Example 05: Sensible heating: 'qSen' (+ve): energy transfer TO humid air

Gallery
Tutorial
TRAIL: Air Conditioning Psychrometrics (vs CED Engineering course): Example results (only) in Mathematica and SysML using the Webel Psy package and MPsy class
Section
Topic level
BASIC
Keywords
Slide kind
plot
table
Example problem from:
CED Engineering course PDF: 'Air Conditioning Psychrometrics (A.Bhatia)'
Example question:
Calculate the amount of sensible heat that must be added to 100lb of air at 85°F dry bulb and 75°F wet bulb to raise the temperature of air to 100°F dry bulb.
There are type-setting errors with the values in the worked course example solution in the source document (not shown here)
Click on the image to view it full size
And now it gets a bit more interesting, because there is a 2-State change, and the Webel Psy library introduces some new visualisation features.

The answers (where available) from the worked example problem are given in the 3rd column in the custom table in the top of the image in IP units.

Note that the values for specific enthalpy per dry air 'hda' as calculated via CoolProp are quite different from those provided by the course Answers and the relative difference in 'hda2 - hda1' departs even more.

When handled by the MPsy class, we now have 2 objects representing the before and after states. Note how the humidity ratio 'w' of the 1st object is used to set the humidity ratio of the 2nd object, because it is assumed that there is no change in the contained water mass within the humid air.

And there is a new kind of table that shows the differences between them, as well as indicating the change in each main psychrometric variable, and the "direction" of change.

We see that, for a pure humid air sensible heating process:

  • The dry bulb temperature 'tdb' increases.
  • The relative humidity 'r' decreases.
  • The mass-specific enthalpy per dry air 'hda' increases.
  • The wet bulb temperature 'twb' increases.
  • The specific volume per dry air 'vda' increases.
  • The humidity ratio 'w' and the dew point temperature 'tdp' remain constant.

There is also a dedicated Psy library function for calculating the sensible heat energy 'qSen' (in this case added to the system so +ve).

Webel: Psy/MPsy: Psychrometrics for Mathematica: Transferred heat (energy "Q") has field names with lower case 'qTot', 'qSen', 'qLat'. Heat rates (energy per time) have field names 'qDotTot', 'qDotSen', 'qDotLat' (to avoid clashes with Mathematica core)
Wikipedia: 'Heat released by a system into its surroundings is by convention a negative quantity (Q < 0); when a system absorbs heat from its surroundings, it is positive (Q > 0). '

And there is a version of the psychrometric chart that now shows both states, as well as an arrow indicating the change.

Up next
Example 06: Sensible heating: 'qSen' per mass (+ve): energy transfer TO humid air
Notes
[COMPLICATION, GOTCHA, TIP]{INFORMATIVE} GOTCHA: Mathematica: Specific enthalpy conversion J/kg to Btu/lb: Does not consider a possible "total" enthalpy reference offset vs 0 °C or 0 °F respectively
[CONVENTION]{STRICT} Webel: Psy/MPsy: Psychrometrics for Mathematica: For Imperial Units (IP), International British Thermal Units (Btu) are assumed
[ASSERTION, GOTCHA, WARNING]{INFORMATIVE} In the course PDF for 'CED Engineering: Air Conditioning Psychrometrics (A.Bhatia)' the term "enthalpy (h)" usually refers to the mass-specific enthalpy per dry air (in CoolProp notation 'Hda')
[CONVENTION]{STRICT} Webel: Psy/MPsy: Psychrometrics for Mathematica: Transferred heat (energy "Q") has field names with lower case 'qTot', 'qSen', 'qLat'. Heat rates (energy per time) have field names 'qDotTot', 'qDotSen', 'qDotLat' (to avoid clashes with Mathematica core)
Snippets (quotes/extracts)
 Calculate the amount of sensible heat that must be added to 100lb of air at 85°F dry bulb and 75°F wet bulb to raise the temperature of air to 100°F dry bulb.
 Heat released by a system into its surroundings is by convention a negative quantity (Q < 0); when a system absorbs heat from its surroundings, it is positive (Q > 0).
Visit also
CED Engineering course PDF: 'Air Conditioning Psychrometrics (A.Bhatia)'
Visit also (backlinks)
Related slides (includes other tutorials)
Related slides (backlinks, includes other tutorials)
SysML4Mathematica: Example 05: Sensible heating: 'qSen' (+ve): energy transfer TO humid air