NAME______BOX .

Fall 2010ME 301Period: 5th 6th

MayhewMech Sanders

Exam #2

Open Text Book

One 8.5” x 11” Equation Sheet (ONE side)

[No Worked Examples, ALEs or HW allowed]

Psychrometric Chart provided

Laptops Permitted for Calculations & Music Only

[EES is NOT permitted; music must not disturb others.]

SCORE

Problem 1_____/ 50

Problem 2_____/ 12

Problem 3/ 38

Total_____ /100

PLEASE NOTE:

The problems are printed on the inside of this folder. Please write the solutions for problems 1 and 3 on blank paper provided. Please write the solution to problem 2 on the question sheet.

Please put your name and CM box on each sheet.

Submit your equation sheet and solutions in the folder before you leave.

DO NOT INTERPOLATE! Use the closest value in the tables.

Problem 1 (50pts)

Refrigerant 134a enters the compressor of a vapor-compression refrigeration cycle at 1.4 bar and -10 °C and is compressed to 10 bar and 70 °C. Liquid enters the expansion valve at 10 bar and 36°C. At the valve exit, the pressure is 1.4 bar. The environment is at 27 °C.

State /

T [C]

/ P [bar] / h [kJ/kg] / s
[kJ/(kg K)] / other
1 /

-10

/ 1.4
2 /

70

/ 10.0
3 /

36

/ 10.0
4 / 1.4

(a)[16pts]Calculate the coefficient of performance of the cycle.

(b)[5pts]Given the flow rate of the R-134a is 6 kg/min., calculate the refrigeration capacity in tons.

(c)[13pts]Calculate the exergetic efficiency of the compressor.

(d)[6pts]Calculate the coefficient of performance of the cycle, if it was a heat pump.

(e)[3pts]Draw a rough sketch of the cycle on a T-s diagram.

(f)[3pts]Draw a rough sketch of the cycle on a P-h diagram.

(g)[4pts]If state 3 was changed to a saturated liquid at 10 bar, how would the following change?
[Circle the correct choices.]

(1)The refrigeration capacity would: increase decrease stay the same

(2)The coefficient of performance would: increase decrease stay the same

Problem 2 (12pts)

A fixed amount of air initially at 52°C, 1 atm, and 10% relative humidity is cooled at constant pressure to 15°C.

Use the psychrometric chart(provided)to determine the following:

(a)[4pts]Will condensation occur? Explain your answer.

(b)[6pts]The following properties at the final state:

(1)Relative humidity.

(2)Wet-bulb temperature.

(3)Humidity ratio.

(c)[2 pts]What are the restrictions for use of the psychrometric chart?

Problem 3 (38pts)

Air at 35 °C, 1 atm, and 50% relative humidity enters a dehumidifier (see diagram) operating at steady-state.

Condensate and saturated moist air exit in separate streams, each at 15 °C.

Neglect changes in kinetic and potential energy.

Determine the heat transfer out of the dehumidifier, in kJ per kg of dry air.