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:


Proposed back radiation test setup - comments?

4 Thermocouples simultaneously monitored
  a. internal temperature of double glazing gap
  b. temperature in gap between external unsealed IR window. IR shield shadows the sensor from the external IR
  c. hot temperature plate (internal)
  d. warm plate (external) ambient plate temperature is not measured.

Fan blowing ambient air between the double glazing and the separate window. This is to reduce thermal conduction and convection from a different warm/cool source affecting the ambient at the outside of the double glazed window.

Angled BB absorber at back of external source (angled to prevent reflection affecting hot plate.

Lining of polished aluminium foil to prevent IR penetrating the insulation foam.

Voltage input to external warm plate heater is stable but differing ambient and convection/conduction will change its temperature - All this needs to do is provide a temperature less than the hot plate and greater than ambient - so the variation is not important.

The voltage to the hot plate heater is also controlled (by a professional Power supply) the temperature reached is approximately 70°C and the variation with external plate at ambient / warm will be less than a couple of °C. The change in the high quality resistors value will be negligible. So constant voltage equates to constant power..

Any comments before trying this set-up


Nenana Ice Classic 2013 - the ice has moved 2013/05/20 14:41

Second latest time from beginning of the year
The record was set in 1964 which was a leap year. The movement happened 140.4868 days from January 1st

This year the movement occurred 139.6118 days from January 1st

Hmmm! Perhaps this all need rejigging to relate the breakup time to the vernal equinox and z-time

Anyway, here are 2 plots using AK time:
The first splits the data into 3 segments
The second assumes that there is no upturn and hence only 2 lines
Smoothing is done with Hodrick Prescott filter from http://www.web-reg.de/hp_addin.html

Breakup data from

Heres the modified plot with days since vernal equinox instead of start of year:

So this year now becomes the latest date for breakup! Otherwise the shape remains.