# BLDG 365 lab 4.docx - Objective The objective of part A is...

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Objective: The objective of part A is to show the change in the law of resistance for both the laminar and turbulent flow, and to find the critical Reynolds number. The objective of part B is to determine the distribution of pressure in a venture meter during flow. Introduction: A. Friction in Pipe Flow Part A of the experiment will look at the flow of water through a pipe at different flowrates. As fluids flow through a pipe it encounters friction. This friction results in the continuous loss of energy or total head loss. This total head loss can be calculated by using two piezometers and finding the difference in the height for piezometer 1 and 2. The rate of total head loss in a pipe of a certain length can be found by using the following formula: i = dh dl = ∆h ∆l (1) Where, i is the hydraulic gradient (rate of loss of total head) dh is the change in height from piezometer 1 to 2 dl is the distance between piezometer 1 and 2 This experiment will also look at the Reynolds number for both laminar and turbulent flow. Osborne Reynolds deigned an experiment where he introduced a filament of dye in water flowing through a glass pipe. He realized that at low velocities the filament flowed in a straight line along the pipe and at high velocities they were dispersed radially and mixed with the surrounding water. The straight line flow indicated laminar flow, while the dispersed flow indicated turbulent flow. Reynolds conducted several tests with different diameter pipe and found that a dimensionless value can be associated with laminar and turbulent flow. This dimensionless parameter can be found using the following formula: ℜ= ρVD μ (2) Where, Re is the Reynolds number ρ is the density of the fluid (kg/m 3 ) V is the velocity of the fluid (m/s) D is the diameter of the pipe (m) μ is the viscosity of the fluid (N-s/m 2 )
A fluid with a Reynolds number less than or equal to 2000 is considered to be laminar and a fluid with a Reynolds number of greater than 2000 is considered to be turbulent. When the fluid transitions between laminar and turbulent flow its Reynolds number is considered the critical Reynolds number. This value will be found using the graph of hydraulic gradient vs. velocity. The intersection of the turbulent curve with the laminar curve give us the critical velocity. Using the critical velocity, the experimental viscosity, and equation 2 the critical Re can be found.