I am having the following problem on a lab write up:
Calculate the approximate distance downstream of the inlet that corresponds to the hydrodynamic entry length for Reynolds numbers of 3,000 - 5,000 (see “Purpose” section). Based on this, what conclusion can you make with respect to the applicability of the Moody chart to predict the behavior of the friction factor vs. Reynolds number in the upstream (between 1st and 2nd taps) and downstream (between 2nd and 3rd taps) sections of the small pipe?
I believe it is referring to this section in the "Purpose"
In this case, the hydrodynamic entry length can be approximated roughly as 500,000(D/Re), where D is the diameter of the pipe and Re is the Reynolds number. Note that for purely laminar ﬂow with no turbulence occurring anywhere in the pipe, the hydrodynamic entry length is approximated by 0.03(D)(Re). The Moody chart is strictly valid only for pipes in which the ﬂow is fully developed. In practical applications, it can be used from end to end of a pipe, as long as the overall length of the pipe is much longer than the hydrodynamic entry length. In this experiment measurements from both upstream (near entrance) and downstream (farther from entrance) sections of the pipe will be taken and compared to observe the effect of the entry length phenomenon the applicability of the Moody chart.
My problem is for starters I don't understand what I'm supposed to derive or find - the previous two equations were basically use the B - pi theorem to the Re - and then derive how you get 64/Re. Other than that I'm confused about this problem. Maybe I just plug in a Re of 3k and 5k into those equations?