water if = 7.70 kJ/kg K, = 25 kPa, using the diagram.
Then find the values of , , and if defined.
UNGRADED: water, if = 3400 kJ/kg and = 10 MPa, using
the diagram. Then find the values of , , and if
defined
In each diagram, list no more than is needed to construct the
phase, but do list the values of the curves/points.
UNGRADED: A Carnot-cycle heat pump uses R-134a as
refrigerant. Heat is absorbed from the outside at -10C. It is
delivered to the heated space at 40C. Assume that the R-134a
enters the hot-side heat exchanger as saturated vapor and exits it
as saturated liquid.
Show the cycle in the diagram. List the entry to the hot
side heat exchanger as 1, the exit of it as 2, and so on.
Find the quality of the R-134a at the beginning and end of the
isothermal heat addition process at -10C.
Determine the coefficient of performance for the cycle.
Two kilogram ammonia in a piston/cylinder at 50C, 1000 kPa is
expanded in a reversible isothermal process to 100 kPa.
Construct the initial phase of the ammonia in both the
and diagrams. In each diagram, list no more than is needed
to construct the phase, but do list the values of the
curves/points used.
Add the final state to the diagrams and then draw the process
in them as a fat curve. (A ``curve'' might have straight parts.)
Find the work and heat transfer.
Water in a piston/cylinder at 400C, 2000 kPa is expanded in a
reversible adiabatic process. The specific work is measured to be
415.72 kJ/kg out.
Construct the initial phase of the water in both the and
diagrams. In each diagram, list no more than is needed to
construct the phase, but do list the values of the curves/points
used. Watch it: the temperature of the critical point is
374.1C, less than 400C. You should find state 1 is SUV.
Find a second intensive variable for the final state. WARNING: Hardcovers have in B.1.3 = 2945.21 listed
incorrectly as 2045.21. Please correct.
Now you need to construct the phase of state 2. Do
first. So in the -diagram that you already made, line 1 will
be a vertical line. You are then interested in where this line
hits the two phase region, which will be at the point on the
saturated vapor line where . Use table B.1.2, not B.1.1
to do so, because then you find to 4 digits accurate already
in the table (it is actually 5 significant digits, because a
single tick does not make a digit insignificant), so you do not have
to interpolate. Now check the value of the second variable at
that point. If you overshot the desired value going down from
state 1, then obviously state 2 is before the line hits the
saturated vapor curve, and state 2 must still be in the SUV
region. On the other hand, if you have not yet reached the target
value of the second variable, then obviously state 2 will be still
lower down, and inside the two phase region. In the unlikely case
that you hit exactly the value of the second variable, then
obviously state 2 is saturated vapor.
Show the final state, and the process line as a fat curve, in
the two diagrams you made earlier.