QUB is an innovative method enabling the experimental measurement of the total heat loss coefficient (HLC) of a building envelope in one night only. It is based on a simple theory, yet can be ...demonstrated to be accurate even in a short time and in real buildings, as long as certain experimental conditions are fulfilled.
This study combines analytical and numerical approaches to exactly solve the temperature response of an equivalent building submitted to a QUB test. This allows understanding that even with a short time experiment (less than a night), a reasonable accuracy on the estimated HLC can be obtained. The experiment has to be designed following a simple heating power criterion.
Calculation is then tested experimentally in various cases whether in climate chamber or in real field, and whether on light weight/not insulated building or a heavy weight/highly insulated building. Results show that the QUB method performed by fulfilling this criterion is a promising method to estimate the HLC of a real building in the field with a reasonable accuracy in one night.
Plate tectonic theory predicts subsidence and decreasing heat flow as young, hot buoyant lithosphere ages and cools. Oceanic cooling models are re-calibrated to a new ‘hydrothermal-free’ heat flow ...dataset to provide a better fit to heat flow on old (>80Ma) seafloor while simultaneously allowing for a more reasonable mantle potential temperature (1350°C). The plate model (constant basal temperature) and chablis (constant basal temperature and constant basal heat flow) are tested as viable solutions to the observed data. Both models fit to reasonable values of misfit, but only the plate cooling model is acceptable after considering additional statistical constraints. The best-fitting plate model results in a thinner lithospheric thickness (90km) than previous estimates. These results improve estimates of global heat loss rate through oceanic crust (29.4TW, ∼44TW globally) and improves the estimated temporal evolution of the thermal structure of oceanic lithosphere suggesting a shallower lithosphere–asthenosphere boundary. This model can serve as a reference for estimating the global redistribution of heat by ventilated hydrothermal circulation through young seafloor.
Cooling models for the oceanic lithosphere fit to heat flow-age data. Previous models (PS77 and GDH1) underpredict heat flow at old ages. New cooling models improve fit to heat flow and suggest plate cooling models provide the best fit. Display omitted
► New plate and chablis cooling models of the oceanic lithosphere are developed. ► Plate cooling models provide a better fit to observed heat flow. ► The new plate model improves the fit to heat flow on old lithosphere. ► Oceanic heat loss is estimated at 29.4TW for a total of 44TW globally. ► Plate thickness is estimated at 90km with reasonable adiabatic temperatures.
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•Hybrid nanofluids Al2O3 and SiC prepared by milling are used in an radiator.•Effect of milling nanoparticles (Al2O3 with SiC) on heat transfer was analysed.•Increase in Nu number of ...8.98 % and 23.4 % for 0.4 % and 0.8 % is recorded.•Increase in heat loss was achieved for Al2O3 with SiCM nanofluid at 0.8 %.
Innovative heat elimination technologies from the radiator are needed for weight reduction in an automotive vehicle to increase the overall performance. The fluids used nowadays are based on a combination of distilled water (DW) and ethylene glycol (EG), and also using nanofluids for improving heat transfer performance has been increased within the last couple of years. The use of aluminum oxide (Al2O3) doped with unmilled silicon carbide (SiCUM) nanoparticles and milled Silicon carbide (SiCM) nanoparticles dispersed in DW and EG at 50:50 volumetric proportions experimented in this work. The focus for the important characterization of the nf which includes thermophysical properties is elaborated in this paper. The outcomes showed an optimum improvement regarding the overall thermal performance of 28.34 % making use of Al2O3 doped with milled Silicon carbide(SiCM) at a volume concentration of 0.8 %. This might be due to the size reduction of SiC nanoparticles by the milling process involved in this experiment.
Excessive sweat secreted from the skin often causes undesired adhesion from wetted textiles and cold sensations. Traditional hydrophilic textiles such as cotton can absorb sweat but retain it. A ...hydrophobic/superhydrophilic Janus polyester/nitrocellulose textile embedded with a conical micropore array with a hydrophilic inner surface that can achieve directional liquid transport (with an ultrahigh directional water transport capability of 1246%) and maintain human body temperature (2–3 °C higher than with cotton textiles) is demonstrated. When the hydrophobic polyester layer with large opening of hydrophilic conical micropores contacts the liquid, the Janus polyester/nitrocellulose textile can pump it to the superhydrophilic nitrocellulose layer through the hydrophilic conical micropores driven by capillary force. The Janus polyester/nitrocellulose textile can weaken undesired wet adhesion and heat loss due to the removal of liquid. The water wicking and air permeability of the Janus polyester/nitrocellulose textile is comparable to those of traditional cloths. This study is valuable for designing of functional textiles with directional water transport properties for personal drying and warming applications.
A hydrophobic/superhydrophilic Janus polyester/nitrocellulose (PE/NC) textile with asymmetric hydrophilic conical micropores can be constructed by combining a simple laser perforating method and plasma modification. This textile can unidirectionally pump excessive sweat from the hydrophobic layer to the superhydrophilic layer through asymmetric hydrophilic conical micropores from large to small openings, thereby avoiding undesirable sticky and excessive cold sensations from sweat.
Buildings in the United States account for nearly half of total U.S. energy use. The energy used for space conditioning can be reduced by utilizing thermal energy storage, such as phase change ...materials (PCMs), into building envelopes; however, the energy savings of PCM-integrated building envelopes reported in the literature vary widely. In the absence of established guidelines, thermophysical requirements of an optimal PCM, its method of application into the building envelope, and the corresponding energy savings under various climates remain unknown. In this study, we perform an extensive numerical investigation on the integration of PCM into building walls to establish the key conditions required for effective utilization of PCM in reducing heat gains in the cooling season and heat losses in the heating season. We also determine the optimal transition temperature, optimal PCM location in the wall, and the energy-saving potential of the PCM-integrated building walls in five U.S. cities located in different International Energy Conservation Code climate zones. Results show that employing PCMs in building walls does not always lead to an improvement; in fact, incorrect applications of PCMs can substantially increase energy use in the buildings. In the climates we studied, PCMs were found effective in reducing heat gains during the cooling season while mostly ineffective in managing heat losses during heating season. Depending on the climate, optimized PCMs in U.S. building walls can provide reduction in the annual heat gain in the range of 3.5%–47.2% and the annual heat loss in the range of −2.8%–8.3%. Future consideration of buildings with substantial solar gains in winter may lead to more reduction in heat losses by PCMs.
•Energy conversion efficiency of STPV can reach ∼60% with spectral selected absorbers and small apertured radiation shields.•A ~1 µm bandwidth PHC emitter is required to reach the maximum ECEs of ...STPVs.•Compared with 1000 times, 100 times solar concentration allows operating temperature of STPVs within engineering limits.
An integrated analysis considering radiative energy transport among each component and carrier generation in the photovoltaic (PV) material is established for solar thermophotovoltaic (STPV) devices. STPV has been estimated with previous thermodynamics analysis to provide up to ∼85% solar energy conversion efficiency (ECE) because of its capability to convert broadband solar radiation to narrowband thermal radiation that can be fully used with PV materials. However, in previous demonstrations, the ECE of STPVs is less than 10%, even with ∼200 solar radiation concentrations. Based on our analysis, the maximum ECE of STPV without any radiation heat loss control is nearly zero when the solar concentration ratio is 1 and is ∼18.78% when the solar concentration ratio is 1000. Maximum ECE of STPV with spectral selected absorber optimized for 1000 K level temperature, which has been proposed in recent STPV studies, can be ∼9.56% when the solar concentration is 1 and can be ∼31.72% when the solar concentration ratio is 1000. Maximum ECE of STPV with our proposed multi-layered radiation shield to prevent radiative heat loss from the STPV to the ambient can provide ECE up to ∼9.53% and ∼57.02%, when the solar concentration ratio is 1 and 1000, respectively. When we combine both the spectral selected absorber and our designed radiation shield, the ECE value of STPV can be up to ∼20.65% and ∼59.23% when the solar concentration ratio is 1 and 1000, respectively. It is also observed that a ∼1 µm level bandwidth of photonic crystal (PhC), a device that can control the emission bandwidth, is required for STPV to achieve high ECE under each solar concentration ratio with difference radiative heat loss control.
Photothermal membrane distillation (PMD) has the potential to address freshwater scarcity, but heat loss during heat transfer from the photothermal surface to the feed bulk inevitably lower the ...photothermal-vapor conversion efficiency of this process. The permeation of VOCs during PMD also threatens the recycling of distilled water. Herein, a zeolitic imidazolate framework-67 (ZIF-67) wrapped graphene membrane (ZGM) was developed and used for the PMD process. The results demonstrated that the hierarchical porous structure and low heat conductivity of ZIF-67 endowed the ZGM with improved light absorbance and heat localization, thus sustaining a high cross-membrane temperature gradient. Under simulated sunlight illumination, the ZGM attained an additional flux of 0.91 kg m−2 h−1, corresponding to a photothermal efficiency of 62.1%, which was 183.2% higher than that of the pristine membrane. The temperature change near the photothermal coating was simulated, which showed that ZGM had slower heat conduction into the feed, demonstrating a confined heat effect. Meanwhile, the ZGM exhibited a good interception for phenol when peroxymonosulfate (PMS) was added to the hot feed. The distilled phenol concentration was 88.0% lower than that of the PMD without PS. Electron paramagnetic resonance (EPR) and radical quenching experiments verified that singlet oxygen (1O2) was the dominant reactive oxygen species during in-situ phenol degradation. This work provides a new strategy to develop advanced photothermal membranes to simultaneously promote the photothermal performance and VOC interception.
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•A novel photothermal membrane with MOF-wrapped graphene was developed.•MOF on the graphene surface significantly promoted light absorbance.•MOF-wrapped graphene exhibited a lower heat loss to feed bulk.•The photothermal membrane performed an increased photothermal efficiency.•The photothermal membrane decreased VOCs permeation via in-situ PMS activation.
•Moisture content in non-hygroscopic insulation materials was measured by a heating needle.•Test domain was released from the required infinite dimension to a finite thickness.•CFD modeling was ...adopted to correct the boundary heat loss effect.•The remedial strategy provided moisture content close to the gravimetric values.
Porous insulation materials may acquire moisture, and the moisture content must be accurately measured for appropriate maintenance of the materials. Current thermal methods for measuring moisture are applicable only to an infinite test domain. This paper used computational fluid dynamics (CFD) to investigate the effects of a finite test domain and the associated boundary heat loss on moisture measurement. Insulation material of various thicknesses, bounded by two solid plates, was modeled. The convective heat loss to the air from both solid plates was considered. The over-measured moisture content due to a finite geometric domain was regressed into formulas, by means of which the excessive amount could subsequently be deduced. The corrected moisture content was then compared with that obtained by gravimetric weighing using a digital precision balance. The results show that significant over-measurement of moisture content can occur for the tested insulation material with a thickness less than 4.5 cm. The remedial strategy is quite effective and can provide moisture content results that are close to the gravimetric values.
Abstract
Owing to its 100% theoretical salt rejection capability, membrane distillation (MD) has emerged as a promising seawater desalination approach to address freshwater scarcity. Ideal MD ...requires high vapor permeate flux established by cross-membrane temperature gradient (∆T) and excellent membrane durability. However, it’s difficult to maintain constant ∆T owing to inherent heat loss at feedwater side resulting from continuous water-to-vapor transition and prevent wetting transition-induced membrane fouling and scaling. Here, we develop a Ti
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MXene-engineered membrane that imparts efficient localized photothermal effect and strong water-repellency, achieving significant boost in freshwater production rate and stability. In addition to photothermal effect that circumvents heat loss, high electrically conductive Ti
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MXene also allows for self-assembly of uniform hierarchical polymeric nanospheres on its surface via electrostatic spraying, transforming intrinsic hydrophilicity into superhydrophobicity. This interfacial engineering renders energy-efficient and hypersaline-stable photothermal membrane distillation with a high water production rate under one sun irradiation.
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