why it is necessary to achieve steady state before taking observation?
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Answers
Explanation:
You do not need to perform any heat balance. If the inlet temperatures of the hot fluid and cold fluid are held steady, then steady state is indicated by the constancy of one of the outlet temperatures. If you are recording the temperatures and can see the temperature history on the computer screen, it is a simple matter to judge steadiness. The effect of noise on temperature of the fluid is so small that your thermometer cannot detect it. If you have serious disturbances, you can never get steady conditions. Eliminate those disturbances.
"Steady state" is a relative term. Unsteadiness can even be caused by, say voltage fluctuations, which may cause a change in flow rate. You might be able to set an arbitrary band (say 1% of the measured value about the mean), so that if the fluctuations are less than that, you may take it as 'nominally steady'. That should do for your purpose.