Hasil untuk "Heat"

E. Benarroch

K. Richter, M. Haslbeck, J. Buchner

R. Kovats, S. Hajat

B. Barnabás, K. Jäger, A. Fehér

T. Oke

A. Hill

N. St-Pierre, B. Cobanov, G. Schnitkey

Peter Kuster

Yuming Guo, A. Gasparrini, B. Armstrong et al.

Background: Few studies have examined variation in the associations between heat waves and mortality in an international context. Objectives: We aimed to systematically examine the impacts of heat waves on mortality with lag effects internationally. Methods: We collected daily data of temperature and mortality from 400 communities in 18 countries/regions and defined 12 types of heat waves by combining community-specific daily mean temperature ≥90th, 92.5th, 95th, and 97.5th percentiles of temperature with duration ≥2, 3, and 4 d. We used time-series analyses to estimate the community-specific heat wave–mortality relation over lags of 0–10 d. Then, we applied meta-analysis to pool heat wave effects at the country level for cumulative and lag effects for each type of heat wave definition. Results: Heat waves of all definitions had significant cumulative associations with mortality in all countries, but varied by community. The higher the temperature threshold used to define heat waves, the higher heat wave associations on mortality. However, heat wave duration did not modify the impacts. The association between heat waves and mortality appeared acutely and lasted for 3 and 4 d. Heat waves had higher associations with mortality in moderate cold and moderate hot areas than cold and hot areas. There were no added effects of heat waves on mortality in all countries/regions, except for Brazil, Moldova, and Taiwan. Heat waves defined by daily mean and maximum temperatures produced similar heat wave–mortality associations, but not daily minimum temperature. Conclusions: Results indicate that high temperatures create a substantial health burden, and effects of high temperatures over consecutive days are similar to what would be experienced if high temperature days occurred independently. People living in moderate cold and moderate hot areas are more sensitive to heat waves than those living in cold and hot areas. Daily mean and maximum temperatures had similar ability to define heat waves rather than minimum temperature. https://doi.org/10.1289/EHP1026

M. Papapetrou, G. Kosmadakis, A. Cipollina et al.

Abstract Industrial waste heat is examined in EU countries, focusing on the amount that can be recovered and exploited, referred to as technical potential of waste heat. An alternative methodology is proposed here, which is based on waste heat fractions derived from a detailed study of the UK industry from the period 2000–2003. These fractions express the part of heat consumption that is wasted and is possible to be recovered. The waste heat fractions have been calculated in this work for each main industrial sector and temperature level. The methodology initially includes the adjustment of waste heat fractions from each industrial sector from the UK industry to the conditions of the different EU countries in the period 2000–2003, in order to account for the different levels of energy efficiency. The second step is to adjust the fractions for the year 2015, using data about the evolution of energy intensity values from 2000 to 2003 to 2015 for each country and sector, resulting to a new set of fractions per country, temperature level and sector. This methodology has enabled the authors to study in detail the waste heat potential per sector and temperature level, using the most recent data. The main outcome is the estimation of waste heat potential for each main industrial sector in the EU, broken down to the amount of waste heat for each temperature range. A similar analysis is conducted for each EU country as well, in order to identify the magnitude of heat recovery opportunities that could exist for every industrial sector at country level. The main result of this analysis is the estimation of the total waste heat potential in EU, which is about 300 TWh/year, with one third corresponding to temperature level below 200 °C, which is often referred to as low-temperature waste heat, another 25% in the range 200–500 °C and the rest above 500 °C (mostly in the range 500–1000 °C). The findings of the current study can be used for assessing the potential of any relevant heat recovery applications, such as heat upgrade and re-use or heat-to-power conversion technologies.

Lei Zhao, M. Oppenheimer, Qing Zhu et al.

Heat waves (HWs) are among the most damaging climate extremes to human society. Climate models consistently project that HW frequency, severity, and duration will increase markedly over this century. For urban residents, the urban heat island (UHI) effect further exacerbates the heat stress resulting from HWs. Here we use a climate model to investigate the interactions between the UHI and HWs in 50 cities in the United States under current climate and future warming scenarios. We examine UHI2m (defined as urban-rural difference in 2m-height air temperature) and UHIs (defined as urban-rural difference in radiative surface temperature). Our results show significant sensitivity of the interaction between UHI and HWs to local background climate and warming scenarios. Sensitivity also differs between daytime and nighttime. During daytime, cities in the temperate climate region show significant synergistic effects between UHI and HWs in current climate, with an average of 0.4 K higher UHI2m or 2.8 K higher UHIs during HWs than during normal days. These synergistic effects, however, diminish in future warmer climates. In contrast, the daytime synergistic effects for cities in dry regions are insignificant in the current climate, but emerge in future climates. At night, the synergistic effects are similar across climate regions in the current climate, and are stronger in future climate scenarios. We use a biophysical factorization method to disentangle the mechanisms behind the interactions between UHI and HWs that explain the spatial-temporal patterns of the interactions. Results show that the difference in the increase of urban versus rural evaporation and enhanced anthropogenic heat emissions (air conditioning energy use) during HWs are key contributors to the synergistic effects during daytime. The contrast in water availability between urban and rural land plays an important role in determining the contribution of evaporation. At night, the enhanced release of stored and anthropogenic heat during HWs are the primary contributors to the synergistic effects.

G. Huminic, A. Huminic

Abstract In recent years, a novel class of working fluids which consists from two solid materials dispersed in a conventional fluid was developed and intensely studied. These fluids are called hybrid nanofluids. This paper presents a review of the research recent results concerning the thermo-physical properties (thermal conductivity, viscosity, density and specific heat) and the heat transfer and flow characteristics of hybrid nanofluids used in various heat exchangers. The hybrid nanofluids leads to an increased thermal conductivity and finally to a heat transfer enhancement in heat exchangers. Experimental and numerical results shown in this review indicate that the hybrid nanofluids are working fluids which could improve significantly the heat transfer in heat exchangers, but, there are still needed research concerning to the study of different combinations of hybrid nanoparticles, their mixing ratio, the stability of the hybrid nanofluids, and the understanding the mechanisms which contribution to the heat transfer enhancement.

H. Ahmed, B. H. Salman, A. Kherbeet et al.

Z. Su, Jinbo Wang, P. Klein et al.

Recent studies highlight that oceanic motions associated with horizontal scales smaller than 50 km, defined here as submesoscales, lead to anomalous vertical heat fluxes from colder to warmer waters. This unique transport property is not captured in climate models that have insufficient resolution to simulate these submesoscale dynamics. Here, we use an ocean model with an unprecedented resolution that, for the first time, globally resolves submesoscale heat transport. Upper-ocean submesoscale turbulence produces a systematically-upward heat transport that is five times larger than mesoscale heat transport, with winter-time averages up to 100 W/m2 for mid-latitudes. Compared to a lower-resolution model, submesoscale heat transport warms the sea surface up to 0.3 °C and produces an upward annual-mean air–sea heat flux anomaly of 4–10 W/m2 at mid-latitudes. These results indicate that submesoscale dynamics are critical to the transport of heat between the ocean interior and the atmosphere, and are thus a key component of the Earth’s climate. Oceanic motions associated with horizontal scales smaller than 50 km remain unresolved in climate models. Here the authors show that motions in this scale range are critical to the global transport of heat between the ocean interior and the atmosphere, and are thus a key component of the Earth’s climate.

N. Akter, M. Rafiqul Islam

J. Goodman, Michael Hurwitz, Jisung Park et al.

We demonstrate that heat inhibits learning and that school air conditioning may mitigate this effect. Student fixed effects models using students who retook the PSATs show that hotter school days in the years before the test was taken reduce scores, with extreme heat being particularly damaging. Weekend and summer temperatures have little impact, suggesting heat directly disrupts learning time. New nationwide, school-level measures of air conditioning penetration suggest patterns consistent with such infrastructure largely offsetting heat’s effects. Without air conditioning, a 1°F hotter school year reduces that year’s learning by 1 percent. Hot school days disproportionately impact minority students, accounting for roughly 5 percent of the racial achievement gap. (JEL I21, I24, J15, Q54)

Zulfiqar Khattak, H. Ali

Abstract With the prologue of new components with more and more heat dissipation, urge for novel heat sink philosophy is becoming a real challenge in today’s world. The new solutions should be able to cope with massive heat emanation while keeping the space and cost constraints. Finned (plate and pin) heat sinks are contrivance to these challenges with growing applications in present-day engineering arena and drawing the concentration of researchers. Paper deals with the critical review of different heat sink designs, limiting factors, effectiveness, limitations of various techniques and recent advancements in the field of innovative heat sinks. This study initiates with brief and comprehensive discussion regarding importance of heat sinks, its methodology; it’s suitability for present day heat dissipation issues, statistical data of various heat sink designs and a rich discussion of the work so far. The sole aspiration for this article is digging out the literature available so far with emphasis on experimental techniques and to propose strategy for future research. The outcome of the research will validate the concept of improved heat transfer approach, provide useful data for innovative design and help better understand the cooling capabilities of the pin fin technology.

Ji-Wang Luo, Li Chen, Kentaro Yaji et al.

Solving flow-related inverse problems such as topology optimization problems is intricate but significant in various engineering fields. The lattice Boltzmann method (LBM) and the related adjoint method are highly suitable to perform sensitivity analysis in flow-related inverse problems thanks to their strong capability to handle complex structures and excellent parallel scalability. However, the current continuous adjoint LBM shows theoretical inconsistency and poor numerical stability for open flow systems. To solve these issues, the present work develops the fully consistent adjoint boundary conditions from the discrete adjoint LBM. For the first time, the gap between the two adjoint LBMs is unveiled by rigorously deriving both the continuous and discrete adjoint LBMs and comprehensively evaluating their numerical performances in the 2D and 3D pipe bend optimization cases. It is revealed that theoretical inconsistency or singularity exists in the continuous adjoint boundary conditions for open flow systems, corresponding to a much inferior numerical stability of the adjoint solution and an obvious numerical error in sensitivity. Fully consistent adjoint boundary conditions in elegant local form are derived from the discrete adjoint LBM in this work, which can always acquire exact sensitivity results and the theoretically highest numerical stability, with a 10 times higher Reynolds number (Re) achieved while without any increase of computational cost. 3D microchannel heat sinks under various Re are designed, and the esthetic and physically reasonable optimized designs are obtained under various parameter settings, demonstrating the necessity and versatility of the presented discrete adjoint LBM.

Ibrahim Abbas, Aboelnour Abdalla, Areej Almuneef et al.

This study investigates generalized thermoelastic interaction in porous asphaltic materials subjected to thermal loading, using fractional model with time-delay effects. The framework incorporates the Riemann-Liouville fractional derivative to account for memory-dependent heat conduction, extending classical thermoelasticity into a more accurate and comprehensive domain. The Lord–Shulman model with one relaxation time is adopted to describe the coupling between mechanical and thermal responses. The governing equations are solved using Laplace transform and the eigenvalues approach, and the Stehfest algorithm is employed for numerical inversion. A detailed analysis is presented for temperature distribution, displacement, and stress fields in both solid and liquid phases of the porous medium under traction-free and thermally loaded boundary conditions. The numerical calculations show how the different sets of fractional parameters have impacted the temperature, stress, and displacement in the solid and liquid phases. Eventually, the visual representation of the data illustrates the distinctions between the fractional poro-thermoelasticity and classical coupled thermoelasticity formulations.

Oguz Emrah Turgut, Mustafa Asker, Hayrullah Bilgeran Yesiloz et al.

This theoretical research study proposes a novel hybrid algorithm that integrates an improved quasi-dynamical oppositional learning mutation scheme into the Mountain Gazelle Optimization method, augmented with chaotic sequences, for the thermal and economical design of a shell-and-tube heat exchanger operating with nanofluids. The Mountain Gazelle Optimizer is a recently developed metaheuristic algorithm that simulates the foraging behaviors of Mountain Gazelles. However, it suffers from premature convergence due to an imbalance between its exploration and exploitation mechanisms. A two-step improvement procedure is implemented to enhance the overall search efficiency of the original algorithm. The first step concerns substituting uniformly random numbers with chaotic numbers to refine the solution quality to better standards. The second step is to develop a novel manipulation equation that integrates different variants of quasi-dynamic oppositional learning search schemes, guided by a novel intelligently devised adaptive switch mechanism. The efficiency of the proposed algorithm is evaluated using the challenging benchmark functions from various CEC competitions. Finally, the thermo-economic design of a shell-and-tube heat exchanger operated with different nanoparticles is solved by the proposed improved metaheuristic algorithm to obtain the optimal design configuration. The predictive results indicate that using water + SiO₂ instead of ordinary water as the refrigerant on the tube side of the heat exchanger reduces the total cost by 16.3%, offering the most cost-effective design among the configurations compared. These findings align with the demonstration of how biologically inspired metaheuristic algorithms can be successfully applied to engineering design.