Compressor Isentropic Efficiency Research Articles

Thermodynamic and advanced exergy analysis of Rankine Carnot battery with cascaded latent heat storage

Cascaded latent heat storage offers significant advantages in Rankine Carnot battery systems by minimizing exergy destruction during heat transfer processes. However, the system performance and the sources of exergy destruction remain unclear, and the configuration of multiple phase change materials remains ambiguous. This paper investigates a Rankine Carnot battery system integrated with cascaded latent heat storage using energy, conventional exergy, and advanced exergy analysis methods. First, a novel phase change material partitioning configuration scheme is proposed, considering the phase change of the working fluid, significantly improving temperature matching within the storage. The number of stages in heat storage devices significantly affects system performance, with roundtrip and exergy efficiencies increasing by 32.2 % and 15.2 % as the number of stages rises from 1 to 4, though further increases have minimal impact. Advanced exergy analysis on a 4-stage system indicates that the endogenous avoidable exergy destruction of the expander, compressor, evaporator, and condenser constitutes 12.4 %, 12.0 %, 10.5 %, and 7.0 % of the total system exergy destruction, respectively, highlighting the priority components for system improvement. Furthermore, raising the heat storage temperature by 45 °C reduces roundtrip efficiency by 26.5 % while increasing power output by 63.2 %. Increasing the heat pump’s evaporation temperature by 30 °C improves roundtrip efficiency by 151.1 % but reduces power output by 33.7 %. Reducing the amount of waste heat and surplus electricity results in a significant decrease in the roundtrip efficiency and exergy efficiency, which is mainly caused by the reduction in the isentropic efficiencies of compressor and expander under partial load conditions. The findings on the priority components for system improvement and the configuration of cascaded latent heat storage provide an effective approach for enhancing Rankine Carnot batteries.

High-fidelity model development of CO2 booster refrigeration systems in supermarkets using field measurements

Supermarket refrigeration systems adopting traditional refrigerants with high global warming potential (GWP) have impacts on global warming for indirect and direct greenhouse gases (GHG) emissions. CO2 is a popular low-GWP alternative. The transcritical operation of CO2 systems worsens their energy performance, but provides recoverable heat as a heat source to reduce gas consumption. To evaluate operation performance, data-driven models, trained by historical data, are weak in implementation with datasets outside the scope of training data; in contrast, theoretical models have better extrapolation ability to calculate all operation conditions of CO2 systems at supermarket. Existing theoretical modeling approaches often lack validation against the limited public-access data, which reduces model reliability for further applications, and adopt oversimplified inference methods for unmeasured variables, which increases the risks of breaking thermodynamic laws and lowering model accuracy. This study therefore develops a steady-state theoretical model for CO2 booster refrigeration systems validated against field measurements from three UK supermarkets. The available measurements are utilized to the best level to ensure model accuracy and physical interpretability. Proposed methods to infer missing variables in CO2 systems include condenser outlet temperature, evaporating temperature, compressor isentropic efficiency and compressor mass flow rate. Results show that proposed inference methods enhance the abilities of the proposed modelling approach to ensure data integrity, avoid breaking thermodynamic laws, and improve model accuracy by reflecting real-time actual values of unmeasured variables rather than rough assumptions. The proposed modeling approach provides satisfactory accuracy validated using high-resolution measurements across the whole year from three real supermarkets.

Thermodynamic and Exergoeconomic Analysis of a Novel Compressed Carbon Dioxide Phase-Change Energy Storage System

As an advanced energy storage technology, the compressed CO2 energy storage system (CCES) has been widely studied for its advantages of high efficiency and low investment cost. However, the current literature has been mainly focused on the TC-CCES and SC-CCES, which operate in high-pressure conditions, increasing investment costs and bringing operation risks. Meanwhile, some studies based on the phase-change CO2 energy storage system also have had the disadvantages of low efficiency and the extra necessity of heat or cooling sources. To overcome the above problems, this paper proposes an innovative compressed CO2 phase-change energy storage system. During the energy charge process, molten salt and water are used to store heat with a smaller temperature difference in heat exchangers, and high-pressure CO2 is reserved in liquid form. During the energy discharge process, throttle expansion is applied to realize the evaporation at room temperature, and CO2 absorbs the reserved heat to improve the power capacity in the turbine and the system energy storage efficiency. The thermodynamic and exergoeconomic studies are performed firstly by using MATLAB. Then, the parametric study based on energy storage efficiency, system unit product cost, and exergy destruction is analyzed. The results show that energy storage efficiency can be improved by lifting liquid CO2 pressure as well as compressor and turbine isentropic efficiencies, and CO2 evaporation pressure has the optimal pressure point. The system unit product cost can be reduced by decreasing liquid CO2 pressure and compressor isentropic efficiency, while CO2 evaporation pressure and turbine isentropic efficiency both have optimal points. Finally, the optimization of two performances is performed by NSGA-II, and they can reach 75.30% and 41.17 $/GJ, respectively. Moreover, the optimal energy storage efficiency is obviously higher than that of other energy storage technologies, indicating the great advantage of the proposed system. This study provides an innovative research method for a new type of large-scale energy storage system.

Thermo-economic assessment of a salt hydrate thermochemical energy storage-based Rankine Carnot battery system

Carnot batteries are critical technologies for increasing the penetration of renewable energy sources because they enable suitable energy storage for long-term periods. The achievement of high efficiencies is an important point that determines the sustainability of the Carnot batteries. In this direction, a novel Rankine Carnot battery with heat upgrading capability based on salt hydrate thermochemical energy storage is proposed herein. The steady thermodynamic and economic models for the basic Carnot battery and recuperators introduced Carnot battery, both with a storage capacity of 10 MW/5h, have been established. The thermo-economic performance of the Carnot battery systems and the effects of several key parameters are quantitatively assessed. Results manifest that the Carnot battery with recuperators behaves better in comprehensive performance thanks to the heat recovery by recuperators. The power-to-power efficiency, exergy efficiency, and levelized cost of storage for the basic Carnot battery and recuperators introduced Carnot battery systems are 48.48 %, 38.48 %, 0.2502 $/kWh and 64.1 %, 48.94 %, 0.1922 $/kWh, respectively. The maximum exergy destruction occurs in the heat exchanger for the Carnot battery systems and the throttle's exergy destruction is diminished by 70 % in the recuperators introduced Carnot battery. The compressor and turbine account for the largest cost ratios, i.e., 26.5 % and 24.8 % in the basic Carnot battery and 28.2 % and 27.2 % in the recuperators introduced Carnot battery; while the cost proportion of throttle in both systems is nearly ignorable (0.3 %). Elevating heat source temperature and the reactant's hydration temperature and descending ambient temperature contribute to the improvement of power-to-power efficiency and levelized cost of storage. The isentropic efficiencies of compressor and turbine, especially the latter, have a great impact on the thermo-economic performances. As the daily charging time expands to 7 h, the levelized cost of storage of the recuperators introduced Carnot battery reduces to 0.1434 $/kWh. Replacing the reactive salt of potassium carbonate sesquihydrate (K2CO3·1.5H2O) with magnesium sulfate tetrahydrate (MgSO4·4H2O) brings a lower levelized cost of storage of 0.18 $/kWh. The findings of this study demonstrate great potential for the exploitation of this thermochemical energy storage-based Carnot battery for large-scale electricity storage.

Transonic Compressor Darmstadt Open Test Case: Experimental Investigation of Stator Secondary Flows and Hub Leakage

Abstract The future trend of clean sky aviation has led to a smaller core engine, resulting in highly loaded stages with increased relative tip gaps and leakage flows, which causes a reinforced influence of secondary flow phenomena. This article experimentally investigates the secondary flow effects in the 3D-optimized shrouded stator of the TUDa-GLR-OpenStage, representative of a transonic high-pressure compressor front stage, and its susceptibility to typical hub leakage flows. The impact of stator hub leakage on efficiency and total pressure ratio is investigated for several operating speeds, from subsonic to nominal transonic operating conditions. Steady five-hole probe and time-resolved virtual multi-hole probe measurements at different operating conditions at nominal speed are conducted to investigate the underlying loss mechanisms. The leakage mass flow is determined using the measured pressure difference within the fin seal. Steady results show that the optimized 3D stator effectively suppresses the hub corner separation compared to the predecessor 2D stator, but its performance is further limited by a near-tip separation. With the increased stator hub leakage (at a leakage-to-main flow ratio of about 0.4%), the compressor isentropic efficiency generally drops (by about −0.5%) at the full operating range due to an enhanced hub corner separation effect. However, the increased leakage also helps alleviate the tip-corner separation when operating near stall, leading to a smaller efficiency penalty under these conditions. Unsteady results reveal the sensitivity of transient compressor performance to the passing rotor wake, but limited interaction between this phenomenon and the increased leakage is observed. These findings provide insight into the stator hub leakage-related penalties on the compressor aerodynamics efficiency.

Experimental Performance Comparison of High-Glide Hydrocarbon and Synthetic Refrigerant Mixtures in a High-Temperature Heat Pump

Several theoretical studies have predicted that refrigerant mixtures with glides of more than 20 K can yield COP improvements in heat pumps for operating conditions where the temperature difference between the heat source and heat sink is large, but experimental validations and quantifications are scarce. The application of high-glide mixtures (>20 K) in industrial heat pumps in the field is, therefore, still hampered by concerns about the behavior and handling of the mixtures. This study experimentally investigates hydrocarbon (HC) mixtures R-290/600 (propane/butane) and R-290/601 (propane/pentane) and compares them to previously tested mixtures of synthetic refrigerants. Comprehensive evaluations are presented regarding COP, compressor performance, pressure drop, heat transfer, and the possibility of inline composition determination. The mixtures were tested over a range of compositions at a source inlet temperature of 60 °C and a sink outlet temperature of 100 °C, with the heat sink and heat source temperature differences controlled to 35 K. R-290/601 at a mass composition of 70%/30% was found as the best mixture with a COP improvement of 19% over R-600 as the best pure fluid. The overall isentropic compressor efficiency was similar for HC and synthetic refrigerants, given equal suction and discharge pressures. Pressure drops in heat exchangers and connecting lines were equal for synthetic and HC mixtures at equal mass flow rates. This allows higher heating capacities of HC mixtures at a given pressure drop (mass flow rate) due to their wider vapor dome. A previously developed evaporator heat transfer correlation for synthetic refrigerant mixtures was applicable to the HC mixtures. A condenser heat transfer correlation previously fitted for synthetic refrigerants performed significantly worse for HC mixtures. Composition determination during operation and without sampling was possible with a deviation of at most 0.05 mass fraction using simple temperature and pressure measurements and REFPROP for thermodynamic property calculations. Overall, high-glide HC mixtures, just like mixtures of synthetic refrigerants, showed significant COP improvements for specific operating conditions despite a decreased heat transfer coefficient. Potential problems like composition shift or poor compressor performance were not encountered. As a next step, testing high-glide mixtures in pilot-plant installations is recommended.

An optimization of efficient combined cycle power generation system for fusion power reactor

Fusion power plants can meet the energy demands of the world. The high thermal performance of a power generation system is still a challenge and one of the developing trends with a fusion reactor due to the high outlet temperature. A combined cycle system has been optimized to work at high outlet temperature and pressure of fusion power reactor with thermal power of 2500 MWth and its input parameter has been optimized along with impact of partial load to achieve high thermal performance very first time. The combined cycle based on the concept of two stages of expansion in the closed-Brayton-cycle and two reheaters in the Rankine cycle named Schematic-IV with the higher thermal performance of 58.19% as compared to Schematic-I, II and III has been proposed for a fusion power reactor. The increase in more than one expansion stage and reheat stage is not economical because it increased the thermal performance by about half of performance as compared to one. The effect of isentropic efficiency of compressor and heat rate have been investigated to validate the thermodynamic model and calculations. The optimized thermal performance of the combined cycle is 58.19% at a feed water mass flow rate of 592 kgs−1 and steam outlet temperature of 277 °C in the combined cycle. The heat rate decreased and thermal performance increased with the mass flow rate verifying that the thermodynamic model is correct. The thermodynamic analysis of the combined cycle-based nuclear reactor provides insights for better system thermal performance and reveals the effect of key parameters on the system performance.

Performance Comparison of High-Temperature Heat Pumps with Different Vapor Refrigerant Injection Techniques

In order to develop a highly efficient and stable high-temperature heat pump to realize high-efficient electrification in the industrial sector, performance of high-temperature heat pumps with a flash tank vapor injection and sub-cooler vapor injection are compared under different evaporation temperatures, condensation temperatures, compressor suction superheat degrees, subcooling degrees and compressor isentropic efficiencies. The results show that the COP, injection mass flow ratio and VHC of the FTVC are higher than those of the SVIC-0, SVIC-5, SVIC-10 and SVIC-20 under the same working conditions, while the discharge temperature of the FTVC is approximately equal to that of the SVIC-0 and lower than those of the SVIC-5, SVIC-10 and SVIC-20. When the evaporation temperature, the condensation temperature and injection pressure are 55 °C, 125 °C and 921.4 kPa, respectively, the system COP of the FTVC is 4.49, which is approximately 6.7%, 7.3%, 7.8% and 8.9% higher than those of the SVIC-0, SVIC-5, SVIC-10, and SVIC-20, respectively.

Thermochemical modeling and performance evaluation of freeze desalination systems

Freeze desalination (FD) is a method in which saline water is cooled below its freezing point and freshwater is separated from the brine in the form of ice crystals. FD is relatively insensitive to the salinity of the feed solution, making it suitable for desalination of high concentration brines such as the brine rejected from the seawater desalination plants. The design of the FD system and the thermochemical behavior of the brine upon freezing are critical factors in the energy performance of this method. To date, thermochemical properties of the concentrated seawater during cooling, such as the threshold of formation of ice and salt-hydrates and their corresponding cooling load of formation, are not well known. Likewise, the optimal configuration of the FD system to achieve the maximum energy efficiency has not been investigated. This work provides comprehensive data about the cooling load of freezing of concentrated brine rejected from seawater desalination plants along with the threshold of formation of ice and salt-hydrates backed-up by validation. Furthermore, the optimal configuration of the FD system is identified and the effects of the compressor isentropic efficiency and effectiveness of the system's heat exchangers on the work consumption of the FD system were investigated.

Exergoeconomic analysis of an integrated electric power generation system based on biomass energy and Organic Rankine cycle

ABSTRACT The present study investigates the thermodynamics analysis of a trigeneration system using a gasifier system. An Organic Rankine Cycle (ORC) system is used to heat recovery and consequently, supplying the cooling demand. The first and second laws of thermodynamics are used to energy and exergy analysis of the system. Some thermodynamic parameters which affect the system performance including combustion temperature, gasifier temperature, compressor isentropic efficiency, gas turbine isentropic efficiency, compressor pressure ratio, and ORC pressure are parametrically analysed and their contribution in improving the efficiency and economy of the system is investigated. To the sustainable performance of the combined system, we need an evolutionary algorithm to identify the optimum values of thermodynamic parameters that have an impact on system performance. Hence, the Multi-Objective Particle Swarm Optimization (MOPSO) algorithm is used to find the best values of decision variables. The most striking result to emerge from the optimisation.optimisation is that implementing the MOPSO algorithm improves the exergy efficiency by 5.17% and reduces the total cost of the system by 1.9%.

Investigation of turbulence models for aerodynamic analysis of a high-pressure-ratio centrifugal compressor

The aerodynamic design and optimization of modern centrifugal compressors are inseparable from computational fluid dynamics (CFD) tools. In a design environment, CFD simulations are expected to predict compressor performance characteristics with reasonable accuracy. Turbulence models and model simplification can play a significant role in the discrepancy between analysis and reality. To investigate the influence of turbulence models on aerodynamic analysis results of centrifugal compressors, the National Aeronautics and Space Administration's high efficiency centrifugal compressor stage is selected as the test vehicle. Six eddy-viscosity models, namely, Spalart–Allmaras (SA), standard k–epsilon (k−ε), renormalization group k–epsilon (RNG k−ε), Wilcox k–omega (k−ω), shear stress transport (SST), and SST-reattachment modification (SST-RM) are considered. In all numerical analyses, measured surface roughness is included with the aim of improving numerical solution accuracy. Although some discrepancies exist, the compressor performance characteristics predicted by the k−ω model are in satisfactory agreement with the test data over the whole speedline. The k−ε model overpredicts the isentropic efficiency than the other models, while the SST-RM model underestimates the total pressure ratio in the near-stall region. The RNG k−ε model matches high flow characteristics but overestimates the choked mass flow rate. The SST model obtains a similar operating range with the test data but underestimates the compressor's isentropic efficiency and total pressure ratio, while the SA model totally overestimates the compressor characteristics due to the wall function. Furthermore, variations caused by turbulence models are discussed together with the flow field analysis. Finally, to verify the impact of the impeller backplate bleed cavity, an additional simulation is conducted that specifically accounts for this feature.

Characterizing Shrouded Stator Cavity Flow on the Performance of a Single-Stage Axial Transonic Compressor

Abstract Shrouded stator cavity flow increases the stator total pressure loss, reduces the compressor isentropic efficiency, and thus limits the compressor pressure rise capability. This paper proposes a simplified cavity flow model that consists of flow injection at the stator inlet and flow suction at the stator outlet. Based on this model, a full-factorial parametric study on the leakage flow ratio and the leakage swirl angle is performed at different rotational speeds and incidences. In the first place, the effectiveness of the numerical method is validated against the experimental data based on the full-scale cavity geometry; then, the numerical simulations on the simplified cavity geometry are validated against that of the full-scale one. Results show that the leakage flow ratio plays a dominant role in determining the compressor performance penalty. The isentropic efficiency drops almost linearly with the leakage flow ratio due to deteriorated near-hub separations, and the slope becomes steeper at higher operating speeds and incidences. The leakage swirl angle only has a pronounced effect under a high leakage flow ratio. The efficiency penalty reduces with increasing swirl angle due to an alleviated tangential flow mixing and suppressed near-hub separations. The swirl angle effect is more pronounced at lower incidence conditions. These findings advance the fundamental understanding of shrouded stator cavity flow effects and provide useful guidance for cavity seal designs.

5E (energy, exergy, energy level, exergoeconomic, and exergetic sustainability) analysis on a carbon dioxide binary mixture based compressed gas energy storage system: A comprehensive research and feasibility validation

Recently, the application of carbon dioxide binary working fluids in compressed carbon dioxide energy storage systems has been proposed to improve the system characteristics, especially for the condensation problem of carbon dioxide. Based on the previous research, a more comprehensive 5E (energy, exergy, energy level, exergoeconomic, and exergetic sustainability) analysis on a typical transcritical compressed carbon dioxide energy storage system using carbon dioxide binary working fluid is carried out. Propane, propylene, R32, R161, R1234ze, and R1234yf are chosen to compose the binary working fluid with carbon dioxide, respectively. The effect of changing parameters, including pump pressure ratio, compressor isentropic efficiency, and heat exahcnger1 outlet temperature on system performance, is also analyzed. In addition, the feasibility of applying carbon dioxide binary working fluid at high ambient temperature is investigated. According to the results, the performance of heat exchanger1, heat exchanger2, and pump decreases while the performance of the turbine is improved with a higher refrigerant mass fraction from the point of energy level. The compressor, pump, and turbine show potential for optimization according to their higher process energy level difference. The pump power and system operating pressure is reduced at the cost of reducing round trip efficiency when using carbon dioxide binary working fluid. A 1% improvement in compressor isentropic efficiency leads to an increase of nearly 0.4% in round trip efficiency, albeit with reduced turbine power. Increasing the heat exchanger1 outlet temperature from 305 K to 315 K results in a 1% increase in round trip efficiency but with a decrease in the performance of heat exchanger1. Both increasing compressor isentropic efficiency and heat exchanger1 outlet temperature benefit the system economy and exergetic sustainability. A noticeable decrease in system performance is observed when the ambient temperature shifts from 293 K to 303 K. However, this deterioration can be mitigated by raising the pressure of saturated working fluid gas at the compressor inlet. Propylene, R32, and R1234yf are suitable candidates to address the condensation issue, considering the system performance at high ambient temperatures. This paper extends research on the compressed carbon dioxide energy storage system based on carbon dioxide mixtures and provides a reference for the working fluid selection and system optimization for related research.

Performance evaluation of a novel heat pump system for drying with EVI-compressor driven precooling and reheating

Heat pump drying is widely used in the agricultural and industrial sectors. This study proposes a novel heat pump system for closed-loop drying, which employs an enhanced vapor injection (EVI) compressor (HPDEVI). The system precools the return air to a closer-to-saturation state to enhance dehumidification and reheats the dehumidified cold air while increasing the refrigerant subcooling. Meanwhile, EVI is fulfilled to modify the heat pump cycle. To demonstrate its superiority, the HPDEVI's energetic, exergetic and economic performances are compared to those of the basic configuration (HPDbasic) and the system with a stand-alone heat pipe (HPDHP). The results show that HPDEVI outperforms the other two systems by increasing latent heat ratio of evaporator, compressor isentropic efficiency and refrigerant subcooling. Under the design condition (Tdb = 45 °C, RH = 40%), HPDEVI reaches a specific moisture extraction rate (SMER) of 3.07 kg/kWh and a moisture extraction rate (MER) of 43.8 kg/h. These values are increased by 16.7% and 12.9% compared to HPDbasic, and 8.9% and 4.5% relative to HPDHP, respectively. Moreover, HPDEVI generates the lowest exergy destruction per latent heat of water removal at 0.367 W/W, and costs only 0.267 CNY per litre of water extracted after ten years of operation. Finally, the performance improvements of HPDEVI under off-design conditions are also revealed.

Comparative Analysis of Isochoric and Isobaric Adiabatic Compressed Air Energy Storage

Adiabatic Compressed Air Energy Storage (ACAES) is regarded as a promising, grid scale, medium-to-long duration energy storage technology. In ACAES, the air storage may be isochoric (constant volume) or isobaric (constant pressure). Isochoric storage, wherein the internal pressure cycles between an upper and lower limit as the system charges and discharges is mechanically simpler, however, it leads to undesirable thermodynamic consequences which are detrimental to the ACAES overall performance. Isobaric storage can be a valuable alternative: the storage volume varies to offset the pressure and temperature changes that would otherwise occur as air mass enters or leaves the high-pressure storage. In this paper we develop a thermodynamic model based on expected ACAES and existing CAES system features to compare the effects of isochoric and isobaric storage. Importantly, off-design compressor performance due to the sliding storage pressure is included by using a second degree polynomial fit for the isentropic compressor efficiency. For our modelled systems, the isobaric system round-trip efficiency (RTE) reaches 61.5%. The isochoric system achieves 57.8% even when no compressor off-design performance decrease is taken into account. This fact is associated to inherent losses due to throttling and mixing of heat stored at different temperatures. In our base-case scenario where the isentropic compressor efficiency varies between 55% and 85%, the isochoric system RTE is approximately 10% lower than the isobaric. These results indicate that isobaric storage for CAES is worth further development. We suggest that subsequent work investigate the exergy flows as well as the scalability challenges with isobaric storage mechanisms.

Optimal retrofit of a novel multi-component supercritical thermal fluid generation system via thermodynamic analysis

• A novel thermal fluid generation system is first developed, introduced and modelled. • Sensitivity analysis of three key single factors and their combinations are performed. • Reactor and heat exchanger are the bottleneck units to overall efficiency improvement. • An optimal retrofit design with around 10% efficiency increased are proposed. Multi-component supercritical thermal fluid (mcSCTF) has been recently recognized as a promising media for enhancing heavy oil recovery. For its economic application, an efficient mcSCTF generation should be studied. In this work, a novel experimental system with various units is being first introduced for mcSCTF generation and theoretically modelled for the energy and exergy analysis as the two contributions of this work. Based on the results, optimal retrofit strategy is proposed as the coming improvement. Starting with a specific experimental setup, theoretical modeling methods including Gibbs free energy minimization and mass balances are employed to predict the output of the core unit of reactor. The models are validated using measured experimental data. Then, energy and exergy analysis are conducted to quantify the energy and exergy losses in each unit. The reactor, heat exchanger and compressor are found to contribute for the major exergy losses accounting for 40.1%, 39.4% and 12.3%, respectively. With this, sensitivity analysis of three key factors (i.e., reactor heat dissipation rate, heat exchanger efficiency, and compressor isentropic efficiency) as well as their combinations are performed to identify potential solutions for improving efficiency. Finally, a retrofit design with around 10% efficiency enhancement is proposed.

The Role of the Compressor Isentropic Efficiency in Non-Intrusive Refrigerant Side Characterization of Transcritical CO2 Heat Pump Water Heaters

Characterizing the refrigerant side of heat pump water heaters (HPWHs) can be intrusive and expensive. On the other hand, direct external measurement techniques can be unfeasible, particularly in commercial HPWHs for residential applications. Non-intrusive in situ characterization methods have already been successfully implemented in subcritical heat pumps. They provide the refrigerant mass flowrate and the equipment energy performance, by using contact temperature sensors and electric power meters. Subcritical suction and discharge-specific enthalpies necessary to apply the method can be obtained from the measured temperatures and their corresponding saturation pressures. Nevertheless, this approach does not apply to the transcritical CO2 HPWHs. In the supercritical region, temperature and pressure are independent variables, and an iterative process regarding the compressor isentropic efficiency has to be considered. However, when isentropic efficiency data are not available, an additional procedure is required, using a validated gas cooler model to verify the physical reliability of the numerical solutions. This work aims at presenting base thermodynamic analysis of a novel methodology for non-intrusive refrigerant side characterization of transcritical CO2 HPWHs, exploring the influence of the compressor isentropic efficiency condition.

Evaluation of the effects of entrainment ratios on the performance parameters of a refrigeration machine having dual evaporator ejector system with R134a and R456A

In this study, a dual evaporator ejector system (DEES) was experimentally investigated in order to determine the effective cooling capacities depending on entrainment ratios (ER). An experimental performance analysis was conducted on the system to assess the range of entrainment ratio in which both evaporators can operate effectively. To this end, superheating temperatures, compressor isentropic efficiencies, compression ratios, pressures at the ejector outlet, cooling capacities, and throttling ratios (for TXV#1) were analysed in association with entrainment ratio values to determine the upper and lower limits for effective operating conditions. The results show that the compressor isentropic efficiency drops with the increase of entrainment ratio. Isentropic efficiency was calculated as 0.69 and 0.71 for R134a and R456A, respectively, when the entrainment ratio was above 0.8. Special attention was paid to the superheating temperatures of the second evaporator of the system. When the entrainment ratio was higher than 0.8, the superheating temperatures was found to be 35 °C for R134a and 30 °C for R456A. Because an expansion device was utilized before the evaporator#2, very low evaporation pressures were obtained in the evaporator#2; but this caused an excessive increase in the superheating temperatures. It can be asserted that both evaporators can be operated at the desired cooling capacities, when the entrainment ratio is between 0.4 and 0.8. Finally, although the cooling performance of R134a was 10% higher than that of R456A, the coefficient of performance (COP) of R456A was higher than R134a.

Transcritical carbon dioxide heat pump cycle: Validation and comparison of one-dimensional models of ejector with independent data sets

Two typical 1-D homogeneous equilibrium models from the literature (constant and variable pressure mixing models) were used to study the ejector expansion transcritical CO 2 heat pump cycle. A sensitivity analysis was performed to study the impact of the isentropic efficiency of the compressor and of each component of the ejector on the overall system performance. Two groups of independent experimental data from the literature were used to validate the two models. It was found that the cycle performance was more sensitive to the isentropic efficiency of the compressor than that of the individual components of the ejector. With appropriate input value of the compressor efficiency, both 1-D models accurately predicted the ejector outlet pressure and vapor quality. However, for the ejector entrainment ratio and cycle COP, the deviations were more than 50 %. These deviations can be significantly minimized to 10 % by eliminating the imbalance occurring in the system operation using a data post-processing method to correct the pseudo steady state in the real operation system. By comparing the simulation results of the two models, it has been shown that there is minor difference on the prediction accuracy. The research can serve as a practical reference for the operation of two-phase-flow ejector expansion transcritical heat pump cycle, and can also provide an insight and orientation for the subsequent optimization of 1-D ejector numerical models. • Two 1-D homogeneous equilibrium models of the ejector are experimental validated. • Neglecting the pressure variation during the mixing has no significant impact. • The liquid imbalance is a predominant source of the modeling deviation. • An innovative data post-processing method is proposed. • The system performance is more sensitive to the compressor isentropic efficiency.

Off-design performance of an organic Rankine-vapor compression cooling cycle using R1234ze(E)

In this study, a 264 kWth organic Rankine-vapor compression cycle (ORVC) was experimentally tested over a range of conditions to quantify the individual impact of off-design external conditions. The ORVC was designed to recover waste heat at 91°C, reject heat to a liquid condenser stream at 30°C, and produce chilled water at 7°C. The condenser heat rejection temperature was varied from 16.6°C to 32.6°C, the chilled water delivery temperature was varied between 2.1°C and 13.1°C, and the heat input temperature was varied from 91°C to 120°C. As the condenser heat rejection temperature decreased, the coefficient of performance (COP) of the ORVC improved from 0.558 at 30°C to 0.682 at 16.6°C, despite a reduction in compressor isentropic efficiency. Although the chilled water temperature variation had almost no impact on the organic Rankine cycle performance, the compressor efficiency decreased when the delivery temperature was below 7°C. At the highest chilled water temperature, 13.1°C, the COP of the ORVC was 0.643. Compressor stall was noted when the condenser heat rejection temperature was greater than 32.6°C and the chilled water delivery temperature was below 2.1°C. Increasing the driving heat source inlet temperature improved the COP of the ORVC and the thermal efficiency of the organic Rankine power cycle, while decreasing the efficiency of the compressor and the COP of vapor compression cycle. In addition, the integrated part load value of the system was determined through experimentation to be 0.682, which provides a realistic estimate of real-world performance.