Systems of Units for Thermal Analysis

All thermal quantities must be given in a consistent system of units. No conversions are performed by the program. Table 1 and Table 2 present examples of consistent sets of units for thermal parameters.

Table 1: System of SI units for thermal problems
Length m m m cm
Density kg/m3 103 kg/m3 106 kg/m3 106 g/cm3
Stress Pa kPa MPa bar
Temperature K K K K
Time s s s s
Specific Heat J/(kg K) 10-3 J/(kg K) 10-6 J/(kg K) 10-6 cal/(g K)
Thermal Conductivity (W/mK) (W/mK) (W/mK) (cal/s)/cm2 K4
Convective Heat-Trans. Coefficient (W/m2 K) (W/m2 K) (W/m2 K) (cal/s)/(cm2 K)
Radiative Heat-Trans. Coefficient (W/m2 K4) (W/m2 K4) (W/m2 K4) (cal/s)/cm2 K4
Flux Strength W/m2 W/m2 W/m2 (cal/s)/cm2
Source Strength W/m3 W/m3 W/m3 (cal/s)/cm3
Decay Constant s-1 s-1 s-1 s-1
Table 2: System of imperial units for thermal problems
Length ft in
Density slugs/ft3 snails/in3
Stress lbf psi
Temperature R R
Time hr hr
Specific Heat (32.17)-1 Btu/(lb R) (32.17)-1 Btu/(lb R)
Thermal Conductivity (Btu/hr)/(ft R) (Btu/hr)/(in R)
Convective Heat-Trans. Coefficient (Btu/hr)/(ft2 R) (Btu/hr)/(in2 R)
Radiative Heat-Trans. Coefficient (Btu/hr)/(ft2 R4) (Btu/hr)/(in2 R4)
Flux Strength (Btu/hr)/ft2 (Btu/hr)/in2
Source Strength (Btu/hr)/ft3 (Btu/hr)/in3
Decay Constant hr-1 hr-1
where: 1K = 1.8 R;
  1J = 0.239 cal = 9.48 × 10-4 Btu;
  1J/kg K = 2.39 × 10-4 btu/lb R;
  1W = 1 J/s = 0.239 cal/s = 3.412 Btu/hr;
  1W/m K = 0.578 Btu/(ft/hr R); and
  1W/m2 K = 0.176 Btu/ft2 hr R.

Note that temperatures may be quoted in the more common units of °C (instead of K) or °F (instead of R), where:

Temp(°C) = [Temp(°F) - 32]×(5/9);
Temp(°F) = [1.8 Temp(°C) + 32];
Temp(°C) = Temp(K) - 273; and
Temp(°F) = Temp(R) - 460.