Back work ratio

Rapidly diverging pressure lines on the h-s diagram—to minimize the back-work ratio and to make reheat modification most effective. 

The simple Rankine cycle is inherently efficient. Heat is added and rejected isothermally and, therefore, the ideal Rankine cycle can achieve a high percentage of Carnot cycle efficiency between the same temperatures. Pressure rise in the cycle is accomplished by pumping a liquid, which is an efficient process requiring small work input. The back-work ratio is large. 

The gas Brayton cycle adds heat in a isobaric process over a large temperature range. The temperature level is independent of the pressure level. No blade erosion occurs in the gas turbine. However, the compression process of the gas Brayton cycle requires large work input. The back-work ratio is small. 

In the gas turbine cycle, the ratio of the compressor work to the turbine work is called back-work ratio. The back-work ratio is very high, usually more than 40%. 

An engine operates on the open Brayton cycle and has a compression ratio of 8. Air, at a mass flow rate of 0.1 kg/sec, enters the engine at 27°C and 100 kPa. The amount of heat addition is IMJ/kg. Determine the efficiency, compressor power input, turbine power output, back-work ratio, and net power of the cycle. Show the cycle on a T-s... 

An engine operates on the closed Brayton cycle (Fig 4.8) and has a compression ratio of 8. Helium enters the engine at 47°C and 200 kPa. The mass flow rate of helium is 1.2 kg/sec and the amount of heat addition is 1 MJ/kg. Determine the highest temperature of the cycle, the turbine power produced, the compressor power required, the back-work ratio, the rate of heat added, and the cycle efficiency. 

The maximum and minimum temperatures and pressures of a 40 MW turbine shaft output power ideal air Brayton power plant are 1200 K (Ta), 0.38 MPa (P3), 290 K (TO, and 0.095 MPa (Pi), respectively. Determine the temperature at the exit of the compressor Tj), the temperature at the exit of the turbine (P4), the compressor work, the turbine work, the heat added, the mass rate of flow of air, the back-work ratio (the ratio of compressor work to the turbine work), and the thermal efficiency of the cycle. 

Air enters the compressor of an ideal Brayton cycle at 100 kPa and 300 K with a volumetric flow rate of 5m /sec. The compressor pressure ratio is 10. The turbine inlet temperature is 1400 K. Determine (a) the thermal efficiency of the cycle, (b) the back-work ratio, and (c) the net power developed. 

Display the T s diagram and cycle properties results. The cycle is a heat engine. The answers are power required for the first compressor = —6.60 kW, power required for the second compressor 14.64 kW, maximum temperature of the cycle = 1169°C, power produced by the first turbine = 47.34 kW, rate of heat added in the reheater = 47.29 kW, power produced by the second turbine = 26.00 kW, net power produced = 52.11 kW, back-work ratio = 28.95%, and efficiency of the cycle 7 = 35.38%. 

An engine operates on an actual reheat open Brayton cycle (Fig. 4.15a)). The air enters the compressor at 60°F and 14.7 psia, and exits at 120psia. The maximum cycle temperature (at the exit of the combustion chamber) allowed due to material limitation is 2000°F. The exit pressure of the high-pressure turbine is 50 psia. The air is reheated to 2000° F, and the mass flow rate of air is 1 Ibm/sec. The exit pressure of the low-pressure turbine is 14.7 psia. The compressor efficiency is 86% and the turbine efficiency is 89%. Determine the power required for the compressor, the power produced by the first turbine, the rate of heat added in the reheater, the power produced by the second turbine, the net power produced, back-work ratio, and the... 

An ideal Brayton cycle with regeneration has a pressure ratio of 10. Air enters the compressor at 14.7 psia and 29°F. Air enters the combustion chamber at 610°F. Air enters the turbine at 1520°F. The turbine exit air pressure is 15.0 psia. The air mass flow rate is 0.41 Ibm/sec. The turbine efficiency is 85%, and the compressor efficiency is 82%. Determine (a) the exit air temperature of the compressor, (b) the inlet air temperature of the combustion chamber, (c) the power required by the compressor, (d) power produced by the turbine, (e) rate of heat added, (f) back-work ratio, (g) net power produced, and (h) the cycle efficiency. 

Determine (a) the exit air temperature of the compressor, (b) the inlet air temperature of the combustion chamber, (c) the power required by the compressor, (d) power produced by the turbine, (e) rate of heat added, (f) back-work ratio, (g) net power produced, and (h) the cycle efficiency. 

BACK WORK RATIO - Is the fraction of the gas turbine work used to drive the compressor. 

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