Review of experimental research on supercritical and transcritical thermodynamic cycles designed for heat recovery application

Supercritical operation is considered a main technique to achieve higher cycle efficiency in various thermodynamic systems. The present paper is a review of experimental investigations on supercritical operation considering both heat-to-upgraded heat and heat-to-power systems. Experimental works are reported and subsequently analyzed. Main findings can be summarized as: steam Rankine cycles does not show much studies in the literature, transcritical organic Rankine cycles are intensely investigated and few plants are already online, carbon dioxide is considered as a promising fluid for closed Brayton and Rankine cycles but its unique properties call for a new thinking in designing cycle components. Transcritical heat pumps are extensively used in domestic and industrial applications, but supercritical heat pumps with a working fluid other than CO2 are scarce. To increase the adoption rate of supercritical thermodynamic systems further research is needed on the heat transfer behavior and the optimal design of compressors and expanders with special attention to the mechanical integrity

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 investigations into power generation with low grade waste heat and R245fa Organic Rankine cycles (ORCs)

In this study, experimental research was conducted to investigate the performance of a small-scale Organic Rankine Cycle (ORC) system utilising low grade heat sources to generate electric power at different operating conditions. The experiment setup consisted of typical ORC system components, such as a turboexpander with high speed generator, finned-tube condenser, ORC pump and plate evaporator. R245fa was selected as a working fluid in the experimental system, considering its appropriate thermosphysical properties for the ORC system and low ozone depletion potential (ODP). At constant heat sink (ambient) parameters, extensive experiments were carried out to examine the effects of various important parameters including heat source temperature and working fluid pump speed etc. on system performance. Results showed that at a fixed working fluid speed, the thermal efficiency of the tested ORC system could be improved with an increased heat source temperature. On the other hand, at a constant heat source temperature, the working fluid pump speed could be optimised to maximise system thermal efficiency. Both the heat source temperature and ORC pump speed were found to be important parameters in determining system thermal efficiency and the component operations. The experimental outcomes can instruct future optimal system design and controls

Design and optimisation of organic Rankine cycles for waste heat recovery in marine applications using the principles of natural selection

Power cycles using alternative working fluids are currently receiving significant attention. Selection of working fluid among many candidates is a key topic and guidelines have been presented. A general problem is that the selection is based on numerous criteria, such as thermodynamic performance, boundary conditions, hazard levels and environmental concerns. A generally applicable methodology, based on the principles of natural selection, is presented and used to determine the optimum working fluid, boiler pressure and Rankine cycle process layout for scenarios related to marine engine heat recovery. Included in the solution domain are 109 fluids in sub and supercritical processes, and the process is adapted to the properties of the individual fluid. The efficiency losses caused by imposing process constraints are investigated to help propose a suitable process layout. Hydrocarbon dry type fluids in recuperated processes produced the highest efficiencies, while wet and isentropic fluids were superior in non-recuperated processes. The results suggested that at design point, the requirements of process simplicity, low operating pressure and low hazard resulted in cumulative reductions in cycle efficiency. Furthermore, the results indicated that non-flammable fluids were able to produce near optimum efficiency in recuperated high pressure processes

Experimental characterization of an ORC (organic Rankine cycle) for power and CHP (combined heat and power) applications from low grade heat sources

An ORC (organic Rankine cycle) module, designed and built for a specific CHP (combined heat and power)) application, is tested in this paper. The aim of the work is to characterize the system performance in the operating range allowed by the ORC. For this purpose, a test procedure has been conducted in a test bench. The heat source has been simulated through a natural gas boiler and a thermal oil heat transfer loop to control the temperature in the low grade range of 90 °C 150 °C. The heat sink has been developed using a dry cooler to control the hot water temperature in the range of 30 °C, corresponding to a power application, to 80 °C, of a small-scale CHP application that provides hot water at 90 °C. Thereby, the results show that the thermal power captured by the ORC, electricity and useful heat produced, increase with the rise of the thermal oil temperature and larger pressure ratios. Moreover, the expander electrical isentropic effectiveness is maximized about 70% for a pressure ratio suitable for a CHP system. The cycle efficiency slightly continues increasing for higher pressure ratios, up to a net electrical efficiency of about 8%.The authors want to acknowledge all the invaluable cooperation of Rank (R), the ORC manufacturer, for its support in this project. Also to thank greatly the Jaume I University for its financial support under the PhD grant PREDOC/2013/28 of 'Convocatoria d'ajudes predoctorals per a la formacio de personal investigador del Pla de promocio de la investigacio de la Universitat Jaume I de Castello (Spain)'.Peris Pérez, B.; Navarro Esbri, J.; Molés Ribera, F.; González, M.; Mota Babiloni, A. (2015). Experimental characterization of an ORC (organic Rankine cycle) for power and CHP (combined heat and power) applications from low grade heat sources. Energy. 82:269-276. https://doi.org/10.1016/j.energy.2015.01.037S2692768

Experimental study of an ORC (organic Rankine cycle) for low grade waste heat recovery in a ceramic industry

This paper deals about an experimental application of an ORC (organic Rankine cycle) in a ceramic industry for low grade waste heat recovery. The ORC module used in this application was initially designed and constructed to satisfy the main specifications for an efficient power system, highlighting a volumetric expander with large built-in volume ratio. Furthermore, the performance of the ORC was experimentally characterized in a test bench in a previous work, achieving a maximum gross electrical efficiency of 12.32%. Taking this as a starting point, the aim of this work is to verify the performance of this ORC operating in actual industrial conditions, besides to profiting the information extracted from the application to assess its profitability. For this, the system performance is experimentally characterized in the industry, discussing and comparing the results obtained to laboratory data. From these experimental results a model of the system is developed, which allows predicting the net electrical production of the system along a typical year of operation and quantifying the energy and environmental benefits of the project. Moreover, from the electrical generation, investment costs required and industrial electricity price, a feasibility study is conducted to address the profitability of the application.The authors are indebted to the Minister of industry of 'Generalitat Valenciana' (Spain) for its financial assistance under project INIDIV2010022 and Rank (R), the ORC manufacturer, for its support in this project. Also to thank greatly the Jaume I University for its financial support under the PhD grant PREDOC/2013/28 of 'Convocatoria d'ajudes predoctorals per a la formacio de personal investigador del Pla de promocio de la investigacio de la Universitat Jaume I de Castello (Spain)'.Peris, B.; Navarro-Esbri, J.; Moles, F.; Mota Babiloni, A. (2015). Experimental study of an ORC (organic Rankine cycle) for low grade waste heat recovery in a ceramic industry. Energy. 85:534-542. https://doi.org/10.1016/j.energy.2015.03.065S5345428