Water in a piston/cylinder arrangement is at 150 psia and 900 °F, as shown in Fig. C. There are two stops, a lower one at which Vmin = 35 ft³ and an upper one at Vmax = 105 ft³. The water undergoes a process of cooling that consists of four states. The piston rests at the upper stops (state 1) until its pressure decreases to 80 psia (state 2). The piston starts then floating until it reaches the lower set of stops (state 3). Finally, the water is cooled at 210 °F (state 4). Determine
Detrermine
(a) The state of water at each state of the process
(b) The amount of heat that is rejected to the environment in Btu
(c) At which part of the process is useful work involved? Calculate the work
in Btu? Is this work useful or spent on the system? What is the magnitude
of change in internal energy of the system at this part of the process?
(d)Show the process in a p-V diagram
Given data,
State 1:- When the piston is in upper stops
Pressure at state 1, P1 = 150 psia
Temperature at state 1, T1 = 900
Since, the piston rests at upper stops until its pressure drops to 80 psia.
So, the process 1 to 2 is an isochoric process (V=C).
Volume at state 1 and 2, V1 = V2 = Vmax = 105 ft3
Pressure at state 2, P2 = 80 psia
The piston is floating at reaches to lower stops (state 3).
So, the process 2-3 is a constant pressure process.
So, pressure at state 3, P3 = P2 = 80 psia
and, volume at state 3, V3 = Vmin = 35 ft3
Now, the water is cooled to 210
So, temperature at state 4, T4 = 210
The piston cannot move further, so, the process 3-4 is a constant volume process.
So, volume at state 4, V4 = 35 ft3
To determine:-
a) State of water at each of the process
b) The amount of heat rejected to the environment in BTU
c) Useful work
d) P-V diagram
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