Vol 110, No 2 (2021)

This study presents a calculation method that can be applied to counterflow and straight-through air coolers operating in “dry” (without condensation), “wet” (with condensation on the entire surface), or “nonbinary” (with condensation on a part of the surface) modes for cases with and without the cooling medium undergoing a phase transition. Comparing the results obtained from the proposed method with those obtained from the method of segmental division of the heat exchange apparatus showed good convergence, with the proposed method requiring considerable lesser time for their execution. Hence, the novel proposed method can be widely used for the selection, verification, and structural calculations related to air coolers.

In the second part of this study, the main mathematical relations used for stationary calculations related to air coolers are provided. These dependencies are applicable to the dry, wet, and combined conditions. The method used for performing calculations related to air coolers operating in “dry” conditions is described herein. Formulas for determining the heat exchange surface with respect to the cooling fluid and humid air are derived herein. Moreover, these formulas can be used for calculations related to air coolers with or without a phase transition of the cooling fluid. Moreover, the criterion of transition of the air cooler from the “dry” operating mode to the “wet” or “combined” mode is provided in this study.

BACKGROUND: The ventilation and air conditioning systems for ice arenas should not only provide a comfortable environment for the people indoors and on the ice but also protect the ice surface from moisture condensation. The use of finite element methods in designing the ventilation systems will make it possible to determine the temperature and humidity conditions in the entire volume of the ventilated room at the calculation stage and, if necessary, to correct the ventilation parameters at minimal costs at the design stage.

AIM: To describe the methods of numerical simulation of heat and mass transfer in a room taking into account the humidity and radiant heat exchange for the case of a small training arena.

MATERIALS AND METHODS: ANSYS CFX software was used for modeling, using the finite volume method for calculations. The object of the study was a digital twin of a small training ice arena, making it possible to take into account the thermal-physical processes occurring in the room. Analysis was performed for the steady-state (stationary) heat and mass transfer condition. The modeling results were evaluated by considering air temperature and humidity contours in the most characteristic secant planes. Given that the direct determination of air humidity was not possible using the software package, a description of a method for the determination of humidity by empirical equations was provided.

RESULTS: It was numerically established that the air targets are met in the ice arena under the given parameters of operation of the ventilation system, with no moisture condensation on the surface of the ice, and comfortable conditions maintained in the areas where people are present.

CONCLUSION: The modeling of the heat and mass exchange processes in the ice arena room makes it possible to avoid ice damage from moisture condensation as well as ensure the comfort of people present on the ice and in the bleachers.

BACKGROUND: With the increase in rotation speeds of turbomachinery shafts, particularly for aviation and space applications due to the requirements for compactness and mass reduction, the issue of bearing life becomes relevant. For such devices, it is promising to use gas lubricated petal bearings (GLPB), which do not require additional systems and operate on the gas of the turbomachine working flow with excellent damping characteristics. Despite the attractiveness of GLPB designs, they are difficult to calculate because the direct work is performed by a thin layer of gas instead of balls, as in classical bearings. The efficiency of a GLPB depends directly on its design, especially the shape of the lobes and the amount of clearance between the shaft and the lobe.

AIM: To develop a mathematical model of the operation of a gas lubricated lobe bearing to determine the pressure distribution across the lobe surface and the corresponding computer program for calculations.

METHODS: Computational modeling of radial GLPB operation is accomplished with the determination of pressure in the lubrication layer. Moreover, its corresponding integral characteristics within the Reynolds model and the equation for the height of the lubrication layer under several assumptions are determined.

RESULTS: In this research, a computer program has been developed that allows for automated calculation of the space of change of variables and functions, the layout of a single table and output, construction of a volumetric model for its subsequent use in CAD systems, and generation of pressure graphs. Herein, the calculation of each variant is faster than similar calculations in the MathCAD environment. The same convenience consists of the block structure of the program, the visual setting of interrelations between blocks, and various and understandable outputs, suitable for both the report (construction of graphs) and drawings and visualization.

CONCLUSION: A specialized software package for parametric optimization of gas dynamic characteristics of GLPB has been developed. The developed tool permits the calculation of several cases and facilitates the selection of the optimal gap shape based on numerous proposed criteria. Among other things, the calculation allows us to see the variations in a different operating mode of the plant, use of a different substance with different dimensions, and choose the optimum that will suit a particular plant. Moreover, it is possible to expand the limits of applicability of petal bearings, such as at low speeds or large diameters.

BACKGROUND: Currently, because of the rapid development of digital technologies, an increasing amount of computer computing power is required where data processing centers are built, which sometimes require power consumption in the megawatt range. For stable year-round operation of data centers, reliable engineering is required, which includes air conditioning systems (ACS) for year-round use with a given level of reliability. Several traditional methods of data center cooling are available, namely, precision air conditioners based on vapor compression refrigeration machines (PCRMs) and systems with intermediate coolant (so-called chiller–fancoil systems). However, in modern settings, when the required capacity of data centers increases every year and the framework for environmental friendliness and energy efficiency of installations becomes stricter, new, more energy-efficient, and environmentally friendly solutions for data center cooling is needed.

AIM: This study aims to compare the proposed energy-efficient ACS with combined vapor compres-sion and indirect-evaporative cycle with the most commonly used ACSs in data centers and to deter-mine the boundaries of transition between the operating modes of the proposed ACS in a data center operating in Moscow as an example.

METHODS: This study employs the following methods: analysis of existing data center cooling sys-tems, determination of a typical design set of outdoor air parameters in the region under consideration, and calculation by comparative analysis of the energy consumption of the proposed and traditional ACSs for data centers.

RESULTS: From our study, the different ACSs currently used for data centers, namely, precision air conditioners and chiller–fancoil systems are highlighted. The main components of each system, the advantages and disadvantages observed in the design, installation, and commissioning processes, and the operation of the systems are described. An alternative ACS that combines PCRM and indirect-evaporative cooling is proposed. The comparative analysis of the proposed scheme and traditional so-lutions demonstrates that the combined ACS allows significant reduction in the energy consumption for data-center cooling. Therefore, under the conditions in Moscow, the proposed system for a particu-lar year will consume energy that is two times less than a chiller–fancoil system with free cooling and 2.5 times less than a system with precision air conditioners that operate on the traditional vapor-compression cycles.

CONCLUSION: The comparative analysis of the proposed energy-efficient ACS with combined vapor compression and indirect-evaporative cycle with the most commonly used ACS in data centers con-firms its high energy efficiency and provides greater environmental safety. The boundaries of the tran-sition between the operating modes of the proposed ACS are determined in a data center that operates in Moscow as an example, which exhibits high energy efficiency and reliable operation.

The increasingly strict legislations in the field of ecology have necessitated the search for novel refrigerants that can be alternatives to the existing refrigerants.

One option is the use of so-called “natural refrigerants,” including ammonia, СО₂, and propane.

Although there is considerable research interest in the use of СО₂ as a refrigerant, the required calculation procedures have not been sufficiently described in literature. In addition to the calculation of cycles and the determination of parameters at the base points, conducting an efficiency analysis to determine the optimal solution is necessary.

The purpose of this study was to develop a methodology for calculating and analyzing the basic transcritical СО₂ cycle of.

The calculation related to the transcritical cycle is based on the fundamental laws of thermodynamics, and the analysis is based on the entropy-statistical method of thermodynamic analysis.

The calculation includes the analysis of compression loss with respect to system components.

A description of the operation of the basic transcritical СО₂ cycle having two temperature levels and the procedure for calculating and analyzing losses in the elements of the refrigerating unit operating according to the basic transcritical СО₂ cycle are reported herein.

Using this method, identifying the elements and processes with the maximum losses and taking measures to improve the efficiency of the refrigeration system would be possible.