Pinch Point Temperature Difference Research Articles

Thermo-economic optimization of a nanofluid based organic Rankine cycle: A multi-objective study and analysis

This paper deals with the thermo-economic optimization of nanofluid based organic Rankine cycle (ORC) system recovering waste heat energy. The main objective of the work is to study the performance of the system by maximizing 1st law efficiency and minimizing levelized energy cost (LEC). Nanoparticles are incorporated into the system by mixing them with the base fluid in the heat exchangers to enhance the heat transfer. Addition of nanofluids enhanced the heat transfer coefficient thus making them compact and cost efficient. Based on the criteria of availability and cost, copper oxide (CuO) nanoparticles are considered and its effect on system performance in terms of thermal efficiency and LEC is analyzed. The effect of pinch point temperature difference for condenser & evaporator, evaporation pressure, mass flow of refrigerant and concentration of nanoparticles is investigated and discussed. The results shows that incorporation of CuO nanoparticles enhance the thermodynamic performance of the system and gives the 19.3% thermal efficiency with LEC of 2.616 $/kWh. Compared to conventional ORC, 3.47% reduction in LEC is obtained in nanofluid based system with higher thermal efficiency. Further, the effect of operating parameters and design variables on the system performance is studied and discussed.

A zero-dimensional model for simulation of a Diesel engine and exergoeconomic analysis of waste heat recovery from its exhaust and coolant employing a high-temperature Kalina cycle

An exergoeconomic assessment is performed for a high-temperature Kalina cycle which is proposed to produce power from a Diesel engine exhaust and coolant. Developed zero-dimensional model for the engine simulation revealed its parameters as well as the influences on the thermodynamic and exergoeconomic parameters of the waste heat recovery system of the engine speed. Moreover, the system responses to the changes of the Kalina important parameters are assessed. Examining the locations of pinch point temperature differences in the system heat exchanging devices showed a proper thermal matching because of using a zeotropic working fluid. Results showed that the proposed cycle could produce 21.74 kW power from the waste heat recovery process, which is significant for a 98.9 kW engine. Energy and exergy efficiencies are also calculated to be 25.55% and 55.52%, respectively, and unit cost of the produced power in the Kalina turbine is measured as 15.52 cent/kWh, for a specific considered condition. The parametric study revealed a rise in the system produced power with the engine speed. Moreover, it is found that the produced power unit cost, as well as the system total cost, is reduced with increasing the turbine inlet temperature and pressure.

Performance assessment of a CCHP and multi-effect desalination system based on GT/ORC with inlet air precooling

This paper proposes a combined cooling, heating and power (CCHP), and multi-effect desalination system to supply cooling, heating, power and freshwater. The proposed system mainly includes a gas turbine (GT), a multi-effect desalination unit with a thermal vapor compressor (MED-TVC), an organic Rankine cycle (ORC) integrated with a steam ejector refrigerator (SER), and heat exchangers. The mathematical model is developed to thermodynamically conduct energy-exergy analysis, and a parametric study is performed to explore the effects of key design parameters such as air compressor pressure ratio, inlet air temperature of air compressor, pinch point temperature difference of waste heat boiler, motive steam pressure of MED-TVC unit, TVC compression ratio and working medium flow rate of ORC on the system performance. The proposed system can provide power, heating, cooling and freshwater at loads of 31.25 MW, 1.108 MW, 4.203 MW and 85.89 kg/s under the design conditions. The electrical, the exergy, and the overall energy efficiencies of the present system are 36.44%, 41.26% and 46.70%, respectively. The results indicate that the power output of GT can be increased by precooling the inlet air of air compressor, and the integration of GT with MED-TVC unit, ORC and heat exchangers can efficiently recover the waste heat from exhaust gas based on the principle of “energy cascade utilization”. In addition, the largest exergy destruction occurs in the combustion chamber followed by regenerator 1 and the MED-TVC unit.

Investigation on steam direct injection in a natural gas engine for fuel savings

In order to improve the natural gas engine (NGE) fuel economy, a steam direct injection method has been presented in the present study. In this method, exhaust was employed to heat water to produce superheated steam firstly. After that, at the power stroke, steam was injected into the cylinder directly. The potentials for fuel savings by this method are evaluated. First, ideal thermodynamic cycle of steam injected NGE is analyzed. Then, a baseline NGE is modeled and validated through experiments. After that, based on the simulation model, the effects of different steam injection parameters on the NGE performance are discussed, including steam mass, temperature and injected timing. The results show that the NGE fuel economy is significantly improved with steam direct injection. With optimal steam mass, 3.9–5.2% reductions of the NGE brake specific fuel consumption (BSFC) are obtained over different speeds, when steam temperature and injected timing are 550 K and 50 deg, respectively. Steam mass and injected timing have great influences on the NGE BSFC. However, steam mass is limited by pinch point temperature difference of the evaporator and exhaust temperature at the evaporator exit. In addition, steam injected timing is restricted by pressure inside the cylinder.

Difference analysis on optimal high pressure of transcritical CO2 cycle in different applications

Optimal high pressure has a key role in transcritical CO2 system performance. In this work, we conducted a quantitative difference analysis on optimal high pressure between CO2 refrigeration system and heat pump water heater (HPWH) using response surface methodology. It revealed that temperature of CO2 leaving gas cooler, with 96.38% contribution, is the predominant factor to optimal high pressure in CO2 refrigeration system. However in HPWH, multiple factors affect optimal high pressure. Water outlet temperature, evaporating temperature, pinch point temperature difference and water inlet temperature account for 55.42%, 25.65%, 5.67%, 3.72% contributions, respectively. Furthermore, new quadratic correlations for HPWH with different number of variables were developed. As a result, when the number of variables increased from 1 to 4, mean error of COP almost linearly decreased from 5.28% to 0.22%.

Thermodynamic and Exergoeconomic Analyses of a Novel Combined Cycle Comprised of Vapor-Compression Refrigeration and Organic Rankine Cycles

In this study, a cooling/power cogeneration cycle consisting of vapor-compression refrigeration and organic Rankine cycles is proposed and investigated. Utilizing geothermal water as a low-temperature heat source, various operating fluids, including R134a, R22, and R143a, are considered for the system to study their effects on cycle performance. The proposed cycle is modeled and evaluated from thermodynamic and thermoeconomic viewpoints by the Engineering Equation Solver (EES) software. Thermodynamic properties as well as exergy cost rates for each stream are found separately. Using R143a as the working fluid, thermal and exergy efficiencies of 27.2% and 57.9%, respectively, are obtained for the cycle. Additionally, the total product unit cost is found to be 60.7 $/GJ. A parametric study is carried out to determine the effects of several parameters, such as turbine inlet pressure, condenser temperature and pressure, boiler inlet air temperature, and pinch-point temperature difference, on the cycle performance. The latter is characterized by such parameters as thermal and exergy efficiencies, refrigeration capacity, produced net power rate, exergy destruction rate, and the production unit cost rates. The results indicate that the system using R134a exhibits the lowest thermal and exergy efficiencies among other working fluids, while the systems using R22 and R143a exhibit the highest energy and exergy efficiencies, respectively. The boiler and turbine contribute the most to the total exergy destruction rate.

Power optimization and comparison between simple recuperated and recompressing supercritical carbon dioxide Closed-Brayton-Cycle with finite cold source on hypersonic vehicles

Closed-Brayton-cycle (CBC) is a potential onboard power generation technology for hypersonic vehicles, but finite cold source limits its power output. To achieve higher electric power, this study presents the power optimization and comparison between the simple recuperated and recompressing supercritical carbon dioxide (S-CO2) CBC. Results indicate that the temperature distribution of precooler is essential to obtain its pinch point temperature difference. There is optimal fuel temperature difference in precooler for electric power of S-CO2 CBCs. Although the recompressing layout has advantages on thermal efficiency, the simple recuperated layout exhibits better on electric power per unit mass flowrate of fuel (219.6 kW vs. 192.5 kW), because the latter utilizes more cooling capacity of fuel. Besides, the optimal inlet temperature of compressor for electric power with finite cold source is far higher than the design value for general S-CO2 compressors (389 K vs. ∼305 K). In a word, it is more reasonable to develop the simple recuperated S-CO2 closed-Brayton-cycle as onboard power generation system of hypersonic vehicles.

Optimization strategies for mixing ratio of biogas and natural gas co-firing in a cogeneration of heat and power cycle

The most suitable design parameters of the cogeneration system, from the exergetic and the exergo-economic viewpoints, were determined using the genetic algorithm based on optimization method. In this study, a cogeneration cycle, consisting of a gas turbine cycle with power generation capacity of 30 MW, an anaerobic digester, a steam generator, and a heat exchanger for heating the digester and pretreatment system, has been used. The air compressor pressure ratio, the isentropic efficiencies of gas turbine and air compressor, biogas and natural gas mixing ratio, air preheater outlet temperature, turbine inlet temperature, and evaporator pinch point temperature difference were selected as the decision variables. Multi-objective optimization based on genetic algorithm using MATLAB software is carried out to discover the optimum point with regard to the total cost rate and exergy efficiency as the objective functions. The optimization was conducted according two scenarios. While the fuel mixing ratio was considered as a decision variable in the first scenario, in the second one this mixing ratio was kept constant, 50%. Optimization of the cycle according to the first scenario raised the exergy efficiency from 46.59% to 53.25% and decreased the system total cost rate from 4385$/h to 2935$/h. As well, compared to the base case, the optimal case of the second scenario had more exergy efficiency and less total cost rate, 48.35% versus 50.5% and 4028$/h versus 3665$/h, respectively.

Exergoeconomic analysis of a novel integrated transcritical CO2 and Kalina 11 cycles from Sabalan geothermal power plant

A new integrated cycle based on different real temperatures and pressures on Sabalan geothermal power plant, located in Iran, has been proposed and thermodynamic and exergoeconomic analyses are performed. The Kalina and Transcritical Rankine cycles are used as bottoming cycles and an algorithm are applied to find the exact location of the pinch points in heat exchangers. Also, a parametric study carried out to reveal the effects on the thermodynamic and exergoeconomic performance of the integrated cycle of such important parameters as separator 1 pressure, separator 2 pressure, pinch point temperature difference in the evaporators, higher pressure of the Kalina cycle and the ratio of the Transcritical cycle higher pressure to the critical pressure. Finally, the proposed cycle performance is optimized from the thermodynamic and exergoeconomic viewpoints. The results show that for the integrated geothermal power plant, the power generation, thermal efficiency, exergy efficiency and power specific cost rate are calculated to be 19,448 kW, 16.63%, 63.78%, and 4.521 $/GJ, respectively, which indicate that the proposed cycle has improved thermodynamically and exergoeconomically compared to previous studies.

Comparative carbon and water footprint analysis and optimization of Organic Rankine Cycle

Carbon footprint (CF) and water footprint (WF) models are established based on exergoenvironmental method for Organic Rankine Cycle (ORC). Sensitivity study and multi-objective optimization are performed. R1233zd (E), R600a and R245fa and R245fa/R600a (0.5/0.5) are selected as the working fluids. The results show that the main methods to decrease CF and WF of ORC system are not the same from both exergoenvironmental analysis viewpoint and sensitivity study aspect. The differences lie in (i) from exergoenvironmental analysis viewpoint, reducing the CF cost of exergy destruction of evaporator and condenser is necessary; While reducing the WF costs rate of condenser is indispensable for WF reduction; (ii) regarding sensitivity study, the increase of evaporating temperature and decline of pinch point temperature difference in evaporator can be adopted to reduce the carbon emission; While increasing evaporating temperature and pinch point temperature difference in evaporator is effective to decrease the water consumption.

Assessment of Methods for Performance Comparison of Pure and Zeotropic Working Fluids for Organic Rankine Cycle Power Systems

In this paper, we present an assessment of methods for estimating and comparing the thermodynamic performance of working fluids for organic Rankine cycle power systems. The analysis focused on how the estimated net power outputs of zeotropic mixtures compared to pure fluids are affected by the method used for specifying the performance of the heat exchangers. Four different methods were included in the assessment, which assumed that the organic Rankine cycle systems were characterized by the same values of: (1) the minimum pinch point temperature difference of the heat exchangers; (2) the mean temperature difference of the heat exchangers; (3) the heat exchanger thermal capacity ( U ¯ A ); or (4) the heat exchanger surface area for all the considered working fluids. The second and third methods took into account the temperature difference throughout the heat transfer process, and provided the insight that the advantages of mixtures are more pronounced when large heat exchangers are economically feasible to use. The first method was incapable of this, and deemed to result in optimistic estimations of the benefits of using zeotropic mixtures, while the second and third method were deemed to result in conservative estimations. The fourth method provided the additional benefit of accounting for the degradation of heat transfer performance of zeotropic mixtures. In a net power output based performance ranking of 30 working fluids, the first method estimates that the increase in the net power output of zeotropic mixtures compared to their best pure fluid components is up to 13.6%. On the other hand, the third method estimates that the increase in net power output is only up to 2.56% for zeotropic mixtures compared to their best pure fluid components.

Multi-objective linear regression based optimization of full repowering a single pressure steam power plant

Full repowering of Be'sat steam power plant has been studied in this work. The methodology is used to simulate the new cycle according to its principal specifications and to optimize it based on the objective functions. Objective functions are electricity cost per kWh and exergy efficiency. These parameters are functions of the pinch and approach point temperature differences at high and low pressure points and at the pre-heater in the heat recovery steam generator (HRSG), steam turbine inlet flow rate, gas turbine (GT) isentropic efficiency, air compressor isentropic efficiency and compressor pressure ratio. Finally, considering the introduced objective functions, it is tried to achieve the most optimized techno-economic characteristics for Be'sat power plant repowering cycle using the genetic algorithm with two scenarios of single and multi-objective optimizations. The results show that the efficiencies of the repowered cycle are 52.59% and 51.3% for two cases of unfired and fired duct burners, respectively.

Performance Assessment and Solution Procedure for Series Flow Double-Effect Absorption Refrigeration Systems Under Critical Operating Constraints

In this study, the effects of critical operational constraints on the operational domain of a double-effect lithium bromide/water absorption refrigeration system and its performance were investigated. These constraints were determined as the equivalence state of concentrations, the thermal unbalance between the system components of high-pressure condenser and low-pressure generator, freezing and crystallization risk of lithium bromide/water solution. For the system analysis, a simulation program was developed, and its detailed solution procedure was presented. The program outputs were initially validated with the literature. Subsequently, parametric studies were conducted for broad ranges of the component temperatures. The results demonstrate that the considered constraints were essential for acceptable design and the operational control of double-effect absorption refrigeration systems. The simulations will help to figure out under which operating conditions a double-effect absorption refrigeration system functions effectively and what kind of control strategies are essentially required to increase the coefficient of performance. Based on the operation scenario of fixed high-pressure generator temperature, the proposed system can enhance the coefficient of performance up to 31% and 84% as compared to its counterparts which function under the variable high-pressure generator temperature and the pinch point temperature difference (5 K between the high-pressure condenser and the low-pressure generator), respectively.

EXERGY ANALYSIS OF THE ORGANIC RANKINE CYCLE BASED ON THE PINCH POINT TEMPERATURE DIFFERENCE

Organic Rankine Cycle (ORC) is a system that uses working fluids with hydrocarbon components instead of water and generates power from the heat recovery of different heat sources. In this study, the exergy analysis of a simple ORC, which produces electrical energy with the help a geothermal source (125°C), was performed. R123, R152a, R245fa and R600a were determined as the fluids to be used in the Cycle. In this analysis, which was carried out according to the pinch point temperature differences (5-20°C) in the evaporator, the exergy performance of the cycle components was evaluated for the geothermal resource unit flow rate and the variation of the exergy efficiency of the system was calculated. With the increase of the pinch point temperature difference in the evaporator, the decrease of the system’s exergy efficiency became maximal (11.7%) with the use of R152a as a refrigerant and the loss in the system’s exergy efficiency became minimal (9.03%) with the use of R123 as a refrigerant.

Energy and Exergy Analysis of a New Power, Heating, Oxygen and Hydrogen Cogeneration Cycle Based on the Sabalan Geothermal Wells

In this paper, a new power, heating and hydrogen cogeneration cycle from Sabalan geothermal two wells is proposed and analyzed. In the proposed system, a new double flash cycle and organic Rankine cycle are used for power production. A proton exchange membrane (PEM) is also used for hydrogen production and the domestic water heater is used for heating. The impacts of some design parameters, such as separators pressures, evaporator temperature, pinch point temperature difference and PEM temperature on the integrated system performance are investigated and then optimization is done from exergy point of view for three considered scenarios. According to the optimization results, the value of heating, net output power, hydrogen production and thermal and exergy efficiencies of the cogeneration system are obtained as 15751 kW, 18436 kW, 11.13 kg/h, 29.48% and 65.23%, respectively.

Thermodynamic analysis of a geothermal-solar flash-binary hybrid power generation system

Abstract In order to achieve efficient utilization of geothermal and solar energies, a new geothermal-solar hybrid power generation system with flash-binary configuration is proposed in this work. This system consists of a solar preheating subsystem, a flash-binary power subsystem, and a binary power subsystem. The thermodynamic performances investigation of the hybrid system is implemented, under the designate condition with the geothermal water temperature and solar collection temperature of 170 ℃ and 390 ℃, respectively, the net power output of the hybrid system is 12.76 MW. In the hybrid system, the proportion of solar energy input is 69.95%, the system energy efficiency and exergy efficiency reach to 10.74% and 23.9%, respectively. The maximum exergy loss is generated within the solar collection process and accounts for 33.27% of system total exergy loss. Additionally, the sensitivity analysis of main operation parameters (i.e., the flash pressure and the evaporation pressure, pinch point temperature difference and superheat degree in organic Rankine cycle) are carried out, the results indicate that the thermodynamic performances of system improved with the increase of flash pressure. In addition, the net power output and energy efficiency can increase to the maximum value at the evaporation pressure of 1.5 MPa. Through the system evaluation, the proposed geothermal-solar hybrid power generation system achieves favorable thermodynamic performances, and it provides an alternative way to improve the energy conversion efficiencies of the geothermal and solar energy.

Determination of an optimal pinch point temperature difference interval in ORC power plant using multi-objective approach

Organic Rankine Cycle (ORC) power plants are constantly developing systems and, apart from Stirling engine, are currently the only commercially available technology, which allows electricity generation using low and medium temperature waste thermal energy. A lot of effort has been devoted to improve analysis techniques, with the aim to find the most favorable parameters of ORC as well as the best working fluid for a certain type of energy source and configuration of the system. The aim of the paper is to present a method to determine an optimal pinch point temperature difference interval (OPPTDI) using multi-criteria approach with G(X) as multi-objective function and pinch point temperature difference as a decision variable. The analysis has been carried out for five selected organic fluids: R245fa, R1234yf, R1234ze, R227ea, and R152a. The optimization model has been solved using the linear weighted sum method. The applied technique specifies OPPTDI by assigning different values of weights w1 and w2 to the individual objective functions f1 (economic index) and f2 (environmental index), which are the components of the global function G. The proposed method should be perceived as an initial evaluation of the pinch point temperature difference interval, giving an insight for the designer what is the potentially optimal range of the considered quantity and moreover – the optimal values region of such parameter, if one of the objective functions is evaluated to be more significant than the other.

A graphical method for the determination of optimum operating parameters in a humidification-dehumidification desalination system

Humidification–dehumidification (HDH) technology is an innovative desalination technology which has received considerable attention from researchers in recent years. In this study, the effects of mass flow rate ratio and pinch point temperature difference (PPTD) on the energy consumption of the HDH system are investigated by pinch analysis. A new parameter, pinch point heat capacity rate ratio (PHCR), is introduced to normalise the optimum point for energy consumption. It is found that the specific energy consumption of the system is minimised when the PHCR of the dehumidifier equals to unity. The value of GIR can be achieved 3.978 when the PHCR of dehumidifier equals to unity, at the inlet temperature of the solution in the humidifier equals to 65 °C and PPTD of the humidifier and dehumidifier equals to 1 °C. Based on this discovery, the regression equations are used to predict the optimum value of the mass flow rate ratio at different operating parameters. Combining the regression equations with the evaporation rate contour plots, an efficient graphical method is proposed for the determination of optimum operating parameters of the HDH system. It can be used to determine the operating parameters efficiently according to the performance requirements of the system.

Multi-objective optimization of CuO based organic Rankine cycle operated using R245ca

The present work deals with multi objective optimization of nanofluid based Organic Rankine Cycle (ORC) to utilise waste heat energy. Working fluid considered for the study is R245ca for its good thermodynamic properties and lower Global Warming Potential (GWP) compared to the conventional fluids used in the waste heat recovery system. Heat Transfer Search (HTS) algorithm is used to optimize the objective functions which tends to maximize thermal efficiency and minimize Levelised Energy Cost (LEC). To enhance heat transfer between the working fluid and source fluid, nanoparticles are added to the source fluid. Application of nanofluids in the heat transfer system helps in maximizing recovery of the waste heat in the heat exchangers. Based on the availability and cost, CuO nanoparticles are considered for the study. Effect of Pinch Point Temperature Difference (PPTD) and concentration of nanoparticles in heat exchangers is studied and discussed. Results showed that nanofluids based ORC gives maximum thermal efficiency of 18.50% at LEC of 2.59 $/kWh. Total reduction of 7.11% in LEC can be achieved using nanofluids.

Simultaneous optimization of multiparameters on a subcritical organic Rankine cycle system for low-grade waste heat recovery

This study aims to improve the thermo-economic performance of the subcritical organic Rankine cycle (ORC). Accordingly, an economical evaluation and the simultaneous multiparametric optimization on the subcritical ORC system for recovering low-grade waste heat of flue gas were conducted using electricity production cost (EPC) as the evaluation indicator. Results show that the optimum evaporating and condensing temperatures are mainly influenced by the inlet temperatures of flue gas and cooling fluid, respectively. High critical temperature of working fluids indicates high thermal-economic performance of the ORC system for 19 kinds of selected working fluids. Furthermore, the optimum pinch point temperature difference of evaporator decreases and that of condenser increases with the variation in the critical temperature of working fluids, but the optimum condensing temperature is unchanged. On the basis of a large number of calculation data, the correlations among the optimum cycle and external operating parameters of the subcritical ORC are proposed. These correlations can guide the engineering design of the subcritical ORC system.