An application of thermal microscopes to the measurement of thermal effusivity of films

The application of thermal microscopes to the measurement of local thermal properties has drawn considerable scientific interest. We report on the application of a thermal microscope to the measurement of thermal effusivity for films comprising alumina deposited on a substrate, which were fabricated by an electrophoretic deposition method. The measured data was analyzed to consider the undulations on the sample surface The thermal effusivity of these samples was approximately 1×10³ Js^?0.5m^?2K^?1; this value is smaller than that for dense alumina because the alumina grain makes contact with a point. © 2008 Wiley Periodicals, Inc. Heat Trans Asian Res; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/htj.20227     

Polycrystalline silicon films prepared by improved pulsed rapid thermal annealing

An improved pulsed rapid thermal annealing (PRTA) has been used for the solid-phase crystallization (SPC) of a-Si films prepared by PECVD. The SPC can be completed with time-temperature budgets such as 10 cycles of 60-s 550°C thermal bias/1-s 850°C thermal pulse. The microstructure and surface morphology of the crystallized films are investigated by X-ray diffraction (XRD). The results indicate that this PRTA is a suitable post-crystallization technique for fabricating large-area poly-Si films on low-cost substrate.     

Determination of thermal parameters of poor conductors by transient techniques

The authors compare the transient hot wire method and the parallel wire method of determining thermal conductivity, using the second to find the thermal diffusivity of two materials. The wires are sandwiched between two samples of the material to be investigated. The influence of pressure is also studied in order to identify the measurement conditions that can be easily achieved. A method is chosen to evaluate thermal parameters and to determine the field of data to be used in relation to sample dimensions.     

Understanding the photothermal contribution to electrocatalysis: A case study of carbon supported NiFe layered double hydroxide

External field assisted water splitting, as a sustainable and highly-efficient route to achieving hydrogen production, has recently attracted a considerable attention in the renewable energy research field. In particular, electrocatalysts with superior light absorption ability is likely to show an excellent electrocatalytic performance under light irradiation. Herein, a composite consisting of NiFe layered double hydroxide (LDH) and carbon is prepared as an electrocatalyst for oxygen evolution reaction (OER). Compared to the pristine NiFe LDH,carbon supported NiFe layered double hydroxide (NiFe LDH@C) composite exhibits an enhanced light harvesting under light irradiation, not only increasing the local temperature of electrocatalyst but also lowering the charge transfer resistance during the OER reaction process. Consequently, the photothermal effect enables NiFe LDH@C composite to facilitate the charge transport and accelerate the reaction kinetics, thereby showing an improved OER performance in comparison to neat NiFe LDH. This work offers a new vision toward the rational design of advanced electrocatalyst for solar-assisted water electrolysis application.     

Measurement of the local convection coefficient by pulsed photothermal radiometry

Pulsed photothermal radiometry is used for the determination of the convection coefficient. The theoretical analysis of the transient wall temperature after a brief excitation is based on the use of the zeroorder temporal moment. Different solutions to determine the convection coefficient from experimental thermograms are proposed and tested for insulating walls as well as conducting ones. Experimental results are compared to those given by a dissipation fluxmeter in order to validate the pulsed method.     

Silver nanoparticle films by flowing gas atmospheric pulsed laser deposition and application to surface-enhanced Raman spectroscopy

For the fast uptake into industrial applications, the further development of robust methods of nanomaterials, which are inexpensive and simultaneously technologically feasible, is one of the major key factors. A newly introduced atmospheric pulsed laser deposition method, based on a flowing gas approach, was used for plasmonic metal nanoparticle (NP) film of silver. Contrary to vacuum, in this method, the ambient air restricts expansion of the ablation plume within 1 to 3 mm above the target surface. These sets constrain on the formation of NP film close to the ablation spot. For deposition on a widely spaced surface, ablation material was entrained in a flow of argon, supplied at ~32 ms⁻¹, and effectively delivered to the substrate at ~20 ms⁻¹. The films produced were crystalline and particulate in nature, showing spectral plasmonic feature of surface plasmon resonance in the visible region. The film was directly tested in surface-enhanced Raman spectroscopy for chemical detection of crystal violet; the film with large particulates and aggregated crystallites was well-performed, showing enhanced Raman signals and detection sensitivity. Certainly, flowing gas atmospheric pulsed laser deposition seems a fast alternative to vacuum-pulsed laser deposition but needs further investigations to bring it in the industry for applications in sensor, catalysis, solar cell, and coating technology.     

Application of soft computing techniques to optimize thermal parameters in a double heat exchanger with cylindrical turbulators

In the present study, the dimensions of the cylindrical turbulators have been optimized to achieve the highest thermal performance. A double pipe heat exchanger with cylindrical turbulators placed in the annulus side is modeled and a numerical simulation is carried out for different operating conditions. The simulation is conducted for different diameters of the turbulators for various Re for the annulus fluid. The Nusselt number (Nu), friction factor (f), and thermohydraulic performance index (THPI) are the responses simulated for the above different cases of input conditions. Response surface methodology has been used to study the influence of operating parameters on the responses. It is observed that Nu, f, and THPI increased as the Re and turbulator diameter increased. Response optimizer is used to optimize the turbulator diameter to obtain the highest thermal performance in terms of highest Nu and THPI and lowest f. The results indicated that maximum performance was obtained for a diameter of 4.45 mm and for a Re of 5530. The Nu and THPI corresponding to the above combinations are 68.4 and 2, respectively.     

热湿侵蚀对镀锗薄膜热光属性的影响

本文实验研究了不同热湿保存环境条件对聚酰亚胺镀锗薄膜热光属性的影响。试验温度分别为20℃和40℃,试验相对湿度条件为40%、60%、95%,温湿度交叉研究。试验在恒温恒湿仪中进行,并分别采用原子力显微镜和紫外可见近红外分光光度计对试验前后的薄膜进行电镜观察扫描和热光属性测量。试验结果表明,热湿处理对聚酰亚胺镀锗薄膜光学属性有重要的侵蚀影响。热湿处理后的薄膜不仅微结构表面发生改变,在部分波段其热光属性也有重大变化。     

The HEATSEP method for the synthesis of thermal systems: An application to the S-Graz cycle

In the last decades component synthesis has become a critical issue in the research field about new highly integrated energy conversion systems. Several heuristic methodologies following experience-based guidelines have been proposed to simplify the problem of synthesis optimization. This paper describes an application of the HEATSEP method, which consists in the isolation of all the heat transfer processes of an energy system in an undefined “black-box”. Then, synthesis optimization can be split in two subproblems, the first about the synthesis/design optimization of the basic plant configuration (which is made up of all the components but heat transfer devices) and the other about the synthesis of the heat exchanger network inside the black-box. The chosen test case is the design optimization of the basic plant configuration of an S-Graz cycle based power plant, as it is suitable to show the potentialities of the method.     

An updated probabilistic fracture mechanics methodology for application to pressurized thermal shock

The US Nuclear Regulatory Commission (NRC) is, in concert with the US nuclear industry, currently revisiting its rule and analysis requirements for pressurized thermal shock (PTS) scenarios. This paper provides an overview of an updated probabilistic risk analysis (PRA) methodology that is continuing to evolve as part of that effort. The evolution process includes a careful assessment of recent advancements that have been made in the various parts of the computational methodologies. The process also involves interactions between experts in relevant disciplines (thermal hydraulics, PRA, materials, fracture mechanics, and non-destructive and destructive examination). Representatives include staff members from the USNRC staff, research laboratories, and the nuclear industry. The updated methodology is being integrated into the FAVOR (Fracture Analysis of Vessels: Oak Ridge) computer code for application to re-examine the adequacy of the current regulations and to determine if the updates provide sufficient technical bases for revisions. This paper also discusses recent modifications to the probabilistic fracture mechanics (PFM) methodology that is central to FAVOR.     

Improvement of the pulsed photothermal technique for the measurement of the convective heat transfer coefficient

<正>The present study concerns the measurement of the convective heat transfer coefficient on the solid-fluid interface by the pulsed photothermal method.This non-intrusive technique is apphed for the measurement of the local heat transfer coefficients in cooling of a rectangular slab that simulates an electronic component.The heat transfer coefficient is deduced from the evolution of the transient temperature induced by a sudden deposit of a luminous energy on the front face of the slab.In order to draw up the heat transfer cartography by a non-destructive tool, the infrared thermography has been used.Two inverse techniques for the identification of the heat transfer coefficient are presented here.The first one is based on the assumption that heat transfer coefficient remains constant during the pulsed experiment,and the second one considered it variable in space and time.The temporal and spatial evolutions are expressed as a constant heat transfer coefficient(h_0)multiplied by a function of time and space f(x,t).The function f is deduced from the resolution of the conjugated convection-conduction problem,by a control volume technique for the case of thermally thick sample.The results are given for different air velocities and deflection angles of the flow.     

热力除氧技术研究及其发展

水中溶解氧的存在是导致锅炉及汽轮机通汽部分设备腐蚀发生的重要原因,也影响给水系统以及整个热力系统的运行安全。随着高参数大容量发电机组的发展,对给水品质的要求不断提高。除氧技术也伴随着热力系统对除氧要求的提高而不断发展。热力除氧过程中加热蒸汽与除氧水之间传热传质过程的强化是确保和提高热力除氧器除氧性能的关键,也是热力除氧器结构改进与优化的基本原则。     

Effective thermal conductivity of compressed woods

Compression is one solution to improve the strength of softwoods. The effective thermal conductivities of compressed Japanese cedars (cryptomeria japonica), which were compressed in the radial direction of the wood, were measured. Both the effective thermal conductivities in the tangential and fiber directions increase proportionally to the density increment due to the compression. However, the thermal conductivity in the radial direction (compression direction) increases slightly with the density increment. Numerical computations were conducted to explain the characteristics of thermal conductivity in the radial direction by using a microscopic heat conduction model for the compressed wood. The numerical results were compared with the measured values. And the physical mechanism of the heat conduction in the compressed woods is discussed.     

Numerical and experimental assessment of thermal performance of vertical energy piles: An application

A district space heating and cooling system using geothermal energy from bearing piles was designed in Shanghai and will be installed in two years before 2010. This paper describes the pile-foundation heat exchangers applied in an energy pile system for an actual architectural complex in Shanghai, 30% of whose cooling/heating load was designed to be provided by a ground-source heat pump (GSHP) system using the energy piles. In situ performance tests of heat transfer are carried out to figure out the most efficient type of energy pile and to specify the design of energy pile system. Numerical investigation is also performed to confirm the test results and to demonstrate the medium temperature variations along the pipes. The averaged heat resistance and heat injection rate of different types of energy piles are calculated from the test and numerical results. The effect of pile type, medium flow rate and inlet temperature on thermal performance is separately discussed. From the viewpoint of energy efficiency and adjustability, the W-shaped underground heat exchanger with moderate medium flow rate is finally adopted for the energy pile system.     

Production of acoustic waves from pulsed thermal radiation

Generation of acoustic waves from a pulsed thermal radiation beam was experimentally investigated in this paper. Unlike other TACs (thermal acoustic converters), acoustic wave frequencies and phases of this type of TACs can be easily adjusted and controlled—a feature essential to the synchronization of TACs in an array. The TACs we developed were made up of a cylindrical aluminum housing, a glass cover, and metallic wool for effective thermal‐to‐acoustic energy conversion. Radiation emitted from an infrared heater was chopped at a constant frequency prior to entering the converter through the glass cover. The metallic wool was periodically heated by the pulsed radiation beam and cooled because of heat losses to the surroundings. Experiments were conducted for different converter designs and metallic wools, as well as different chopper speeds and radiation intensities. The amplitudes of generated sound waves were found to be dependent on the radiation intensity, the grade and properties of the metallic wool, and the cooling rate of the wool. Higher radiation intensities and thinner wools of lower thermal conductivity produced sounds of higher amplitude. More effective cooling of the metallic wool also helped. Acoustic energy output can also be enhanced by reducing the amount of air in the converter. Copyright © 2015 John Wiley & Sons, Ltd.     

SOLAR CONTROL: An integrated approach to solar control techniques

In the framework of the CE JOULE III Programme, further to the SCL activities in PASCOOL Project, the project SOLAR CONTROL has been supported. The project participants, co-ordinated by Conphoebus, include also Universities of Sevilla and Ljubljana, NOA, TNO, BRE, VTT, Fraunhofer and GENEC, as well as leading manufacturers such as SOMFY and Pilkington.The project is aimed at undertaking investigations on the performance of shading devices in order to overcome the existing lack of support towards industry and final user, thus improving the dissemination of knowledge and the effectiveness of the application of these techniques.The final outputs of this project are:

• ll Proposal of Prenormative Testing Standards for shading devices;

• ll Upgrade of the existing simulation models by integration of new validated algorithms;

• ll Design and implementation of a smart solar control assembly;

• ll Design Guidelines & Shading Component Handbook.

In the light of the above objectives, the main ongoing activities concern:

• - characterisation of the most interesting shading devices (external, interpane and internal, isotropic and non isotropic) for the assessment of the overall performance (thermal, daylighting, ventilation)

• - development, validation and integration in existing simulation tools of new algorithms of the shading devices behaviour in respect to solar radiation, visible radiation and ventilation

• - development of new smart solar control systems for integration into the building envelope, with special attention on their impact on energy consumption and improvement of the indoor comfort as well

• - preparation of Design Guidelines and a Shading Component Handbook for European architects and building designer.

     

An analytical model for silicon MIS/IL solar cells to optimize cell parameters through thermal annealing

A model has been developed which simulates the effect of cell parameters in order to optimize them by controlling the fabrication conditions, namely, annealing time and annealing temperature. Calculation of the efficiency as a function of surface states density D_it, positive fixed oxide charge density Q_f and mobile charge density Q_m, that depend on anealing conditions are carried out. A compromise between D_it and Q_m for different anealing temperatures for high performance cells has been investigated.     

Effective thermal conductivity of granular porous materials

In this study, various conduction models for two-phase materials are considered and the range of applicability of these models is discussed. Experimental work is carried out on construction sand of various grain size and different porosity in air at atmospheric pressure, and the results are compared with theoretical models. A modified hot-wire method is used in the measurement of effective thermal conductivities.     

Effective thermal conductivity of common geometric shapes

This work explores the porous block paradigm based on replacing an actual heat sink by the volume of fluid that once enveloped the fins. Thermal equivalence is achieved by increasing the thermal conductivity of the lumped fluid above the base plate until the thermal resistance of the actual heat sink is matched. The popularity of the porous block model can be attributed to its ability to approximate the three-dimensional isotherms corresponding to a detailed heat sink. While previous investigations have focused on a numerically calculated, effective thermal property of the compact model, we employ a methodology leading to a closed-form alternative. The explicit solutions that we provide are not limited to the rectangular porous block models used in former studies. Rather, we extend the analysis to cover most fundamental body shapes and flow configurations under both free and forced convection modes. The exact or approximate formulations that we provide apply to most common Nusselt number correlations and obviate the need for guesswork or user-intervention to reach convergence.