# 5 - Prob 4.12 PROBLEM 4.12 PROBLEM STATEMENT In an air...

This preview shows pages 1–4. Sign up to view the full content.

Prob 4.12 9/18/04 PROBLEM 4.12 PROBLEM STATEMENT: In an air conditioning system, saturated liquid refrigerant R-134a at T=40°C flows through an insulated expansion valve, and reaches a final pressure of 320 kPa. What is the quality of the refrigerant after the expansion? DIAGRAM DEFINING SYSTEM AND PROCESS: 2 1 Expansion valve State 1: T 1 = 40°C x 1 = 0 State 2: P 2 = 320 kPa GIVEN: R-134a through an expansion valve T 1 = 40°C, x 1 = 0, P 2 = 320 kPa FIND: Exit quality, x 2 . ASSUMPTIONS: Adiabatic process, NKEPE, SFSS GOVERNING RELATIONS: 1. Mass balance, m = 1 2 m & & 2. Energy balance, = & & & & 2 2 OUT IN IN IN IN IN OUT OUT OUT OUT c c c c g g Q + m h + + z - W m h + + z 0 2g g 2g g v v QUANTITATIVE SOLUTION: From the energy balance equation: & IN Q & 2 IN IN IN c + m h + 2g v IN c g + z g & OUT - W & 2 OUT OUT OUT c m h + 2g v OUT c g + z g = & & 1 1 2 2 0 m h = m h Applying the mass balance equation, h 1 = h 2 . From Table 14s: 1 L 2 h = h (T = 40°C) =106.19 kJ/kg = h From Table 15s, at State 2, the refrigerant exists as a saturated mixture. The quality x 2 can be calculated as follows: 2 L,2 2 LV,2 h -h 106.19 - 53.31 x = = h 195.3 = 0.27 = 27% 5 DISCUSSION OF RESULTS: The process of dropping the pressure of a fluid through a restriction (valve, orifice, capillary tube) is called “throttling”. This problem shows that adiabatic throttling causes a saturated liquid to “flash” into a liquid-vapor mixture, an important part of refrigeration cycles.

This preview has intentionally blurred sections. Sign up to view the full version.

View Full Document
Prob 4.12 9/18/04 PROBLEM 4.14 PROBLEM STATEMENT: An adiabatic condenser operates as shown below. If the process is steady-state steady flow, determine the mass flow rate of cooling water required (kg/s). DIAGRAM DEFINING SYSTEM AND PROCESS: Q & & STM m = 80 kg/s 4 3 2 1 Cooling water Steam P 4 = P 3 T 4 = 60°C P 3 = 60 kPa x 3 = 92% P 2 = P 1 T 2 = 85°C P 1 = 0.1013 MPa T 1 = 50°C GIVEN: Water, m , adiabatic and SSSF & STM = 80 kg/s State 1: P 1 = 0.1013 MPa, T 1 = 50°C State 2: P 2 = P 1 , T 2 = 85°C State 3: P 3 = 60 kPa, x 3 = 92% State 4: P 4 = P 3, T 4 = 60°C FIND: m ( & W kg/s). ASSUMPTIONS: Externally adiabatic, no work, NKEPE, SSSF, treat liquid water as incompressible liquid. GOVERNING RELATIONS: 3. Mass balance, in out m = m & & 4. Energy balance, 2 IN IN IN IN c Q + m h + 2g & & v 2 OUT IN OUT OUT OUT c c g + z - Q m h + g 2g & & v = OUT c g + z g 0 & QUANTITATIVE SOLUTION: Conservation of mass: & & & & & & & & & & & IN OUT 1 3 2 4 1 2 W 3 4 STM m = m m +m = m +m m = m = m , m = m = m Conservation of energy: { } { } & & & & & & & & IN IN OUT OUT 1 1 3 3 2 2 4 4 W 2 1 STM 3 4 m h = m h m h +m h = m h +m h m (h - h ) = m (h - h )
Prob 4.12 9/18/04 The specific enthalpy values at each state can be determined from the tables for water.

This preview has intentionally blurred sections. Sign up to view the full version.

View Full Document
This is the end of the preview. Sign up to access the rest of the document.

{[ snackBarMessage ]}

### What students are saying

• As a current student on this bumpy collegiate pathway, I stumbled upon Course Hero, where I can find study resources for nearly all my courses, get online help from tutors 24/7, and even share my old projects, papers, and lecture notes with other students.

Kiran Temple University Fox School of Business ‘17, Course Hero Intern

• I cannot even describe how much Course Hero helped me this summer. It’s truly become something I can always rely on and help me. In the end, I was not only able to survive summer classes, but I was able to thrive thanks to Course Hero.

Dana University of Pennsylvania ‘17, Course Hero Intern

• The ability to access any university’s resources through Course Hero proved invaluable in my case. I was behind on Tulane coursework and actually used UCLA’s materials to help me move forward and get everything together on time.

Jill Tulane University ‘16, Course Hero Intern