Maximum Temperature Reduction Research Articles

Transient Thermal Analysis in an Intermittent Ceramic Kiln with Thermal Insulation: A Theoretical Approach

Increasing the thermal efficiency of drying and firing processes of ceramic products plays an important role for industries that want to remain competitive in the market. Thus, this work aims to evaluate the influence of the type and thickness of thermal insulations, applied on the external sidewalls of an intermittent ceramic kiln, on heat transfer, temperature distribution in the insulating material, maximum external surface temperature, and energy gain, compared to the kiln without thermal insulation. All proposed mathematical formulations are based on the energy conservation, and mathematical procedures are implemented in Microsoft Excel software. Here, it was tested four types of thermal isolators: fiberglass, rockwool, calcium silicate, and ceramic fiber. Results indicate that the greater the thickness of the thermal insulation, the lower the maximum external surface temperature and the greater the energy gain when compared to the kiln without thermal insulation. In addition, fiberglass is the insulating material, among the four types analyzed, which provides greater energy gain and greater reduction in maximum external surface temperature.

The Effects of Gate-Connected Field Plates on Hotspot Temperatures of AlGaN/GaN HEMTs

To increase the reliability and the maximum performance of AlGaN/GaN high electron mobility transistors (HEMTs), gate field plates are frequently used with surface passivation. Although significant research has been done to understand the electrical effects of gate field plates on devices, their thermal effects are still not fully understood. For this purpose, electrothermal simulations are performed on devices with and without gate field plates having different thicknesses of Si3N4 surface passivation at two different biasing conditions. These simulations prove that more than 8% reduction of maximum temperature can be achieved with the use of gate field plates on devices operated at ${P}={4}$ W/mm. Field plates, when used in multifinger device configurations, have a greater impact on the outermost fingers’ temperatures and can be used to achieve temperature uniformity. Surface passivation studies suggest that while thick passivation layers (~200 nm in case of Si3N4) eliminate the thermal advantages of the field plate technology, very thin passivation layers (~45 nm) cause an increase in the electric field and a decrease in the breakdown voltage. Thus, significant thermal advantages can be achieved when gate field plates are introduced following a field plate length and passivation thickness optimization based on the device biasing conditions.

Quantitative evaluation of thermal performance and energy saving potential of the building integrated with PCM in a subarctic climate

This research quantitatively investigates the thermal performance and energy efficiency of the residential building integrated with nine PCMs (PCM19 to PCM27) in different cities of subarctic climate (Dfc according to Koppen-Geiger climate classification). The thermal performance was evaluated by using the concept of average temperature fluctuation reduction (ATFR), maximum temperature reduction (MTR) and discomfort hours. ATFR allowed estimating the monthly PCM performance and determining the periods where it worked the best. MTR was used to quantitatively estimate the effect of PCM on maximum air temperature reduction during different seasons (swing and summer) while the concept of discomfort hours was used to investigate the effect of PCM on human thermal comfort. Thereafter, the concept of annual energy savings was used to evaluate the possibility of using a few PCMs for the whole Dfc climate zone. Finally, economic and environmental analyses were performed to evaluate the utility of PCMs in the subarctic climate. The results showed that the residential building integrated with PCM demonstrated better performance in terms of ATFR, especially during the warm season. Based on maximum temperature reduction results, PCMs with low melting temperatures were optimum during swing season, whereas PCMs with high melting temperatures were optimum in the summer period. According to the energy analysis results, the annual energy savings for the subarctic climate were up to 10000 kWh. It was confirmed that few optimum PCMs (PCM23 and PCM24) can be used for the whole subarctic climate to enhance the energy efficiency of the building. Finally, from the economic analysis, the payback period varied from 16 to 32 years while from environmental analysis, the annual CO2 savings up to 4817 kg were obtained. Conclusively, PCMs can significantly improve the thermal and energy performance of the buildings in the Dfc region.

Performance Comparison of Two Hybrid Si/SiC Device Concepts

Various Si/SiC hybrid device concepts aim at achieving SiC performance at a significantly reduced cost in comparison to full SiC solutions. Both the insulated-gate bipolar transistor (IGBT)(Si)/Schottky(SiC) hybrid pair and the IGBT(Si)/MOSFET(SiC) hybrid switch offer a substantial reduction in switching losses but operate quite differently. This article compares the performance of these two hybrid device concepts in a voltage source inverter (VSI). The basic operation principle, conduction, and switching characteristics of the two hybrid configurations are directly compared, and an improved power loss model is developed for these two solutions in VSI. Two single-phase VSI prototypes using these two hybrid devices are built and tested, respectively. Experimental results show that a 1200-V hybrid IGBT/MOSFET solution achieves a significant efficiency improvement and a maximum junction temperature reduction compared to the hybrid IGBT/Schottky counterpart. The hybrid IGBT/MOSFET solution achieves a 40% higher power handling capability in the 20-kHz single-phase VSI or 1.5 times higher switching frequency in the 2-kW single-phase VSI than the hybrid IGBT/Schottky solution.

RETRACTED: Generic method for creating waterborne coatings with sub-ambient daytime cooling–Part II: Cooling effect under real working conditions and key physical properties

Abstract Current sub-ambient daytime radiative cooling (SDRC) designs are generally evaluated in a well-insulated apparatus to suppress heat convection and conduction with the surrounding environment. In a companion study, we experimentally demonstrated that serial waterborne coatings, which combined particle scattering, sunlight-excited fluorescence, and mid-infrared broadband radiation, exhibited pronounced SDRC effects on various substrates installed on a well-designed rooftop setup under different climatic conditions. In this study, we experimentally show that the coating with yellow-green fluorescence (termed as the FR coating) can achieve meaningful SDRC under real working conditions. When applied to a concrete scale-model building, the FR coating showed a significant SDRC effect compared with other substrates installed on the rooftop cooling device and an assembled corrugated steel house. The average decrease in sub-ambient temperature under direct sunlight was 10.1 ± 1.4 °C with a maximum value of 12.4 °C under a peak solar intensity of 999 W/m2. Moreover, during the coldest day in winter, the maximum sub-ambient temperature reduction during the midday hours was 5.3 °C. The maximum difference between the lowest temperatures of the coated and uncoated scale-model buildings’ room interiors was 1.5–1.6 °C. Therefore, excessive heating energy consumption in the winter might be completely compensated for or exceeded by the cooling energy savings in the summer in areas that require both heating and cooling depending on the season. Additionally, the coating possesses excellent weather and salt spray resistance, self-cleaning capabilities, and excellent visible appearance, which are essential for practical applications.

Transient influence of water injection on the flow field of a hot launch in a W-shaped silo

This study attempts to determine the effect of and mechanisms for the suppression of the ignition pressure and back-flowing exhaust during a hot launch process in a W-shaped silo, considering the missile movement via dynamic mesh technology. The mixture model for the multiphase and the turbulent model employed were experimentally proved to be accurate and reliable. The numerical results show that the injection of water into a missile exhaust can effectively suppress the ignition overpressure, thereby reducing the time of oscillation and oscillation amplitude, and reducing the maximum pressure at missile bottom from 3.68 × 105 Pa to 2.39 × 105 Pa. In addition, water injection makes the back-flowing exhaust remain at the bottom of the launch duct instead of filling the duct, and it cools the missile bottom, thus leading to a reduction in the maximum temperature from 3000 K to approximately 500 K.

Numerical thermal evaluation of laminated binary microencapsulated phase change material drywall systems

Microencapsulated phase change materials (MEPCMs) have the potential for energy storage applications in buildings. However, current MEPCMs are limited by their singular phase change transitional temperatures and are therefore unable to satisfy all year seasonal energy storage applications. This study was focused on numerically assessing the energy saving potential of a binary MEPCM drywall system which is capable of operating within two different phase change transitional temperature ranges. In this study, Ansys Fluent and the ESP-r simulation tools were employed because Fluent could offer a detailed quantification of the temperature changes within the composite drywall system and ESP-r has the capability of thermal modelling of phase change materials at whole building scale by using annual weather data as boundary conditions. The Fluent simulation results demonstrated that the thermal energy charge time and thermal energy charge/discharge amount of the binary MEPCM drywall were significantly increased when the MEPCM thickness increased from 1 mm to 5 mm, and the 5 mm thick layer had adequate capacity to balance the thermal energy during day and night. The ESP-r results showed that for the hot period in Hangzhou (China), the 5 mm thick binary MEPCM drywall was able to achieve a maximum peak air temperature reduction of about 6.7 °C and to increase the number of hours the indoor air temperatures were within the 21–28 °C range by about 12% in comparison with other drywalls. Experimental evaluation is therefore being recommended to verify the full practical potential of MEPCMs with two phase change temperature ranges.

Numerical Investigation of an Innovative Metal Structure in a PCM Based Heat Sink

Numerical simulations were performed to examine the time-dependent melting in a PCM enclosure with two designs of conductive metal fins: a baseline design with conventional heat sink fin structure and a topologically optimized innovative structure. Two orientations of the PCM enclosures were investigated to characterize the orientation effects on the behaviours of PCM melting. The proposed simulation model was firstly validated by the published experimental results. The simulated device temperature, material phases and flow fields within the PCM enclosure developed under different operating conditions were presented and discussed. The simulation results showed that the optimized design generally outperformed the baseline design by obtaining a lower device temperature and alleviating the effects of orientations. At q = 50,000W/m2, the optimized design achieved a maximum temperature reduction of 8°C under Orientation 1 and 2.5°C under Orientation 2 in comparison to the baseline during the main stage of PCM melting. It was suggested that the promoted heat transfer performance by the optimized design was attributed to the improved heat diffusion capability as well as the intensified natural convection provided by its innovative metal structure.

A reduced-scale experiment to evaluate the thermal performance of building envelopes containing phase change material spheres

To reduce the heat transfer between outdoor and indoor environments, phase change materials (PCMs) were introduced to building envelopes. Research has shown that the position of PCMs is a key factor that influences the thermal behaviour of building envelopes containing PCMs. In the present paper, experiments were conducted to define the optimum PCM position to enhance the cooling and heating energy performance. PCMs with a melting temperature between 27 °C and 29 °C were encapsulated in spheres, arranged in an insulation layer. An electric heating film was adopted to simulate the solar radiation that was received by the outer surface of building envelopes. The thermal performance of the envelopes with PCM spheres was analysed in terms of temperature reduction and elevation, surface temperature amplitude and PCM phase transition temperature and time. With higher heating rate, the temperature reduction was higher for the PCM spheres at same positions. With same heating rate, the temperature reduction increased and then decreased when the PCM spheres moved from outdoor to indoor. The maximum temperature reduction using PCM spheres was 13.03 °C by 23.0% when the solar radiation was 200 W/m2 and the maximum temperature elevation using PCM spheres was 7.8 °C by 56.7%. The allowable thermal resistance between PCMs and outdoor environment under different heating rate was given. The PCMs are recommended to install on the inward-most layer of the wall if they can complete their melting process.

Impact of evaporative cooling due to wetting of urban materials on local thermal comfort in a street canyon

The choice of urban materials strongly influences the outdoor thermal comfort through their role in the absorption, transport and storage of heat and moisture. The present study investigates the level of evaporative cooling reached after rain events of varying intensities using urban materials with distinct thermal and moisture transport properties. Further, the resulting impact on thermal comfort is studied. The local climate in a street canyon is modeled using a fully-integrated model that couples computational fluid dynamics (CFD) simulations of wind flow with the three-dimensional heat and moisture transport (HAM) in porous urban materials. Wetting due to rain deposition on each surface is calculated using an Eulerian multiphase wind-driven rain model. The results show that an increase in the rainfall intensity extends the effective duration of evaporative cooling, but does not change the reduction in maximum surface temperatures. The improvement in the thermal comfort in the street canyon depends on a combination of factors such as moisture permeability, moisture capacity and thermal diffusivity of materials.

Numerical CFD analysis and experimental investigation of the geometric performance parameter influences on the counter-flow Ranque-Hilsch vortex tube (C-RHVT) by using optimized turbulence model

This research article demonstrates how using different turbulence models may affect the temperature detachment (the temperature diminution of cold air (∆Tc = Ti − Tc)) inside straight counter-flow Ranque-Hilsch Vortex Tube (RHVT). The code is utilized to find the optimized turbulence model for energy separation by comparison with the experimental data of the setup. To obtain the results with a minimum error, various turbulence models have been investigated in steady state and transient time-dependence modes. Results show that RNG k-e turbulence model has the best correspondence with the obtained experimental data from the setup; therefore, by using a RNG k-e turbulence model with respect to Finite Volume Method (FVM), all the computations have been carried out. Moreover, some geometric parameters are focused on the length of hot tube and number of nozzle intakes within divergent and convergent hot-tube. Numerical results present that there is an optimum angle for obtaining the highest refrigeration performance, and 2ο divergence is the optimal candidate under our numerical analysis conditions. Length of hot tube which exceeds a critical length has slight effect on the refrigeration capacity. The critical length is L = 166 mm in our study. Temperature reduction sensitivity can be reduced by increasing number of nozzles and maximum temperature reduction can be obtained.

A Comparison of Neighborhood-Scale Interventions to Alleviate Urban Heat in Doha, Qatar

Recent evidence suggests that many densely populated areas of the world will be uninhabitable in the coming century due to the depletion of resources, climate change, and increasing urbanization. This poses serious questions regarding the actions that require immediate attention, and opportunities to stave off massive losses of infrastructure, populations, and financial investments. The present study utilizes microclimate modeling to examine the role of landscape features as they affect ambient temperatures in one of the fastest growing regions of the world: Doha, Qatar. By modeling three study sites around Doha—one highly urbanized, one newly urbanizing, and one coastal low-density urbanized—the research indicates that at the neighborhood scale, the most effective scenario was that of adding mature trees along the sides of roads. In the coastal study area, the model results estimated a maximum hourly air temperature reduction of 1.35 °C, and in the highly urbanized inland site, surface temperature reductions were up to 15 °C at 12:00. While other scenarios were effective at reducing air and surface temperatures, the mean radiant temperature was also increased or nearly neutral for most of the other scenarios. This result highlights the need to develop improved shading measures for pedestrian pathways and outdoor recreational areas, especially for highly urbanized inland areas in Doha and cities with similar climatic conditions.

Performance Augmentation of Single-Phase Heat Transfer in Open-Type Microchannel Heat Sink

Single- and two-phase heat transfers from a microchannel heat sink (MCHS) are emerging as innovative methods of cooling for diversified engineering applications including microelectronics, power production, medical, and chemical industries. However, high-pressure drops and miscellaneous flow boiling instabilities are the major impediments of the technology. Open-type microchannels are recently projected to ameliorate a few of these limitations, including flow boiling instabilities and pressure drop penalties. In the current experimental study, heat transfer performance augmentation of single-phase flow in an open-type microchannel heat sink has been studied. Two configurations of the open-type microchannel heat sink, plain open MCHS and extended open MCHS, were fabricated and tested under a mass flux range of and an effective heat flux range of . Water was used as a cooling medium. It has been observed that fins in the plain open MCHS intensify heat transfer performance by 15%, and a maximum wall temperature reduction of 3.7°C has been observed in the current study for the extended open MCHS. On the contrary, a pressure drop penalty of around 18% has been witnessed for the extended open MCHS due to the additional flow obstacle offered by the extended surfaces. The overall thermal performance of the extended open MCHS indicated that the configurations can become substitutes for the closed MCHS in the future.

Pyrolysis of Polystyrene: The Influence of Commercially Available Oxides as Catalysts

In this study four catalysts (ƴ –Alumina, α- Alumina, silica gel and silica ppt) with different physicochemical characteristics were tested for the pyrolysis of polystyrene (PS) under inert atmosphere in the temperature range 200-650 and#176;C at heating rate 5 and#176;C/min. The silica gel a mesoporous catalyst, with a greater pore size and surface area was found to be the most active materials in terms of reduction in maximum temperature. The ƴ –Alumina catalyst also shows good result because of the acidic sites, surface area, and pores size, however, its degradation effect is less than silica gel. The effect of α- Alumina catalyst on the pyrolysis of PS is less pronounced due to its small surface area, pore size and lack of acidic sites on its surface. The effects of these catalysts show that surface area, number of acidic sites and pore size were observed as the key factors for effective degradation of polymers.

The effect of forced ventilation by using two movable fans on thermal smoke movement in a tunnel fire

In this work, tests were conducted to investigate the propagation characteristics of buoyancy-driven thermal smoke for different multiple movable fan layouts in a full-scale road tunnel. The temperatures along the longitudinal direction of the tunnel ceiling upstream and downstream of the fire source were measured and the thermal smoke development was recorded using the laser sheet visualization technique. The spread velocity and descent velocity were derived based on the longitudinal and vertical temperature distributions in order to analyze the differences in thermal smoke propagation for various movable fan layouts. The results showed that the best configuration, which gives the highest reduction of maximum temperature and enhanced propagation of thermal smoke, is to install one fan downstream of the fire source rather than installing both of fans upstream. However, this configuration also increases the descent velocity of the thermal smoke. In addition, there may be a critical range for the distance between the fire source and fan installed downstream of the fire source because the conclusions above are no longer valid if this range is exceeded.

Optimal Design of Three-Dimensional Heat Flow Structures for Power Electronics Applications

AbstractDesign optimization of a three-dimensional (3D) heat flow structure for power electronics gate drive circuit thermal management is described. Optimization methods are described in the creation of several structural concepts targeted toward simultaneous temperature reduction of multiple gate drive integrated circuit (IC) devices. Each heat flow path concept is intended for seamless integration based on power electronics packaging space constraints, while maintaining required electrical isolation. The design synthesis and fabrication of a select concept prototype is presented along with the development of an experimental test bench for thermal performance characterization. Experimental results indicate a significant 45 ∘C maximum temperature reduction for the gate drive IC devices in a laboratory environment, which translates to an estimated 41 °C maximum temperature reduction under high temperature (∼100 °C) ambient conditions. The technical approach and design strategy are applicable to future wide band-gap (WBG) electronics packaging applications, where enhanced 3D thermal routing is expected to be critical to maximizing volumetric power density.

Improvement Of The Energy Efficiency Of Portland Cement Production During The Use Of The Natural Gas Liquid Processing Residue

The possibility is shown of improvement the energy efficiency of the high-temperature process of the Portland cement production through adding the organic-mineral addition - the gas residues. It was found that the use of gas condensation processing residues ensure the intensification of the phase formation during clinker burning with the reduction of maximum temperature by 150°C, which facilitates solving the issues of the resource preservation through the reduction of energy consumption when producing the Portland cement and gas residues recovery.

Analysis of the Efficiency of Elaborating the Technology of Producing the Portland Cement Clinker Through the Application of the Gas Production Industry Wastes

The authors show the possibility of improvement the energy efficiency of the high-temperature process of the Portland cement production through adding the organic-mineral addition – the gas residues. It was determined that the use of gas condensation processing residues provides for the intensification of the phase formation during clinker burning with the reduction of maximum temperature by 150°C, which facilitates solving the issues of the resource preservation through the reduction of energy consumption when producing the Portland cement and gas residues recovery.

Thermal, Mechanical, and dielectric properties of Injection Molded Graphene Nanocomposites Based on ABS/PC and ABS/PP Blends

In this research, graphene nanocomposites of poly(acrylonitrile‐butadiene‐styrene)/polycarbonate (ABS/PC) and ABS/polypropylene (ABS/PP) blends were prepared by melt blending and their thermal and mechanical properties were studied. The incorporation of graphene into ABS/PC and ABS/PP blends caused a significant decrease of their melt flow index values. Although graphene led to reduction of onset degradation temperature (Tonset) and maximum degradation rate temperature (Tpeak) of ABS/PC blends, and mainly of pure PC, the obtained residue from thermogravimetric analysis showed an increase. The thermal degradation of PC phase, in PC‐rich blends, was completed at higher temperatures. In ABS/PP blends, the effect of graphene was an outstanding increase ofTonsetandTpeakin the case of pure PP, while increasing the residue at all proportions. Regarding the Young's modulus, in ABS/PC blends the result of the addition of graphene was dependent on the blend composition. In ABS/PP hybrids, the elastic modulus increased by the incorporation of graphene and this increase, reached anabout 43% in pure PP. The addition of graphene to pure ABS, pure PP and their blend 50/50 w/w resulted in an increasing trend of the dielectric constant (κ′), whereas the loss factor (tanδ) was similar in non‐reinforced and graphene‐reinforced samples, within the entire range of the examined frequencies. POLYM. COMPOS., 40:E1662–E1672, 2019. © 2018 Society of Plastics Engineers

Preparation and thermal properties of encapsulated ceramsite-supported phase change materials used in asphalt pavements

Two kinds of phase change materials (PCMs), poly(ethylene glycol) (PEG) and ethylene glycol distearate (EGD), were incorporated with ceramsite (CS) to obtain the composite PCMs (CPCMs) by vacuum impregnation method. The morphology of the samples was observed using scanning electron microscope (SEM) and the chemical compatibility was characterized by X-ray diffraction (XRD) and Fourier transformation infrared (FTIR). The PEG and EGD could be retained by 42.1 wt% and 34.0 wt% into pores of the CS, which was calculated according to the curves of the thermogravimetric (TG) analysis. The thermal properties and thermal reliability of the CPCMs were investigated via differential scanning calorimetry (DSC). The phase change temperature (Tm) and heat of fusion (ΔHm) of prepared CPCMs are in the range of 54–60 °C and 29–50 J/g, respectively. The ΔHm of the CPCMs decreased obviously after 100 melting/freezing cycling, which was improved by encapsulating the prepared CPCMs with novolac epoxy resins (NER) to produce the encapsulated CPCMs (E-CPCMs). The results of the leakage experiment and storage/release test also show that the E-CPCMs have good thermal exudation stability and thermal storage/release properties. Based on all the results of the experiment, the encapsulated PEG/CS composite (E-PEG/CS) was added into the asphalt mixture to substitute the corresponding aggregate for simulating the actual temperature-adjusting effects. The results indicate that the maximum temperature reduction of the upper surface reaches about 9.1 °C at 210 min. Therefore, the E-CPCMs have the potential to decrease the high temperatures and temperature fluctuations in the asphalt pavements.