On measurement techniques for the spectral absorptance of glazing materials in the solar range

Advanced glazing materials may be thick, scattering, and inhomogeneous, and this poses problems for conventional absorptance measurement techniques. This paper describes a technique for accurately measuring the spectral absorptance of such materials. The measurement technique, in which the sample is mounted at the centre of an integrating sphere, was analysed and the errors that occur when applying the technique to large samples were analysed. The technique was used to measure absorptance of several materials, and the results are presented. For heterogeneous materials it is necessary to irradiate a relatively large area to get a representative sample. It was found that under certain conditions (depending on the sample absorptance), sample sizes as large as 30% of the sphere diameter can be used without incurring a prohibitively large error. This paper examines the effect of the finite absorptance of the rod supporting the sample, showing that it can be important unless certain precautions are taken.     

Spectral emissivity of ytterbium oxide-based materials for application as selective emitters in thermophotovoltaic devices

The spectral emissivity of Yb³⁺ in a series of compounds has been investigated to study the effects of crystal structure type, chemical environment, ytterbium concentration, impurity concentration and temperature on the spectral radiant intensity of the selective emitter peak and emitted power from the material. A figure of merit has been defined which enables the compounds to be ranked for application in a practical thermophotovoltaic energy conversion device. It is shown that significant selective emission can be achieved from compounds in which the Yb³⁺ concentration is as low as 10 mol%. Apart from pure Yb₂O₃, the compounds Yb₃Al₅O₁₂, YbNbO₄ and Y_0.9Yb_0.1O_1.5 are found to have emission spectra suitable for efficient matching to silicon photovoltaic cells.     

An apparatus for the routine measurement of thermal conductivity of materials for building application based on a transient hot-wire method

An apparatus has been designed and developed for the measurement of the thermal conductivity of samples of non-metallic materials whose thermal conductivity is quite low (in the range between 0.2 and 4 W/m K) by the transient hot-wire method. It is especially conceived to ensure short time consuming and economic measurement of the thermal conductivity of mortar and lateritic bricks for building application.Thermal conductivity is measured by tracking the thermal pulse propagation induced in the sample by a heating source consisting of a Nickel alloy wire. The temperature is measured on the wire by means of two T type (Copper–Constantan) thermocouples. The heat impulse transferred to the wire between two observed times gives a temperature increment of 2–10 °C, depending on the thermal conductivity of the material tested and on the preselected level of the heating power supplied.The thermal conductivity of the materials can be obtained in a comparative way or in a semi-absolute way. In both cases a preliminary calibration of the instrument, obtained with a reference sample whose thermal conductivity previously certified by absolute methods, is in the range required. In the second case, the calibration is necessary to obtain the characteristic curves of the instrument.The paper shows the measurement obtained using materials with thermal conductivity between 0.2 and 1.5 W/m K. In good experimental conditions the accuracy of the measurements is within 5%.The proposed apparatus offers significant advantages, mostly in terms of economy and flexibility, over systems currently in use and over similar systems based on transient methods.     

A spectral method for the estimation of a thermomechanical heat source from infrared temperature measurements

The inverse problem of 2D time-dependent heat source reconstruction is solved. The scientific objectives are the quantification of thermal effects associated to the mechanical deformation of materials during tensile tests. The experiment provides infrared measurements of the specimen’s surface temperature and the inverse algorithm aims at providing a volumic heat source that is free of errors due to heat diffusion. This algorithm is based on an analytical solution of the direct problem in the Laplace-Fourier domain. The solution proposed here is compared to a previously used method [1] based on an adjoint formulation and a regularization of Tikhonov type. This allows to check the validity of the results.     

Method for the diagnostic evaluation of thin-film solar modules based on I–V measurement using a line light source

We propose a technique for detecting unevenness and abnormalities in the active area of a thin-film solar module based on measurement of its I–V characteristics using a line light. The outline of this technique and the results of an evaluation experiment are described. This method can be applied to the evaluation of the module's performance and to the detection of defects.     

Clear sky emissivity as a function of the zenith direction

Using the Bliss's theory [1] which assimilates the atmosphere as a column constituted of plane and parallel layers, the expression of the clear sky emissivity as a function of the zenithal direction is established. Other relations as the mean emissivity and the temperature of a part of the celestial vault are also established. The power emitted by some parts of the sky are calculated. Experiments have been conducted. This paper describes the study and presents the results.     

A compilation of data on the radiant emissivity of some materials at high temperatures

This paper gives a compilation of experimental data from a variety of sources of the emissivity of materials used in high temperature applications. The data is given in the form of temperature dependent correlation equations which can be used for modelling purposes. The data on refractory materials show the importance of surface properties, the effect of surface coatings and ways in which these can be taken into account for more accurate predictions of emissivity. Information is also given on chars, ash particles and furnace deposits resulting from the combustion of coal and biomass.     

Performance evaluation of a hot‐box reflector solar cooker using a microcontroller‐based measurement system

The performance of a low‐cost compound box‐reflector solar cooker designed and constructed by the department of Mechanical Engineering, at the University of Zimbabwe, was investigated and evaluated using a microcontroller‐based measurement system over a period of 3 months. Solar radiation and temperature measurements are sent directly to the computer for monitoring and subsequent analysis using a spreadsheet program. The system is connected to the computer through the RS232 port. Temperature was measured by LM335 temperature sensors, whereas solar radiation was measured by a Kipp & Zonen CM3 thermopile‐based pyranometer that was initially calibrated against the Eppley Precision Spectral Pyranometer. Peak temperatures of about 90°C for the food can be attained in about 5 h on a clear day in Bindura, Zimbabwe (18°S, 31°E). A standardized cooking power of 11 W and an overall efficiency of 15% were found for this cooker. Copyright © 2008 John Wiley & Sons, Ltd.     

A new methodology for the production of furfural as a renewable energy source from bagasse in acidic aqueous media

Sugarcane is one of the most promising agricultural sources of biomass energy. Sugarcane produces mainly two types of biomass, cane trash and bagasse. Furfural is synthesized from bagasse hydrolysis in an acidic environment and as a result of pentose dehydration. This study has been focused on the production of furfural by using sulfuric acid plus an inorganic salt (NaCl + H₂SO₄) as catalyst in a pilot plant. The obtained experimental data show that sulfuric acid plus NaCl can be more effective in the production of furfural. Furthermore, in order to predict the outlet furfural percentage from reactors, a three-layer Feed-Forward Neural Network using temperature and pressure of reactor, time of reaction, sulfuric acid percentage, and bagasse humidity has been considered. In fact, using H₂SO₄ + NaCl as the catalyst, significant improvement is observed in the furfural production process and energy consumption.     

Experimental study of hydrogen production using electrolyte nanofluids with a simulated light source

In this research, we conducted water electrolysis experiments of a carbon black (CB) based sodium sulfate electrolyte using a Hoffman voltameter. The main objective was to investigate hydrogen production in such systems, as well as analyse the electrical properties and thermal properties of nanofluids. A halogen lamp, mimicking solar energy, was used as a radiation source, and a group of comparative tests were also conducted with different irradiation areas. The results showed that by using CB and light, it was possible to increase the hydrogen production rate. The optimal CB concentration was 0.1 wt %. At this concentration, the hydrogen production rate increased by 30.37% after 20 min of electrolysis. Hence, we show that using CB in electrolytes irradiated by solar energy could save the electrical energy necessary for electrolysis processes.     

Improvement of hydrogen sorption measurement using a Sieverts apparatus with consideration of thermal transpiration

Improvement of hydrogen sorption measurement using a Sieverts apparatus was performed by considering volumetric change due to the valve movement and the thermal transpiration. The newly suggested measurement method was evaluated by comparing the results from a blank test and a sample test with previous ones. The valve movement was found to be main measurement errors when the measurement temperature was near room temperature. The thermal transpiration became the major sources of errors as the difference between measurement temperature and room temperature increased. The modified equation for the PCI curve in this study gave the best performance compared with the previous ones at all measurement temperatures. These findings suggested the volumetric change due to thermal transpiration as well as the valve movement should be considered for more accurate measurements of hydrogen sorption.     

A review on microalgae,a versatile source for sustainable energy and materials

Increasing energy demands, predicted fossil fuels shortage in the near future, and environmental concerns due to the production of greenhouse gas carbon dioxide on their combustion have motivated the search for alternative ‘clean’ energy sources. Among many resources for this, microalgae have been found to be most promising due to their high production capacity of vegetable oils. They possess a high growth rate, need abundantly available solar light and CO₂, and thus are more photosynthetically efficient than oil crops. Also, they tolerate high concentration of salts allowing the use of any type of water for the agriculture and the possibility of production using innovative compact photobioreactors. In addition, microalgae are a potential source of biomass, which may have great biodiversity and consequent variability in their biochemical composition. This paper presents an overview on microalgae with particular emphasis as a source for energy (biofuel/electricity) and new materials. Critical issues involved in production of microalgae and their use, future R & D to overcome these, including the work initiated by the authors at Federal University of Paraná, UFPR, in Brazil are discussed. Copyright © 2010 John Wiley & Sons, Ltd.     

A new approach for soil solarization by using paraffin-wax emulsion as a mulching material

Soil mulching material significantly affects the energy balance and soil thermal regime. In order to study the effect of soil mulching with a paraffin-wax emulsion on soil thermal regime, we developed a one-dimensional numerical model, which simulates the microclimate of the mulched soil. The model consists of two layers: soil and paraffin-wax emulsion film. Climatic conditions, soil physical characteristics, and photometric properties of the mulching material are considered. Field measurements verify the model's ability to predict the temperature regime of the paraffin-wax mulched soil. Both numerical and field experiments show that mulching the soil with paraffin-wax emulsion, rather than transparent polyethylene ones, results in more effective heating of the soil and, therefore, faster killing of pathogenic soil fungi. Physically based explanations are given for the measured and computed results.     

Harnessing power from sea water using nano material as photocatalyst and solar energy as light source: the role of hydrocarbon as dual agent

The splitting of water in the presence of ordinary and nano TiO₂ was carried out using hydrocarbon as a dual agent and solar energy as a light source for these experiments. The hydrogen gas evolved was tested and measured using downward displacement of water. The observed results show that more hydrogen was evolved when nano TiO₂ was used as catalyst due to the larger surface area of the nano material. The splitting of sea water yields more hydrogen compared with ordinary water due to the presence of electron donating sodium ions in water. The added hydrocarbon plays a dual role as electron donor and as a trapping agent, which enhances the production of hydrogen to a greater extent compared with the regular donors such as olefin. Copyright © 2013 John Wiley & Sons, Ltd.     

A comparison of spectral irradiance profiles for two nigerian cities using the spectral 2 computer code

The spectral profiles of two Nigerian cities were studied using SERI's SPECTRAL 2 computer code to reveal the nature of the irradiance reaching the ground at the two locations. The spectral profiles show a high diffuse content in the Lagos area even for a clear day and a lower diffuse content and high beam content for Sokoto. The implications of these to photovoltaic systems have been discussed and the conclusions are firstly, PV systems mounted in the fixed tilt position would be practicable in Lagos because the available and usable solar energy inthe global solar spectrum is larger than in the direct solar spectrum due to the high diffuse content. A tracking system would not be very efficient due to the high diffuse content. Secondly, PV systems in the fixed and tracking modes would work well in Sokoto since the global total and the beam irradiance are high. A tracking device would be more efficient here than in Lagos.     

A copper based metal-organic framework as single source for the synthesis of electrode materials for high-performance supercapacitors and glucose sensing applications

The article describes the conversion of MOF-199 to Cu–Cu₂O–CuO/C 700 (1) and Cu–Cu₂O–CuO/C 800 (2) nanostructures by simple pyrolysis at 700 and 800 °C under inert atmosphere. The X-ray photoelectron spectroscopy analysis reveals that the nanostructures Cu–Cu₂O–CuO/C consist of graphitic carbon functionalized with carboxylic, carbonyl and hydroxyl functional groups with copper/copper oxide particles on surfaces. The electrochemical properties of 1 and 2 are evaluated as electrode material for supercapacitors using cyclic voltammetry, galvanostatic charge/discharge and electrochemical impedance spectroscopy. The results for the capacitive performance from cyclic voltammetry and galvanostatic charge/discharge reveal that both the samples have gravimetric capacitance greater than 750 F g⁻¹ at a scan rate of 2 mV s⁻¹ and current density of 2 mA cm⁻². The samples retain about 43% of their initial capacitance even at high scan rate of 75 mV s⁻¹. The cycling performance of the nanostructures illustrate that there is 5.5% capacitance loss after 3000 cycles. The sample 1 and 2 are washed with 1 mol L⁻¹ HCl solution to obtain copper oxide free materials Cu/C 700 (3) and Cu/C 800 (4). Samples 3 and 4 are tested as electrocatalysts for glucose sensing and the cyclic voltammetry measurement shows enhanced current densities compared to the literature values.     

A study on the design and analysis of a heat pump heating system using wastewater as a heat source

In this study, the compression heat pump system using wastewater, as a heat source, from hotel with sauna was designed and analyzed. This study was performed to investigate the feasibility of the wastewater use for heat pump as a heat source and to obtain engineering data for system design. This heat pump system uses off-peak electricity that is a cheap energy compared to fossil fuel in Korea. For this, the charging process of heat into the hot water storage tank is achieved only at night time (22:00–08:00). TRNSYS was used for the system simulation with some new components like the heat pump, which we create ourselves.As a result, it was forecasted that the yearly mean COP of heat pump is about 4.8 and heat pump can supply 100% of hot water load except weekend of winter season. The important thing that should be considered for the system design is to decrease the temperature difference between condenser and evaporator working fluids during the heat charging process by the heat pump. This heat pump system using wastewater from sauna, public bath, building, etc. can therefore be effectively applied not only for water heating but also space heating and cooling in regions like as Korea.     

A new type of air-breathing photo-microfluidic fuel cell based on ZnO/Au using human blood as energy source

The purpose of this work was the evaluation of a microfluidic fuel cell (μFC), in which human blood glucose was photo/electrochemically oxidized. In this regard, ZnO/Au composites with different Au content (1, 2 and 3%) were synthesized, as well as physicochemical and electrochemically characterized. In order to know if these ZnO/Au composites would serve as photo-electrocatalysts in a μFC, their photo- and electrochemical activities were analyzed. In this sense, the optical band gap of composites was determined as 3.15 eV, showing the typical surface plasmon resonance between 530 and 550 nm, while the electrocatalytic activity of ZnO/Au composites was evaluated in terms of the 5 mM glucose, showing that the minimum negative potential shift of the glucose oxidation peak corresponds to the composite with 3% of Au content. A μFC was fabricated using ZnO/Au 3% as photo-anode under visible-light, Pt/C as air-breathing cathode, and human blood and air coming from environment as fuel and oxidant, respectively. It was observed that μFC presented a 1.5-fold more power density under visible-light than in the darkness. This work represents an advantage in the use of photo-electrocatalyst materials towards the development of a new type of air-breathing photo-microfluidic fuel cells employing physiological fluids opening the possibility to be used as a power source in non-implantable medical devices.     

A study on utilization of ground source energy for space heating using a nanofluid as a heat carrier

Ground source heat pump (GSHP) systems are well established as an energy-efficient space conditioning device. However, for better utilization of the ground source, improvement in GSHP performance is desirable, which limits the small temperature difference between the ground and the circulating fluid. In this study, efforts have been made to investigate the performance of a ground heat exchanger (GHX) with a nanofluid as a heat carrier. Mathematical modeling is performed for the closed-loop vertical U-tube GHX with six different (Al₂O₃, CuO, graphite, multiwalled carbon nanotube, graphene, and Cu) water-based nanofluids. The effect of different operating parameters on GHX length, fluid temperature, and pressure drop with nanofluids is determined. On the basis of the analytical results, it is found that the graphite particle-based nanofluid plays a prominent role to enhance the performance of the GHX as compared with other nanoparticles. The maximum enhancement in the increase in outlet fluid temperature and reduction in pipe length with graphite particle-based nanofluid are 68.3% and 63.3%, respectively, for an increase in temperature difference from 7°C to 15°C between the atmosphere and the ground. Also, with the graphite particle-based nanofluid and the increase in pipe diameter from 20 to 50 mm, the fluid outlet temperature increases up to 11.2%, and the requirement in GHX length reduces up to 55%.     

A new fuel cell using aqueous ammonia-borane as the fuel

Ammonia-borane (NH₃BH₃), as a source of protide (H⁻), is initially proposed to release its energy through a fuel cell (direct ammonia-borane fuel cell, DABFC). Cell performance has been elucidated in a 25 cm² laboratory cell constructed with an oxygen cathode and an ammonia-borane solution fed anode, where the catalyst layers are made of Vulcan XC-72 with 30 wt.% Pt. The potential is 0.6 V at the current density of 24 mA cm⁻², corresponding to power density >14 mW cm⁻² at room temperature. The direct electron transfer from protide (H⁻) in NH₃BH₃ to proton (H⁺) has been further proved by the open circuit potential and the cyclic voltammetry results, which show the possibility of improvement in the performance of DABFC by, for example, exploring new electrode materials.