torsdag 17 januari 2013

Bolometer Fiction of OLR and DLR

Berkeley Bolometer tells us:
  • A bolometer (or calorimeter) is a detector for radiation or particles. We use bolometers to detect light in the far-infrared and mm-waves. These detectors typically function as follows: An absorber of heat capacity C is thermally connected to a heat reservoir at temperature T0 by a weak thermal link G. The absorber sees the power of the incoming light Psignal and an electrical bias power Pbias and hence has a temperature T=T0+ (Psignal+Pbias)/G>T0. If the incoming power Psignal changes and Pbias stays constant the temperature T will change. A bolometer works by measuring this change of T with a thermometer which is directly attached.
A bolometer thus records absorbed net heat energy per unit time using as sensor a temperature dependent resistance. What is primarily recorded is thus temperature from which net absorbed power can be determined through the thermal link. If the bolometer also reports gross incoming radiance (DLR), this is based on a Planck formula specifying what is to be considered as gross outgoing radiation from the detector. But this formula represents a misconception of Planck's law as describing two-way gross heat transfer. The OLR and DLR reported by a bolometer is thus fiction, as is that reported by a pyrgeometer.

4 kommentarer:

  1. You may not directly measure a flow of heat, then you use a bolometer measuring directly two temperatures and indirectly a heat flux. That is, you're measuring something by measuring something else, but that is a very common practice in the technique.
    If the heat is arriving by radiation, you can assume that it is coming from a black body and you can compute its temp using Planck’s law, making a further indirect measurement.
    The measured temp has nothing to do with the calculated BB temp: if you use another bolometer you read a different sensor temp because of its different characteristic, but the calculated heat flux remains the same.
    There is no trick, the logic is correct. Rather it may be necessary to evaluate whether the obtained value is correct or not.


  2. This does not make sense to me.

  3. I'm sorry for you, but this is the physics.


  4. I have to agree with Claes. Michael's comment does not make sense. Michael may think he knows about what he has read in physics but he sure knows nothing about the engineering subjects of thermodynamics and heat&mass transfer.