Useful Formulas and Conversions

Temperature Rise Across a Heat Load:
Liquid Cooling Systems

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In a liquid cooled system the heat rise of the coolant across a load can be related to its flow rate and the heat load by the general formula:

P = F×ΔT×SG×SH×145.7
or
ΔT = P/(F×SG×SH×145.7)

Where:
P = Power or heat load, in Watts
F = Flow Rate, GPM
Δ T = Temperature rise of the coolant, °F
SG = Specific gravity of the coolant at average coolant temp.
SH = Specific heat of the coolant at average coolant temp., Btu/(lb m × °F)

If the specific gravity and specific heat of the coolant are not known use "K" from the coolant selection chart , assuming 100°F average coolant temperature, in the following formula:

P = F×ΔT×K
or
ΔT = P/(F×K)

Temperature Rise Across a Heat Load:
Air Cooling Systems

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Air temperature rise across a heat load can be related to the air flow rate and the heat load by a similar formula:

P = C×ΔT×D×SH×17.58
or
ΔT = P/(C×D×SH×17.58)

Where:
P = Power or heat load, in Watts
C = Flow Rate, CFM
Δ T = Temperature rise of the air, °F
D = Density of the air at average temp., lb m /ft³
SH = Specific heat of the air at average temp., Btu/(lb m ×°F)

If the density and specific heat of the air are not known use "K" from the coolant selection chart , assuming 70°F average air temperature at sea level, in the following formula:

P = C×ΔT×K
or
ΔT = P/(C×K)

Power Conversion Factors

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1W = 3.413 Btu/hr
1HP = 745.7 W

Flow Conversion Factors

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1 LPM = .264 GPM

Specific Heat Conversion Factors

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1kj/(kg × °C) = .23885 Btu/(lb m × °F)

Density Conversion Factors

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1kg/m ³ = .062428 lbm/ft ³

Pressure Conversion Factors

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1kPa = .145 psi
1 psi = 2.307 ft head

Temperature Conversion Factors

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°F = °C × (9/5) + 32
°C = (°F-32) × (5/9)
K = °C + 273.15