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EGR 334 Thermodynamics Chapter 12:

EGR 334 Thermodynamics Chapter 12: . Lecture 40: Pyschrometic Chart. Quiz Today?. Today’s main concepts:. Understand the structure of the pyschrometric chart and identify air/vapor properties from it. Be able to solve air conditioning problems using the chart. . Final Exam: .

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EGR 334 Thermodynamics Chapter 12:

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  1. EGR 334 ThermodynamicsChapter 12: Lecture 40: Pyschrometic Chart Quiz Today?

  2. Today’s main concepts: • Understand the structure of the pyschrometric chart and identify air/vapor properties from it. • Be able to solve air conditioning problems using the chart. Final Exam: 1:00 p.m. on Tuesday, May 15 Reading Assignment: no assignment Homework Assignment: No Assignment

  3. Sec 12.8 : Analyzing Air-Conditioning Processes Air-Conditioning Heat from “hot side” is used for evaporation of the coolant. Heat is rejected to the outside by condensation.

  4. Sec 12.8 : Analyzing Air-Conditioning Processes “Swamp” Coolers (evaporative cooler) Evaporation of water provides cooling.

  5. 1) Identify State Properties of as many individual mixture components Procedure for analysis of air conditioning systems: Use ideal gas law: or Table A20 and A22 Steam tables: Tables A2, A3, A4, etc. Humidity definitions: Constant process data: isobaric, isothermal, isentropic, polytropic, etc. Psychrometric Chart: Figures A9 and A9E. 2) Apply mass balance to each individual component of the mixture. 3) Apply energy balance to each separate stream of the mixture. 4) Solve equations

  6. Sec 12.7 : Psychrometric Charts Psychrometric Chart Figure A-9

  7. Sec 12.7 : Psychrometric Charts To open the windows or not? Inside: T = 85°F,  = 60% Outside: T = 80°F,  = 75% • Open only if ωi< ωo. Figure A-9 (pages 920,1)

  8. Sec 12.7 : Psychrometric Charts To open the windows or not? Inside: T = 85°F,  = 60% Outside: T = 80°F,  = 80% • Open only if ωi> ωo. • Since ωi< ωo, don’t open, house will cool. Don’t let extra moisture in. Figure A-9 (pages 920,1)

  9. Sec 12.8 : Analyzing Air-Conditioning Processes Problems can be solved using 1) tabulated data 2) Psychrometric chart. Mass balance: Often can neglect with and Energy balance:

  10. Sec 12.8 : Analyzing Air-Conditioning Processes Air-Conditioning Energy balance: But, we can re-write in a more convenient form. with and and • Evaluate hv1, hv2 & hv3 at steam tables for hv1 & hv3 use saturation point • Evaluate ha1 & ha3 using Table A-22 • or • Evaluate moist air specific enthalpy using the pyschrometric chart

  11. Example (12.67): Moist air at 22°C, and a wet bulb temperature of of9°C • enters a steam spray humidifier. The mass flow of the dry air is 90 kg/min. Saturated water vapor at 110 C is injected into the mixture at a rat of 52 kg/hr. There is no heat transfer with the surroundings, and the pressure is constant throughout at 1 bar. Determine at the exit • a) the humidity ratio • b) the temperature in oC. Moist air • T2=? ω2=? • T1=22°C, Twb=9°C 1 2 3 Saturated vapor: T3=110 oC

  12. Example (12.67): • a) the humidity ratio • b) the temperature in oC. Mass Balance Equations: for air: for H20: with 1 2 Energy Balance Equations: 3

  13. Example (12.67): • a) the humidity ratio • b) the temperature in oC. State 1: Use the psychrometric chart to find properties. 1 2 State 3: Saturated vapor at 110oC 3 Use Steam table, A2:

  14. Example (12.67): • a) the humidity ratio • b) the temperature in oC. Mass Balance Equations: and 1 2 therefore: From the energy balance: 3

  15. Example (12.67): • a) the humidity ratio • b) the temperature in oC. therefore at State 2: Using the pyschrometric chart: 1 2 At the intersection of the humidity ratio and the specific enthalpy of moist air, the dry bulb temperature can be directly looked up: 24 oC. 3 24oC

  16. End of slides for lecture 40

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