I thought I should look at the boiler heat loss versus published data. Although my test object is just a short length of copper pipe, it does represent a copper pipe. So, I went searching for some data and there is a table of data on the Engineering Toolbox (Ref 1).
This data is really aimed at the hot water system used in your house and commercial buildings. Therefore, the delta temperatures are quite low compared to model steam boilers.
The pipe sizes are stated based on their ID when in fact the losses will be based on the external surface area and hence OD. Therefore, I converted these nominals using reference 2.
Zooming into the section that relates to the pipe heat loss data.
The two data sets should lay either side of the data I have for the boiler. The 1.5 inch ID pipe has an OD that is within 10% of the boiler. The larger 2 inch ID pipe shows a trend
Boiler heat loss versus published data for copper pipes used in a central heating system shows that there is a close relationship.
Considering my experiment is very simple, this looks like a good match. That gives me a lot more confidence in the testing that I’m doing.
The test object I’m using would be improved by using a 300mm length of boiler rather than 50mm. Therefore, reducing the losses through the ends compared to that radiated through the surface.