What does maximum boiler insulation look like? When I say “look” I mean in terms of heat loss as this is then something to aim at in terms of design. How much insulation is required? What do those thermal values look like? Are these thermal values achievable?
I think I might be asking more than I can calculate with my simple boiler mathematical model.
The first task I think is to work out how to electrically heat the boiler. This will allow me to then get better data, correlate the model and work with materials that are not fire proof.
The heat loss from the boiler is being calculated using the cooling curve.
The boiler is constructed from copper and has a known quantity of water in it. Thus the heat capacity of the boiler is known.
If I then measure the bulk temperature and calculate the differential of the temperature of the boiler I can estimate the heat loss.
The heat loss in J/s is Watts.
There are a number of areas on the boiler that can be insulated.
- Cylindrical barrel
- Top and bottom circular surfaces
- Flue
However, only the cylindrical barrel and the top surface can be insulated if the boiler is to be heated with methylated spirit or coal.
Insulating the Boiler
For the purpose of this test of maximum insulation I wrapped the boiler in ~10mm thick light fibre, typically used for insulating jackets. I then wrapped the boiler in bubble wrap that has aluminium on both sides.
This was all fixed in place with masking tape. The masking tape closes any gaps and so stops air flow.
This is what I’m calling “Maximum Boiler Insulation” and this forms one bookend for the testing.
The experiment was only run up to just over 110°C, however, the curve fit with the quadratic looks very good. Using this equation I can estimate that at the operating point for the boiler of 40psi and 140°C bulk water temperature the loss would be ~12W.
Maximum Insulation versus Unclad Boiler
For the maximum boiler insulation condition at the operating pressure the heat loss is around 1/3 of that from the unclad boiler. The graph below shows this comparison. However, in the unclad condition the boiler is attached to the firebox and has been heated with methylated spirit.
