Inter-stage Pressure Research Articles

Performance evaluation of supercritical CO2 Brayton cycle with two-stage compression and intercooling

Due to its small structures and high energy efficiency, the Brayton cycle using supercritical carbon dioxide (sCO2) can be implemented in various energy industries. The simulation model for a sCO2 recompression Brayton (RB) system with a two-stage compression and intercooling process (TCIP) is developed. At the design working conditions, there are minimum and optimum split ratios for the sCO2 RB with TCIP cycle. The sCO2 RB with TCIP cycle has a broader range of split ratios compared to the RB cycle. The sCO2 RB with TCIP cycle can achieve a minimum split ratio of 0.315, compared to 0.36 for the sCO2 RB cycle. The maximum efficiency of the sCO2 RB with TCIP cycle is 50.95 %, which surpasses the efficiency of the sCO2 RB cycle by 3.14 %. There exists an optimal value for the first-stage pressure ratio because the maximum efficiency of the sCO2 RB with the TCIP system tends to increase and then decrease with the increase in the first-stage pressure ratio. The pressure ratio of 1.1 for the first-stage compressor, corresponding to an interstage pressure of 8.25 MPa, maximizes the efficiency of the sCO2 RB with the TCIP cycle. The results can be used to further explore the applicability of sCO2 RB with TCIP.

Effect of Inter-Stage Pressure on Performances of Two-Stage Transcritical CO2 Refrigeration Cycle with Dedicated Absorption Dual-Subcooling and Mechanical Recooling

Effect of Inter-Stage Pressure on Performances of Two-Stage Transcritical CO2 Refrigeration Cycle with Dedicated Absorption Dual-Subcooling and Mechanical Recooling

Resolving nonuniform flow in gas turbines: challenges, progress, and moving forward

Abstract The flow in gas turbines exhibits a highly unsteady, complex and nonuniform manner, which presents two main challenges. Firstly, it introduces instrumentation errors, contributing to uncertainties when calculating one-dimensional performance metrics during rig or engine tests using fixed-location rakes. Secondly, it raises mechanical concerns, including high-cycle fatigue due to blade row interactions in turbomachines and thermal fatigue caused by hot-streaks at the combustor exit. Experimental characterisation of the flow nonuniformity in gas turbines is highly challenging due to the confined space and harsh environment for instrumentation. This paper presents recent efforts to address this issue by resolving the nonuniform flow in gas turbines using spatially under-sampled measurements. The proposed approach utilises discrete probe data and leverages a ‘Fourier-based approximation’ method developed by the author. The technique has undergone preliminary experimental validation involving reconstruction of the total pressure distribution in a multi-stage axial compressor and the total temperature field at the exit of the combustor and high-pressure turbine. Results show that, in the multi-stage axial compressor environment, reconstruction of inter-stage total pressure is achieved using a reduced dataset covering less than 20% of the annulus with reasonably good accuracy. The reconstructed total pressure yields almost identical mean total pressure values at all spanwise locations, with a maximum deviation of less than 0.02%. Additionally, reconstruction of the total temperature distribution at an engine-representative full annulus combustor is achieved using measurements at ten carefully selected circumferential locations. Results show that the reconstructed temperature field successfully captures the primary features associated with combustor exit temperature flow. The reconstructed temperature field yields excellent agreement in the magnitude of radial temperature distribution factor (RTDF) and overall temperature distribution factor (OTDF) predictions to the experiment, with a deviation of less than 0.5% for RTDF and less than 2.5% for OTDF. Lastly, reconstruction of the total temperature distribution at the exit of the GE E3 high-pressure turbine (HPT) is achieved using measurements at eight carefully selected circumferential locations. Results demonstrate remarkable robustness in resolving the temperature profile at the HPT exit with high fidelity, irrespective of the HPT inlet conditions. The initial validation results are promising, demonstrating that the new probe layout scheme and the Fourier-based approximation method enable effective characterisation of flow nonuniformity in gas turbines, thereby providing valuable insights into the complex flow of gas turbine engines.

Harnessing dimethyl ether with ultra-low-grade heat for scaling-resistant brine concentration and fractional crystallization

Solvent-driven separations may enable scalable concentration of hypersaline brines, supporting a circular resource economy from the extraction of lithium and rare earth elements from spent battery and magnet leachates. This work analyses a novel solvent-driven water extraction (SDWE) system employing dimethyl ether (DME) and ultra-low-grade heat for brine concentration and fractional crystallization. SDWE exploits DME’s unique properties: (1) a low dielectric constant that promotes water solubility over charged solutes by a factor of 103, and (2) a high volatility that facilitate efficient DME reconcentration with ultra-low-grade heat. The techno-economic viability of SDWE is assessed with a computational framework that encompasses a liquid–liquid separator and a solvent concentrator. We integrate the extended universal quasichemical model with the virial equation of state to predict the compositions of the complex three-phase DME-water mixture at vapor–liquid and liquid–liquid equilibrium. Subsequently, we optimize the thermodynamic and economic performance of SDWE, by controlling the interstage flash pressure, heat source temperature, and the number of concentrating stages. DME-based SDWE concentrates an input saline feed to 5.5 M and regenerates over 99 % of the DME using ultra-low-grade heat below 50 °C, with a DME/water selectivity ratio of 125. Our calculations reveal that optimal performance is achieved at interstage flash pressures of 0.4 – 0.5 bar for heat source temperatures between 323–373 K, with improved exergetic efficiencies at lower temperatures. At a heat source temperature of 323 K and an interstage pressure of 0.489 bar, DME-driven SDWE achieves an optimal thermodynamic efficiency of 20.5 % and a projected specific cost of US$ 1.93 m−3. These specific costs suggest that SDWE is competitive with commercialized thermal distillation technologies, while mitigating the traditional risks associated with scaling in heat and mass exchangers with hypersaline brines.

Investigations on interstage boosting pressure and pressurization prediction of a multistage centrifugal pump under gas-liquid condition

Accurate prediction of gas-liquid pressurization performance of multistage centrifugal pumps is of vital importance to evaluate oil/gas production. In this paper, interstage boosting pressure and pressurization prediction of a 25-stage centrifugal pump under air-water condition were studied experimentally. A method was developed to measure gas volume fraction under high-pressure condition by using double-ring probes. Moreover, a new method was proposed to predict boosting pressure of multistage pump by training artificial neural network of boosting pressure in 3-stage booster units, updating interstage gas volume fraction and pressure. The assumption of isothermal compression was proposed to calculate the interstage gas volume fraction, which was verified by measuring gas volume fraction at pump outlet using double-ring probes with errors lower than ±15%. The increasing stage number led to the decrease of interstage gas volume fraction and better pressurization performance in downstream stages. Besides, the head degradation in downstream stages was obviously delayed with the increase of rotational speed due to the decreasing interstage gas volume fraction. For inlet pressure 0.5–2 MPa, rotational speed 2500–3500 rpm, liquid flow rate 14–26 m³·h−1 and inlet gas volume fraction 0–44.0%, the relative errors of the predicted boosting pressure of pumps were less than 20%.

Inter-Stage Pressure Drop of Multi-Stage Brush Seal With Differentiated Structure

Abstract Uneven pressure drops among stages of multistage brush seal (MBS) leads to early failure of single-stage seal units, which directly affects service life of the seal used in aeroengines, gas turbines, and steam turbines. In this paper, influence factors of interstage pressure drop were studied to analyze formation mechanism of the uneven pressure drops. Moreover, an MBS with differentiated structure was presented, and its interstage pressure drops were further investigated. The results showed that the MBS with several same single-stage seal units had uneven pressure drops among stages under high inlet/outlet pressure ratios. In view of remarkably increasing velocity and decreasing pressure in downstream region of bristle pack near rotor surface during flow of airflow, adjustments of structural parameters (i.e., increasing height of backing plate to rotor surface Hb, increasing seal clearance Hg, and decreasing axial width of bristle pack B) could improve the uneven pressure drops among different stages due to increasing outlet air flow area of the stage. The closer pressure drop proportions of different stages to ideal average value indicated increase of Hb had a more effective effect to balance the pressure drops among different stages compared to increase of Hg and decrease of B. An MBS with differentiated structure, in which both Hb and Hg of all the single-stage seal units were increased progressively and B was decreased step by step, showed a good performance to obtain even interstage pressure drops.

Thermodynamic evaluation of two-stage refrigeration cycle with deep intercooling and series-parallel integration of thermal and mechanical compression

ABSTRACT A novel two-stage refrigeration cycle with deep intercooling and series-parallel integration of thermal and mechanical compression is proposed. Its mechanical energy consumption can be reduced by supplementing it with low-grade non-large-scale heat sources. Firstly, to show the advantages of the proposed cycle, the comparison with a two-stage refrigeration cycle with series integration of thermal and mechanical compression as well as the cascade system driven by heat and power is implemented. Secondly, the effects of the major operating parameters affecting the performance such as inter-stage pressure, inlet quality of high-pressure stage mechanical compressor and thermal compressor flow rate are analyzed. Finally, the near-optimal operating parameters for different working conditions are proposed. It is exhibited that the ECOP of the proposed layout increases by 19.4–43.7% as compared to the traditional system layouts. It is recommended that the inlet quality of 0.9 in the high-pressure mechanical compressor serves as a good guide for different operational conditions. The results show that the proposed system has a clear potential of lowering the energy consumption of cold storage refrigeration systems by supplementing with available low-grade heat. It is believed that the proposed cycle promotes a more sustainable development of fresh produce e-commerce logistics.

Thermodynamic Study of Solar-Assisted Hybrid Cooling Systems with Consideration of Duration in Heat-Driven Processes

Solar-assisted hybrid cooling systems are promising for the energy saving of refrigeration systems. In most cases, the solar thermal gain is only able to power the heat-driven process of facilities during part of the working period. Therefore, the reduction of compressor power strongly depends upon the duration of heat-driven processes, which has not been addressed properly. Motivated by such a knowledge gap, the thermodynamic understanding of solar-assisted hybrid cooling systems is deepened through considering the duration in heat-driven processes. Three absorption–compression-integrated cooling cycles were taken as examples. It was found that optimal parameters, e.g., inter-stage pressure and temperature, corresponding to various performance indicators tend to be identical, as the duration of heat-driven processes is taken into account. Furthermore, the optimal parameter for different working conditions was obtained. The dimensionless optimal intermediate temperature of layout with the cascade condensation process varies slightly, e.g., 4%, for different conditions. Moreover, the fall of compressor power in the entire working period was nearly independent upon the intermediate temperature. The paper is favorable for the efficient design and operation of solar-assisted hybrid cooling systems.

Dynamic study of the extraction ratio and interstage pressure ratio distribution in typical layouts of SCO2 Brayton cycle under temperature fluctuations

Supercritical CO2 Brayton cycle is widely used in industry because of its small compression work and considerable cycle efficiency. In this work, dynamic simulation numerical models of Supercritical CO2 Brayton cycle with three typical layouts (recompression, reheating, intercooling) and a newly proposed layout are developed using thermodynamic equations. After verifying the simulated steady-state values with the experimental ones, key parameters in the recompression and the new layout, as well as their responses under temperature perturbations, are calculated for different extraction ratios. It has been found that larger extraction ratios correspond to lower efficiency but higher stability, and similarly, the new proposed layout is 4.1% less efficient but with a 34% smaller fluctuation amplitude compared to the recompression layout. Then system parameters are calculated for different interstage pressure ratio assignments for the turbine in the reheating model and for the compressor in the intercooling model. The results show the 1st-stage with a pressure ratio of 1.2 has higher power generation and cycle efficiency, as well as more stable generated power. For the newly proposed layout, the pre-compressor power, as well as the fluctuation amplitude of the (RC + IC + PC) model, is much larger than the other compression powers, and the fluctuation amplitude from largest to smallest are IC, (RC + IC + PC), RC, RH. The effects of extraction ratio on efficiency and generated power are much greater than the distribution of interstage pressure ratio, and the maximum efficiency is obtained at the small extraction ratio and the equal pressure ratio of the two stages.

Investigating the effect of interstage pressure on cooling performance of a real-world CO2 heat pump system

The study reveals the effect of interstage pressure with the consideration of gas cooler outlet temperature on the cooling performance of an operating CO2 heat pump system currently in use at a dairy plant. Based on the numerical model and CO2 properties, it was found that the maximum mass fraction of liquid allocated for cooling can be achieved in the middle of the operating range of interstage pressure when the enthalpy at the location of the gas cooler outlet is between 341 kJ/kg. K and 399 kJ/kg. K (that is, the gas cooler outlet temperature is between 37.34 °C and 43.02 °C with a fixed discharge pressure of 85 bar), however, the maximum liquid fraction can be achieved at the upper limit of the pressure when the enthalpy is less than 341 kJ/kg. K and can be achieved at the lower limit of the pressure when the enthalpy is higher than 399 kJ/kg. K, respectively. In the comparative study on fixed and variable interstage pressure, it was found that there is small difference in cooling COP when the gas cooler outlet temperature is lower than 38.5 °C , while the COPs with variable interstage pressures surpass those with fixed pressures when the gas cooler outlet temperatures are even higher.

Optimal interstage pressures of multistage compression with intercooling processes

This study develops a method to determine the optimal interstage pressures for two-stage and three-stage compressions with intercoolers. The developed method can also be applied using multi-loop calculation for compression involving more than three stages. The developed relationship is expressed in terms of temperatures, densities and the derivative of entropy with respect to pressure. The properties used in this study are calculated from the multiparameter equations of state. Equations of optimal interstage pressures for the nonequal inlet temperature of compressors based on the ideal gas assumption, called an ideal gas model, are found and investigated. The study results show that for the high pressure and low temperature region, the ideal gas model cannot predict the interstage pressure that minimizes the total specific compression work. High pressure and low temperature are considered by comparing the critical pressure and temperature of the considered gas. The developed model can provide the optimal interstage pressure which causes minimum total compression work even if the compressions are conducted in a high pressure and low temperature region. For two-stage compression of CO2 from 6.25 MPa, 305 K to 20 MPa with isentropic efficiencies of 0.9, the developed method can save 16.63% of specific compression work, comparing to the ideal gas model. For the developed method, if the isentropic efficiency of the stage compressor increases, the calculated optimal interstage pressure raised by that stage also increases. The increase in outlet temperature of the intercooler causes increasing optimal value of interstage pressure raised by the previous compression stage.

An optimisation study on a real-world transcritical CO2 heat pump system with a flash gas bypass

The configuration of a recently installed CO2 heat pump system with a cooling capacity of 33.5 kW and heating capacity of 35.8 kW used on a dairy farm is presented. This system has been studied in order to determine the optimal performance when used for combined water heating and refrigeration. Furthermore, the effect of the interstage pressure on the CO2 heat pump system has been investigated. This required the development of a thermodynamic cycle based on the configuration of the actual constructed system and data acquired from monitoring. A compressor model with a compression ratio over three was developed and validated against experimental data with an acceptable agreement. The numerical model of the counter-flow heat exchanger between water and sCO2 has been developed assuming that the water outlet temperature is variable (just over the set water temperature), which is more consistent with actual practice. In the desktop study, the optimal COPs for heating, cooling and combined performance have been simulated considering the interstage pressure, discharge pressure and gas cooler outlet temperature. It was found that the optimal combined COPs generally decrease from 3.84 to 3.68 with the interstage pressure from 29.65 bar to 53.60 bar. Through optimisation of discharge pressure, it was found that the optimal combined COP of 4.27 occurs at the same pressure where the optimal heating COP of 2.63 is achieved (at a discharge pressure of 94 bar), while the optimal cooling COP of 1.66 occurs when the discharge pressure is around 88 bar. A further optimisation study was conducted based on a fixed cooling capacity, and it was found that the optimal cooling COP of 1.78 can be achieved when the discharge pressure is 80 bar, while the optimal heating and combined COPs are still achieved at the same discharge pressure of 93 bar (with the heating COP of 2.59 and combined COP of 4.18). Based on the simulation results, it can be summarised that the overall system thermal performance designed for heating and refrigeration is dominated by the heating performance.

Interstage Pressures of a Multistage Compressor with Intercooling.

This paper considers the criterion of minimum compression work to derive an expression for the interstage pressure of a multistage compressor with intercooling that includes the gas properties, pressure drops in the intercoolers, different suction gas temperatures, and isentropic efficiencies in each compression stage. The analytical expression for the interstage pressures is applied to estimate the number of compression stages and to evaluate its applicability in order to estimate interstage pressures in the operation of multistage compressors, which can be especially useful when their measurements are not available.

Study on the Leakage and Inter-Stage Pressure Drop Characteristics of Two-Stage Finger Seal

To solve the high leakage and high wear problems faced by sealing devices in aeroengines under the condition of high axial pressure difference, the two-stage finger seal is proposed in this paper. The finite element method and computational fluid dynamics (FEM/CFD) coupling iterative algorithm of the two-stage finger seal is developed and validated. Then the performance advantages of two-stage finger seal compared to the one-stage finger seal are studied, as well as the leakage and the inter-stage pressure drop characteristics of two-stage finger seal are investigated. Finally, the measure to improve the inter-stage imbalance of pressure drop of two-stage finger seal is proposed. The results show that the two-stage finger seal has lower leakage and lower contact pressure than the one-stage finger seal at high axial pressure difference, but there exists an inter-stage imbalance of pressure drop. Increasing the axial pressure difference and the root mean square (RMS) roughness of finger element can aggravate the imbalance of pressure drop, while the radial displacement excitation of rotor has little influence on it. The results also indicate that the inter-stage imbalance of pressure drop of the two-stage finger seal can be improved by increasing the number of finger elements of the 1st finger seal and decreasing the number of finger elements of the 2nd finger seal.

Coupling analysis of contra-rotating fan interstage pressure pulsation and blade vibration based on wavelet reconstruction.

In recent years, the flow characteristics research of the interstage region in counter-rotating axial fans in terms of fluid dynamics has attracted much attention. Especially, the dynamic relationship between interstage pressure pulsation and blade vibration in counter-rotating axial fans has not yet been clarified. This paper performs the signal processing method of wavelet decomposition and reconstruction in time-frequency analysis process. Under different flow conditions, weak-coupling numerical simulation program is employed to analyze the fluid-structure coupling interaction between interstage pressure pulsations and blade vibrations in counter-rotating axial fans. The results indicate that the fluid-structure coupling interaction field in the interstage of counter-rotating axial fans mainly excites the first-order vibration of the second-stage blade. At the same time, the consistency between the pulsation frequency and the vibration frequency of the airflow reflects the good coupling property. Two stage blades cut the airflow to cause field changes and airflow pulsation, and then, airflow pulsation causes blades deformation and produces vibrations of the same frequency at the blade. The deformation of the blades, in turn, causes the flow field changes. Rotating stall, vortex movement and breakdown produced low-frequency airflow pulsation and vortex vibration of the blade.

Thermoeconomic analysis and inter‐stage pressure ratio optimization of nuclear power supercritical CO 2 multi‐stage recompression

Implemented optimization and full life cycle economic analysis on the inter-stage pressure ratio were rarely paid attention to in supercritical carbon dioxide multi-stage recompression. In this article, a thermodynamic model of supercritical carbon dioxide recompression Brayton cycle was established based on gas-cooled fast reactor and the sensitivity analysis was performed. With the aim of seeking the optimal pressure ratio for two-stage, three-stage, and four-stage recompression configuration, the full life cycle economic indicators were predicted, respectively. Parameter sensitivity analysis indicated that the thermodynamically optimized result could not coincide with that of the economically optimized. The optimal PR distribution scheme may result in the improvement of the initial cycle system efficiency from 46.89% to 48.07%. Meanwhile the levelized cost of electricity decreased from 57.40$/MWh to 55.87$/MWh. The approaching equilibrium trend of thermoeconomic parameters confirmed the existence of the optimal number of recompression stages, which could also be derived from the prediction tendency based on full life cycle economic indicators. Furthermore, it was discovered that reducing the year of repayment and the loan proportion enhanced the net present value of nuclear power plant, but the former method gave rise to longer payback period and lower internal rate of return. The present work preserves the guiding significance for nuclear power plant investors and the utilization of the supercritical carbon dioxide Brayton system.

Investigating the frictional force distributions and inter-stage imbalance of a two-stage brush seal

Although a two-stage brush seal (TSBS) plays an important role in gas turbine machinery, few studies have investigated the complex flow and tip frictional force distributions of the TSBS. This article contributes to the ongoing investigation of the TSBS by proposing a 3D slice model employing computational fluid dynamics to analyze the flow and tip frictional force characteristics of a contacting TSBS using the torque balance principle and linear superposition methods. Our calculations reveal that as the inter-stage imbalance of the pressure decreases, so do the aerodynamic and tip frictional forces between the upstream and downstream bristle packs. In addition, the effects of the number of bristle axial rows and protection clearance height on the inter-stage imbalance are analyzed. The results indicate that the TSBS exhibited significantly less leakage and lower aerodynamic and tip frictional forces than a single-stage brush seal. However, the inter-stage pressure differential results in an inter-stage imbalance in the aerodynamic and tip frictional forces that can be aggravated under high pressure conditions. This study determined that reasonable adjustments can be made to the number of bristle axial rows and protection clearance heights of the upstream and downstream stages to alleviate this inter-stage imbalance. The findings of this study contribute to the design and implementation of more efficient TSBSs.Although a two-stage brush seal (TSBS) plays an important role in gas turbine machinery, few studies have investigated the complex flow and tip frictional force distributions of the TSBS. This article contributes to the ongoing investigation of the TSBS by proposing a 3D slice model employing computational fluid dynamics to analyze the flow and tip frictional force characteristics of a contacting TSBS using the torque balance principle and linear superposition methods. Our calculations reveal that as the inter-stage imbalance of the pressure decreases, so do the aerodynamic and tip frictional forces between the upstream and downstream bristle packs. In addition, the effects of the number of bristle axial rows and protection clearance height on the inter-stage imbalance are analyzed. The results indicate that the TSBS exhibited significantly less leakage and lower aerodynamic and tip frictional forces than a single-stage brush seal. However, the inter-stage pressure differential results in an inter-stage i...

All-Metal Scroll Vacuum Pumps for Tritium Processing Systems

Over the past decade, Air Squared has been actively developing and improving the highly anticipated 15 m3/h tritium vacuum pump to replace the obsolete industry standard Normetex scroll pump. The all-metal pump features a metal bellows that hermetically seals all tritium gas from any material other than metal. Air Squared has listened to the tritium market’s needs and is currently developing the latest addition to the Air Squared tritium vacuum pump line: the 150 m3/h liquid cooled all-metal (LCAM) scroll vacuum pump. Through numerous hours of testing, Air Squared has demonstrated the advantages of LCAM scroll vacuum pumps. The effect that thermal expansion has on highly toleranced all-metal pumps has been observed and characterized to predict pump performance as well as provide safe operational temperature limits. Performance characteristics of the 15 m3/h pump have been analyzed with different process gases to understand the effects of pumping light gases. Vacuum pumping speed curves have been generated at various interstage pressures to understand the advantages that roughing pump systems have when used in series with all-metal scroll vacuum pumps. This paper presents Air Squared’s 15 m3/h designs and highlights the performance characteristics. The effects that pump temperature, process gas, and fore-vacuum have on all-metal scroll vacuum pumps are explained with empirical data collected over a decade of research. With the knowledge and data collected, Air Squared has a pathway for a new industry standard 15 m3/h and 150 m3/h positive displacement scroll pump for tritium service to support international nuclear fusion and tritium research.

Multistage pressure-retarded osmosis configurations: A unifying framework and thermodynamic analysis

Pressure-retarded osmosis has enjoyed increasing research interest over the last decade. Recent studies focusing on single-stage PRO designs have raised doubts regarding the long-term economic viability of the technology. While most of the analyses are based on single-stage operation, comprehensive analysis of multistage PRO which shows promise for better energetic performance is absent. Previous studies on multistage PRO differ in their design philosophies and performance metrics, leading to an incomplete assessment regarding the potential benefits of multistaging. In this paper, we develop a unifying framework to classify several existing multistage configurations. In addition, we analyze the multistage PRO system from a thermodynamic perspective. Among the two major multistage design strategies, namely interstage pressure control and independent feed inputs to each stage, we found the latter to be more effective towards increasing net power density. In comparison to a single-stage device, a 10-stage system achieves around 9% higher net power density while using the same membrane area.

Analysis of performance and economical efficiency of two-stage compression heat pump system with inter-stage injection in cold regions of northern China

The low temperature adaptability of air source heat pump in the field of building heating in cold regions has always been a hot topic. At present, the combination of inter-stage injection technology and two-stage compression can effectively solve the problem of low temperature adaptability. Therefore, in the present paper, the two-stage compression heat pump system with inter-stage injection was taken as the research project. Based on the simulation model of the two-stage compression heat pump system, the process of inter-stage injection coupling between the low-stage compressor and the high-stage compressor was analyzed. Based on the experimental results, the effects of inter-stage injection process on the inter-stage pressure, inter-stage temperature and thermal performance parameters of the two-stage compression system were analyzed. The results show that as the mass of inter-stage injection increases, the inter-stage pressure will increase significantly and then increase slowly; and the inter-stage temperature will increase slowly and then decrease significantly; both the heat output and the COP will increase first and then slightly decrease. In addition, the heat output will increase by about 8%–15%, and the COP will increase by about 5%–12%. Finally, the two regions including Beijing and Dalian in China were selected, and the economical efficiency of the system in applications was analyzed in combination with the experimental results of variable working conditions of the system.