Heat Dissipation Media Research Articles

Research Status of Heat Dissipation Technology for Electric Vehicle Drive Motors

Background:: The application of electric vehicles in daily life is becoming increasingly widespread. However, the heat dissipation issues of the electric motors directly impact electric vehicles' stability and safety. Thus, research on the heat dissipation of the electric motor is conducive to improving the reliability of the drive motor and ensuring the overall stability and safety of electric vehicles; there is a growing emphasis on the development trends of heat dissipation technologies for electric vehicle drive motors. Objective:: In order to meet the increasing requirements of electric vehicles for stability and safety and to solve the problems of low heat dissipation efficiency of electric vehicle drive motors, the size of heat dissipation devices, and the short life span caused by the high temperature of drive motors, the heat dissipation of drive motors is optimized and the heat dissipation structure is improved. Methods:: Based on the structural characteristics of heat dissipation of electric vehicle drive motors, various representative patents related to the current heat dissipation technology of electric vehicle drive motors are summarized. Results:: By summarizing a large number of patents on electric vehicle drive motor heat dissipation technology, it is concluded that the current research on electric vehicle drive motor heat dissipation mainly focuses on liquid heat dissipation or gas heat dissipation and that the main reason for the heat dissipation problem of electric vehicle drive motors is the low heat dissipation efficiency due to over-reliance on a single heat dissipation method, and the reliability is poor due to failure to reasonably control heat dissipation according to the need for heat dissipation. This paper proposes a new idea of heat dissipation for electric vehicle drive motors, which effectively combines liquid heat dissipation and gas heat dissipation. Moreover, the heat dissipation efficiency will be significantly higher than the existing heat dissipation scheme, and the proposed heat dissipation concept of "ondemand distribution" will effectively improve the utilization rate of the heat dissipation medium and reduce the heat dissipation cost and the reasonable heat dissipation structure will reduce the volume of the heat dissipation device. The reasonable heat dissipation structure will also reduce the volume of the heat dissipation device. In addition, the future development of heat dissipation technology for electric vehicle drive motors is also discussed. Conclusion:: The heat dissipation scheme proposed in this paper will effectively improve the heat dissipation problem of electric vehicle drive motors. Compared with the existing heat dissipation methods, the heat dissipation efficiency of the heat dissipation scheme proposed in this paper will be improved by more than 8.5%, and the service life of the drive motor will be extended by more than 5.1%, while the size of the electric vehicle drive motor will be reduced by 6%. More related patents will be invented in the future.

Thermal management system study of flame retardant solid–solid phase change material battery

The maximum temperature, temperature homogeneity and flame retardancy of the battery module are crucial to its safe and stable operation. In this paper, a new flame retardant solid–solid phase change material is successfully prepared for the battery thermal management system. Firstly, a new solid-solid phase change material was prepared by using polyethylene glycol (PEG) as the phase change matrix and N,N'-Methylenebisacrylamide (MBA) as the cross-linking agent. Next, a flame retardant material with high thermal conductivity was prepared using microcapsule-coated ammonium polyphosphate (MFAPP) as a flame retardant, expanded graphite (EG) as a thermal conductivity additive and expanded carbon source. The experimental results show that the composite phase change material with 19% MFAPP can provide good thermomechanical properties while having excellent flame-retardant properties. Its Limiting oxygen index (LOI) can reach 32.6 and pass the vertical combustion V-0 grade test. It also maintains good shape stability when heated at 250 °C for 30 min. In addition, the charging and discharging the battery module using CPCM as the heat dissipation medium and air cooling is compared. The results show the maximum temperature of the module is 18.83 °C lower at 2C discharge rate and the maximum temperature difference of the cycle is 7.511 °C lower.

All-climate thermal management structure for batteries based on expanded graphite/polymer composite phase change material with a high thermal and electrical conductivity

With the large-scale application of lithium battery technology, a thermal management system is required to ensure battery performance and safety in all climates. This study reports an all-climate battery thermal management structure based on an expanded graphite/polymer/paraffin wax ternary composite phase change material with high thermal (19.3 Wm−2/K) and electrical (1590.5 S/m) conductivity. The thermal management structure adopts a double-layer structure, an inter phase change material with high thermal and electrical conductivity, and an outer phase change material with low thermal conductivity as a heat preservation and insulation medium. The thermal management structure innovation uses the phase change material and the battery to form a preheating circuit to generate Joule heat to warm up the battery at low temperatures. This heating method uses the energy of the battery to greatly improve the adaptability of the thermal management system. The preheating speed reaches 20.5 °C/min at –20 °C. The phase change material can continue to generate heat during the discharge process of the battery to ensure normal operation. At a discharge rate of 1C and at –20 °C, the discharge energy increased by 35.5% compared with the case without preheating. In addition to acting as a heating element, phase change materials also act as heat dissipation media in high temperature environments, the structure exhibited a good heat dissipation capacity. At 35 °C, the temperature of the battery was controlled at 42.2 °C after the battery was discharged at a rate of 2C.

Water cooled micro-hole cellular structure as a heat dissipation media: An experimental and numerical study

Thermal performance of micro-hole cellular structure using water as a cool?ing fluid was investigated through CFD and then numerical results were validated with the experimental results. The minimum base temperature for the micro-hole cellular structure was found to be 29.7?C and 32.3?C numerically and experimentally, respectively, with volumetric flow rate of 0.000034 m3/s (2 Lpm) at a heating power of 345 W. Numerical values of the base temperature are in close agreement with experimental results with an error of 8.75%. Previously, the base temperatures of heat sinks using alumina nanofluid with 1% of volumetric concentration and water with volumetric flow rate of 0.000017 m3/s (1 Lpm) have been reported to be 43.9?C and 40.5?C, respectively.

Streamer characteristics of dielectric natural ester-based liquids under long gap distances

Natural esters, as the renewable resources, offer excellent physiochemical and dielectric properties such as the fire-resistance, high biodegradability and satisfactory dielectric breakdown performance. Thus, natural esters are selected as the insulation and heat dissipation medium for electrical equipment. However, the electrical performance of natural esters with different structures under the long gap and higher electrical stress needs further evaluations. In this paper, streamer propagation of various natural esters under the long gap and higher electrical stress were observed optically. The influence of voltage polarity, liquid types and gap distances on streamer characteristics of natural esters were analyzed. Results show that the maximum propagation velocity of streamer in natural esters is greater than that in the hydrocarbon liquids. Breakdown voltage of natural esters under negative polarity is much higher than that under positive polarity for the same gap distance. Among all the natural esters concerned, the camellia liquid demonstrates slower streamer velocity and slight greater lightning breakdown voltages for the positive and negative polarity. The lower content of unsaturation triacylglycerol molecules in camellia liquid contributes to the inhibition of ionization and streamers propagation. Results would be valuable reference for the design, manufacture and operation of the electrical equipment filled with natural ester.

Numerical and experimental study of cellular structures as a heat dissipation media

High heat flux generation in electronic devices demands new modes, methods and structures to dissipate heat effectively. We investigate the thermal performance of cellular structures using computational fluid dynamics (CFD) and obtained an optimal cellular structure for effective heat dissipation. Then, we validate our numerical results with experimental results obtained using optimized cellular structure. We found the minimum base temperature for the optimized cellular structure to be 43.6 °C and 47.4 °C numerically and experimentally respectively at inlet velocity of 10 m/s. We carried out experiments and simulations at the heat flux of 35,503 W/m2. We found a close agreement between numerical and experimental results with an error of 8.71% for the base temperature. Previously the best base temperatures were reported to be 55 °C and 40.5 °C using air and water respectively [1, 2].

Simulation analysis of air cooling for vehicle power battery

Because of its high voltage, strong storage and circulation ability, no memory effect, high safety, low environmental pollution, Lithium ion batteries are the most widely used as power battery in the electric cars, but its heat dissipation problem can not be ignored. When the power battery is working, the heat is accumulated. If it cannot be discharged in time, it will seriously affect the normal operation of the battery and even cause danger. As a heat dissipation medium, air can give good consideration to heat dissipation effect and cost. In this paper, CFD software was used to simulate the flow field of the power battery when working. Specific research method of this article is that the heating characteristics of lithium ion battery are studied, by studying thermal field distribution of the battery pack, and the battery pack is optimized to improve. Finally the temperature of the battery pack was kept a reasonable range.

Thermal performance of direct illumination high-power LED backlight units with different assembling structures

This work presents a detailed study about the heat dissipation performance of direct illumination high-power light emitting diode (LED) backlight units with two different assembling structures, one of which is traditional and the other is new. The traditional structure, referred to by structure-1, consists of multiple LEDs being directly welded to the printed circuit board (PCB), where the PCB is used as a physical support, an electrical connector and also as a heat dissipation medium. The new structure, referred to by structure-2, places the LEDs directly on the cooling boss; in this case the PCB plays mainly the role of an electrical connector. Thermal characteristics related to the two backlight units are analyzed in terms of thermal resistance network, numerically simulated and experimentally tested. The obtained results by different methods accord with each other reasonably well and all indicate that both structures can meet the requirements of heat dissipation for backlight units at an ambient temperature of 30 °C. Among the two structures, the LED junction temperature of structure-1 backlight unit is 7–8 °C higher and the temperature distribution in the back plane of the backlight unit is also more uniform.

Simultaneous determination of five common additives in insulating mineral oils by high-performance liquid chromatography with ultraviolet and coulometric detection.

Dielectric mineral oils are used to impregnate power transformers and large electrical apparatus, acting as both liquid insulation and heat dissipation media. Antioxidants and passivators are frequently added to mineral oils to enhance oxidation stability and reduce the electrostatic charging tendency, respectively. Since existing standard test methods only allow analysis of individual additives, new approaches are needed for the detection of mixtures. For the first time we investigate and discuss the performance of analytical methods, which require or do not require extraction as sample pretreatment, for the simultaneous reversed-phase high-performance liquid chromatography determination of passivators (benzotriazole, Irgamet(®) 39) and antioxidants (N-phenyl-1-naphtylamine, 2,6-di-tert-butylphenol, 2,6-di-tert-butyl-p-cresol), chosen for their presence in marketed oils. Quick easy, cheap, effective, rugged and safe and solid phase extractions were evaluated as sample pretreatments. Direct sample-injection was also studied. Ultraviolet spectrophotometry and direct-current coulometry detection were explored. As less prone to additive concentrations variability, the direct-injection high-performance liquid chromatography with ultraviolet and coulometric detection method was validated through comparison with Standard Method IEC 60666 and through an ASTM interlaboratory proficiency test. Obtained detection limits are (mg kg(-1) ): benzotriazole (2.8), Irgamet(®) 39 (13.8), N-phenyl-1-naphtylamine (11.9), 2,6-di-tert-butylphenol (13.1), 2,6-di-tert-butyl-p-cresol (10.2). Simultaneous determination of selected additives was possible both in unused and used oils, with good precision and accuracy.

Effective Heat Dissipation from Color-Converting Plates in High-Power White Light Emitting Diodes by Transparent Graphene Wrapping

We have developed a hybrid phosphor-in-glass plate (PGP) for application in a remote phosphor configuration of high-power white light emitting diodes (WLEDs), in which single-layer graphene was used to modulate the thermal characteristics of the PGP. The degradation of luminescence in the PGP following an increase in temperature could be prevented by applying single-layer graphene. First, it was observed that the emission intensity of the PGP was enhanced by about 20% with graphene wrapping. Notably, the surface temperature of the graphene-wrapped PGP (G-PGP) was found to be higher than that of the bare PGP, implying that the graphene layer effectively acted as a heat dissipation medium on the PGP surface to reduce the thermal quenching of the constituent phosphors. Moreover, these experimental observations were clearly verified through a two-dimensional cellular automata simulation technique and the underlying mechanisms were analyzed. As a result, the proposed G-PGP was found to be efficient in maintaining the luminescence properties of the WLED, and is a promising development in high power WLED applications. This research could be further extended to generate a new class of optical or optoelectronic materials with possible uses in a variety of applications.

Fluid Flow and Heat Transfer Characteristics of Composite Lattice Core Sandwich Structures

The fluid flow and heat transfer performance of composite lattice truss core sandwich structures with a constant localized internal heat source are numerically investigated under conditions of forced water convection for a wide range of Reynolds numbers. Three kinds of heat transfer methods are adopted: normal convective heat transfer, incident flow enhancement, and column support enhancement. The local thermal and fluid flow characteristics for this structure are analyzed to reveal the heat transfer mechanism, verifying that the multiform local vortical structures greatly contribute to the improvement in heat transfer efficiency. The heat transfer performance is characterized and assessed in terms of the thermal field distribution and the nondimensional heat transfer parameters of structure. In comparison with other heat dissipation media, a significant advantage is displayed for the comprehensive heat transfer performance of the structures. Much improvement and development space remain for the structural heat transfer performance, even for the achievement of multifunctional integration.

Efficient Heat Dissipation of Photonic Crystal Microcavity by Monolayer Graphene

Graphene, which exhibits excellent thermal conductivity, is a potential heat dissipation medium for compact optoelectronic devices. Photonic devices normally produce large- quantity of unwanted heat, and thus, a heat dissipation strategy is urgently needed. In this study, single-layer graphene (SLG) grown by chemical vapor deposition (CVD) is used to cover the surface of a photonic crystal (PhC) cavity, where the heat flux produced by the PhC cavity can be efficiently dissipated along the in-plane direction of the SLG. The thermal properties of the graphene-capped PhC cavity were characterized by experiments and theoretical calculations. The thermal resistance of the SLG-capped PhC cavity obtained from experiments is lower than half of that of a bare PhC cavity. The temperature of a SLG-capped PhC cavity is 45 K lower than that without SLG capping under an optical power of 100 μW. Our simulation results indicate that SLG receives the majority of the heat fluxes from the device, leading to the efficient heat dissipation. Both the experimental and simulation results suggest that the SLG is a promising material to enhance the heat dissipation efficiency for optoelectronic applications.

Si and SixGe1‐x NWs studied by Raman spectroscopy

AbstractGroup IV nanostructures have attracted a great deal of attention because of their potential applications in optoelectronics and nanodevices. Raman spectroscopy has been extensively used to characterize nanostructures since it provides non destructive information about their size, by the adequate modeling of the phonon confinement effect. The Raman spectrum is also sensitive to other factors, as stress and temperature, which can mix with the size effects borrowing the interpretation of the Raman spectrum. We present herein an analysis of the Raman spectra obtained for Si and SiGe nanowires; the influence of the excitation conditions and the heat dissipation media are discussed in order to optimize the experimental conditions for reliable spectra acquisition and interpretation. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Raman spectroscopy study of group IV semiconductor nanowires

Group IV nanostructures have attracted a great deal of attention because of their potential applications in optoelectronics and nanodevices. Raman spectroscopy has been extensively used to characterize nanostructures since it provides non destructive information about their size, by the adequate modeling of the phonon confinement effect. However, the Raman spectrum is also sensitive to other factors, as stress and temperature, which can mix with the size effects borrowing the interpretation of the Raman spectrum. We present herein an analysis of the Raman spectra obtained for SiGe nanowires; the influence of the excitation conditions and the heat dissipation media are discussed in order to optimize the experimental conditions for reliable spectra acquisition and interpretation. The interpretation of the data is supported by the calculation of the temperature inside the NWs with different diameters.

Review of Recent Patents Related to Electrical Cable Cooling

This paper reviews the current techniques being applied and that have been patented in relations to the cooling of insulated electrical cables. Patents in three specific areas of application are described. The first set of patents relates to cooling methods applying water and cryogenic coolant technology. These fluid-based cooling systems have been applied to underground transmission lines, superconductors and welding cables. The second area relates to the application of redox reactive material to the cooling of electrical cables. By utilising the endothermic/exothermic characteristics of the oxidation-reduction reaction, the temperature of the cable can be controlled. The third application area is the use of phase change materials (PCM) as a heat dissipation medium utilising their high latent heat of melting. Finally, the current and future developments in the field are briefly discussed.

Application of multiwall carbon nanotubes for thermal dissipation in a micro-processor

One of the most valuable properties of the carbon nanotubes materials is its high thermal conductivity with 2000 W/m.K (compared to thermal conductivity of Ag 419 W/m.K). It suggested an approach in applying the CNTs in thermal dissipation media to improve the performance of computer processors and other high power electronic devices. In this research, the multiwall carbon nanotubes (MWCNTs) made by thermal chemical vapour deposition (CVD) at our laboratory was employed as the heat dissipation media in a microprocessor a Personal Computer with configuration: Intel Pentium IV 3.066 GHz, 512Mb of RAM and Windows XP Service Pack 2 Operating System. We directly measured the temperature of the microprocessor during the operation of the computer in two modes: 100% usage CPU mode and over-clocking mode. The measured results showed that when using our thermal dissipation media (a mixture of the mentioned commercial thermal compound and 2 wt.%. MWCNTs), the temperature of the microprocessor decreased 5°C, and the time for increasing the temperature of the microprocessor was three times longer than that when using commercial thermal compound. In over-clocking mode, the processor speed reached 3.8 GHz with 165 MHz of system bus clock speed; it was 1.24 times higher than that in non over-clocking mode. The results confirmed a promising way of using MWCNTs as the thermal dissipation media for microprocessor and high power electronic devices.

Experimental Studies on Friction Factor and Heat Transfer Characteristics Through Wire-Woven Bulk Kagome Structure

Periodic cellular metals with open, periodic cell topologies have received much attention owing to their potential for multi-functionality such as load bearing, thermal dissipation, and actuation. Recently, a new technique, known as wire-woven bulk Kagome, has been introduced, which is used for fabricating multi-layered Kagome with truss periodic cellular metal. The fabrication of the wire-woven bulk Kagome is based on a concept where continuous helical wires are systematically assembled in six directions. Besides its excellent load-bearing capability with light weight, the wire-woven bulk Kagome has potential for a heat dissipation media because of the high ratio of surface area to volume and low flow resistance. This article presents the experimental results of the fluid flow and heat transfer characteristics of the multi-layered wire-woven bulk Kagome composed of aluminum 1100 helix wires. Under forced-air convection conditions, the friction factor and heat transfer rate of the wire-woven bulk Kagome specimen were investigated for two specimen orientations. The results showed that the friction factor of the wire-woven bulk Kagome was mainly affected by the flow blockage area, and the heat transfer characteristics depended on the open-area ratio. In addition, the results were compared with other heat dissipation media (e.g., open-celled foams, woven screens, lattice-frame materials, and cast Kagome structures). The results showed that the heat transfer performance of the multi-layered aluminum wire-woven bulk Kagome competed favorably with the best heat dissipation media currently available.

Mechanical Properties of 2-D Lattice Materials

Lattice structures have ranges of thermo-mechanical properties that suggest their implementation in ultralight structures, as well as for impact/blast amelioration systems and heat dissipation media. Considering that proper anisotropy of structure could increase load efficiency, two kinds of 2-D lattice materials designable in specific stiffness and strength of arbitrary direction have been brought forward: variational thickness cell and variational direction cell. The mechanical properties of variational thickness Kagome cell have been analyzed, including effective elastic modulus, yield strength and elastic buckling strength in arbitrary directions. Since the shear buckling of 2-D lattice materials is an important collapse mode especially when relative densities are low, shear buckling strength of various 2-D lattice materials have also been calculated. It is found that compared with the diamond cell, the variational thickness Kagome cell of thickness ratio, m=0.5, possesses the same elastic modulus and yield surface, and higher buckling strength.

Raman Spectroscopy of Group IV Nanostructured Semiconductors: Influence of Size and Temperature

AbstractGroup IV nanostructures have attracted a great deal of attention because of their potential applications in optoelectronics and nanodevices. Raman spectroscopy has been extensively used to characterize nanostructures since it provides non destructive information about their size, by the adequate modeling of the phonon confinement effect. However, the Raman spectrum is also sensitive to other factors, as stress and temperature, which can mix with the size effects borrowing the interpretation of the Raman spectrum. We present herein an analysis of the Raman spectra obtained for Si nanowires; the influence of the excitation conditions and the heat dissipation media are discussed in order to optimize the experimental conditions for reliable spectra acquisition and interpretation.

Contribution of vortex structures and flow separation to local and overall pressure and heat transfer characteristics in an ultralightweight lattice material

Ultralightweight lattice-frame materials (LFMs) with open, periodic microstructures are attractive multifunctional systems that can perform structural, thermal, actuation, power storage and other functions [A.G. Evans, J.W. Hutchinson, M.F. Ashby, Multifunctionality of cellular metal systems, Prog. Mater. Sci. 43 (1999) 171–221]. This paper presents experimental and numerical studies of local fluid flow behaviour and its contribution to local and overall pressure and heat transfer characteristics of such a lattice material with tetrahedral unit cells. A single layer of the LFM with porosity of 0.938 is sandwiched between impermeable endwalls that receive uniform heat flux and the heat transfer is subjected to forced air convection. Experimental measurements with particle image velocity (PIV) and thermochromic liquid crystal (TLC), backed by computational fluid mechanics (CFD) simulations, revealed two dominant local flow features in the LFM. Distinctive vortex structures near the vertices where the LFM meets the endwalls and flow separation on the surface of LFM struts were observed. The vortex structures formed around the vertices include horseshoe vortices and arch-shaped vortices. The horseshoe vortex increases local heat transfer on the endwall region up to 180% more than that in regions where the least influence of the horseshoe vortex is present. The arch-shaped vortex behind the vertices creates regions of flow recirculation and reattachment, leading to relatively high heat transfer. The location of flow separation along the struts varies with the spanwise position due to the presence of vertices (or endwalls). The regions on the strut surface before flow separation contribute approximately 40% of the total heat transfer in the LFM. The delay of the flow separation leads to an increase in the overall heat transfer. Comparisons with foams and other heat dissipation media such as packed beds, louvered fins and microtruss materials suggest that the LFMs compete favourably with the best available heat dissipation media.