Compressor Volumetric Efficiency Research Articles

Enhancement performance of a diaphragm compressor in hydrogen refueling stations by managing hydraulic oil temperature

The objective of this study is to address the issue of high gas temperature for diaphragm compressors in hydrogen refueling stations, which leads to a high failure rate and low volumetric efficiency. The heat transfer between the gas and oil through the diaphragm is a significant heat dissipation path of the diaphragm compressor. This paper studies the performance of a 90 MPa diaphragm compressor used in hydrogen refueling stations by managing hydraulic oil temperature. Experimental results indicate that lowering the oil temperature can significantly improve the compressor volumetric efficiency and reduce the discharge temperature. For the test case, as the oil temperature decreases from 95 °C to 35 °C, the volumetric efficiency increases from 36.2 % to 43.5 %, and the measured discharge temperature decreases by 49 °C. This study proposes a thermodynamic simulation model for diaphragm compressors, and the simulation results agree with the experimental results. This model can be used to calculate the thermodynamic characteristics of diaphragm compressors and provide guidance to designers.

Performance evaluation of ecofriendly R1234ze(E) refrigerant in an automotive air conditioning system

AbstractA mathematical model for an air conditioning system used in five‐seater cars is developed with R1234ze(E) and R134a refrigerants, consisting of real system geometry like an evaporator, compressor, condenser, and thermostatic expansion valve. The mathematical model includes refrigerant properties, heat transfer, and pressure loss correlations for two‐phase and single‐phase regions. The performance parameters of a system like evaporator cooling duty, condenser heat loss, compressor power, refrigerant flow rate, and compressor volumetric efficiency obtained from a mathematical model are validated with the results of an experimental facility developed with R134a. The uncertainty analysis performed for the testing facility showed below 11% deviation. The simulation and experimental results showed an overall 10%–15% difference. It is found that the experimental cooling capacity with R134a and numerical cooling capacity with R134a show a 4%–12% variation, experimental cooling capacity with R134a and numerical cooling capacity with R1234ze(E) show a 7%–20% variation, and numerical cooling capacity with R134a and numerical cooling capacity with R1234ze(E) show a 5%–15% variation for the given range of compressor speed (500–1500 rpm), and condensing temperature (26–45°C). The study concluded that R1234ze(E) could potentially replace R134a because it has similar thermophysical properties and an average performance difference of up to 10% with R134a. Due to the limitations of the electric motor used to drive the compressor, tests in the current study were conducted at modest compressor speeds (500–1500 rpm). Future research will focus on experiments with high compressor speed (in the range of 1500–4000 rpm) and R1234yf and R1234ze(E) refrigerants for performance evaluation of automobile air conditioning systems.

Field energy performance of cold storage in East China: A case study

The energy consumption cold storage is rapidly increasing due to fast development of cold chain. However, the energy consumption composition, energy efficiency, and cooling load composition of cold storage are not clear, which become a barrier for increasing energy efficiency in cold storage. In the previous research, an accurate and convenient field cooling capacity test method is lacking. In this study, an extended compressor energy conservation –compressor volumetric efficiency method was proposed to calculate the cooling capacity of each cold room in centralized cold storage. A cold storage system in Jiangsu Province was selected for field testing. The operational characteristics and composition of electricity consumption were investigated firstly. The field test results show that the refrigeration system accounts for 80% of the total energy consumption of cold storage. Statistical analysis revealed that the valley electricity price interval and compressors accounted for 64.0% and 67.3% of the total energy consumption of the refrigeration system, in time and space, respectively. Furthermore, during the transition season (4/1–5/31), with a cold storage temperature of −18 ℃, the average daily energy efficiency ratio of the refrigeration system in the cold storage is 1.33 kWh·kWh−1. An analysis of the composition of the refrigeration load was also conducted, and the results indicated that for the overall cooling load of the cold storage, the envelope cooling load, door leakage & personnel operating cooling load, income cargo cooling load, and electrical equipment cooling load accounted for 26%, 27%, 32%, and 15%, respectively.

Energy, financial and environmental impact analysis of solar thermal heat pump systems using a direct expansion packed bed evaporator-collector

The volumetric efficiency of a compressor in solar thermal heat pump systems was reduced due to excess superheating during maximum sunshine hours. The loss of volumetric efficiency has affected the overall performance of the system. In this research, the compressor volumetric efficiency was enhanced by a direct expansion packed bed evaporator-collector to harvest the solar energy effectively during maximum sunshine hours and maintain the superheat below 5 °C. The excess solar energy harvested during maximum sunshine hours was stored in the evaporator-collector using paraffin wax – graphite composite phase change material. The performances of solar thermal heat pump systems using direct expansion flat plate and packed bed evaporator-collectors are studied and compared in terms of heating capacity, power consumption, coefficient of performance and solar fraction. The results showed that the coefficient of performance of a solar thermal heat pump system with a direct expansion packed bed evaporator-collector was improved by 1–9.5% and the heating capacity was enhanced by 1–10.8% than direct expansion flat bed evaporator collector. Further, the proposed heat pump configuration has pay-back duration of 9.9 months with 70.4% reduced CO2 emissions compared to electrical resistance heaters for the twenty years lifetime.

A study of a low pressure ratio vapor injection scroll compressor for electric vehicles under low ambient conditions

Vapor injection technology is a promising method to improve the performance of heat pump systems on electric vehicles. In this work, an experimental study on a low pressure ratio vapor injection scroll compressor was carried out under low ambient temperature conditions. Comparative experiments were conducted for various injection pressures, compressor speeds, and evaporation temperatures. The typical flow and heat transfer characteristics were obtained and analyzed, especially the compressor volumetric efficiency and compressor efficiency. The results showed that the heating performance was improved and discharge temperature was reduced with the increasing injection pressure at a higher compressor speed and a lower evaporation temperature. The volumetric efficiency and compressor efficiency both decreased with the increasing injection pressure. The maximum heating capacity could increase by 16% and the maximum discharge temperature reduction would reach 8 °C for the vapor injection process compared with non-injection process under the evaporation temperature of -22 °C. Furthermore, a semi-empirical model with correlations of volumetric efficiency and compressor efficiency was developed. The results were validated and showed a reasonable agreement with experimental results.

Investigation of flow behaviour and heat rejection for an air-cooled small multi-stage swash-plate compressor

Modelling the working process of a multi-stage reciprocating compressor is essential for improved performance and reliability. However, the squeeze-like thermal flows in the cylinder and valve plate-seat chamber, and their interactions with the inter-stage and exterior cooling flows, are so complex that detailed treatments of interactions with the surrounding environment have yet to be reported. To facilitate real-environment modelling, a numerical method is proposed within the framework of a multi-physics computational fluid dynamics package by incorporating a squeeze-like dynamic mesh and the fluid-structure interaction. With the developed approach, a three-stage four-cylinder compressor is simulated, where the valve dynamics, cylinder head heat rejection mechanism, and interior and exterior thermal-flow behaviour are exhibited. The results showed that the maximum impact velocity of the Stage 1 discharge valve is 4.8 times larger than that of the suction valve, which means that the Stage 1 discharge valve is more prone to fatigue damage. The suction air temperature is superheated owing to the heating of the cylinder head, which reduces the compressor volumetric efficiency and increases the compressor work. The predicted outer surface temperature of the cylinder head is comparable to the experimentally measured value, with a deviation of less than 6.9%, thus verifying the proposed method.

Field performance of household room air conditioners in Yangtze River Region in China: Case studies

The field performance of room air conditioners (RACs) directly affects energy consumption. In this study, a long-term field test was conducted in six residential rooms in the Yangtze River Region, China. Using specially developed test equipment, the occupancy pattern, control level, and energy performance factors for constant frequency and inverter RACs were investigated. The field test results showed that the performance of RACs was dependent on the behavior of the occupants and the properties of the service space. The occupancy pattern for RACs was classified as part-time-part-space basis. The control level for constant frequency and inverter RACs indicated that their respective hourly operation ratios and compressor frequency distributions were quite different. Furthermore, based on the compressor energy conservation – compressor volumetric efficiency method, the part load and annual performance were calculated. The results showed that the energy efficiency of inverter RACs was relatively higher with a steady evaporating temperature and small capacity loss. In addition, the actual annual energy efficiency ratios were between 2.38 and 3.83, and the gap between laboratory tests and field test APF ranges from 8.4 to 32.0%, which shows a large difference in the cooling/heating seasonal performance efficiency compared with the laboratory tests.

All-condition measuring methods for field performance of room air conditioner

Room air conditioners (RACs) are used worldwide and have become one of the major energy consumers in buildings. Because the actual field performance directly affects the energy consumption, the actual performance of an RAC must be determined. The compressor energy conservation (CEC) method exhibits better adaptability to the existing field test methods. However, the refrigerant mass flowrate cannot be calculated accurately under two-phase suction conditions, which is common for current high-energy-efficiency RACs. Therefore, two all-condition field measurement methods based on the CEC and compressor efficiency (CE) methods are proposed, and the isentropic and volumetric efficiency under wet compression working conditions is predicted with data-driven models trained using a back-propagation neural network (BPNN). The accuracy verification indicates that the relative errors of the refrigerant flowrate and cooling/heating capacities of both methods are approximately within ±15%, which is sufficient for the field performance evaluation; in addition, the CEC–compressor volumetric efficiency (CVE) method performs better. Furthermore, the proposed methods are compared, and the accuracy of the dynamic conditions is analyzed to improve the calculation performance.

Experimental Analysis of the Performances of Unit Refrigeration Systems Based on Parallel Compressors with Consideration of the Volumetric and Isentropic Efficiency

The performances of a refrigeration unit relying on compressors working in parallel have been investigated considering the influence of the compressor volumetric efficiency and isentropic efficiency on the compression ratio. Moreover, the following influential factors have been taken into account: evaporation temperature, condensation temperature and compressor suction-exhaust pressure ratio for different opening conditions of the compressor. The following quantities have been selected as the unit performance measurement indicators: refrigeration capacity, energy efficiency ratio (COP), compressor power consumption, and refrigerant flow rate. The experimental results indicate that the system refrigeration capacity and COP decrease with a decrease in evaporation temperature, increase of condensation temperature, and increase in pressure ratio. The refrigerant flow rate increases with the increase in evaporation temperature, decrease in condensing temperature and increase in pressure ratio. The compressor power consumption increases with the increase in condensing temperature and increase in pressure ratio, but is not significantly affected by the evaporation temperature.

Design and commissioning of an experimental facility for performance evaluation of pure and mixed refrigerants

The recent regulations about fluorinated greenhouse gases introduce a rapid phase-down of traditional, environmentally harmful refrigerants. Consequently, new working fluids are continuously appearing on the market, leading to the need of testing them to analyse their performance before making an ultimate choice. In the present paper, a test rig built to carry out experimental studies on different refrigerant in a drop-in application is described and first results for the set-up commissioning are commented. The experimental campaign was carried out in typical water-to-water heat pump operating conditions, varying the cold water temperature at evaporator inlet from 10 °C to 20 °C, with a step of 2.5 °C, and hot water temperature at condenser inlet from 30 °C to 50 °C, with a step of 10 °C and the compressor shaft rotational frequency from 30 Hz to 80 Hz, with a step of 10 Hz. The first findings demonstrate that the experimental results of some key performance parameters, namely heating capacity, COP and compressor volumetric efficiency, agree well with open literature trends, allowing to state that the experimental facility was correctly designed and can be used to deep the analysis on performance assessment of new refrigerants in a drop-in application.

CFD pretending of vapor and liquid refrigerant mixing in variable speed scroll compressor

The mixing of two-phase refrigerant dual ports through a variable speed scroll compressor has been simulated numerically using the shear stress transport turbulence model of the Ansys-CFX code taking into consideration the variable refrigerant flow (VRF) rate, inlet ports ratio range (0.1–0.3) at corresponding R407C flow pressure ratio of suction to secondary flow (1.5–1.8) at two variable speeds of the compressor. The investigation of the increased pressurized flow due to the mixing of the two-phase mixture with the main vapor flow port was performed. The proof of the numerical solution technique showed a percentage error within the orbit of (6–8%) with the mathematical and experimental works. The pressure ratio resultant related to refrigerant mixing volume fraction after reaching the steady state condition has been calculated, the and total mass flow rate ratio influence on the volumetric efficiency is introduced in this report. The injection technique with the designated flow ratio range has achieved an increment in the scroll compressor volumetric efficiency by 6% and achieved a decline in the outlet flow discharge temperature by (13–17) %.

Research on Energy-Saving Operation of Screw Air Compressor

Based on analysis of a screw air compressor volumetric efficiency under different discharge pressure conditions, this study establishes the mathematic model of the adiabatic compression power consumption. Under load/unload conditions, to change the offline pressure with step of 0.01 MPa, the power consumption floats up and down with the change of unloading and loading and then the screw compressor power consumption is simulated in MATLAB. The results shows that the optimal offline pressure exists at the given air consumption and meanwhile power consumption is minimal with the optimal offline pressure. It also reveals that the required optimal offline pressures will vary by air consumptions. Then, based on dynamic mechanical analysis for fluid motion in the pipe, considering that there is a causal relationship between pressure variation and gas flow variation, a method for measuring flow rate of one dimensional unsteady flow dynamically is proposed based on theory of linear approximation. In order to lower the online pressure and further reduce the energy consumption of screw air compressor, we propose a method is to calculate the rate of pressure drop and predict times for the discharge pressure dropping to the online pressure. And the further optimal control method of screw air compressor is given. It is correct and feasible, which proved by experiments.

Analysis of Energy Factor Effectiveness in Air-Conditioning Refrigeration System

This paper deals with the energy-saving product design involving the product energy property into design process. On the basis of the energy factors concepts, the paper analyzes the extraction process and energy effectiveness model of energy factors. To study the air-conditioning refrigeration system, the paper establishes the energy information model, recognizes the crucial and controllable energy element and extracts the energy factor set C = {compressor volumetric efficiency λ, motor efficiency ηd, power frequency fd, heat transfer performance coefficient φ, finned lateral general area Ao}. Then it makes a further decomposition of coupling energy factors λ, φ and finds out the corresponding design parameter. In the end, the paper maps the energy factors and design parameter into design process, establishes the energy effectiveness model and presents several measurers for decreasing the energy consumption during the actual use of air-conditioner.

Parametric study of pressure increase across a compressor in ethanol-water vapour recompression distillation column

Heat pumping has been used in reducing energy consumption in distillation columns. However, the effects of some parameters have not been taken into consideration in the determination of energy consumption in such systems. The consideration of these parameters may give more insight into the performance of such systems. The purpose of this study was to develop a thermodynamic simulation model for comparing two distillation systems: one operating with pressure increase across the compressor and the other with negligible pressure increase over the compressor. An ethanol-water conventional distillation column with direct vapour recompression was used as a case study. The study shows that when the pressure across the compressor increases, the compressor power input, compressor displacement rate, compressor heat load rate and total energy consumption increased while the coefficient of performance and compressor volumetric efficiency decreased. The significance of this work is the provision of information for the determination of energy effectiveness as well as appropriate capacity of the auxiliary equipment for ethanol separation which is becoming a more competitive fuel. Key words: Compressor, distillation column, energy, pressure drop, vapour recompression.

Analysis of the gas compressibility effects on the constant-entropy reversible processes of refrigerants and refrigerant mixtures

Thermally and calorically real gas modelling based on the Martin–Hou equation of state is assumed for pure and mixed refrigerants in the superheated vapour phase. It allows the constant-entropy reversible processes which take place within the work transfer components of ideal vapour compression cycles to be properly analysed. These processes, in fact, occur in a region of the Mollier diagram close to the saturated vapour curve where covolume and molecular forces alter the equation of state of an ideal gas. Thus, real gas effects are significant and cannot be ignored. They give a more accurate indication of the refrigerant end temperature associated with an isentropic compression as well as of the corresponding work exchanged and volumetric efficiency. In particular, it is shown that the gas compressibility effects play a ‘ favourable’ role during the isentropic compression processes since they allow the work transferred to be reduced up to 10% for HFC-refrigerant 134a, and HFC-refrigerant mixtures 407C and 410A. But, at the same time, they play an ‘ unfavourable’ role since they can reduce the compressor volumetric efficiency (i.e. refrigerant mass flow rate) and, consequently, the cooling (or heating) capacity of the vapour compression system up to 7%.

The Relationship of Optimum Heat Exchanger Allocation and Minimum Entropy Generation Rate for Refrigeration Cycles

This paper investigates the effect of heat exchanger allocation on overall system performance using both reverse Carnot and vapor compression refrigeration cycle models to calculate system performance and entropy generation rate. The algebraically simple constraints applied in previous studies are shown to be justifiable. The vapor compression model considers nonideal compressor performance, compressor volumetric efficiency, refrigerant properties, and throttling, in addition to mechanistic heat exchanger models. The results support the conclusions of previous studies in that maximum performance is observed when the condenser and evaporator thermal sizes are approximately equal. For air-to-air systems, this result indicates that the areas of the heat exchangers should be approximately equal. However, it is found that minimizing the entropy generation rate does not always result in the same design as maximizing the system performance unless the refrigeration capacity is fixed. Minimizing the entropy generation rate per unit capacity is found to always correspond to maximizing the coefficient of performance of refrigeration systems.

高効率ヘリウム用油噴射型スクリュ圧縮機

Two-stage screw compressors incorporating oil injection systems are extensively applied to helium refrigeration systems used in cooling superconducting equipment. The investigation of the optimum condition and the reliability of the two-stage oil injection type helium screw compressor have been carried out, in order to determine ways of enhancing compressor performance with the high reliability. In result, it was found that the compressor volumetric efficiency is increased by reducing the mass flow ratio of the helium gas/lubricating oil while accelerating the compressor revolution speed. And it was proved that the compressor volumetric efficiency is significantly influenced by the sound speed in the mixture of gas and lubricating oil. Furthermore, authors were able to derive a formula for predicting the change of the compressor volumetric efficiency, when the mass flow ratio of gas/lubricating oil and the revolution speed are changed. It was also found that the shaft power is decreased by setting the ratio of the high- and low-stage theoretical volumetric flow rates to 1:4 and utilizing a low viscosity lubricating oil. In result, the advanced experimental machine achieved an isothermal efficiency level of 60% without any trouble.