How to Convert Heat Flux

Heat flux is also called thermal flux and describes the rate of heat energy that is transferred through a specific surface. Heat flux is measured as heat rate per unit area. For instance, heat rate is denoted by Q and has units of British thermal units per hour (BTUs/hr). If this heat rate is taken over a large surface with a surface area in units of square feet, then the heat flux would have the units BTU/hr-ft2. Conversely, if the heat flux is known for the rate of energy transferred through a specific substrate, then the total heat rate can be calculated by multiplying the heat flux by the surface area. This is important where a heat flux is measured in a small scale and the total heat transfer is needed for scale-up design.

Things You'll Need

• Calculator

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Instructions

1. • 1

     Determine the heat flux for a given material. For instance, assume a 1 square foot sample of metal to be used in a large furnace casing has a heat flux of 120 BTUs/hr-ft2.

   • 2

     Determine the total surface area of the metal to be used for the casing of a furnace. Assume the furnace box is a 10 foot square box with a roof. This is 10 x 10 x 5 or 500 square feet.

   • 3

     Convert the heat flux into the heat rate by multiplying the heat flux by the total square footage of the furnace surface. This is calculated by 120 BTU/hr-ft2 x 500 sq. ft. or 60,000 BTUs/hr. This means that the thermal radiation given off by the furnace into the surrounding room will be 60,000 BTUs/hr.