The Pressure-Drop Experiment

The classic pressure-drop experiment is performed on an apparatus like that shown in Fig. 6.1, In this experiment we set the flow of the fluid with the flow-regulating valve. We measure the flow rate with the bucket and stop watch. At steady state we read pressure gauges and P2 and record their difference. Usually we are interested in the pressure drop per unit length, so we divide the pressure drop by distance Ax (the length of the test section) and plot (Pj - P2) /Ax versus volumetric flow rate Q. 

Regardless of what newtonian liquid is flowing or of what kind of pipe we use, the result is always of the form shown in Fig. 6.2, and for all gases at low velocities the result is the same as that shown. The salient features of Fig. 6.2 are.that/or one specific fluid flowing in one specific pipe  

At very low flow rates, the pressure drop per unit length is proportional to the volumetric flow rate to the 1.0 power. 

At intermediate flow rates, there is a region where the experimental results are not easily reproduced. 

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Garimella and Bandhauer [32] conducted heat transfer experiments using the same test sections that were used for the pressure drop experiments of Garimella et al. [24, 25, 27, 28] described above. The high heat transfer coefficients and low mass flow rates in microchannels necessitate modifications to the test facility and test procedures described above. For the small zlx required in the test section, the heat duties at the mass fluxes of interest are relatively small. Calculating this heat duty from the test section inlet and outlet quality measurements would result in considerable... 

Consider a porous medium consisting of sand or some porous rock or glass beads or macaroni or cotton cloth contained in a pipe see Fig. 12.2. If we attach this pipe to the apparatus for the pressure-drop experiment shown in Fig. 6.1 and run exactly the same tests on it that we described there for a pipe, we find results of the same form as those shown in Fig. 6.2, except that the abrupt transitions region on Fig. 6.2 will be replaced with a smooth curve for a porous-medium flow. From these results we guess that the two end parts of the curve correspond to laminar and turbulent flows this is experimentally verifiable. I... 

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