Experimental Study of Thermodynamic Assessment of a Small Scale Solar Thermal System

In this study, a scaled solar thermal system, which utilises HFE 7000, an environmentally friendly organic fluid has been designed, commissioned and tested to investigate the system performance. The proposed system comprises a flat-plate solar energy collector, a rotary vane expander, a brazed type water-cooled condenser, a pump and a heat recovery unit. In the experimental system, the flat-plate collector is employed to convert HFE-7000 into high temperature superheated vapour, which is then used to drive the rotary vane expander, as well as to generate mechanical work. Furthermore, a heat recovery unit is employed to utilise the condensation heat. This heat recovery unit consists of a domestic hot water tank which is connected to the condenser. Energy and exergy analysis have been conducted to assess the thermodynamic performance of the system. It has been found that the collector can transfer 3564.2 W heat to the working fluid (HFE 7000) which accounts for the 57.53% of the total energy on the collector surface. The rotary vane expander generates 146.74 W mechanical work with an isentropic efficiency of 58.66%. In the heat recovery unit, 23.2% of the total rejected heat (3406.48 W) from the condenser is recovered in the hot water tank and it is harnessed to heat the water temperature in the domestic hot water tank up to 22.41 ºC which subsequently will be utilised for secondary applications. The net work output and the first law efficiency of the solar ORC is found to be 135.96 W and 3.81% respectively. Exergy analysis demonstrates that the most exergy destruction rate takes place in the flat plate collector (431 W), which is the thermal source of the system. Post collector, it is followed by the expander (95 W), the condenser (32.3 W) and the pump (3.8 W) respectively. Exergy analysis results also show that the second law efficiency of the solar ORC is 17.8% at reference temperature of 15 ºC. Parametric study analysis reveals that both increase in the expander inlet pressure and the degree of superheat enhances the thermodynamic performance of the solar ORC

Experimental investigation of a heat pipe heat exchanger for heat recovery

An air-to-air heat pipe heat exchanger has been designed, constructed and tested. Gravity-assisted wickless heat pipes (thermosiphons) were used to transfer heat from one air stream to another air stream, with a low temperature difference. A thermosiphon heat exchanger has its evaporation zone below the condensation zone. Heat pipes allow keeping a more uniform temperature in the heat transfer area. The heat exchanger consists of 20 copper tubes with circular copper fins on their outer surface. The tubes were arranged in a row and the air passed across the pipes. R245fa was used as a working fluid in the thermosiphons. Each heat pipe had a 40 cm evaporation section, a 20 cm adiabatic section and a 40 cm condensation section. The thermosiphon heat exchanger has been tested in different conditions of air stream parameters (flows, temperatures and humidity). The air face velocity ranged from 1,0 m/s to 4,0 m/s. The maximum thermal efficiency of the thermosiphon heat exchanger was between 26÷40%, depending on the air velocity. The freezing of moisture from indoor air was observed when the cold air temperature was below - 13°C

Cooperation of the Organic Rankine system with a cogeneration steam power plant - case study

The cooperation of the ORC system with a cogeneration steam power plant has been considered. A district heating network is supplied from a bleeder turbine. An ORC system can utilize redundant heat, especially during the summer season, when only domestic hot water needs are served. The aim of the study was a selection of an extraction steam flow to produce the maximum electric power in an ORC system and also to cover the changing heating demand in the district heating network under consideration. Various values of extraction steam flows obtained from the bleeder turbine were considered. For a given extraction steam flow, the optimum ORC size has been adjusted. The average annual efficiency of the ORC was estimated at 0,12 (for the cyclic temperatures 120/35°C). The shortest simple payback time has been estimated at 4 years, assuming that heat from the bleeder turbine meats the heating demand throughout the year and thus the ORC system also operates throughout the year

Organic Rankine Cycles in power generation systems

W referacie przedstawiono możliwości zastosowań układów ORC. Omówiono podstawowe elementy tych układów i sposoby doboru czynników roboczych. Przedstawiono zastosowania obiegów ORC do podniesienia sprawności nowoczesnych układów wytwarzających energię w oparciu o turbiny gazowe, ogniwa paliwowe.The paper presents possible applications of Organic Rankine Cycles (ORC) in decentralized energy generation systems. The basic elements of these systems and methods of working fluid selection were discussed. ORC systems can cooperate with modern power generation systems based on gas turbines and fuel cells to increase their efficiency

Using of solar energy in a small electricity generation system

The paper presents the review of small solar power generation systems, high- and low-temperature. It focused on the study on organic Rankine cycles (ORC). Such a system using the HFC245fa as a working fluid, was constructed and tested experimentally. As a heat source the evacuated solar collectors were used. The ORC system with internal and external heat exchangers was build. The evaporator was heated with the medium circulating in the solar collector loop. Basic elements of the thermodynamic cycle were presented. The problems connected with power generation in such a system were discussed, especially the control and design of the generator and energy storage system. The ORC with heat regeneration has the maximum thermodynamic efficiency about 8% and its power output was about 2 kWel. Considered ORC system can also cooperate with another small heat source (waste heat) with the power input of 20 - 40 kW and the maximum temperature about 100°C

The analysis of the differences between the results of the thermal response test and the data from the operation of the brine-to-water heat pump’s vertical exchanger

The article discusses the principles and the problems of obtaining an accurate data input for the design of brine-to-water heat pump’s vertical exchangers. Currently, the most accurate method is the thermal response test (TRT). Unfortunately, the test procedure has its limitations and the quality of the results depends on many factors that cannot be fully controlled during the test. As an illustration of the problems, the results of the TRT were presented. The test was executed on the vertical boreholes (one actively regenerated and one not actively regenerated during the summer) which are parts of the operating heat pump system. The test results were compared to the data from the device’s operation, in particular with the measurements of the undisturbed ground temperature profiles and the actual unit energy gains from the boreholes. The level of difference between the results of the test and the data from the operation of the boreholes under the real load and the threats concerning the boreholes overload were shown. Additionally the performance differences between the actively regenerated and not actively regenerated boreholes have been emphasised

The analysis of the differences between the results of the thermal response test and the data from the operation of the brine-to-water heat pump’s vertical exchanger

The article discusses the principles and the problems of obtaining an accurate data input for the design of brine-to-water heat pump’s vertical exchangers. Currently, the most accurate method is the thermal response test (TRT). Unfortunately, the test procedure has its limitations and the quality of the results depends on many factors that cannot be fully controlled during the test. As an illustration of the problems, the results of the TRT were presented. The test was executed on the vertical boreholes (one actively regenerated and one not actively regenerated during the summer) which are parts of the operating heat pump system. The test results were compared to the data from the device’s operation, in particular with the measurements of the undisturbed ground temperature profiles and the actual unit energy gains from the boreholes. The level of difference between the results of the test and the data from the operation of the boreholes under the real load and the threats concerning the boreholes overload were shown. Additionally the performance differences between the actively regenerated and not actively regenerated boreholes have been emphasised