Thermal Resistance Characteristics Research Articles

A fracture aperture dependent thermal-cohesive coupled model for modelling thermal conduction in fractured rock mass

Due to thermal resistance characteristics of fractures, to realistically assess thermal effects of fractured rock mass, it should correctly reflect the thermal interaction between fracture interfaces. In this study, the coupled FEM-DEM method is extended to model transient thermal conduction in fractured rock mass. Rock matrix and fractures are discretized into solid elements and cohesive elements, respectively. To simulate thermal conduction across fractures, the cohesive element is coupled with a thermal model (thermal-cohesive model) by incorporating an aperture dependent interfacial thermal conductivity. Validation simulations indicate that the proposed model is capable of capturing the temperature jumps across the fractures with different apertures. Then, the influences of fracture characteristics on thermal conduction were numerically investigated. Finally, thermal conduction in highly fractured rock mass was studied by a model with multiple randomly distributed fractures generated through Monte-Carlo algorithm. The results indicate that the temperature gradient and heat flux field of rock mass containing a single fracture are quite sensitive to fracture orientation and aperture. Compared with the linear behavior between the ETC and fracture aperture in rock mass containing a single fracture, the relationship between the ETC and fracture aperture in highly fractured rock mass presents strong nonlinear characteristic.

A compatible and crosslinked poly(2‐allyl‐6‐methylphenol‐co‐2,6‐dimethylphenol)/polystyrene blend for insulating adhesive film at high frequency

ABSTRACTA polymer blend consisting of poly(2‐allyl‐6‐methylphenol‐co‐2,6‐dimethylphenol) (APPE) and polystyrene (PS) with additives such as 1,2‐bis(4‐vinylphenyl)ethane, cyanate ester, and nitrile butadiene rubber was formulated as an insulating high‐frequency adhesive film. The polymer blend of APPE and PS showed very high compatibility to these additives, and the resulting thermally cured polymer blend exhibited an excellent mechanical strength, as shown by an ultimate tensile strength of 51 MPa and Young's modulus of 1.4 GPa. Moreover, the blend exhibited very good dielectric properties, with a dielectric constant of 2.3 and a dissipation factor of 0.0030 at 10 GHz. The glass‐transition temperature of the cured polymer blend was 141 °C, as determined by differential scanning calorimetry, and the 5% weight loss temperature was 372 °C, indicating relatively high thermal resistance characteristics. Furthermore, its peel strength to a copper foil reached 0.80 N/mm. The present study suggested that the thermally cured APPE/PS polymer blend with additives will have potential applications for the next‐generation high‐frequency adhesives in microelectronic circuits. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019, 136, 47828.

Studying the loading impact of silane grafted Fe2O3 nanoparticles on mechanical characteristics of epoxy matrix

This study investigates the loading impact of iron oxide (IO) and silane treated iron oxide (SIO) nanoparticles on thermal, mechanical and morphological behavior of epoxy matrix. Both IO and SIO nanoparticles were loaded with 1, 3 and 5 wt% from the total weight of epoxy matrix. The morphology of IO, and SIO epoxy nanocomposites are investigated by TEM. FTIR spectra are successfully able to confirm the good chemical interaction between SIO nanoparticles and epoxy matrix. Thermal resistance of epoxy IO, and SIO nanocomposites is studied by TGA. The mechanical properties of prepared nanocomposites including storage modulus, tan δ, stress-strain curves and toughness are studied using DMA at temperature range 25 °C–100 °C. The results approved that loading 3 wt% of SIO nanoparticles improved the morphological, thermal resistance and mechanical characteristics of epoxy matrix.

Properties of the Triangular Excitation Pulse and the 3D Heat Transfer Effects in the Excitation Pulse Method

Concerning the high levels of energy consumption in the existing building stock, the necessity for characterization of the building envelop is a well-known issue. Accordingly, numerous methods and practices have been developed and studied to measure the thermal resistance and other thermal characteristics of the walls in-situ. In the current paper, a previously proposed method, the Excitation Pulse Method, EPM, based on the theory of thermal response factors, is further studied and investigated through simulations, to rapidly measure the thermal resistance of existing walls. A prototype is built and introduced to carry out larger number of measurements on site. The triangular pulse’s properties such as the relation between its magnitude and its time interval on its corresponding response are investigated. It is shown how changes in time interval can make the method sensitive to the number of residuals and affect its reliability. General constraints and validity domain of the method are studied. In addition, the effect of 3D heat transfer on the performance of the method is further illustrated in light and heavy constructions. It is shown in which cases it is possible to apply the method in-situ and measure the thermal resistance within a couple of hours.

Development of high temperature material for cellular ceramic regenerative storage heater

Ceramic Regenerative Storage Heater (RSH) is the preferable solution to provide clean hot air in Hypersonic Wind Tunnel (HWT) and Scramjet Test facilities to prevent the liquefaction of air during expansion in the high Mach number nozzles. Selection of the heater storage material for such operational requirements is a challenging task. As per the theoretical background; alumina, zirconia or mullite compositions have the capability to withstand at such high operating conditions. In the current study, a series of experiments were carried out to estimate the thermal characteristics of the material. This paper highlights the simplified approach by combining theoretical and experimental methods for economic (reduced time and cost) selection process of high temperature material. The desired material must possess good thermal shock resistance and low dust generation characteristics. Al2O3 and SiO2 based matrix composition fused in a transcrystalline phase exhibits significant improvement on the overall material integrity. Several Al2O3 and SiO2 matrix compositions were examined and the final matrix composite ratio of 90% of Al2O3 and 10% of SiO2 is considered as the desired candidate material. The ceramic matrix was sintered at a temperature of 2123 K, under the specific pressure of 1400 kg/cm2 for a period of 2 h, at a heating rate of 3.5 °C/min. The results of the thermal shock tests on various samples are presented. To improve the anti-dust characteristics, the final samples were coated with fine particles (5 µm) of Al2O3 and SiO2 matrix. Based on the experimental evaluation, Al2O3 and SiO2 fused matrix composition found to be meeting all the requirements of high temperature storage material.

Predictable and unpredictable survival of foodborne pathogens during non-isothermal heating

In previous work, extreme survival of various bacterial species during cooking was reported when attached to chicken meat. In this paper the effects of an extremely high challenge temperature on survival of Salmonella Typhimurium and Campylobacter jejuni, attached to chicken breast fillets or pork to test for matrix effects are reported. Survival was predicted, using standard D- and z-values from the literature, and compared to experimentally obtained data. Attached to meat, both S. Typhimurium and C. jejuni survived longer than predicted, longer when attached to chicken meat than when attached to pork.Additionally, the effect of non-isothermal heating on survival of almonella in buffer is described. In buffer, when slowly heated, Salmonella died off as predicted. When Salmonella was heated in buffer according to a heating profile mimicking that of the surface of meat in boiling water, it appeared that cells died off much slower than predicted. It is shown that the thermal characteristics of Salmonella surviving the first 35 s of fast heating had changed. After these 35 s, remaining Salmonella survived for minutes, even at a challenge temperature of 90 °C.During heating, cell size decline was observed. A loss of intracellular water during cooking might have resulted in smaller, dehydrated cells, in cells with altered thermal resistance characteristics. This could explain why the use of standard D-and z-values did not allow the correct prediction of survival of Salmonella during fast heating in buffer, or during cooking, being attached to the surface of meat.Many factors affect the level of heat resistance of bacteria. The results of this and a former study show that attachment to meat contributes to an increased level of heat resistance of bacteria. A fast heating process further contributes to the increased level of heat resistance possibly as the result of changed thermal characteristics due to a loss of water.

Power cycle tests of high temperature Ag sinter die-attach on metalized ceramic substrate by using micro-heater SiC chip

Abstract Next generation power semiconductors, e.g. SiC and GaN, are emerging for the further minimization and high current/voltage of power devices with high reliability covering wider operating environments than those based on Si. To implement high reliability operation, the key technology is the control of the temperature distribution in the module, and thermal stress caused by the heat generated by power loss. In the present study, we have developed SiC micro-heater chip with temperature probe to evaluate thermal characteristics of an assembled system of Ag sinter die-attach on metalized ceramic substrate (Cu/Si3N4/Cu) during the repetitive power cycling. The test specimens were fixed on a water cooling system, and steady-state heat resistance of the system was measured during the power cycling. For comparison, Pb-Sn, Sn-Cu-Ni-P, Sn-Ag-Sb-Cu solders were used as die-attach material bonded on the same metalized ceramic substrates. The maximum applied power exceeds 200 W with cycles of 2 seconds of heating and 5 seconds of cooling, and the test cycles was over 5000 cycles. The power cycle number dependence on the temperature swing and thermal resistance characteristics would be discussed, in connected with the power cycle testing for real power devices.

A robust flat-chip solid oxide fuel cell coupled with catalytic partial oxidation of methane

This study demonstrates a module that consists of solid oxide fuel cell (SOFC) with flat-chip configuration and a catalytic partial oxidation (CPOX) reformer. The CPOX reformer uses Rh supported by Al2O3 as catalyst and functions effectively. The optimized temperature of CPOX reformer is 800 °C and the optimal C/O ratio to operate the reformer is ca. 0.8 where the maximum reforming efficiency, i.e. 86.1% can be obtained. The CPOX reformer can be coupled with a flat-chip SOFC, which is advantageous for its good thermal shock resistance, quick startup and good response characteristics. The flat-chip SOFC is able to function with a temperature difference over 850 °C across the cell itself and can survive the harsh tests of rapid thermal cycling with the temperature change rate well above 200 °C·min−1, and repetitive redox cycling at least 23 times.

Thermal performance enhancement of vapor chamber by coating mini-channel heat sink with porous sintering media

This paper have been investigated on the thermal performance enhancement of air cooling vapor chamber by coating mini-channel heat sink inside with porous sintering wick sheet. The results obtained from experiments are considered and compared with without porous sintering wick sheet. The effects of power input, amount of filled working fluid into the vapor chamber and mass flow rate of air on the cooling performance and thermal resistance characteristics are considered. It can be found that the porous sintering wick sheet has significant effect on the increment of the capillary force which results in higher heat transfer rate. Therefore, the thermal performance of air cooling vapor chamber with porous sintering wick sheet inside mini-channel shows 20% maximum higher than that without porous sintering wick sheet. In addition, the increasing of power in put and cooling air mass flow rate have significantly increased thermal performance of the vapor chamber. The passive cooling device with vapor chambers is favorable technique that can enhanced thermal performance and reduce heat accumulate on the electronic component.

Analysis of influence factors on the cooling capacity for the tracked vehicle radiator

Numerical method is usually used to solve the engineering problems. To analyze the cooling capacity for the tracked vehicle radiator with full-scale, especially with a large volume and a small size for its waved fins, a large number of grids should be employed with a poor quantity. To solve this pr oblem, in this paper, a sufficient numerical method is proposed for a tracked vehicle radiator with full-scale to analyze the cooling capacity. This method is based on the simplified model of three-dimension resistance characteristics for the radiator fins, including the air flow resistance characteristics and air thermal resistance characteristics. The air flow resistance characteristics are verified by the experiments. The maximum error is 8.06%, while the mean error is 3.21%. The results agree well with experiments. This paper provides a comprehensive study on the cooling capacity for a tracked vehicle radiator working at different operating conditions, especially for the environmental factors and coolant fluid factors influencing on the cooling capacity. The results depict the influence degree of different factors on the cooling capacity, and this simplified method is reasonable and could be recommended to future study on other radiators with complex geometric features.

Hydrothermal synthesis of high quality free-standing VO2(B) thin film and its thermal resistance characteristics

Vanadium oxide is a type of material with high temperature coefficient of resistance (TCR) for bolometric infrared detection. In this letter, the effects of growth conditions of B-phase crystalline VO2, including reaction temperature, reaction time and quantities of precursors, were systematically investigated. Free-standing VO2(B) thin film composed of nano-sheets stacking on the (0 0 1) plane was prepared. The in-plane and out-of-plane TCRs were measured. A superior in-plane TCR of −3.0%/K was observed at room temperature, while the out-of-plane TCR only was −1.7%/K. We further showed that the I-V behavior of VO2(B) was voltage-dependent, and its possible origin was discussed.

Ultra-low thermal conductivity of high-interface density Si/Ge amorphous multilayers

Owing to their phonon scattering and interfacial thermal resistance (ITR) characteristics, inorganic multilayers (MLs) have attracted considerable attention for thermal barrier applications. In this study, a-Si/a-Ge MLs with layer thicknesses ranging from 0.3 to 5 nm and different interfacial elemental mixture states were fabricated using a combinatorial sputter-coating system, and their thermal conductivities were measured via a frequency-domain thermo-reflectance method. An ultra-low thermal conductivity of κ = 0.29 ± 0.01 W K−1 m−1 was achieved for a layer thickness of 0.8 nm. The ITR was found to decrease from 8.5 × 10−9 to 3.6 × 10−9 m2 K W−1 when the interfacial density increases from 0.15 to 0.77 nm−1.

Variation of hardness and modulus of sodium borosilicate glass irradiated with different ions

Borosilicate glass with characteristics of high thermal, mechanical and chemical resistance has plenty of applications. As one of the candidates who are possible to vitrify high level radioactive waste, the borosilicate glass has been studied extensively. The borosilicate glass was added with sodium to increase electrical conductivity and decrease viscosity. The tolerance of sodium borosilicate glass on irradiation is important to vitrification. In this work, the sodium borosilicate glass samples were irradiated with different ions. The dependence of hardness and modulus on irradiation dose was studied. A semi-empirical formulation was proposed. Possible reasons for the change of modulus and hardness were discussed.

Power Output Stability Research for Harvesting Automobile Exhaust Energy with Heat Capacity Material as Intermediate Medium

Automobile exhaust energy thermoelectric utilization can promote energy-saving and emission-reduction. Unexpected urban traffic conditions lead to the hot-end temperature instability of the exhaust pipe-mounted thermoelectric generator (TEG), and influence the TEG power generation efficiency. The heat conduction oil circulation located at the hot-end could smooth the temperature fluctuation, at the expense of larger system size and additional energy supply. This research improves the TEG hot-end temperature stability by installing solid heat capacity material (SHCM) to the area between the outer wall of the exhaust pipe and the TEG, which has the merits of simple structure, light weight and no additional energy consumption. The exhaust temperature and flow rate characteristics with various driving conditions are firstly studied for the target engine. Then the convective heat transfer models of SHCM’s hot-end and thermoelectric material’s cold-end are established. Meanwhile, SHCM thermal properties’ effects on the amplitude and response speed of the TEG hot-end temperature are studied. The candidate SHCM with the characteristics of low thermal resistance and high heat capacity is determined. And the heat transfer model going through from TEG’s hot-end to the cold-end is established. The results show that the SHCM significantly improves the TEG hot-end temperature stability but slightly reduces the average power output. When the engine working conditions change a lot, the SHCM’s improvement on the TEG hot-end temperature stability is more significant, but the reduction of the average power output becomes more remarkable.

Thermodynamic Compatibility, Crystallizability, Thermal, Mechanical Properties and Oil Resistance Characteristics of Nanostructure Poly (ethylene-co-methyl acrylate)/Poly(acrylonitrile-co-butadiene) Blends

AbstractThis paper addresses the compatibility, morphological characteristics, crystallization, physico-mechanical properties and thermal stability of the melt mixed EMA/NBR blends. FTIR spectroscopy reveals considerable physical interaction between the polymers that explain the compatibility of the blends. DSC results confirm the same (compatibility) and reveals that NBR hinders EMA crystallization. Mechanical and thermal properties of the prepared EMA/NBR blends notably enhance with increasing the fraction of EMA in the blends. Morphology study exhibit the dispersed particles in spherical shape in the nanometer level. Swelling and oil resistance study have also been carried out in details to understand the performance behaviour of these blends at service condition

Effect of acrylation on the properties of waterborne epoxy: evaluation of physicochemical, thermal, mechanical and morphological properties

The present work addresses the critical requirements for the coating industry such as developing the sustainability of biobased materials and simultaneously achieving a balanced combination of coating properties. In this study, acrylated epoxidized soybean oil (AESO) has been successfully synthesized from epoxidized soybean oil and acrylic acid. Subsequently, AESO was modified using a biobased long chain diacid (Pripol-1009) with the assistance of a water/ethanol blend to form waterborne epoxy acrylate (WBEA). The properties of the cured WBEA with 2,5-bis(tert-butylperoxy)-2,5-dimethylhexane as initiator were studied through spectral analysis, coating properties evaluation, corrosion resistance, and morphological and thermal analysis. The results revealed that WBEA exhibited relatively better mechanical, thermal and corrosion resistance characteristics over cured waterborne epoxy.

МЕТОД ОПРЕДЕЛЕНИЯ РЕАЛЬНЫХ ТЕПЛОПОТЕРЬ СУЩЕСТВУЮЩИХ СТРОИТЕЛЬНЫХ ОБЪЕКТОВ

This article is dedicated to the issues of energy saving, in particular to the problems of improving energy efficiency of modern buildings by experimental studies of thermo physical properties (TPP) of materials in order to eliminate excessive heat losses through building envelope. Based on the analysis of the existing methods of determining the materials’ TPP, the authors developed an algorithm to de­termine the actual heat losses of a facility under study. Operation of an installation for determining the TPP (heat transfer coefficient, thermal resistance and specific heat characteristics) of the facility under study is described. The formulas required for the calculation of TPP are given. Experimental results of the study are provided. Main advantages of the developed installation are described.

The influence of stabilizers on the properties of silicone rubber

The influence of various stabilizers on the properties of rubber based on silicone rubber SKTV is studied. It is established that the use of the Ca/Zn stabilizer in the resin composition makes it possible to increase thermal resistance and physico-mechanical characteristics of the rubber used to make sealing elements in the automotive industry.

Značilnosti odpornosti zlitin litega železa za valje 3.1C, 0.8Si, 0.9Mn, 1.7Cr, 4.5Ni IN 0.3Mo na ICDP termično utrujanje pri 600 °C

Značilnosti odpornosti zlitin litega železa za valje 3.1C, 0.8Si, 0.9Mn, 1.7Cr, 4.5Ni IN 0.3Mo na ICDP termično utrujanje pri 600 °C

Operational characteristics of loop heat pipes with porous copper fiber sintered sheet as wick

Porous copper fiber sintered sheets (PCFSS) as wick are fabricated for loop heat pipes (LHP) using low-temperature solid-phase sintering technology and smooth and rough copper fiber as the manufacturing material. The operational characteristics of LHP with varied wick surface morphologies and filling ratios are analyzed. This study focuses on evaluating the following characteristics: thermal resistance characteristics under increasing and decreasing heat load patterns, evaporator surface thermal homogeneity, thermal inertia, and limit operational characteristics. Experimental results demonstrated that LHP with rough PCFSS exhibited lower thermal resistance. As compared to decreasing heat load conditions, relatively lower thermal resistance of LHP under increasing heat load conditions was obtained. The evaporator surface thermal homogeneity yielded improvement with rough PCFSS and increased filling ratio. A larger thermal inertia of LHP was observed when the low filling ratio was applied, and it will be improved when the filling ratio was increased and the smaller heat load variation intensity was selected. When rough PCFSS wick with 70% porosity and a deionized water filling ratio of 30% were selected, the LHP was able to effectively operate under 5–200W heat load conditions and yielded prompt response to heat load variation.