Question

LLLS Moran, Shapiro, Boettner, Bailey, Fundamentals of Engineering Thermodynamics, 9e Help I n Assignment NEXT URCES Problem 4.067 S The figure below provides steady-state data for a throttling valve in series with a heat exchanger. Saturated liquid Refrigerant 134a enters the valve at a pressure of 9 bar and is throttled to a pressure of p2-3 bar. The refrigerant then enters the heat exchanger, exiting at a temperature of 10°C with no significant decrease in pressure. In a separate stream, liquid water at 1 bar enters the heat exchanger at a temperature of 25*C with a mass flow rate of r4-4 kg/s and exits at 1 bar as liquid at a temperature of 15°C. Stray heat transfer and kinetic and potential energy effects can be ignored Heat exchanger Ps=P2 7-10°C Saturated liquid R-134a at p-9 bar y Study Valve P Ts- 15 C Water 7,-25? P4-I bar Determine (a) the temperature, in °C, ofthe refrigerant at the exit of the valve. (b) the mass flow rate of the refrigerant, in kg/s Version 4.24.7 meacenicy 2000-201820m.mlex ASonatnc. All Rights Reserved. A p vision or 20mino a sos.?k. et i

Answer 1

Refrigerant R-134a enters the throttling valve at the pressure of 9 bar and exists at 3 bar.

a)Followin figure shows the whole process.

Throttling process is a constant enthalpy process. From the pressure enthalpy diagram of R-134a as shown above, the temperature of the refrigerant should be T ₂ = 0°C.

b) The refrigerant then flows through a heat exchanger, where in a separate stream water enters at 1 bar and T ₄ = 25°C.

Water exits the heat exchanger at temperature T ₅ = 15°C.

Average specific heat of refrigerant R-134a is C _ref= 1.351 KJ/Kgk.

Specific heat of water, C _w = 4.18 KJ/KgK.

Let m be the mass flow rate of the refrigerant and m ₄be the mass flow rate of water, then, applying energy balance for heat exchanger,

mC _ref(T ₃ - T ₂) = m ₄ C _w( T ₄ - T ₅)

m * 1.351 ( 10 - 0) = 4 * 4.18 ( 25 - 15 )

m = 12.37 kg/s