A rigid tank contains 9 L of saturated liquid refrigerant-134a and the same volu

Question

A rigid tank contains 9 L of saturated liquid refrigerant-134a and the same volume of saturated vapor refrigerant-134a at 0oC. The tank is connected to a refrigerant 134-a feeding line. A safety valve is installed on the top of the tank such that the pressure inside the tank never exceeds 600 kPa (mass will leave the tank through the valve when the pressure reaches 600 kPa). The valve of the feeding line is opened and R134a at 16oC, 900 kPa flows in the tank and closed when 4.2 kg has entered. At the end of the process, only 6.8 kg of R-134a remains inside the tank.
(a) How much mass has left the tank through the safety valve during the entire process?
(b) Determine the amount of heat transfer during the process

Explanation / Answer

see the basic equation for mass flow in and out of the system is
m(in)xh(in)+Q=m(out)xh(out)+W+u

here m(initial)=mass of saturated liquid+gas

we find that using the relation v_specifice=volume/mass

we can v_specific from steam table or using the software EES given the temperature and x.and thus determine mass

x=mg/(mg+ml)=0 for liquid and 1 for gas

now 4.2 kg entered and final mass is 6.8kg so mass exited is m(initial)+4.2-6.8

h(in) can be found out from given P=900kpa and t=16C

h(out) occurs when pressure is 600 kpa.and only vapour can exit from the top so x=1

using these 2 parameters we determine h(out)

w=0 as system is constant volume

change in internal energy is primitive and can be esaily determined from intial and final conditions

fp=600kPa at final condition since gas exits and stops at the equilibrium pressure of 600kPa.putting these in equation we get the answer

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