ME340A: Prof. Sameer Khandekar http://home.iitk.ac.in/~samkhan ME340A: Refrigeration and Air Conditioning Department of Mechanical Engineering Instructor: Prof. Sameer Khandekar Indian Institute of Technology Kanpur Tel: 7038; e-mail: [email protected] Kanpur 208016 India Introduction to Vapor Compression Refrigeration Systems – Part II Sameer Khandekar Sir M. Visvesvaraya Chair Professor Department of Mechanical Engineering Indian Institute of Technology Kanpur Kanpur (UP) 208016 INDIA Sameer Sameer Khandekar Webpage: home.iitk.ac.in/~samkhan/ 1 ME340A: Refrigeration and Air Conditioning Department of Mechanical Engineering Instructor: Prof. Sameer Khandekar Indian Institute of Technology Kanpur Tel: 7038; e-mail: [email protected] Kanpur 208016 India In this presentation… ◉ Performance measurement ◉ Ideal vapor compression system ◉ Real/Practical system ◉ Refrigerators and Heat Pumps Sameer Sameer Khandekar 2 Department of Mechanical Engineering Indian Institute of Technology Kanpur 208016 Kanpur India 1 ME340A: Prof. Sameer Khandekar http://home.iitk.ac.in/~samkhan ME340A: Refrigeration and Air Conditioning Department of Mechanical Engineering Instructor: Prof. Sameer Khandekar Indian Institute of Technology Kanpur Tel: 7038; e-mail: [email protected] Kanpur 208016 India Measuring performance of 1 refrigeration systems Rating, Carnot cycle, Ideal and real cycles Sameer Sameer Khandekar 3 ME340A: Refrigeration and Air Conditioning Department of Mechanical Engineering Instructor: Prof. Sameer Khandekar Indian Institute of Technology Kanpur Tel: 7038; e-mail: [email protected] Kanpur 208016 India Refrigeration effect Refrigerating effect (N): It is defined as the quantity of heat extracted from a cold body or space to be cooled in a given time. N = Heat extracted from the cold space/(time taken) Note: 1 Metric ton = 1000 kg (also referred to as ‘tonne’, to distinguish it with a ‘short ton’ 1 Short ton = 2000 pounds = 907 kg (in US a short ton is called as ‘ton’) Sameer Sameer Khandekar 4 Department of Mechanical Engineering Indian Institute of Technology Kanpur 208016 Kanpur India 2 ME340A: Prof. Sameer Khandekar http://home.iitk.ac.in/~samkhan ME340A: Refrigeration and Air Conditioning Department of Mechanical Engineering Instructor: Prof. Sameer Khandekar Indian Institute of Technology Kanpur Tel: 7038; e-mail: [email protected] Kanpur 208016 India Refrigeration Capacity or Tonnage rating ◉ Capacity of refrigerating machines are expressed by their cooling capacity. The commonly used unit for expressing the capacity of a refrigerating machine is Ton of refrigeration. ◉ One ton of refrigeration is defined as the quantity of heat extracted (refrigerating effect) to freeze one metric ton of water at 0°C into ice in 24 hours. ◉ Latent heat of ice = 334 kJ/kg i.e., 334 kJ of heat should be extracted from one kg of water at 0°C to convert it into ice. ◉ One ton of refrigeration = 334 x 1000 kJ/24 hrs. = 336 x 1000/(24 X 60 X 60) kJ/s = 3.86 kW (or = 3.5 kW if we use a short ton) Sameer Sameer Khandekar 5 ME340A: Refrigeration and Air Conditioning Department of Mechanical Engineering Instructor: Prof. Sameer Khandekar Indian Institute of Technology Kanpur Tel: 7038; e-mail: [email protected] Kanpur 208016 India Coefficient of performance ◉ How to estimate the efficiency of the system? for fixed values of QL and QH Sameer Sameer Khandekar 6 Department of Mechanical Engineering Indian Institute of Technology Kanpur 208016 Kanpur India 3 ME340A: Prof. Sameer Khandekar http://home.iitk.ac.in/~samkhan ME340A: Refrigeration and Air Conditioning Department of Mechanical Engineering Instructor: Prof. Sameer Khandekar Indian Institute of Technology Kanpur Tel: 7038; e-mail: [email protected] Kanpur 208016 India Reversed Carnot cycle ◉ The reversed Carnot cycle is the most efficient refrigeration cycle operating between TL and TH. ◉ However, it is not a suitable model for refrigeration cycles since processes 2-3 and 4-1 are not practical because: ○ Process 2-3 involves the compression of a liquid–vapor mixture, which requires a compressor that will handle two phases, and, Schematic of a Carnot refrigerator and T- ○ Process 4-1 involves the expansion of s diagram of the reversed Carnot cycle. high-moisture-content refrigerant in a turbine. Sameer Sameer Khandekar 7 ME340A: Refrigeration and Air Conditioning Department of Mechanical Engineering Instructor: Prof. Sameer Khandekar Indian Institute of Technology Kanpur Tel: 7038; e-mail: [email protected] Kanpur 208016 India COP of reversed Carnot cycle ◉ Both COPs increase as the difference between the two temperatures decreases, that is, as TL rises or TH falls. Schematic of a Carnot refrigerator and T-s diagram of the reversed Carnot cycle. Sameer Sameer Khandekar 8 Department of Mechanical Engineering Indian Institute of Technology Kanpur 208016 Kanpur India 4 ME340A: Prof. Sameer Khandekar http://home.iitk.ac.in/~samkhan ME340A: Refrigeration and Air Conditioning Department of Mechanical Engineering Instructor: Prof. Sameer Khandekar Indian Institute of Technology Kanpur Tel: 7038; e-mail: [email protected] Kanpur 208016 India Ideal vapor compression refrigeration cycle ◉ The vapor-compression refrigeration cycle is the ideal model for refrigeration systems. ◉ Unlike the reversed Carnot cycle, the refrigerant is vaporized completely before it is compressed and the turbine is replaced with a throttling device. ◉ This is the most widely used cycle for refrigerators, A-C systems, and heat pumps. Schematic and T-s diagram for the ideal Sameer Sameer Khandekar vapor-compression refrigeration cycle. 9 ME340A: Refrigeration and Air Conditioning Department of Mechanical Engineering Instructor: Prof. Sameer Khandekar Indian Institute of Technology Kanpur Tel: 7038; e-mail: [email protected] Kanpur 208016 India Ideal vapor compression cycle ◉ The ideal vapor-compression refrigeration cycle involves an irreversible (throttling) process to make it a more realistic model for the actual systems. ◉ Replacing the expansion valve by a turbine is not practical since the added benefits cannot justify the added cost and complexity. Sameer Sameer Khandekar 10 Department of Mechanical Engineering Indian Institute of Technology Kanpur 208016 Kanpur India 5 ME340A: Prof. Sameer Khandekar http://home.iitk.ac.in/~samkhan ME340A: Refrigeration and Air Conditioning Department of Mechanical Engineering Instructor: Prof. Sameer Khandekar Indian Institute of Technology Kanpur Tel: 7038; e-mail: [email protected] Kanpur 208016 India Ideal vapor compression refrigeration cycle Steady-flow energy balance Sameer Sameer Khandekar 11 ME340A: Refrigeration and Air Conditioning Department of Mechanical Engineering Instructor: Prof. Sameer Khandekar Indian Institute of Technology Kanpur Tel: 7038; e-mail: [email protected] Kanpur 208016 India A refrigeration cycle drawn on T-s diagram 1-2: Compression 2-3: Condenser 3-4: Expansion 4-5: Evaporator Sameer Sameer Khandekar 12 Department of Mechanical Engineering Indian Institute of Technology Kanpur 208016 Kanpur India 6 ME340A: Prof. Sameer Khandekar http://home.iitk.ac.in/~samkhan ME340A: Refrigeration and Air Conditioning Department of Mechanical Engineering Instructor: Prof. Sameer Khandekar Indian Institute of Technology Kanpur Tel: 7038; e-mail: [email protected] Kanpur 208016 India Refrigeration cycle on a P-v diagram Sameer Sameer Khandekar 13 ME340A: Refrigeration and Air Conditioning Department of Mechanical Engineering Instructor: Prof. Sameer Khandekar Indian Institute of Technology Kanpur Tel: 7038; e-mail: [email protected] Kanpur 208016 India Example: A household refrigerator General Electric: 1927 Sulphur dioxide/ Methyl formate) Modern: 21st century Fridge advert of 1905 Sameer Sameer Khandekar 14 Department of Mechanical Engineering Indian Institute of Technology Kanpur 208016 Kanpur India 7 ME340A: Prof. Sameer Khandekar http://home.iitk.ac.in/~samkhan ME340A: Refrigeration and Air Conditioning Department of Mechanical Engineering Instructor: Prof. Sameer Khandekar Indian Institute of Technology Kanpur Tel: 7038; e-mail: [email protected] Kanpur 208016 India Example: A household refrigerator ◉ −18 °C (0 °F) (freezer) ◉ 0 °C (32 °F) (meat zone) ◉ 5 °C (41 °F) (cooling zone) ◉ 10 °C (50 °F) (crisper) An ordinary household refrigerator. Sameer Sameer Khandekar 15 ME340A: Refrigeration and Air Conditioning Department of Mechanical Engineering Instructor: Prof. Sameer Khandekar Indian Institute of Technology Kanpur Tel: 7038; e-mail: [email protected] Kanpur 208016 India Actual vapor compression cycle ◉ An actual vapor-compression refrigeration cycle differs from the ideal one in several ways, owing mostly to the irreversibilities that occur in various components, mainly due to fluid friction (causes pressure drops) and heat transfer to or from the surroundings. ◉ The COP decreases as a result of irreversibilities. Schematic and T-s diagram of actual vapor compression refrigeration cycle. Sameer Sameer Khandekar 16 Department of Mechanical Engineering Indian Institute of Technology Kanpur 208016 Kanpur India 8 ME340A: Prof. Sameer Khandekar http://home.iitk.ac.in/~samkhan ME340A: Refrigeration and Air Conditioning Department of Mechanical Engineering Instructor: Prof. Sameer Khandekar Indian Institute of Technology Kanpur Tel: 7038; e-mail: [email protected] Kanpur 208016 India Actual vapor compression cycle DIFFERENCES ◉ Non-isentropic compression ◉ Superheated vapor at evaporator exit ◉ Subcooled liquid at condenser exit ◉ Pressure drops in condenser