Use Of Lab Experiments To Build Transport Concepts

One of the difficult concepts to teach in junior students’ class is momentum transport. Derivation of Bernoulli equation is one of the first equation products from the momentum balance that can be used in many flow evaluations. Use of the equation to specific situation of various fluid flows will require knowledge of friction losses, flow rate measurement by means of orifice flow meter, and rotameter. Calibration of an orifice meter requires use of a manometer that allows us to measure the difference in fluid pressures. The differential pressures are transduced into the current signals that can be easily interfaced by the computer through the acquisition board. The foundation of flow rate measurements is pail and scale method for our water flow system. The water-receiving tank is sat on a built-in accurate electronic scale so that the precise flow rate can be measured with a stopwatch. Each week experiments will calibrate one instrument at a time so that they begin to build their confidence on the instruments. They understand with confidence the flow system because they confirm by themselves the accuracy of orifice meter as well as rotameter. The friction losses in a straight copper tube can be calculated based on the Bernoulli equation and these values are checked by actual measurement of differential pressures between the two points. This also allows them to compute the orifice coefficients and see why this parameter has to exist. The friction losses due to a sudden expansion or contraction or fittings in the line can be calculated and confirm with actual measurements. These experiments help them to understand the friction losses due to entire piping system and enable them to construct a system curve on the pumping diagram to find an operating point. Once these concepts are developed, the computer data acquisition system will help them in bookkeeping the data against time. At this point students fully appreciate the roles of the flow instruments and the computer.