10 FLUID FLOW PUMPS CHEMICAL ENGINEERING 170 FLUID

FLUID FLOW SCHEDULE Today Pumps Power, efficiency, pump curves Tuesday Chem. E Car Project

PUMPS! A pump is a mechanical device that moves liquid. OUT IN It can:

EXAMPLE: PUMPING WATER TO A SHOWER In order to conserve water, shower heads in

MECHANICAL ENERGY BALANCE ACROSS A PUMP Something interesting happens when we do an energy

BACK TO THAT SHOWER Shower What happens between 1 and 2? The pump raises

EXAMPLE: SHOWER PUMP EFFICIENCY If the pump we use to get water to our

PUMP CURVES It turns out that for any given pump, a specific volumetric flowrate

REVIEW Pump If you could measure pressure and velocity at any point in this

EXAMPLE: PUMP A pump increases the pressure of flowing fluid by 30 k. Pa.

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10. FLUID FLOW: PUMPS CHEMICAL ENGINEERING 170

FLUID FLOW SCHEDULE Today Pumps Power, efficiency, pump curves Tuesday Chem. E Car Project Introduction Also: short balances review Next Thursday Balances quiz for points back on exam (up to a total grade of 75) Mid-Semester Evaluation (online)

MECHANICAL ENERGY BALANCE

PUMPS! A pump is a mechanical device that moves liquid. OUT IN It can: Speed a fluid up/get a still liquid moving Lift fluid up (how does water get to the top floor of a building? ) Raise the pressure of a fluid

EXAMPLE: PUMPING WATER TO A SHOWER In order to conserve water, shower heads in the US are legally required to deliver less than 2. 5 gallons per minute of flow. A shower head is two meters above the floor on the third floor, which is six meters above the ground. A tank open to the atmosphere sits at ground level, with water one meter deep inside. If friction is negligible, what work must be supplied by a pump to move water at 2. 5 gpm through a 1. 25 cm-diameter pipe? 2. 5 gpm = 1. 58 x 10 -4 m 3/s

MECHANICAL ENERGY BALANCE ACROSS A PUMP Something interesting happens when we do an energy balance just across the pump. OUT IN The energy the pump puts into the liquid raises its pressure!

BACK TO THAT SHOWER Shower What happens between 1 and 2? The pump raises the pressure of the water. What happens next? That high pressure pushes Water Tank Pump the water up to the shower.

POWER

PUMPING POWER

EXAMPLE: SHOWER POWER

EFFICIENCY

EXAMPLE: SHOWER PUMP EFFICIENCY If the pump we use to get water to our shower is 50% efficient at that flow rate, how much electrical power will be required to operate the pump?

PUMP CURVES It turns out that for any given pump, a specific volumetric flowrate will produce a specific pressure gain and efficiency. That’s why it’s common to characterize pumps with a pump curve: You will be creating a pump curve in next week’s lab.

REVIEW Pump If you could measure pressure and velocity at any point in this system, how would you figure out the power that must be delivered to the fluid by the pump? Discuss with your neighbor—come up with at least two ways. Say exactly where you would make your measurements and what you would measure.

EXAMPLE: PUMP A pump increases the pressure of flowing fluid by 30 k. Pa. Given that the pump requires 70 W of electrical power to run and water flows out of the pump at 0. 1 m 3/min, what is the pump’s efficiency? Hint: Pay attention to units!