# Refrigeration Questions and Answers – Multiple Evaporators and Compressor System – 2

This set of Refrigeration written test Questions & Answers focuses on “Multiple Evaporators and Compressor System – 2”.

1. What is the value of enthalpy when refrigerant enters the compressor, i.e., point 1?

a) m1 h11 + m2 h8 + m3 h5 / (m1 + m2 – m3)
b) m1 h11 + m2 h8 + m3 h5 / (m1 – m2 + m3)
c) m1 h11 + m2 h8 + m3 h5 / (m1 + m2 + m3)
d) m1 h5 + m2 h5 + m3 h4 / (m1 + m2 + m3)

Explanation: Let, mass m1, m2 and m3 be the mass of refrigerant circulated through evaporators EP1, EP2 and EP3.
Where, m1 = 210 Q1 / h11 – h10
m2 = 210 Q2 / h8 – h7
m3 = 210 Q3 / h5 – h4
At point 1, mass of refrigerant coming from each evaporator is converging.
So, (m1 + m2 + m3) h1 = m1 h11 + m2 h8 + m3 h5
h1 = m1 h11 + m2 h8 + m3 h5 / (m1 + m2 + m3).

2. What is the value of the refrigeration effect in the following arrangement?

a) m1 (h11 – h10) + m2 (h8 – h1) + m3 (h5 – h2)
b) m1 (h11 – h10) + m2 (h8 – h7) + m3 (h5 – h4)
c) m1 (h11 – h10) + m2 (h8 – h2) + m3 (h2 – h4)
d) m1 (h11 – h10) + m2 (h8 – h7) + m3 (h1 – h4)

Explanation: Let, mass m1, m2 and m3 be the mass of refrigerant circulated through evaporators EP1, EP2 and EP3.
Where, m1 = 210 Q1 / h11 – h10
m2 = 210 Q2 / h8 – h7
m3 = 210 Q3 / h5 – h4
So, Refrigeration effect across EP1 = m1 (h11 – h10)
Refrigeration effect across EP2 = m2 (h8 – h7)
Refrigeration effect across EP3 = m3 (h5 – h4)
Total refrigeration effect produced in the system is the summation of refrigeration effect across each evaporator.
Total refrigeration effect = m1 (h11 – h10) + m2 (h8 – h7) + m3 (h5 – h4) = 210 (Q1 + Q2 + Q3).

3. What is the value of C.O.P. in the following arrangement?

a) m1 (h11 – h10) + m2 (h8 – h7) + m3 (h5 – h4) / (m1 + m2 + m3) (h2 – h3)
b) m1 (h11 – h10) + m2 (h8 – h7) + m3 (h5 – h4) / (m1 + m2 + m3) (h2 – h7)
c) m1 (h11 – h10) + m3 (h8 – h7) + m2 (h5 – h4) / (m1 + m2 + m3) (h2 – h1)
d) m1 (h11 – h10) + m2 (h8 – h7) + m3 (h5 – h4) / (m1 + m2 + m3) (h2 – h1)

Explanation: Let, mass m1, m2 and m3 be the mass of refrigerant circulated through evaporators EP1, EP2 and EP3.
Where, m1 = 210 Q1 / h11 – h10
m2 = 210 Q2 / h8 – h7
m3 = 210 Q3 / h5 – h4
So, Refrigeration effect across EP1 = m1 (h11 – h10)
Refrigeration effect across EP2 = m2 (h8 – h7)
Refrigeration effect across EP3 = m3 (h5 – h4)
Total refrigeration effect produced in the system is the summation of refrigeration effect across each evaporator.
Total refrigeration effect = m1 (h11 – h10) + m2 (h8 – h7) + m3 (h5 – h4) = 210 (Q1 + Q2 + Q3)
Work = (m1 + m2 + m3) (h2 – h1)
C.O.P. = Total refrigeration effect / Work
= m1 (h11 – h10) + m2 (h8 – h7) + m3 (h5 – h4) / (m1 + m2 + m3) (h2 – h1)
= 210 (Q1 + Q2 + Q3) / (m1 + m2 + m3) (h2 – h1).

4. What is the value of enthalpy when refrigerant enters the compressor, i.e., point 1?

a) me1 h11 + me2 h9 + me3 h6 / (me1 + me2 + me3)
b) me1 h11 + me2 h9 + me3 h5 / (me1 + me2 + me3)
c) me1 h11 + me2 h8 + me3 h6 / (me1 + me2 + me3)
d) m1 h5 + m2 h5 + m3 h4 / (m1 + m2 + m3)

Explanation: Let, mass m1, m2 and m3 be the mass of refrigerant circulated through evaporators EP1, EP2 and EP3.
Where, m1 = me1 = 210 Q1 / h11 – h10
m2 = 210 Q2 / h9 – h7, me2 = m2 + me1 (x7 / 1 – x7)
m3 = 210 Q3 / h6 – h4, me3 = m3 + (me1 + me2) (x4 / 1 – x4)
At point 1, mass of refrigerant coming from each evaporator is converging.
So, (me1 + me2 + me3) h1 = me1 h11 + me2 h9 + me3 h6
h1 = me1 h11 + me2 h9 + me3 h6 / (me1 + me2 + me3).

5. What is the value of the refrigeration effect in the following arrangement?

a) m1 (h11 – h10) + m2 (h8 – h1) + m3 (h5 – h2)
b) m1 (h11 – h10) + m2 (h9 – h7) + m3 (h6 – h4)
c) m1 (h11 – h10) + m2 (h8 – h2) + m3 (h2 – h4)
d) m1 (h11 – h10) + m2 (h8 – h7) + m3 (h1 – h4)

Explanation: Let, mass m1, m2 and m3 be the mass of refrigerant circulated through evaporators EP1, EP2 and EP3.
Where, m1 = 210 Q1 / h11 – h10
m2 = 210 Q2 / h9 – h7
m3 = 210 Q3 / h6 – h4
So, Refrigeration effect across EP1 = m1 (h11 – h10)
Refrigeration effect across EP2 = m2 (h9 – h7)
Refrigeration effect across EP3 = m3 (h6 – h4)
Total refrigeration effect produced in the system is the summation of refrigeration effect across each evaporator.
Total refrigeration effect = m1 (h11 – h10) + m2 (h9 – h7) + m3 (h6 – h4) = 210 (Q1 + Q2 + Q3).
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6. What is the value of C.O.P. in the following arrangement?

a) m1 (h11 – h10) + m2 (h9 – h7) + m3 (h6 – h4) / (me1 + me2 + me3) (h2 – h1)
b) m1 (h11 – h10) + m2 (h8 – h7) + m3 (h5 – h4) / (m1 + m2 + m3) (h2 – h7)
c) m1 (h11 – h10) + m2 (h9 – h7) + m3 (h6 – h1) / (me1 + me2 + me3) (h2 – h8)
d) m1 (h11 – h10) + m2 (h8 – h7) + m3 (h5 – h4) / (m1 + m2 + m3) (h2 – h1)

Explanation: Let, mass m1, m2 and m3 be the mass of refrigerant circulated through evaporators EP1, EP2 and EP3.
Where, m1 = 210 Q1 / h11 – h10
m2 = 210 Q2 / h9 – h7
m3 = 210 Q3 / h6 – h4
So, Refrigeration effect across EP1 = m1 (h11 – h10)
Refrigeration effect across EP2 = m2 (h9 – h7)
Refrigeration effect across EP3 = m3 (h6 – h4)
Total refrigeration effect produced in the system is the summation of refrigeration effect across each evaporator.
Total refrigeration effect = m1 (h11 – h10) + m2 (h9 – h7) + m3 (h6 – h4) = 210 (Q1 + Q2 + Q3)
Work = (me1 + me2 + me3) (h2 – h1)
C.O.P. = Total refrigeration effect / Work
= m1 (h11 – h10) + m2 (h9 – h7) + m3 (h6 – h4) / (me1 + me2 + me3) (h2 – h1)
= 210 (Q1 + Q2 + Q3) / (me1 + me2 + me2) (h2 – h1).

7. What is the value of the refrigeration effect in the following arrangement?

a) m1 (h1 – h10) + m2 (h8 – h1) + m3 (h5 – h2)
b) m1 (h1 – h10) + m2 (h8 – h7) + m3 (h5 – h4)
c) m1 (h1 – h10) + m2 (h3 – h9) + m3 (h5 – h8)
d) m1 (h11 – h10) + m2 (h8 – h7) + m3 (h1 – h4)

Explanation: Let, mass m1, m2 and m3 be the mass of refrigerant circulated through evaporators EP1, EP2 and EP3.
Where, m1 = 210 Q1 / h1 – h10
m2 = 210 Q2 / h3 – h9
m3 = 210 Q3 / h5 – h8
So, Refrigeration effect across EP1 = m1 (h1 – h10)
Refrigeration effect across EP2 = m2 (h3 – h9)
Refrigeration effect across EP3 = m3 (h5 – h8)
Total refrigeration effect produced in the system is the summation of refrigeration effect across each evaporator.
Total refrigeration effect = m1 (h1 – h10) + m2 (h3 – h9) + m3 (h5 – h8) = 210 (Q1 + Q2 + Q3).

8. What is the value of total power required to run the following arrangement?

a) m1 (h2 – h1) + m3 (h4 – h3) + m2 (h6 – h1)
b) m1 (h2 – h1) + m2 (h4 – h3) + m3 (h6 – h5)
c) m2 (h2 – h1) + m3 (h4 – h3) + m1 (h6 – h5) / 60
d) m1 (h2 – h1) + m2 (h4 – h3) + m3 (h6 – h5) / 60

Explanation: Let, mass m1, m2 and m3 be the mass of refrigerant circulated through compressors C1, C2 and C3
So, Power required to run compressor C1 = m1 (h2 – h1) / 60
Power required to run compressor C2 = m2 (h4 – h3) / 60
Power required to run compressor C3 = m3 (h6 – h5) / 60
Total power required to run the system will be summation of power required to run each compressor.
Total power required to run the system = m1 (h2 – h1) + m2 (h4 – h3) + m3 (h6 – h5) / 60.

9. What is the value of C.O.P. in the following arrangement?

a) m1 (h11 – h10) + m2 (h8 – h7) + m3 (h5 – h4) / (m1 + m2 + m3) (h2 – h3)
b) m1 (h1 – h10) + m2 (h3 – h9) + m3 (h5 – h8) / m1 (h2 – h1) + m2 (h4 – h3) + m3 (h6 – h5)
c) m1 (h1 – h10) + m2 (h3 – h9) + m3 (h5 – h8) / m1 (h2 – h1) + m2 (h4 – h2) + m3 (h6 – h3)
d) m1 (h11 – h10) + m2 (h8 – h7) + m3 (h5 – h4) / (m1 + m2 + m3) (h2 – h1)

Explanation: Let, mass m1, m2 and m3 be the mass of refrigerant circulated through evaporators EP1, EP2 and EP3.
Where, m1 = 210 Q1 / h1 – h10
m2 = 210 Q2 / h3 – h9
m3 = 210 Q3 / h5 – h8
So, Refrigeration effect across EP1 = m1 (h1 – h10)
Refrigeration effect across EP2 = m2 (h3 – h9)
Refrigeration effect across EP3 = m3 (h5 – h8)
Total refrigeration effect produced in the system is the summation of refrigeration effect across each evaporator.
Total refrigeration effect = m1 (h1 – h10) + m2 (h3 – h9) + m3 (h5 – h8) = 210 (Q1 + Q2 + Q3)
Total Work = m1 (h2 – h1) + m2 (h4 – h3) + m3 (h9 – h5)
C.O.P. = Total refrigeration effect / Work
= m1 (h1 – h10) + m2 (h3 – h9) + m3 (h5 – h8) / m1 (h2 – h1) + m2 (h4 – h3) + m3 (h6 – h5)
= 210 (Q1 + Q2 + Q3) / m1 (h2 – h1) + m2 (h4 – h3) + m3 (h9 – h5).

10. What is the value of the refrigeration effect in the following arrangement?

a) m1 (h1 – h12) + m2 (h3 – h10) + m3 (h5 – h8)
b) m1 (h11 – h10) + m2 (h9 – h7) + m3 (h6 – h4)
c) m1 (h1 – h12) + m2 (h9 – h10) + m3 (h5 – h4)
d) m1 (h11 – h10) + m2 (h8 – h7) + m3 (h1 – h4)

Explanation: Let, mass m1, m2 and m3 be the mass of refrigerant circulated through evaporators EP1, EP2 and EP3.
Where, m1 = 210 Q1 / h1 – h12
m2 = 210 Q2 / h3 – h10
m3 = 210 Q3 / h5 – h8
So, Refrigeration effect across EP1 = m1 (h1 – h12)
Refrigeration effect across EP2 = m2 (h3 – h10)
Refrigeration effect across EP3 = m3 (h5 – h8)
Total refrigeration effect produced in the system is the summation of refrigeration effect across each evaporator.
Total refrigeration effect = m1 (h1 – h12) + m2 (h3 – h10) + m3 (h5 – h8) = 210 (Q1 + Q2 + Q3).

11. What is the value of total work done in the following arrangement?

a) me1 (h2 – h1) + me2 (h4 – h3) + me3 (h4 – h5)
b) me1 (h2 – h1) + me3 (h4 – h3) + me2 (h6 – h5)
c) me1 (h2 – h1) + me3 (h4 – h3) + me3 (h6 – h5)
d) m1 h5 + m2 h5 + m3 h4 / (m1 + m2 + m3)

Explanation: Let, mass m1, m2 and m3 be the mass of refrigerant circulated through evaporators EP1, EP2 and EP3.
Where, m1 = me1 = 210 Q1 / h1 – h12
m2 = 210 Q2 / h3 – h10, me2 = m2 + me1 (x10 / 1 – x10)
m3 = 210 Q3 / h5 – h8, me3 = m3 + (me1 + me2) (x8 / 1 – x8)
Total work done is the summation of work done by each compressor.
So, Work done by compressor C1 = me1 (h2 – h1)
Work done by compressor C2 = me2 (h4 – h3)
Work done by compressor C3 = me3 (h6 – h5)
Total work = me1 (h2 – h1) + me2 (h4 – h3) + me3 (h6 – h5).

12. What is the value of C.O.P. in the following arrangement?

a) m1 (h1 – h12) + m2 (h3 – h10) + m3 (h5 – h8)
b) m1 (h1 – h12) + m2 (h3 – h10) + m3 (h5 – h8) / me1 (h2 – h1) + me2 (h4 – h3) + me3 (h6 – h5)
c) m1 (h1 – h12) + m2 (h3 – h10) + m3 (h5 – h8) / me1 (h2 – h5) + me2 (h4 – h2) + me3 (h6 – h5)
d) m1 (h1 – h12) + m2 (h3 – h10) + m3 (h5 – h8) / me1 (h2 – h1) + me2 (h4 – h1) + me3 (h6 – h1)

Explanation: Let, mass m1, m2 and m3 be the mass of refrigerant circulated through evaporators EP1, EP2 and EP3.
Where, m1 = 210 Q1 / h1 – h12
m2 = 210 Q2 / h3 – h10
m3 = 210 Q3 / h5 – h8
So, Refrigeration effect across EP1 = m1 (h1 – h12)
Refrigeration effect across EP2 = m2 (h3 – h10)
Refrigeration effect across EP3 = m3 (h5 – h8)
Total refrigeration effect produced in the system is the summation of refrigeration effect across each evaporator.
Total refrigeration effect = m1 (h1 – h12) + m2 (h3 – h10) + m3 (h5 – h8) = 210 (Q1 + Q2 + Q3)
So, Work done by compressor C1 = me1 (h2 – h1)
Work done by compressor C2 = me2 (h4 – h3)
Work done by compressor C3 = me3 (h6 – h5)
Total work = me1 (h2 – h1) + me2 (h4 – h3) + me3 (h6 – h5)
C.O.P. = Total refrigeration effect / Total work done
= m1 (h1 – h12) + m2 (h3 – h10) + m3 (h5 – h8) / me1 (h2 – h1) + me2 (h4 – h3) + me3 (h6 – h5).

13. What is the value of enthalpy when refrigerant enters the second compressor, i.e., point 4?

a) m1 h2 + m2 h3 / (m1 + m2)
b) m1 h11 + m2 h8 + m3 h5 / (m1 – m2 + m3)
c) m1 h2 + m2 h1 / (m1 + m2)
d) m1 h5 + m2 h5 + m3 h4 / (m1 + m2 + m3)

Explanation: Let, mass m1, m2 and m3 be the mass of refrigerant circulated through evaporators EP1, EP2 and EP3.
Where, m1 = 210 Q1 / h1 – h12
m2 = 210 Q2 / h2 – h11
m3 = 210 Q3 / h6 – h10
At point 4, mass of refrigerant coming from evaporator 1 and 2 is converging.
So, (m1 + m2) h4 = m1 h2 + m2 h3
h4 = m1 h2 + m2 h3 / (m1 + m2).

14. What is the value of enthalpy when refrigerant enters the third compressor, i.e., point 7?

a) m1 h2 + m2 h3 / (m1 + m2)
b) m1 h11 + m2 h8 + m3 h5 / (m1 – m2 + m3)
c) (m1 + m2) h5 + m3 h6 / (m1 + m2 + m3)
d) m1 h5 + m2 h5 + m3 h4 / (m1 + m2 + m3)

Explanation: Let, mass m1, m2 and m3 be the mass of refrigerant circulated through evaporators EP1, EP2 and EP3.
Where, m1 = 210 Q1 / h1 – h12
m2 = 210 Q2 / h2 – h11
m3 = 210 Q3 / h6 – h10
At point 4, mass of refrigerant coming from evaporator 1 and 2 is converging.
So, (m1 + m2 + m3) h7 = (m1 + m2) h5 + m3 h6
h7 = (m1 + m2) h5 + m3 h6 / (m1 + m2 + m3).

15. What is the power required for the following arrangement?

a) m1 (h2 – h11) + (m1 + m2) (h5 – h8) + (m1 + m2 + m3) (h8 – h7) / 60
b) m1 (h2 – h1) + (m1 + m2) (h5 – h4) + (m1 + m2 + m3) (h8 – h7) / 60
c) m1 (h2 – h1) + (m2 + m3) (h5 – h4) + (m1 + m2 + m3) (h8 – h7) / 60
d) m1 h5 + m2 h5 + m3 h4 / (m1 + m2 + m3)

Explanation: Let, mass m1, m2 and m3 be the mass of refrigerant circulated through evaporators EP1, EP2 and EP3
So, Power required to run compressor C1 = m1 (h2 – h1) / 60
Power required to run compressor C2 = (m1 + m2) (h5 – h4) / 60
Power required to run compressor C3 = (m1 + m2 + m3) (h8 – h7) / 60
Total power required to run the system will be summation of power required to run each compressor.
Total power required to run the system = m1 (h2 – h1) + (m1 + m2) (h5 – h4) + (m1 + m2 + m3) (h8 – h7) / 60.

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