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Heat Release Rate formula

The Heat Release Rate is the crucial parameter to characterize a fire. There is a variety of methods to estimate Heat release rate. The most used techniques are based on mass balance. When the heat of combustion of fuel is known, the measure of mass loss can be evaluated.

The heat produced by the burning sample is precisely accompanied by the reduction in the heat generated by the burner. The rate of heat release of the sample is measured by recording the decrease in the flow of gas. The constant temperature of the system removes the impact of inertia and permits a rapid change in the heat release rate.

The record of heat release rate is a measure of what would be released into the lit room. The heat release rate formula from the first law of thermodynamics is given by,

ΔQc = ΔW + ΔQh + ΔU


Qc is the Chemical energy released in KJ/Kg,

W is the Work output in KJ/Kg,

Qh is the Heat transfer in KJ/Kg,

U is the Internal energy of the contents in KJ/Kg.

Example 1

Determine the heat released of a cylinder whose internal energy is 245 KJ/Kg and heat transfer is 420 KJ/Kg for the work 280 KJ/Kg.


Given parameters are,

Work = 280 KJ/Kg

Internal energy = 245 KJ/Kg

Heat transfer = 420 KJ/Kg

Substitute all the values in the given formula.

ΔQc= ΔW + ΔQh + ΔU

      = 280 + 420 + 245

      = 945 KJ/Kg

Therefore, Heat release rate = 945 KJ/Kg

Example 2

The heat produced in a burner is 280 KJ/Kg and internal energy is 430 KJ/Kg. Determine the heat transfer for the work done 260 KJ/Kg.


Given parameters are,

Work = 260 KJ/Kg

Internal energy = 430 KJ/Kg

Heat transfer = 280 KJ/Kg

Substitute all the values in the given formula.

ΔQc = ΔW + ΔQh + ΔU

        = 260+ 430 + 280

Therefore, heat release rate = 970 KJ/Kg