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Laboratory exercise in pumps Purpose of the exercise Become acquainted with measuring equipment relevant to turbo machinery Become acquainted with cavitation and NPSH Apply the velocity triangles Rig Flow meter WaterTank (open at top) Pump p1 Valve 1 p2 Valve 2 Equipment Pump: radial, KSB Euro-CPK. The rotational speed of the electrical engine is controlled by a frequency converter. Mass flow meter: Coriolis type, Danfoss Massflo MASS 2100 (now owned by Siemens) Pressure: “old style” pressure gauge (-1 to 10 Bars gauge) 1 1 Absolute pressure is zero referenced against a perfect vacuum, so it is equal to gauge pressure plus atmospheric pressure. Gauge pressure is zero referenced against ambient air pressure, so it is equal to absolute pressure minus atmospheric pressure. Differential pressure is the difference in pressure between two points. Lund University, Energy Sciences, Division of Thermal Power Engineering. JK 1301014 Questions 2 be discussed before exercise 1. The pump has an impeller with 176 mm diameter. Assuming blades that are straight at the outlet (β2 = 0) and no losses, what is the expected pressure rise at 2900 rpm speed ? (draw the outlet velocity triangle and apply the Euler pump equation, assuming no swirl at inlet) 2. How does this compare to dimensional analyses? ψ = Q ρND 2 l1 l2 gH = f , , , ,... (ND )2 4 ND 3 µ D D 3. How does it compare to charted values (see below)? H real = η ⋅ H teo 4. Discuss the pressure in front of the pump and the significance of it. What is the Net Positive Suction Head (NPSH or Hs) 5. What alternative instrumentation could have been used? Tasks at the lab (please read through this before) 1. Measure Δp and volume flow at a few different flows, setting the speed of rotation to n = 2900 rpm. Here the volume flow is controlled by valve 2, valve 1 fully open. Plot into the chart below. Are the measurements in accordance to the chart? Why or why not? 2. Leaving valve 2 at fixed position, reduce the speed of rotation. Again note Δp and volume flow at a few different speeds. Plot into same chart. Explain what this is. 3. The NPSH required by the pump (a.k.a. NPSHR or NPSH(r) or NPSH-3) is provided by the manufacturer (next page, second graph). The available NPSH from the system (NPSHA or NPSH (a)) may be changed by closing valve 1. At what inlet pressure can cavitation be heard? How does this agree with specifications? NPSH = p0 − pv ρg where p 0 is the absolute stagnation pressure at inlet p v is the vapour pressure at the fluid temperature Lund University, Energy Sciences, Division of Thermal Power Engineering. JK 1301014 10 m Lund University, Energy Sciences, Division of Thermal Power Engineering. JK 1301014