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Heat Transfer Triangle
lance.hitchins
Created on March 10, 2025
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Transcript
The components in the bottom of the triangle will either be multiplied or divided by one another, depending on what you're trying to calculate.
The component in the top of the triangle will always be divided by either of the components below.
You cover the part of the triangle you want to calculate and this shows you what to do for working it out.
With any mathematical triangle, you need to have two pieces of information to work out the third.
(DTxSHC)
l/s
kW
Heat Transfer Triangle
Always start with the part of the equation that is in brackets, so: 5x3.8=19. Next: 8.5/19=0.447 l/s (3dp). Finally, multiply this answer by 60 to convert from l/s to l/m: 0.447x60=26.82 l/m
Cover the bottom left part of the triangle (the bit you want to find), the equation you're left with is kW/(DTxSHC)
Let's start by working out the required litres per minute (l/m) to deliver 8.5kW with a 5K DT and SHC of 3.8 (75:25 water to glycol mix)
(DTxSHC)
l/s
kW
Calculating Flow Rate
As always, start with the brackets, so: 5x4.2=21. Next, convert l/m to l/s: 40/60=0.667 l/s (3dp). Finally: 0.667x21=14.01kW (2dp).
Cover the top part of the triangle (the bit you want to find), the equation you're left with is l/sx(DTxSHC).
This time, let's work out how many kW can be achieved with a given flow rate of 40 l/m, this time using a 5K DT and SHC of 4.2 (pure water).
(DTxSHC)
l/s
kW
Calculating Output
This time there are no brackets and the equation has to be done in the order stated above, so: 11.2/0.533=21.013 (3dp), 21.013/4.2=5.00 k (2dp)
Cover only the DT part of the triangle (the bit you want to find), the equation you're left with is kW divided by l/s divided by SHC.
The last way of using the mass flow rate triangle is to claculate Delta T (DT). For this example we will use 11.2kW with a flow rate of 0.533 l/s and a SHC of 4.2.
(DTxSHC)
l/s
kW
Calculating Delta T
There are 1000 grams in a Kilogram. So 3,520 grams is equal to 3.52 kg
There are 1000 Joules in a Kilojoule. So 4,186 Joules is equal to 4.186 kJ
The amount of energy required to change the temperature of a substance is measured in Joules per kilogram (J/kg).
Multiplying the Delta T by the Specific Heat Capacity calculates the amount of energy required to change the temperature of 1 gram of a substance by 1 degree kelvin.