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One of the steps in a typical refrigeration process is a condenser. Freon® 22 enters a condenser at steady state as superheated vapor at P = 3 bar and T = 30°C. It leaves the condenser as saturated liquid at P = 3 bar. Use the data in Appendix F for the following. A. Find the heat removed from the condenser, per kilogram of entering Freon. B. Find the flow rate of Freon in the condenser, if the rate at which heat is expelled from the condenser is Q ˙ = 250 kJ/min. C. Determine the change in entropy of the universe resulting from the process in part B, assuming the coolant used for the condenser is a heat reservoir at a temperature 5°C lower than the temperature of the Freon exiting the condenser.

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Fundamentals of Chemical Engineeri...

1st Edition
Kevin D. Dahm + 1 other
Publisher: Cengage Learning
ISBN: 9781111580704

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Section
BuyFindarrow_forward

Fundamentals of Chemical Engineeri...

1st Edition
Kevin D. Dahm + 1 other
Publisher: Cengage Learning
ISBN: 9781111580704
Chapter 4.8, Problem 23P
Textbook Problem
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One of the steps in a typical refrigeration process is a condenser. Freon® 22 enters a condenser at steady state as superheated vapor at P = 3 bar and T = 30°C. It leaves the condenser as saturated liquid at P = 3 bar. Use the data in Appendix F for the following.

  1. A. Find the heat removed from the condenser, per kilogram of entering Freon.
  2. B. Find the flow rate of Freon in the condenser, if the rate at which heat is expelled from the condenser is Q ˙ = 250 kJ/min.
  3. C. Determine the change in entropy of the universe resulting from the process in part B, assuming the coolant used for the condenser is a heat reservoir at a temperature 5°C lower than the temperature of the Freon exiting the condenser.

(A)

Interpretation Introduction

Interpretation:

Determine the heat is removed from the condenser per kilogram (Q˙/m˙) of entering Freon 22.

Concept Introduction:

The steady state energy equation for the condenser.

ddt{M(U^+V22+gh)}=[m˙in(H^in+Vin22+ghin)m˙out(H^out+Vout22+ghout)+W˙S+WEC+Q˙]

Here, time taken is t, total mass is M, specific internal energy is U^, velocity is V, acceleration due to gravity is g, height is h, initial mass flow rate is m˙in, initial specific enthalpy is H^in, initial velocity is Vin, initial height of the gas is hin, final mass flow rate is m˙out, final height of the gas is hout, rate at which shaft work is added to the system is W˙S, rate at which work is added to the system through expansion or contraction of the system is W˙EC, and rate at which heat is added to the system is Q˙.

Explanation of Solution

Given information:

Initial pressure of 3bar and initial temperature of 30°C.

Final pressure of 3bar.

Calculate the heat transfer rate using steady state energy equation.

ddt{M(U^+V22+gh)}=[m˙in(H^in+Vin22+ghin)m˙out(H^out+Vout22+ghout)+W˙S+WEC+Q˙]        (1)

Rewrite the Equation (1) by neglecting the internal energy, height, mass, external work is added to the system.

0=m˙inH^inm˙outH^out+Q˙Q˙m˙=H^outH^in        (2)

Refer the appendix table F, “Thermodynamic diagrams-Freon 22”, obtain the value of initial specific enthalpy (H^in) corresponding to initial pressure (P1) of 3bar and initial temperature (T1) of 30°C

(B)

Interpretation Introduction

Interpretation:

Determine the flow rate (m˙) of Freon in the condenser.

Concept Introduction:

Write the flow rate (m˙) of Freon in the condenser.

m˙=Q˙(1Q˙/m˙)

Here, rate of heat addition is Q˙.

(C)

Interpretation Introduction

Interpretation:

Determine the change in entropy of the universe.

Concept Introduction:

Write an entropy balance for the coolant side only.

d(MS^)dt=j=1j=Jm˙j,inS^jk=1k=Km˙k,outS^k+n=1n=NQ˙nTn+S˙gen

Here, time is t, mass of the system is M, specific entropy of the system is S^, mass flow rates of individual streams entering and leaving the system are m˙j,in and m˙k,out respectively, specific entropies of the streams entering and leaving the system is S^j and S^k respectively, the actual rate at which heat is added to or removes from the system at one particular location is Q˙n, temperature of the system at the boundary where the heat transfer labeled n occurs is Tn, and rate at which entropy is generated within the boundaries of the system is S˙gen.

Write the entropy energy for the system.

0=m˙Freon,inS^Freon,in+m˙coolant,inS^coolant,inm˙Freon,outS^Freon,outm˙coolant,outS^coolant,out+S˙gen

Here, initial mass flow rate of Freon in m˙Freon,in, initial specific entropy of Freon is S^Freon,in, initial mass flow rate of coolant is m˙coolant,in, initial specific entropy of coolant is S^coolant,in, final mass flow rate of Freon is m˙Freon,out, final specific entropy of Freon is S^Freon,out, final mass flow rate of coolant is m˙coolant,out, and final specific entropy of coolant is S^coolant,out.

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