Research on the performance of a high pressure 5.3MPa twin screw compressor

High pressure twin screw compressors have been widely employed in fuel gas boosting and petrochemical industry. Recently, such compressors, whose maximum of discharging pressure is 5.3MPa, are also adopted in high temperature NH3 heat pumps and NH3/CO2 cascade refrigeration system. However, high pressure twin screw compressors are required to have large capacity, good performance and excellent stability at high operating pressure. In this paper, a semi-empirical model for open-type high pressure twin screw compressor is developed. Experimental research is conducted for identification of parameters, while validation is also made on the accuracy of the model. On the basis of theoretical and experimental research, the performance of the compressor, which includes volumetric efficiency, adiabatic efficiency, discharge temperature and lubricant oil flow rate/temperature, are illustrated. The change pattern of such features on the operating conditions, slide valve loadings and ambient features are then analyzed. Additionally, the stability test results of the high pressure twin screw compressor including the vibration and noise are also shown

Experimental Investigation on the Operating Characteristics of a Semi-hermetic Twin Screw Refrigeration Compressor by means of p-V Diagram

In this paper, a comprehensive experimental investigation is carried out to evaluate the operating characteristics of a semi-hermetic twin screw refrigeration compressor at different oil flow rates and slide valve positions under various conditions. The working volume pressure of the compressor is recorded by a serial of sensors arranged in consecutive positions in the housing. These measured pressure data are then transformed into an indicator diagram. Based on the p-V diagrams, the effect mechanism of some factors such as evaporation temperature, condensation temperature, slide valve positions, oil flow rates for the suction and discharge end bearings lubricating and oil flow rate returned from the suction pipe on the compressor performance and working process is analyzed. These results can be useful for optimum design of oil flow passage assembly and selection of optimal built-in volume ratio to improve the energy efficiency of refrigeration system with semi-hermetic twin screw compressor

Experiment Study of a Water Injected Twin Screw Compressor for Mechanical Vapor Compression System

The mechanical vapor compression (MVC) system is a promising way for energy saving among energy intensive industries such as desalination, food and beverage, chemistry and waste water concentration etc. In practical its application is limited by the vapor compressor technology which is demanded to have high pressure ratio for large saturation temperature difference and low discharge steam temperature. Due to the ability of wet compression, twin screw compressor can overcome the technical limitation above by the injection of liquid water into the working chamber. In this paper a test rig of a MVC system with water injected twin screw compressor has been designed and built. Compressor performance of flow rate, power consumption and discharge temperature was measured. Moreover, operation characteristics of the water injected twin screw compressor were studied by the measurement of its working process p-V diagram. Volumetric efficiency and adiabatic efficiency of the compressor variation under different operation conditions were calculated. The mass flow rate and temperature of injected water was also measured and adjusted for optimization. The results of the experiment study can provide some design guidances of water injected twin screw compressor for mechanical vapor compression system

Field Evaluation for Air-source Transcritical CO2 Heat Pump Water Heater with Optimal Pressure Control

Air-source transcritical CO2 heat pump water heater (ATHW) can supply hot water from 60 ? to 90 ? at high efficiency with environment-friendly refrigerant CO2 for commercial, residential and industrial applications. Several optimal discharge pressure correlations for transcritical CO2 heat pump have been proposed in the past few years, most of which are related to the ambient temperature, the evaporation temperature and the gas cooler outlet temperature. In an earlier study, the authors’ research group had presented a study on the dependency of the optimal discharge pressure on the ambient temperature and the hot water outlet temperature. In this study, a revised model for optimal discharge pressure is developed based on experimental results. In order to validate the optimal discharge pressure model developed, field tests are conducted to evaluate the performance of an air-source transcritical CO2 heat pump water heater in practical application. The system is comprised of a semi-hermetic reciprocating compressor, a counter-flow tube-in-tube gas cooler, a counter-flow internal heat exchanger, a fin-and-tube evaporator, and an electronic expansion valve (EEV) driven by electrically operated step motor. A Siemens SIMATIC S7-200 Programmable Logic Controller (PLC) was used to regulate the compressor discharge pressure by adjusting the EEV opening and the water flow rate by changing the frequency of the variable speed water pump. Field tests were conducted under three different operating scenarios: the nominal test condition, high water supply temperature condition and low ambient air temperature condition. The results show that the coefficient of performance (COP) can achieve 3.76 in the nominal test condition with 15? water inlet temperature and 80? hot water supply temperature. Even when the hot water temperature is higher than 90?, the COP remains at 3.21 with 20? dry-bulb temperature and 15? wet-bulb temperature. Under low ambient air temperature condition, the COP was 2.19 with the hot-water supply temperature of 60?. Comparison between the field test results and the model predictions show that the maximum relative error of discharge pressure control was 5.6% in the low temperature condition, while the maximum relative error of system COP was only 4.7%. With the reasonable agreement observed between the field test results and the model prediction. It is reasonable and effective to model the optimal discharge pressure as the function of the ambient temperature and the water outlet temperature

Study on Optimal Middle Temperature of Cascade-condenser in CO2/NH3 Cascade Refrigeration Systems with Two Temperature Ranges

This paper analyzes a CO2/NH3 cascade refrigeration system of two temperature range applied in the cold storage. A mathematical model is presented to determine the optimal middle temperatures of the cascade-condenser for obtaining the maximum coefficient of performance (COP) under different operation conditions. Three main parameters including the evaporation temperature in the cold storage, the evaporation temperature in the refrigerated storage and the condensation temperature in the high temperature stage are used to study the optimal middle temperature of CO2 in the cascade-condenser. The results show that the optimal middle temperature increases with the increment of three main parameters. Moreover, under specific conditions, the optimal temperature is equal to the evaporation temperature of refrigerated storage. The results shown in this paper is helpful to the control strategy of CO2/NH3 cascade refrigeration systems for two temperature ranges

Numerical Analysis on a Perforated Muffler Applied in the Discharge Chamber of a Twin Screw Refrigeration Compressor Based on Fluid-Acoustic Coupling Method

The twin screw compressor has been widely used in the refrigeration systems due to advantages such as compact structure, stable operation, high efficiency and good adaptability. Intermittent gas flow generates gas pulsation that cause serious problems such as structural vibration and noise in the twin screw refrigeration compressor. Because the mechanical noise can be controlled well with the improvement of machining and assembly accuracy, the aerodynamic noise induced by gas pulsation even has become the main noise source of the twin screw refrigeration compressor. In order to reduce the pressure pulsation, a broadband perforated panel muffler applied in the discharge chamber of the twin screw refrigeration compressor is proposed based on the noise spectrum and flow characteristics of the compressor. In order to obtain the noise spectrum of the twin screw refrigeration compressor, the pressure fluctuation in discharge chamber based on a three-dimensional CFD simulation model is calculated, and the acoustical model is established based on fluid-acoustic coupling method. Then the impacts of different structural parameters on the performance of a perforated panel muffler are investigated, including perforation rate, perforation diameter and panel thickness. Through the optimization of the perforated muffler, a better reduction effect of broadband noise can be achieved. Results of fluid-acoustic coupled analysis can provide guidance on the design and optimization of the perforated muffler and noise reduction of the twin screw refrigeration compressor

SPI1-induced downregulation of FTO promotes GBM progression by regulating pri-miR-10a processing in an m6A-dependent manner

As one of the most common post-transcriptional modifications of mRNAs and noncoding RNAs, N6-methyladenosine (m6A) modification regulates almost every aspect of RNA metabolism. Evidence indicates that dysregulation of m6A modification and associated proteins contributes to glioblastoma (GBM) progression. However, the function of fat mass and obesity-associated protein (FTO), an m6A demethylase, has not been systematically and comprehensively explored in GBM. Here, we found that decreased FTO expression in clinical specimens correlated with higher glioma grades and poorer clinical outcomes. Functionally, FTO inhibited growth and invasion in GBM cells in vitro and in vivo. Mechanistically, FTO regulated the m6A modification of primary microRNA-10a (pri-miR-10a), which could be recognized by reader HNRNPA2B1, recruiting the microRNA microprocessor complex protein DGCR8 and mediating pri-miR-10a processing. Furthermore, the transcriptional activity of FTO was inhibited by the transcription factor SPI1, which could be specifically disrupted by the SPI1 inhibitor DB2313. Treatment with this inhibitor restored endogenous FTO expression and decreased GBM tumor burden, suggesting that FTO may serve as a novel prognostic indicator and therapeutic molecular target of GBM.publishedVersio

Numerical Study on Rotor Deformation of Multiphase Twin-Screw Pumps Under High Gas Volume Fraction Conditions

Multiphase pumping with twin-screw pumps is a relatively new technology that has been proven successful in a variety of field applications. It has three advantages such as less environment pollution, few separation equipments and more convenient operation than the conventional system. Despite many advantages of this technology, some problems have been encountered when operating under conditions with high gas volume fractions (GVF). While twin-screw multiphase pump is operating under high GVF conditions, the inner temperature of the pump increases obviously. The clearances between rotors change greatly and influence the volumetric efficiency of the twin-screw multiphase pumps. In some severe conditions, it may cause the pump damage. In this paper, the actual force and thermal boundary conditions are proposed through further investigations of pressure distributions and heat transfer. And then the screw rotor deformation and temperature field are calculated under different GVF conditions with ANSYS software. The results indicate that the main deformation of screw rotors is thermal deformation and the maximum radial deformation occurs on the top of the rotor in the discharge port. Through analyzing the influence of screw rotor deformation on the clearance, it can be realized that the greatest clearance changes are in the root of the rotor, followed by circumferential clearance, and there is no changes in flank clearance