Faculty of Mechanical Engineering

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Energy efficiency of combined compressor-ejector vapor compression systems applied in industrial concentrators
(National Library of Serbia, 2025)
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Gjerasimovska, Natasha
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Sarevski, Vasko
Investigations of the energy characteristics of thermocompression systems applied in industrial concentrators are presented in this paper. A significant increase of the energy efficiency in comparison with traditional industrial concentrators is achieved with the implementation of turbocompressor and/or ejector thermocom-pression. Single stage centrifugal compressors with water (R718) as a refrigerant are especially suitable for application in concentrators for production of fruit or grape concentrates because of the relatively small temperature difference between condensation and evaporation temperatures (Tc – Te). The heat pump cycle in the ejectors is realized with thermocompression of one part of the waste water vapor in the solution, which together with the primary steam from the boiler, or other heat generator, is used as a motive steam for the process of concentration. Several solutions of highly efficient single stage and multistage concentrator systems with turbocompressor and/or ejector thermocompression are proposed. The process of boiling - evaporation of the water from the treated solution in the concentrator is realized at low temperatures, under deep vacuum conditions, which is a guarantee for a high product quality. Due to the low costs of conventional fuels used in the processes of production of concentrate, the products made with these procedures are relatively low-priced, which makes them competitive on the market. A solution of a polygeneration system for production of electricity and thermal energy (steam and hot water) for the needs of technological processes in industrial concentration plants is presented.
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Thermal characteristics of combined compressor - ejector refrigeration/heat pump systems for HVAC&R
(National Library of Serbia, 2024)
Gjerasimovski, Aleksandar
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Sharevska, Maja
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Gjerasimovska, Natasha
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Sharevska, Monika
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<jats:p>Thermal characteristics of combined compressor ? ejector refrigeration/heat pump systems applied in heating, ventilation, air conditioning and refrigeration (HVAC&R) of buildings are investigated. An original model for estimation of the thermal characteristics of the combined cycles is developed, to determine the influence of the evaporation, interstage, condensation, and generating temperature conditions on mechanical and thermal COP of the combined system, and to optimize the thermal parameters of the cycle. Results are presented for different temperature conditions, with R134a as a suitable refrigerant. A comparison between the thermal characteristics of the simple mechanical vapor compression cycle, the simple ejector thermocompression cycle, and the combined compressor ? ejector refrigeration/heat pump cycle is given. The benefits of implementation of combined compressor ? ejector refrigeration/heat pump cycles in HVAC&R systems are discussed. The temperature lift or temperature difference between condensing temperature and interstage temperature significantly influences the thermal (ejector) COP. If temperature lift is between 10 K and 20 K, high values of thermal COP can be achieved (0.5-1.0, for generating temperature equal to 80?C; 1.0-1.8, for generating temperature equal to 120?C). If temperature lift is between 30 K and 40 K, very low values of COPth can be obtained</jats:p>
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Thermal characteristics of combined compressor - ejector refrigeration/heat pump systems for HVAC&R
(National Library of Serbia, 2023)
Gjerasimovski, Aleksandar
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Sharevska, Maja
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Gjerasimovska, Natasha
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Sharevska, Monika
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Thermal characteristics of combined compressor - ejector refrigeration/heat pump systems applied in heating, ventilation, air conditioning and refrigeration (HVAC&R) of buildings are investigated. An original model for estimation of the thermal characteristics of the combined cycles is developed, to determine the influence of the evaporation, interstage, condensation, and generating temperature conditions on mechanical and thermal COPs of the combined system, and to optimize the thermal parameters of the cycle. Results are presented for different temperature conditions, with R134a as a suitable refrigerant. A comparison between the thermal characteristics of the simple mechanical vapor compression cycle, the simple ejector thermocompression cycle, and the combined compressor - ejector refrigeration / heat pump cycle is given. The benefits of implementation of combined compressor - ejector refrigeration/heat pump cycles in HVAC&R systems are discussed. The temperature lift or temperature difference between condensing temperature and interstage temperature significantly influences the thermal (ejector) coefficient of performance. If temperature lift is between 10 K and 20 K, high values of thermal COPs can be achieved (0.5÷1.0, for generating temperature equal to 80ºC; 1.0÷1.8, for generating temperature equal to 120ºC); If temperature lift is between 30 K and 40 K, very low values of COPth can be obtained (0.05÷0.3). High values of mechanical COPs can be achieved (24.8÷6.9), for compressor stage temperature lift 10÷30 K.
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Energy efficient buildings and combined thermal systems for electricity production, heating, refrigeration and air conditioning
(SMEITS, 2020-12-23)
Gjerasimovski, Aleksandar
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Sharevska, Maja
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Gjerasimovska, Natasha
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Sharevska, Monika
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Šarevski, Vasko
<jats:p>Thermal characteristics of energy efficient buildings are analyzed and energy demands are estimated. A concept of combined compressor – ejector thermal system for simultaneous production of electricity, heating, refrigeration and air conditioning is exposed. The performance characteristics of the natural gas prime motor – electric generator are assessed and optimum construction of the combined compressor – ejector refrigeration / heat pump unit is proposed to satisfy the energy demands for electricity, heating, cooling and air conditioning. Basic thermal calculations, material and energy balances of the complete thermal system are carried out and optimizing procedures for the thermal system components are given. A comparison of the proposed thermal systems and energy (natural gas) consumption with the conventional thermal systems and energy consumption for electricity, heating (natural gas - boiler), cooling (electricity – compressor refrigeration system) and air conditioning is made.</jats:p>

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