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  • #16
    Do you have any measurements for the air flow ? Also, were the inlets/outlets plugged for the static test portion or was free convection allowed ?

    My guess might be that they were not blocked or some unintended free convection occurred under the no flow condition given the increase temps. for chambers 3 & 4, and also for when flow began and (assumed) long enough to stabilize, which would sort of make me guess, as a 1st approx., that pressure drop in chambers 3 & 4 is greater than chambers 1 & 2.

    Assuming the paint is uniformly black for all 4 chambers and all 4 absorbers are equally opaque to sunlight, without any air circulation, I'd expect the stagnation temps. to be close. That they are not close would cause me to think there is some natural air circulation going on under no flow, perhaps unintended. Natural convection is much more sensitive to pressure drop than forced convection, hence the greater temp. diff. between chambers (1 & 2) and (3 & 4) under no flow than when forced convection begins. I looks to me that the resistance to flow (pressure drop) is greater for chambers 3 & 4 which results in reduced flow and higher temps. for chambers 3 & 4 for both flow and no flow conditions.

    On the outgassing: If you let the paint cure for several days, some of the VOC's will off gas. However, off gassing can also be f(temp.), that is, off gassing at, say 80 deg. F. for a week will help, but the first, say +140 deg. F. temp. excursion will cause more, and the next, say 160 deg. F temp. excursion will cause more yet. It's a time + temp. thing, sort of like annealing steel.

    On duct tape: the alum. stuff is good, just don't use the cloth/weave/fabric variety, and don't expose the adhesive side of the alum tape to air - it'll outgas too.

    Good luck.

    Thanx for the update.

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    • #17
      I'm also curious to hear more. Perforated aluminum soffit was quite easy to work with in my heater, but the filters are interesting, and likely more versatile. Any chance of a pic? Interested to see configuration of the filters in the box, how close to the glazing, etc.

      Anemometer is a useful tool, I find.

      I broke mine recently, unfortunately. An infrared heat gun will suffice for now, until I begin testing another unit, or modifications to my existing one.

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