Organic Working Fluids Research Articles

Experimental study on flow boiling characteristics of R-245fa in circular tube under non-uniform heat flux

The direct vapor generation with parabolic trough solar collector utilizing organic working fluids has a significant potential of large-scale application. In such a system, the non-uniform heat flux commonly exists outside the collector tube which would result in the unique characteristics of two-phase flow and moreover boiling heat transfer. However, few studies pay attention to the effects of the non-uniform heat flux on flow pattern transitions and flow boiling, which have important influence on the long-term stable operation of the system. Therefore, in this study, an experimental system was established to study the two-phase flow boiling of R-245fa in a horizontal tube under the condition of the non-uniform heat flux. The experiment was performed with the mass flow rate from 192.9 to 385.8 kg/(m2 s), heat fluxes from 9.95 to 35.9 kW/m2 and saturation temperatures from 40 to 60 °C. Using a high-speed camera and the image processing, the differences between the flow pattern with non-uniform and uniform heating were analyzed. A comparison study on four available flow pattern I/A transition lines in the literature has been demonstrated as well. The effects of vapor quality, mass velocity, saturation temperature and heat flux on the two-phase heat transfer coefficient were analyzed. Furthermore, based on the experimental data, the correlation of boiling heat transfer of R245fa under non-uniform heat flux was developed. The results indicate that under the same heat addition, the vapor quality where the non-uniform I/A phase transition is lower than the uniform one. Furthermore, the non-uniform heat flux makes R245fa in the tube easier to form nucleation sites, therefore the nucleation boiling can be significantly enhanced. Taking account of the strengthening factor “S” of nucleate boiling, the new correlation of boiling heat transfer can reproduce 94% of data sets under non-uniform heat flux within the uncertainty of ±20%.

Experimental investigation and performance analysis of an Organic Rankine Cycle for low-temperature heat to electricity generation

Abstract This paper presents experimental investigation of low-temperature heat to electricity generation system based on Organic Rankine Cycle (ORC) using R152a as the working fluid. Both energy efficiency and exergy efficiency were analyzed based on the experiments. Although energy efficiency was low to 5.0% when the evaporating and cooling temperatures were 65°C and 11°C, respectively, the exergy efficiency reached 25%, which showed great competitiveness among low-temperature heat utilization technologies. To reveal the energy recovery proportion from the waste heat, both energy extraction efficiency and exergy extraction efficiency as well as energy and exergy loss paths were analyzed. When the heat source was 65°C, 14.9% of the maximum possible thermal energy in the heat source was absorbed by the organic working fluid, and 10.7% was transferred to the cooling medium. The power output contributed 0.64%. A total of 1.8% of the exergy in the heat stream flowed to the cooling medium. The start-up work takes dramatically 0.16% and 1.7% of energy and exergy, respectively. Other energy and exergy loss occurs due to the irreversibility of the heat transfer process and expansion process. Cascade ORC system could enlarge the temperature difference of the heat stream and raise the power output. However, the energy efficiency of the multi-stage ORC system is lower than single-stage system, since there was a downward trend of the temperature of heat source for the latter stage. ORC cycle can lower the temperature of heat source to 45°C.

Environmental and energy assessment of a small-scale solar Organic Rankine Cycle trigeneration system based on Compound Parabolic Collectors

During the last years, combined cooling, heating, and power (CCHP) systems have drawn a lot of attention thanks to their low greenhouse gas (GHG) emissions, high efficiency and cost benefits. Considering the increasing interest on sustainability assessment of novel energy generation technologies, in this paper a life cycle assessment of an innovative small-scale solar Organic Rankine Cycle (ORC) trigeneration plant is performed.The plant under investigation is composed of a 50 m2 Compound Parabolic Collectors (CPC) solar field, a 3 m3 diathermic oil storage tank, a 3.5 kWe ORC plant and a 17 kWc absorption chiller. After the set-up of the inventory data of the different subsystems, a sensitivity analysis of the environmental and energy performance of the plant has been conducted by varying: (i) the system adjustment parameters; (ii) the size of the solar field and the consequent solar multiple index of the plant; and (iii) the organic working fluid of the ORC unit. Results of the analysis confirmed that the Life cycle assessment (LCA) is of paramount importance for the appropriate selections of component specifications and operating conditions of the integrated system. In particular, the investigation has revealed that the variation of the adjustment parameters brings to slight modifications of the energy performance and has a limited impact on the environmental output whilst the proper selection of the working fluid and the size of the solar field can result in an appreciable environmental optimization of the whole plant.

Selection and Evaluation of Dry and Isentropic Organic Working Fluids Used in Organic Rankine Cycle Based on the Turning Point on Their Saturated Vapor Curves

The organic Rankine cycle (ORC) is a popular technique used in the utilization of low-grade thermal energy. Among wet, dry, and isentropic organic working fluids, the latter two types are more appropriate for ORC systems. In this paper, the definition of turning point on saturated vapor curve of dry fluid and isentropic fluid was given according to the shape of the saturated curve of working fluids in a T-s diagram. On this basis, the model of near-critical region triangle was established. Using this model, the thermodynamic performance of 57 kinds of dry and isentropic organic working fluids in ORC was evaluated. The performance includes the relation between turning point temperature and cycle thermal efficiency, the relation between near-critical region triangle area and cycle thermal efficiency, the relation between near-critical region triangle area and exergy at turning point temperature, the relation between near-critical region triangle area and reciprocal value of slope of saturated vapor curve. Moreover, working fluid selection was also conducted in terms of heat source type. It was found through theoretical analysis results that the popular R123 is an acceptable choice especially for the utilization of closed type heat source. Considering it will be phased out in near future, then cis-butene, butane, trans-butene, and isobutene are worth studying as its successor. Dodecane is worthy of attention and further research and it can be a good choice for utilization of open type heat source.

Analysis of a hybrid (topping/bottoming) ORC based CHP configuration integrating a new evaporator design concept for residential applications

The recommended design principles for the development of evaporators for ORC based micro-CHP systems attempting to retrofit the current combi-boilers are presented and discussed in this paper. From those principles, among which is the need of organic fluid direct vaporization, emerged a hybrid (topping/bottoming) CHP configuration in which the thermal energy is produced stepwise: firstly in the ORC-condenser and then in a post-heater, that is integrated on the ORC-evaporator, directly with the combustion gases. A model of this configuration was developed to determine the fraction of the CHP water heating process performed in the post-heater that maximizes the primary energy savings and ORC net power output for a wide range of CHP operating conditions. When compared to a standard CHP configuration, this solution show benefits for the greater part of those conditions. Besides solving the safety issue posed by the ORC-evaporator requirements and the performance benefits shown, this configuration has an additional positive side effect: the decrease of the combustion gases’ temperature before they reach the organic working fluid heat-exchanger section in the ORC-evaporator that leads to a reduction of the risk of the working fluid thermal degradation.

Comparison of single and double stage regenerative organic rankine cycle for medium grade heat source through energy and exergy estimation

Regenerative organic Rankine cycle (RORC) can be used to improve organic Rankine cycle (ORC) performance. This paper presents a comparison of a single (SSRORC) and double stage regenerative organic Rankine cycle (DSRORC) using a medium grade heat source. Performance for each system is estimated using the law of thermodynamics I and II through energy and exergy balance. Solar thermal is used as the heat source using therminol 55 as a working fluid, and R141b is used as the organic working fluid. The initial data for the analysis are heat source with 200°C of temperature, and 100 L/min of volume flow rate. Analysis begins by calculating energy input to determine organic working fluid mass flow rate, and continued by calculating energy loss, turbine power and pump power consumption to determine net power output and thermal efficiency. Exergy analysis begins by calculating exergy input to determine exergy efficiency. Exergy loss, exergy destruction at the turbine, pump and feed heater is calculated to complete the calculation. Energy estimation result shows that DSRORC determines better net power output and thermal efficiency for 7.9% than SSRORC, as well as exergy estimation, DSRORC determines higher exergy efficiency for 7.69%. ©2019. CBIORE-IJRED. All rights reserved

Investigation of an efficient and environmentally-friendly CCHP system based on CAES, ORC and compression-absorption refrigeration cycle: Energy and exergy analysis

Combined cooling heating and power (CCHP) is a promising energy supply technology which is widely installed in buildings due to its feasibility from techno-economic, performance and environmental points of view. In present paper, a novel cogeneration system based on compressed air energy storage (CAES), organic rankine cycle (ORC) and hybrid compression-absorption refrigeration cycle is proposed. The main objective of the proposed system is to improve the efficiency of the CAES system by providing cooling capacity from the rest of hot gases in turbine exhaust through employing an ORC driven refrigeration system. Also, the effect of the maximum to minimum pressure ratio of CAES vessel as a critical parameter on CAES volume and round trip efficiency (RTE) has been scrutinized. Using the environmentally-friendly compression-absorption refrigeration system, high temperature thermal energy storage (HTES) and R407C as the organic working fluid decrease fossil fuel consumption and make the proposed system fully environmentally-friendly. The results indicate that 2280 kW electrical energy and 416.7 kW cooling capacity are simultaneously generated during peak period. As a result, with 13.15% RTE enhancement in comparison to the individual CAES system, it reaches to 65.15% based on the proposed modification. Also, the results show that the overall exergy efficiency and total exergy destruction of the components are 49.17% and 1419 kW, in which the pressure regulating valve and the air turbine have the highest irreversibility and exergy destruction.

Design and manufacturing of organic rankine cycle (orc) system using working fluid r-134a with helical evaporator and condenser

Waste heat from industries such as steam power plants can be utilized to meet the world’s electricity need. However, it cannot be converted efficiently to electric power by using conventional power generation methods as opposed to a technology called Organic Rankine Cycle (ORC). ORC is one of the power plant systems that is a modification of the Rankine Cycle using organic working fluid. In this research, ORC was designed and manufactured using R-134a as working fluid and helical heat exchanger as evaporator and condenser. The design of ORC systems based on simulation using Cycle Tempo 5.0 with evaporator temperature of 90°C, condenser temperature of 10°C, inlet pressure of pump of 0.55 MPa, and inlet pressure of turbine of 0.79 MPa. The results of this study showed the length of tube evaporator and condenser of 10.61 m and 10.56 m, respectively, with system efficiency achieved at 3.8%. Based on experiment, with evaporator temperature of 95°C, condenser temperature of 10°C, inlet pressure of pump of 0.48 MPa and inlet pressure of turbine of 0.52 MPa so resulted of system efficiency of 3.33%.

ПАРАМЕТРИЧЕСКИЙ АНАЛИЗ СХЕМЫ ПАРОГАЗОВОЙ УСТАНОВКИ С КОМБИНАЦИЕЙ ТРЕХ ЦИКЛОВ ДЛЯ ПОВЫШЕНИЯ КПД ПРИ РАБОТЕ В СЕВЕРНЫХ ГАЗОДОБЫВАЮЩИХ РАЙОНАХ

Актуальность. Парогазовые установки рассматриваются как одно из перспективных направлений развития теплоэнергетических установок, работающих на природном газе. Интерес к их внедрению в России объясняется большими запасами природного газа, низкими капиталовложениями и минимальными выбросами вредных веществ в окружающую среду. Из термодинамики известно, что для достижения высокого КПД цикла необходимо иметь высокую температуру подвода теплоты и низкую температуру ее отвода, а также обеспечить работу оборудования с минимальными внутренними потерями и иметь рациональную тепловую схему взаимосвязи оборудования в цикле. На современном этапе максимальная температура подвода теплоты в камере сгорания газотурбинной установки при существующих конструкционных материалах и способах охлаждения элементов турбины достигла 1600 °С, а температура отвода теплоты в конденсаторе при работе цикла Ренкина на воде по условиям экономичности не может быть ниже 15 °С. При этих условиях на наиболее совершенных трехконтурных парогазовых установках с промежуточным перегревом пара достигнут электрический КПД 63 %. Для цикла Ренкина при работе на воде температура конденсации пара по условию замерзания должна быть выше 0 °С. Для парогазовой установки при работе в условиях низких среднегодовых температур окружающей среды, что характерно для России и особенно отдаленных северных районов добычи газа, можно отводить теплоту в цикле Ренкина значительно ниже 0 °С, но это надежно можно выполнить только применяя конденсаторы с воздушным охлаждением, если в качестве рабочего тела в цикле Ренкина использовать органическое рабочее тело. Недостатком современных органических рабочих тел является низкая предельная температура их термического разложения, которая составляет 300…400 °С. Объект: парогазовые установки с циклами на трех рабочих телах, где верхний цикл Брайтона работает на продуктах сгорания природного газа, средний – цикл Ренкина – работает на воде и водяном паре в интервале температур 100…650 °С, а нижний – Органический цикл Ренкина – работает на органических рабочих телах в интервале температур –30…250 °С. Цель: выбор рациональной технологической схемы парогазовой установки c применением циклов на трех рабочих телах и воздушного конденсатора для возможности надежного отвода теплоты от органического рабочего тела при температуре ниже 0 °С и определение оптимальных параметров циклов. Методы. Сложные теплоэнергетические системы, включая парогазовые установки, характеризуются многообразием процессов, протекающих в их элементах. Такие установки можно эффективно исследовать только с помощью методов математического моделирования и оптимизации. При проведении исследований в данной работе использован системный подход, методы энергетических балансов и расчет термодинамических и теплофизических параметров рабочих тел с помощью современных сертифицированных программ. Результаты. Разработана оригинальная схема парогазовой установки утилизационного типа с циклами на трех рабочих телах, где верхний цикл Брайтона работает на продуктах сгорания природного газа, средний цикл Ренкина работает на воде и водяном паре, нижний – Органический цикл Ренкина – работает на органическом рабочем теле с конденсацией его в воздушном конденсаторе. Разработана математическая модель и программа расчета предложенной схемы. Определено наиболее эффективное органическое рабочее тело для нижнего цикла Ренкина. Проведен параметрический анализ влияния основных параметров циклов на КПД брутто и нетто парогазовой установки.

Parametric Study of Combined Cooling and Power (CCP) Plant Integrated with Parabolic Trough Solar Collectors (PTSCs)

This study presents a detailed energy analysis of a Combined Cooling and Power (CCP) plant operated by Parabolic Trough Solar Collectors (PTSCs). The integrated cycles; Vapor Absorption Refrigeration Cycle (VARC) and Organic Rankine Cycle (ORC) are used to produce cooling and power, respectively. Six organic working fluids, namely, R113, R141b, R123, R245fa, R142b, and isobutane were selected for ORC, while LiBr-H2O solution used in VARC. Four key energetic parameters, useful heat gain, work output, cooling rate, and energy utilization factor (EUF) were examined during varying direct normal irradiance (DNI). A parametric study was carried out in three modes of operation, power only, combined power and cooling and cooling only under the limits of DNI from 0.6 kW/m2to 0.88 kW/m2recorded on the yearly-average basis in two cities of Pakistan, Lahore, and Quetta respectively. Results enunciated that R113 given the highest thermal efficiency of 17.12%, while isobutane gave the least thermal efficiency of 7.88%, hence R113 was chosen as organic working fluid for further study. The maximumEUF was found in the cooling mode of operation which increased from 63.95% to 66.79% at 0.6 kW/m2 and 0.88 kW/m2 respectively. During the combined cooling and power mode, maximum cooling rate, power output, and EUF were 3456 kW, 822.5 kW, and 41.34% respectively at 0.88 kW/m2.

Experimental and numerical investigation of direct liquid injection into an ORC twin-screw expander

The Organic Rankine Cycle (ORC) is a thermal engine, which is used to convert low temperature heat to electrical power using organic working fluids. It is an established technique for waste heat recovery and for the utilization of renewable heat. This study presents a novel operational strategy of an ORC, which allows for reliable control of process parameters while simultaneously ensuring high power output. Preheated liquid working fluid is injected directly into a volumetric screw expander at an intermediate pressure level. The injected mass flow bypasses the evaporator and can be controlled by a valve. Thus, direct liquid injection into the expander reduces the exhaust temperature, leading to a lower risk of thermal damages in case of a hermetic or semi-hermetic expander. This strategy is analyzed experimentally and compared with a system simulation. The experimental and simulation results show that the exhaust vapor temperature can be reduced by approx. 40 K for the investigated operational conditions. This enables the expander to run at higher live vapor conditions by simultaneously ensuring sufficient cooling of the generator and thus allows for up to 40% higher power production depending on the operational conditions.

Thermodynamic Investigation of an Integrated Solar Combined Cycle with an ORC System.

An integrated solar combined cycle (ISCC) with a low temperature waste heat recovery system is proposed in this paper. The combined system consists of a conventional natural gas combined cycle, organic Rankine cycle and solar fields. The performance of an organic Rankine cycle subsystem as well as the overall proposed ISCC system are analyzed using organic working fluids. Besides, parameters including the pump discharge pressure, exhaust gas temperature, thermal and exergy efficiencies, unit cost of exergy for product and annual CO2-savings were considered. Results indicate that Rc318 contributes the highest exhaust gas temperature of 71.2℃, while R113 showed the lowest exhaust gas temperature of 65.89 at 800 W/m2, in the proposed ISCC system. The overall plant thermal efficiency increases rapidly with solar radiation, while the exergy efficiency appears to have a downward trend. R227ea had both the largest thermal efficiency of 58.33% and exergy efficiency of 48.09% at 800W/m2. In addition, for the organic Rankine cycle, the exergy destructions of the evaporator, turbine and condenser decreased with increasing solar radiation. The evaporator contributed the largest exergy destruction followed by the turbine, condenser and pump. Besides, according to the economic analysis, R227ea had the lowest production cost of 19.3 $/GJ.

Experimental Study Of R141b Flow Boiling Compact Evaporator in Organic Rankine Cycle for Waste Heat Recovery

Indonesia is one of country that has plenty geothermal energy resource. Because of the significant potential, the energy can be used as a power plant. Geothermal resource with low pressure and temperature can be used in Organic Rankine Cycle (ORC) technology. ORC is one of power plant system which can use waste energy by using organic working fluid or refrigerant that is able to evaporate at low pressures and temperatures . In this research, experimental of evaporator by using the organic Rankine cycle system from the gas stove heat source.The experimental study was conducted by experimenting of evaporator Compact Heat Exchanger continuous fin type. For know typical of heat transfer, evaluation proses make three region, subcooled, evaporation and superhaet. The prediction of the Two phase change flow pattern was observed in detail against the effect of heat flux and mass velocity variations by Chen and Shah Correlation. The phase change process occurs under pressure conditions P = 5 bar where the saturation temperature is 86.9 oCFrom the calculation and analysis, the maximum rate of heat transfer is 17.345 kW at 468 kg/m2s and heat flux 83 kW/m2. The evaporation process occurs at temperatures above 95 oC. Internal tube heat transfer coefficient of two-phase convection with consideration of the highest nucleate boiling and convective boiling of the evaporator was 2443.69 W/m2K in 234 kg/m2s mass flux refrigerant. Heat Flux with 1.94 kW/m2 heaten (Chen's Methode) and from the result of analysis proposed by Shah's Methode was obtained 1624.90 W/m2K in 468 kg/m2s mass flux refrigerant and 1.94 kW/m2 heat flux. the value of convection coefficient varies to the value of heat flux, mass flux and quality vapor

Absorption refrigeration processes with organic working fluid mixtures- a review

The presented work includes a detailed review of organic working fluid mixtures and corresponding Absorption Refrigeration (ABR) cycles available in published literature. Such processes are important as they enable exploitation of cleaner and renewable energy sources for cooling generation. Research efforts may be benefited by a systematically organized account of previous works in organic working fluids, which have received considerably less attention than conventional inorganic options. The reviewed developments are separated into working fluids used in single effect cycles and alternative configurations such as double effect, half effect and so forth. Details are reported regarding the operating conditions tested, the criteria used for working fluid selection and the ones selected as desirable options either experimentally or in simulation studies. Research on thermodynamics of organic working fluids suitable for ABR processes is also reported with respect to measured properties, experimental conditions and types of thermodynamic models. The characteristics of different process flowsheets are also analyzed, while commercial scale ABR applications are reported to motivate research in industrial/commercial scale systems. It is observed that there are few types of chemical groups repeated in working fluid investigations, with halogenated refrigerants and ether- and amide-based absorbents prevailing compared to other substances. Most experimental works pertain to single effect systems, with model-based approaches mainly used due to introduction of increasingly complex process modifications. The latter have been assessed with considerably fewer different fluid options compared to single effect systems. Thermodynamic investigations mainly combine experiments with parameter estimation for model development. Most works derive data and employ the NRTL activity coefficient model, often combined with cubic equations of state.

A study of brine supply system to binary cycle unit at Namora I Langit Geothermal power plant

The geothermal binary cycle’s power plant is formed by two cycles. The primary cycle that contains the geothermal fluid and the secondary cycle in which the organic working fluid is enclosed. The geothermal fluid can either be water or steam. In Namora I Langit Integrated Geothermal Combined Cycle Power Plant if its water is called brine unit and if its steam is called bottoming unit. Main issues to consider in binary cycle unit are corrosion, scaling, fouling, working fluid flammability, cascade use/cogeneration, vapour plume, large footprint and noise emissions from the fans in case of air cooling. This paper is focus on corrosion, scaling and fouling on surface equipment facility. As we know, the heat exchanger transfers heat from the brine to the working fluid in the pre heater and evaporator. Brine flows through the tube and working fluid in the shell tube. The problems found in the heat exchanger are corrosion, scaling and fouling. Because of that, for a heat exchanger can function properly, a lot of work should be made to mitigate scaling and fouling. This paper presents a study of brine supply system at Namora I Langit geothermal power plant. How the equipment, method and operation that used at brine line can deliver brine which is appropriate with binary unit.

Thermodynamic and economic analyses of a hybrid waste-driven CHP–ORC plant with exhaust heat recovery

A smart hybrid power plant comprising a waste-fired CHP (combined heat and power) plant accompanied by a small-scale organic Rankine cycle was recently designed and analyzed thermodynamically. The objective of this hybridization is to maximize the share of electricity production of waste-CHP plants rather than a higher heat production rate in a cost-effective manner. In this work, utilization of the exergy of the hot flue gas of the waste-fired CHP unit in order to increase the potential of the organic Rankine cycle for maximizing the net power output of the hybrid cycle is proposed and techno-economically analyzed. In addition, the effect of using alternative environmentally-friendly organic working fluids on the performance of the system was investigated. The results of the study show that by the flue gas potential utilization of the same CHP unit, the size of the organic Rankine cycle may increase significantly, leading to a larger power output of the plant. As such, the net exergy and energy efficiency values of the combined plant in various operational conditions are improved compared to its primary configuration by, respectively, about 10% and 20%, when both of the main CHP cycle and the organic Rankine cycle are working at nominal load. In addition, this exergy utilization is beneficial economically as well, decreasing the payback period of the parallelization project by about 10% (from 7.4 years to 6.7 years). The alternative organic working fluid does not make a significant change in the technical and economic performance indices of the system.

Working fluid selection for a combined system based on coupling of organic Rankine cycle and air source heat pump cycle

Abstract The performance of thermodynamic cycle strongly depends on the properties of working fluids. A gas-fuelled hot water system based on coupling of an organic Rankine cycle and an air source heat pump cycle (ORC-ASHP) was investigated in this paper. This system is integrated with a gas burner to provide heat for ORC. The power generated in ORC is used to drive the air source heat pump cycle. Comparisons on the system performance are presented for seven different organic working fluids, with emphasis on the effect of thermodynamic properties of the working fluids. In terms of fuel-to-heat efficiency, benzene, toluene and cyclohexane have better performance for the high temperature heat source. The results indicate that working fluids presenting higher decomposition temperatures shows a higher fuel-to-heat-efficiency. When benzene is used as working fluids, the fuel-to-heat efficiency reaches 161.7% and 139.47% to provide 50 °C and 65 °C hot water respectively.

A Simple Method of Finding New Dry and Isentropic Working Fluids for Organic Rankine Cycle

One of the most crucial challenges of sustainable development is the use of low-temperature heat sources (60–200 °C), such as thermal solar, geothermal, biomass, or waste heat, for electricity production. Since conventional water-based thermodynamic cycles are not suitable in this temperature range or at least operate with very low efficiency, other working fluids need to be applied. Organic Rankine Cycle (ORC) uses organic working fluids, which results in higher thermal efficiency for low-temperature heat sources. Traditionally, new working fluids are found using a trial-and-error procedure through experience among chemically similar materials. This approach, however, carries a high risk of excluding the ideal working fluid. Therefore, a new method and a simple rule of thumb—based on a correlation related to molar isochoric specific heat capacity of saturated vapor states—were developed. With the application of this thumb rule, novel isentropic and dry working fluids can be found applicable for given low-temperature heat sources. Additionally, the importance of molar quantities—usually ignored by energy engineers—was demonstrated.

Trilateral Flash Cycle (TFC): a promising thermodynamic cycle for low grade heat to power generation

Energy crisis, fossil fuel depletion and growing environmental concern pushing not only for new source of energy but also developing advance technology for power generation. Besides conventional heat sources, low grade heat source of below 100 °C temperature like solar thermal, geothermal or waste heat has a good potential to become a sustainable source of power. Organic Rankine Cycle is the widely use thermodynamic power cycle for low grade heat to power generation where low boiling point pressurised organic working fluid is vaporised and expands through a turbine fed generator thus outputting usable electrical energy. The used fluid then returns to a reservoir before it is condensed and forced through the same process again via a high-pressure pump. Another thermodynamic cycle namely Trilateral Flash Cycle (TFC) which is nothing but a modified ORC where the organic working fluid is heated up to the saturation temperature under high pressure rather than evaporated. In this paper, an analytical comparative study on ORC and TFC shows that TFC has about at least 50% more power generation potential than that of conventional ORC for the same heat source and heat sink conditions if the heat source temperature is just below 100 °C. TFC even has the potential of power generation from the heat source below 80 °C where ORC is not economically viable.

Comparison on Thermodynamic Performances between Basic and Regenerative Sub-Critical Organic Rankine Cycles Coupled with Low Grade Heat Source

The coupling effects of low grade heat source on thermodynamic performances of both the basic and regenerative sub-critical Organic Rankine cycle (ORC) systems are investigated and compared. Turbine inlet pressure and turbine inlet temperature are treated as independent variables. The system exergy efficiency is selected as the thermodynamic performance criterion. The waste hot water with temperature range of 373.15K to 423.15K is selected as the low grade heat source. Optimization studies are carried out by using eight common organic working fluids to recover heat energy, and relevant operating conditions are obtained respectively. The results indicate that both hot fluid inlet temperature and the allowable minimum hot fluid outlet temperature influence the optimal working fluid, relevant turbine inlet condition and system exergy efficiency. Optimal system exergy efficiency increases monotonously with increasing of hot fluid temperature for both ORC systems above. In comparison to the basic cycle configuration, optimal system exergy efficiency for the regenerative system using the same working fluid is not changed if relevant turbine inlet vapor is saturated, but is significantly improved if relevant turbine inlet vapor is overheating. Besides, the optimal working fluid is dependent on the heat source temperature and specific cycle configuration.