Structure and optical properties of electrochromic copper oxide films prepared by reactive and conventional evaporation techniques

Copper oxide films (Cu_xO) are deposited by thermal evaporation techniques using copper oxide (CuO) or copper (Cu) as starting material. By varying the deposition parameters, two main types of Cu_xO film exhibiting different optical properties form. These are reddish gray and colorless films. The samples are characterised optically and morphologically. X-ray diffraction spectra reveal that evaporated Cu_xO films are amorphous. Fourier-transform infrared spectra of the samples were studied to evaluate chemical identification. The refractive index, the extinction coefficient and the thickness of the films are evluated from transmittance characteristics in the ultraviolet, visible and near-infrared regions. The refractive indices of the samples are between 2.9 and 3.1. The values determined for the optical constants are in aggreement with the results found in the literature. We report for the first time that Cu_xO films show reversible optical switching from the colored to bleached state. Optical transmittance measurements of the copper oxide film relative to indium tin oxide coated glass varied during coloring from spectral transmittance T_s = 85−40%     

Volumetric hydrogen sorption measurements – Uncertainty error analysis and the importance of thermal equilibration time

The design of a volumetric measurement apparatus is studied by means of an uncertainty analysis to provide guidelines for optimum hydrogen sorption measurements. The reservoir volume should be as small as possible (i.e., 10 cc) to minimize the uncertainty. In addition, the sample mass loading has a profound effect on the uncertainty and the optimum loading is a function of the sample's intrinsic storage capacity. In general, the higher the sample mass loading the lower the uncertainty, regardless of any other parameter. In cases where the material to be tested is not available in gram quantities, the use of high accuracy pressure and temperature transducers significantly mitigates the uncertainty in the sample's hydrogen uptake. Above all, the thermal equilibration time is an important parameter for high accuracy measurements and needs to be taken into consideration at the start of the measurements. Based on a computational analysis, a 5 min wait time is required for achieving thermal equilibrium when the instrument enclosure temperature is different than the ambient temperature.     

Spectral transmittance of water and sodium chloride water solution as working substance for a solar pond

The transmission properties of water and sodium chloride water solutions with various salt concentrations were investigated. This paper concerns the measurement of the spectral transmittance and the calculation of the total transmittance for water and NaCl water solutions. The spectral transmittance of the NaCl water solutions over the infrared and nearby regions increased with increasing salt concentration for constant specimen thickness and air mass. The spectral transmittance was found to be useful for precisely calculating the thermal performance of a solar pond, and by using an effective absorption coefficient, a five-partition method dividing the wavelengths into five bands by which the total transmittance up to a water depth of 3 m could be calculated, was found to be important as a practical method of solar pond technology. © 1997 Scripta Technica, Inc. Heat Trans Jpn Res, 26(1): 1–15, 1997     

A method for improving global pyranometer measurements by modeling responsivity functions

Accurate global solar radiation measurements are crucial to climate change research and the development of solar energy technologies. Pyranometers produce an electrical signal proportional to global irradiance. The signal-to-irradiance ratio is the responsivity (RS) of the instrument (RS = signal/irradiance = microvolts/(W/m²)). Most engineering measurements are made using a constant RS. It is known that RS varies with day of year, zenith angle, and net infrared radiation. This study proposes a method to find an RS function to model a pyranometer’s changing RS. Using a reference irradiance calculated from direct and diffuse instruments, we found instantaneous RS for two global pyranometers over 31 sunny days in a two-year period. We performed successive independent regressions of the error between the constant and instantaneous RS with respect to zenith angle, day of year, and net infrared to obtain an RS function. An alternative method replaced the infrared regression with an independently developed technique to account for thermal offset. Results show improved uncertainties with the function method than with the single-calibration value. Lower uncertainties also occur using a black-and-white (8-48), rather than all-black (PSP), shaded pyranometer as the diffuse reference instrument. We conclude that the function method is extremely effective in reducing uncertainty in the irradiance measurements for global PSP pyranometers if they are calibrated at the deployment site. Furthermore, it was found that the function method accounts for the pyranometer’s thermal offset, rendering further corrections unnecessary. The improvements in irradiance data achieved in this study will serve to increase the accuracy of solar energy assessments and atmospheric research.     

Thermal conductivities study on silica aerogel and its composite insulation materials

This paper presents a theoretical and experimental study on thermal conductivities of silica aerogel, xonotlite-type calcium silicate and xonotlite–aerogel composite insulation material. The transmittance spectra of silica aerogel and xonotlite-type calcium silicate samples are obtained through FTIR measurements. The corresponding extinction coefficient spectra of the three materials are then obtained by applying Beer’s law. The thermal conductivities of aerogel, xonotlite-type calcium silicate, and xonotlite–aerogel composite insulation material are measured from 300 to 970 K and from 0.045 Pa to atmospheric pressure with the transient hot-strip (THS) method. The thermal conductivity models developed for coupled heat transfer of gas and solid based on the unit cell method are compared with the experimental measurement results. It is shown that the effective thermal conductivity models matches well with the experimental data. The specific spectral extinction coefficients of xonotlite-type calcium are larger than 10 m² kg^?1, and the specific spectral extinction coefficients of aerogel are larger than 7 m² kg^?1 over the whole measured spectra. The density of xonotlite-type calcium silicate is the key factor affecting the effective thermal conductivity of xonotlite–aerogel composite insulation material, and the density of aerogel has little influence. The effective thermal conductivity can be lowered greatly by composite of the two materials at an elevated temperature.     

Total infrared radiation property measurements of diathermanous films with a reflectometer

A procedure is described for the rapid evaluation of total infrared radiation properties of thin diathermanous films with an infrared reflectometer. Two different back reflecting surfaces are used for measurements and the resulting calculated properties are based on the assumption that the sample is gray. The transmittance value obtained by the procedure will be subject to some error, with the magnitude of the error dependent on the spectral transmittance characteristics of the sample. A statistical model spectral transmittance formula for correcting the gray result is proposed.     

Measuring method of three thermophysical parameters of solids by a thermal probe with instantaneous point contact: Measuring principle

A new method for instantaneous measurement of three thermophysical parameters of solids in situ is proposed. The measurement principle is based on a transient heat conduction model of a thermal probe point contacting a testing body. The measurement of temperature response has been made using the probe of a sheathed K‐type thermocouple in this experiment. Ratios of both thermal conductivity and thermal effusivity between the probe and the testing body are determined from curve‐fitting with the theoretical response to the measured one. As a result, it is shown that the measurement is reproducible and the accuracies of measured thermophysical parameters are good enough to apply this method to many kinds of solids. © 2003 Wiley Periodicals, Inc. Heat Trans Asian Res, 32(3): 191–201, 2003; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/htj.10084     

Determination of the temperature profile of axisymmetric combustion-gas flow from infrared spectral measurements

A numerical iteration technique for determining both the temperature and CO₂ concentration profiles of axisymmetric combustion-gas flow from low resolution infrared spectral measurements has been developed. The technique includes inversion of the temperature profile from emission measurements when the CO₂ concentration distribution is known, inversion of the CO₂ concentration profile from transmittance measurements when the temperature distribution is known, and inversion of both temperature and CO₂ concentration profiles simultaneously from emission and transmittance data of the combustion-gas flow. The iteration technique is accurate, efficient, and effective even under structured temperature distributions. The effects of temperature, optical thickness, wave number, and band model parameters on the determined profiles are analyzed. It is found that a deviation of 40% in CO₂ concentration results in a difference of only about 5% in the determined temperature profile. This implies a possibility of passive scanning. The determined temperature profile of a laboratory combustion-gas flow agrees well with probe measurements.     

Thermal properties of building materials evaluated by a dynamic simulation of a test cell

A method for the measurement of thermal properties of building components under controllable conditions is presented. It is based on the use of a test cell designed to enable calculation of thermal properties solely from temperature readings, without the need for power measurements. The test cell’s low thermal inertia allows short testing times (about 3 h). Using an appropriate thermal network to simulate the dynamic behavior of the test cell, predicted results were found to have a 0.6°C maximum temperature deviation with measured test cell responses. The thermal transmittance (U-value) of an insulating block, a single glass sheet and a double glazing have been measured with an accuracy of about 5%. A simulation of a scaled-up test cell with dimensions 6.0 m×6.0 m×4.5 m has revealed that the test cell’s response to temperature changes depends strongly on the amount of wall insulation. The scaled-up test cell exhibits a relatively fast response to temperature changes (9 to 18 h) due to its low thermal mass.     

Electrochromic properties of one-dimensional tungsten oxide nanobundles

In this study, one-dimensional (1D) tungsten oxide nanobundles (TNB) were synthesized via a simple solvothermal method. The phase of 1D tungsten oxide was W₁₈O₄₉, and the diameter and length of the building units (nanowires) were about 7 and 800 nm, respectively. TNB films were fabricated by the Langmuir–Blodgett (LB) method. The locally arranged domains of the long nanobundles form the LB films, but it is difficult for them to align perfectly owing to the inter-nanobundle interaction and dispersion problems. The electrochromic (EC) property of the TNB LB films was characterized by electrochemical potential cycling tests and in situ transmittance measurement. The deposition condition of the LB films influenced their EC property. The heat treatment and surface pressure of the TNB LB films plays an important role in the response time and transmittance of the TNBs.     

Sensitivity analysis for room thermal response

The sensitivity theory is a suitable approach for assessing the room thermal response. It results in the ‘sensitivity coefficients’ (SCs) which, as derived here, evaluate the variation of the thermal load due to a fluctuation in a given design parameter around its nominal value. In this paper the general method is presented and a number of SCs are derived to evaluate the sensitivity of the building energy demand to the window surface area, to the overall transmittance and mass thermal capacity of a given wall, and to other structural data.     

The measurement of heat transfer from hot surfaces to non-wetting droplets

An experimental method to measure the heat transfer between a hot surface and a non-wetting droplet is reported in this paper. By means of transient, high resolution, infrared microscopy, surface temperature measurements with spatial and temporal resolutions of ～100 μm and ～4 ms, respectively, are obtained, by observing a thin metallic layer from beneath through an infrared-transparent substrate. Data from the infrared camera is generated at each time-step in the form of a set of temperatures, at closely-spaced locations on the surface of the infrared transparent plate. Subsequent solution of the transient thermal conduction equation within the substrate permits all thermal quantities (heat flux, energy, etc.) to be determined. As a typical result, the heat transferred by a 1.5 mm droplet is measured to be 0.19 J, with the heat flux peaking at 3.5 MW/m² during the 10 ms it spends in the vicinity of the surface, and with a peak transient surface temperature reduction of 47 °C. Error analysis indicates that the uncertainty in this measurement of heat transfer is about 15%.     

Ground water level influence on thermal response test in Adana,Turkey

For optimum design of borehole thermal energy storage (BTES) and ground sources heat pump (GSHP) applications, determination of underground thermal properties is required. The design and economic feasibility (number and depth of boreholes) of these systems need thermal conductivity of geological structure, λ (W m^?1 K^?1), and thermal resistance of ground heat exchanger, R (K W^?1 m). Thermal properties measured in laboratory experiments do not coincide with data of in situ conditions. Therefore, in situ thermal response test equipment has been developed and used in Canada, England, Germany, Norway, U.K., U.S.A. and Sweden to ensure precise designing of BTES systems. This paper describes the results and evaluations of the Adana continual thermal response test measurements. Copyright © 2007 John Wiley & Sons, Ltd.     

Numerical investigation on optical and heat transfer characteristics of a rapid thermal annealing system for LCD manufacturing

The objectives of present study are to propose a method to evaluate the quality of polycrystalline silicon film by using the thin film optics analysis, and to investigate heat transfer characteristics in a rapid thermal annealing system for liquid crystal display (LCD) manufacturing. The transmittance of polycrystalline silicon film is calculated by the characteristic transmission matrix method, and predicted results are compared with the experimental data for two different samples. The transient one-dimensional conduction and radiation heat transfer equations are additionally solved to predict the surface temperature of thin films. The two-flux method is employed to evaluate radiation heat transfer, and the ray-tracing method is utilized to take into account of the wave interference effect. As the film thickness increases, the peak transmittance value increases and the wavelength where the peak appears becomes longer due to wave interference. These characteristics can be used for in situ and practical estimation of the extent of crystallization of the silicon film during the process. From the thermal analysis, it is shown that the selective heating in the multilayer film structure acts as an important mechanism during the annealing of silicon film deposited on the glass.     

Transparent heat mirrors based on tungsten oxide-silver multilayer structures

Transparent heat mirrors based on tungsten oxide/silver three-layer structures were fabricated using thermal evaporation. The optical and morphological properties of the single layers were first investigated to serve as a basis for the fabrication of the heat mirrors. Only silver films with a thickness higher than 18 nm were found to be continuous. Subsequently, WO₃/Ag/WO₃ multilayers were deposited, where the WO₃ layers thickness was fixed at 35 nm, and the thickness of the silver layer was varied from 18 to 39 nm. The optical properties of the multilayers were measured over the visible and near infrared ranges. These multilayers exhibited the desired heat mirror behavior, namely the transmittance was largely confined to the visible range and the reflectance was diminished in that range. The maximum visible transmittance was 88.3% at 554 nm. Increasing the thickness of the silver films resulted in a decrease of the visible transmittance, with a corresponding increase in the infrared reflectance. Optimization of these two opposing trends was evaluated using a figure of merit, from which the best performance was obtained for multilayers with a silver layer of thickness of 24 nm.     

Calibration of a spinner anemometer for yaw misalignment measurements

The spinner anemometer is an instrument for yaw misalignment measurements without the drawbacks of instruments mounted on the nacelle top. The spinner anemometer uses a non‐linear conversion algorithm that converts the measured wind speeds by three sonic sensors on the spinner to horizontal wind speed, yaw misalignment and flow inclination angle. The conversion algorithm utilizes two constants that are specific to the spinner and blade root design and to the mounting positions of the sonic sensors on the spinner. One constant, k₂, mainly affects the measurement of flow angles, while the other constant, k₁, mainly affects the measurement of wind speed. The ratio between the two constants, k_α=k₂/k₁, however, only affects the measurement of flow angles. The calibration of k_α is thus a basic calibration of the spinner anemometer. Theoretical background for the non‐linear calibration is derived from the generic spinner anemometer conversion algorithm. Five different methods were evaluated for calibration of a spinner anemometer on a 500 kW wind turbine. The first three methods used rotor yaw direction as reference angular, while the wind turbine, was yawed in and out of the wind. The fourth method used a hub height met‐mast wind vane as reference. The fifth method used computational fluid dynamics simulations. Method 1 utilizing yawing of the wind turbine in and out of the wind in stopped condition was the preferred method for calibration of k_α. The uncertainty of the yaw misalignment calibration was found to be 10%, giving an uncertainty of 1° at a yaw misalignment of 10°. © 2014 The Authors. Wind Energy published by John Wiley & Sons, Ltd.     

Theoretical and experimental investigation of a heat pipe heat exchanger for energy recovery of exhaust air

Heat pipes and two-phase thermosyphon systems are passive heat transfer systems that employ a two-phase cycle of a working fluid within a completely sealed system. Consequently, heat exchangers based on heat pipes have low thermal resistance and high effective thermal conductivity, which can reach up to the order of (10⁵ W/(m K)). In energy recovery systems where the two streams should be unmixed, such as air-conditioning systems of biological laboratories and operating rooms in hospitals, heat pipe heat exchangers (HPHEs) are recommended. In this study, an experimental and theoretical study was carried out on the thermal performance of an air-to-air HPHE filled with two refrigerants as working fluids, R22 and R407c. The heat pipe heat exchanger used was composed of two rows of copper heat pipes in a staggered manner, with 11 pipes per row. Tests were conducted at different airflow rates of 0.14, 0.18, and 0.22 m³/h, evaporator inlet-air temperatures of 40, 44, and 50°C, filling ratios of 45%, 70%, and 100%, and ratios of heat capacity rate of the evaporator to condenser sections (C_e/C_c) of 1 and 1.5. For HPHE's steady-state operation, a mathematical model for heat-transfer performance was set and solved using MATLAB. Results illustrated that the heat transfer rate was in direct proportion with the evaporator inlet-air temperature and flow rate. The highest HPHE's effectiveness was obtained at a 100% filling ratio and (C_e/C_c) of 1.5. The predicted and experimental values of condenser outlet-air temperature were in good agreement, with a maximum difference of 3%. HPHE's effectiveness was found to increase with the increase in evaporator inlet-air temperature and number of transfer units (NTU) and with the decrease in airflow rate, up to 33% and 20% for refrigerants R22 and R407c, respectively. Refrigerant R22 was the superior of the two refrigerants investigated.     

In-plane Thermal Conductivity Measurement with Nanosecond Grating Imaging Technique

We develop a nanosecond grating imaging (NGI) technique to measure in-plane thermal transport properties in bulk and thin-film samples. Based on nanosecond time-domain thermoreflectance (ns-TDTR), NGI incorporates a photomask with periodic metal strips patterned on a transparent dielectric substrate to generate grating images of pump and probe lasers on the sample surface, which induces heat conduction along both cross- and in-plane directions. Analytical and numerical models have been developed to extract thermal conductivities in both bulk and thin-film samples from NGI measurements. This newly developed technique is used to determine thickness-dependent in-plane thermal conductivities (κ_x) in Cu nano-films, which agree well with the electron thermal conductivity values converted from four-point electrical conductivity measurements using the Wiedemamn–Franz law, as well as previously reported experimental values. The κ_x measured with NGI in an 8 nm x 8 nm GaAs/AlAs superlattice (SL) is about 10.2 W/m?K, larger than the cross-plane thermal conductivity (8.8 W/m?K), indicating the anisotropic thermal transport in the SL structure. The uncertainty of the measured κ_x is about 25% in the Cu film and less than 5% in SL. Sensitivity analysis suggests that, with the careful selection of proper substrate and interface resistance, the uncertainty of κ_x in Cu nano-films can be as low as 5%, showing the potential of the NGI technique to determine κ_x in thin films with improved accuracy. By simply installing a photomask into ns-TDTR, NGI provides a convenient, fast, and cost-effective method to measure the in-plane thermal conductivities in a wide range of structures and materials.     

Development and application of a thermal model for the relined ladle in China Steel Corporation

Refractory-lined ladles are utilized in transporting the molten steel from a converter to a continuous casting machine in the steelmaking process. A proper heating schedule for the ladle dryer will be in practice desirable for energy saving and the production of higher-quality steels. This work develops a thermal model to dynamically simulate the thermal response in the walls of relined ladles after bricking, and the temperature drop of molten steel. After being validated by the in situ measurement from the practical heating process, this model is illustratively applied to determine the proper heating schedule of the ladle dryer and the blown-end temperature for converter for various operation condition in the steelmaking plant of China Steel Corporation.     

Transmittance from visible to mid infra-red in AZO films grown by atomic layer deposition system

We report transmittance and conductivity measurements of aluminum-doped zinc oxide films grown by atomic layer deposition. The results show that the films have 80–90% transmittance in the visible region and good transmittance in the infrared. To our knowledge, this is the first time that the transmittance of aluminum-doped zinc oxide is reported to extend beyond 2500–5000 nm. Following annealing, an optimal sheet resistance of 25 Ω/□ was obtained for a 575 nm thick film with a carrier density of 2.4 × 10²⁰ cm^?3 without compromising the transmittance in the visible regime.