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The paper considers the analysis and comparison of three methods of thermodynamic calculation for real gas in relation to the design of the flow part and modeling of the working process of centrifugal compressors for refrigeration, gas, chemical and other industries. A comparative analysis of these equations and comparison with experimental data were carried out. The equations were studied and their applicability was checked. Practical recommendations were given on the application of the considered equations. [ABSTRACT FROM AUTHOR]

The temperatures of the condensers' cooling media (water and air) can vary in a wide range depending on the ship's route. For example, on the route from Odessa to Hopen (Norway), the water temperature changes in the range from 18 ° C to -2 ° C, and air does from 20 ° C to -13 ° C (according to the data for April 13, 2018). Therefore, the well-known recommendations for determining the condensation temperature in the existing calculation methods cannot be applied to a refrigeration unit with composite cooling condensers because they provide different condensation temperature values. To determine the condensation temperature and study the operation of the marine refrigeration unit with composite cooling, a technical-and-economic calculation methodology has been developed. This methodology includes the calculation peculiarities of the composite condenser cooling, the cost of the main refrigeration equipment, the electricity cost and climate data for the ship's route. This method solves the problem of determining the condensation temperature to calculate the condensers and compressors of a marine refrigeration unit. The paper shows the results of the parametric analysis performed for a marine refrigerating unit for the route Odessa – Hopen. The recommended design value for the condensation temperature was 27°C (which corresponds to a pressure of 1066 kPa). It has been proven that the condensation temperature can be precisely determined for a composite condenser cooling at constantly changing cooling medium temperatures, while the technical-and-economic parameters of the refrigerating unit will be optimal. New design values of condensing pressures (temperatures) are obtained to calculate and select heat-exchange surfaces of refrigerating unit's condensers. [ABSTRACT FROM AUTHOR]

The paper presents the theoretical assessment of the energy efficiency of the vapor compression refrigeration cycle based on the compression in the wet vapor region. The estimation is based on the calculation of the compression process in the wet vapor region using the developed mathematical model. The mathematical model is a differential equations system including the equation of the first law of thermodynamics for the wet vapor and Clausius–Clapeyron relation. The assessment of the refrigeration cycle efficiency was based on the numerical solution of the mathematical model in Mathcad. Ammonia was used as the working fluid. The working fluid in the vapor-liquid state is compressed in a low-speed reciprocating compressor. Calculations have shown that compression in the wet vapor region results in decreasing the compression power and consequently in increasing the performance coefficient. [ABSTRACT FROM AUTHOR]

The results presented in the paper show that the implementation of the compression process in the oil-free slow-speed stage of a reciprocating compressor with intensive external cooling allows one to increase the cooling coefficient and improve the weight and size characteristics of the heat exchange and compressor equipment of steam compression refrigerating machines. Therefore, the use of slow-speed long-stroke compressor units in refrigeration plants is a very promising direction of their development. In addition, the research of providing the required power characteristics of single-stage compressor units with a linear hydraulic actuator by synthesizing the law of motion of the linear hydraulic actuator, the piston of which is rigidly connected with the piston compressor stage of the example refrigerant such as ammonia, will improve the parameters of the refrigeration machine and further reduce the overall dimensions of the compressor unit. [ABSTRACT FROM AUTHOR]

The paper presents the results of a numerical study of the viscous gas flow in a model stage centrifugal compressor with a low-flow coefficient using the Ansys CFX software package. The object of study is a model stage centrifugal compressor with low-flow coefficient, designed and tested at the Department of Compressor, Vacuum and Refrigeration Engineering of St. Petersburg Polytechnic University (hereinafter referred to as the Department of CVRE). To conduct a numerical experiment, a study on grid independence is carried out. The characteristics obtained from the results of a numerical study are compared with experimental characteristics. In the mathematical model of the stage, the magnitude of the axial clearance between the covering disk of the impeller and the compressor housing varies from 1 mm to 5.5 mm and the effect of changes in this value on the characteristic of the loss complex 1 + βfr + βpr is estimated. [ABSTRACT FROM AUTHOR]

At the Department of Compressor, Vacuum and Refrigeration Engineering (KVHT), St. Petersburg Polytechnic University is studying processes in a centrifugal compressor [4-12], including non-stationary processes. One of the main goals of these studies is to develop ways to protect centrifugal compressors from surging. The work performed showed the advantages of the so-called feature method of protecting centrifugal compressors from surging in comparison with the parametric method [5-7]. With the parametric method, the approach of the turbocharger to the zone of global stability loss (surge) is determined by the current flow rate determined by measuring the statistical pressure at the inlet to the machine. The essence of the characteristic method is to detect characteristic signs of the behavior of the flow of the working medium (gas, air) in the flow part of the turbocharger before the surge. [ABSTRACT FROM AUTHOR]

Compressor machines are an integral part of power plants, used in the oil and gas industry, refrigeration and many other industries. Increasing the efficiency of the stage is necessary, especially for centrifugal compressors. The relatively low efficiency of such machines is due to the complexity of the processes taking place in the flow section. For complex tasks solution to increase operation efficiency of the whole stage it is necessary to consider both rotating parts of compressor (impeller) and stationary parts (diffuser, inlet chamber, reverse guide vanes). In operation, the inlet radial chambers of the centrifugal compressor are investigated, which have a significant influence on the operation of the compressor stage. When designing inlet chambers to reduce loss and flow non-uniformity at the compressor impeller inlet, it is important to thoroughly investigate the flow in the flow part in order to improve the efficiency of the stage. [ABSTRACT FROM AUTHOR]

The paper presents the results of studying a combination of new technological solutions in the processes of natural gas liquefaction and helium extraction. The most common and effective way to ensure cooling capacity in the natural gas liquefaction process is to use a cascade cycle on mixed refrigerant (MFC) as external cooling. The influence of introduction an absorption refrigeration unit on the technological process has been studied. To extract helium, the combined separation and rectification method is used. The purity of helium obtained is 50% (in moles). The running conditions of operation and the corresponding technical characteristics of the devices are presented and described. The curves of the resulting characteristics of heat exchangers indicate the correctness of the thermo hydraulic calculations performed. The relative value of energy costs for obtaining 1 kg of liquefied natural gas in a technological process using MFC is 0.265 kWh/kg of LNG. Introducing an absorption refrigeration unit into the cycle reduces the ratio presented to 0.1849 kWh/kg of LNG. In the process of extracting helium, using an absorption refrigeration unit gives the result of 0.951 and 132.9 kW/kmol of helium, respectively. When using an absorption refrigeration unit, the helium extraction rate and power consumption ratio are 0.951 and 132.9 kW/kmol of helium, respectively. Application of the exergic analysis methods to the processes under consideration shows that the greatest value of exergic losses relative to other devices is observed in compressors. A detailed economic analysis has been carried out. It shows that the cost of the product obtained in the normal MFC cycle and in the MFC cycle using an absorption refrigeration machine is $ 0.1939 and $ 0.2069 per kg of LNG, respectively. [ABSTRACT FROM AUTHOR]

With a decrease in ambient temperature, the heat gain on the refrigeration machine and condensation pressure decrease, which requires a decrease in cooling capacity and geometric compression ratio of the screw compressor. A condensation pressure decrease below a certain value disrupts the stable operation of the throttling devices. The article describes the operation scheme of the refrigeration machine with a screw compressor and a liquid pump before the throttling devices, which allows it to work at a decreased condensation pressure. The dependences of changes in net efficiency, cooling capacity, power consumption and cooling coefficient at full and partial capacity with co-regulation of cooling capacity and geometric compression ratio are given. The experimental and calculated characteristics of a screw compressor operating with R22 freon were used. [ABSTRACT FROM AUTHOR]