As an increasing attention towards sustainable development of energy and environment, the power electronics (PEs) are gaining more and more attraction on various energy systems. The insulated gate ...bipolar transistor (IGBT), as one of the PEs with numerous advantages and potentials for development of higher voltage and current ratings, has been used in a board range of applications. However, the continuing miniaturization and rapid increasing power ratings of IGBTs have remarkable high heat flux, which requires complex thermal management. In this paper, studies of the thermal management on IGBTs are generally reviewed including analyzing, comparing, and classifying the results originating from these researches. The thermal models to accurately calculate the dynamic heat dissipation are divided into analytical models, numerical models, and thermal network models, respectively. The thermal resistances of current IGBT modules are also studied. According to the current products on a number of IGBTs, we observe that the junction-to-case thermal resistance generally decreases inversely in terms of the total thermal power. In addition, the cooling solutions of IGBTs are reviewed and the performance of the various solutions are studied and compared. At last, we have proposed a quick and efficient evaluation judgment for the thermal management of the IGBTs depended on the requirements on the junction-to-case thermal resistance and equivalent heat transfer coefficient of the test samples.
Pool boiling is an effective heat transfer process in a wide range of applications related to energy conversion, including power generation, solar collectors, cooling systems, refrigeration and air ...conditioning. By considering the broad range of applications, any improvement in higher heat-removal yield can ameliorate the ultimate heat usage and delay or even avoid the occurrence of system failures, thus leading to remarkable economic, environmental and energy efficiency outcomes. A century of research on ameliorating critical heat flux (CHF) has focused on altering the boiling surface characteristics, such as its nucleation site density, wettability, wickability and heat transfer area, by many innovative techniques. Due to the remarkable interest of using nanoparticle deposition on boiling surfaces, this review is targeted towards investigating whether or not metal oxide nanoparticles can modify surface characteristics to enhance the CHF. The influence of nanoparticle material, thermo-physical properties, concentration, shape, and size are categorized, and the inconsistency or contradictions of the existing research results are recognized. In the following, nanoparticle deposition methods are presented to provide a worthwhile alternative to deposition rather than nanofluid boiling. Furthermore, possible mechanisms and models are identified to explain the amelioration results. Finally, the present status of nanoparticle deposition for CHF amelioration, along with their future challenges, amelioration potentials, limitations, and their possible industrial implementation, is discussed.
Corrugating channel wall is considered to be an efficient procedure for achieving improved heat transfer. Further enhancement can be obtained through the utilization of nanofluids and porous media ...with high thermal conductivity. This paper presents the effect of geometrical parameters for the determination of an appropriate configuration. Furthermore, the optimization of forced convective heat transfer and fluid/nanofluid flow through a sinusoidal wavy-channel inside a porous medium is performed through the optimization of entropy generation. The fluid flow in porous media is considered to be laminar and Darcy-Brinkman-Forchheimer model has been utilized. The obtained results were compared with the corresponding numerical data in order to ensure the accuracy and reliability of the numerical procedure. As a result, increasing the Darcy number leads to the increased portion of thermal entropy generation as well as the decreased portion of frictional entropy generation in all configurations. Moreover, configuration with wavelength of 10 mm, amplitude of 0.5 mm and phase shift of 60° was selected as an optimum geometry for further investigations on the addition of nanoparticles. Additionally, increasing trend of average Nusselt number and friction factor, besides the decreasing trend of performance evaluation criteria (PEC) index, were inferred by increasing the volume fraction of the nanofluid (Al
O
and CuO).
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•Effect of surface structuring with vertical, Inclined and orthogonal minichannels on pool boiling was investigated.•Geometry dimensions of inclined minichannels in range of 0.5–1.4 ...mm were changed.•In addition to surface area augmentation, increasing minichannel depth and decreasing pitch are enhanced boiling performance.•Fabrication of inclined minichannels with EDM method is a practical surface structuring.
Pool boiling heat transfer performance from horizontal circular surfaces with wirecutted inclined minichannels configurations, immersed in saturated water at atmospheric pressure was experimentally investigated. Further, the effect of 45° inclination, geometry dimensions (in range of 0.5–1.4mm) and orthogonal intersection of optimized minichannels which were wirecutted on copper surface was examined. The experimental results showed that the heat dissipation increases with inclined channel, increased channel depth and decrease in pitch. The orthogonally intersected minichannels exhibited the highest HTC and CHF, up to 170% and 65% compared to the plain surface. The improved heat transfer is attributed to bubble dynamics, heat transfer area, bubble slide and scrape, and capillary flow.
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•Pool boiling experiment performed on mesochannel, microstructured porous.•The combination of two enhancement techniques was also included.•Mesochannel was cut with EDM method on ...copper surface.•Micro porous coating was fabricated with electrodeposition method.•Boiling curves for water at atmospheric pressure was obtained.•Enhancement mechanisms identified based on nucleation site density.•Bubble-induced liquid motion and increasing surface area were also identified.
Increasing the computational capability of microelectronics and growing miniaturization trend lead to high heat flux hot spots that require efficient thermal management. Pool boiling has the ability to remove large heat fluxes at low wall superheat and this can be further enhanced by using surface modification methods. In this paper, the experimental investigation of nucleate pool boiling heat transfer on copper mesochannel, microstructured porous coating and combination of them is performed. The mesochannel with a width of 400μm and a depth of 500μm is cut with Wire Electric Discharge Machine (WEDM) on copper surface. Microstructured porous coating is prepared by two-stage electrodeposition of copper on polished copper surface. Then by the combination of these methods, porous copper electrodeposited on mesochannel to achieve the high performance boiling surface. The morphology of three samples are examined with Scanning Electronic Microscopy (SEM). The nucleate pool boiling experiments were conducted under atmospheric pressure using a water under saturation conditions and their pool boiling heat transfer performances were compared. It was found that the integration of microporous copper on microchannel surface can effectively enhance the boiling performance. A critical heat flux (CHF) of 170W/cm2 (2.1-fold enhancement) and heat transfer coefficient (HTC) of 23.5W/cm2k (3.9-fold enhancement) was obtained in comparison to plain surface. A visualization study on bubble formation and release from individual plates was conducted to bolster the experimental results.
In this paper, the compressive stress of pristine and coated vertically-aligned (VA) multi-walled (MW) carbon nanotube (CNT) pillars were investigated using flat-punch nano-indentation. VA-MWCNT ...pillars of various diameters (30–150 µm) grown by low-pressure chemical vapor deposition on silicon wafer. A conformal brittle coating of niobium-titanium-nitride with high superconductivity temperature was deposited on the VA-MWCNT pillars using atomic layer deposition. The coating together with the pillars could form a superconductive vertical interconnect. The indentation tests showed foam-like behavior of pristine CNTs and ceramic-like fracture of conformal coated CNTs. The compressive strength and the elastic modulus for pristine CNTs could be divided into three regimes of linear elastic, oscillatory plateau, and exponential densification. The elastic modulus of pristine CNTs increased for a smaller pillar diameter. The response of the coated VA-MWCNTs depended on the diffusion depth of the coating in the pillar and their elastic modulus increased with pillar diameter due to the higher sidewall area. Tuning the material properties by conformal coating on various diameter pillars enhanced the mechanical performance and the vertical interconnect access (via) reliability. The results could be useful for quantum computing applications that require high-density superconducting vertical interconnects and reliable operation at reduced temperatures.
Nanostructured microporous surfaces were electrodeposited at various electrolyte temperatures on copper substrate to investigate the saturated pool boiling enhancement of distilled water at ...atmospheric pressure. Surface structure topography and wickability were analyzed to investigate their relation to critical heat flux. Scanning electron microscope showed that the micro-clusters have nanostructures from cubic at 5°C to dendritic at 60°C electrolyte temperature. Rate-of-rise experiments demonstrated that dendritic copper structure has the best capillary performance. The experimental results of pool boiling heat transfer indicate that the critical heat flux increased with surface wickability. Electrodeposited porous surface in hot electrolyte showed the highest critical heat flux and heat transfer coefficient of the 124 W/cm
2
and 17 W/cm
2
K, respectively, which is 50% and 270% higher than that of plain surface. However, the two-step electrodeposition and annealing were used in fabrication of surfaces, but the mechanical strength of layer needs more improvement by changing the electrochemical process parameters.
•Combination of nanocoating, microchannel inclination and reentrancy enhance boiling.•Hydrophilic fin and hydrophobic channel increase 120% HTC compare to polished copper.•This study was investigated ...effect of silver nanocoating on structured surfaces.•Durability of the coating is as important as its effect in enhancing pool boiling.
Silver nanoparticles were deposited on copper substrate by boiling a new industrial nanofluid (DZ nanocoolant) in two different concentrations to investigate the saturated pool boiling enhancement of distilled water under atmosphere pressure. Microstructure, surface topography, and contact angle of the surfaces were examined. The optimum concentration with hydrophobic characteristics was deposited on the re-entrant inclined minichannel. Effects of reentrancy and hydrophobicity on bubble dynamics were observed and pool boiling curves were compared. As the nanoparticle concentration increased, the cluster deposition and hydrophobicity increased, however the deposition stability was decreased. The experimental results indicated that by increasing the nanofluid concentration to reach nanocoated polished surface, the critical heat flux (CHF) and heat transfer coefficient (HTC) of pool boiling increased. Nano-fins are introduced as a new concept for heat transfer enhancement. It was observed that inclination and reentrancy enhanced pool boiling performance in comparison with polished copper. Finally, as expected, the combined modification including coating the surface with deposited silver nanoparticles in internal side of re-entrant inclined minichannel possesses the highest CHF and HTC of 196W/cm2 and 10W/cm2K, respectively which are 120% and 100% higher than those of the plain surface.
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•Vertically-aligned multi-walled carbon nanotube(VA-MWCNT) was synthesized by low-pressure chemical vapour deposition(LPCVD).•Effect of synthesis parameters on the near-to-mid ...infrared absorption of the forest was measured at various incident angles.•As synthesize time and temperature rising, height of the MWCNT forest was increased and other properties were changed.•Increased height of the forest results in increased absorption and reduced absorption coefficient.•Circular graphite waveguide system was proposed to model the absorption characteristics.
In this paper, the growth of optimized vertically aligned multi-walled carbon nanotube (VA-MWCNT) forests by LPCVD method for use in a large-area absorber in infrared detectors is presented. The effect of synthesis temperature (500−700 °C) and time (1−10 min) on the optical absorption coefficient in the infrared (2−20 μm) is investigated by FT-IR measurement at various incident angles (15-80°). The structural properties of VA-MWCNT are characterized by SEM, TEM and Raman spectroscopy. Spectral measurements show an increasing absorption with the height of the forest that results at increased synthesis time and temperature. However, the absorption coefficient decreases with increasing synthesize time and temperature, while it is also affected by other properties, such as diameter, density, alignment, and uniformity. Moreover, the reduction in absorption at oblique incident angles demonstrates the relevance of surface properties. Finally, a circular graphite waveguide system is used to model the absorption characteristics of an MWCNT forest.
Copper nanowires (NWs) were constructed on a dendritic copper powder precursor by a facile thermal oxidation–reduction method. First, copper oxide NWs were grown from high purity dendritic copper ...powder by thermal oxidation at 500°C. Next, these oxide NWs were reduced to copper NWs under a hydrogen flow at two different temperatures of 220 and 500°C. Oxide NW diameters distribution was in the range of 50–105 nm with length ranging from 1 to 5 µm while copper NWs were shorter and wider. A time-dependent study of oxide NWs growth was carried out. The morphology, composition and crystal structure of the resulting products were characterised by X-ray diffraction and scanning electron microscope. The results indicated that the final product of oxidation process was dispersed cupric oxide (CuO) NW whose density and length increased with time. Furthermore, it was observed that as the reduction temperature increased, the copper NW melted and adhered to the powder surface.
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