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???
04/01/09 07:45
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#164124 - Who cares
Responding to: ???'s previous message
Per Westermark said:
Yes, I do expect it to be possible to measure thermal conductivity in that material. Because it has cells, the granularity means that you have to be careful about the size of the material sample, or the conductivity (or in this case probably better termed isolation) has to be formed as an average over many samples, and qualified with a standard deviation.

A material may be a very good isolator. In that case, the measuring of [electrical/thermal/...] conductivity will of course manage to establish this. A challenge will be the number of value digits when the conductivity is getting closer to zero, since the conductivity of the surrounding air may be way higher than the conductivity of the measured sample, in which case the output of the measurement may conclude that the conductivity of the material is less < eps [suitable unit] with a certainty of x. Depending on the expected measurement range, the "best" way to measure the property may vary. An example is the goal of measuring a resistor. For small resistors, you may send a constant current through the resistor, and measure the voltage drop. When instead measuring the isolation, you may have to use high voltages and try to establish if there is any leak current. An example is a Megger instead of a normal multimeter. In the same way, the "best" test setup for measuring thermal conductivity will differ depending on the material properties of the test subject - the material may even have different material properties in different directions, such as for example diamond. But that does not make it impossible or irrelevant to measure the physical properties. It just represents an additional challenge.

Measuring things are not always producing large numbers of value digits. In a number of situations, you do the measuring to bound the possible values. After all - all measurements can do is produce upper and lower bounds with a probability.


Who cares for a reading of 0.00000000000000234 ? do you

-Ap


List of 38 messages in thread
TopicAuthorDate
Thermal and Electrical Conductivity devices            01/01/70 00:00      
   Pardon?            01/01/70 00:00      
      Get it right            01/01/70 00:00      
         Get down to work!            01/01/70 00:00      
   I have no clue what you mean...            01/01/70 00:00      
      neither do I            01/01/70 00:00      
         may be            01/01/70 00:00      
   Only possible for metals ? not for materials I guess?            01/01/70 00:00      
      Why limit to metals?            01/01/70 00:00      
         all solid material            01/01/70 00:00      
         For all solid materials, are you sure?            01/01/70 00:00      
            Just a question of bounds and quality            01/01/70 00:00      
               Who cares            01/01/70 00:00      
                  Usage and physical units needed for a value to be meaningful            01/01/70 00:00      
                     Dont use only the thermal part thermal conductivity wont            01/01/70 00:00      
                        Your point is?            01/01/70 00:00      
                           Not mine but the OPs            01/01/70 00:00      
            Speed of sound?!            01/01/70 00:00      
               Google it , these are Basics of the topic            01/01/70 00:00      
            Homogenous or not            01/01/70 00:00      
               Per the topic is THERMAL & ELECTRICAL            01/01/70 00:00      
                  Any material , more info here Wiedemann-Franz law            01/01/70 00:00      
                     Relevance for the OP?            01/01/70 00:00      
                        No relevance at all!            01/01/70 00:00      
                         For now, such .... ?            01/01/70 00:00      
                           OP said "all solid material"            01/01/70 00:00      
      For the Material research            01/01/70 00:00      
         Already answered            01/01/70 00:00      
   Setting a question mark makes it clearer            01/01/70 00:00      
      I need the solution            01/01/70 00:00      
         Make or buy            01/01/70 00:00      
            re make or buy            01/01/70 00:00      
               Why would smaller samples give better results?            01/01/70 00:00      
               and why do you suppose that is?            01/01/70 00:00      
         A warning...            01/01/70 00:00      
            Thermal conductivity            01/01/70 00:00      
               Difficult            01/01/70 00:00      
                  Interesting            01/01/70 00:00      

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