Question

Asked Apr 10, 2019

33 views

Consider an ice-producing plant that operates on the ideal vapor-compression refrigeration cycle and uses refrigerant-134a as the working fluid. The refrigeration cycle operating conditions require an evaporator pressure of 180 kPa and the condenser pressure of 1400 kPa. Cooling water flows through the water jacket surrounding the condenser and is supplied at the rate of 250 kg/s. The cooling water has a 10°C temperature rise as it flows through the water jacket. To produce ice, potable water is supplied to the chiller section of the refrigeration cycle. For each kg of ice produced, 333 kJ of energy must be removed from the potable water supply.

(Take the required values from saturated refrigerant-134a tables.)

Determine the mass flow rate of the potable water supply, in kg/s.

The mass flow rate of the potable water supply is_______ kg/s.

Step 1

Assume an ideal vapor-compression cycle.

In an ideal vapor compression cycle, the refrigerant enters the compressor at state 1 as saturated vapor at 180kPa and is compressed isentropically to the condenser pressure of 1400kPa. The vapor then enters the compressor as superheated vapor at state 2 and leaves as saturated liquid at state 3. Heat is rejected to the water jackets around the condenser.

The saturated liquid is throttled to state 4 such that the enthalpy at state 3 is the same as the enthalpy at state 4, which is the state of entry of the refrigerant in the evaporator as a low-quality saturated mixture.

The T-S diagram of the process is drawn.

Here, Q_{H} is the heat lost by the condenser and Q_{L }is the heat gained by the evaporator. It is also the refrigeration effect in this case. W_{in} is the work put into the compressor in pumping the refrigerant from the evaporator pressure to condenser pressure.

Step 2

Find the enthalpy in h_{i, }where enthalpy is kJ/kg and i denotes the corresponding points 1,2,3,4 using the standard pressure table for saturated refrigerant 134-a.

Enthalpy of saturated vapor h_{1} at pressure 180kPa is 242.90 kJ/kg.

Enthalpy of saturated liquid h_{3} at pressure 1400kPa is 127.25 kJ/kg.

Process 3-4 is a throttling process where enthalpy remains constant so the enthalpy of the saturated mixture h_{4 }is also 127.25 kJ/kg.

Step 3

To find the enthalpy at point 2, use the fact that the process 1-2 is isentropic.

So, S1 equals S2.

S1 is the entropy for the saturated vapor at 180 kPa, which is equal to 0.93979 kJ/kg∙k, evaluated using the standard pressure table for saturated refrigerant 134-a.

Hence, S2 is also 0.93979 kJ/kg∙k.&nb...

Tagged in

Find answers to questions asked by student like you

Show more Q&A

Q: A snowplow mounted on a truck clears a path 12 ft through heavy wet snow, as shown in Figure P5.80. ...

A: Draw the schematic diagram for the snow removal process showing the control volume as in figure belo...

Q: on the plates A and B, which are moving in opposite directions as shown. If vA = 75 mm/s to The atta...

A: Consider the diagram when the wheels roll.

Q: QUESTION 9 In a jet engine rotor the high pressure axial compressor rotates at a speed of 15000 rpm....

A: Write the expression to calculate the polytropic efficiency of compressor.

Q: NOTE: This is a multi-part question. Once an answer is submitted, you will be unable to return to th...

A: Show the T-s diagram as in Figure (1).

Q: The mass fractions of a mixture of gases are 10 percent nitrogen, 3 percent helium, 55 percent metha...

A: Assume the mass of the mixture as 100 grams.Given mass of Nitrogen is 10% of mixture which equals 10...

Q: Refrigerant-134a enters a diffuser steadily as saturated vapor at 700 kPa with a velocity of 150 m/s...

A: Given information:For saturated vapor,Inlet pressure(P1) = 700KPa,Inlet velocity(V1) = 150m/sExit pr...

Q: An FCC iron-carbon alloy initially containing 0.10 wt% C is carburized at an elevated temperature an...

A: Find the error function using Fick’s second law.

Q: The question is: Calculate the velocity of sound propagating in water at 20 degrees C. Assume that t...

A: The expression to find the velocity of sound in water is:

Q: The dry- and wet-bulb temperatures of atmospheric air at 92.5 kPa are 25°C and 17°C, respectively. T...

A: Given in the problem:Dry bulb temperature T is 25 0Wet bulb temperature Tw is 17 0Total atmospheric ...