176
table a.7 Electromechanical Design
Functions and Constraints
Maximize
Bus bars
Minimum life cost; high current conductor
1/ρ e ρC m
Electromagnet windings
Maximum short-pulse field; no mechanical failure
σ f
Maximize field and pulse length, limit on temperature rise
C p ρ/ρ e
Windings, high-speed electric motors
Maximum rotational speed; no fatigue failure
σ e /ρ e
Minimum ohmic losses; no fatigue failure
1/ρ e
Relay arms
Minimum response time; no fatigue failure
σ e /Eρ e
Minimum ohmic losses; no fatigue failure
σ
ρ
e
e
E
2
table a.8 Thermal and Thermomechanical Design
Functions and Constraints
Maximize
Thermal insulation materials
Minimum heat flux at steady state; thickness specified
1/λ
Minimum temp rise in specified time; thickness
specified
1/a=ρC p /λ
Minimize total energy consumed in thermal cycle (kilns,
etc.)
a
C p
λ
λρ
= 1
Thermal storage materials
Maximum energy stored/unit material cost (storage
heaters)
C p /C m
Maximize energy stored for given temperature rise and
time
λ
λ ρ
a
C p
=
Precision devices
Minimize thermal distortion for given heat flux
λ/a
Thermal shock resistance
Maximum change in surface temperature; no failure
σ f /Eα
Heat sinks
Maximum heat flux per unit volume; expansion limited
λ/Δa
Maximum heat flux per unit mass; expansion limited
λ/ρΔa
Heat exchangers (pressure-limited)
Maximum heat flux per unit area; no failure under Δp
λσ f
Maximum heat flux per unit mass; no failure under Δp
λσ f /ρ
Appendix: Material Indices