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. The tables below present examples of consistent sets of units for thermal parameters.

Table 1: System of SI units for thermal problems

Property	Units
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

Property	Units
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.