Effect of condensation temperature glide on the performance of organic Rankine cycles with zeotropic mixture working fluids

Liu, Qiang; Duan, Yuan-Yuan; Yang, Zhen

doi:10.1016/j.apenergy.2013.11.036

Cited by 185 publications

(59 citation statements)

References 35 publications

Supporting

Mentioning

Contrasting

Unclassified

Order By: Relevance

“…The output power for the case study was selected as 10 kW. The pinch point temperature difference in the heat exchangers was taken to be 5 °C which is consistent with previous research [36,37], and an additional 2 °C of subcooling was added to the cycle at State 1 to ensure an adequate Net Positive Suction Head was provided to the pump. This allowed the condition of the working fluid at State 1 to be characterised using the equations = + 5 and = at ( = + 2).…”

Section: Numerical Modellingmentioning

confidence: 76%

Numerical Analysis of an Organic Rankine Cycle with Adjustable Working Fluid Composition, a Volumetric Expander and a Recuperator

Collings

2017

Energies

View full text Add to dashboard Cite

Conventional Organic Rankine Cycles (ORCs) using ambient air as their coolant cannot fully utilize the greater temperature differential available to them during the colder months. However, changing the working fluid composition so its boiling temperature matches the ambient temperature as it changes has been shown to have potential to increase year-round electricity generation. Previous research has assumed that the cycle pressure ratio is able to vary without a major loss in the isentropic efficiency of the turbine. This paper investigates if small scale ORC systems that normally use positive-displacement expanders with fixed expansion ratios could also benefit from this new concept. A numerical model was firstly established, based on which a comprehensive analysis was then conducted. The results showed that it can be applied to systems with positive-displacement expanders and improve their year-round electricity generation. However, such an improvement is less than that of the systems using turbine expanders with variable expansion ratios. Furthermore, such an improvement relies on heat recovery via the recuperator. This is because expanders with a fixed expansion ratio have a relatively constant pressure ratio between their inlet and outlet. The increase of pressure ratio between the evaporator and condenser by tuning the condensing temperature to match colder ambient condition in winter cannot be utilised by such expanders. However, with the recuperator in place, the higher discharging temperature of the expander could increase the heat recovery and consequently reduce the heat input at the evaporator, increasing the thermal efficiency and the specific power. The higher the amount of heat energy transferred in the recuperator, the higher the efficiency improvement.

show abstract

Section: Numerical Modellingmentioning

confidence: 76%

Numerical Analysis of an Organic Rankine Cycle with Adjustable Working Fluid Composition, a Volumetric Expander and a Recuperator

Collings

2017

Energies

View full text Add to dashboard Cite

show abstract

“…ORC systems that use mixed working fluids may have better running performances than pure working fluids [24][25]. Mixed working fluids have drawn the attention of several scholars [26][27]. The change in the mass fraction of components in mixed working fluids can cause changes in the properties of mixed working fluids, such as critical temperature, critical pressure, and slip temperature.…”

Section: Introductionmentioning

confidence: 99%

Study on Mixed Working Fluids with Different Compositions in Organic Rankine Cycle (ORC) Systems for Vehicle Diesel Engines

Yang

Zhang

Wang

et al. 2014

Entropy

View full text Add to dashboard Cite

Abstract:One way to increase the thermal efficiency of vehicle diesel engines is to recover waste heat by using an organic Rankine cycle (ORC) system. Tests were conducted to study the running performances of diesel engines in the whole operating range. The law of variation of the exhaust energy rate under various engine operating conditions was also analyzed. A diesel engine-ORC combined system was designed, and relevant evaluation indexes proposed. The variation of the running performances of the combined system under various engine operating conditions was investigated. R245fa and R152a were selected as the components of the mixed working fluid. Thereafter, six kinds of mixed working fluids with different compositions were presented. The effects of mixed working fluids with different compositions on the running performances of the combined system were revealed. Results show that the running performances of the combined system can be improved effectively when mass fraction R152a in the mixed working fluid is high and the engine operates with high power. For the mixed working fluid M1 (R245fa/R152a, 0.1/0.9, by mass fraction), the net power output of the combined system reaches the maximum of 34.61 kW. Output energy density of working fluid (OEDWF), waste heat recovery OPEN ACCESSEntropy 2014, 16 4770 efficiency (WHRE), and engine thermal efficiency increasing ratio (ETEIR) all reach their maximum values at 42.7 kJ/kg, 10.90%, and 11.29%, respectively.

show abstract

“…It was found that when the maximum condensation temperature glide were larger than cooling water temperature raises, two optimal zeotropic mixture mole fractions were found. In contrast, there is only one optimal working fluid mole fraction if the condensation temperature glide is smaller than the cooling water temperature increase [92]. When the increase in cooling water temperature matches the condensation temperature glide, a higher mole fraction of the more volatile mixture component results in the largest net power output [92].…”

mentioning

confidence: 99%

“…Octamethyltrisiloxane/decamethyltetrasiloxane (MDM/MD2M) was the working fluid for a biomass-fired cogenerative organic Rankine cycle [92]. It was found that when the maximum condensation temperature glide were larger than cooling water temperature raises, two optimal zeotropic mixture mole fractions were found.…”

mentioning

confidence: 99%

“…As the condensing pressure is constant, the net power output of the mixtures was always intermediated. Andreasen et al [90] Liu et al [92] provided a way to optimize the condensation pressure in an ORC with a zeotropic mixture. The research focused on how first law efficiency was affect by temperature glide in the condenser, and consequent dependence on mixture composition.…”

mentioning

confidence: 99%

See 1 more Smart Citation

Mixed-Fluid Organic Rankine Cycles for Low Temperature Power Conversion

Zhang¹

View full text Add to dashboard Cite

The purpose of the thesis is to investigate and optimize refrigerant fluid mixtures for applications in low-temperatures ORC in order to maximize brine effectiveness ( ) rate for geothermal energy conversion in organic Rankine cycles. An in-house developed Matlab program interfaced with the Simulis TM thermodynamic database software was used to ascertain the performance of cycles having various mixture compositions. Brine effectiveness (the ratio of net work to geofluid mass flow rate) was used as the main metric to measure the performance of the Organic Rankine Cycle according to mixture composition, turbine inlet temperature and pressure. The optimum mixture concentrations have been found to depend on the plant design. There is an optimal pressure at different composition. The results highlight that it is not possible to obtain the maximum brine effectiveness, the maximum thermal efficiency, the smallest exergy destruction in the condenser and minimum turbine size factor simultaneously. For a geothermal plant, it is significant to maximize the power generated per unit flow of the geothermal fluid. The first-law efficiency is of secondaryimportance. These results demonstrate the importance of using brine effectiveness as the main performance metric rather than the thermal efficiency, which may not always describe the cycle that makes optimal use of the available energy. Similar optimization goals are presented in waste heat recovery, and the methods and findings of this thesis may be of interest in waste heat recovery applications.Based on the results obtained so far, selection of working fluids should depend on the specific conditions for each application, most notably the temperature of the resource. Working fluid critical temperature is very important in selecting the optimal working fluid. It is better to use a fluid with a critical temperature lower or a little bit higher than the heat resource temperature for cycles without superheating. The fluid's critical temperature then tends to determine the optimal cycle pressure.Mixed fluids have some advantages over pure working fluids. Most importantly, temperature glide (non-isothermal phase change) improves the performance in power cycle heat exchangers, especially the condenser, improving the performance of the overall power cycle.According to the fluid selection criteria, this thesis will focus on isentropic and dry fluids, which have higher thermal efficiencies because the turbine's expansion process terminates in the superheated region. 17 pure fluids were identified for low-moderate temperature power conversion and the performances of their mixtures were simulated at various ratios at 90 , 110 and 130, respectively. and for the optimization of the binary interactions parameters of the Non-Random-Two-Liquid (NRTL) model used for the calculation of the Gibbs Free Energy of Excess inside of the Michelsen-Huron-Vidal-second-order mixing rule (MHV2) used in combination with the Soave-Redlich-Kwong (SRK) equation of state. At the very least that the VLE...

show abstract

Effect of condensation temperature glide on the performance of organic Rankine cycles with zeotropic mixture working fluids

Cited by 185 publications

References 35 publications

Numerical Analysis of an Organic Rankine Cycle with Adjustable Working Fluid Composition, a Volumetric Expander and a Recuperator

Numerical Analysis of an Organic Rankine Cycle with Adjustable Working Fluid Composition, a Volumetric Expander and a Recuperator

Study on Mixed Working Fluids with Different Compositions in Organic Rankine Cycle (ORC) Systems for Vehicle Diesel Engines

Mixed-Fluid Organic Rankine Cycles for Low Temperature Power Conversion

Contact Info

Product

Resources

About