Back Radiation Early Results - No Fan

Using the setup of the previous post
 but with no fan and no shadow dot used the following results have been obtained.
(x-axis is in seconds from start of test - many tests were done and recorded over about 12 hours - the main problem is trying to keep ambient constant or at least clear of low frequency noise)

Detrended by the air gap temperature between double glazed and single IR window the plot shows that with Warm source in place Hot body is 0.3°C hotter than when ambient source is in place

This shows a continuous recording of the warm source temperature - the Red line indicates that the source is facing the IR windows -  the dotted lines indicate that it has been placed away from the IR windows. No attempt has been made to stabilise the warm source temperature - It simply has to be above ambient and below the hot plate temperature.

This plot shows the detrended temperature of the air between the double glazed IR window

This plot shows the air between the double glazed window and the isolated IR window. Note that it shows no sign of being warmed by the warm source. The trend is because of ambient changes. This trend was removed from the "detrended"  plots

It should be noted that the radiation from the warm plate has to pass through 3 layers of poly film to reach the hot plate. In a previous post
I showed that this food wrap (LDPE) is not 100% transparent to IR.

Again I am certain that the hot body temperature increase is caused by the IR from the warm source.

Again criticism of the experiment is welcomed!

Full recorded data is available.

other posts on this subject:


  1. Sorry but In Your graphs I don't get units of x-axis. 3000-10000 what ? Seconds ?

  2. Apologies - yes the x axis is in seconds.

    These plots are taken from a days worth of recording trying to keep the ambient relatively stable. the section shown here was chosen since it had a flat profile.

    As can be seen it takes nearly 2000 seconds for the hot plate to reach a stable temperature - a long time!

  3. Thanks !

    I wonder Your thermocouples precision. Wikipedia claims accuracy is only ~ 1 C. Well perhaps in this case relative temps with good precision is good enough?

    I myself have made same kind of test. But I used cheap NTC resistor and wood-burning owen and my quite stable chest and parabolic mirror and long distance (2m). Small NTC is fast. Warming and cooling happens in minute or two.


    Of course thermocouples are better for really hot places. I'm planning greenhouse test that is perhaps too hot for NTC thermistors..

  4. Thermocouples are very fast responders (the temperature is measured at the junction - a welded bead about 0.4mm diameter. This of course also intercepts little radiation and is shiny (paint it black to improve).

    The problem with any of these experiments is to remove any possibility that disbelievers can find a hole in the method.

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