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MoistAirTab™ Technical Information

Design

MoistAirTab uses an equation of state to compute all of the thermodynamic properties. MoistAirTab uses formulations that are approved by the American Society of Heating, Refrigeration and Air-Conditioning Engineers, Inc. (ASHRAE) as documented in the 1997 ASHRAE Handbook: Fundamentals. The equation-of-state used to compute the moist air properties are given in:

Reference

Formulations for the thermodynamic properties of the saturated phases of H2O from 173.15 K to 473.15 K, W. Hyland and A. Wexler, ASHRAE Transactions, Vol. 89, No. 2A, pp. 500-519, 1983.

Formulations for the thermodynamic properties of dry air from 173.15 K to 473.15 K, and of saturated moist air from 173.15 K to 372.15 K, at pressures to 5 MPa, R. W. Hyland and A. Wexler, ASHRAE Transactions, Vol. 89, No. 2A, pp. 520-535, 1983.

MoistAirTab Functions

The MoistAirTab add-in package is based on a set of 18 core functions that together calculate over 25 thermodynamic and transport properties of steam. You can use these functions directly in your spreadsheet or you can use MoistAirTab’s easy-to-use dialog boxes to automatically generate the appropriate function call with the correct arguments.

All of the MoistAirTab functions begin with the prefix MA. The MoistAirTab functions require as input two independent variables in addition to the total pressure. The first independent variable can be either: Dry bulb temperature (Tdb), Humidity Ratio (W), or Relative Humidity (RH). The second independent variable can be either: Dry-bulb Temperature (Tdb), Wet-bulb Temperature (Twb), Humidity Ratio (W), or Relative Humidity (RH), Enthalpy (H), Entropy (S), or Volume (V). These functions are summarized in Table 1 below.

MoistAirTab also includes functions for obtaining the barometric pressure and temperature as a function of altitude.

Table 1: MoistAirTab Worksheet Functions

Function

Calculates at Specified

Calling Sequence Example

Psychrometric Property Functions
MATDBTWBDry bulb temperature and
Wet bulb temperature
MATDBTWB(dry bulb, wet bulb, property code, pressure, units)
MATDBRHDry bulb temperature and
Relative humidity
MATDBRH(dry bulb, relative humidity, property code, pressure, units)
MATDBWDry bulb temperature and
Humidity ratio
MATDBW(dry bulb, humidity ratio, code, pressure, units)
MATDBHDry bulb temperature and
Enthalpy
MATDBH(dry bulb, enthalpy, property code, pressure, units)
MATDBSDry bulb temperature and
Entropy
MATDBS(dry bulb, entropy, property code, pressure, units)
MATDBVDry bulb temperature and
Volume
MATDBV(dry bulb, volume, property code, pressure, units)
MAWTWBHumidity ratio and
Wet bulb temperature
MAWTWB(humidity ratio, wet bulb, property code, pressure, units)
MAWTDBHumidity ratio and
Dry bulb temperature
MAWTDB(humidity ratio, dry bulb, property code, pressure, units)
MAWRHHumidity ratio and
Relative Humidity
MAWRH(humidity ratio, relative humidity, property code, pressure, units)
MAWHHumidity ratio and
Enthalpy
MAWH(humidity ratio, enthalpy, property code, pressure, units)
MAWSHumidity ratio and
Entropy
MAWS(humidity ratio, entropy, property code, pressure, units)
MAWVHumidity ratio and
Volume
MAWV(humidity ratio, volume, property code, pressure, units)
MARHTWBRelative Humidity and
Wet bulb temperature
MARHTWB(relative humidity, wet bulb, property code, pressure, units)
MARHTDBRelative Humidity and
Dry bulb temperature
MARHTDB(relative humidity, dry bulb, property code, pressure, units)
MARHWRelative Humidity and
Humidity ratio
MARHW(relative humidity, humidity ratio, property code, pressure, units)
MARHHRelative Humidity and
Enthalpy
MARHH(relative humidity, enthalpy, property code, pressure, units)
MARHSRelative Humidity and
Entropy
MARHS(relative humidity, entropy, property code, pressure, units)
MARHVRelative Humidity and
Volume
MARHV(relative humidity, volume, property code, pressure, units)
Constant Properties
MAMWWMolecular weight of waterMAMWW(units)
MAMWAMolecular weight of airMAMWA(units)
MATMINMinimum dry bulb temp.MATMIN(units)
MATMAXMaximum dry bulb temp.MATMAX(units)
MAPMINMinimum pressureMAPMIN(units)
MAPMAXMaximum pressureMAPMAX(units)
MAPZPressure at specified heightMAPZ(height, units)
MATZTemperature at specified heightMATZ(height, units)

The MoistAirTab functions return the requested property in either Metric/SI or English units. The thermodynamic properties and the units in which they are available is shown in the following table. Properties highlighted in red are MoistAirTab V2 additions.

Table 2: MoistAirTab V2 Thermodynamic and Transport Properties

CodePropertyMetric/SI UnitsEnglish Units
0TdbDry bulb temperature°C°F
1TwbWet bulb temperature°C°F
2TdewDew point temperature°C°F
3PPressurebarpsia
4PwsSaturation water vapor pressurebarpsia
5PwetSaturation pressure at wet bulb temperaturebarpsia
6PdewSaturation pressure at dew point temperaturebarpsia
7XwWater mole fractionmol%mol%
8XaAir mole fractionmol%mol%
9MwWater weight fractionwt%wt%
10MaAir weight fractionwt%wt%
11WHumidity ratiodimensionlessdimensionless
12WsSaturation humidity ratiodimensionlessdimensionless
13RHRelative humidity%%
14VaVolume of dry airm3/kg dry airft3/lb dry air
15VmVolume of moist airm3/kg dry airft3/lb dry air
16VwVolume of condensed water or icem3/kgft3/lb
17VgVolume of steamm3/kgft3/lb
18HaEnthalpy of dry airkJ/kg dry airBtu/lb dry air
19HmEnthalpy of moist airkJ/kg dry airBtu/lb dry air
20HwEnthalpy of condensed water or icekJ/kgBtu/lb
21HgEnthalpy of steamkJ/kgBtu/lb
22SaEntropy of dry airkJ/(kg dry air.°C)Btu/(lb dry air.°F)
23SmEntropy of moist airkJ/(kg dry air.°C)Btu/(lb dry air.°F)
24SwEntropy of condensed water or icekJ/(kg.°C)Btu/(lb.°F)
25SgEntropy of steamkJ/(kg.°C)Btu/(lb.°F)
26CpaHeat capacity at constant pressure of dry airkJ/(kg.°C)Btu/(lb.°F)
27CpmHeat capacity at constant pressure of moist airkJ/(kg.°C)Btu/(lb.°F)
28CpwHeat capacity at constant pressure of waterkJ/(kg.°C)Btu/(lb.°F)
29CpgHeat capacity at constant pressure of steamkJ/(kg.°C)Btu/(lb.°F)
30MuaViscosity of dry airPa.slb/(ft.hr)
31MumViscosity of moist airPa.slb/(ft.hr)
32MuwViscosity of waterPa.slb/(ft.hr)
33MugViscosity of steamPa.slb/(ft.hr)
34KaThermal conductivity of dry airW/(m.°C)Btu/(hr.ft.°F)
35KmThermal conductivity of moist airW/(m.°C)Btu/(hr.ft.°F)
36KwThermal conductivity of waterW/(m.°C)Btu/(hr.ft.°F)
37KgThermal conductivity of steamW/(m.°C)Btu/(hr.ft.°F)
38PraPrandtl number of dry airdimensionlessdimensionless
39PrmPrandtl number of moist airdimensionlessdimensionless
40PrwPrandtl number of waterdimensionlessdimensionless
41PrgPrandtl number of steamdimensionlessdimensionless
42DawDiffusivity of water vapor in airm2/sft2/hr
43ScmSchmidt number of moist airdimensionlessdimensionless
44RhoDensity of moist airkg/m3lb/ft3
45DsDegree of saturationdimensionlessdimensionless