CE311 Fall 2016 Mid-Term Exam 1

CE311 Fall 16 Mid-Term Exam 1 Name Instructions 1. Please solve the problems using the specified SI or IP system of units. 2. Please show all of your calculations to get full credit and pay attention to assumptions. 3. Neatly mark points and outline processes on the ASHRAE SI or IP psychrometric chart. 4. Final solutions should be clearly summarized and marked/boxed.. Use only the attached equation sheet. 6. Please attach additional pages of your work, clearly marking each problem. Problem 1 (/pts) Moist air exists at 8 F dry-bulb temperature, % relative humidity, and a total pressure of 1 atm. Use the psychrometric chart to determine the following values (with units, neatly mark points on chart) (a) Dew-point temperature (1pt) (b) Wet-bulb temperature (1pt) (c) Humidity ratio (1pt) (d)mixture enthalpy (1pt) (e) Specific volume (1pt) Problem 2 (2./pts) Would you recommend an evaporative cooling system for use in the summer in Florida? Briefly explain why. In Arizona? 1/6

CE311 Fall 16 Mid-Term Exam 1 Name Problem 3 (2./pts) It s February here in West Lafayette, Indiana. Describe how you would condition the outdoor air in an air handling unit (AHU) of a building in order to meet the thermal comfort preferences of the occupants. Please list the AHU components you would use and neatly illustrate the process on the psychrometric chart to the right. Problem 4 (2./pts) Briefly explain Dalton s Law of Partial Pressures (Dalton s Model) through both words and equation(s). Problem (2./pts) What is the difference between the humidity ratio and relative humidity? temperature. Explain their relationship to 2/6

CE311 Fall 16 Mid-Term Exam 1 Name Problem 6 (/pts) It s winter and you re in a large classroom with a volume 1 m 3 at a dry-bulb temperature of 22 C, a total pressure of 96 kpa, and a relative humidity of %. Determine (a) Humidity ratio (pts) (b) Mass of dry air in the room (pts) (c) Mass of water vapor in the room (pts) (d) Will condensation occur on a window with a surface temperature of 2 C? (pts) 3/6

CE311 Fall 16 Mid-Term Exam 1 Name Problem 7 (/pts) An AHU is operating to heat and humidify the outdoor air before it is supplied to a room. The air first passes over a pre-heat coil, then through an evaporative cooler, and finally, a re-heat coil. The pre-heat coil is used to prevent the water in the evaporative cooler from freezing. The air flows through a perfectly insulated rectangular galvanized steel duct of cm by cm. Conditions Total pressure of 1atm at all points. Point 1 Dry-bulb temperature of 8 C, relative humidity of 7%, velocity of m/s. Point 3 Relative humidity of %. Point 4 Dry-bulb temperature of 23 C, relative humidity of %. Determine (a) Neatly sketch the process on a psychrometric chart and label all points (pts) (b) The amount of heat added by the pre-heat (pts) and re-heat coils (pts). heat added by the pre-heat coil to the re-heat coil (4pts)? What is the ratio of the (c) The rate at which water is added in the evaporative cooler (6pts) ( " ) 4/6

CE311 Fall 16 Mid-Term Exam 1 Name Problem 8 (/pts) It s Dubai in July. You need to provide cool air to occupants in a building. First, you adiabatically mix outdoor air with recirculation air. The mixed air stream is then cooled and dehumidified, followed by re-heat, before it is supplied to occupied spaces. Conditions Total pressure of 1atm at all points. Outdoor air dry-bulb temperature of 44 C, relative humidity of %, and mass flow rate is $% = kg dry air/min. Recirculation air wet-bulb temperature of 19 C, specific volume of.867 m 3 /kg dry air, and mass flow rate, $&, is 33% greater than $%. Supply air dry-bulb temperature of C, relative humidity of %. Collected condensate temperature of 8 C. (a) Draw a schematic of an AHU for this process. Label each point and the components (pts) (d)neatly sketch the process on a psychrometric chart and label all points (pts) (b) Determine the heat removed by the cooling coil (7.pts) and heat added by the re-heat coil (7.pts). /6

CE311 Fall 16 Mid-Term Exam 1 Name (c) Determine the amount of water removed from the air during the cooling and dehumidification process as kg water/kg dry air (pts) 6/6

" = $ " $ " &'()*+,-./'$ $ " $1&2),*'+*&'()3*'+*.'&4'$)$/*-3** &'( 7 " = & " $ " 7 89*;"9 = 28.97 7 A;BC9*D;EF9 = 18.2 I = 8.314 I " = I 7 " ideal*gas*equation*of*state PV = nig ω = & D & ; ω =.622 n D n ; φ = n D n p φ = qn (.622 + q)n p h = h ; + qh D conservation*of*mass $ /'/-(*$1&2),*'+*&'()3*'+*&6/1,)* &'( 7 " &'().1(-,*L)h/*'+*-3**(/&'() & " &-33*'+*-3**() 7 89*;"9 = &'().1(-,*L)h/*'+*Q,*-,*(g/mol) 7 A;BC9*D;EF9 = &'().1(-,*L)h/*'+*L-/),*(g/mol) I 1$V),3-(*-3*.'$3/-$/*(WX/W&'( Z) I " = -3*.'$3/-$/*'+*-3* T temperature* V volume P pressure ω humidity*ratio (e.g.kgwv/kgda) & D mass*of*water*vapor & ; mass*of*dry*air n D partial*pressure*of*water*vapor n ; partial*pressure*of*dry*air φ relative*humidity (-) n p saturation*vapor*pressure h moist*air*mixture*enthalpy*(kj/kg*dry*air) h ; )$/h-(4*'+*q,*-,*(kj/kg*dry*air) h D )$/h-(4*'+*l-/),*v-4',*(kj/kg*water*vapor) & ; = & ; " C & D + & A = & D + " " C C & A e*exit*******i inlet & ; &-33*+('L*,-/)*'+*Q,*-,*(W*Q,*-,/&$) & D &-33*+('L*,-/)*'+*L-/),*V-4',*(W*L-/),*V-4',/&$) & A &-33*+('L*,-/)*'+*(zQ*L-/),*(W*(zQ*L-/),/&$) conservation*of*energy { = & C h C & } h } C "

ASHRAE PSYCHROMETRIC CHART NO.1 NORMAL TEMPERATURE BAROMETRIC PRESSURE 29.921 INCHES OF MERCURY R R Copyright 1992 AMERICAN SOCIETY OF HEATING, REFRIGERATING AND AIR-CONDITIONING ENGINEERS, INC. SEA LEVEL.28.26..24.22 8 WET BULB TEMPERATURE - F..18 14..16.14.12..8.6.4.2 ENTHALPY - BTU PER POUND OF DRY AIR ENTHALPY - BTU PER POUND OF DRY AIR SATURATION TEMPERATURE - F 6 7 8 9 1 1 1 DRY BULB TEMPERATURE - F HUMIDITY RATIO - POUNDS MOISTURE PER POUND DRY AIR 1 VOLUME- CU.FT. PER LB. DRY AIR 7 1. 1. % 6 6 % % % % % 7 8.8 - -.6 8. - -8. SENSIBLE HEAT Qs TOTAL HEAT Qt. - -.4-1..3 -. -.4 -.3.2 -.2 -.1 -.1 ENTHALPY HUMIDITY RATIO Dh DW 13. % 13. % % RELATIVE HUMIDITY 12.

1 1 1 1 ASHRAE PSYCHROMETRIC CHART NO.1 NORMAL TEMPERATURE BAROMETRIC PRESSURE 1.3 kpa R R Copyright 1992 AMERICAN SOCIETY OF HEATING, REFRIGERATING AND AIR-CONDITIONING ENGINEERS, INC. SEA LEVEL..29.28.27.94.26..24.23 WET BULB TEMPERATURE - C.22.92.21..19.18.17..16..14.13.12.11..9.8.7.6..4.3.2 SATURATION TEMPERATURE - C DRY BULB TEMPERATURE - C HUMIDITY RATIO - KILOGRAMS MOISTURE PER KILOGRAM DRY AIR.1.88 % % % % %.86 VOLUME - CUBIC METER PER KG DRY AIR 1. 1..8 1. -..7..6 - - SENSIBLE HEAT Qs TOTAL HEAT Qt. - -.4-1..3 -..2 -.2 -.. 1..1 3. 2. ENTHALPY HUMIDITY RATIO Dh DW.84 % %.82 %. % RELATIVE HUMIDITY.78

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