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Equivalent thermal conductivity of heat pipes

LU Zesheng, MA Binghui

《机械工程前沿（英文）》 2008年 第3卷 第4期   页码 462-466 doi: 10.1007/s11465-008-0087-1

摘要： In precision machining, the machining error from thermal distortion carries a high proportion of the total errors. If a precision machining tool can transfer heat fast, the thermal distortion will be reduced and the machining precision will be improved. A heat pipe working based on phase transitions of the inner working liquid transfers heat with high efficiency and is widely applied in spaceflight and chemical industries. In mechanics, applications of heat pipes are correspondingly less. When a heat pipe is applied to a hydrostatic motorized spindle, the thermal distortion cannot be solved during the heat transfer process because thermal conductivity or equivalent thermal conductivity should be provided first for special application in mechanics. An equivalent thermal conductivity model based on equivalent thermal resistances is established. Performance tests for a screen wick pipe, gravity pipe, and rotation heat pipe are done to validate the efficiency of the equivalent thermal conductivity model. The proposed model provides a calculation method for the thermal distortion analysis of heat pipes applied in the motorized spindle.

关键词： proposed     distortion analysis     hydrostatic motorized     motorized spindle     Performance    

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Characterization of 3D microstructure, thermal conductivity, and heat flow of cement-based foam using

《结构与土木工程前沿（英文）》 2021年 第15卷 第3期   页码 643-651 doi: 10.1007/s11709-021-0709-9

摘要： This study presents the results of the 3D microstructure, thermal conductivity, and heat flow in cement-based foams and examines their changes with a range of densities. Images were captured using X-ray micro computed tomography (micro-CT) imaging technique on cement-based foam samples prepared with densities of 400, 600, and 800 kg/m3. These images were later simulated and quantified using 3D data visualization and analysis software. Based on the analysis, the pore volume of 11000 µm3 was determined across the three densities, leading to optimal results. However, distinct pore diameters of 15 µm for 800 kg/m3, and 20 µm for 600 and 400 kg/m3 were found to be optimum. Most of the pores were spherical, with only 10% appearing elongated or fractured. In addition, a difference of 15% was observed between the 2D and 3D porosity results. Moreover, a difference of 5% was noticed between the experimentally measured thermal conductivity and the numerically predicted value and this variation was constant across the three cast densities. The 3D model showed that heat flows through the cement paste solids and with an increase in porosity this flow reduces.

关键词： 3D pore volume distribution     X-ray tomography     3D shape factor     heat flow    

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Analysis of flow and heat transfer characteristics of porous heat-storage wall in greenhouse

OUYANG Li, LIU Wei

《能源前沿（英文）》 2008年 第2卷 第4期   页码 406-409 doi: 10.1007/s11708-008-0094-2

摘要： The flow and heat transfer characteristics of porous heat-storage wall in greenhouse are studied by using the one-dimensional steady energy two-equation model for saturated porous medium. The results show that the heat exchange between the air and the solid matrix of the porous heat-storage wall depends upon the inlet air velocity, the porosity and the permeability of porous medium, and the thermal conductivity of the solid matrix. Because the incidence of solar radiation on the porous heat-storage wall is not uniform, the new composite porous solar wall with different porosity is proposed to reduce the disadvantageous effect.

关键词： incidence     thermal conductivity     heat-storage     exchange     composite    

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A building unit decomposition model for energy leakage by infrared thermography image analysis

Yan SU, Fangjun HONG, Lianjie SHU

《能源前沿（英文）》 2020年 第14卷 第4期   页码 901-921 doi: 10.1007/s11708-020-0679-y

摘要： A quantitative energy leakage model was developed based on the thermography image data measured for both external and internal building surfaces. The infrared thermography images of both surfaces of doors, windows, and walls of an office building in the Hengqin Campus of University of Macao were taken at various times in a day for four seasons. The transient heat flux for sample units were obtained based on measurements of the seasonal transient local temperature differences and calculations of the effective thermal conductivity from the multiple-layer porous medium conduction model. Effects of construction unit types, orientations, and seasons were quantitatively investigated with unit transient orientation index factors. The corresponding electric energy consumption was calculated based on the air conditioning system coefficient of performance of heat pump and refrigerator cycles for different seasons. The model was validated by comparing to the electric meter records of energy consumption of the air conditioning system. The uncertainties of the predicted total building energy leakage are about 14.7%, 12.8%, 12.4%, and 15.8% for the four seasons, respectively. The differences between the predicted electric consumption and meter values are less than 13.4% and 5.4% for summer and winter, respectively. The typical daily thermal energy leakage value in winter is the highest among the four seasons. However, the daily electric energy consumption by the air conditioning system in summer and autumn is higher than that in winter. The present decomposition model for energy leakage is expected to provide a practical tool for quantitative analysis of energy leakage of buildings.

关键词： heat conductivity     heat coefficient     heat &fllig     ux     infrared thermography     thermal image    

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Preparation, with graphene, of novel biomimetic self-healing microcapsules with high thermal stability and conductivity

《结构与土木工程前沿（英文）》   页码 1188-1198 doi: 10.1007/s11709-023-0027-5

摘要： This paper reports a comparative study of microcapsules with enhanced thermal stability and electrical conductivity inspired by the bionic thermal insulation of birds’ feathers for self-healing aged asphalt. The work is based on an in situ polymerization with composite shell components of graphene and hexamethoxymethylmelamine resin. By using graphene, microcapsules with rough surfaces are achieved, improving the interface between microcapsules and asphalt. In addition, the microcapsules’ initial thermal decomposition temperature is appropriately high, so that the stability of the microcapsule in the asphalt highway system is protected. The proportion of graphene in the microcapsule shell can regulate the microcapsule’s heat resistance because graphene modifies the shell’s structural makeup. Additionally, the microcapsules’ electrical conductivity is relatively high. The self-healing capability of bitumen sharply increases, providing benefit to the effect of microcapsules on the properties of aged asphalt.

关键词： graphene     microcapsule     bitumen     heat insulation     conductivity    

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Activated carbon induced oxygen vacancies-engineered nickel ferrite with enhanced conductivity for supercapacitor

《化学科学与工程前沿（英文）》 2023年 第17卷 第12期   页码 2088-2100 doi: 10.1007/s11705-023-2352-6

摘要： Activated carbon induced oxygen vacancies-engineered nickel ferrite with enhanced conductivity for supercapacitor application

关键词： nickel ferrite conductivity     carbon oxygen vacancies    

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Permeability and thermal conductivity of host compressed natural graphite for consolidated activated

Bo TIAN, Liwei WANG, Zhequan JIN, Ruzhu WANG

《能源前沿（英文）》 2011年 第5卷 第2期   页码 159-165 doi: 10.1007/s11708-011-0145-y

摘要： Permeability and thermal conductivity test units were set up to study the heat and mass transfer performance of the host material, i.e. expanded natural graphite (ENG), for consolidated activated carbon (AC) adsorbent. The permeability was tested with nitrogen as the gas source, and the thermal conductivity was studied using steady-state heat source method. The results showed that the values of permeability and thermal conductivity were 10 to 10 m and 1.7 to 3.2 W/(m·K), respectively, while the density compressed expanded natural graphite (CENG) varied from 100 to 500 kg/m . The permeability decreased with the increasing density of CENG, whereas the thermal conductivity increased with the increasing density of CENG. Then the thermal conductivity and permeability of granular AC were researched. It was discovered that the thermal conductivity of samples with different grain size almost kept constant at 0.36 W/(m·K) while the density was approximately 600 kg/m . This means that the thermal conductivity was not related to the grain size of AC. The thermal conductivity of CENG was improved by 5 to 10 times compared with that of granular AC. Such a result showed that CENG was a promising host material for AC to improve the heat transfer performance, while the mass transfer performance should be considered in different conditions for utilization of adsorbent.

关键词： permeability     thermal conductivity     expanded nature graphite     activated carbon    

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Tailoring electrical conductivity of two dimensional nanomaterials using plasma for edge electronics:

Aswathy Vasudevan, Vasyl Shvalya, Aleksander Zidanšek, Uroš Cvelbar

《化学科学与工程前沿（英文）》 2019年 第13卷 第3期   页码 427-443 doi: 10.1007/s11705-019-1805-4

摘要： Since graphene has been discovered, two-dimensional nanomaterials have attracted attention due to their promising tunable electronic properties. The possibility of tailoring electrical conductivity at the atomic level allows creating new prospective 2D structures for energy harvesting and sensing-related applications. In this respect, one of the most successful way to manipulate the physical properties of the aforementioned materials is related to the surface modification techniques employing plasma. Moreover, plasma-gaseous chemical treatment can provide a controlled change in the bandgap, increase sensitivity and significantly improve the structural stability of material to the environment as well. This review deals with recent advances in the modification of 2D carbon nanostructures for novel ‘edge’ electronics using plasma technology and processes.

关键词： graphene     edge electronics     2D nanomaterials     plasma     electrical conductivity    

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Modeling of ion conductivity in Nafion membranes

YANG Zhen, PENG Xiaofeng, WANG Buxuan, DUAN Yuanyuan, LEE Duujong

《能源前沿（英文）》 2007年 第1卷 第1期   页码 58-66 doi: 10.1007/s11708-007-0005-y

摘要： A theoretical investigation was conducted to describe the ion transport behavior in a Nafion Membrane of proton exchange membrane fuel cells (PEMFC). By analyzing the surface energy configuration of the ionic clusters in a Nafion membrane, an equivalent field intensity, , was introduced to facilitate the analysis of surface resistance against ion conduction in the central region of clusters. An expression was derived for ionic conductivity incorporating the influence of surface resistance. A face-centered cubic (FCC) lattice model for a spatial cluster distribution was used to modify the effect of water content on ionic conductivity in the polymeric matrix, i.e., the regions between clusters. Compared with the available empirical correlations, the new expression showed much better agreement with the available experimental results, which indicates the rationality to consider the structural influence on ion conduction in water-swollen Nafion membranes.

关键词： face-centered     polymeric     theoretical investigation     conduction     equivalent    

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phosphorus-nitrogen based flame retardant and multi-walled carbon nanotubes for enhanced electrical conductivity

Yong Luo, Yuhui Xie, Renjie Chen, Ruizhi Zheng, Hua Wu, Xinxin Sheng, Delong Xie, Yi Mei

《化学科学与工程前沿（英文）》 2021年 第15卷 第5期   页码 1332-1345 doi: 10.1007/s11705-021-2035-0

摘要： Design and exploitation of flame retardant polymers with high electrical conductivity are desired for polymer applications in electronics. Herein, a novel phosphorus-nitrogen intumescent flame retardant was synthesized from pentaerythritol octahydrogen tetraphosphate, phenylphosphonyl dichloride, and aniline. Low-density polyethylene was combined with the flame retardant and multi-walled carbon nanotubes to form a nanocomposite material via a ball-milling and hot-pressing method. The electrical conductivity, mechanical properties, thermal performance, and flame retardancy of the composites were investigated using a four-point probe instrument, universal tensile machine, thermogravimetric analysis, and cone calorimeter tests, respectively. It was found that the addition of multi-walled carbon nanotubes can significantly improve the electrical conductivity and mechanical properties of the low-density polyethylene composites. Furthermore, the combination of multi-walled carbon nanotubes and phosphorus–nitrogen flame retardant remarkably enhances the flame retardancy of matrixes with an observed decrease of the peak heat release rate and total heat release of 49.8% and 51.9%, respectively. This study provides a new and effective methodology to substantially enhance the electrical conductivity and flame retardancy of polymers with an attractive prospect for polymer applications in electrical equipment.

关键词： MWCNTs     PEPA     electrical conductivity     flame retardant     low density polyethylene    

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Absorption heat pump for waste heat reuse: current states and future development

Zhenyuan XU, Ruzhu WANG

《能源前沿（英文）》 2017年 第11卷 第4期   页码 414-436 doi: 10.1007/s11708-017-0507-1

摘要： Absorption heat pump attracts increasing attention due to its advantages in low grade thermal energy utilization. It can be applied for waste heat reuse to save energy consumption, reduce environment pollution, and bring considerable economic benefit. In this paper, three important aspects for absorption heat pump for waste heat reuse are reviewed. In the first part, different absorption heat pump cycles are classified and introduced. Absorption heat pumps for heat amplification and absorption heat transformer for temperature upgrading are included. Both basic single effect cycles and advanced cycles for better performance are introduced. In the second part, different working pairs, including the water based working pairs, ammonia based working pairs, alcohol based working pairs, and halogenated hydrocarbon based working pairs, for absorption heat pump are classified based on the refrigerant. In the third part, the applications of the absorption heat pump and absorption heat transformer for waste heat reuse in different industries are introduced. Based on the reviews in the three aspects, essential summary and future perspective are presented at last.

关键词： absorption     heat pump     heat transformer     waste heat     working pair    

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Ultrafast-laser-treated poly(3,4-ethylenedioxythiophene): poly(styrenesulfonate) electrodes with enhanced conductivity

《化学科学与工程前沿（英文）》 2023年 第17卷 第2期   页码 206-216 doi: 10.1007/s11705-022-2203-x

摘要： Poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) is an important organic electrode for solution-processed low-cost electronic devices. However, it requires doping and post-solvent treatment to improve its conductivity, and the chemicals used for such treatments may affect the device fabrication process. In this study, we developed a novel route for exploiting ultrafast lasers (femtosecond and picosecond laser) to simultaneously enhance the conductivity and transparency of PEDOT:PSS films and fabricate patterned solution-processed electrodes for electronic devices. The conductivity of the PEDOT:PSS film was improved by three orders of magnitude (from 3.1 to 1024 S·cm–1), and high transparency of up to 88.5% (average visible transmittance, AVT) was achieved. Raman and depth-profiling X-ray photoelectron spectroscopy revealed that the oxidation level of PEDOT was enhanced, thereby increasing the carrier concentration. The surface PSS content also decreased, which is beneficial to the carrier mobility, resulting in significantly enhanced electrical conductivity. Further, we fabricated semitransparent perovskite solar cells using the as-made PEDOT:PSS as the transparent top electrodes, and a power conversion efficiency of 7.39% was achieved with 22.63% AVT. Thus, the proposed route for synthesizing conductive and transparent electrodes is promising for vacuum and doping-free electronics.

关键词： PEDOT:PSS     ultrafast laser     transparent electrode     ST-PSCs     patterning    

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Largely reduced cross-plane thermal conductivity of nanoporous In

Dongchao XU, Quan WANG, Xuewang WU, Jie ZHU, Hongbo ZHAO, Bo XIAO, Xiaojia WANG, Xiaoliang WANG, Qing HAO

《能源前沿（英文）》 2018年 第12卷 第1期   页码 127-136 doi: 10.1007/s11708-018-0519-5

摘要： In recent year, nanoporous Si thin films have been widely studied for their potential applications in thermoelectrics, in which high thermoelectric performance can be obtained by combining both the dramatically reduced lattice thermal conductivity and bulk-like electrical properties. Along this line, a high thermoelectric figure of merit (ZT) is also anticipated for other nanoporous thin films, whose bulk counterparts possess superior electrical properties but also high lattice thermal conductivities. Numerous thermoelectric studies have been carried out on Si-based nanoporous thin films, whereas cost-effective nitrides and oxides are not systematically studied for similar thermoelectric benefits. In this work, the cross-plane thermal conductivities of nanoporous In Ga N thin films with varied porous patterns were measured with the time-domain thermoreflectance technique. These alloys are suggested to have better electrical properties than conventional Si Ge alloys; however, a high ZT is hindered by their intrinsically high lattice thermal conductivity, which can be addressed by introducing nanopores to scatter phonons. In contrast to previous studies using dry-etched nanopores with amorphous pore edges, the measured nanoporous thin films of this work are directly grown on a patterned sapphire substrate to minimize the structural damage by dry etching. This removes the uncertainty in the phonon transport analysis due to amorphous pore edges. Based on the measurement results, remarkable phonon size effects can be found for a thin film with periodic 300-nm-diameter pores of different patterns. This indicates that a significant amount of heat inside these alloys is still carried by phonons with ~300 nm or longer mean free paths. Our studies provide important guidance for ZT enhancement in alloys of nitrides and similar oxides.

关键词： nanoporous film     thermoelectrics     phonon     mean free path     diffusive scattering    

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Experimental research on thermal transport properties of crystallized palladium-based alloys

Siyuan CHENG, Xuguo SHI, Weigang MA, Xing ZHANG, Guanglai LIU, Mingxiang PAN, Weihua WANG

《能源前沿（英文）》 2018年 第12卷 第1期   页码 121-126 doi: 10.1007/s11708-018-0531-9

摘要： Palladium-based alloy is a kind of material with a high glass forming ability and can be easily formed into an amorphous state. After an annealing process, it can also be maintained at a crystallized state. To study the thermal and electrical transport properties of crystallized palladium-based alloys, the steady-state T-type method, standard four-probe method, and AC heating-DC detecting T-type method were used to measure the thermal conductivity, electrical conductivity, and Seebeck coefficient of crystallized Pd Ni Cu P and Pd Ni Cu P alloys respectively. The results show that compared to amorphous samples, the thermal conductivity and electrical conductivity of crystallized palladium-based alloys are significantly higher, while the Seebeck coefficient is lower. The ratio of crystallized and amorphous thermal conductivity is higher for Pd Ni Cu P alloy fiber which has a higher glass forming ability, while the ratio of electronic thermal conductivity almost remains constant for both alloy fibers. The results also show that the slope of electrical resistivity to temperature is a function of elemental composition for crystallized quaternary palladium-based alloy fibers. The sensitivity of thermal conductivity and electrical conductivity to the composition is high, while the correlation between Seebeck coefficient and composition is relatively weak.

关键词： palladium-based alloy     T-type method     thermal conductivity     electrical conductivity     Seebeck coefficient    

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Effects of radiation and heat source/sink on unsteady MHD boundary layer flow and heat transfer over

Krishnendu Bhattacharyya

《化学科学与工程前沿（英文）》 2011年 第5卷 第3期   页码 376-384 doi: 10.1007/s11705-011-1121-0

摘要： In this paper, an investigation is made to study the effects of radiation and heat source/sink on the unsteady boundary layer flow and heat transfer past a shrinking sheet with suction/injection. The flow is permeated by an externally applied magnetic field normal to the plane of flow. The self-similar equations corresponding to the velocity and temperature fields are obtained, and then solved numerically by finite difference method using quasilinearization technique. The study reveals that the momentum boundary layer thickness increases with increasing unsteadiness and decreases with magnetic field. The thermal boundary layer thickness decreases with Prandtl number, radiation parameter and heat sink parameter, but it increases with heat source parameter. Moreover, increasing unsteadiness, magnetic field strength, radiation and heat sink strength boost the heat transfer.

关键词： MHD boundary layer     unsteady flow     heat transfer     thermal radiation     heat source/sink     shrinking sheet     suction/injection    

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标题 作者 时间 类型 操作

Equivalent thermal conductivity of heat pipes

LU Zesheng, MA Binghui

期刊论文

Characterization of 3D microstructure, thermal conductivity, and heat flow of cement-based foam using

期刊论文

Analysis of flow and heat transfer characteristics of porous heat-storage wall in greenhouse

OUYANG Li, LIU Wei

期刊论文

A building unit decomposition model for energy leakage by infrared thermography image analysis

Yan SU, Fangjun HONG, Lianjie SHU

期刊论文

Preparation, with graphene, of novel biomimetic self-healing microcapsules with high thermal stability and conductivity

期刊论文

Activated carbon induced oxygen vacancies-engineered nickel ferrite with enhanced conductivity for supercapacitor

期刊论文

Permeability and thermal conductivity of host compressed natural graphite for consolidated activated

Bo TIAN, Liwei WANG, Zhequan JIN, Ruzhu WANG

期刊论文

Tailoring electrical conductivity of two dimensional nanomaterials using plasma for edge electronics:

Aswathy Vasudevan, Vasyl Shvalya, Aleksander Zidanšek, Uroš Cvelbar

期刊论文

Modeling of ion conductivity in Nafion membranes

YANG Zhen, PENG Xiaofeng, WANG Buxuan, DUAN Yuanyuan, LEE Duujong

期刊论文

phosphorus-nitrogen based flame retardant and multi-walled carbon nanotubes for enhanced electrical conductivity

Yong Luo, Yuhui Xie, Renjie Chen, Ruizhi Zheng, Hua Wu, Xinxin Sheng, Delong Xie, Yi Mei

期刊论文

Absorption heat pump for waste heat reuse: current states and future development

Zhenyuan XU, Ruzhu WANG

期刊论文

Ultrafast-laser-treated poly(3,4-ethylenedioxythiophene): poly(styrenesulfonate) electrodes with enhanced conductivity

期刊论文

Largely reduced cross-plane thermal conductivity of nanoporous In

Dongchao XU, Quan WANG, Xuewang WU, Jie ZHU, Hongbo ZHAO, Bo XIAO, Xiaojia WANG, Xiaoliang WANG, Qing HAO

期刊论文

Experimental research on thermal transport properties of crystallized palladium-based alloys

Siyuan CHENG, Xuguo SHI, Weigang MA, Xing ZHANG, Guanglai LIU, Mingxiang PAN, Weihua WANG

期刊论文

Effects of radiation and heat source/sink on unsteady MHD boundary layer flow and heat transfer over

Krishnendu Bhattacharyya

期刊论文