Energy Collection System Research Articles

Radiation and mass transfer effects on MHD free convection flow past an impulsively started isothermal vertical plate with dissipation

This paper is focused on the study of effects of thermal radiation on the natural convective heat and mass transfer of a viscous, incompressible, gray absorbing-emitting fluid flowing past an impulsively started moving vertical plate with viscous dissipation. The governing boundary-layer equations are formulated in an (x, y, t) coordinate system with appropriate boundary conditions. The Rosseland diffusion approximation is used to analyze the radiative heat flux in the energy equation, which is appropriate for non-scattering media. The dimensionless governing equations are solved using an implicit finite-difference method of Crank-Nicolson type. The influence of Prandtl number, radiation-conduction parameter, thermal Grashof number, species Grashof number, Schmidt number, and Eckert number on the dimensionless velocity, temperature and concentration are studied. In addition the variation of the local and average skin-friction, Nusselt number, and Sherwood number for selected thermophysical parameters are computed and shown graphically. Increasing the Eckert number is seen to accelerate the flow. Thermal radiation reduces both velocity and temperature in the boundary layer. This model finds applications in solar energy collection systems, geophysics and astrophysics, aero space and also in the design of high temperature chemical process systems.

Network Numerical Simulation of Impulsively-Started Transient Radiation-Convection Heat and Mass Transfer in a Saturated Darcy-Forchheimer Porous Medium

We study the effects of thermal radiation and porous drag forces on the natural convection heat and mass transfer of a viscous, incompressible, gray, absorbingemmitting fluid flowing past an impulsively started moving vertical plate adjacent to a non-Darcian porous regime. The governing boundary-layer equations are formulated in an (X∗, Y∗, t∗) coordinate system with appropriate boundary conditions. The Rosseland diffusion approximation is employed to analyze the radiative heat flux and is appropriate for non-scattering media. The model is non-dimensionalized and solved with the network simulation model. We study the influence of Prandtl number, radiation-conduction parameter, thermal Grashof number, species Grashof number, Schmidt number, Darcy number and Forchheimer number on the dimensionless velocity, temperature and species function distributions. Additionally we compute the variation of the local skin friction, Nusselt number and Sherwood number for selected thermophysical parameters. Increasing Darcy number is seen to accelerate the flow; the converse is apparent for an increase in Forchheimer number. Thermal radiation is seen to reduce both velocity and temperature in the boundary layer. The interactive effects of second order porous drag and thermal radiation are also considered. The model finds applications in solar energy collection systems, porous combustors, transport in fires in porous media (forest fires) and also the design of high temperature chemical process systems.

Energy efficiency in new museum build: THEpUBLIC

The project MUSEUMS, awarded the Thermie Grant from the European Commission, has applied and tested new and innovative technologies for optimizing energy efficiency and sustainability in nine retrofitted and new museum buildings in Europe. The project will significantly contribute to the acceptance of innovative and renewable technologies in public buildings by demonstrating that retrofitted and new museum buildings can fully meet architectural, functional, comfort, control and safety requirements as well as achieve total energy savings of over 35% and reduce CO2 emissions by over 50%. THEpUBLIC will be a stunning and modern flagship building containing six storeys, with a total area of 11,000 m2 of galleries for exhibitions, digital art and hands-on displays. In addition, there will be workspaces, creative spaces, retail opportunities, restaurant facilities, public areas, conference rooms and other multi-function spaces. Initiated by Jubilee Arts, the THEpUBLIC, designed by Alsop Architects, will introduce and engage its 400,000 expected visitors in the principles of energy and the environment through a display of art, education, technology and entertainment in the centre of West Bromwich, Sandwell. It will serve as a catalyst for urban regeneration within Sandwell. Battle McCarthy’s key environmental design solutions for THEpUBLIC include natural daylighting, mixed-mode ventilation system with operable windows, low energy and maintenance cost systems, potential for integrating renewable energy collection systems, borehole water systems for cooling and water supply, an intelligent facade system with external shading and natural ventilation and night cooling systems.

Optimum size and structure for solar energy collection systems

Procedures for sizing and optimizing the structure of solar collection systems are proposed. Four economical indices, including net present value and internal return rate, are given as examples of objective functions. Three solar energy applications were considered. A rather involved but still simple flat-plate solar collector model is used in calculations. The implementation was made for a specific geographical location with a detailed meteorological database available. In the case of solar collectors with uniformly distributed parameters, the procedure allows one to select the best devices from a given set of solar collectors. For every selected device the optimum range of the operation temperature is also determined. The best solution corresponds to systems with optimal non-uniformly distributed parameters. The general theorem proposed here shows how the modified optical efficiency and heat loss coefficient should be distributed for cost minimization. One finds that unglazed, single- and double-glazed collectors should be used on the same collection area in order to obtain the best performance. Also, the bottom insulation thickness should be changed accordingly.

05/00561 Study of low-temperature oxidation of buckskin subbituminous coal and derived chars produced in ENCOAL process

Solar energy is the cleanest, renewable and most abundant source of energy available on earth. The main use of solar energy is to heat and cool buildings, heat water and to generate electricity. There are two types of solar energy collection system, the photovoltaic systems and the solar thermal collectors. The efficiency of any solar thermal system depend on the thermophysical properties of the operating fluids and the geometry/length of the system in which fluid is flowing. In the present research a simplified mathematical model for the solar thermal collectors is considered in the form of non-uniform unsteady stretching surface. The flow is induced by a non-uniform stretching of the porous sheet and the uniform magnetic field is applied in the transverse direction to the flow. The non-Newtonian Maxwell fluid model is utilized for the working fluid along with slip boundary conditions. Moreover the high temperature effect of thermal radiation and temperature dependent thermal conductivity are also included in the present model. The mathematical formulation is carried out through a boundary layer approach and the numerical computations are carried out for cu-water and TiO2-water nanofluids. Results are presented for the velocity and temperature profiles as well as the skin friction coefficient and Nusselt number and the discussion is concluded on the effect of various governing parameters on the motion, temperature variation, velocity gradient and the rate of heat transfer at the boundary.

Optimization of bed parameters for packed bed solar energy collection system

Use of packed bed for the improvement of performance of solar air heater has been proposed by several investigators. However, this enhanced efficiency is accompanied by substantial increase in pressure loss, which results in higher running cost of the system. So, the solar energy collection system should be optimized in such a way that it will give energy with minimum cost. In this work two types of packed bed collectors, one with wire mesh screen matrix bed and other with pebble bed, were optimized on the basis of minimum cost per unit energy delivered. Tables for optimum values of bed parameters namely number of layers, porosity, pitch to wire diameter ratio and pebble diameter have been prepared on the basis of minimum cost per unit energy delivered. These tables can be used by a designer for selecting the optimum values of bed parameters.

Ambient energy for low-cost water desalination

The papers presents the results of a feasibility study to assess the potential of ambient energy in producing low-cost desalinated water. The proposed method uses conventional off-the-shelf desalination equipment linked up to an innovative energy harvesting system made of extruded aluminium planks which form part of the building and which is able to provide low-cost energy for the desalination process. The most common energy collection system forms an engineered roof of a building. Water is pumped through this roof to collect solar and ambient energy that can then be used for a variety of applications. Results from an EC-funded feasibility study to assess the potential of using ambient energy to produce fresh water from seawater are presented here. It is felt that the technology offers good potential for water desalination in arid and semi-arid regions of the world where there is an abundance of solar and ambient energy.

Silicon PV Cell Production on the Moon

A concept has been developed for the production of photovoltaic energy collection systems on the Moon by vacuum deposition directly onto the lunar surface. Using this technique it would be possible to quickly install quite large capacities of power on the Moon at relatively low cost. Most of the material required for photovoltaic devices is readily available on the Moon, and taking production machinery to the Moon can further lower the cost of power if the machinery can be operated for long periods of time. Low-cost energy on the Moon could enable a wide range of activities including support of robust human outposts, production of propellants for use on the Moon or for export, production of a wide range of other materials for use in space, and beaming of energy from the Moon to space and to Earth. A proposed strategy by which lunar power can be developed in the near future is closely connected to the establishment of a human outpost on the Moon.

Performance Limits of Heliostat Fields

Geometric and thermodynamic arguments are used to derive upper limits on the performance of a solar energy collection system, consisting of an axisymmetric heliostat field, a solar tower, secondary optics and a black receiver. Performance limits on collected power, concentration, and work output are presented. Performance of tower systems with several secondary optics options is compared: tower-top Compound Parabolic Concentrator (CPC), Tailored Edge-Ray Concentrator (TERC) approximated by a cone, and Cassegrainian with ground-level CPC or Compound Elliptic Concentrator (CEC). Optimized ray tracing is used to generate the design parameters of the secondary concentrators that yield the highest optical efficiency. The results show that the tower-top Cone provides the best performance regarding both concentration and efficiency, except for very large fields. The Cassegrainian designs come in second, but become equal and even better than the Cone for large fields. The results for the Cassegrainian are sensitive to the value of the reflectivity, due to the additional reflections incurred. The choice of a CEC is better than a CPC for the terminal concentration in a Cassegrainian system, but the difference is small. The suitability of the different design options for high-temperature solar applications is discussed. The recommendations regarding optical configuration depend on field size, as well as on application-specific constraints.

The design of an evaporator/absorber and thermodynamic analysis of a vapor absorption chiller driven by solar energy

An experimental absorption cooling system is being developed, driven by the heat generated by the solar energy collection system installed at Coventry University. The proposed absorption cooling system comprises an evaporator/absorber cell and a generator/condenser cell. These components are housed in evacuated glass cylinders to allow the processes involved to be observed. The refrigerant-absorbent pair used is water and Lithium Bromide since a low temperature heat source can be used to drive the refrigerant from the carrier fluid. A thermodynamic analysis of the absorption cooling cycle has been performed to study the effect of various operating conditions on the thermal performance. This paper presents the design of the evaporator/absorber cell and the results of the thermodynamic analysis.

Modeling the solar irradiation on flat plate collectors augmented with planar reflectors

An analytical model has been developed and used to determine solar irradiation on flat collectors augmented with planar reflectors. The model uses measured insolation data from the NREL National Solar Radiation Data Base. In addition the model accounts for direct and reflected components of beam, diffuse and ground reflected insolation, considers finite length systems, accounts for shading of the collector by the reflector, and considers different configurations of the reflector relative to the collector. Thus the model represents an extension and refinement of many previous models. Computer simulations have been carried out over different time spans to assess the effects of including these features. In general, the addition of reflectors enhances the radiation received by the collector. Reflected beam radiation is the major contributor to the enhancement, although reflected sky diffuse and ground reflected radiation can be significant in many instances. To optimize effectively the design of the system with respect to selecting tilt angles and specifying a reflector-above or below-collector configuration requires proper modeling of the energy received by the collector system. Finite length analysis used in the model enables the optimization of reflector size relative to that of the collector. The model presented can be the basis of an analytical design tool for optimizing the design of a variety of reflector-enhanced solar energy collection systems.

Using fiber optics to tap the sun's power

This paper discusses a solar energy collection system in which optical fibers are used to transport energy from a single-stage and a double-stage, three-dimensional Compound Parabolic Concentrator (CPC). After developing a thermo-mathematical model for the assembly of CPC and fibers, numerical simulations are used to optimize the system design. The modules filled with plastic and glass are shown to perform considerably better than those filled with air. A two-stage system performs better than a single-stage module. CPC surface reflectance improves the yield but an increase in fiber length decreases the performance.

Wood burning for residential space heating in the United States: an energy efficiency analysis

Biomass combustion is commonly perceived as an alternative energy source which will reduce reliance on, and thus conserve, conventional non-renewable fuels. However, in the United States wood collection is energy intensive and requires the expenditure of high-quality fossil fuels to support the technology. The efficiency of an energy collection or delivery system can be estimated by using a net energy analysis (NEA). An energy accounting framework is employed to compare the total output of energy (in joules) delivered for residential space heating to the total energy input required to make the wood energy available. Energy inputs are either direct, such as the petrol used to power the transport vehicle, or indirect, such as the energy required to manufacture the transport vehicle. This study analyses the energy efficiency of three wood-gathering strategies commonly practised in the United States. Energy output-input ratios, calculated for each of the three cases, indicate that the ratios are strongly influenced by situation-specific variables, particularly (1) the distance fuelwood must be transport, (2) the load capacity of the transport vehicle and (3) the combustion efficiency of the wood-burning unit. Incorporating indirect energy costs significantly reduces the energy ratio but, in some situations, burning renewable wood can be as energy efficient as conventional heating systems based on non-renewable fossil fuels, thus providing a locally viable alternative.

Performance ratio, area economy and economic return for an integrated solar energy/multi-stage flash desalination plant

The use of solar energy for desalination may be achieved in a variety of ways - the commonest technique being the conventional / improved solar stills. An alternative approach proposed by us earlier (International Solar Energy Congress, 1977) involves the integration of a solar energy collection system with a conventional MSF desalination unit. This paper presents the performance ratio and area economy such a unit for a variety of process conditions. The economic returns are found to be comparatively favourable over a wide range of operating conditions.

Performance assessment of a paraboloid dish collector field

This article deals with performance assessment of thermal energy collection and storage subsystem of a 100-kW solar power station in the desert area of Kuwait. An energy analysis of the solar energy collection system was made accounting for various thermal loss as in the collector field. Results have been compared with the respective design and expected values. Comparison shows a substantial reduction in mirror reflectivity and an increase in piping thermal losses. These results along with the analyses are presented and discussed here.

Technical and economical aspects of solar desalination with particular emphasis on solar pond powered distillation plants

Desalination remains an important and interesting application for the use of solar radiation as a source of undepletable energy. After almost a decade of research and development including the installation and testing of various smaller pilot systems, our solar desalination technology - among others - is now becoming available on a commercial level. The paper discusses the evolution of the technology both of the desalination and the collector-subsystems as a result of the technical and economical constraints associated with the utilization of solar energy, a highly fluctuating energy source of low surface density. Performance data is presented in particular for the coupling of a selfregulating MSF unit with a solar pond energy collection and storage system, both inhouse developments. The performance and layout data was obtained both from computer simulation and experimental results with a small sized solar pond and desalination subsystem in Switzerland. The economy assessment, which is presented for Middle East climate conditions, clearly demonstrates that solar desalination already becomes competitive for medium sized installation at remote locations. Potential further cost reductions also through upscaling may lead to the use of desalinated water for agricultural applications one day.

Electrochemical solar ponds hybrid thermal and electric storage

A hybrid thermal and electric energy collection and storage system for solar application is proposed. Hybrid storage is achieved by transforming a conventional solar pond into a secondary activity cell, where the inert electrolyte (NaCl solution) has been partially replaced by active ones totally soluble on both oxidated and reduced phases, which produce highly reversible reactions. The tested REDOX pairs were: Pb/Cr ++ , Cr +++ , H 3 O + //Fe +++ , Fe ++ , H 3 O + /C Pb/Cr ++ , Cr +++ , H 3 O + //Cr 2 O 7 = , Cr +++ ,H 3 O + /C. The suggested hybrid system has been designed for static operation and large storage capacity. Changing the solar pond into an electrical accumulator improves thermal efficiency of the pond and does not increase building expenses; furthermore solar pond high temperature is advantageous for the accumulator operation and helps for current extraction.

Successive lumped analysis simulation of solar energy collection systems

A methodology for deriving an analytical, simplified solar system performance prediction model is presented. Factors related to system design can be examined; for example, storage tank temperature variations, solar system turn-on and turn-off times and system ‘memory’. A simple domestic water heating type system is used as a basis for illustrating derivation of performance models. Predicted performance results are in good agreement with results obtained from another design method. A generalized procedure is described for deriving new system models. The lumped analysis simulation may prove useful for non-standard applications where other simplified design methods are not defined and where detailed simulation capability is not available.

Enhanced solar desalination unit: Modified cascade still

At the present time, all solar stills can be viewed as being in various stages of development, rather than as an established technology. This paper presents the design, analysis and performance of ordinary and new modified cascade stills. In the modified cascade still, the condensation and evaporation operations are separeted. The unit consists of two main parts, the energy collection and evaporation system, and a separate condenser. The operational data are discussed and analysed. The temperature distribution is analysed and the results obtained indicate that the performance of the modified unit is superior to that of the ordinary cascade still.

Effective antireflection coatings of transparent polymeric materials by gas-phase surface fluorination

There is a dramatic need in solar energy collection systems for lightweight, inexpensive polymeric materials,that exhibit improved performance and durability. One approach to altering the properties of polymeric materials, surface fluorination, is appealing because of its potential for low cost. The literature indicates that such properties as permeability, wettability, bondability, thermal stability, weatherability and optical transmittance can be improved by treating the surface with gaseous fluorine. A gas phase fluorination reactor system (GPFRS) was designed, built and used. The initial emphasis was on improving optical transmittance by having an effective antireflection coating form on the surface of a wide variety of commercially available transparent polymeric films. These included such materials as polypropylene, acrylic, polyacrylonitrile, highly cross-linked polyethylene, polyester, polycarbonate and polymethylpentene. Two techniques were used to quantify the effect of exposing the surface of the polymers to gaseous fluorine. Transparent films were characterized before and after fluorine exposure by specular transmittance measurements. Surface analysis of selected treated and untreated samples was accomplished by X-ray photoelectron spectroscopy and depth profiling. Surface analysis confirmed the deposit of fluorine at the surface and into the bulk of all specimens examined after treatment in the GPFRS. Optical measurements revealed substantial improvement in specular transmittance following surface fluorination of almost all materials considered. Increases in solar weighted specular transmittance as high as 4.6% were measured.