Business. Professional application due Nov 17

Transcription

1 Business Professional application due Nov 17 Need to estiate what elective courses you will take Mark how you fulfilled Math & Cheistry Major and Total GPA Fill out fors and spreadsheet Then eet with your faculty advisor Case Study is Chapter probles, all connected Please report Dean s lecture attendance

2 Class 29 Heat and Huidity

3 How Do You Measure Huidity? Cool the air and weigh the oisture Cheically absorb the oisture Correlate soe other property, such as theral conductivity show Kestrel instruent Use IR spectra Sling psychroeter How can I use soething that I cannot pronounce?

4 Wet Bulb Teperature Air Flow Theroeter Wet wick Water Theroeter has a wet cloth around bulb Air blows past cloth As water evaporates, the bulb is cooled Like when you get cold when you get out of a swiing pool The difference between dry and wet bulb teperatures is related to relative huidity (RH) No water will evaporate at 100% RH, so T dry = T wet bulb Biggest T with driest air

5 Sling Psychroeter Two theroeters One dry One kept in wet cloth Twirl the wet theroeter High velocity air through cloth Measures: Dry bulb T Wet bulb T

6 Other Psychroeters Wind speed T dry bulb, T wet bulb Relative huidity T dew point

7 Air-Water Systes Extreely coon Chart developed for ease of use LOTS of data on chart! Based on dry air balance Like on the HW and practice exa!! n dry air Huid air Cooler 90F 85% RH T 1 Liquid water n dry air

8 Psychroetric Chart Figure (p. 433) Psychroetric chart SI units. Reference states: H 2 O (liquid, 0 C, 1 at), dry air (0 C, 1 at). (Data obtained fro Carrier Corporation.) Eleentary Principles of Cheical Processes, 4/E by Richard M. Felder, Ronald W. Rousseau, and Lisa G. Bullard Copyright 2016 by John Wiley & Sons, Inc. All rights reserved.

9 Aerican Units Figure (p. 434) Psychroetric chart U.S. custoary units. Reference states: H2O (liquid, 32 F, 1 at), dry air (0 F, 1 at). (Data obtained fro Carrier Corporation.) Eleentary Principles of Cheical Processes, 4/E by Richard M. Felder, Ronald W. Rousseau, and Lisa G. Bullard Copyright 2016 by John Wiley & Sons, Inc. All rights reserved.

10 Psychroetric Chart (yes, I know the obvious nicknae) Air-Water systes at 1 at Hˆ Hˆ H 2 O, Lat 0 C,1at air, gas at 0 C,1at 0 0 (h a = kg of H 2 O/kg of dry air) Figure (p. 433) For this chart only! Psychroetric chart SI units. Reference states: H 2 O (liquid, 0 C, 1 at), dry air (0 C, 1 at). (Data obtained fro Carrier Corporation.) Eleentary Principles of Cheical Processes, 4/E by Richard M. Felder, Ronald W. Rousseau, and Lisa G. Bullard Copyright 2016 by John Wiley & Sons, Inc. All rights reserved.

11 Psychroetric Chart (yes, I know the obvious nicknae) Air-Water systes at 1 at Hˆ Hˆ H 2 O, Lat 0 C,1at air, gas at 0 C,1at 0 0 (h a = kg of H 2 O/kg of dry air) Figure (p. 433) For this chart only! Psychroetric chart SI units. Reference states: H 2 O (liquid, 0 C, 1 at), dry air (0 C, 1 at). (Data obtained fro Carrier Corporation.) Eleentary Principles of Cheical Processes, 4/E by Richard M. Felder, Ronald W. Rousseau, and Lisa G. Bullard Copyright 2016 by John Wiley & Sons, Inc. All rights reserved.

12 Psychroetric Chart A. Trace the line of 40% relative huidity B. Trace the line of 22C wet bulb teperature

13 Psychroetric Chart A. Trace the line of Huid Volue = /kg Dry Air B. Trace the line of sat d enthalpy = 65 kj/kg Dry Air This is the enthalpy of the (air + oisture) divided by the ass of dry air ( 3 of air + water vapor)/(kg of dry air)

14 What if I want an enthalpy that is not saturated? (e.g., at 50% RH?) H dev given on chart H true = H sat d + H dev

15 Psychroetric Chart Trace the line of Enthalpy Deviation = -.4 kj/kg Dry Air

16 Psychroetric Chart Find point where T = 85 F and 30% RH What is the dew point for this condition? Note that the dew point has the sae absolute huidity (lb oisture/lb dry air) but a different T Tdp = 50 F

17 When working with these charts, what is the enthalpy of liquid water? Reference enthalpy is liquid water at 0C or 32F Hˆ T H O LatT at Hˆ,,1 C H O Lat C at p H O LdT C 2, 0,1, 2, p, H2O, L 2 0 C C p,h2o,l = 1 Btu/lb F = J/g C T T ref Exaple: Hˆ o C Btu / lb H O, Lat 45 F,1at p, H 2O, 2 L

18 In-Class Assignent

19 Psychroetric Chart Cheical Engineering 273, Class 29 In-Class Assignent The psychroetric chart for air and oisture (i.e., H 2 O) at 1 at total pressure is shown on the next page. Please coplete the following: A. Air at 1 at, 28C, 70% relative huidity. Label this point A. Find the following fro the psychroetric chart (and show your work on the graph, and don t forget units): 1. absolute huidity (h a ) 2. Wet bulb teperature (T wb ) 3. Dew point teperature (T dp ) 4. Saturated enthalpy ( Ĥ sat ) 5. Specific enthalpy ( Ĥ ) 6. Huid volue (V h ) B. Air at 1 at, 80F, T wb = 70F. Label this point B. Find the following fro the psychroetric chart (and show your work on the graph, and don t forget units): 1. absolute huidity (h a ) 2. Relative huidity (h r or RH) 3. Dew point teperature (T dp ) 4. Saturated enthalpy ( Ĥ sat ) 5. Specific enthalpy ( Ĥ ) 6. Huid volue (V h ) C. Air at 90F, 80% RH, 100 ft 3 /in is cooled to 60F, 20% RH. Assue that the liquid water leaves at 60F as well. Find the following: 1. The ass flow rate of condensed water (lb H 2 O (liq)/in) 2. Cooling requireent (in tons of cooling, where 1 ton = 12,000 Btu/hr). Air strea in Air strea out Condensed water out h a (lb H 2 O/lb dry air) Not applicable V h (ft 3 /lb dry air) Not applicable Ĥ (Btu/lb dry air) dry air H 2 O, in H 2 O, vapor out H 2 O, liquid out Q

20 Q Air 90 F 80% RH 100 ft 3 /in Air 60 F 20% RH Liquid Water 60 F

21 Psychroetric Chart A. 28C, 70% RH Absolute huidity (h a ) kg H 2 O/kg dry air Wet bulb teperature (T wb ) 23.6C Dew point teperature (T dp ) 21.6C Saturated enthalpy (H sat ) 71 kj/kg dry air Specific enthalpy (H) = kj/kg d.a. Huid volue (V h ) /kg d.a. A

22 Psychroetric Chart B. T = 80 F and Twb = 70 F Absolute huidity (ha) lb H2O/lb dry air Relative huidity (%RH) 60.5% Dew point teperature (Tdp) 65.2 F Saturated enthalpy (Hsat) 34 Btu/lb dry air Specific enthalpy (H) = Btu/lb d.a. Huid volue (Vh) ft3/lb d.a. B

23 Psychroetric Chart C C. T = 90 F and 80% R.H. D. T = 60 F and 20% R.H. Ha (lb H2O/lb dry air) Vh (ft3/lb d.a.) H (Btu/lb dry air) C D D

24 Enthalpy of liquid water out? H = H ref + c p T = 0 + (1 Btu/lb -F)(60-32F) = 28 Btu/lb (liq)

25 dry air 3 1 ft / in 6.94lb dry air / in ft / lbdry air H 2 O, in dry air lb H O lb H2O 6.94lb in lb dry air in 2 in H 2 O, vapor out dry air lb H O lb H2O 6.94lb in lb dry air in 2 out H 2 O, liquid out Q lb H O in H ˆ H ˆ out lb lb 6.94 H O 2 in dry air in out lb H2O in lb in out 2 liquid, out in liq, out Btu lb lb ( liq) lb Btu dry air Btu Btu , ton cooling in hr dry air in out H O in lb Btu dry air