Refrigeration Compressor Research Articles

Automation of Temperature Measurement in Induction Motors of Hermetic Compressors Based on the Method of Temperature Rise by Resistance

Recent studies have proposed the use of artificial neural networks to establish a correlation between the cooling capacity of refrigeration compressors and the results of quick production quality tests. However, the temperature measurement method used in the tests reflects a high uncertainty in the estimated performance parameters, primarily because the measurement is performed on the compressor shell, which has large thermal inertia and does not accurately reflect the temperature changes observed during the tests. This study proposes a set of modules that allow the application of the method of temperature rise by resistance to estimate the winding temperature of the single-phase induction motor of the compressor in quick quality tests. The winding temperature is a better estimate of the temperature at which the refrigerant fluid enters the compression cylinder and its use solves many of the problems associated with the traditional method. Validation tests show that the proposed solution is capable of automating the measurement in a safe, agile, and metrologically more reliable manner than the method currently used in quick quality tests in the industry.

IMPROVEMENT OF VOLTAGE STRESS ON MOTOR CONTROL HARDWARE VIA OPTIMAL LOCATION OF RC SNUBBER CIRCUIT

While the increase in the customer failure rate in the consumer electronics sector affects the manufacturers negatively in terms of cost. It has also become one of the issues that cause customer loss and customer satisfaction. In addition to the economic losses, during the production and distribution of the spare parts and products that are changed at the customer's home due to the reliability problems experienced in the field, extra carbon emissions are released to the nature for this operation. For these reasons, it has become important to reduce the rate of customer failure. 
 With the increase in electronic components, the quality and reliability precautions that may occur in the electronic circuits, have become the subject of study today. As in many white goods products, it is advantageous to have variable speed motors in refrigerators due to energy efficiency and energy regulation issues. For this reason, the compressor of refrigerator comes to the forefront as the component that dissipates the highest power proportionally. With the use of variable speed compressors, the need for an electronic board with including power conversion and motor driving capability has arisen.
 In this paper, RC Snubber circuits have been studied in order to prevent quality problems that may occur due to high switching frequency in flyback converter topology, which is one of the DC-DC converters that provide isolation. The methods in the literature based on the location of the RC Snubber in the circuit and the determination of its related values were examined and experiments were made on the simulation program. At the same time, a test mechanism was set up on the variable speed compressor motor control card of the refrigerator and measurements were taken with the help of an oscilloscope. The measurements taken in the simulation program and the experimental environment were compared.

Suppression of the HFO-1123 disproportionation reaction by adding R290

Trifluoroethylene (HFO-1123) is a promising next-generation refrigerant candidate for refrigeration and air-conditioning applications owing to its low global warming potential (GWP) of less than one and zero ozone depletion potential. However, HFO-1123 may undergo a thermal decomposition reaction under high-temperature and high-pressure conditions. The refrigerant compressor is heated when glitches occur. Pressure and temperature inside the compressor are assumed to be approximately 6.0 MPa and 150 °C, respectively, in the worst practical situation. Subsequently, energy is input by short circuits between the enameled windings of the motor in the compressor. Consequently, a thermal decomposition reaction called disproportionation reaction propagates in the compressor, potentially causing the compressor to explode. From a safety perspective, it is mandatory to suppress this reaction under practical use. A previous study evaluated the suppression effect of inhibitors such as R32 and R13I1; herein, we explored an optimized inhibitor composition that simultaneously fulfills the requirements of excellent suppression of the disproportionation reaction under the worst practical condition and low GWP. R290 was selected as a new inhibitor owing to its extremely small thermal decomposition energy. Subsequently, suppression of the disproportionation reaction was investigated using mixtures of R290 and HFO-1123. The results revealed that the disproportionation reaction was suppressed at a critical concentration of R290. The suppression effect of R290 was confirmed by validation experiments using actual compressors.

Design and performance of solar-refrigerated, evaporatively-cooled structure for off-grid storage of perishables

Stand-alone cooling systems for the storage of perishables are needed in regions of the world lacking reliable electricity and the financial wherewithal to make sufficient investments in on-grid cold stores. To meet this need, we have designed an off-grid, batteryless solar refrigerated and evaporative cooled (SREC) structure that can be self-built by smallholder farmers. Several innovative features have been incorporated including a "water battery" (a thermal reservoir) to provide nighttime cooling, a dual-use refrigeration coil to cool the thermal reservoir and interior air simultaneously, and a solar adaptive controller to regulate power demand by refrigeration compressor based on available solar energy. Two SREC designs were built with frames of concrete (c-SREC) and iron (i-SREC) and evaluated for their ability to regulate temperature and humidity. The temperature data was used to estimate percent respiratory reduction and relative change in storability (RCIS) and compared with a structure operating only on evaporative cooling (EC) alone (i.e., the same structure without refrigeration). The inverter and solar panels specifications and the design of water battery and solar adaptive controller (SAC) are described; the structures were constructed and evaluated in the northern part of India (Delhi, Haryana, and Rajasthan) from 2017 to 2022. The interior temperature reduction relative to ambient ranged between 5 and 35 °C, varying throughout the day and across the seasons. During the hot, dry season of the year, the temperatures inside the i-SREC structures were lower than those in c-SREC structures, however, when solar insolation declined during the monsoon season, the two structure types performed similarly. In accordance with its slightly poorer temperature performance, c-SREC structure yielded a lower average reduction in the estimated rate of respiration (56–78 %), compared to i-SREC (74–83 %). The estimated respiratory reduction in EC storage was much lower (13–39 %) when compared with SREC structures due to the lack of active cooling. The estimated RCIS was between 0.16 and 0.65 for the EC storage relative to ambient from March-June whereas the RCIS was 3–5 for the i-SREC structure and 1–3 for the c-SREC structure. The i-SREC out-performed the c-SREC during periods of high solar radiation, likely a result of the much-reduced thermal mass of the roofing materials in the i-SREC. A significant reduction in storage temperature and improvement in storability of perishables can be achieved, relative to ambient and relative to evaporative cooling alone, in SREC structures. The SREC structure is feasible for perishables storage by smallholder farmers and farmer organizations, however, it should be noted that the cloudier months caused a sharp decline in cooling capability as solar radiation levels restricted compressor function, so storability limitations for target crops will need to be considered as a function of season.

LUBRICATING PROPERTIES OF POLYESTER OILS AND R404A REFRIGERANT MIXTURES UNDER STARVED LUBRICATION CONDITIONS

There has been a dynamic shift towards the use of ecological refrigerants in the refrigeration industry. Until recently, R404A was a quite commonly used HFC refrigerant for commercial refrigeration equipment, in both small and large systems resulting in the need to select appropriate compressor lubricants. In refrigeration compressors, the amount of oil in friction pairs in certain situations may be insufficient. In that event, starved lubrication conditions or lubrication only by refrigerant may occur. The article contains a methodical selection of test parameters for polyester oils allowing one to assess the lubricating properties of the mixtures of oils for refrigeration compressors and refrigerants under the conditions of poor lubrication. The article also includes the results of wear tests which allow one to evaluate the lubricating properties of oil-refrigerant mixtures under starved lubrication conditions for R404A refrigerant and polyester oils.

Study on the coupled characteristics of high-speed centrifugal compressor and turboexpander of a reverse Brayton air refrigerator

Reverse Brayton air refrigerators are environmentally friendly and have broad application prospects, which can work under various conditions. In this paper, the characteristics of a open-loop air cycle for room temperature applications were investigated. The compressor and turboexpander in the cycle were modeled by numerical simulation. Based on coupled characteristics of the compressor and expander, a system model was established. The effects of the first stage compression ratio and the expander inlet temperature on the refrigerator performance were studied by experiments. The accuracy of the system model is verified by comparing with the experiments, and the maximum deviations of expander rotating speed and supplied mass flow are 3.1% and 4.83%, respectively. With the increase of the first-stage compression ratio and the decrease of expander inlet temperature, the mass flow rate of supplied air and cooling capacity of the cycle increase. The expander efficiency can be maintained near the optimal value. At the expander inlet temperature of 313.2 K, COP drops by 31.7 % when the cooling capacity is reduced from 3.34 kW to 0.74 kW.

Economics/safety trade-off in compression refrigeration with superheat

The widespread use of compression refrigeration in modern society is an example of a societal need that was unheard of two centuries ago. Ancient civilizations developed and flourished in hot climates without any widespread use of methods to provide more comfortable conditions. Modern society now considers it virtually a constitution right to have air conditioning in all homes, schools, office buildings and transportation vehicles. Modern food industries are dependent on refrigeration for preservation and distribution of many food products.This paper descripts an experimental laboratory compression refrigeration unit and presents quantitative dynamic simulations to show the effectiveness of a proposed control structure. Two conventional PI controllers control the amount of superheat and the refrigeration load by manipulating refrigerant flowrate and compressor power. The novel contribution of this paper is a quantitative exploration of the important engineering trade-off between safety and operating cost in compression refrigeration systems with superheat.

Mixtures of Lubricants and Ecological Refrigerants under Starved Lubrication Conditions.

The presented results show that the presence of refrigerant significantly deteriorates the lubricating properties of compressor oil under starved lubrication conditions (with a small amount of oil). The change can be 40-120% compared to the properties of the oil alone. Additionally, in the group of oils that are substitutes (operational alternatives) compatible with a given refrigerant, the effect of the refrigerant on the lubricating properties varies. The differences can be as much as 25%. In order to evaluate and properly select compressor oils for the refrigerant, the lubricating properties should be tested in a mixture with the refrigerant under conditions similar to actual operation. Such an evaluation of lubricating properties is made possible by the author's method of testing the wear of the block-on-ring friction node. The obtained rankings of lubricating properties for oils (due to the wear volume) can provide good guidelines for the suitable selection of a lubricant for refrigeration compressors (especially for new, environmentally friendly refrigerants, such as R452A). The research was carried out for mixtures of zeotropic refrigerants (R404A, R452A) with polyester oils (POE) and natural refrigerant (R600a) with mineral oils (MO). In each group of refrigerants, different mechanisms of oil-refrigerant mixture formation occur. Each refrigerant was tested with three different compressor oils recommended for each other for alternative uses in refrigeration systems.

Effect of internal structure installed in pressure vessel in HFO-1123 disproportionation reaction

Trifluoroethylene (HFO-1123) has been attracting considerable attention as a promising low-global-warming-potential refrigerant for new residential split air conditioners. However, if the refrigerant compressor short circuits, the disproportionation reaction of HFO-1123 may propagate under high-temperature and high-pressure conditions, which may lead to compressor explosion. Studies seeking to suppress the disproportionation reaction by adding refrigerants that do not cause the disproportionation HFO-1123 reaction have been performed; two refrigerant mixtures have been proposed as next-generation refrigerants. However, these mixtures could not suppress the disproportionation reaction under the worst condition (150 °C, 6.0 MPa) in practical use. Consequently, the difference in the reaction propagations between the experimental vessel and actual compressor for further suppression was investigated in this study. The experiment was conducted by introducing an internal part that mimics the actual compressor into the vessel. We investigated whether the flame ignited at the bottom of the vessel would pass through a small slit installed in the center and propagate to the entire vessel. The parameters were the volume of the ignition space and the width and thickness of the slit. When a combustion flame passes through a narrow gap, it may be cooled by a solid wall and extinguished. It was expected that the flame would be cooled and extinguished when passing through a narrow space, even in the disproportionation reaction. It was found that the reaction suppression effect was significant when the slit width was 1 mm or less.

Effect of reaction inhibitor on diesel explosion of split air conditioners

A compressor rupture accident may occur because of erroneous operation during the pump-down of residential split air conditioners. An engine for a model airplane was used to simulate a refrigerant compressor, and experiments were conducted on the diesel combustion of mixtures of refrigeration oil, refrigerant, and air. The effect of the reaction inhibitor concentration in the refrigeration oil on combustion suppression was investigated. The refrigeration base oil used was polyol ester oil, and the additives were phenolic antioxidants (A1), epoxy stabilizers (A2), and phosphorus antiwear agents (P1). The refrigerants used were R22, R32, R1234yf, and R290. R22 is old and non-flammable; however, it was selected because it is the refrigerant with the most reports of compressor explosion accidents. R1234yf is not currently used in split air conditioners, but a mixture of R32 and R1234yf may be used in the future; therefore, R1234yf was chosen. The combustion range became narrower and the maximum pressure decreased as the concentration of the additive increased. Additive A2 showed a suppression effect on many refrigerants even when 1 wt% was added. In particular, for R290 and R1234yf, the concentration range of diesel explosions was significantly reduced.

Fracture of Alloy Steel Cap Screws in a Refrigeration Compressor

Fracture of Alloy Steel Cap Screws in a Refrigeration Compressor

Research on motor cooling process of centrifugal refrigeration compressor with gas bearings

Centrifugal refrigeration compressor with gas bearings is an important development direction for the water chiller. The high-speed and compact structure leads to worse heat dissipation conditions for the motor and cooling it with refrigerant directly is an effective method. In this paper, the flow field of the refrigerant and the temperature distribution of the motor under different operating conditions and structural parameters are simulated. The results show that the highest temperature point of the motor is at the central position, and the stator winding temperature is much lower than the permanent magnet. The cooling process is related to the inlet pressure, inlet dryness, back pressure, and the structure of the cooling passage. Increasing the inlet pressure and decreasing the back pressure will reduce the temperature of the stator winding and the permanent magnet in the motor. The inlet dryness will influence the windage loss change obviously so that the temperature change trend of the stator winding and permanent magnet is different, the temperature variation range of winding and the permanent magnet is 16 °C and 40 °C respectively. Increasing the inlet diameter, outlet diameter, and injection orifice diameter will reduce the motor temperature, but the temperature changes slightly after it reaches a certain value. In the selected adjustment range, the outlet diameter has the greatest influence on the motor temperature, and the temperature variation ranges of winding and permanent magnet are 28 °C and 120 °C respectively.

Simulation of CO2 heat pump air conditioning system for new energy vehicle

The CO2 heat pump air conditioning system of new energy vehicle is designed, and the vehicle model of CO2 heat pump module and heat management system is established based on KULI simulation. The effects of refrigerant charge, running time and compressor speed on the heat pump air conditioning system is studied, and the energy consumption is compared with the PTC heating system and the CO2 heat pump air conditioning system without waste heat recovery. The results show that the optimal charge for full-service operation is 750 g; increasing the compressor speed can increase the cooling capacity, so that the refrigerant temperature in the passenger compartment and battery inlet can quickly reach the appropriate temperature, but the COPh, COPc are reduced by 2.5% and 1.8% respectively. By comparing it with PTC heating and CO2 heat pump air conditioning systems without waste heat recovery, it is found that the energy consumption of this system is only for the PTC heating systems 42.5%, without waste heat recovery carbon dioxide heat pump air conditioning system of 86.6%. It greatly saves energy, but also increased the waste heat recovery function, so that the system supply air temperature increased by 26%, improve passenger cabin comfort. This provides a reference for the future experimental research of CO2 heat pump air conditioning and heat management system.

Study on suction pressure loss near suction end and stagnant pressure rise in p-θ diagram of Twin-screw refrigeration compressor for chiller

• A twin-screw refrigeration compressor is tested under different operating conditions. • Two phenomena of efficiency loss are analyzed and causes are founded. • A three-dimensional CFD model is established to further analyze these phenomena. • Some optimization to avoid these efficiency losses is proved to be effective. To improve the efficiency of the twin-screw refrigeration compressor, two pressure characteristics in the p-θ diagram, such as suction pressure loss near the suction end (SESPL) and stagnant pressure rise in the compression process (CPSPR), were investigated in this paper. A three-dimensional CFD model of a twin-screw refrigeration compressor for chillers was established to analyze the generating mechanism of these phenomena. The p-θ diagram and performance of the compressor were tested and compared under variable working conditions, to verify the simulation results. Analysis results showed that the SESPL is caused by the small flow area between the working volume and suction chamber, and the CPSPR is mainly caused by inflow and outflow in the closed cavity of the vapor injection port. On the basis, some improvement directions were put forward to avoid these efficiency losses, i.e. appropriately delaying the suction end angle and blocking the vapor injection port. Experimental results indicated that the volumetric efficiency and total efficiency both increased by about 2% under different condensing temperatures after delaying the suction end angle of the axial suction port by 18° and blocking the vapor injection port of the compressor.

Investigations on Force Characteristics of Orbiting Scroll in Asymmetricsuction Scroll Compressors

Background: Scroll refrigeration compressors are the critical equipment for the refrigeration system in air conditioners and vehicles. The asymmetric suction structure can be applied to reduce the scroll compressors' size. However, the pressure difference between the symmetric working chambers becomes larger and leads to the special force characteristics of the orbiting scroll. Objective: This paper illustrates the force characteristics of the orbiting scroll in an Asymmetric-suction Scroll Compressor (ASC) to improve its stability and reliability Methods: The theoretical model has been established to calculate the force and moment acting on the orbiting scroll of ASC and the Symmetric-suction Scroll Compressor (SSC) based on the transient numerical simulation results. Results: The variations of gas force and moment in ASC and SSC are displayed and compared. Their pulsation intensities are calculated and discussed. Conclusion: The pressure in the outer compression chamber of ASC was always higher than that in the inner compression chamber, which caused significant discharge loss. Affected by the tangential leakage flow, the radial force of the compressor fluctuated sharply. As the tangential force on the orbiting scroll segments of symmetrical working chambers in ASC led to the negative spin moment, the total average spin-torque decreased by 71.3%. Still, the pulsation intensity increased by ten times. Furthermore, the direction of the spin moment reversed at 275°~355°, which indicated that the orbiting scroll impacted the Oldham ring every rotation. The noise and vibration would happen, and the Oldham ring would be damaged easily.

Cost-Effective Assessment of Surface-Mounted Permanent-Magnet Motors for Refrigerant Compressor Applications Used in High-Temperature Environments

With the introduction of stricter energy-efficiency-ratio regulations, the surface-mounted permanent-magnet motor (SPM) is gaining increasing attention due to its inherent high-power density. This article investigates the feasible SPM structures for refrigerant compressor applications, particularly those used in metal industry factories with high surrounding temperatures so that cost-effective solutions can be achieved. A theoretical model is first established to aid structural parameter optimizations and the management of specific operational objectives and constraints; multiple SPM arrangements are investigates, with ease of manufacturing implementation being one consideration, as shown in Liu <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">et al.</i> , 2021. Detailed finite element calculations and experimental measurements are performed to develop feasible SPMs with optimized structural arrangements that meet the desired operational objectives.

Inherent capacity modulation of a linear refrigeration compressor

Conventional refrigeration compressors sized for peak cooling load actually operate at partial load mostly which could cause excessive on-off cycling loss. Linear compressor could overcome this challenge by varying the compressor stroke in response to transient cooling load. The present work establishes a numerical model for the capacity modulation of linear compressor using R134a through changing the input voltage to meet the cooling load. The numerical model contains a linear compressor model (including three sub-models describing the in-cylinder thermodynamic process, the piston mechanical dynamic process and the electrical part behaviour, respectively) and an input voltage modulation loop. Experimental data are collected for the validation of the numerical model. The results show that the capacity modulation, aiming to meet the cooling load within the error of 5%, can be achieved through varying the input voltage while fixing temperatures of heat exchangers. An increased voltage brings increased compressor stroke and mass flow rate in a linear trend with the heat exchanger temperature unchanged. Lower input voltage leads to higher motor efficiency due to lower copper loss. At a fixed condenser temperature and cooling load, the inherent capacity modulation can save energy with evaporator temperature increasing as the power consumption decreases. At condenser temperature of 50 °C, 40 °C and 30 °C, the CoP only changes by 1.5%, 0.9% and 2.7% when the cooling load changes from 100 W to 200 W. The inherent capacity modulation will allow the linear compressor to maintain a high annual efficiency for refrigeration.

Analisa kerja alat uji prestasi mesin pendingin udara dengan kapasitas daya kompresor 1 PK

The purpose of the study was to determine the temperature value at each point of the refrigeration performance tool, heat absorption, refrigerant flow rate, compressor power, and the working speed of the refrigeration performance test tool or (Coefficient Of Performance) COP during the 60 minute test time. The method that will be used in this research is to modify the test equipment and conduct real experiments by analyzing several variables that affect the performance of the air conditioning system. The independent variables in this study were the refrigerant pressure of 60 Psi, 70 Psi, and 80 Psi. The addition of several components of measuring instruments that function to display data will be carried out at each point as needed. Digital reading of data will function to display test result data in the form of numbers for air temperature, temperature, and refrigerant pressure in the air conditioning machine (AC). The study was conducted in a room with a size of 4 x 5 x 2.5 meters, and using LG AC with a compressor power of 1 PK. Based on the test results, changes in temperature that occur at each point of the performance of the air conditioning machine and heat absorption affect the temperature changes of each cooling machine performance, namely the use of 60 Psi of 23.9 C for 70 Psi of 24.8 C and 80 Psi is 22.1 C. Then changes to heat absorption by the condenser and evaporator are at a refrigerant pressure of 60 Psi of 171.6 kJ/s for 70 Psi of 201.1 kJ/s and 80 Psi of 215.3 kJ/s. And the heat absorption that occurs in the evaporator with a pressure of 60 Psi is 143.3 kJ/s for 70 Psi of 161.6 kJ/s and 80 Psi is 172.2 kJ/s. The resulting refrigerant flow rate and compressor power, for the refrigerant flow rate, affect the changes that occur in the use of 60 Psi of 0.003 kg/s, for 70 Psi of 0.004 kg/s, and 80 Psi of 0.005 kg/s. Then for the compressor power at the use of 60 Psi of 0.446 kW, for 70 Psi of 0.521 kW, and 80 Psi of 0.611 kW. The refrigerant flow rate value of the refrigeration machine performance test tool or COP produced at a refrigerant pressure of 60 Psi is 3.26 for 70 Psi, namely 4.45 and 80 Psi is 5.11.

Failure analysis and improvement measures for crankshaft connecting rod of refrigerator compressor

With the improvement of family life quality and the implementation of energy-saving green household appliances, the volume of refrigerator increases rapidly and the energy efficiency ratio continues to decrease. However, the compressor size is required to be smaller, and the startup and shutdown are more frequent, which aggravates the wear of crankshaft connecting rod. Here, the failure compressor (300 ppm) provided by the manufacturer was disassembled and analyzed. The results showed that there were abrasive wear and adhesive wear on the surface of crankshaft and connecting rod. The source of solid particles in compressor was further analyzed, and the process control measures were proposed. In addition, combined with its failure mechanism and production process, the crankshaft surface composite treatment process was designed and bench test was carried out, which shows excellent anti-wear and self-lubricating performance.

Numerical modeling of noise and vibration due to discharge in hermetic compressors

The pulsive and intermittent nature of the operation of a hermetic refrigeration compressor leads to the generation of noise and vibration during the operation. Specifically, in hermetic compressors, gas pulsation induced by refrigerant discharge is a major source of NVH effects. The generation of noise and vibration due to refrigerant gas discharge is a process that involves thermo-mechanical operation within compressor cylinder, cavity acoustic resonance, valve opening/closing, hermetic shell vibration, and exterior sound radiation. In the presented study, a numerical simulation model was developed to address the multi-physical process of noise generation due to refrigerant gas discharge. The thermodynamics aspects of the compression process and the vibro-acoustics aspects are coupled together. The thermo-mechanical submodel is based on a compressor mechanistic model based on control volume analysis with lumped parameters. The vibro-acoustics submodel is based on finite element analysis, and it describes the two-way coupled interaction of compressor cavity acoustic resonances and hermetic shell vibration. Meanwhile, the acoustics response in the cavity is coupled with the thermodynamics submodel through proper modeling dynamics of discharge valves. Numerical simulations were conducted to demonstrate how simulation models work and how they can potentially help compressor manufacturers to gain a better understanding of the physical reasons behind NVH effects of compressors.