Question

A rigid copper tank, initially containing 1 m3 of air at 295 K, 4 bar, is connected by a valve to a large supply line carrying air at 295 K, 15 bar. The valve is opened only as long as required to fill the tank with air to a pressure of 15 bar. Finally, the air in the tank is at 310 K. The copper tank, which has a mass of 20 kg, is at the same temperature as the air in the tank, initially and finally. The specific heat of the copper is c = 0.385 kJ/kg · K. Assuming ideal gas behavior for the air, determine: (a) the initial and final mass of air within the tank, each in kg, and (b) the heat transfer to the air and copper tank from the surroundings, in kJ, ignoring kinetic and potential energy effects.

Answer #1

A rigid, well-insulated tank, with a volume of 0.057 m3 ,
contains air at p1 = 1.4 bar, T1 = 280 K. The air is stirred by a
paddle wheel, resulting in an energy transfer to the gas of
magnitude 6.78 kJ. Assuming ideal gas behavior for the air,
determine the final temperature, in K, and the final pressure, in
bar. Neglect kinetic and potential energy effects

Q3. A tank with rigid walls and a volume of
0.05 m3 initially has a two-phase liquid- vapor mixture of ammonia
at a pressure of 4 bar and a quality of 10%. The tank is then
heated such that the pressure is kept constant through a
pressure-regulating valve that allows saturated vapor to escape.
The heating continues until the quality of the mixture in the tank
is 40%. Assume kinetic and potential energy changes are
insignificant. Determine:
(i) The final...

A tank of 0.1 m3 volume initially containing nitrogen
at 25 C and 1 bar will be filled with compressed nitrogen at a rate
of 20 mol/s. The nitrogen coming from the compressor and into the
tank is at an absolute pressure of 110 bar and a temperature of 80
C. The filling process occurs sufficiently rapidly that there is
negligible heat transfer between the gas and the tank walls, and a
valve is closed to stop the filling process...

Air at 1 bar, 295 K, and a mass flow rate of 0.7 kg/s enters a
compressor operating at steady state and exits at 3 bar. During the
compressing from inlet to exit, the air experiences a polytropic
process as PV^n=constant. m=6, n=1.48.
(1) Determine the power required by the compressor.
(2) Determine the heat transfer between the compressor and the
surrounding.
(s) Determine the rate of exergy destruction. Kinetic and potential
energy effects are negligible. Let T_0 = 300...

Air at 1 bar, 295 K, and a mass flow rate of 0.7 kg/s enters a
compressor operating at steady state and exits at 3 bar. During the
compressing from inlet to exit, the air experiences a polytropic
process as PV^n=constant. m=6, n=1.48
(1) Determine the power required by the compressor.
(2) Determine the heat transfer between the compressor and the
surrounding.
(s) Determine the rate of exergy destruction. Kinetic and potential
energy effects are negligible. Let T_0 = 300...

A rigid tank has a volume of 0.01 m3. It
initially contains saturated water at a temperature of 200
oC and a quality of 0.4. The top of the
tank contains a pressure regulating valve which maintains the vapor
at constant pressure. This system undergoes a process where it is
heated until all the liquid vaporizes. How much heat in (kJ) is
required? You may assume there is no pressure drop in the exit
line.

A 50 kg copper block initially at 350 oC is quenched in a
closed, rigid insulated tank containing 120 L of liquid water at 25
oC. Specific heat of copper, Cc = 385 J/(kgK), specific heat of
liquid water, Cw = 4180J/(kgK). (i) Calculate the entropy change
(kJ/K) of copper block. (ii) Determine the entropy change (kJ/K) of
liquid water.

An initially empty, well insulated, rigid tank with a volume of
2 m3 is fitted with a mixing device. The tank has two inlets and
zero outlets. One inlet is water at 1 MPa and 600◦C while the other
is saturated liquid water. Both enter the tank slowly. If the
amount of work done by the mixing device is 300 kJ, what must the
temperature of the saturated liquid water be if the same mass is
added through both inlets...

A 0.2 m3 piston-cylinder initially contains 400 K air. A heavy
frictionless piston maintains a pressure of 500 kPa abs. Then, a
weakness in the cylinder wall blows out and creates a hole. Air
escapes through the hole until the piston drops far enough to cover
the hole. At that point, the volume is half the initial volume.
During this process, 75 kJ of heat is transferred to the 100 kPa,
300 K surroundings. Using Cp = 1.005 kJ/kg-K and...

Initially (state 1) a well-insulated rigid tank contains 20 kg
of a saturated liquid-vapor mixture of water at 100 kPa and half of
the mass is in the liquid phase. An electric resistance heater
placed in the tank is now turned on and kept on until all the
liquid in the tank is vaporized (state 2). Determine (a) the
initial specific volume in m3/kg, (b) the final specific
entropy in kJ/kg.K and (c) change of entropy in kJ/K.

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