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Unformatted text preview: i—‘Houmm; +112UNm;+1845Nm;—1515Nm) \/ 1.5 A ﬂuid at 0.7 bar occupying 0.09 m3 is compressed reversibly to a pressure of 3.5 bar
according to a law pv" = constant. The ﬂuid is then heated reversibly at constant volume
until the pressure is 4 bar; the speciﬁc volume is then 0.5 m3 / kg. A reversible expansion
according to a law pv2 = constant restores the ﬂuid to its initial state. Sketch the
cycle on a p—v diagram and calculate: (i) the mass of ﬂuid present;
(ii) the value of n in the ﬁrst process;
(iii) the net work of the cycle. (0.0753 kg; 1.847; —-640 N m) J 1.6 A ﬂuid is heated reversibly at a constant pressure of 1.05 bar until it has a speciﬁc
volume of 0.1 ms/kg. It is then compressed reversibly according to a law pv = constant
to a pressure of 4.2 bar, then allowed to expand reversibly according to a law
pi)"7 = constant. and is ﬁnally heated at constant volume back to the initial conditions.
The work done in the constant pressure process is —515 N m, and the mass of ﬂuid present is 0.2 kg. Calculate the‘ net work of the cycle and sketch the cycle on a p—U
diagram. 2.3 Steam at 7 bar and 250°C enters a pipeline and ﬂows along it at constant pressure. J If the steam rejects heat steadily to the surroundings, at what temperature Will droplets
of water begin to form in the vapour? Using the steady-ﬂow energy equation, and
neglecting changes in velocity of the steam, calculate the heat rejected per kilogram of 1 Steam ﬂowmg. (165 0C; 191 kJ/kg) 2.4 0.05 kg of steam at 15 bar is contained in a rigid vessel of volume 0.0076 m3. What
is the temperature of the steam? If the vessel is cooled: at what temperature Will the 1; \
steam be just dry saturated? Cooling is continued until the pressure in the vessel is 1
11 bar; calculate the ﬁnal dryness fraction of the steam, and the heat rejected between i ' ' ' l (1 th ﬁnal states. .
the mma an 6 (250°C; 191.4 °C; 0.857; 18.5 H) 2.10 ~/ 2.11 ./ 2.12 Oxygen, 02, at 200 bar is to be stored in a steel vessel at 20°C. The capacity of the
vessel is 0.04 m3. Assuming that 02 is a perfect gas, calculate the mass of oxygen
that can be stored in the vessel. The vessel is protected against excessive pressure by
a fusible plug which will melt if the temperature rises too high. At what temperature
must the plug melt to limit the pressure in the vessel to 240 bar? The molar mass of
oxygen is 32 kg/kmol. ~ (10.5 kg; 78.6 °C) When a certain perfect gas is heated at constant pressure from 15°C to 95 °C, the heat
required is 1136 kJ/kg. When the same gas is heated at constant volume between
the same temperatures the heat required is 808 kJ/kg. Calculate cp, c”, y, R and the molar mass of the gas.
(14.2 kJ/kg K; 10.1 kJ/kg K; 1.405; 4.1 kJ/kg K; 2.028 kg/kmol) In an air compressor the pressures at inlet and outlet are 1 bar and 5 bar respectively.
The temperature of the air at inlet is 15°C and the volume at the beginning of
compression is three times that at the end of compression. Calculate the temperature of the air at outlet and the increase of internal energy per kg of air.
(207 °C; 138 kJ/kg) A quantity of a certain perfect gas is compressed from an initial state of 0.085 m3,
lbar to a ﬁnal state of 0.034 m3, 3.9 bar. The speciﬁc heat at constant volume is
0.724 kJ/kg K, and the speciﬁc heat at constant pressure is 1.020 kJ / kg K. The observed - temperature rise is 146 K. Calculate the speciﬁc gas constant, R, the mass of gas present, and the increase of internal energy of the gas.
(0.296 kJ/kg K; 0.11 kg; 11.63 kJ) ...
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- Spring '09