Vol 110, No 1 (2021)

In this part of the article, a literary review of various methods of stationary calculations of air coolers operating under dehumidifying or frost conditions is performed. The approaches used at the moment are reviewed, namely, the dehumidification coefficient method, logarithmic enthalpy difference method, equivalent dry-bulb temperature method, and the efficiency–number of heat transfer units (ε–NTU) method, for calculating counterflow, chilled water coils. Their main differences are demonstrated, and the key expressions used in them are provided. A comparison of the advantages and disadvantages of the methods showed the rationality of using the ε–NTU approach owing to the possibility of its application for both design and verification calculations of heat exchangers. The classical ε–NTU method is not directly applicable under dehumidifying or frost conditions. Hence, we must adapt it to calculations of air coolers of all types (both counterflow and parallel-flow air coolers with and without phase transition of cooling fluid, respectively) to correctly describe the effect of the abovementioned processes on heat exchange.

Cold supply systems are significant in many industries. Their improvement is currently associated with two main areas: energy saving and ecology.

The problems associated with energy saving are paid considerable attention both at the state level (Federal Law No. 261-FZ “On Energy Saving and on Improving Energy Efficiency and on Amending Certain Legislative Acts of the Russian Federation”) and by owners of refrigeration equipment.

The costs of electricity consumed by cold supply systems constitute a considerable part both in the total energy consumption of an enterprise (for catering enterprises, it ranges from 48% to 60%) and in the country’s total energy consumption (for example, the share of energy consumption by air conditioning systems in Europe ranges from 2% to 6%).

Additionally, the ratification of the Montreal Protocol (Resolution No. 539 of the Government of the Russian Federation of 27.08.2005) and the Kyoto Protocol (FZ 128-FZ of November 4, 2004) by the Russian Federation, the entry of the Russian Federation into force of European Regulations 517/2014 governing the decommissioning of refrigerants with global warming potential above 2500 (for example, refrigerants R404A and R507A currently in active use), and the adoption of a new environmental legislation by the Russian Federation in connection with the signing of the Paris Agreement necessitates the need to use new refrigerants, which are not always more efficient than traditionally used solutions and require changes to their technological scheme.

Accordingly, we need to improve efficiency calculation methods based on classical methods of thermodynamic analysis.

BACKGROUND: Gas drying is widely used in many applications of science, technology and industry: high-purity gas media (microelectronics), and its methods are constantly being improved. One of them, membrane separation of gases, although considered as one of the most promising, is currently understudied.

AIM: The purpose of this work is to show the possibilities of the membrane gas separation method when it is used for drying compressed gases.

METHODS: The results of the study of the drying of compressed gases were obtained using the membrane method of gas separation.

CONCLUSIONS: The dependence of the degree of drying (dew point temperature) on such parameters of the gas separation process as the relative pressure drop across the membrane, the permeability and selectivity of the membrane for water vapor, the value of the working pressure and the value of the dried gas flow per unit area of the membrane is shown. It is shown that, with the help of membrane gas separation, drying can be performed to a dew point temperature of –100 ˚С and below. On the example of drying air and methane, the conditions are given under which membrane drying can be energetically more profitable compared to drying by cooling.

BACKGROUND: The utilization of heat pumps (variation of vapor compressing machines) for heat transfer between different temperature levels is a promising development trend, considering their low-cost heat energy, environmental friendliness of working media, economically sufficient solutions, and low-cost maintenance. Heat pumps are used for heating in building structures, where low potential heat sources include wastewater streams, groundwater streams, air, and the heat of the soil. The low potential heat of heat emissions from industrial plants may also be used, which can be cost-effective in terms of production resource usage.

AIMS: This study aims to select a refrigerant and its composition to provide operational stability for heat pumps at temperature levels from 48°C to 95°C with minimum energy consumption for the most widespread thermodynamical cycles.

MATERIALS AND METHODS: Standard thermodynamic cycles of heat pumps were simulated using the Aspen HYSYS software. Further optimization and parameter selection was performed using the MATLAB module Global Optimization Toolbox.

RESULTS: In compliance with demanded design parameters, the results of each working medium simulation were obtained. Energy-efficient parameters of common heat pump thermodynamical cycles were determined.

CONCLUSIONS: According to the exergy analysis of the thermodynamical cycles, mixed refrigerants, pentane, and ammonia were determined as the most suitable and energy-efficient working fluids for heat pumps.

Development of automation and programming tools is one of the priority areas determined by the State Program “National Technology Initiative,” which requires development of methods on the basis of which algorithms will be built.

Simultaneously, energy saving is one of the directions toward development of refrigeration equipment. This issue has been given attention both at the state level (Federal Law No. 261-FZ “On Energy Saving and Increasing Energy Efficiency and Amending Certain Legislative Acts of the Russian Federation”) and by users of refrigeration equipment. Importantly, the share of electricity consumed by refrigeration equipment constitutes a considerable part of the total energy balance of a particular enterprise. For example, the share of energy consumption by air conditioning systems in Europe ranges from 2% to 6%.

The existing systems for monitoring the operating parameters of refrigeration plants do not completely use their resource because they are frequently used only to identify emergencies and raise alarm.

This article describes a procedure of assessing the energy efficiency of refrigeration plants operating on a single-stage compression cycle with single throttling. This procedure allows for evaluation both at the design stage and during the operation of a refrigeration plant and enables to obtain a distribution of losses by the elements and processes of the refrigeration plant.