the extended grain boundary area. Reanalysis of the above authors’ data for sintered copper powders using the modified equation shows a degree of contact of 1.8 compared to their earlier value of 2 times the number of pore-grain boundary contacts expected from random intersections. Application of the modified equation to new data for sintered tungsten shows a similar degree of contact of 1.7 throughout all stages of sintering.

Deformation characteristics and fracturing of sintered copper powder strips during cold forging

The industrial processing of sintered powder preforms has recently been developed for manufacturing various engineering components. The present investigation has been undertaken with a view to studying the deformation characteristics and fracture mechanism during the cold forging of sintered copper powder strips. The influence of compacting pressure, sintering temperature and forging parameters on the relative density of the copper powder strip is explored. Experiments have been conducted and measurements made on the development of barrelling and strain variations at the free surface. Crack formation at the free surface has also been examined. The theoretical and experimental results are analysed and discussed critically to explain the deformation characteristics and the fracturing of sintered copper powder strips during cold forging. Results are presented graphically.

Effective thermal conductivity of sintered heat pipe wicks

The effective thermal conductivity of sintered metal materials similar to those used in heat pipe wicks has been investigated. Experimental tests were conducted using both sintered Nickel 200 and sintered copper powders over a temperature range of 25°C to 100 QC. Data were obtained for samples with several porosities in both dry and water-saturated conditions. The effective thermal conductivity of the sintered materials was found to be a function of the thermal conductivity of the solid material from which the sintered metal was made, the porosity, the mean sample temperature, and whether the material was dry or saturated. The results of the experimental investigation are presented and compared with the experimental results and analytical solutions of other investigators. Nomenclature b = dummy variable c = dummy variable ke = effective thermal conductivity k( = thermal conductivity of the liquid ks = thermal conductivity of the solid r == radius of the contact point R = radius of the powdered particles x = dummy variable a = experimental parameter P =(l-v)/(l+v) g = porosity v =*,/*. pb = bulk density of the sintered material pg = density of the solid material

Thermal resistance between phonon and quasiparticle excitations in dilute mixtures of3He in4He

As part of a Kapitza resistance study, the thermal resistance between the phonon and3He quasiparticle excitations in three dilute3He-4He mixtures (0.03%, 0.1%, and 0.3%3He) has been measured over the temperature range 20–50 mK. The results are compared with a theory based upon the Baym-Ebner interaction between the excitations. The temperature dependences agree, but the measured resistance is smaller than the theoretical resistance by a factor of ∼2 that varies inversely with concentration. This concentration-dependent phonon-quasiparticle coupling discrepancy is consistent with the results of recent heat pulse absorption experiments by Husson et al. An indirect measurement was made of the same thermal resistance in3He-4He mixtures confined within the pores of a submicrometer sintered copper powder, with the results confirming a size-effect model for the resistance.