Hasil untuk "Heat"

Renyuan Li, Lianbin Zhang, Le Shi et al.

H. Jouhara, N. Khordehgah, Sulaiman Almahmoud et al.

Horizon 2020 Project “Design for Resource and Energy efficiency in CerAMic Kilns- DREAM Project (Grant No: 723641), Horizon 2020 Industrial THERMal energy recovery conversion and management (Grant No:680599) and ESPRC (Grant No: EP/P004636/1)

Naohiko Ohama, H. Sato, K. Shinozaki et al.

Vanessa Hertzog

Ziqiang He, Yunfei Yan, Zhien Zhang

Abstract The electronic equipment developing towards miniaturization and high integration is facing the danger of high heat flux and non-uniform temperature distribution which leads to the reduction of life and reliability of electronic devices. The micro heat sinks have gained significant attention in heat dissipation of electronic devices with a high heat flux due to its large heat transfer surface to volume ratio, compact structure and outstanding thermal performance. In this review, we present the advantages and shortcomings of thermal enhancement technologies in different structural micro heat sinks. Moreover, the non-uniform temperature distribution which includes the temperature rising along the flow direction and hotspots, especially, the random hotspot with high heat flux, has been the serious issues in the thermal management of electronic devices. They are the main challenges for the efficient operation and service life of electronic components. Thus, it is urgent to develop an effective and economic process in automatic adaptive cooling of random hotspots. The purpose of this article is to introduce the existing thermal enhancement technologies in micro heat sinks and the reduction of non-uniform temperature distribution. Finally, the barriers and challenges for the developments of thermal management of electronic devices by micro heat sinks are discussed, and the future directions of the research topic are provided.

Dawn L. Morden

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Gregory Nellis, Sanford Klein

Y. Xuan, W. Roetzel

N. Berline, E. Getzler, M. Vergne

Y. Çengel

Wangxia Wang, B. Vinocur, O. Shoseyov et al.

J. Crank, P. Nicolson

Y. Xuan, Qiang Li

Ying Li, Wei Li, Tiancheng Han et al.

The demand for sophisticated tools and approaches in heat management and control has triggered the fast development of fields that include conductive thermal metamaterials, nanophononics, and far-field and near-field radiative thermal management. In this Review, we offer a unified perspective on the control of heat transfer, summarizing complementary paradigms towards the manipulation of physical parameters and the realization of unprecedented phenomena in heat transfer using artificial structures. The Review is divided into three parts that focus on the three main categories of heat flow control. Thermal conduction and radiation, at both the macroscale and microscale, are emphasized in the first and second parts. The third part discusses efforts to actively introduce heat sources or tune the material parameters with multiphysical effects in conduction, radiation and convection. We conclude by analysing the challenges in this research area and surveying new possible directions, in particular topological thermal effects, heat waves and quantum thermal effects. Artificial structures with novel thermal properties are promising for heat-transfer applications. This Review provides an overview of thermal metamaterials and devices, discussing the working principles underlying the manipulation of thermal conduction and radiation at different length scales.

H. Hussain, S. Men, S. Hussain et al.

Maize is a sensitive crop to drought and heat stresses, particularly at the reproductive stages of development. The present study investigated the individual and interactive effects of drought (50% field capacity) and heat (38 °C/30 °C) stresses on morpho-physiological growth, yield, nutrient uptake and oxidative metabolism in two maize hybrids i.e., ‘Xida 889’ and ‘Xida 319’. The stress treatments were applied at tasseling stage for 15 days. Drought, heat and drought + heat stress caused oxidative stress by the over-production of ROS (O2−, H2O2, OH−) and enhanced malondialdehyde contents, which led to reduced photosynthetic components, nutrients uptake and yield attributes. The concurrent occurrence of drought and heat was more severe for maize growth than the single stress. However, both stresses induced the metabolites accumulation and enzymatic and non-enzymatic antioxidants to prevent the oxidative damage. The performance of Xida 899 was more prominent than the Xida 319. The greater tolerance of Xida 889 to heat and drought stresses was attributed to strong antioxidant defense system, higher osmolyte accumulation, and maintenance of photosynthetic pigments and nutrient balance compared with Xida 319.

M. Sajid, H. Ali

Abstract This paper presents a critical review of heat transfer applications of nanofluids. The effects of nanoparticle concentration, size, shape, and nanofluid flow rate on Nusselt number, heat transfer coefficient, thermal conductivity, thermal resistance, friction factor and pressure drop from numerous studies reported recently are presented. Effects of various geometric parameters on heat transfer enhancement of system using nanofluids have also been reviewed. Heat transfer devices covered in this paper include radiators, circular tube heat exchangers, plate heat exchangers, shell and tube heat exchangers and heat sinks. Various correlations used for experimental validation or developed in reviewed studies are also compiled, compared and analyzed. The pros and cons associated to the applications of nanofluids in heat transfer devices are presented in details to determine the future direction of research in this arena.

Tauseef-ur-Rehman, H. Ali, M. M. Janjua et al.

Abstract Phase change material (PCM) is promising media for thermal energy storage owing to its extensive value of latent heat (140–970 KJ/Kg). However, thermal conductivity of PCMs is too low which obstructs energy storage and retrieval rate. In recent days, thermally enhanced PCMs are considered promising materials for efficient heat transfer in many applications. This article designates the review on improved thermal properties and heat transfer of PCMs by using porous materials. Enhanced heat transfer of PCMs can be achieved using extended surfaces (triangular, conical, square, and rectangular fins), heat pipes, and addition of highly conductive nanoparticles (e.g. Cu, Al2O3, Au, SiC, SiO2 and TiO2). Major focus of this article is to study the enhanced heat transfer of PCMs through metallic (copper, nickel, and aluminum) and carbon based (carbon, graphite and expanded graphite) porous materials/foams. Effects of porosity and pore density on heat transfer, thermal conductivity, specific heat, latent heat and charging/discharging time are critically reviewed. Porous materials/foams are reported to be efficient for heat transfer/thermal conductivity enhancement by 3–500 times. Furthermore, correlations to find the effective thermal conductivity of PCM/foam are reported. Important applications of PCM/foam reported by different researchers are also discussed in this paper. Finally, conclusions and recommendations are presented to highlight the research gap in this area.

Ahmad Hajatzadeh Pordanjani, Saeed Aghakhani, M. Afrand et al.

Abstract In this paper a brief review on application of nanofluids in heat exchangers has been addressed. One of the barriers to increase the capacity of different industries is the lack of response of heat devices in higher capacities. In addition, increasing capacity leads to an increase in pressure drop and this is one of the most important restrictions on the large industries. Conventional methods of increasing heat transfer greatly increase the pressure drop, and according to the results of previous studies, using the special nanofluids, the thermal efficiency of the heat exchanger can be increased significantly, which is one of the most important thermal devices in the industry. In this research, firstly a review of nanofluids studies and introduction of nanofluids is presented, then their simulation methods are investigated, and finally, studies on the used tubes in the heat exchangers have been investigated, and studies of the plate heat exchanger, helical heat exchanger, shell and tube heat exchanger, and double-tube heat exchanger have been examined. The enhancement of thermal and hydraulic performance of heat exchangers is very important in terms of energy conversion, and also is important in the economic recovery of systems through savings. This paper examines previous studies on heat exchangers and using of nanofluids in them. The purpose of the paper is not only to describe the previous studies, but also to understand the mechanisms of heat transfer in the field of using nanofluids in heat exchangers, and also to evaluate and compare different heat transfer techniques. Finally, it can be concluded that the nanofluids in most cases improve heat transfer, which reduce the volume of heat exchangers, saving energy, consequently water consumption and industrial waste.

M. Ghalambaz, Ali J. Chamkha, D. Wen

Abstract Free convective flow and heat transfer of a suspension of Nano Encapsulated Phase Change Materials (NEPCMs) in an enclosure is studied. NEPCM particles are core-shell structured with Phase Change Material (PCM) as the core. The enclosure is a square cavity with top and bottom insulated walls and differentially-heated isothermal vertical walls. The NEPCM particles circulate under natural convection inside the cavity. The PCM cores undergo phase change from solid to liquid and absorb some of the surrounding’s heat in the form of latent heat in the hot region, and release the absorbed heat in the cold region by solidification. The governing equations representing the conservation of mass, flow, and heat of NEPCM suspension are introduced in the form of partial differential equations. The governing equations are transformed into non-dimensional form and solved by the finite element method. A grid check and validation test are performed to ensure the accuracy of the results. The outcomes show that the fusion temperature of NEPCM particles is the key factor affecting the heat transfer enhancement of NEPCMs in the natural convection flow. The enhancement of heat transfer is highly dependent on the non-dimensional fusion temperature, θf, and very good performance can be achieved in the range of ¼

Yongping Huang, Dongcheng Cao, Dongke Sun et al.

Abstract To improve the thermal performance of horizontal latent heat storage (LHS) units, this study investigates two innovative LHS units using uniform and gradient tree-shaped fins. By coupling visualization experiments and three-dimensional numerical simulations, the melting/solidification behavior and thermal properties of innovative LHS units are comprehensively analyzed and compared with traditional LHS units. The results show that tree-shaped fins facilitate heat diffusion from point to area, breaking the heat transport hysteresis in traditional LHS units, thus accelerating the melting/solidification rate. During the melting process, the gradient tree-shaped fins strengthen the heat transfer in lower parts of the LHS unit and extend the convective heat transfer duration in upper regions, promoting the synergistic strengthening of natural convection and heat conduction in the late melting stage. Compared to the uniform fin layout, the gradient tree-shaped fins effectively increase the melting rate, shortens the melting duration by 9%, and further improve the overall temperature uniformity of LHS units. However, the non-uniform transport path of gradient tree-shaped fins is not conducive to solidification heat transfer with conduction as the primary thermal regime, which increases the temperature gradient of LHS units and prolongs the solidification duration by 57.4% compared to the uniform tree-shaped fins.