To ensure good thermal performance is delivered consistently and at scale, there is a need to measure and understand the as-built heat loss of dwellings. Co-heating is a steady state, linear ...regression method, used to measure whole building heat transfer coefficients. This paper assesses the uncertainties in such outdoor, in situ, measurements due to the presence and treatment of solar gains. Uncertainties relating to solar gains are explored through both a number of field test results and simulated co-heating tests. Results demonstrate the potential for fractions of solar gains received on one day to be re-emitted on subsequent days. This dynamic behaviour can lead the steady state analysis to underestimate heat loss. Furthermore, inappropriate measurements of on-site solar radiation are shown to lead to bias in heat loss measurements. In particular, horizontal on-site solar radiation measurements are shown to significantly overestimate heat loss in buildings experiencing high proportions of direct gains through vertical openings. Both forms of uncertainty are dependent upon both the environmental test conditions and the characteristics of a test dwelling. Highly glazed, low heat loss and heavyweight buildings prove to be the most susceptible to such uncertainties, which ultimately limit both when tests can be successfully performed and which buildings can be tested.
A new dataset of nearly 15,000 oceanic heat flow measurements is analyzed to determine the conductive heat loss through the seafloor. Many heat flow values in seafloor younger than 60
Ma are lower ...than predicted by models of conductively cooled lithosphere. This heat flow deficit is caused by ventilated hydrothermal circulation recharge and discharge at crustal outcrops or areas of thin sedimentary cover. Filtering heat flow data, retaining only sites with >
400
m of sediment cover and located >
60
km from the nearest seamount, minimizes the effect of hydrothermal ventilation. Filtered heat flow exhibits a much higher correlation coefficient with seafloor age (up to 0.95 for filtered data in contrast to 0.5 for unfiltered data) and lower variability (reduction by 30%) within an age bin. A small heat flow deficit still persists at ages <
25
Ma, possibly as a result of global filtering limitations and incomplete thermal rebound following sediment burial. Detailed heat flow surveys co-located with seismic data can identify environments favoring conductive heat flow; heat flow collected in these environments is higher than that determined by the filtered global dataset, and is more consistent with conductive cooling of the lithosphere. The new filtered data analysis and the growing number of site specific surveys both support estimates of global heat loss in the range 40–47 TW.
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► We analyze ~
15,000 ocean heat flow observations globally. ► Sediment and seamount filters improve conductive heat loss estimates. ► Site-specific analyses provide robust estimates of conductive heat loss. ► Filtered heat flow vs. age is consistent with conductive plate cooling models. ► Estimated heat flow vs. age is consistent with oceanic heat loss, 40–47 TW.
Present global warming is amplified in the Arctic and accompanied by unprecedented sea ice decline. Located along the main pathway of Atlantic Water entering the Arctic, the Barents Sea is the site ...of coupled feedback processes that are important for creating variability in the entire Arctic air‐ice‐ocean system. As warm Atlantic Water flows through the Barents Sea, it loses heat to the Arctic atmosphere. Warm periods, like today, are associated with high northward heat transport, reduced Arctic sea ice cover, and high surface air temperatures. The cooling of the Atlantic inflow creates dense water sinking to great depths in the Arctic Basins, and ~60% of the Arctic Ocean carbon uptake is removed from the carbon‐saturated surface this way. Recently, anomalously large ocean heat transport has reduced sea ice formation in the Barents Sea during winter. The missing Barents Sea winter ice makes up a large part of observed winter Arctic sea ice loss, and in 2050, the Barents Sea is projected to be largely ice free throughout the year, with 4°C summer warming in the formerly ice‐covered areas. The heating of the Barents atmosphere plays an important role both in “Arctic amplification” and the Arctic heat budget. The heating also perturbs the large‐scale circulation through expansion of the Siberian High northward, with a possible link to recent continental wintertime cooling. Large air‐ice‐ocean variability is evident in proxy records of past climate conditions, suggesting that the Barents Sea has had an important role in Northern Hemisphere climate for, at least, the last 2500 years.
Key Points
Large air‐ice‐ocean decadal fluctuations
Recent winter sea ice loss due to Atlantic heat transport
Intense heat fluxes causes dense water formation and Carbon uptake
In the present theoretical study, a comparative performance analysis of a single cylinder compression ignition engine with diesel, 5% and 10% water in diesel emulsion as fuels have been investigated. ...Effect of variation in engine operating parameters like inlet pressure, friction coefficient compression ratio, equivalence ratio, and a residual gas fraction on engine performance parameters, i.e., effective power, effective power density, and total heat loss have been analyzed. Analysis has been carried out on the basis of isobaric heat addition and isochoric heat rejection assumptions with temperature variable specific heats and composition of alternative fuels. Microexplosion phenomenon for secondary atomization in water in diesel emulsion fuels improves the fuel combustion efficiency for better performance.
The theoretical analysis revealed that the effective power and effective power density for diesel fuel are found to be increased by 14.4% and 28.6% respectively, compared to 5% and 10% water in diesel emulsion fuels in compression ignition engine at 1 bar inlet pressure. Highest effective power and effective power density are obtained with an equivalence ratio of 1.2 for all mentioned fuels. Increase in inlet pressure results in increase effective power, effective power density, and total heat loss performances. Highest effective efficiency has been found with an equivalence ratio of 0.89 for diesel, 5% and 10% water in diesel emulsion fuels and is highly affected by inlet pressure for all mention fuel type. Also, an increase in friction coefficient and residual gas fraction decreases effective power, effective power density and effective efficiency for diesel, 5% and 10% water in diesel emulsion fuels. Obtained results are an essential tool for compression ignition engine designer and also provoked to use the water in diesel emulsion fuels as an alternative fuel in place of neat diesel fuel.
•EP and EPD for diesel, 5%WiDE, 10%WiDE fuels have been investigated.•Effective efficiency is higher for 10%WiDE and followed by 5%WiDE and diesel fuels.•Diesel fuel having 11.16% higher total heat loss compared to 10% WiDE fuel.•Optimum EP and EPD are observed at an equivalence ratio of 1.2 for all mentioned fuels.•EP and EPD significantly increases with inlet pressure but EE is negligible.
Softening of thermoelectric generators facilitates conformal contact with arbitrary-shaped heat sources, which offers an opportunity to realize self-powered wearable applications. However, existing ...wearable thermoelectric devices inevitably exhibit reduced thermoelectric conversion efficiency due to the parasitic heat loss in high-thermal-impedance polymer substrates and poor thermal contact arising from rigid interconnects. Here, we propose compliant thermoelectric generators with intrinsically stretchable interconnects and soft heat conductors that achieve high thermoelectric performance and unprecedented conformability simultaneously. The silver-nanowire-based soft electrodes interconnect bismuth-telluride-based thermoelectric legs, effectively absorbing strain energy, which allows our thermoelectric generators to conform perfectly to curved surfaces. Metal particles magnetically self-assembled in elastomeric substrates form soft heat conductors that significantly enhance the heat transfer to the thermoelectric legs, thereby maximizing energy conversion efficiency on three-dimensional heat sources. Moreover, automated additive manufacturing paves the way for realizing self-powered wearable applications comprising hundreds of thermoelectric legs with high customizability under ambient conditions.
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•The conductive heat loss of an interfacial photothermal evaporator is harvested.•The evaporation rate is up to 4.51 kg m-2 h−1 with excellent salt-resistance.•The device obtains a ...considerable power density of 1.2 W m−2 at 4 suns.•The output current becomes stable within 2 min if the light intensity is changed.
The solar-driven interfacial water evaporation technique enables to sustainably produce potable water from sewage, wastewater, and seawater. Limited by the advanced functional materials and structures, however, the contradiction between high evaporation rate and low heat loss needs to be further optimized in terms of improving energy efficiency. Herein, a two-dimensional solar absorber in which the vertical substrate pumps water to the top surface for sustainable evaporation and reducing heat conduction channels between the evaporation surface and the bulk water is introduced. In addition, the surplus heat of the solar absorber is directly and quickly conducted to a thermoelectric device for electricity generation. This configuration endows the hybrid device with a power density of 1.2 W m−2 at an external resistance of 4 Ω together with an evaporation rate of 4.51 kg m−2 h−1 at 4 suns illumination. Importantly, both the fast response of the hybrid device to the optical concentration and the repeatability of the output current are well supported. Such a hybrid device provides an opportunity to construct an on-site and/or off-network water treatment system with low energy consumption and trade investment.
Predicted Mean Vote (PMV) predicts thermal sensation for a group of people from the human thermal load, and is well recognized by thermal comfort standards for energy-efficient design of thermally ...comfortable buildings. However, the oversimplified skin evaporative heat loss in the thermal load calculation contributes to the frequently reported discrepancies between the PMV and the real thermal sensation vote. This study modifies the PMV by using the skin wettedness from the standard effective temperature model. The standard effective temperature model, with advanced human thermoregulation, reasonably predicts the skin wettedness based on the core temperature, skin temperature, and peripheral blood flow. The skin wettedness is used to calculate the skin evaporative heat loss to replace the oversimplified one. The modified PMV with the improved skin evaporative heat loss is validated by the largest thermal comfort database, i.e., ASHRAE Global Thermal Comfort Database II, for different types of climate, buildings, and HVAC systems. Compared with the original PMV, the modified PMV improves the overall accuracy and robustness in thermal sensation prediction by 64% and 32% respectively. This study contributes to improving the PMV for the updating of thermal comfort standards.
•Skin wettedness is used to improve skin evaporative heat loss for modified PMV.•Skin wettedness is from standard effective temperature model.•Modified PMV is validated by ASHRAE Global Thermal Comfort Database II.•Modified PMV is validated for different types of climate, buildings and HVAC.
Microwave processing has received significant attention based on the energy efficient volumetric processing. The internal heat generation during the microwave heating unleashes the heat transfer ...limitations of the conventional furnaces and thus, the microwave processing can be performed at much faster rates than the conventional furnaces. Susceptors further accelerate the microwave processing via providing a two-way heating with reduced heat losses from the surface of the material. In addition, the rapid initial heating via susceptors becomes the key factor to execute the energy efficient microwave processing for the poorly microwave absorbing materials. These characteristics have been massively exploited for various applications (material processing, synthesis and waste treatments) over the last few decades and this review evaluates those processing characteristics with an emphasis on the energy efficiency. Till date, the advancement of the susceptor assisted microwave processing is primarily based on the experimental trials and this review brings together various case studies so that the readers can have a clear idea about the current status in each field of applications. This can be of immense help not only to select the appropriate susceptor, but also to select the future research direction for the advancement of the energy efficient processing.
•Susceptor assisted hybrid microwave processing has been reviewed.•Energy efficiency of the hybrid heating has been analyzed for various applications.•The applications include material processing, synthesis and waste treatment.•The role of susceptors on the energy efficient material processing is highlighted.•The enhancement of the processing via the susceptors has been reported.
•Whole house heat loss test method using dwelling’s own heating system is proposed.•HLC estimates from integrated coheating are compared with electric coheating.•Good agreement between the HLC ...estimates obtained using each method.•Integrated HLC estimate could be more indicative of how a dwelling performs in-use.•Efficiency of the dwelling’s heating system can also be obtained using test method.
This paper presents the methodology, along with some of the initial findings and observations from tests performed on two dwellings, of differing construction and form, in which a coheating test was performed using the dwelling’s central heating system; this method is referred to as integrated coheating. Data obtained during the integrated coheating tests using a dwelling’s heating system have been compared with data obtained during electric coheating of the same dwelling. In one instance, integrated coheating test data from one dwelling was compared to a similar adjoining control dwelling that was simultaneously subject to an electric coheating test. The results show a good agreement between the heat loss coefficients (HLC) obtained using a dwelling’s own heating system and those obtained through electrical coheating. Initial analysis suggests the HLC estimate obtained from integrated coheating is likely to be more representative of how a dwelling performs in-use. The findings question the appropriateness of comparing current steady-state HLC predictions to those derived from in-use monitoring data. Integrated coheating has the potential to provide a more cost-effective and informative indication of whole house heat loss than electric coheating, as it enables in situ quantification of both fabric and heating system performance.
The synthesis and processing of most thermoplastics and thermoset polymeric materials rely on energy-inefficient and environmentally burdensome manufacturing methods. Frontal polymerization is an ...attractive, scalable alternative due to its exploitation of polymerization heat that is generally wasted and unutilized. The only external energy needed for frontal polymerization is an initial thermal (or photo) stimulus that locally ignites the reaction. The subsequent reaction exothermicity provides local heating; the transport of this thermal energy to neighboring monomers in either a liquid or gel-like state results in a self-perpetuating reaction zone that provides fully cured thermosets and thermoplastics. Propagation of this polymerization front continues through the unreacted monomer media until either all reactants are consumed or sufficient heat loss stalls further reaction. Several different polymerization mechanisms support frontal processes, including free-radical, cat- or anionic, amine-cure epoxides, and ring-opening metathesis polymerization. The choice of monomer, initiator/catalyst, and additives dictates how fast the polymer front traverses the reactant medium, as well as the maximum temperature achievable. Numerous applications of frontally generated materials exist, ranging from porous substrate reinforcement to fabrication of patterned composites. In this review, we examine in detail the physical and chemical phenomena that govern frontal polymerization, as well as outline the existing applications.
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