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More Thermodynamic Cycles. P M V Subbarao Professor Mechanical Engineering Department. The Engineering Systems for High end Extra-somatic Needs…. Brayton Cycle for Power Generation. 1-2 Adiabatic compression (in a compressor) 2-3 Constant pressure heat addition
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More Thermodynamic Cycles P M V Subbarao Professor Mechanical Engineering Department The Engineering Systems for High end Extra-somatic Needs…
Brayton Cycle for Power Generation 1-2 Adiabatic compression (in a compressor) 2-3 Constant pressure heat addition 3-4 IAdiabaticexpansion (in a turbine) 4-1 Constant pressure heat rejection
Thermodynamic Analysis of Adiabatic Compression For an infinitesimal compression:
Cycle Analysis 1 –2 : Specific work input : 2 – 3 : Specific heat input : 3 – 4 : Specific work output : 4 – 1 : Specific heat rejection : Adiabatic Processes:
Reciprocating IC Engine : A Heat Engine Qout Qin Wout
Greatness of Heat Engines • Balance Sheet for A Heat Engine: • All heat inputs consume resources : Total Input Heat : Qin (Cost incurred). • All heat outputs are just mere a loss. • Net work Out put is positive and this is the final benefit : Wnet (Benefit Achieved) • Performance : Benefit to cost ratio (in energy units).
Modification of Brayton Cycle for Air Craft Propulsion : Invented by Frank Whittle
Air Craft Engine Refrigeration System Air to Cabin
Gas Refrigeration Systems • The gas power cycle can be used as refrigeration cycles by simply reversing them. • Of these, the reversed Brayton cycle, which is also known as the gas refrigeration cycle, is used to cool aircraft. • Further Modification this cycle is used to obtain very low (cryogenic) temperatures. • The work output of the turbine can be used to reduce the work input requirements to the compressor. • Thus, the performance index of a gas refrigeration cycle is defined as
An Urban world that was present till the end of first decade of the 20th century. • Only fresh foods that could be grown locally were available, and they had to be purchased and used on a daily basis. • Meat was bought during the daily trip to the butcher's; the milkman made his rounds every morning. • If you could afford weekly deliveries of ice blocks—harvested in the winter from frozen northern lakes—you could keep some perishable foods around for 2 or 3 days in an icebox. • New York was a virtual ghost town in the summer months. • Homes were built with natural cooling in mind. • Ceilings were high, porches were deep and shaded, and windows were placed to take every possible advantage of cross-ventilation
Urban Life after the end of first decade of the 21st century. • Frozen foods of all kinds were available just about anywhere in the world all year round. • The milkman was all but gone and forgotten, and the butcher now did his work behind a counter at the supermarket. • Indeed, many families concentrated the entire week's food shopping into one trip to the market, stocking the refrigerator with perishables that would last a week or more. • New York is a busy town even in the summer months. • Buildings are totally isolated from fresh air.
Why not use the reversed Rankine cycle for Refrigeration ? • Very costly to expand the liquid using a turbine with very low or negligible power output!?! • May become negative under friction. • Cheaper to have irreversible expansion through an expansion valve.
Thermodynamics of Ideal VCR Cycle • Ideal Vapor-Compression Refrigeration Cycle • Process Description • 1-2 Adiabatic compression • 2-3 Constant pressure heat rejection in the condenser • 3-4 Throttling in an expansion valve • 4-1 Constant pressure heat addition in the evaporator
Performance Index The performance of refrigerators and heat pumps is expressed in terms of coefficient of performance (COP), defined as Under the same operating conditions, the COPs are related by
Samsung Split A/c Model No : AQ24UUA Cooling Capacity : 7.03kW Power Consumption (Cooling) : 2,600Watts Refrigerant Type R22 The refrigerant leaves the evaporator at 7.2oC Condenser pressure : 2.71 MPa.
