Chapter 9: Problem 95
How does regeneration affect the efficiency of a Brayton cycle, and how does it accomplish it?
Chapter 9: Problem 95
How does regeneration affect the efficiency of a Brayton cycle, and how does it accomplish it?
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Get started for freeAn ideal diesel engine has a compression ratio of 20 and uses air as the working fluid. The state of air at the beginning of the compression process is \(95 \mathrm{kPa}\) and \(20^{\circ} \mathrm{C}\). If the maximum temperature in the cycle is not to exceed \(2200 \mathrm{K}\) determine \((a)\) the thermal efficiency and \((b)\) the mean effective pressure. Assume constant specific heats for air at room temperature.
A gas-turbine power plant operates on a simple Brayton cycle with air as the working fluid. The air enters the turbine at 120 psia and \(2000 \mathrm{R}\) and leaves at 15 psia and \(1200 \mathrm{R} .\) Heat is rejected to the surroundings at a rate of 6400 \(\mathrm{Btu} / \mathrm{s},\) and air flows through the cycle at a rate of \(40 \mathrm{lbm} / \mathrm{s}\) Assuming the turbine to be isentropic and the compresssor to have an isentropic efficiency of 80 percent, determine the net power output of the plant. Account for the variation of specific heats with temperature.
A simple ideal Brayton cycle is modified to incorporate multistage compression with intercooling, multistage expansion with reheating, and regeneration without changing the pressure limits of the cycle. As a result of these modifications, (a) Does the net work output increase, decrease, or remain the same? (b) Does the back work ratio increase, decrease, or remain the same? \((c) \quad\) Does the thermal efficiency increase, decrease, or remain the same? (d) Does the heat rejected increase, decrease, or remain the same?
Consider the ideal regenerative Brayton cycle. Determine the pressure ratio that maximizes the thermal efficiency of the cycle and compare this value with the pressure ratio that maximizes the cycle net work. For the same maximumto- minimum temperature ratios, explain why the pressure ratio for maximum efficiency is less than the pressure ratio for maximum work.
Air at \(7^{\circ} \mathrm{C}\) enters a turbojet engine at a rate of \(16 \mathrm{kg} / \mathrm{s}\) and at a velocity of \(300 \mathrm{m} / \mathrm{s}\) (relative to the engine). Air is heated in the combustion chamber at a rate \(15,000 \mathrm{kJ} / \mathrm{s}\) and it leaves the engine at \(427^{\circ} \mathrm{C}\). Determine the thrust produced by this turbojet engine. (Hint: Choose the entire engine as your control volume.
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