Reduction In Peak Temperature Research Articles

Outdoor Performance of Fluidic Glass–Glass Laminate Windows for Building Integration

Fluidic windows enable the implementation of liquids in building envelopes. Such liquids may act as a heat reservoir and exchange medium or provide additional functionality to the building skin. Here, outdoor operations of double‐glazed windows which include a transparent capillary panel as one of the glazings are reported. The capillary devices were used as heat exchangers by which water circulates across the window surface. A mobile demonstration facility is built, which uses 1.6 m2 of active window surface for thermal input to a test room of 9 m3. Outdoor operations are conducted over multiple weeks in winter and summer seasons to demonstrate hydronic heating and cooling, respectively, by varying the inlet temperature and the flow rate of the circulating liquid. For heating operations at an outdoor air temperature of −5 °C, an overall heat transfer coefficient of 22 W m−2 K−1 is demonstrated. Using the same system for cooling with southeast façade orientation at an average solar irradiance of 800 W m−2 enables significant reduction of peak and average room temperature. In comparison to conventional heating, ventilation and air‐conditioning technology, a significant reduction of the applied temperature gradient and air circulation rates is achieved.

Passive Thermal Management of Tablet PCs Using Phase Change Materials: Intermittent Operation

This paper presents an experimental study of thermal management in a tablet PC under intermittent operation, with phase change materials (PCMs) encapsulated in a very thin aluminized laminate film container. It complements a study of the same system under continuous operation that was published in 2018. Two different types of PCMs were used for the experimental work; PT-37 and n-eicosane. A commercially available tablet PC was used as a test subject to ensure representative dimensions and material properties of every intricate part of the real tablet PC. For intermittent operation, the cycle used corresponds to fifteen minutes of operation (heat generation) followed by fifteen minutes of rest, to imitate a regular usage pattern of a tablet PC. It was observed that thin PCM thermal energy storage (TES) units are capable of providing a reduction in the rate of temperature increase during transient operations for both the electronics and the tablet cover. Reduction in peak temperature of the heat source and external surfaces of the tablet PC was also observed. At the maximum of 8 W operating power, PCMs were able to reduce the back-cover temperature by 20 °C. At all power inputs, heat storage in PCMs resulted in back-cover temperatures lower than 40 °C. Moreover, it was found that the PCM thermal management system tested was not affected by the inclination of the tablet PC. Results obtained from this study confirm that thin PCM encapsulation is indeed a suitable solution to control the temperature in tablet PCs during intermittent operation.

Blending effect between the natural gas and the liquefied petroleum gas using multiple co- and cross-flow jets on NOx emissions

Abstract A burner comprising multiple co- and cross-flow jets was developed to address the effect of blending the natural gas (NG) with the liquefied petroleum gas (LPG) on the NOx emissions from laminar/turbulent diffusion and triple flames in the normal and inverse configurations. Increasing the NG mole fraction in the blend from 0.0 to 1.0 decreased the effective Schmidt number from 1.4 to 0.7 thus displacing the flame envelope into higher velocity regions such that the corresponding decrease in residence time caused NOx reduction by 46%. While the prompt NOx increased by 11%, there was an additional NOx reduction by 238% due to the residence time decrease pertaining to the density/velocity difference. Conversely, increasing the LPG mole fraction from 0.0 up to 1.0 extended the flame stability limit from 8.2 to 12.7 m/s whereby the residence time decrease caused NOx reduction by 49%. Furthermore, the peak temperature reduction by the flame increased soot-radiation additionally caused exponential NOx reduction. The NG optimum mole fraction in the blend for reaching minimum NOx emissions of about 0.035 g/kW hr in the normal diffusion flame decreased from 0.80 to 0.25 as the firing rate increased 9.5 times, while a further NOx reduction to 0.028 g/kW hr was obtained in the inverse diffusion flame. Employing cross-flow opposing air jets reduced the NOx emissions further to 0.017 g/kW hr and shortened the flame by 36% as increasing the strain rate to 2900 s−1 enlarged the peak turbulent kinetic energy to 11.9 m2/s2 with 12 jets. In the triple flame mode, supplying the LPG across the fuel-rich wing and the NG across the lean wing combined high radiation efficiencies, flame shortening and extensive stability limits of 4.8 m/s. The NOx emission index thus reached 0.3 g/kg fuel for the inverse triple flames.

High-Speed Friction Stir Welding of SiCp/Al–Mg–Si–Cu Composite

A 17 vol% SiCp/Al–Mg–Si–Cu composite plate with a thickness of 3 mm was successfully friction stir welded (FSWed) at a very high welding speed of 2000 mm/min for the first time. Microstructural observation indicated that the coarsening of the precipitates was greatly inhibited in the heat-affected zone of the FSW joint at high welding speed, due to the significantly reduced peak temperature and duration at high temperature. Therefore, prominent enhancement of the hardness was achieved at the lowest hardness zone of the FSW joint at this high welding speed, which was similar to that of the nugget zone. Furthermore, the ultimate tensile strength of the joint was as high as 369 MPa, which was much higher than that obtained at low welding speed of 100 mm/min (298 MPa). This study provides an effective method to weld aluminum matrix composite with superior quality and high welding efficiency.

Thermal impact of adhesive-mounted rooftop PV on underlying roof shingles

Adhesive mounting of residential rooftop photovoltaics (PV) is an alternative to traditional rack mounting that reduces installation costs. Adhesive mounting is fast, simple and reduces the need for skilled labor. In our novel design that further reduces the installation costs, a lightweight (glassless and frameless) PV module is directly adhered to a shingled roof using an adhesive tape, creating a <5 mm air gap between the PV back-panel and the roof shingle surface. Although the gap is sufficient for moisture and rainwater transport under the PV panel, potential heat buildup under the module may adversely impact the long-term durability of the shingles. Heat buildup may also increase the heat flux through the roof, resulting in an overall increase in building cooling loads. This study investigates the thermal behavior of the roof under an adhered PV system. Two identical test huts with dark shingle-covered roofs were located in the hot, desert climate of Albuquerque, NM. Adhesively-mounted lightweight PV modules were installed on the south-facing roof of one of the test huts (PV hut), with the other one serving as a reference hut. During the summer season, the asphalt roof shingles under the PV modules experienced a 13 °C reduction in daytime peak temperature compared with the exposed shingles. No evidence of heat buildup under the PV module was observed. It was also found that the temperature of shingles underneath the adhesive was up to 6 °C higher than for shingles underneath the gap space at the daily peak time. Thin but ventilated air gap between the PV back-panel and the roof shingles helped remove the heat, while the adhesive pads (patches) served as thermal bridges between the PV module and the roof. Daily peak heat flow through the attic ceiling was almost 49% lower in the PV hut compared to the reference hut. These results show no evidence of an adverse thermal impact of the adhesive-mounted PV system on the roofing materials, while demonstrating a potential for a notable reduction in space conditioning energy requirements.

Numerical Thermal Characterization and Performance Metrics of Building Envelopes Containing Phase Change Materials for Energy-Efficient Buildings

Residential and commercial buildings consume nearly 40 percent of total USA energy use and account for one-third of total greenhouse gas emissions. The challenges are how to effectively promote energy efficiency in buildings to respond to the high financial burden of energy consumption, while reducing pollution. Phase change materials (PCMs) have been used as passive energy storage for building systems. Along this vein, this study aims to numerically elucidate the design parameters of building envelopes strengthened by PCM layers, and unveil their impacts on building energy efficiency. Critical design variables, such as the thickness of the PCM layer, the latent heat of PCMs, or melting temperature of PCMs were selected for a parametric study, while performance metrics were used to assess building efficiency. Results revealed that PCM-enabled building walls exhibited different levels of improvement, in terms of reduction of peak temperature and temperature swings. Among the variables, the selection of the proper melting point for a PCM was identified as the most crucial parameter for determining building energy efficiency, while the heat of fusion was also observed as a critical property of PCM for building potential. Findings also demonstrated that the placement of the PCM near the interior wall surface could achieve higher efficiency, as compared to other cases. Results also showed that the thermal conductivity of PCM has a minimum contribution to energy storage capacity.

Genetic Algorithm-based thermal uniformity–aware X-filling to reduce peak temperature during testing

High temperature occurs in testing of complex System-on-Chip designs and it may become a critical concern to be carefully taken into account with continual development in Very Large Scale Integration technology. Peak temperature significantly affects the reliability and the performance of the chip. So it is essential to minimize the peak temperature of the chip. Heat generation by power consumption and heat dissipation to the surrounding blocks are the two prominent factors for the peak temperature. Power consumption can be minimized by a careful mapping of don’t cares in precomputed test set. However, it does not provide the solution to peak temperature minimization because the non-uniformity in spatial power distribution may create localized heating event called “hotspot.” The peak temperature on the hotspot is minimized by Genetic Algorithm–based don’t care filling technique that reduces the non-uniformity in spatial power distribution within the circuit under test while maintaining the overall power consumption at a lower level. Experimental results on ISCAS89 benchmark circuits demonstrate that 6%–28% peak temperature reduction can be achieved.

Evaluation of processing variables in polymer projection sintering

PurposeProjection sintering, a system for selectively sintering large areas of polymer powder simultaneously with a high-power projector is introduced. This paper aims to evaluate the suitability of laser sintering (LS) process parameters for projection sintering, as it uses substantially lower intensities, longer exposure times and larger areas than conventional LS.Design/methodology/approachThe tradeoffs in sintering outcomes are evaluated by creating single layer components with varied exposure times and optical intensities. Some of these components were cross-sectioned and evaluated for degree of densification, while the single-layer thickness and the maximum tensile force was measured for the rest.FindingsShorter exposure times and higher intensities can create thicker and therefore stronger parts than when equal energy is applied over longer exposures. This is different from LS in which energy input (Andrew’s Number) is accepted as a reliable process variable. This difference is likely because significant thermal energy is lost from the sintering region during the exposure time – resulting in reduced peak temperatures. These thermal losses can be offset by imparting additional energy through increased exposure time or light intensity.Practical implicationsMost methods for evaluating LS process parameters, such as the energy melt ratio and Andrew’s Number, estimate energy input from basic process parameters. These methods do not account for thermal losses and assume that the powder absorbs all incident light. These methods become increasingly inaccurate for projection sintering with visible light where exposure times are much higher (>1s) and a larger portion of the light is reflected from the power’s surface. Understanding the appropriate sintering criteria is critical for the development of long-exposure sintering.Originality/valueA new method of selectively sintering large areas is introduced that could sinter a wider variety of materials by enabling longer sintering times and may increase productivity relative to LS. This work shows that new processing parameters are required for projection sintering as traditional LS process parameters are inadequate.

Passive thermal energy storage, part 1: Design concepts and metrics

Thermal energy storage (TES) systems can be designed in order to maximize their impact on a specific design target, such as reducing indoor temperature diurnal swings. Identifying the foremost design objective(s) is highly important since different design objectives result in distinct optimal designs. This paper compares several design concepts and associated criteria that can be satisfied with passive TES in various applications with a focus on isolated gain spaces like solaria and greenhouses.Potential design targets for thermal mass design strategies are compared along with common metrics used to characterize the performance of TES systems. Different design objectives/parameters are discussed, such as: 1) optimal time lag; 2) optimal decrement factor and transfer admittance; 3) reduction of space heating and cooling energy consumption; 4) minimizing indoor temperature swings; 5) maximizing the room average temperature under passive response; 6) reducing peak temperatures. This review of targets and metrics provides a basis for identifying the most relevant performance variables for solaria and greenhouses. A novel metric is presented for characterizing the time lag between the peak absorbed solar radiation and the peak TES surface temperature: τ[Qa−Ts]. A methodology and design recommendations for integrating TES into solaria and greenhouses are presented in Part 2.

Thermal-hydraulic design and analysis of a small modular molten salt reactor (MSR) with solid fuel

Summary A 20 MWth, 540 EFPD once through fuel cycle small modular molten salt reactor with solid fuel is proposed by Massachusetts Institute of Technology for off-grid applications. In this paper, various thermal-hydraulic analysis methods including computational fluid dynamics, Reactor Excursion Leak Analysis Program (RELAP5), and DAKOTA are adopted step-by-step for the reactor design based on the neutronic analysis results. First, 1/12th full core thermal hydraulic analysis is performed by using STAR CCM+ with most conservative considerations. Second, the transient safety behaviors of reactor system with risky assumptions are conducted by using REALP5. Finally, due to the unknown factors affecting reactor thermal-hydraulic characteristics, the uncertainty quantification and sensitivity analysis for the designed reactor is performed with DAKOTA code coupled with RELAP5. Numerical results show that a more uniform temperature distribution with reduced peak temperatures of fuel and coolant across the reactor core has been achieved. Enough safety margin is maintained even under most severe transient accident. The uncertainties in the heat transfer coefficient and helium gap conductivity factor are the most remarkable contributors to the statistical results of peaking fuel temperature. All above results preliminarily indicate the feasibility of the current small modular molten salt reactor design and provide the further optimization direction from reactor thermal-hydraulic prospective.

Going Cooler With Timing-Constrained TeSHoP: A Temperature Sensing-Based Hotspot-Driven Placement Technique for FPGAs

The continuous shrinking of the feature size in CMOS technology has significantly increased the power densities of integrated circuits, leading to severe temperature issues. However, the previous offline simulation-based thermal optimization works cast large deviations with the reality, while online sensing-based thermal managements usually incur significant performance overhead. Therefore, it is crucial to propose a method that could achieve fine-grained optimization with accurate temperature profiles. In this paper, we propose a timing-constraint temperature sensing-based hotspot-driven placement technique for field-programmable gate arrays (FPGAs). The hotspot optimization issue is modeled as a hyper minimum bipartite matching problem and is solved by a place adjustment with the input of an online sensed temperature profile. We propose an open-source/commercial hybrid design flow to implement the whole optimization in Xilinx Virtex-6 FPGA. Experimental results demonstrate a significant reduction in peak temperature and a great improvement on thermal uniformity, with slight performance overhead under timing constraints.

Thermal characterization of polycrystalline diamond thin film heat spreaders grown on GaN HEMTs

Polycrystalline diamond (PCD) was grown onto high-k dielectric passivated AlGaN/GaN-on-Si high electron mobility transistor (HEMT) structures, with film thicknesses ranging from 155 to 1000 nm. Transient thermoreflectance results were combined with device thermal simulations to investigate the heat spreading benefit of the diamond layer. The observed thermal conductivity (κDia) of PCD films is one-to-two orders of magnitude lower than that of bulk PCD and exhibits a strong layer thickness dependence, which is attributed to the grain size evolution. The films exhibit a weak temperature dependence of κDia in the measured 25–225 °C range. Device simulation using the experimental κDia and thermal boundary resistance values predicts at best a 15% reduction in peak temperature when the source-drain opening of a passivated AlGaN/GaN-on-Si HEMT is overgrown with PCD.

Determination of Temperature Rise and Temperature Differentials of CEMII/B-V Cement for 20MPa Mass Concrete using Adiabatic Temperature Rise Data

Experimental test was carried out to determine the temperature rise characteristics of Portland-Fly-Ash Cement (CEM II/B-V, 42.5N) of Blaine fineness 418.6m2/kg and 444.6m2/kg respectively for 20MPa mass concrete under adiabatic condition. The estimation on adiabatic temperature rise by way of CIRIA C660 method (Construction Industry Research & Information Information) was adopted to verify and validate the hot-box test results by simulating the heat generation curve of the concrete under semi-adiabatic condition. Test result found that Portland fly-ash cement has exhibited decrease in the peak value of temperature rise and maximum temperature rise rate. The result showed that the temperature development and distribution profile, which is directly contributed from the heat of hydration of cement with time, is affected by the insulation, initial placing temperature, geometry and size of concrete mass.The mock up data showing the measured temperature differential is significantly lower than the technical specifications 20°C temperature differential requirement and the 27.7°C limiting temperature differential for granite aggregate concrete as stipulated in BS8110-2: 1985. The concrete strength test result revealed that the 28 days cubes compressive strength was above the stipulated 20MPa characteristic strength at 90 days. The test demonstrated that with proper concrete mix design, the use of Portland flyash cement, combination of chilled water and flake ice, and good insulation is effective in reducing peak temperature rise, temperature differential, and lower adiabatic temperature rise for mass concrete pours. As far as the determined adiabatic temperature rise result was concern, the established result could be inferred for in-situ thermal properties of 20MPa mass concrete application, as the result could be repeatable on account of similar type of constituent materials and concrete mix design adopted for permanent works at project site.

Peak temperature reduction by optimizing power density distribution in 3D ICs with microchannel cooling

Liquid cooling with microchannels is a very attractive idea for 3D ICs which could help solving the problem of ever-increasing power dissipation due to its good cooling efficiency and potential scalability. However, this cooling method has some very different properties compared to the well-understood forced air convection. In particular, its cooling efficiency with respect to power variations in the chip is still not completely analyzed. Therefore, in this paper a thorough study of microchannel cooling efficiency as a function of intra- and interlayer power consumption variability is presented. We use a finite element method analysis to run a coupled thermo-fluidic simulation of a dedicated 3D chip model. An analytical analysis is also provided which calculates analytically the optimal power density profile along the channel. Then, steps necessary for finding the optimal power distribution for chip units are proposed. It is also shown that by appropriately managing the power density according to the proposed methodology, it is possible to significantly reduce the peak chip temperature. In particular, for a 3D chip including Intel's i7-6950X 10-core processor, a temperature reduction of 8.9°C was achieved by a proper orientation of microchannels and another 5.8°C reduction was obtained by optimally distributing power consumption between processor cores.

Notched K-wire for low thermal damage bone drilling

The Kirschner wire (K-wire) is a common bone drilling tool in orthopedic surgery to affix fractured bone. Significant heat is produced due to both the cutting and the friction between the K-wire and the bone debris during drilling. Such heat can result in high temperatures, leading to osteonecrosis and other secondary injuries. To reduce thermal injury and other high-temperature associated complications, a new K-wire design with three notches along the three-plane trocar tip fabricated using a thin micro-saw tool is studied. These notches evacuate bone debris and reduce the clogging and heat generation during bone drilling. A set of four K-wires, one without notches and three notched, with depths of 0.5, 0.75, and 1mm, are evaluated. Bone drilling experiments conducted on bovine cortical bone show that notched K-wires could effectively decrease the temperature, thrust force, and torque during bone drilling. K-wires with notches 1mm deep reduced the thrust force and torque by approximately 30%, reduced peak temperatures by 43%, and eliminated blackened burn marks in bone. This study demonstrates that a simple modification of the tip of K-wires can effectively reduce bone temperatures during drilling.

Multi-focal HIFU reduces cavitation in mild-hyperthermia

BackgroundMild-hyperthermia therapy (40–45 °C) with high-intensity focused ultrasound (HIFU) is a technique being considered in a number of different treatments such as thermally activated drug delivery, immune-stimulation, and as a chemotherapy adjuvant. Mechanical damage and loss of cell viability associated with HIFU-induced acoustic cavitation may pose a risk during these treatments or may hinder their success. Here we present a method that achieves mild heating and reduces cavitation by using a multi-focused HIFU beam. We quantify cavitation level and temperature rise in multi-focal sonications and compare it to single-focus sonications at the transducer geometric focus.MethodsContinuous wave sonications were performed with the Sonalleve V2 transducer in gel phantoms and pork at 5, 10, 20, 40, 60, 80 acoustic watts for 30 s. Cavitation activity was measured with two ultrasound (US) imaging probes, both by computing the raw channel variance and using passive acoustic mapping (PAM). Temperature rise was measured with MR thermometry at 3 T. Cavitation and heating were compared for single- and multi-focal sonication geometries. Multi-focal sonications used four points equally spaced on a ring of either 4 mm or 8 mm diameter. Single-focus sonications were not steered.ResultsMulti-focal sonication generated distinct foci that were visible in MRI thermal maps in both phantoms and pork, and visible in PAM images in phantoms only. Cavitation activity (measured by channel variance) and mean PAM image value were highly correlated (r > 0.9). In phantoms, cavitation exponentially decreased over the 30-second sonication, consistent with depletion of cavitation nuclei. In pork, sporadic spikes signaling cavitation were observed with single focusing only. In both materials, the widest beam reduced average and peak cavitation level by a factor of two or more at each power tested when compared to a single focus. The widest beam reduced peak temperature by at least 10 °C at powers above 5 W, and created heating that was more spatially diffuse than single focus, resulting in more voxels in the mild heating (3–8 °C) range.ConclusionsMulti-focal HIFU can be used to achieve mild temperature elevation and reduce cavitation activity.

Experimental study of a modified solar phase change material storage wall system

Aiming at satisfying demands of buildings in hot summer and cold winter regions, this work proposed a dual-channel and thermal-insulation-in-the-middle type solar phase change material storage wall system. The system has four independent functions: passive solar heating, heat preservation, heat insulation, and passive cooling, and it can agilely cope with requirements of climatization of buildings in different seasons throughout the year. The analysis of measured data from comparative tests on a hot-box test platform, shows that in summer, the daily average temperatures in the experimental room are 29.8 °C, 30.9 °C and 31.0 °C respectively, while those in the reference room are 29.6 °C, 30.7 °C and 30.8 °C, and thereby the difference is small. The south-facing wall with solar collector module shows reduction in peak temperature and delay phenomenon compared with that without solar collector module. These aspects highlighted by the results together indicate that effective prevention from summer overheating problem can be achieved by this system. In winter, by comparison with the ambient temperatures and those of the reference room, the air temperatures in the experimental room, both its maximum and average, raise greatly showing good heating effect. In addition, some distinct thermal characteristics of the system operated in summer or winter are obtained.

Energy‐Efficient Heat Storage using Gypsum Board with Fatty Acid Ester as Layered Phase Change Material

AbstractThe thermal performance of phase change materials (PCMs) for energy savings is important in various fields. Fatty acid waxes are types of organic fatty acid ester PCMs made from under‐used and renewable feedstocks. However, they possess one major drawback, namely their phase instability in the liquid state. Therefore, to improve stability during phase transitions, a new method of leakage prevention was developed to form the layer. The thermal properties of the layered PCM gypsum boards were analyzed by differential scanning calorimetry (DSC), phase change, enthalpy, and leakage tests. Finally, a dynamic heat transfer analysis of the layered PCM gypsum board was performed for the evaluation of the peak temperature reduction time lag effects of the prepared specimen. The latent heats of palm wax (PW) and beeswax (BW) were 178.1 and 173.6 J g−1 during heating, 159.7 and 140.9 J g−1, during freezing, respectively. Furthermore, the peak temperatures of the three wax‐infused layered PCM gypsum board samples were reduced by 4.6, 6.6 and 0.9 °C, respectively, compared with reference gypsum board.

Recycling of poly (lactic acid)/silk based bionanocomposites films and its influence on thermal stability, crystallization kinetics, solution and melt rheology

In this study, the effect of silk nanocrystals (SNCs) on the thermal and rheological properties of poly (lactic acid) (PLA) under repetitive extrusion process is investigated. The presence of SNCs facilitates the crystallization process and delaying the thermal degradation of PLA matrix. This leads to the reduction in cold crystallization peak temperature with lower crystallization half-time and higher growth rate. The substantial improvement in nucleation density observed through Polarized Optical Microscope (POM) proves the nucleating effect of SNC in all processing cycles. Moreover, the rheological investigation (complex viscosity, storage and loss modules values) revealed the stabilizing effect of SNC and the drastic degradation of neat PLA (NPLA) in third and fourth cycle is observed to be fortified by the presence of SNC. Cole–Cole plot and cross over frequencies have been correlated with the molar mass distribution of PLA and PLA-Silk composite during processing, which is further supported by the intrinsic viscosity measurement and acid value analysis. This investigation suggests that the melt viscosity and thermal properties of PLA can be stabilized by addition of silk nanocrystals.

Controlling processing temperatures and self-limiting behaviour in intense pulsed sintering by tailoring nanomaterial shape distribution

Intense pulsed light sintering of Ag nanoparticle–nanowire films shows reduced peak temperatures and a self-limiting behavior controlled by NW content.