Q1. A volume of 0.02 m3 of air at a pressure and temperature of 1.05 bar and 15ºC respectively is heated at constant volume until the pressure is 4.2 bar. It is then cooled at constant pressure to the initial temperature.
(a) Sketch the processes on a Temperature-specific entropy diagram.
(b) Calculate EACH of the following:
(i) The net heat flow
(ii) The net change in entropy.
Note: for air R = 0.287 kJ/kg K and γ = 1.4
Q1. A fuel of mass analysis 84% carbon and 16% hydrogen is completely burned in air.
The dry flue gas analysis shows they contain 81% nitrogen by volume.
(a) Determine, using molar volumes, the full combustion equation for 1 kg of fuel.
(i) The air fuel ratio by mass
(ii) The mass of water condensed per kg of fuel when the flue gas is at 1.01 bar and 20ºC.
Note: Relative atomic masses H =1, C =12, N =14, O =16
Air contains 21% oxygen by volume.
The Molar mass of air may be taken as 29 kg/kmol.
Q1. An annular cooling water jacket surrounds a 75 mm mean diameter pipe carrying a hot gas, in a counter flow arrangement. The hot gas enters the cooler at 350ºC and leaves at 100ºC. The cooling water enters the cooler at 10ºC.
The flow rate of the gas is 200 kg/hour and that of the water is 1400 kg/hour.
The wall thickness of the pipe may be ignored. Calculate EACH of the following:
(a) The exit temperature of the water
(b) The log mean temperature difference
(c) The length of the cooler.
Note: For cooling water Cp = 4.19 kJ/kg K
For the hot gas Cp = 1.13 kJ/kg K
The Inner surface heat transfer coefficient = 0.3 kW/m2K
The outer surface heat transfer coefficient = 1.5 kW/m2K
Q1. In a single acting two stage reciprocating air compressor, air is compressed from an inlet pressure and temperature of 0.9 bar and 20ºC respectively to a delivery pressure of 12 bar. The low-pressure cylinder has a bore of 250 mm, stroke of 160 mm and the clearance volume is 2.5% of the swept volume. The air enters the second stage at a pressure and temperature of 3 bar and 35ºC respectively. The compressor speed is 300 rev/min. The index of compression and expansion in both stages is 1.25. The mechanical efficiency is 0.85.
(a) Sketch the process on a p-V diagram.
(i) The free air delivered per hour at free air conditions of 1 bar and 15℃
(ii) The input power required to drive the compressor
(iii) The heat removed in the inter-cooler.
Note: for air R = 0.287 kJ/kg K Cp = 1.005 kJ/kg K
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