Hasil untuk "Heat"

C. Forman, I. Muritala, Robert Pardemann et al.

H. Ghasemi, G. Ni, A. Marconnet et al.

Francis Agyenim, N. Hewitt, P. Eames et al.

L. Polsky, M. A. V. von Keyserlingk

C. Arpagaus, F. Bless, M. Uhlmann et al.

Abstract This study reviews the current state of the art and the current research activities of high temperature heat pumps (HTHPs) with heat sink temperatures in the range of 90 to 160 °C. The focus is on the analysis of the heat pump cycles and the suitable refrigerants. More than 20 HTHPs from 13 manufacturers have been identified on the market that are able to provide heat sink temperatures of at least 90 °C. Large application potentials have been recognized particularly in the food, paper, metal and chemical industries. The heating capacities range from about 20 kW to 20 MW. Most cycles are single-stage and differ primarily in the refrigerant (e.g. R245fa, R717, R744, R134a or R1234ze(E)) and compressor type used. The COPs range from 2.4 to 5.8 at a temperature lift of 95 to 40 K. Several research projects push the limits of the achievable COPs and heat sink temperatures to higher levels. COPs of about 5.7 to 6.5 (at 30 K lift) and 2.2 and 2.8 (70 K) are achieved at a sink temperature of 120 °C. The refrigerants investigated are mainly R1336mzz(Z), R718, R245fa, R1234ze(Z), R600, and R601. R1336mzz(Z) enables to achieve exceptionally high heat sink temperatures of up to 160 °C.

Xiangrong Wang, A. Mujumdar

E. Craig

J. Lienhard

R. Morimoto

Our cells and tissues are challenged constantly by exposure to extreme conditions that cause acute and chronic stress. Consequently, survival has necessitated the evolution of stress response networks to detect, monitor, and respond to environmental changes (Morimoto et al. 1990, 1994a; Baeuerle 1995; Baeuerle and Baltimore 1996; Feige et al. 1996; Morimoto and Santoro 1998). Prolonged exposure to stress interferes with efficient operations of the cell, with negative consequences on the biochemical properties of proteins that, under ideal conditions, exist in thermodynamically stable states. In stressed environments, proteins can unfold, misfold, or aggregate. Therefore, the changing demands on the quality control of protein biogenesis, challenges protein homeostasis, for which the heat shock response, through the elevated synthesis of molecular chaperones and proteases, repairs protein damage and assists in the recovery of the cell. The inducible transcription of heat shock genes is the response to a plethora of stress signals (Lis and Wu 1993; Morimoto 1993; Wu 1995) (Fig. 1), including (1) environmental stresses, (2) nonstress conditions, and (3) pathophysiology and disease states. Although changes in heat shock protein (HSP) expression are associated with certain diseases (Morimoto et al. 1990), these observations leave open the question of whether this is an adaptation to the particular pathophysiological state, a reflection of the suboptimal cellular environment associated with the disease, or serves to warn other cells and tissues of imminent danger. The protective role of HSPs is a measure of their capacity to assist in the repair of protein damage. Whether in prokaryotes, plants, or animals, overexpression of one or more HSPs is often sufficient to protect cells and tissues against otherwise lethal exposures to diverse environmental stresses including hydrogen peroxide and other oxidants, toxic chemicals, extreme temperatures, and ethanol-induced toxicity (Parsell and Lindquist 1994). In vertebrate tissue culture cells and animal models, elevating HSPs level, either by modulation of the heat shock response or by constitutive overexpression of specific heat shock proteins, restricts or substantially reduces the level of pathology and cell death (Mizzen and Welch 1988; Huot et al. 1991; Jaattela et al. 1992; Parsell and Lindquist 1994; Mestril et al. 1994; Plumier et al. 1995; Marber et al. 1995; Mehlen et al. 1995; Mosser et al. 1997). This has led to the recognition that HSPs, via their chaperoning effects on proteins, protect cells from many forms of stress-induced cell damage and could influence the course of disease.

M. Lamaoui, M. Jemo, R. Datla et al.

Drought and heat are major abiotic stresses that reduce crop productivity and weaken global food security, especially given the current and growing impacts of climate change and increases in the occurrence and severity of both stress factors. Plants have developed dynamic responses at the morphological, physiological and biochemical levels allowing them to escape and/or adapt to unfavorable environmental conditions. Nevertheless, even the mildest heat and drought stress negatively affects crop yield. Further, several independent studies have shown that increased temperature and drought can reduce crop yields by as much as 50%. Response to stress is complex and involves several factors including signaling, transcription factors, hormones, and secondary metabolites. The reproductive phase of development, leading to the grain production is shown to be more sensitive to heat stress in several crops. Advances coming from biotechnology including progress in genomics and information technology may mitigate the detrimental effects of heat and drought through the use of agronomic management practices and the development of crop varieties with increased productivity under stress. This review presents recent progress in key areas relevant to plant drought and heat tolerance. Furthermore, an overview and implications of physiological, biochemical and genetic aspects in the context of heat and drought are presented. Potential strategies to improve crop productivity are discussed.

C. Heaviside, H. Macintyre, S. Vardoulakis

Jianming Wu, Tuoen Liu, Zechary Rios et al.

T. Hayat, S Nadeem

Abstract Nanofluids are of great importance to researchers as they have significant uses industrially due to their high heat transfer rates. Recently, a new class of nanofluid, “hybrid nanofluid” is being used to further enhance the heat transfer rate. This new model in 3D is employed to examine the impact of thermal radiation, heat generation and chemical reaction over stretching sheet in the presence of rotation. It is concluded from the current research that even in the presence of radiation, heat generation and chemical reaction the heat transfer rate of Hybrid nanofluid is higher than the simple nanofluid.

Nasiru I. Ibrahim, F. Al-Sulaiman, S. Rahman et al.

H. Jouhara, A. Chauhan, T. Nannou et al.

Abstract Heat pipes are becoming increasingly popular as passive heat transfer technologies due to their high efficiency. This paper provides a comprehensive review of the state-of-the-art applications, materials and performance of current heat pipe devices. The paper is divided into four main parts; low temperature heat pipes, high temperature heat pipes, thermal modelling of heat pipes and discussion. The low and high temperature sections present an extended list with suitable working fluids and operating temperatures, along with their compatibility with casing materials. Furthermore, the sections focus on some of the most widespread industrial applications, such as solar, nanoparticles, Rankine cycles, nuclear, thermoelectric modules and ceramics, in which heat pipe technologies offer many key advantages over conventional practises. The third part of the paper consists of a thorough analysis of the thermal modelling side of heat pipes. Internal and external thermal modelling techniques, theories and methodologies are presented in this section, for various applications such as non-Newtonian fluids, nano-fluids, solar, geothermal, automotive, hybrid storage and nuclear systems. The final part of the paper discusses the limitations of heat pipes and the reasons why they are not implemented in more aspects of our lives. Operational limitations, cost concerns and the lack of detailed theoretical and simulation analysis of heat pipes are some of the point covered in this section. Finally, some of the recent and future developments in the field are discussed.

Heng Tang, Yong Tang, Z. Wan et al.

Abstract The development of miniaturization and high-density packaging of electronic components demands heat dissipation components that are compact and exhibit high performance. An ultra-thin micro heat pipe (UTHP), as a novel heat pipe with a flat shape that is highly suitable for application with high power and limited heat dissipation space, has been extensively investigated and widely used in mobile electronics. Understanding the influence of the manufacturing processes, capillary wick structures and flattened thickness on the thermal performance of UTHPs has been the aim of numerous studies. This paper presents a comprehensive review of the recent developments and applications of UTHPs for thermal management of electronics. The different types and applications of UTHPs are introduced, and the packaging technologies of UTHPs are summarized and compared. Furthermore, the fabrication methodology and heat transfer characteristics of various wick structures used for UTHPs are reviewed and analysed in detail. Finally, the challenges affecting the development and application of UTHPs are outlined, and recommendations for future research are presented.

A. Bloess, W. Schill, Alexander Zerrahn

A flexible coupling of power and heat sectors can contribute to both renewable energy integration and decarbonization. We present a literature review of model-based analyses in this field, focusing on residential heating. We compare geographical and temporal research scopes and identify state-of-the-art analytical model formulations, particularly considering heat pumps and thermal storage. While numerical findings are idiosyncratic to specific assumptions, a synthesis of results indicates that power-to-heat technologies can cost-effectively contribute to fossil fuel substitution, renewable integration, and decarbonization. Heat pumps and passive thermal storage emerge as particularly favorable options.

Bao-jie He, Junsong Wang, Huimin Liu et al.

Heat waves (HWs) and urban heat islands (UHIs) can potentially interact. The mechanisms behind their synergy are not fully disclosed. Starting from the localized UHI phenomenon, this study aims i) to reveal their associated impacts on human thermal comfort through three different definitions of HW events, based on air temperature (airT), wet-bulb globe temperature (WBGT) and human-perceived temperature (AppT) respectively, and ii) to understand the role of air moisture and wind. The analysis was conducted in four districts (NH, JD, MH and XJH) with different urban development patterns and geographic conditions, in the megacity of Shanghai with a subtropical humid climate. Results evidenced the localized interplay between HWs and UHIs. The results indicate that less urbanized districts were generally more sensitive to the synergies. JD district recorded the highest urban heat island intensity (UHII) amplification, regardless of the specific HW definition. Notably, during AppT-HWs, the increment was observed in terms of maximum (1.3 °C), daily average (0.8 °C), diurnal (0.4 °C) and nocturnal UHII (1.0 °C). Nevertheless, localized synergies between HWs and UHIs at different stations also exhibited some commonalities. Under airT-HW, the UHII was amplified throughout the day at all stations. Under WBGT-HW, diurnal UHII (especially at 11:00-17:00 LST) was consistently amplified at all stations. Under AppT-HW conditions, the nocturnal UHII was slightly amplified at all stations. Air moisture and wind alleviated the synergistic heat exacerbation to the benefit of thermal comfort. The extent depended on geographic condition, diurnal and nocturnal scenarios, temperature type and HW/normal conditions. Stronger HW-UHI synergies indicate the necessity to develop specific urban heat emergency response plans, able to capture and intervene on the underlying mechanisms. This study paves to way to their identification.

G. Jiang, Shengbiao Hu, Yizuo Shi et al.

Abstract Terrestrial heat flow is a crucial parameter to indicate the thermal state within the Earth, containing integrated information of the ground temperature, thermal conductivity, and crustal/mantle heat flow. We present an updated heat flow dataset and map in continental China. The data increases from 862 to 1230 observations since the year 1999 and the sites cover the major tectonic units, although their spatial distribution remains uneven. Excluding the local anomalies related to hydrothermal activities, the background heat flow values display a range from 30 to 140 mW m–2 with a mean of 60.4 ± 12.3 mW m–2. The updated heat flow map exhibits a heat flow pattern consisted of four heat flow provinces in continental China: eastern mantle-induced high flow province, southwestern crust-induced high heat flow province, central normal heat flow province and northwestern low heat flow province. The major heat flow provinces correspond to the Cenozoic lithosphere-scale tectonic units. The heat flow shows good correlation with crustal thickness and elevation, agreeing with the thermal isostasy. The heat flow distribution also corresponds with the Meso-Cenozoic tectonic activities. The present heat flow-tectonic pattern in continental China is formed by the Meso-Cenozoic geodynamic processes, including the Cenozoic India-Eurasian collision and the Mesozoic-Cenozoic western subduction of the Pacific Plate.

Jiu Yu, Yubo Hu, Yaoxing Peng

The wick structure functions as a core component for heat pipe (HP) and stands as one of the critical factors that dictate the performance of HP. Consequently, this paper puts forward an three-segmented composite wick structure, which is manufactured using 80–100 mesh, 60–80 mesh, and 40–60 mesh copper powder. Experimentally, the influences of filling ratio as well as testing direction on the heat transport performance of HP equipped with segmented composite wick are explored, and the results are contrasted against those of HP featuring single wicks. Additionally, testing direction has a notable effect on the thermal behavior of HP. The maximum heat transfer capacity of HP using 40–60 mesh copper powder as the evaporation section (S1-P2) and that with 80–100 mesh copper powder as the evaporation section (S1-P1) are >90 W and 45 W, respectively. In comparison with S1-P1, S1-P2 has raised its maximum heat transfer capacity by 100 %, while its average thermal resistance of S1-P2 is no more than 0.028 °C/W. Compared with single wicks, the three-segmented composite wick design can effectively lower the thermal resistance of the HP while boosting the heat transfer capacity. Relevant research provides valuable references for optimizing the performance of HP.