Hasil untuk "Heat"

K. Vignarooban, Xinhai Xu, A. Arvay et al.

M. Åkerfelt, R. Morimoto, L. Sistonen

A. Bejan, J. Kestin

E. Vierling

D. A. Frank-Kamenet︠s︡kiĭ

P. Setlow

M. Caterina, Tobias A. Rosen, M. Tominaga et al.

L. Schwartz

Kathrin J. Ward, Steffen Lauf, B. Kleinschmit et al.

A. Akbarian, J. Michiels, J. Degroote et al.

Heat as a stressor of poultry has been studied extensively for many decades; it affects poultry production on a worldwide basis and has significant impact on well-being and production. More recently, the involvement of heat stress in inducing oxidative stress has received much interest. Oxidative stress is defined as the presence of reactive species in excess of the available antioxidant capacity of animal cells. Reactive species can modify several biologically cellular macromolecules and can interfere with cell signaling pathways. Furthermore, during the last decade, there has been an ever-increasing interest in the use of a wide array of natural feed-delivered phytochemicals that have potential antioxidant properties for poultry. In light of this, the current review aims to (1) summarize the mechanisms through which heat stress triggers excessive superoxide radical production in the mitochondrion and progresses into oxidative stress, (2) illustrate that this pathophysiology is dependent on the intensity and duration of heat stress, (3) present different nutritional strategies for mitigation of mitochondrial dysfunction, with particular focus on antioxidant phytochemicals. Oxidative stress that occurs with heat exposure can be manifest in all parts of the body; however, mitochondrial dysfunction underlies oxidative stress. In the initial phase of acute heat stress, mitochondrial substrate oxidation and electron transport chain activity are increased resulting in excessive superoxide production. During the later stage of acute heat stress, down-regulation of avian uncoupling protein worsens the oxidative stress situation causing mitochondrial dysfunction and tissue damage. Typically, antioxidant enzyme activities are upregulated. Chronic heat stress, however, leads to downsizing of mitochondrial metabolic oxidative capacity, up-regulation of avian uncoupling protein, a clear alteration in the pattern of antioxidant enzyme activities, and depletion of antioxidant reserves. Some phytochemicals, such as various types of flavonoids and related compounds, were shown to be beneficial in chronic heat-stressed poultry, but were less or not effective in non-heat-stressed counterparts. This supports the contention that antioxidant phytochemicals have potential under challenging conditions. Though substantial progress has been made in our understanding of the association between heat stress and oxidative stress, the means by which phytochemicals can alleviate oxidative stress have been sparsely explored.

Fateh Mebarek-oudina

A. Arshad, H. M. Ali, Muzaffar Ali et al.

Zeyu Zhang, Long Wan, Yong Yang et al.

Overcoming the strength-ductility trade-off dilemma is paramount for advanced materials engineering. Herein, we prepared 7075 aluminium alloys with superior strength and ductility via additive friction stir deposition (AFSD) and subsequent heat treatment. Compared with the commercial base material, the heat-treated 7075 aluminium alloy maintained a high ultimate tensile strength of 556 MPa, while the uniform elongation increased from 12.2% to 26.7%, exhibiting the highest strength-ductility synergy reported among commercial Al-Zn-Mg-Cu alloy systems. Grain boundary sliding was activated via the equiaxed grains to accommodate substantial plastic strain. This method provides a promising and cost-effective pathway for developing strength-ductility on Al-Zn-Mg-Cu alloys.

Mehmet Zahid Malasli

Since cherries are a seasonal product, it is not possible to obtain them at all times of the year. Due to their high moisture content, they cannot be stored for long periods of time. For these reasons, the drying of sweet cherries is of great importance in preventing product losses and preserving market value. In this study, cherries were dried with different solar energy using passive (without fan; P1), active (with three fan speed; F1, F2, F3) and open (exposed to the sun) methods in order to extend the shelf life and provide access in all seasons. The kinetics of the drying processes, energy consumption parameters, thermophysical properties and their effects on color parameters were investigated. Drying rate in drying processes changed in the range of 6.09–13.98 × 10−4 g moisture/g dry matter min. It was determined that effective moisture diffusion values ranged between 1.43 × 10−8–9.62 × 10−9 m2/s. The highest average specific heat, thermal conductivity, thermal diffusivity and specific mass of the dried samples were obtained at activated type-F1 fan speed. The dry product closest to fresh according to all color values was determined in the open drying method. According to the results, it is recommended that solar drying at a single fan speed (F1) be prioritized as a promising approach for sweet cherry drying in future applications and studies, while further optimization of active systems can improve specific moisture extraction rate (SMER) and specific energy consumption (SEC) performance.

M. Sheikholeslami, Arman Ghasemi

Abstract In this research, nanofluid unsteady heat transfer process (solidification) under the impact of thermal radiation is reported. In order to simulate this problem, Finite element method with adaptive mesh is employed. CuO-water nanofluid is utilized and Brownian motion effect on thermal conductivity is taken into consideration. Total energy, average temperature, isotherm and solid fraction contours are reported as results. Results demonstrate that total energy reduces with increase of radiation parameter and solidification process is completed in lower time in presence of thermal radiation. Also, it can be understand that using Nano-enhanced phase change material (NEPCM) instead of pure PCM leads to higher heat transfer rate.

T. Rehman, H. Ali, A. Saieed et al.

Abstract Copper foam (with porosity 97% and pore density 35 pores per inch) based heat sink without phase change material (PCM) and copper foam/PCM composites heat sinks are investigated to observe the behavior of operational time of heat sinks with respect to specific temperature both for charging and discharging. Paraffin wax, RT-35HC, RT-44HC and RT-54HC are used as PCM. Investigations are performed at heat flux of 0.8–2.4 KW/m2 with a gap of 0.4 KW/m2 uniformly distributed. PCM volume fractions of 0.68 and 0.83 are used in composites. Results indicated that at the end of 90 min charging, maximum temperature reduction of 25% is noted for RT-35HC/Copper foam at 0.8 KW/m2 for PCM volume fraction 0.83. Afterwards, RT-44HC/Copper foam reveals maximum temperature reduction of 24% for 1.6 KW/m2. RT-35HC/Copper foam is least efficient at 2.4 KW/m2 which reduces the base temperature only by 5–7%. Maximum enhancement ratio in operation time is noticed as 8 and 7.7 for RT-35HC/Copper foam and RT-44HC/Copper foam respectively at set point temperature (SPT) of 40 °C and 60 °C for respective composites.

Wang Qian

Current humanistic design of urban public spaces focuses on specific design elements while ignoring the conflicts and couplings between multiple user needs. This leads to spatial strategies stuck in local optima and lacking overall balance and adaptability. This paper constructs a multi-objective optimization model that integrates user preferences, multidimensional spatial indicators, and behavioral simulation. This model collects field data such as heat maps, path trajectories, and dwell time, identifies user types through K-means clustering, and models their spatial preferences using fuzzy membership functions. Design variables are set in Grasshopper; an optimization function is constructed; the optimal solution is searched using NSGA-III. Finally, pedestrian simulation is performed in AnyLogic, and the optimization results are corrected for function deviation to improve the coordination and adaptability of the design. Experimental results show that this strategy framework significantly improves spatial coordination, increasing weighted average satisfaction from 0.61 to 0.81 (+32.8%), reducing safety risks by 30.8% to 63.2%, and increasing interaction promotion by 71.2%. Multi-dimensional indicators verify the effectiveness of the optimization strategy in balancing user needs, alleviating local conflicts, and enhancing spatial adaptability, providing a quantitative basis and practical path for systematically solving the local optimal problem of humanized design of public spaces.

Yangyang He, Qing Liu, Qing Li

Since its introduction 30 years ago, the lattice Boltzmann (LB) method has achieved great success in simulating fluid flows and modeling physics in fluids. Owing to its kinetic nature, the LB method has the capability to incorporate the essential microscopic or mesoscopic physics, and it is particularly successful in modeling transport phenomena involving complex boundaries and interfacial dynamics. The LB method can be considered to be an efficient numerical tool for fluid flow and heat transfer in porous media. Moreover, since the LB method is inherently transient, it is especially useful for investigating transient solid-liquid phase-change processes wherein the interfacial behaviors are very important. In this article, a comprehensive review of the LB methods for single-phase and solid-liquid phase-change heat transfer in porous media at both the pore scale and representative elementary volume (REV) scale. The review first introduces the fundamentals of the LB method for fluid flow and heat transfer. Then the REV-scale LB method for fluid flow and single-phase heat transfer in porous media, and the LB method for solid-liquid phase-change heat transfer, are described. Some applications of the LB methods for single-phase and solid-liquid phase-change heat transfer in porous media are provided. In addition, applications of the LB method to predict effective thermal conductivity of porous materials are also provided. Finally, further developments of the LB method in the related areas are discussed.

H. Ali, M. Ashraf, A. Giovannelli et al.

Abstract This study implies experimental investigation for optimization of heat transfer in electronic integrated circuits using close packed phase change materials (PCMs) filled pin-fin heat sinks. The aim of this study is to find the most efficient pin-fin configuration filled with optimum PCM to extend the operating range of electronic circuits. The experimental methodology is based upon variation of pin-fin configurations in rectangular, round and triangular cross-sections. Each configuration is allowed a pin-fin volumetric percentage of 9%. For analysis using PCM a volume fraction of 90% is maintained and six PCMs with different thermo-physical properties (varying melting temperatures, latent heats and heat capacities) are selected. These include paraffin wax, RT-54, RT-44, RT-35HC, SP-31 and n-eicosane. Moreover, the power levels mimicking heat input range between 5 W and 8 W. The resulting information is analyzed for the performance of a heat sink with and without PCM. Besides that, PCM ascendency is manipulated in terms of operational time, enhancement ratios, Stefan number and storage ratio. The outcomes suggest that triangular pin-fins are found to be the most effective pin-fin configuration for heat transfer both with and without PCM.

A. Ronzani, B. Karimi, J. Senior et al.

Quantum thermodynamics is emerging both as a topic of fundamental research and as a means to understand and potentially improve the performance of quantum devices1–10. A prominent platform for achieving the necessary manipulation of quantum states is superconducting circuit quantum electrodynamics (QED)11. In this platform, thermalization of a quantum system12–15 can be achieved by interfacing the circuit QED subsystem with a thermal reservoir of appropriate Hilbert dimensionality. Here we study heat transport through an assembly consisting of a superconducting qubit16 capacitively coupled between two nominally identical coplanar waveguide resonators, each equipped with a heat reservoir in the form of a normal-metal mesoscopic resistor termination. We report the observation of tunable photonic heat transport through the resonator–qubit–resonator assembly, showing that the reservoir-to-reservoir heat flux depends on the interplay between the qubit–resonator and the resonator–reservoir couplings, yielding qualitatively dissimilar results in different coupling regimes. Our quantum heat valve is relevant for the realization of quantum heat engines17 and refrigerators, which can be obtained, for example, by exploiting the time-domain dynamics and coherence of driven superconducting qubits18,19. This effort would ultimately bridge the gap between the fields of quantum information and thermodynamics of mesoscopic systems. The state of a superconducting circuit qubit governs the photonic heat flow through an integrated assembly, constituting a quantum heat valve that provides a testbed for exploring quantum thermodynamics in a circuit quantum electrodynamics setting.