Hasil untuk "Heat"

R. Webb

H. S. Carslow, J. Jaeger, J. Morral

H. Pollack, D. Chapman

G. Raithby, E. Chui

M. Marber, R. Mestril, Shun-Hua Chi et al.

A. Majumdar

K. Cole, J. Beck, A. Haji-Sheikh et al.

P. Kew, K. Cornwell

Baowen Li, Lei Wang, G. Casati

By coupling two nonlinear one dimensional lattices, we demonstrate a thermal diode model that works in a wide range of system parameters. We provide numerical and analytical evidence for the underlying mechanism which allows heat flux in one direction while the system acts like an insulator when the temperature gradient is reversed. The possible experimental realization in nanoscale systems is briefly discussed.

K. Knowlton, Miriam Rotkin-Ellman, G. King et al.

Background Climate models project that heat waves will increase in frequency and severity. Despite many studies of mortality from heat waves, few studies have examined morbidity. Objectives In this study we investigated whether any age or race/ethnicity groups experienced increased hospitalizations and emergency department (ED) visits overall or for selected illnesses during the 2006 California heat wave. Methods We aggregated county-level hospitalizations and ED visits for all causes and for 10 cause groups into six geographic regions of California. We calculated excess morbidity and rate ratios (RRs) during the heat wave (15 July to 1 August 2006) and compared these data with those of a reference period (8–14 July and 12–22 August 2006). Results During the heat wave, 16,166 excess ED visits and 1,182 excess hospitalizations occurred statewide. ED visits for heat-related causes increased across the state [RR = 6.30; 95% confidence interval (CI), 5.67–7.01], especially in the Central Coast region, which includes San Francisco. Children (0–4 years of age) and the elderly (≥ 65 years of age) were at greatest risk. ED visits also showed significant increases for acute renal failure, cardiovascular diseases, diabetes, electrolyte imbalance, and nephritis. We observed significantly elevated RRs for hospitalizations for heat-related illnesses (RR = 10.15; 95% CI, 7.79–13.43), acute renal failure, electrolyte imbalance, and nephritis. Conclusions The 2006 California heat wave had a substantial effect on morbidity, including regions with relatively modest temperatures. This suggests that population acclimatization and adaptive capacity influenced risk. By better understanding these impacts and population vulnerabilities, local communities can improve heat wave preparedness to cope with a globally warming future.

Ying Yang, Z. G. Zhang, E. Grulke et al.

Sidi El Becaye Maïga, C. T. Nguyen, N. Galanis et al.

C. T. Nguyen, G. Roy, C. Gauthier et al.

Jaeseon Lee, I. Mudawar

Kong Junran, Mao Mang, Liu Huan et al.

Nonequilibrium heat transport and quantum thermodynamics in light-matter interacting systems have received increasing attention. Quantum thermal devices, e.g., heat valve and head diode, have been realized. Recently, it has been discovered that the anisotropic light-matter interactions can greatly modify the eigenvalues and eigenvectors of hybrid quantum systems, leading to nontrivial quantum phase transitions, quantum metrology, and nonclassicality of photons. To explore the influences of anisotropic light-matter interactions on quantum transport, we investigate heat flow in the nonequilibrium anisotropic Dicke model. In this model, an ensemble of qubits collectively interacts with an anisotropic photon field. Each component interacts with bosonic thermal reservoirs. Quantum dressed master equation (DME) is included to properly study dissipative dynamics of the anisotropic Dicke model. Within the eigenbasis of the reduced anisotropic Dicke system, strong qubit-photon couplings can be properly handled. Our results demonstrate that anisotropic qubit-photon interactions are crucial for modulating steady-state heat flow. In particular, it is found that under strong coupling the heat flow is dramatically suppressed by a large anisotropic qubit-photon factor. While under moderate coupling, the anisotropic qubit-photon interactions enhance the heat flow. Moreover, the increase in the number of qubits amplifies the flow characteristics, with the peaks increasing and the valleys decreasing. Besides, we derive two analytical expressions of heat flows in thermodynamic limit approximation with limiting anisotropic factors. These heat currents exhibit the cotunneling heat transport pictures. They also serve as the upper boundaries for the heat flows in the finite-size anisotropic Dicke model. We also analyze the thermal rectification effect in the anisotropic Dicke model.

Ido Ben-Hertzel, Nathan Blanc, Avishai Meir et al.

Low-grade heat from industrial waste streams, solar-thermal and geothermal, represents a significant energy source currently under-utilized. Phase-Change Thermoacoustic Engines, also known as Wet Thermoacoustic Engines (WTE) consist of a stack (porous medium) sandwiched between two heat exchangers, and an acoustic resonator. In this configuration, the stack walls are wet - soaked with a liquid, whose periodic evaporation and condensation drive acoustic oscillations, augmented by the latent heat transfer. However, implementation at standard acoustic frequencies involves the use of small stack pores ( < 1mm) that are not easy to wet consistently and without clogging. A possible solution is enlarging the stack pore size, which then mandates a reduction of the operating frequency. In an attempt to achieve this, the present work examines the operating characteristics of a water-based standing-wave WTE, coupled with a liquid column - in order to reduce its operating frequency. The results demonstrate a drive ratio of 5% in the wet mode, with an onset temperature difference as low as 20 ∘C, compared to 200 ∘C in the dry mode. This onset temperature difference is lower than any previously reported in similar systems, wet or dry. Operating a thermoacoustic engine under these conditions makes it suitable for various low-temperature heat sources, and the significantly larger pores (1 cm) help prevent issues related to clogging or inconsistent wetting. Experimental results are complemented by a theoretical model, obtaining fair agreement with the results and predicting high efficiency (>20% of the Carnot efficiency) and a power density >10 kW/m3 when operating at higher pressures.

A. Gasparrini, B. Armstrong

Musharafa Saleem, A. Al-Zubaidi, Neyara Radwan et al.

The present research analyzes the properties of a Casson ternary nanofluid over a stretching sheet with Thomson and Troian slip conditions, taking into consideration the influences of electromagnetohydrodynamic (EMHD). The ternary nanofluid comprises three different nanoparticles, which include titanium dioxide (TiO2), copper (Cu), and silver (Ag), all being suspended in oil, which is the base fluid. They are involved because of their good thermal conductivity and chemical stability, and AgCuTiO2 /Oil nanofluid is a composite of copper, titanium oxide, and oil. Hence, carrying out the said procedure, the ternary nanofluid becomes AgCuTiO2/Oil. The sheet is, however, thought to be stretching vertically while the flow is determined by the effect of the gravity force through the free convention. Moreover, the phenomena of EMHD, porous medium, thermal slip, thermal radiation, Joule heating, and heat source/sink are included to make the energy equation more real-life. This leads to a set of partial differential equations (PDEs) based mathematical models transformed into ordinary differential equations (ODEs)-appropriate similarity transformation. The Runge–Kutta–Fehlberg (RKF-45) method solves the given ordinary differential system. According to the research’s findings, the temperature of the ternary Casson nanofluid rises when the suspension of silver, copper, and titanium dioxide nanoparticles increases, and the velocity of flow for merely silver and copper decreases when the density decreases. This causes the flow rate to be constricted through the velocity slip condition, at the same time as the nanofluid’s temperature increases.

A. Faghri

M. Sawka, Lisa R Leon, S. Montain et al.

This article emphasizes significant recent advances regarding heat stress and its impact on exercise performance, adaptations, fluid electrolyte imbalances, and pathophysiology. During exercise‐heat stress, the physiological burden of supporting high skin blood flow and high sweating rates can impose considerable cardiovascular strain and initiate a cascade of pathophysiological events leading to heat stroke. We examine the association between heat stress, particularly high skin temperature, on diminishing cardiovascular/aerobic reserves as well as increasing relative intensity and perceptual cues that degrade aerobic exercise performance. We discuss novel systemic (heat acclimation) and cellular (acquired thermal tolerance) adaptations that improve performance in hot and temperate environments and protect organs from heat stroke as well as other dissimilar stresses. We delineate how heat stroke evolves from gut underperfusion/ischemia causing endotoxin release or the release of mitochondrial DNA fragments in response to cell necrosis, to mediate a systemic inflammatory syndrome inducing coagulopathies, immune dysfunction, cytokine modulation, and multiorgan damage and failure. We discuss how an inflammatory response that induces simultaneous fever and/or prior exposure to a pathogen (e.g., viral infection) that deactivates molecular protective mechanisms interacts synergistically with the hyperthermia of exercise to perhaps explain heat stroke cases reported in low‐risk populations performing routine activities. Importantly, we question the “traditional” notion that high core temperature is the critical mediator of exercise performance degradation and heat stroke. Published 2011 This article is a U.S. Government work and is in the public domain in the USA. Compr Physiol 1:1883‐1928, 2011.