The engineering library

The engineering library is a set of scripts in the Script workspace's library (craftlib/eng). Each one is a function you can read from top to bottom, with a header that gives its method, its units, its limits, its references and a check with a worked number. They use SI units throughout and return quantities that carry a unit and a source, so a data sheet can print where every number came from.

Units that are checked

to_si(10, 'bar', 'Pa') converts a value and refuses a unit that measures something else (a length where a pressure is expected). from_si, unit_convert(1, 'bar', 'psi') and unit_kind('W/(m K)') ("thermal conductivity") work the same way. temp_k(25, 'C') and temp_from_k convert temperatures, which have an offset.

Properties

• fluid('water', T) and fluid('air', T, p): density, viscosity, conductivity, specific heat, Prandtl number. Water 0 to 100 °C, air 250 to 600 K; outside that it stops instead of extrapolating.
• material('ss304'): Young's modulus, Poisson's ratio, density, yield, conductivity, specific heat, expansion: room-temperature values from the same data sheets as Simulation. A real design uses the supplier's certified figures. Temperature curves are not built yet.

Flow in pipes and channels

reynolds, hydraulic_diameter, friction_factor (laminar, then the Colebrook equation for turbulent flow; the 2300 to 4000 range has no reliable formula and says so), darcy_weisbach, minor_loss, pipe_flow (round pipe, everything at once) and rect_channel (laminar rectangular ducts by the Shah and London fit).

Heat transfer

nusselt_dittus_boelter, nusselt_gnielinski, nusselt_tube (picks laminar or turbulent and names the correlation), htc, fin_efficiency, lmtd, effectiveness and ntu_for (the effectiveness-NTU relations for counterflow, parallel, shell-and-tube, crossflow and a single changing stream) and hx_size (the size UA a duty needs; it says how much is possible when the duty cannot be met).

Pressure parts

allowable_stress (yield over a safety factor), wall_thin_cylinder, barlow, wall_thick_cylinder (Lamé, on the hoop or the shear criterion) and wall_sphere. These are textbook margins, not a pressure-vessel code calculation: no corrosion allowance, joint efficiency or code factors.

Gas dynamics

isentropic (the ratios at a Mach number), mach_from_area, choked_flow, throat_area and exit_mach, for a perfect gas without friction, heat or shocks.

Check the result

check_stress, check_thermal and check_flow run PartCraft's own stress, conduction and flow solvers on a generated part from the script and read back the maximum stress and displacement, the temperatures and heat flow, and the permeability of a channel network. They change nothing in the solvers. The stress and temperature checks use voxels, so a curved face is a staircase and the stress at a sharp inner corner or under a point load depends on the voxel size.