Advanced Vapour Compression systems.ppt
- 1. Sanjivani Rural Education Society’s Sanjivani College of Engineering, Kopargaon-423 603 (An Autonomous Institute, Affiliated to Savitribai Phule Pune University, Pune) NAAC ‘A’ Grade Accredited, ISO 9001:2015 Certified Department of Mechanical Engineering Subject:- Heating, Ventilation and Air Conditioning (ME 411) B.Tech.Mechanical Purushottam W. Ingle Assistant Professor
- 2. • Advanced Vapor Compression Cycles: Trans-critical cycle and their types, Ejector refrigeration cycle and their types. Presentation of cycle on P-h and T-s chart. 9/4/2023 P.W. Ingle Department Of Mechanical Engineering, Sanjivani COE, Kopargaon
- 3. Transcritical Cycle • Due to harmful effects of the synthetic refrigerants on the environment, CO2 has been revived as a potential refrigerant. • Due to the low critical temperature of CO2, the gas cooler is operated above the critical pressure and the evaporator is operated below that; hence the cycle is called transcritical cycle. • Along with eco-friendliness, CO2 systems have various advantages over conventional systems such as, compatibility with normal lubricants and common machine construction materials, non- flammability and non-toxicity, greatly reduced compression ratio, easy availability, high volumetric refrigerant capacity, and excellent heat transfer properties. 9/4/2023 P.W. Ingle Department Of Mechanical Engineering, Sanjivani COE, Kopargaon
- 4. • The major disadvantage of CO2 cycle is lower COP due to huge expansion loss compared to conventional refrigerants and hence the cycle needs modifications. • There are several reasons for modifying the basic single-stage transcritical cycle, including improvement of COP, capacity enhancement for a given system and component size, adaptation of the heat rejection temperature profile to given requirements and keeping the pressure ratio and discharge temperature of the compressor within limit. • Cycle modifications such as use of internal heat exchanger, expansion turbine, multi-staging, two-phase ejector, vortex ntube and parallel compression economization. 9/4/2023 P.W. Ingle Department Of Mechanical Engineering, Sanjivani COE, Kopargaon
- 5. TRANSCRITICAL CO2 CYCLE AND OPTIMUM DISCHARGE PRESSURE • In the transcritical refrigeration cycle (Fig. 1), the vapor from evaporator is compressed to supercritical (gas cooler) pressure (1-2), rejected heat at gliding temperature (2-3) and expanded (2-3) from supercritical pressure to subcritical (evaporator) pressure to give cooling (4- 1). 9/4/2023 P.W. Ingle Department Of Mechanical Engineering, Sanjivani COE, Kopargaon
- 6. • For the conventional cycle, condensing temperature is chosen based on coolant temperature in the condenser and corresponding saturated pressure is taken as the condensing pressure. • But for supercritical heat rejection no saturation point exists, so the gas cooler pressure is independent of the refrigerant temperature at gas cooler exit (point 3 in Fig. 1). 9/4/2023 P.W. Ingle Department Of Mechanical Engineering, Sanjivani COE, Kopargaon
- 7. • Simple vapour compression cycle and transcritical cycle are same but only Difference in Heat rejection Process. • In the transcritical cycle process, the heat rejection takes place at pressures and temperatures above the critical point – that is, in the fluid region. • A condition in the fluid region is often referred to as a gas condition. • For the transcritical cycle process, the heat rejection is therefore called gas cooling and subsequently the heat exchanger used is called a gas cooler. 9/4/2023 P.W. Ingle Department Of Mechanical Engineering, Sanjivani COE, Kopargaon
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- 9. Transcritical cycle process • Process 1-2 :The transcritical cycle process begins with a one-stage compression from state point 1 to 2. During this process, the temperature rises significantly – and, for carbon dioxide, can reach a level of 130°C. • Process 2-3:The heat rejection process from state point 2 to 3 occurs at constant pressure above the critical point. The temperature during this process varies continuously from the inlet temperature (at state point 2) to the outlet temperature (at state point 3). • Process 3 - 4: The expansion process from state point 3 to 4 occurs at constant specific enthalpy. The inlet condition is supercritical (above the critical point) and the outlet is two-phase (mixture of liquid and vapour). • Process 4 - 1: The heat absorption process (evaporation) from state point 4 to 1 occurs at constant pressure, and the evaporation part also at constant temperature. The outlet condition (compressor inlet condition) is slightly superheated. 9/4/2023 P.W. Ingle Department Of Mechanical Engineering, Sanjivani COE, Kopargaon
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- 11. Simple vapour compression cycle 9/4/2023 P.W. Ingle Department Of Mechanical Engineering, Sanjivani COE, Kopargaon
- 12. Transcritical cycle process 9/4/2023 P.W. Ingle Department Of Mechanical Engineering, Sanjivani COE, Kopargaon
- 13. Types of Transcritical cycle • Transcritical cycle with throttle valve 9/4/2023 P.W. Ingle Department Of Mechanical Engineering, Sanjivani COE, Kopargaon
- 14. Transcritical refrigeration system with internal heat exchanger (suction line heat exchanger) 9/4/2023 P.W. Ingle Department Of Mechanical Engineering, Sanjivani COE, Kopargaon
- 15. • Enhancement on cycle efficiency can be a substantial 25%. • The internal heat exchanger can increase the cooling capacity and COP up to 11.9% and 9.1%, respectively. • COP may improve by 10% by using internal heat exchanger in residential application. Through the experimental study on CO2 residential air-conditioning system with internal heat exchanger. 9/4/2023 P.W. Ingle Department Of Mechanical Engineering, Sanjivani COE, Kopargaon
- 16. 9/4/2023 P.W. Ingle Department Of Mechanical Engineering, Sanjivani COE, Kopargaon Expansion with work recovery
- 17. • Another option to reduce the expansion losses is the use of a work producing device (expander), which has potential for COP improvement. Enthalpy decreases in expansion process (process 3-4 in Fig. 4) and hence the net work requirement reduces and cooling effect increases, which will improve the COP of the cycle. • Work recovery turbine with isentropic efficiency of 60%, may reduce contribution to total irreversibility by about 35% and cause an average increase of COP by 25%. 9/4/2023 P.W. Ingle Department Of Mechanical Engineering, Sanjivani COE, Kopargaon
- 18. MULTISTAGE CYCLE • Performance of the CO2 transcritical cycle can be improved by using multistage compression with inter-cooling. • By using ‘subcooling’, the COP could be improved while the capacity increased and the necessary high pressure reduced. • The subsequent theoretical and experimental investigations on the multistage transcritical CO2 cycles for refrigeration/heat pump and air conditioning showed the significant performance improvement over the basic single stage cycle. • Several types of configurations such as flash gas removal, flash gas inter-cooling, compression inter-cooling for a multistage transcritical CO2 cycle can be adopted to improve the system performance depending on the requirement. 9/4/2023 P.W. Ingle Department Of Mechanical Engineering, Sanjivani COE, Kopargaon
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- 21. Two stage cycle with Intercooler 9/4/2023 P.W. Ingle Department Of Mechanical Engineering, Sanjivani COE, Kopargaon
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- 23. Ejector refrigeration cycle • In transcritical CO2 cycle, regenerating expansion energy and increasing refrigerant pressure by means of an ejector is an effective way to improving the COP. In addition, the ejector simplifies the process of controlling the gas cooling pressure in the CO2 cycle. • The gas cooling pressure of the CO2 cycle could be controlled by changing the throat area of ejector nozzle. • Ejector refrigeration is similar to normal vapour compression system, only compressor is replaced by liquid circulation pump, boiler and ejector. 9/4/2023 P.W. Ingle Department Of Mechanical Engineering, Sanjivani COE, Kopargaon
- 24. • Due to heat added in the boiler evaporated refrigerant goes in high temperature and pressure by using low grade heat energy. • The high pressure refrigerant expand through the primary nozzle in the ejector and create very low pressure region at the primary nozzle exit plane. • Low pressure allows a liquid refrigerant in the evaporator to vaporize at low temperature to create refrigerating effect. • Evaporated fluid (secondary fluid) will mix with primary fluid in mixing chamber of ejector, the mix stream is discharged through diffuser to condenser where vapour is condensed. 9/4/2023 P.W. Ingle Department Of Mechanical Engineering, Sanjivani COE, Kopargaon
- 25. • Liquid refrigerant which accumulated in condenser is return back to the boiler by pump and other remaining fluid expanded through throttling valve to the evaporator to complete the cycle. 9/4/2023 P.W. Ingle Department Of Mechanical Engineering, Sanjivani COE, Kopargaon
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- 28. • In ejector expansion refrigeration cycle (Fig. 6), the primary flow from the gas cooler (state 3) and the secondary flow from the evaporator (state 8) are going through primary and secondary nozzles, respectively. • Constant pressure/area mixing chamber (p-h diagram of CO2 cycle with constant pressure mixing ejector is shown Fig. 7) and diffuser (10-5) of the ejector and then separated in forms of vapour (state 1) and liquid (state 6) so that this ratio should matched with the inlet ratio of primary and secondary flows. 9/4/2023 P.W. Ingle Department Of Mechanical Engineering, Sanjivani COE, Kopargaon
- 29. • Then the liquid circulates through expansion valve (6- 7) and evaporator (7- 8), whereas the vapour circulated through compressor (1-2) and gas cooler (2-3). 9/4/2023 P.W. Ingle Department Of Mechanical Engineering, Sanjivani COE, Kopargaon
- 30. • cooling capacity and COP simultaneously improve by up to 8% and 7%, respectively compared to conventional valve expansion system, and ejector is able to recover up to 14.5% of the throttling losses. • Experiments confirmed that the high-side pressure control integrated into the ejector could be used to maximize the system performance. 9/4/2023 P.W. Ingle Department Of Mechanical Engineering, Sanjivani COE, Kopargaon
- 31. Single Ejector Refrigeration System with precooler and pre-heater 9/4/2023 P.W. Ingle Department Of Mechanical Engineering, Sanjivani COE, Kopargaon
- 32. • The liquid refrigerant returning to generator is pre-heated by using hot refrigerant arriving from ejector exhaust. • The liquid refrigerant cooled by pre-cooler using cold vapour refrigerants leaving the evaporator before reaching the evaporator. • Refrigerants arriving from condenser cooled and heated before passing through boiler. 9/4/2023 P.W. Ingle Department Of Mechanical Engineering, Sanjivani COE, Kopargaon
- 33. SERS combined with power cycle 9/4/2023 P.W. Ingle Department Of Mechanical Engineering, Sanjivani COE, Kopargaon
- 34. • If we required multiple output from one system then it will be congeneration and generation. • This system widely applied for solving present challenges at small scale. • Primary flow of ejector is turbine discharge and secondary flow is evaporated fluid from evaporator mixed each other at mixing chamber of ejector. 9/4/2023 P.W. Ingle Department Of Mechanical Engineering, Sanjivani COE, Kopargaon