This paper deals about the response of envelope to various climatic conditions and it is the main reason to know the amount of energy needed to maintain thermal comfort of the inner environment. The ...building envelope reduces external stress especially in hot climates and it was determined by subjecting its individual orientations and composition. The study is to reconstruct the envelope parts by changing wall material, thermal insulation materials in wall pattern and minimize its U-value to reduce the heat the heat transfer and determine it by using AUTOCAD and FOURLY ANALYSIS PROGRAM of ASHRAE 2013 standard.
This work investigates interfacial thermal transport in phononic‐mismatched heterostructures that consists of pristine black phosphorene and its phononic crystal. It is found that the presence of the ...sub‐periodic structure results in reduced thermal conductivity in phononic crystals. As opposed to intuitive expectations, a slight temperature jump is observed at the interface of nanophononic heterostructures, which is only about 10% of that at conventional interfaces consisting of dissimilar materials. Consequently, contact thermal conductance in the nanophononic heterostructure is 10−30 times higher than that of mass‐mismatched interfaces in a comparative study. Moreover, in contrast to conventional heterostructures achieved by interfacing dissimilar materials, weak temperature dependence is observed in interfacial thermal conductance, and thermal rectification is sharply suppressed. These phenomena are well explained based on lattice dynamic insights. This work not only enhances the understanding of the fundamental physics of phonons transport across interface, but also facilitates the possible spectrum of application ranges from thermoelectrics, thermal management, to thermal cloak.
As opposed to intuitive expectation, a slight temperature jump is observed at the interface of nanophononic heterostructures, which is about 10% of that at the interface of dissimilar materials. Consequently, its contact thermal conductance is 10−30 times higher than that of mass‐mismatched interfaces. This work enhances the understanding of phonon transport, and facilitates the possible spectrum of application ranges from thermoelectrics, thermal management, to thermal cloaks.
•A detailed thermal resistance analysis of the PV-TE hybrid system is proposed.•c-Si PV and p-Si PV cells are proved to be inapplicable for the PV-TE hybrid system.•Some criteria for selecting ...coupling devices and optimal design are obtained.•A detailed process of designing the practical PV-TE hybrid system is provided.
The thermal resistance theory is introduced into the theoretical model of the photovoltaic-thermoelectric (PV-TE) hybrid system. A detailed thermal resistance analysis is proposed to optimize the design of the coupled system in terms of optimal total conversion efficiency. Systems using four types of photovoltaic cells are investigated, including monocrystalline silicon photovoltaic cell, polycrystalline silicon photovoltaic cell, amorphous silicon photovoltaic cell and polymer photovoltaic cell. Three cooling methods, including natural cooling, forced air cooling and water cooling, are compared, which demonstrates a significant superiority of water cooling for the concentrating photovoltaic-thermoelectric hybrid system. Influences of the optical concentrating ratio and velocity of water are studied together and the optimal values are revealed. The impacts of the thermal resistances of the contact surface, TE generator and the upper heat loss thermal resistance on the property of the coupled system are investigated, respectively. The results indicate that amorphous silicon PV cell and polymer PV cell are more appropriate for the concentrating hybrid system. Enlarging the thermal resistance of the thermoelectric generator can significantly increase the performance of the coupled system using amorphous silicon PV cell or polymer PV cell.
With the current development of modern electronics toward miniaturization, high-degree integration and multifunctionalization, considerable heat is accumulated, which results in the thermal failure ...or even explosion of modern electronics. The thermal conductivity of materials has thus attracted much attention in modern electronics. Although polymer composites with enhanced thermal conductivity are expected to address this issue, achieving higher thermal conductivity (above 10 W m–1 K–1) at filler loadings below 50.0 wt % remains challenging. Here, we report a nanocomposite consisting of boron nitride nanotubes and cellulose nanofibers that exhibits high thermal conductivity (21.39 W m–1 K–1) at 25.0 wt % boron nitride nanotubes. Such high thermal conductivity is attributed to the high intrinsic thermal conductivity of boron nitride nanotubes and cellulose nanofibers, the one-dimensional structure of boron nitride nanotubes, and the reduced interfacial thermal resistance due to the strong interaction between the boron nitride nanotubes and cellulose nanofibers. Using the as-prepared nanocomposite as a flexible printed circuit board, we demonstrate its potential usefulness in electronic device-cooling applications. This thermally conductive nanocomposite has promising applications in thermal interface materials, printed circuit boards or organic substrates in electronics and could supplement conventional polymer-based materials.
In this paper, self-heating effects (SHEs) in three-stacked nanoplate FETs were investigated through the TCAD simulation. In order to obtain high reliability, the evaluation of SHEs was performed ...after <inline-formula> <tex-math notation="LaTeX">{I}_{D} </tex-math></inline-formula>-<inline-formula> <tex-math notation="LaTeX">{V}_{G} </tex-math></inline-formula> curve fitting based on the experimental data. First, general analysis on SHEs was conducted to confirm the influence of SHEs to electrical characteristics. The optimized nanoplate width for great electrical properties was proposed by using the figure-of-merit factor under the consideration of SHEs. In addition, difference of heat flux between FinFET and stacked nanoplate FET was analyzed. Based on the analysis, the two-step thermal resistance (<inline-formula> <tex-math notation="LaTeX">{R}_{\text {th}} </tex-math></inline-formula>) model depending on drain voltage was proposed. The two-step <inline-formula> <tex-math notation="LaTeX">{R}_{\text {th}} </tex-math></inline-formula> model in the stacked nanoplate FET matched well with the Berkeley short-channel IGFET model-common multigate model compared the other <inline-formula> <tex-math notation="LaTeX">{R}_{\text {th}} </tex-math></inline-formula> models. A seven-stage ring oscillator with the proposed <inline-formula> <tex-math notation="LaTeX">{R}_{\text {th}} </tex-math></inline-formula> model was demonstrated, and SHEs in the circuit level were confirmed.
A three-dimensional (3D) integrated packaging method is proposed in this letter. Re-distributed layers (RDLs) are realized by integrating flexible printed circuit (FPC) boards onto gallium nitride ...(GaN) high electron mobility transistor (HEMT) dies to enlarge the electrodes area and the clearance between them. GaN HEMTs with RDLs are sandwiched between a multi-layer printed circuit board (PCB) and an active metal brazing (AMB) board. Additionally, components like decoupling capacitors, gate driver, digital isolator and isolated power supply are integrated into this package. Silver sintering processes are employed to maintain consistent processing temperature for multiple interconnections, addressing reliability concerns associated with conventional multi-temperature gradient soldering methods. Furthermore, sintered silver significantly improves both electrical and thermal performances. Power and thermal managements are decoupled by using a PCB and AMB substrate, resulting in low parasitic inductances, minimal thermal resistance and electric field shielding. The experiment-measured power loop inductance is as low as 0.54 nH, and the simulated thermal resistance from GaN die to AMB board bottom is only 0.05 ℃/W. A detailed description of manufacturing processes, thermal performance test, dynamic switching performance with circuit-level simulated verification are provided in this letter.
The combination of crystallization, transparency, and strength is still a challenge for broadening the application of polylactic acid (PLA) films, while it is also difficult to balance. In this work, ...the long aliphatic chains of octadecylamine (ODA) were grafted onto the surface of cellulose nanocrystal (CNC) by tannic acid oxidation self-polymerization and Michael addition/Schiff base reaction between polytannic acid and ODA. Furthermore, the ODA grafted CNC (g-CNC) was used as green reinforcement for the PLA matrix and a series of PLA/g-CNC nanocomposite films were prepared by the casting method. The DSC, WAXD, POM, UV–vis and stretching test were employed to examine the effect of g-CNC on the properties of the as-prepared PLA/g-CNC nanocomposite films. It shows that the g-CNC is effective to improve the melt crystallization rate of PLA from 11 min to 7.3 min. Most importantly, the crystal size of the PLA spherulites was significantly reduced due to the well dispersion in the amorphous PLA matrix, which would effectively improve the transmittance of the PLA films and synchronously realize the combination of crystallization (62 %) and transparency (80.6 %). Moreover, the improved crystallization could also enhance the heat deformation performance of the PLA films since the heat resistance is closely associated with the crystallinity. Besides, the grafted ODA long chains improve the compatibility between CNC and PLA, leading to the reinforcement of PLA matrix, where the tensile strength reaches 65.05 MPa from 44.31 MPa. Compared with the pristine CNC, the addition of g-CNC makes more comprehensive improvement in the properties of the PLA films.
This paper examines the thermal resistances of energy piles and surrounding soils. A field-scale bored energy pile was installed through stiff sandy clay and dense sand and instrumented to measure ...temperatures on the external walls of the heat exchanger pipes, at the pile-soil interface, and in the soil. The radial temperature gradients between the pipes and the pile-soil interface, and the pile-soil interface and the soil, were used to evaluate the pile and soil thermal resistances, respectively. The thermal resistances were on the same order of magnitude with values of 0.053 mK/W, 0.072 mK/W, and 0.066 mK/W for the pile, stiff sandy clay, and dense sand due to similarities in their thermal properties. The analysis suggests that pile and soil thermal resistances are influenced by the pile dimensions, number of pipes, concrete cover, soil type and duration of heating. Hence, meticulous interpretation of thermal resistances considering these parameters should be conducted to understand heat transfer processes in energy piles accurately. Estimates of the pile thermal resistance from the equivalent diameter and thermal response test methods were found to be inconsistent with each other, highlighting the significance of considering steady state in-situ radial temperature gradients in designing energy pile systems.
•Crystallization fouling of mixed salt in double-pipe heat exchanger is studied.•Na2SO4 is the main fouling substance in mixed salts.•Rf is determined by Na2SO4 content and heat transfer temperature ...difference.•Crystallization fouling of mixed salt is controlled by chemical kinetics.•NaCl decreases fouling thermal resistance and fouling rate.
The fouling behavior of normal solubility pure salt (Na2SO4) and mixed salt (Na2SO4 and NaCl) in counter-current double-pipe heat exchanger was investigated. Through real-time monitoring of inlet and outlet temperatures of hot and cold fluids, the influences of various factors such as the inlet temperature, inlet velocity of hot solution and solute mass ratio on the fouling thermal resistance were determined. The results show that the fouling thermal resistance is determined by the sodium sulfate content at the experimental temperature and the change of the solubility of sodium sulfate within the temperature difference of heat transfer. With the increase of the inlet velocity of hot solution, the thermal resistance of fouling decreases gradually, indicating that the fouling process is controlled by chemical kinetics. In the fouling experiment of mixed salt solution, the main deposition material is sodium sulfate. Due to the common ion effect, sodium chloride greatly affects the saturated solubility of sodium sulfate, with the increase of the mass ratio of sodium chloride, the fouling thermal resistance and the fouling rate decreases gradually, and the time when the fouling thermal resistance reaches the asymptotic value is prolonged. The research results can provide theoretical guidance for scale inhibition of cooling surface of double-pipe heat exchanger in the treatment of wastewater containing sodium sulfate.
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•Flow boiling heat transfer of MgO/therminol 66 was investigated.•Fouling thermal resistance of nanoparticles was modeled.•A new model for flow boiling heat transfer of nanofluid was developed.•The ...boiling surface was a copper made disc.
An experimental investigation was performed on the flow boiling heat transfer characteristics of MgO/therminol 66 nanofluid as a potential coolant on a copper-made disc. Nanofluids were prepared using two step method at wt.% = 0.1, and wt.% = 0.3. Results showed that the presence of MgO/therminol 66 increases the flow boiling heat transfer coefficient in comparison with the base fluid. However, with an increase in the mass concentration of nanoparticles, the heat transfer coefficient decreased. Results also revealed that bubble formation induces a pressure drop within the test section. Heat flux had no influence on the pressure drop, while an increase in the fluid flow rate caused an increase in the pressure drop. It was also found that the heat transfer coefficient decreased with operating time due to the presence of nanoparticles on the boiling surface resulting in the creation of thermal resistance on the surface. Also, an asymptotic behavior for the fouling thermal resistance over the time was registered. Two correlations were re-developed to accurately predict the heat transfer coefficient and fouling thermal resistance of the system. Experiments proved that MgO nanoparticles offer a potential to be used in thermal engineering systems with boiling heat transfer mechanism. The maximum enhancement for the heat transfer coefficient was 23.7% at wt.% = 0.1. For wt.% = 0.2 and wt.% = 0.3, the maximum enhancement of 16.2% and 13.3%, were achieved, respectively.
