Siddig Omer

Design optimization of thermoelectric devices for solar power generation

Abstract We present an improved theoretical model of a thermoelectric device which has been developed for geometrical optimization of the thermoelectric element legs and prediction of the performance of an optimum device in power generation mode. In contrast to the currently available methods, this model takes into account the effect of all the parameters contributing to the heat transfer process associated with the thermoelectric device. The model is used for a comparative evaluation of four thermoelectric modules. One of these is commercially available and the others are assumed to have an optimum geometry but with different design parameters (thermal and electrical contact layer properties). Results from the model are compared with experimental data of the commercial thermoelectric module in power generation mode with temperature gradient consistent with those achievable from a solar concentrator system. These show that it is important to have devices optimized specifically for generation, and to improve the contact layer of the thermoelements accordingly.

Design and thermal analysis of a two stage solar concentrator for combined heat and thermoelectric power generation

Abstract A design procedure and thermal performance analysis of a two stage solar energy concentrator suited to combined heat and thermoelectric power generation are presented. The concentrator is comprised of a primary one axis parabolic trough concentrator and a second stage compound parabolic concentrator mounted at the focus of the primary. The thermoelectric device is attached to the absorber plate at the focus of the secondary. A cooling tube is fitted to the cold side of the thermoelectric device to extract the waste heat and maintain a high temperature gradient across the device to improve conversion efficiency. The key requirements of the concentrator design are to be tolerant of tracking misalignment, maintain temperature gradients to suit thermoelectric generation and minimise heat losses. A design methodology is presented which allows interception of rays within an angular region ±δ . This results in a wider receiver for the parabolic trough concentrator than would usually be used for a similar concentration ratio. The role of the second stage concentrator in limiting heat losses from the absorber plate is evaluated. Results indicate that in addition to improving the concentration efficiency, the second stage compound parabolic concentrator of the proposed design also inhibits convective air movement and, consequently, improves the overall performance of the solar concentrator.

A novel thermoelectric refrigeration system employing heat pipes and a phase change material: an experimental investigation

This paper presents results of tests carried out to investigate the potential application of heat pipes and phase change materials for thermoelectric refrigeration. The work involved the design and construction of a thermoelectric refrigeration prototype. The performance of the thermoelectric refrigeration system was investigated for two different configurations. The first configuration employed a conventional heat sink system (bonded fin heat sink) on the cold side of the thermoelectric cells. The other configuration used an encapsulated phase change material in place of the conventional heat sink unit. Both configurations used heat pipe embedded fins as the heat sink on the hot side. Replacement of the conventional heat sink system with an encapsulated phase change material was found to improve the performance of the thermoelectric refrigeration system. In addition, it provided a storage capability that would be particularly useful for handling peak loads and overcoming losses during door openings and power-off periods. Results showed that the heat sink units employing heat pipe embedded fins were well suited to this application. Results also showed the importance of using a heat pipe system between the cold junction of the thermoelectric cells and the cold heat sink in order to prevent reverse heat flow in the event of power failure.

Experimental investigation of a thermoelectric refrigeration system employing a phase change material integrated with thermal diode (thermosyphons)

This paper presents results of tests carried out to investigate the potential application of phase change materials (PCMs) integrated with thermosyphons in a thermoelectric refrigeration system. The work involved design, fabrication and test of a 150 W thermoelectric refrigeration system. The system was first fabricated and tested using a conventional heat sink system (bonded fin heat sink system) at the cold heat sink. In order to improve the performance and the storage capability, the system was reconstructed and tested using an encapsulated PCM as a cold sink. Results of tests of the latter system showed an improved performance compared with the former system. However to improve the storage capability, in particular during off-power periods, it was found necessary to integrate the PCM with a thermal diode, which would allow heat flow in one direction only. Results of tests carried out on the new system showed considerable improvement in the storage capability of the thermoelectric refrigeration system compared with the previous ones. Overall the system suits operation with renewable energies, e.g., solar energy.

Monitoring results of two examples of building integrated PV (BIPV) systems in the UK

This paper presents monitoring results of two examples of building integrated PV system investigated at the School of the Built Environment, University of Nottingham in the UK. One of the systems is installed on an educational building, and consists of a thin film PV facade appropriate for commercial or office suites. The other system is installed on a detached house, and uses crystalline PV roof slates, appropriate for domestic buildings. As the two buildings are significantly different in size, construction and occupancy, the design and selection of the PV system for each was also different. The monitoring investigation has assisted identification of shortfalls in performance and possible explanations have been suggested. The results presented in this paper provide information on the design process, and highlight similarities and differences in the design, installation, performance and economics of the two systems.

Optimum Design of a Solar-Driven Ejector Cooling System

A novel solar-powered ejector air-conditioning system with a nominal capacity of 5 kW cooling is described in this chapter. The system comprised an evacuated tube solar collector system, an ejector cooling system, and an MEPCM cooling storage system. The full size system has been laboratory tested, and the results are in good agreement with CFD simulation. A COP of up to 0.32 is obtained for the ejector cooling system during the test at the boiler temperature around 90 °C. Coefficient of performance of is up to 0.16 is predicted for the integrated system in operation. Guidelines for the design of system components based on the results of computer modeling and laboratory testing is given. Related correlations between these parameters will be obtained and presented in an easy step-by-step manner, in order to facilitate design and integration of system components for various applications. These will include analytical equations to match climate conditions and building air-conditioning load.

Experimental study of an adsorption heat storage systems for building applications

Abstract In this paper, an Adsorption Heat Storage System (AdHS-R134a)/heating system utilising Vermiculite and Calcium Chloride composite adsorbent material was experimentally investigated. The main aim of the experimental

Environmentally Friendly Systems: Earth Heat Pump System with Vertical Pipes for Heat Extraction for Domestic Heating and Cooling

Geothermal heat pumps (GSHPs), or direct expansion (DX) ground source heat pumps, are highly efficient renewable energy technology, which use the earth, groundwater or surface water as heat sources when operating in heating mode or as heat sink when operating in cooling mode. They are receiving an increasing interest because of their potential to reduce primary energy consumption and thus reduce emissions of the GHGs. The main concept of this technology is that it utilises the lower temperature of the ground, which approximately remains relatively stable throughout the year, to provide space heating, cooling and domestic hot water for buildings. The main goal of this study is to stimulate the uptake of the GSHPs. Recent attempts to stimulate alternative energy sources for heating and cooling of buildings has emphasised the utilisation of the ambient energy from ground source and other renewable energy sources. The purpose of this study, however, is to highlight the fact that use of the GSHPs as an environmental friendly technology able to provide efficient utilisation of energy in the buildings sector in an attempt to promote using of the GSHPs for heating and cooling. The paper presents experimental and theoretical results of the DX GSHPs carried out at the Department of Architecture and Built Environment in the University of Nottingham. The study highlights the potential energy cost saving that could be achieved through the use of ground energy sources. It also focuses on the optimisation and improvement of the operation conditions of the heat cycle and performance of the DX GSHP. It is concluded that the direct expansion of the GSHP, combined with the ground heat exchanger in foundation piles and the seasonal thermal energy storage could play a major role reducing building energy needs.