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

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

Optimal sizing of a solar water pumping system for Koyli Alpha Village, Senegal

Our objective is to solve problems of water supply in the village of Koyli Alpha, in Senegal. Theirs boreholes are supplied by diesel fuels causing environmental drawbacks and the populations don’t satisfy their water demand. In order to bring a positive response, we used solar energy to give back the borehole’s autonomous and proposed intuitive and numerical methods applying on solar water pumping for finding the best method. A previous study used intuitive methods for determining the size of various components. In order to optimize the energy production, we propose two numerical sizing approaches in order to have an optimal operation. Then, we developed two solar cell temperature models in the numerical sizing method and did a simulation of system operating in MATLAB software. The first model of solar cell temperature depends only on the ambient temperature and the second one combines wind speed and ambient temperature. The results of simulation showed that among these numerical sizing methods, we choose the second solar cell temperature expression, which gives the best performance. The numerical sizing method which uses the second solar cell temperature model yields to the reduction of battery’s size and the total life cycle cost found in the intuitive method, by 54% and 32%, respectively

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

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

Solid state generators and energy harvesters for waste heat recovery and thermal energy harvesting

This review covers solid state thermal to electrical energy converters capable of transforming low grade heat directly into electricity for waste heat recovery and thermal energy harvesting. Direct solid state heat engines, such as thermoelectric modules and thermionic converters for spatial temperature gradients, are compared with pyroelectric energy harvesters and thermomagnetic generators for transient changes in temperature. Temperature and size limitations along with the maturity of the technologies are discussed based on energy density and temperature range for the different generator technologies. Despite the low energy conversion efficiency with solid state generators, electric power density ranges from 4 nW/mm2 to 324 mW/mm2. The most promising sector to implement changes while reducing the primary energy consumption and saving resources, is the processing industry along with stationary and mobile electronics