Modified polycaproamide fibres with improved heat resistance

Despite the availability of various materials for chimney applications, ongoing research seeks alternatives with improved thermal and chemical resistance. Geopolymers are a promising solution, exhibiting exceptional resistance to high temperatures, fire, and aggressive chemicals. This study investigates fly ash-based lightweight geopolymer concretes that incorporate expanded clay aggregate (E.C.A.), perlite (P), and foamed geopolymer aggregate (F.G.A.). The composites were designed to ensure a density below 1200 kg/m3, reducing overall weight while maintaining necessary performance. Aggregate content ranged from 60 to 75 wt.%. Physical (density, thickness, water absorption), mechanical (flexural and compressive strength), and thermal (conductivity, resistance) properties were evaluated. F.G.A. 60 achieved a 76.8% reduction in thermal conductivity (0.1708 vs. 0.7366 W/(m·K)) and a 140.4% increase in thermal resistance (0.1642 vs. 0.0683). The F.G.A./E.C.A./P 60 mixture showed the highest compressive strength (18.069 MPa), reaching 52.7% of the reference concrete's strength, with a 32.3% lower density (1173.3 vs. 1735.0 kg/m3). Water absorption ranged from 4.9% (REF.) to 7.3% (F.G.A. 60). All samples, except F.G.A. 70 and F.G.A. 75, endured heating up to 800 °C. The F.G.A./E.C.A./P 60 composite demonstrated well-balanced performance: low thermal conductivity (0.2052 W/(m·K)), thermal resistance up to 1000 °C, flexural strength of 4.386 MPa, and compressive strength of 18.069 MPa. The results confirm that well-designed geopolymer lightweight concretes are suitable for chimney and flue pipe linings operating between 500 and 1000 °C and exposed to acidic condensates and aggressive chemicals. This study marks the initial phase of a broader project on geopolymer-based prefabricated chimney systems.

This paper presents an evaluation of the reliability of hybrid power modules using a metal matrix composite baseplate. In this study, we investigate the possible damage in the assemblies by measuring their thermal resistance. Several 2/spl times/1 power module samples including four bipolar transistors (BUX48) have been realized with the use of a vacuum bake soldering machine allowing reduction of voids in the solder joints. The test vehicles have been submitted to liquid-liquid thermal shocks (+125/spl deg/C/-55/spl deg/C). Every 250 thermal shocks, two samples were extracted in order to measure the thermal resistance. Results show that even after 2700 shocks, only a very small increase in the thermal resistance of the assemblies is observed. In comparison, modules with a copper baseplate show a strong increase in thermal resistance and fail much earlier. As a consequence, in applications where thermal cycling is involved, hybrid power modules with metal matrix composite baseplates will offer much better reliability. SEM observations conducted on cross-sectioned samples and acoustic analysis do not show the typical cracks generally observed in solder joints between the direct bonded copper substrate and the copper baseplate of aged modules.

The cubic silicon carbide (3C-SiC) has been considered as a candidate structural material for several types of advanced nuclear reactors. The effects of cascade collision on thermal conductivity in symmetrical tilt grain boundary (GB) were studied by Molecular dynamics (MD) simulations. The thermal conductivity of 3C-SiC at Σ5(210)[001] GB was calculated using non-equilibrium molecular dynamics (NEMD) methods. A relatively small simulation unit was used to analyze the effect of different energies of incident PKA (primary knock-on atoms) on the thermal conductivity of 3C-SiC and to compare the results with perfect structure GB system. Finally, the vibrational density of states (VDOS) of atoms in the GB region was calculated to analyze the phonon mismatch at the interface. Calculations show that cascade collisions generated by energetic atoms will result in a decrease in thermal conductivity of the Σ5(210) GB system, but the effect varies in different regions, with a sharp decrease in thermal conductivity and an increase in thermal resistance for the intracrystalline region, while the magnitude of change in either thermal resistance or thermal conductivity is not significant in the GB region. Irradiated model shows a higher GB energy compared to the unirradiated model. For all irradiated models, lattice defects have a significant effect on the thermal conductivity of the GB system, depending on the spatial structure of the GBs. the results of the VDOS analysis suggest that an increase in the degree of atomic lattice mismatch near the interface is responsible for a further increase in the thermal resistance of the irradiated GB system.

A study of thermal cycling endurance of three different die attach adhesives by measuring the increase in thermal resistance during a thermal cycling test is discussed. Test chips were bonded to three substrates with different coefficients of thermal expansion. The thermal resistance increased with increased number of temperature cycles. A large mismatch in thermal expansion gave the fastest increase in thermal resistance. The study also revealed a significant difference in behavior between the different adhesives. >

Strategies and techniques for improving heat resistance and mechanical performances of poly(lactic acid) (PLA) biodegradable materials

A series of experiments on one commonly available loose-fill fiberglass attic insulation has been performed using the guarded hot box capability of the Large Scale Climate Simulator at the Oak Ridge National Laboratory. These experiments were conducted using an attic test module that was built to simulate typical residential construction. Under simulated winter conditions, the surface-to-surface thermal resistance between the bottom of the gypsum board and the top of the insulation was found to decrease substantially as the surface-to-surface temperature difference increased from 10 to 40 K. At the largest temperature differences, the resistances were as much as a factor of two lower than the estimated nominal thermal resistance of the insulation. This change in thermal resistance has been attributed to natural convection within the insulation. It should be noted that the present experiments were performed with one type of loose-fill fiberglass insulation, and the results may not be applicable to other loose-fill insulations with different air flow and thermal properties. A series of experiments was also performed with various materials laid on top of the insulation. The most effective of these covering systems produced increases in thermal resistance of more than 100 percent at the largest temperature differences, and appeared to nearly eliminate heat transfer by natural convection in the temperature range investigated.

In pursuit of sustainable energy solutions and to combat the environmental challenges posed by fouling in thermal devices, this study developed Ni-P-TiO2 and Ni-P-Polytetrafluoroethylene (Ni-P-PTFE) surfaces and explored the effectiveness of coatings in minimizing fouling on heat exchange surfaces. We conducted heat exchange experiments to compare the both coating surfaces with copper surface under identical clean conditions in microchannels. Further analyses explored fouling resistance across surfaces at various flow rates and solution hardness, complemented by Scanning Electron Microscope (SEM) images of fouling morphology. The findings revealed that decreasing surface energy and enhancing hydrophobic properties can reduce crystal fouling. Notably, both Ni-P-TiO2 and Ni-P-PTFE surfaces demonstrated superior performance, showing significantly lower thermal resistance compared to copper surface. Despite the increase in thermal resistance with solution concentration, the growth rate of fouling resistance declined gradually. The Ni-P-PTFE coating, benefiting from its lower surface energy and greater hydrophobicity, showed superior looseness and porosity. This study demonstrates the effectiveness of Ni-P-TiO2 and Ni-P-PTFE coatings in reducing fouling thermal resistance, offering a promising approach for improving microchannel device performance.

The use of local biomaterials in construction is becoming an imperative to save the planet and to reduce the cost of construction in sub-Saharan region. The aim of this research work is to study the effect of the mucilage of Grewia bicolor fiber on the properties of mud bricks. the mucilage from Grewia bicolor bark was used to stabilize raw earth bricks. Two formulations of samples are obtained. The first one is with 100% of soil and without mucilage. The second one the soil stabilized with mucilage at three different viscosities (25.30s, 20s and 10s). The output measurement are compressive and flexural strengths, as well as the thermal conductivity, thermal resistance and thermal effusivity of the composite material formulated. The results show an increase in compressive strength with the increase in viscosity of the mucilage. An increase in flexural strength when the viscosity of the mucilage is increased. A decrease in thermal conductivity when the viscosity of the mucilage is increased. An increase in thermal resistance when the viscosity of the mucilage is increased. Effusivity decreased with increasing of mucilage viscosity. These results show that the mucilage of Grewia bicolor can significantly improve the characteristics of mud bricks and this may have potential use in eco-construction for habitat.

Research was carried out on the influence of various silicone compounds on the properties of pressure-sensitive adhesives. Silicone-based pressure-sensitive adhesives have good self-adhesive properties and are used in many different industries. However, their thermal resistance is relatively low. In order to improve this property, modifications were made to these adhesives. Compositions were tested, such as viscosity or thermogravimetric analysis, as well as tests of finished products in the form of self-adhesive tapes, i.e., peel adhesion, tack, cohesion at room and elevated temperature, SAFT test (Shear Adhesive Failure Temperature), pot-live (viscosity) and shrinkage. During the tests, an increase in thermal resistance (225 °C), lower shrinkage (0.08%), and lower viscosity was achieved (16.5 Pas), which is a positive phenomenon in the technology of pressure-sensitive adhesives. Thanks to this research, the properties of silicone self-adhesive adhesives have been significantly improved.

A physical model is presented that describes mechanisms for operating-equipment junction-to-ambient thermal resistance in excess of a typical component manufacturer's data-sheet value by as much as a factor of four under constant cooling conditions. The model accounts for the discrepancy between system thermal performance of a package and data-sheet thermal resistance value which are not accompanied by qualifying data in the form of junction-to-header thermal resistance, board temperature rise over ambient, convection coefficient, mounting sensitivity, and power dissipation. The eight constants used to predict inherent increases in package thermal resistance when going from the data-sheet-specified operating conditions to the excess-value conditions are described. These constants and procedures for obtaining them are given for dual in-line packages (DIPs), pin-grid arrays (PGAs), small-outline transistors (SOTs), and plastic leaded chip carriers (PLCCs). >

Advanced insulations for refrigerator/freezers: the potential for new shell designs incorporating polymer barrier construction

Experimental study of the effects of the thermal contact resistance on the performance of thermoelectric generator

With the rapid spread of high-power density equipment, the vapor chamber must adapt to more applicable environments and exhibit a better heat transfer performance. The copper mesh and powder are sintered in this work to make a composite wick vapor chamber (CW-VC). Six sections of copper wire are cut and sintered together with the wick as the inner support column of the CW-VC. The effects of filling ratio and inclination on the heat transfer performance of the vapor chamber are investigated. The experimental results showed that the maximum thermal power of the CW-VC is 23.29 W at the optimal liquid filling ratio of 80% and the lowest thermal resistance is 0.33 °C/W. Below the liquid filling ratio of 60%, when the inclination angle of the CW-VC increases, its thermal resistance increases. At filling ratios of 70%, 80%, and 90%, the inclination angle of 30° can reduce the thermal resistance of the CW-VC. It implies that the inclination angle of the CW-VC can be increased appropriately to reduce the thermal resistance when the filling ratio is high. However, when the liquid filling ratio is low, increasing the inclination angle of the CW-VC will make the liquid film of the evaporator thinner and dry out earlier and its thermal resistance will increase.

Alkali-activated foams (AAFs) present one of the most promising materials for use in the construction sector. Their main advantages lie in their utilization of waste material and their ability to form at temperatures well below 100 °C, while still competing in performance with foamed glass or ceramics. The present body of research has focused on improving the thermal stability of fly-ash foams by i) adding metakaolin, and ii) changing the activator from sodium-based to potassium-based components. It has been confirmed that a certain increase in thermal resistance is achieved through the addition of metakaolin while changing activators played a crucial role. While sodium-based AAFs without metakaolin start to shrink at approximately 600 °C, samples that have had metakaolin added start to shrink at approximately 700 °C. Samples without metakaolin that have used a potassium activator start to shrink at approximately 800 °C, whereas potassium-based samples with the addition of metakaolin start to shrink at approximately 900 °C.

We investigated the role of alpha B-crystallin expression in the development of thermotolerance in murine L929 cells. An initial heat-shock of 10 min at 45 degrees C induced thermotolerance in these cells to a heat challenge at 45 degrees C administered 24 h later. The thermotolerance ratio at 10(-1) isosurvival was 1.7. Expression of alpha B-crystallin gene was not detected during the 24 h incubation at 37 degrees C following heat shock by either northern or western blots. In contrast, inducible HSP70 synthesis was observed during this time period. Thus, this cell line provided an unique system in which to examine the effects of transfected alpha B-crystallin on thermoresistance and thermotolerance. Cells stably transfected with alpha B-crystallin under the control of an inducible promoter did not show a significant increase in the ability to develop thermotolerance. However, a stably transfected L929 clone expressing high levels of constitutive alpha B-crystallin exhibited an approximately 50% increase in thermal resistance over parental and control cells. Though expression of alpha B-crystallin is not requisite for the development of thermotolerance in L929 cells, overexpression of transfected alpha B-crystallin can contribute to increased thermoresistance.