Hasil untuk "Heat"

D. Tzou

B. Vrancken, L. Thijs, J. Kruth et al.

Abstract The present work shows that optimization of mechanical properties via heat treatment of parts produced by Selective Laser Melting (SLM) is profoundly different compared to conventionally processed Ti6Al4V. In order to obtain optimal mechanical properties, specific treatments are necessary due to the specific microstructure resulting from the SLM process. SLM is an additive manufacturing technique through which components are built by selectively melting powder layers with a focused laser beam. The process is characterized by short laser-powder interaction times and localized high heat input, which leads to steep thermal gradients, rapid solidification and fast cooling. In this research, the effect of several heat treatments on the microstructure and mechanical properties of Ti6Al4V processed by SLM is studied. A comparison is made with the effect of these treatments on hot forged and subsequently mill annealed Ti6Al4V with an original equiaxed microstructure. For SLM produced parts, the original martensite α′ phase is converted to a lamellar mixture of α and β for heat treating temperatures below the β-transus (995 °C), but features of the original microstructure are maintained. Treated above the β-transus, extensive grain growth occurs and large β grains are formed which transform to lamellar α + β upon cooling. Post treating at 850 °C for 2 h, followed by furnace cooling increased the ductility of SLM parts to 12.84 ± 1.36%, compared to 7.36 ± 1.32% for as-built parts.

S. Kakaç, A. Pramuanjaroenkij

Felix Hueber

P. Keblinski, S. Phillpot, Stephen U. S. Choi et al.

D. Tzou

J. W. West

B. Coleman, W. Noll

M. Kaviany

Zhigang Li, Wenchuan Wu, M. Shahidehpour et al.

M. Ziegler, F. Seneca, Lauren K. Yum et al.

Ocean warming threatens corals and the coral reef ecosystem. Nevertheless, corals can be adapted to their thermal environment and inherit heat tolerance across generations. In addition, the diverse microbes that associate with corals have the capacity for more rapid change, potentially aiding the adaptation of long-lived corals. Here, we show that the microbiome of reef corals is different across thermally variable habitats and changes over time when corals are reciprocally transplanted. Exposing these corals to thermal bleaching conditions changes the microbiome for heat-sensitive corals, but not for heat-tolerant corals growing in habitats with natural high heat extremes. Importantly, particular bacterial taxa predict the coral host response in a short-term heat stress experiment. Such associations could result from parallel responses of the coral and the microbial community to living at high natural temperatures. A competing hypothesis is that the microbial community and coral heat tolerance are causally linked. Coral-associated microbes could enhance the capacity of their host organism to respond to environmental change. Ziegler and colleagues use a reciprocal transplant experiment to show that microbiomes of heat-tolerant corals are more resilient to change than those of heat-sensitive corals.

Mohsen Sheikholeslami, R. Haq, A. Shafee et al.

Abstract The current article investigates the impact of using fins and nano sized materials on performance of discharging system. Various shapes for nanoparticle have been considered. Cold fluid flows in both inner and outer layers and middle layer is full of PCM. To make a careful choice of designing heat storage based on uniform solidification, two factor has been examined; length of fins and shape factor. Temperature and solid fraction distributions were reported at various time steps. The homogeneous model for nanofluid has been extended by incorporating various shapes of CuO nanoparticles. The mathematical model has been offered in the form of PDE's, which were solved using Galerkin FEM. It can be observed that the employing nanofluid augments the discharging rate and best performance is obtained for platelet shape.

Huijin Xu, Z. Xing, Fuqiang Wang et al.

Abstract Increasing the heat transfer rate of heat transfer equipment is an ever-lasting topic in thermal engineering. Due to the advantages of light weight, high specific surface, high thermal conductivity, metal foam is a good extending surface for heat transfer enhancement. Nanofluid has a higher thermal conductivity than the traditional base fluid, so it can be used as an efficient heat transfer medium. This paper focuses on various flow and heat transfer modes of nanofluid, metal foam and the combination of the two, with the physical properties of nanofluid and metal foam summarized. The characteristics of flow and heat transfer are introduced. The motivation of this review paper is to arouse the researchers to pay attention to the basic transport understandings for the heat transfer enhancement of nanofluids in porous media. The knowledge reviewed in this paper is useful for improving the performance of compact heat exchangers, and heat sinks for cooling electronics with porous media and nanofluids.

M. Larrañaga

Z. Jiang, Z. Qu

Abstract Thermal management of lithium–ion battery has become a critical issue in recent years. In this study, a thermal management module with a sandwich structure consisting of a battery, phase change material, and heat pipe is assembled. The battery temperature response is experimentally investigated for battery, heat pipe and phase change material composite with three discharge and charge cycles. A lumped thermal model is built to consider the coupling of battery heat generation, phase change material melting, and transient thermal response of heat pipe. The underlying coupling mechanism of battery temperature and phase change process is revealed at different environmental temperatures, heat transfer coefficients at condensation section, and thickness ratios of phase change material and battery. The model is validated with the experimental data in one discharge/charge cycle. A continuous safe cycling is difficult to maintain for battery with the air convection and only phase change material. The utilization of heat pipe can recover the latent heat of phase change material with an appropriate melting point at the end of each cycle to ensure a low battery temperature for long-time cycling. Four stages, namely, sensible heat, latent heat, solidification, and steady stage, are found in each cycle for the proposed cooling module. Then, the coupling mechanism of battery heat generation and heat transfer in heat pipe and phase change material is identified. The condensation section for heat pipe may operate at the unsustainable, sustainable, and uneconomic regions. To guarantee safe battery temperature, low energy consumption, and sufficient module energy density in long-time cycling simultaneously, the phase change material melting point is recommend to be at least 3 °C higher than environmental temperature, and the heat transfer coefficient in the condenser is recommended to range from 30 W/m2·K to 60 W/m2·K with an optimum thickness ratio of 0.17 associated with a phase change ratio of approximately 0.55.

M. Sheikholeslami, Behnoush Rezaeianjouybari, M. Darzi et al.

Abstract This research presents the outputs for nano-refrigerant (R600a/oil/CuO) boiling heat transfer within flattened channels utilizing experimental method. The influence of flattened percentage, flow rate, vapor quality as well as the mass fraction of CuO on boiling heat transfer (h) were discussed. Outcomes reveal that increasing the flattened percentage enhances the h. Also, within the ranges of present experiment, h augments by increasing nanoparticle’s concentration.

Jasim M. Mahdi, Sina Lohrasbi, Emmanuel C. Nsofor

Abstract The potential of phase-change materials (PCMs) for application in the fields of thermal energy storage and thermal management is well recognized, due to their remarkable energy storage density and negligible temperature variation during operation. However, these materials do face the primary challenge of low thermal conductivity which necessitates incorporation of heat transfer enhancement techniques. Heat transfer enhancement in these systems has been a subject of interest for numerous studies, many of which have focused on employing only one enhancement technique. Very few studies have investigated the combination of two or more techniques. This combination of techniques is referred to as hybrid heat transfer enhancement. This paper provides a review of the major studies on the hybrid heat transfer enhancement techniques. It was found from the study that best enhancement is achieved via the hybrid application of the heat pipe with fins or metal foam. It was also found that the hybrid use of nanoparticles with fins or metal foam is more efficient than the use of nanoparticles alone within the same containment volume. Further research is recommended to explore other possible hybrid enhancement techniques which could lead to improved performance of PCM-based systems.

Mohsen Sheikholeslami, M. Jafaryar, A. Shafee et al.

Abstract In current modeling, turbulent heat transfer of homogeneous nanofluid due to inserting double twisted tapes has been carried out. To better describing performance of unit, generation of entropy has been examined. CuO nanomaterial has been dispersed in to H2O, to help its conductivity. The pipe was under the impact of uniform heat flux. Equations describing the flow and energy balance were solved applying finite volume method. The simulations illustrate that both augmenting pumping power and height of tape result in the reduction of thermal component and the augmentation of frictional component.

M. Sheikholeslami, M. Jafaryar, M. Hedayat et al.

Abstract In this research, combined turbulator was proposed to achieve good thermal performance. Steady turbulent flow of copper oxide nanofluid with homogeneous model was simulated involving k-ɛ model. Among various geometric parameters, height of turbulator (b) has been selected and its variation as well as Reynolds number was demonstrated in outputs. Exergy loss as well as flow and heat transfer was analyzed. Augmenting b is capable of increasing heat transfer. More disturbances can be seen with augmenting inlet velocity. Exergy loss is inversely proportional to increase of pumping power.

Z. Y. Xu, Ruzhu Wang, Chun Yang

Abstract In this forward-looking perspective, the current technologies for low-temperature waste heat recovery are first analyzed from two aspects: (i) the local waste heat recovery technology and (ii) global optimization of energy flow network. Based on the analysis, barriers for the further promotion of waste heat recovery are outlined, and they include the lack of global optimization methodology, distributed waste heat recovery system with high costs, and mismatches between waste heat source and demand. To address these issues, perspectives on three aspects are provided. First, advanced graphical analysis and optimization methodology integrating the heat exchange and energy conversion can promote the user-friendly optimization. Second, concentrated waste heat recovery and supply can save the investment, installation area and operation costs, thereby making the waste heat recovery cost-effective. Third, thermal storage, thermal transportation and high temperature heat pump can better couple the waste heat source and user demand from time-scale, spatial scale and energy grade, respectively. Visions for the future are combined with technical details to provide comprehensive perspectives for the next-step waste heat recovery.