Refrigeration engineering and technology

6-11

Authors: V. M. Arsenyev, V. V. Miroshnichenko, N. A. Borisov

The deterioration of the fuel efficiency of the gas turbine unit is especially severe when the temperature of the intake air is 30°C and above. A significant increase in the thermodynamic efficiency of the gas turbine unit can be provided by the anthropogenic impact on the temperature and humidity of the intake air, which leads to a propor-tional reduction of the energy consumption for the compressor drive. Maintenance of lower temperatures of the intake air is especially important for the climatic conditions of gas producing countries in North Africa and the Middle East. Gas turbine plant has a large discharge energy potential, which can be utilized for the production of cold with a clear choice of the cooling method by using absorption refrigeration machines. To compare different combinations of gas turbine unit and waste heat recovery refrigeration machines it is advisable to use exergy method of thermodynamic analysis. During the exergy analysis of gas turbine units by using of absorption refrig-erating machines it is necessary to take into consideration that the reset of thermo transformed heat flows requires a supply of electricity to drive pumps and fans in the recycling water supply system and to drive the pumps, the hot coolant and pumps in the intermediate circulation loops of heating the coolant and cooling water to the air cool-er in the evaporator. Exergetic evaluation of the degree of excellence of gas turbine unit with absorption refriger-ation machine was made based on the methodology set out in the work of the scientific school J. Tsatsaronis. This work presents an exergy analysis of cooling efficiency of cyclic air suction in the gas turbine unit by using of lith-ium bromide absorption refrigerating machine with taking into account of the flow resistance of the air cooler. The results of exergetic efficiency of technical complex of gas-turbine unit with an absorption refrigeration ma-chine were compared with the gas turbine unit without cooling air to the compressor suction. It is also shown that when you increase the flow resistance of the air cooler the growth of efficient cooling power and exergy efficiency of the gas turbine unit stops.

17-20

Authors: N. V. Zhіkhareva

The paper deals with the calculation of heat gains especially in the design of air conditioning systems for buildings. The features of calculating the heat and humidity loads: calculation of heat gains through the fence taking into account the direct and scattered radiation in view of the delay and heat gains from various sources. According to research data, a comprehensive model for calculating air conditioning has been carried out including the determination of the opti-mum parameters; defining cost-effective insulation thickness; selection of the air conditioning system.

27-34

Authors: V.G. Rifert, P.A.Barabash, V.V. Gorin, V.V. Sereda

This paper proposes a method for heat transfer calculation during condensation inside hori-zontal tubes based on the theory of film condensation with substantiation of the basic defin-ing the process systems and the improvement of the dependencies for friction coefficient cal-culation at the interface between the phases.

46-50

Authors: E. Arsiriy, V. Smyrnona, D. Panich

Boilers KVGM type often used in heating systems of cities. Analysis of the operating parameters of the boiler showed that most KVGM operate with limited power, that is, the maximum boiler output by 15-30% lower than the nominal. During low-temperature district heating systems do not provide a com-fortable environment in apartments because of the limitations of power boilers. One of the main reasons for the limitations of power boilers is insufficient capacity fans or smoke exhausts. The analysis of op-tions to improve performance by increasing the fan speed of rotation of the impeller, or increase its di-ameter. These two options increase the performance of the fans based on the existing rules of design wind systems. Analysis of the results showed that the efficiency of the compressors in both cases keeps the predetermined high value, but significantly increases the unit cost of electric power. For KVGM-50 boilers developed and implemented energy-saving version of the lifting of restrictions boiler output without replacing the fan, but only by adjusting the aerodynamics flow paths. Increased productivity by reducing the fan flow resistances pieces of auxiliary equipment can increase the boiler output while re-ducing the cost of electric power to the fans.

61-65

Authors: Yu. Mitikov, S. Kubanov

Study relates to rocket engine liquid oxygen fuel systems. The evaporation of oxygen was determined in ~5 long cylindrical tank. Experiments were taken under natural conditions. The tank was fuelled with boiling oxygen. The tank pressurization during flight was done with hot helium. It was input into tank as centralized jet with ~180 m/sec speed and mass average temperature ~500 K. The total avg-integral aero-dynamic heat flow into oxygen ~16 KW/sq.m. The inner tank surface is waffled (mechanical milling). The gas temperature in free tank volume was measured in 25 spots using rods. The amount of free volume in tank was determined using fuel usage control system. The oxygen upper layer temperature inside the tank reaches the saturated vapour temperature by the middle of the flight when the absolute gas pressure is 1.3-1.5 bar. Oxygen evaporation insignificant speed was determined during engine working time (less than 1kg/sec). The correlation between evaporation speed and the value of aerodynamic heat flow was not determined. The likely reason is tank inner waffled surface and the presence of the power cone. The highest evaporation speed was measured in the beginning of the pressurization system functioning. The hot helium flow interacts with oxygen surface at that time. The necessity to decrease helium input speed was shown.

72-77

Authors: V.Z. Geller, N.A. Shimchuk, S.N. Gubanov

A review and analysis of experimental studies and calculation methods of thermal conductivity and viscosity of nanofluids with Al2O3 particles are presented. Analysis of published data shows that the results are not consistent. The greatest influence on the thermal conductivity and viscosi-ty of nanofluids make a concentration of the nanoparticles. In addition to concentration, a major factors influencing the transport properties are the following: a method of producing nanofluids and the methods of their preparation for the research; the size and shape of initial nanoparti-cles; the ability of the nanoparticles to form clusters with different size; temperature and pres-sure; surface–active substances (surfactants); type and properties of the base fluids; the method-ology of the experiment and its adaptation to the specifics of nanofluids. The results of experi-mental research of thermal conductivity and viscosity for the model system isopropyl alcohol – Al2O3 nanoparticles at various nanoparticle concentrations and temperatures are given. Study of thermal conductivity was carried out by two independent methods – steady-state and transient hot wire ones. The viscosity was measured with the capillary viscometers. The influence of nano-particles additives on the viscosity of refrigeration compressor oil is also studied. The results of the measurements are presented in the form of simple models.

83-91

Authors: A. Gurskiy, V. Denisenko, A. Goncharenko

The aim of the scientific work is to improve the accuracy of static modes simulation of the cen-trifugal compressors operation. To achieve this scientific aim the models designing the centrifu-gal compressors characteristics have been carried out. These characteristics must be obtained at various speeds of rotation and the angles of the vanes of the diffuser. The model of the refrigera-tion centrifugal compressor presented in this article is realized in MATLAB\Simulink program. The modern achievements review in the field of centrifugal compressors modeling is presented. The necessity of the centrifugal compressor modeling has been substantiated. The tabular data describing static characteristics of the compressors is shown. These tabular data are determined in the Lookup Table blocks. The model is represented by these blocks in the MATLAB\Simulink program. The alternative compressor model has been also presented. This realized model is based on the interpolation spline functions. This alternative model is presented in the DC-Net program. DC-Net program is destined for modeling and research of the logical-dynamic systems. The cen-trifugal compressors model is presented in the DC-Net program as the logical-dynamic systems. The compressor static characteristic set received as a modeling result is shown. Twelve charac-teristics in axes are presented. The pressure ratio and the refrigerant flow are denoted on the ax-es. These static characteristics can be compared with experimental characteristics to assess the model adequacy. The assessment of the model adequacy is realized on the basis of the simulation results comparison. Simulation results comparison obtained in the various models is presented. The conclusions about the optimal methods of the model synthesis are given.

94-99

Authors: A. O. Stopakevych

Classical automatic control systems of crude oil distillation columns are used to stabilize indi-rect parameters (temperature, pressure, level) which are considered as independent. Such systems can be used in case of small disturbances and fluctuation of oil composition. The article de-scribes the set of linear mathematical dynamical models of multi-component crude oil atmospher-ic distillation column K-2 which is based on direct parameters of material balance. For devel-opment of modern multivariable automatic control systems it’s preferable to use direct material balance parameters because change of products flow ratios leads to economical loses. Devel-oped models shows that the plant is significantly multivariable with big lag, so effective auto-matic control system can be designed only with use of modern control theory. The developed set of models can be used for research of robustness and quality of multivariable automatic control systems (optimal, suboptimal, model-predictive, etc) of crude oil distillations columns which ori-ented on material balance parameters.