Units Tab

About

Choose the unit for each quantity separately. There is no global SI/Imperial switch, because engineers mix bar with °C and psi with °F.

Changing a unit converts what you have already typed rather than reinterpreting it, and clears any results, which were calculated in the old units. This holds on every tab: a value typed as 20 bar on the Property tab becomes 290.08 psi if you switch pressure to psi, not 20 psi. The Open documentation icon icon beside the tab heading opens this page in your browser.

Choosing a unit

Every physical quantity the app shows has its own dropdown. The first unit in each list is the default.

Quantity	Units
Temperature	°C, K, °F
Pressure	bara, barg, kPa, MPa, psi, atm
Pressure drop	kPa, Pa, mbar, bar, psi
Mass	kg, g, lb, tonne
Volume	L, m³, ft³, US gal
Energy	J, kJ, MJ, BTU, kWh
Power	W, kW, MW, hp
Density	kg/m³, g/cm³, lb/ft³
Amount	mol, kmol
Mass flow	kg/h, kg/s, t/h, lb/h
Molar flow	mol/s, kmol/h
Volumetric flow	m³/h, L/min, ft³/h
Normal volumetric flow	NL/min, NL/h, Nm³/h, Nm³/min, Nft³/h, Nft³/min, Sm³/h, SCFM
Viscosity	Pa·s, cP
Thermal conductivity	W/(m·K)
Electrical conductivity	S/m, mS/cm, S/cm, µS/cm
Enthalpy of vaporization	J/kg, kJ/kg
Surface tension	N/m, mN/m
Enthalpy/Gibbs energy of formation	J/mol, kJ/mol, J/kg, kJ/kg
Specific heat capacity	J/(kg·K), kJ/(kg·K), J/(mol·K), kJ/(mol·K)
Length	m, mm, cm, µm, inch, ft
Area	m², mm², cm², in², ft²
Time	s, min, h

Two of these deserve a note. barg is gauge pressure, an offset from atmospheric rather than a scale factor, so 0 barg is 1.01325 bara. Pressure drop is separate from Pressure because a drop has no gauge form, and its natural size, a fluidized bed's or a distributor plate's, is far smaller than the pressure it is measured against.

Where a quantity can be shown per unit mass or per mole (specific heat capacity, and the enthalpy and Gibbs energy of formation), the app needs the chemical's molecular weight to switch between the two, and takes it from the chemical you are looking at.

Normal / standard reference

The Normal-flow reference defaults to 20 °C and 1 atm and is worth checking against your instrument: "normal" conditions are not standardised, and a 0 °C reference reads about 7 % higher in mass terms. DIN 1343 uses 0 °C, while standard-litre mass flow controllers commonly use 20 °C or 25 °C.

Set it with Normal reference temperature (°C) and Normal reference pressure (bara). The value is committed when you leave the field, not on every keystroke, so a half-typed number never becomes the live reference. A pressure at or below zero, or a temperature at or below absolute zero, is refused with a message and the old reference stays in force.

NL/min, NL/h, Nm³/h, Nm³/min, Nft³/h and Nft³/min are all measured at your reference. Sm³/h and SCFM are the exception: they keep their own standards (Sm³ is ISO 13443 at 15 °C and 101.325 kPa, SCFM is 60 °F and 14.696 psia) because that is what those names mean on an instrument. Selecting one puts a second reference state in play next to yours, and the conversion between the two is applied for you.

Every place a normal flow can be entered (Phase Equilibrium, Reaction, Heater, Heat Exchanger, Fluidized Bed) uses this one reference, and each says which reference is in force.

Unit Convertor

The Unit Convertor button opens a standalone converter: choose a quantity, type a value, pick From and To units, and the answer appears as you type. The swap button exchanges the two units.

It is independent of the tab's own choices. Looking a figure up from a datasheet never changes the units the rest of the app displays in.

Quantities whose units need a chemical's molecular weight to convert (specific heat capacity, and the enthalpy and Gibbs energy of formation) are left out, because a general converter has no substance to take the weight from. The dialog lists which ones are absent.

Saving your choices

The Open, Save and Reset buttons sit under the tab heading. Save stores every unit choice and the Normal reference together under a name of up to 40 characters, up to 25 sets; saving under an existing name replaces it. Open lists them, and lets you load, rename or delete each one. The set you last saved or opened comes back when the app starts, and units are restored before any other tab so the values on those tabs land in the right units. Reset returns every quantity to its default and the reference to 20 °C and 1 atm, and leaves your saved sets untouched. Saved sets are kept inside the app and are deleted with it, so to keep a copy safe, use Save to a file… in the Save dialog and Open from a file… in the Open list; see Saving and opening.