Optimized transparent and heat reflecting oxide and nitride films

Films of indium oxide and indium oxide doped with tin have been produced by reactive planar magnetron sputtering of the pure metal and the alloy and from two metal sources simultaneously. In each case the oxygen partial pressure was controlled to give the higher sheet resistance in the oxide film which was deposited onto a plastic sheet transferred over a drum at ambient temperature. Films prepared under these conditions with the best properties for heat reflecting and visible transparent filters were found to be the oxide of the pure metal.A radio frequency discharge used in conjunction with the magnetron allowed the operating pressure to be considerably reduced, which allowed the preparation of titanium nitride films from a titanium metal target and the construction of simple metal and dielectric-metal-dielectric filters, which match theoretical predictions. A sandwich filter could be made from one titanium target by varying the active gas between oxygen and nitrogen to give a structure of: TiO₂TiNTiO₂.     

Photoelectrochemical characterisation of indium nitride and tin nitride in aqueous solution

Indium nitride (InN) and tin nitride (SnN_x) films were produced with reactive d.c. magnetron sputtering technique. The thin film semiconductors were optically and photoelectrochemically characterised and the energetic positions of the two semiconductors’ band edges were determined with respect to the normal hydrogen electrode. The sputtered InN thin film showed an indirect bandgap of 1.4 eV and a direct bandgap of 1.8 eV. The optical spectra of SnN_x indicated a bandgap energy of approximately 1.4 eV. All nitride films showed n-type photoresponse in KI (aq) electrolyte at an irradiation intensity of 1000 W/m². The photoelectrochemical characterisation indicated that InN and SnN_x with a bias of about 400 mV or less can be used for photo-oxidation of water.     

Spectrally selective laminated glazing consisting of solar control and heat mirror coated glass: preparation, characterization and modelling of heat transfer

In this study, solar control coatings were prepared by sequential depositions of thin films of ZnS (40 nm)–CuS (150 nm) and ZnS (40 nm)–Bi₂S₃ (75 nm)–CuS (150 nm) from chemical baths on 3 mm thick commercial sheet glass. These were laminated to 3 mm thick clear glass or commercially available SnO₂ based heat mirror coating of sheet resistance 15 Ω on float glass of 3 mm thickness using a poly(ethylene vinyl acetate), EVA, sheet of 0.36 mm thickness in a vacuum process at 120 °C for 30 min. In total, the thickness of the glazing was 6.35 mm. The glazings possess visible transmittance, weighted for D65 solar spectra and sensitivity of the human eye for daylight vision, of 36% or 14% with solar absorptance of 71% or 78% depending on the coating type, i.e ZnS–CuS or ZnS–Bi₂S₃–CuS-heat mirror respectively. The solar heat gain coefficient (SHGC) was evaluated for these glazings at exterior temperatures of 15 and 32 °C for an exterior convective heat transfer coefficient (h_ex) of 6–100 Wm⁻² K⁻¹ using a mathematical model. The model predicts the extent of reduction in SHGC through the presence of the heat mirror coating as a function of h_ex and hence helps to decide on the relative benefit, which may be derived through their use in different locations. Though the deposition technique mentioned here involves longer duration compared with vacuum techniques, it may be developed into a low throughput, low-capital alternate technology for small-scale production.     

Chemical vapour deposited SnO2:Sb heat mirror coatings for cylindrical solar collectors

A chemical vapour deposition technique for growth of SnO₂:Sb heat mirror coatings on the inner walls of long cover glass tubes for cylidrical solar collectors is reported. The best performance of the tin-oxide film is obtained for those films grown from a source of SnCl₂ + 1 mol% Sb on Corning glass tubes at 520°C. These films, supported on 2 mm glass substrates, have a solar transmittance of 0.85 and an infrared reflectance of 0.8. The heat mirror coatings are observed to increase the stagnation temperature of the absorber in anevacuated tubular collector from 142 to 161°C under incident optical flux of 1150 W/m²     

Metal hydride heat pump—New type of heat converter

Selection of materials for metal hydride couples is considered for the development of refrigerating machines and hydride heat pumps (MHHP) in the temperature ranges from −30 to 200 °C. The slope of the plateau and hysteresis of “pressure-composition” isotherms, the influence of the mass of the reactor on the efficiency of cycle, and the choice of operating parameters are taken into account as opposed to the ideal thermodynamic cycle described in literature. Some results, obtained during the development and installation of MHHP for water cooling are presented. MHHP are assembled from modules with heat/cold capacity of 150–200 W. The design of the modules provides hydrogen transfer at approximately equal pressure in the high- and low-temperature sides of reactor when the valves between them are absent.     

玻璃用透明隔热水性纳米涂料研究进展

玻璃用透明隔热水性纳米涂料因其环保、节能和良好的视觉效果而日益受到研究者和相关产业界重视,但存在现场施工不便,隔热性能欠缺、涂层耐水性不佳等问题。简要介绍了二氧化锡锑基透明隔热涂料的研究进展和产业化状况,着重介绍了隔热机理、实际应用中存在的问题以及可能的解决办法。     

Anodic and optical characterisation of stain-etched porous silicon antireflection coatings

Porous silicon (PS) antireflection coatings have been obtained by stain etching of crystalline Si in HF:HNO₃:H₂O solutions at different etching times and HNO₃ concentrations. The morphology of the PS samples was characterised by anodic oxidation and revealed the increase of the porous surface area with the HNO₃ concentration. Upon a certain critical concentration of HNO₃, the surface of crystalline Si immersed in the solution becomes polished, and a decrease of its surface area is observed. The samples were also characterised by a spectrophotometer in the range 300–900 nm, showing an effective reflectance below 4% in most of the spectral range for samples obtained in an etching solution, where the HNO₃ is below its critical concentration. Anodic oxidation after etching can be used as an useful tool for the qualitative and quantitative analysis of porous surface areas.     

Greenhouse warming — A comment

In the short term there are logistic constraints on the extent to which nuclear power or renewable energy sources can reduce greenhouse gas emissions by substituting for fossil fuels, although a much greater impact is possible in the longer term. Contrary to views sometimes expressed the nuclear option can be economically attractive when compared with conservation measures, and the two technologies should be seen as complementary rather than as competitors.     

Chemical heat pumps—A basic thermodynamic analysis

The concept of a thermochemically driven chemical heat pump/refrigerator is discussed. Using Carnot analysis, it is shown that these systems can work closely to the maximal second-law efficiency. Criteria to be used in selection of chemical reactions for maximal efficiency are formulated.     

Optical and morphological characterisation of low refractive index materials for coatings on solar collector glazing

Nanostructured coatings based on the elements Si, O, Mg, and F have been deposited as thin films by sol–gel dip-coating in a particle-free atmosphere. The refractive index of the prepared SiO₂ and quaternary Mg–F–Si–O thin films has been determined from spectrophotometric and ellipsometric data. The morphology of those thin films has been observed by TEM.Nanoporous SiO₂ coatings with a pore size smaller than 3 nm (TEM) and a pore volume fraction of 30% (as inferred from ellipsometric measurements) have been achieved. They are characterised by significantly lower refractive index values (approx. 1.32 at 550 nm) than compact SiO₂ (approx. 1.46).Quaternary Mg–F–Si–O thin films are characterised by a surprisingly low refractive index (approx. 1.26 at 550 nm), even lower than that of dense MgF₂ coatings (approx. 1.38). Preliminary results of transmission electron microscopy suggest that these films are of nanocomposite nature.In both cases, highly transparent samples have been produced in a single dip-coating step followed by simple thermal annealing in air. Broad spectral transmittance maxima are observed exceeding values of 98.5% (nanoporous SiO₂) and 99.5% (quaternary Mg–F–Si–O films).The quaternary films might exhibit a higher ageing stability than porous SiO₂ films with respect to pore-filling and could therefore be a promising alternative for single-layered anti-reflection coatings as well as for multi-layered coloured coatings on solar collector glazing.     

HIDA databank — its development and future

Task 15 of the European Commission supported HIDA Project (BE1702) has involved the preparation of a post-processed databank to contain information on creep and fatigue crack growth characteristics on the materials studied in the project. It also includes information on plant operator experiences relating to component cracking/failure under steady loading and plant cycling conditions. The HIDA Databank is one of the few databanks initiated in this field of activity.The HIDA Databank has been released on CD as two computer files based on Microsoft^® Access 97 software and has a purpose built Graphical User Interface to allow easy addition of data and examination of existing information. The data included in the HIDA Databank are: (1) plant and research experience information collected from HIDA Task 2 (non-HIDA data); (2) HIDA test data generated from laboratory and feature tests; and (3) test specimen characteristics, product or component properties.The HIDA Databank also contains some post process parameters such as lower and upper bound scatter bands (as derived from the test data).The crack growth data stored in the databank has been used to develop the HIDA procedure for defect assessment and has also assisted in refining existing assessment methodologies. The HIDA Databank also acts as a data source for the Knowledge Based System developed in the HIDA project.This paper outlines the main development of the HIDA Databank and briefly considers how it will be used and developed in the future in order to act as an independent source of information on creep and fatigue crack growth, and component behaviour, in high temperature plant.     

Optimum fluid layer thickness for heat transfer effectiveness using water‐based nanofluids—A numerical estimation

Nanofluids are considered to be the novel method for heat transfer in heat pipes and heat exchangers. But its application in microlevel cooling systems is still limited because of the paradox that once convection onsets in the base fluid, the effectiveness of nanofluid as a heat transfer medium will be reduced. The onset of convection in the nanofluid occurs only after its onset in the base fluid which is mostly water. Hence, it is vital to estimate the fluid layer thickness of the base fluid at which convection will just onset. The problem is analyzed using the concept of the critical Rayleigh number. The study of velocity and temperature profiles in the fluid gap also gives an indication of convection in the fluid gap.     

Solar absorption cooling with low grade heat source — a strategy of development in South China

Based on experiences with an operating solar cooling system in south China, a low temperature driven solar cooling system has been proposed, and a new model of two-stage lithium bromide absorption chiller has been developed. Test results have proved that the two-stage chiller could be driven by low temperature hot water ranging from 60 to 75°C, which can be easily provided by conventional solar hot water systems. Relying on the successes of the above system, an integrated solar cooling and heating system with two-stage absorption chiller was constructed (cooling CAPACITY=100 kW). Preliminary operating data of the system has indicated that this type of system could be efficient and cost effective. Compared to the conventional cooling system (with single-stage chiller), the proposed system with a two-stage chiller could achieve roughly the same total COP as of the conventional system with a cost reduction of about 50%.     

Integrated low-emittance–electrochromic devices incorporating ZnS/Ag/ZnS coatings as transparent conductors

We have prepared and tested integrated low-emittance–electrochromic devices using ZnS/Ag/ZnS coatings as transparent electrodes and WO₃ films as electrochromic layers. These devices exhibit adequate coloration and can withstand more than 1000 bleaching-coloration cycles, provided that the metal layer is protected from the liquid electrolyte by a combination of thick dielectric films (ZnS/WO₃). We have also predicted the optimum configuration of the WO₃/ZnS/Ag/ZnS/Glass stack that maximizes transmission in the visible. Integration of low emittance and electrochromic films into one device could improve the performance and reduce the cost of electrochromic windows.     

Renewable energy — the way forward

This paper outlines the growing need of energy in the developing countries and the acute population growth, which will exceed 10 billion by the year 2050. It describes the achievement and progress made in geothermal, hydro-power, biomass conversion, solar thermal technology, wind energy conversion and the ever increasing usage of photovoltaics. The paper also addresses the barriers and problems which face renewable energy users and producers. It is evident now that global warming is setting in and is going to change the climate as well as the terrain of many countries unless drastic measures are taken. The recent Kyoto meeting emphasised the importance of limiting CO₂ emissions and to abide by some form of agreement to reduce emissions. Countries such as India, China and Indonesia, which represent nearly half the world's population, are actively involved in using renewable energy as the only means of sustaining their energy growth. It concludes that renewable energy penetration into the energy market is much faster than was expected a few years ago and by the year 2020, 10–15% of our prime energy will be met by renewable energy.     

Solar energy resource assessment — Brazil

Appropriate information on solar resources is very important for a variety of technological areas, such as: agriculture, meteorology, forestry engineering, water resources and particularly for an innovating technology such as solar energy. In the market entry process of an innovating technology such as solar energy, the enlarged and sustained reproduction of this energy strongly depends on the economy and reliability of the demonstrative solar systems installed (within a restricted or wide scale). The economy and reliability of a system are the consequence of a well-prepared project, resulting from an accurate knowledge of the solar resource available. Therefore, knowing the potential of the solar resource accurately is not only a need, it is also an imperative for a larger diffusion and use of the solar energy.The existing sources of information on radiation in Brazil are quite varied, both at the institutional level and in different types of publications. At the institutional level these sources are: the National Institute of Meteorology, secretary of agriculture, research centers, universities, and electric power generating and distributing companies, among others. The publications with this information are project reports, internal reports of institutions or several magazines. Thus, the quality of the data varies considerably, the information presents spatial and temporal discontinuity and the instruments as well as the measurement units are not standardized.The general objective of this paper is to recover, qualify, standardize and make available the best information from the current existing solar resource in Brazil, either in the form of isoline charts of solar radiation, insolation, numeric tables or analytic summaries of a great part of the publications on the theme over the last forty years.     

Energy resources—are we planning for the future?—a review

Many governments are at present attempting to formulate energy strategies for ensuring future supplies. the debate over nuclear power is continuing and ‘pollution-free’ alternative energy sources are also being considered. Points for and against each of the possible energy sources are discussed here and the possible hazards of nuclear power (e.g. radioactivity) are compared with the possible dangers of ‘free-energy’ sources (e.g. an increased ‘greenhouse’ effect). the importance of an integrated energy policy is stressed. Such a policy does not rely on a single energy source but utilizes the full spectrum of possibilities and can incorporate the more immediate concepts of energy savings.