Abhijit Date

Comparison between Rankine Cycle and Trilateral Cycle in Binary System for Power Generation

An experimental validation on laboratory scale has been conducted to investigate and to compare two thermodynamic cycles, Trilateral Flash Cycle (TFC) and Organic Rankine Cycle (ORC). The research covers the heat engine utilizing a hydrothermal resource to compare the performance of TFC and ORC. This research would help to analysis the thermal efficiency and power efficiency for both cycles. TFC shows a higher power production than in ORC for the same applied parameters. ORC, however, can be operated at lower rotational speed than for TFC. This project could help, also, to evaluate the current two phase screw expander for both cycles. It is concluded to propose a larger heat exchanger for TFC as the heat recovery can be more reliable in this cycle than in ORC. This research can be applied to generate electrical power from hydrothermal resources such as geothermal energy and solar thermal.

Heat extraction from gradient layer using external heat exchangers to enhance the overall efficiency of solar ponds

A salinity gradient solar pond is a combined solar collector and thermal energy storage system, and in past heat has been successfully extracted from the lower convective zone (LCZ) in working ponds. This paper discusses possibility of heat extraction from the non convective zone (NCZ) using an external heat exchanger. Here, two methods of heat extraction from different levels within the NCZ using external heat exchanger are presented. The first method uses thermosyphon effect to transfer the heat from different levels in NCZ to the binary fluid. The second method uses pumps (forced convection) for heat extraction. This paper presents theoretical modeling and experimental results for thermosyphon based heat extraction method. Later theoretical predictions and experimental results have been compared. This investigation shows good prospects for application of this system for heat extraction from NCZ of large solar ponds. By extracting heat from the NCZ the efficiency of a solar pond could be increased up to 30%.

Experimental Investigation on Effect of Adhesives on Thermoelectric Generator Performance

Thermoelectric generators (TEGs) convert heat energy into electricity. Currently, these devices are attached to heat exchangers by means of mechanical devices such as clamps or fixtures with nuts and bolts. These mechanical devices are not suitable for use in harsh environments due to problems with rusting and maintenance. To eliminate the need for such mechanical devices, various kinds of adhesives used to attach thermoelectric generators to heat exchangers are investigated experimentally in this work. These adhesives have been selected based on their thermal properties and also their stability to work in harsh environments to avoid damage to the integrity of the attachment over long periods of time. Stainless-steel plates were attached to a thermoelectric generator using the adhesives. The introduction of the adhesive as a means of attachment for thermoelectric generators contributes to increase the thermal resistance to heat transfer across the TEG. The adhesive layers increased the thermal resistance of the thermoelectric generator by 16% to 109%. This work examines the effect of the adhesives on the thermal performance and power output of a single thermoelectric generator for various heat inputs.

Experimental investigation of power generation from salinity gradient solar pond using thermoelectric generators for renewable energy application

Low grade heat (<100°C) is currently converted into electricity by organic rankine cycle (ORC) engines. ORC engines require certain threshold to operate as the organic fluid generally boils at more than 50°C, and fails to operate at lower temperature. Thermoelectric generators (TEGs) can operate at very low temperature differences and can be good candidate to replace ORC for power generation at low temperatures. In this paper, the potential of power generation from TEG and salinity-gradient solar pond (SGSP) was investigated. SGSP is capable of storing heat at temperature up to 80°C. The temperature difference between the upper convective zone (UCZ) and lower convective zone (LCZ) of a SGSP can be in the range of 40°C 60°C. This temperature difference can be used to power thermoelectric generators (TEG) for electricity production. This paper present result of a TEG system designed to be powered by the hot and cold water from the SGSP. The system is capable of producing electricity even on cloudy days or at night as the SGSP acts as a thermal storage system. The results obtained have indicated significant prospects of such system to generate power from a low grade heat for remote area power supply.

Investigation of Thermal Performance of a Solar Pond With External Heat Addition

This study addresses the method of adding heat to a salt gradient solar pond (SGSP) from external sources and investigates the thermal performance of the pond. In this case, the external heat source is solar heat collected by evacuated tube solar collectors (ETSC), and collected heat is transferred to the lower-convective zone (LCZ) of the SGSP by circulating fluid from the LCZ. Results show that heat addition from the external source enhances the thermal performance of the SGSP in terms of heat recovery and thermal efficiency but with certain constraints. The heat addition efficiency reduces with increase in aperture area of the ETSC. Also with increasing heat addition, the heat removal from the SGSP has to be increased; otherwise, the SGSP efficiency reduces rapidly. Heat removal from SGSP has to be performed keeping in mind the heat demand and the quality of heat. The latter reduces with an increase of heat extraction beyond a certain limit. Hence, optimizing the range of parameters in case of adding heat from external sources is very important for the best performance of a SGSP.

Experimental Analysis of Thermoelectric Heat Exchanger for Power Generation from Salinity Gradient Solar Pond Using Low-Grade Heat

Salinity gradient solar ponds act as an integrated thermal solar energy collector and storage system. The temperature difference between the upper convective zone and the lower convective zone of a salinity gradient solar pond can be in the range of 40–60°C. The temperature at the bottom of the pond can reach up to 90°C. Low-grade heat (<100°C) from solar ponds is currently converted into electricity by organic Rankine cycle engines. Thermoelectric generators can operate at very low temperature differences and can be a good candidate to replace organic Rankine cycle engines for power generation from salinity gradient solar ponds. The temperature difference in a solar pond can be used to power thermoelectric generators for electricity production. This paper presents an experimental investigation of a thermoelectric generators heat exchanger system designed to be powered by the hot water from the lower convective zone of a solar pond, and cold water from the upper convective zone of a solar pond. The results obtained have indicated significant prospects of such a system to generate power from low-grade heat for remote area power supply systems.

Theoretical analysis to determine the solar concentration limit with passive cooling of solar cells

This re search was conducte d to de te rmine the limiting values of the ge ome tric concentration whe n use d with solar thermal system (the rmoe lectric ge nerator) (TEG) to maintain desir ed hot and cold side te mpe ratures for powe r ge neration. An optimum heat sink fin gap is conside re d to achieve maximum heat transfer rate using passive cooling. A theore tical mode l is de ve lope d for de termining the optimum solar concentration using a the rmoe lectric ge nerator sandwiche d be twee n the targe t p late and passive cooling heat sink. The rmal resistance and Seebeck coefficie nt of a thermoe lectric ge nerator unde r conside ration is ex pe rimentally de te rmine d. Heat flow path for this syste m is de fine d and e nergy balance e quations are establishe d. A computer mode l is de ve lope d to solve the en ergy balance equations and find the optimum value s for geome tric conce ntration and hot & cold side tempe rature of thermoe lectric ge nerator. It was obse rve d that for the specific configuration of heat sink and thermoe le ctric ge ne rator in a sy stem, the tre nd of te mperature differe nce be twee n the hot and cold sides re main the same at diffe rent heat input conditions. The optimum ge ome tric conce ntration for solar radiation inte nsity of 800 W/m2 and heat sink fin le ngth of 0.15m is pre dicte d to be 13. The the ore tical mode l is capable of optimizing the values of geome tric conce ntration for desire d hot side or cold side tempe rature .

Humidification-dehumidification desalination cycle

Abstract Water availability is an essential requirement for continuing human life on Earth. With the increasing world population and rapid industrial growth in some regions of the world, the demand for freshwater has increased significantly over the past decade. The availability of freshwater in many densely populated regions is a critical issue for socioeconomic stability. Seawater or brackish water desalination using solar energy can offer a solution for some of these areas. The humidification-dehumidification (HDH) desalination cycle is one of these technologies for producing freshwater from seawater or salty water for small-scale and remote area applications. The major form of energy needed for the technology is a low-temperature thermal energy that can be provided by sources such as industrial waste heat, solar thermal, geothermal, etc. This chapter is divided into the following subsections: HDH desalination, working principle, theoretical analysis method, humidifier and dehumidifier, heat sources, applications.

Effectiveness of bottom insulation of a salinity gradient solar pond

This technical brief presents a study on the effectiveness of the bottom insulation of a salinity gradient solar pond (SGSP) in Melbourne, Australia. Insulation is applied at the bottom of a SGSP in order to minimize the heat loss from the SGSP to the ground underneath. But selection of optimum thickness of the insulation to extract the best thermal performance of an SGSP is a challenge as insulation involves significant investment. Hence, modeling heat loss from SGSP to the ground before and after applying the insulation is thus very essential. In this study, a layer of polystyrene is used as insulation at the bottom of SGSP. The temperature distribution in the SGSP and ground below it, the efficiency of the SGSP and the heat removal from SGSP are estimated for the SGSP without insulation and with insulation of different thicknesses. The results show that the insulation definitely reduces the heat loss from the SGSP to the ground, but to a certain extent. Insulation beyond a certain thickness is proved to be ineffective in increasing the efficiency or reducing the heat loss to ground and thus unable to enhance the thermal performance of the SGSP.

Sustainable desalination by permeate gap membrane distillation technology

Abstract Membrane distillation (MD) as a thermally driven process with moderate operating temperatures is a known effective technology for saltwater desalination. In this chapter, the permeate gap membrane distillation (PGMD) configuration, as a novel sustainable MD design having internal heat recovery characteristics, is introduced and numerical modeling of the heat and mass transfer phenomena in this configuration is studied. To investigate the efficiency of the PGMD system, the results of two experimental projects are described one a laboratory-scale flat PGMD rig, which was developed at RMIT University, and the other, for commercial-scale PGMD modules, which was developed by the Franhaufer Institute. Moreover, in this chapter, a literature survey is included based on recent case studies involving MD integrated with different sources of solar energy and those driven by waste heat. The chapter is completed by a general techno-economic feasibility study of PGMD systems.