Brewery Engineering Pumps and Whirlpools

1. Brewery EngineeringPumps and Whirlpools Lecture 1 Brewery Engineering Lecture 1- P 1

2. Learning Objective – Goals for Today • Pump Types • Centrifugal Pump • Air-operated Diaphragm Pump • Pump Properties & Pump Curves • Whirlpools • Theory • Practice Fluid Dynamics Lecture 1- P 2

3. Pumps • Fluids are moved through pipes or ducts using pumps, fans, blowers and compressors. • These devices impart mechanical energy to the fluid which can be used to move the fluid (increase its velocity), increase the pressure in the fluid, or lift the fluid vertically against the force of gravity Brewery Engineering Lecture 1- P 3

4. Pumps • The term pump, fan, blower and compressor are often used rather loosely and do not really have a universally accepted, precise definition • We generally speak of pumps moving liquids, while fans, compressors, or blowers either move or compress gases. Pumps move liquids. Fluid Dynamics Lecture 2- P 4

5. Pumps • In a brewery, you are most likely to encounter pumps that are widely used throughout industry and available from many different commercial vendors. • Common types of pumps that you might see in the brewery include: • Centrifugal pumps • Air-operated Diaphragm pumps • Of these, the centrifugal pump is generally the “workhorse” within the brewery Brewery Engineering Lecture 1- P 5

6. Pumps - Centrifugal • Although there are many, many different types of pumps available in the marketplace, the kind of pump that is most often used to move most kinds of liquids in a brewery is a centrifugal pump. • A centrifugal pump is a fairly simple machine that is designed to impart energy to a fluid. The energy can cause the fluid to rise against gravity or flow through a closed system (pipes). Brewery Engineering Lecture 1- P 6

7. Pumps - Centrifugal • The centrifugal pump achieves liquid movement and flow by “slinging” the fluid out of the impeller using centrifugal force. • The two main parts of a centrifugal pump head are the impeller and the diffuser (or volute). • The impeller is the only moving part within the pump head • The impeller spins within the pump head housing and the diffuser captures and directs the flow of liquid from the impeller. Brewery Engineering Lecture 1- P 7

8. Pumps - Centrifugal • Liquid is drawn into the pump head near the center of the impeller and pushed outwards by the movement of the blades on the impeller • The liquid is “slung out” by the movement of the spinning impeller Brewery Engineering Lecture 1- P 8

9. Pumps - Centrifugal • Here’s a picture to help you visualize what’s going on inside the pump head housing: Brewery Engineering Lecture 1- P 9

10. Pumps - Centrifugal • For a centrifugal pump, the flow rate that can be achieved is an inverse function of pressure. A centrifugal pump will deliver less flow when pumping against a higher back-pressure. • The specific way in which this relationship holds true depends upon the details of the pump design. • In general, as back-pressure increases, flow decreases. Brewery Engineering Lecture 1- P 10

11. Pumps - Centrifugal • The velocity of fluid flow within a particular piping system is an important consideration as it directly impacts the overall restive pressure associated with moving liquid through the system. • Higher liquid flow rates will result in higher resistive pressure within the system due to pipe friction; recall that the pressure drop due to pipe friction and component friction is directly proportional to the square of the velocity of the liquid flowing through a pipe: Brewery Engineering Lecture 1- P 11

12. Pumps - Centrifugal • Here is a graph that illustrates the general relationship between flow velocity, system pressure and centrifugal pump capability: Brewery Engineering Lecture 1- P 12

13. Pumps - Centrifugal • This graph also illustrates how actual pump performance for a particular system is determined. • The blue curve is known as the system curve, and it shows how backpressure within the system varies with flow rate • The orange curve is the pump performance curve and it shows how the capability of a centrifugal pump to deliver a given flow rate is affected by system pressure. • The intersection of the two curves is known as the “operating point “ for the system. Operating Point Brewery Engineering Lecture 1- P 13

14. Pumps - Centrifugal • The characteristics of the system curve change depending upon the physical configuration of the system • The system curve characteristics depend upon the height to which liquid must be pumped, the diameter and length of the piping within the system, and the number and types of fittings, valves, etc. within the system • Recall that hLtot= hLelev+ hLpipe+ S hLcomp Brewery Engineering Lecture 1- P 14

15. Pumps - Centrifugal • This means that we are able to manipulate the flow rate of liquid delivered by the pump by increasing or decreasing the total amount of back pressure within the system • We can do this by increasing or decreasing the friction within the system by closing or opening a valve • Increasing and decreasing the friction within the system will shift the system curve and change the operating point within the system Brewery Engineering Lecture 1- P 15

16. Pumps - Centrifugal • Here’s a graph that illustrates the concept using the opening & closing of a valve: System Curve With 1/2 Opened Valve 100 90 80 70 60 50 40 30 20 10 0 System Curve With Fully Opened Valve Pressure change due to closing or opening valve Head, ftH2O Pump Capability Curve 0 5 10 15 20 25 30 35 40 45 50 Flow rate change due to closing or opening valve Flow, gpm Brewery Engineering Lecture 1- P 16

17. Pumps - Centrifugal • There are several ways to modify the flow output of a centrifugal pump • Change impeller diameter • Change impeller speed • Increasing the impeller diameterwill increase the flow output of a centrifugal pump. The extent to which the flow will change is shown on manufacturer’s pump curves. • Increasing the rotational velocity of the impeller will increase the flow output for a centrifugal pump. The amount of flow increase is directly proportional to the rotational velocity increase. • Changing the rotational velocity also has other operational performance implications. The relationship between impeller rotational velocity and flow, pressure head, and power requirements are know as the pump Affinity Laws. Brewery Engineering Lecture 1- P 17

18. Pumps - Centrifugal • The pump Affinity Laws are: • Flow is directly proportional to impeller speed • Pressure (head) is proportional to the square of impeller speed • Power requirement is proportional to the cube of impeller speed • Succinctly stated: Where: Q = Flow rate H =Delivered pressure (head) P = Power required Brewery Engineering Lecture 1- P 18

19. Pumps - Centrifugal • We can write the pump affinity laws in another, equivalent, way: • Then use these forms of the pump affinity law equations to predict what happens when the rotational velocity of the impeller is changed. Brewery Engineering Lecture 1- P 19

20. Pumps - Centrifugal • Example Problem: Flow from a pump is measured to be 100 gpm. Delivered pressure head is 100 ftH2O. Power requirements are 5 h.p. The pump impeller rotational velocity is increased from 1750 rpm to 3500 rpm. What effect does increasing the impeller rotational velocity have on flow rate, delivered pressure and power consumption? Brewery Engineering Lecture 1- P 20

21. Pumps - Centrifugal • Solution: Use the pump affinity law equations and substitute the information in the problem statement: • Q1 = 100 gpm • H1 = 100 ftH2O • P1 = 5 h.p. • N1 = 1750 rpm • N2 = 3500 rpm Doubling impeller velocity increases flow by factor of 2, pressure by a factor of 4, and power consumption by a factor of 8

22. Pumps - Centrifugal • Another Example Problem: For an existing system, flow from a pump is measured to be 100 gpm. Maximum delivered pressure head is 100 ftH2O, and current power requirements are 8 h.p. at an impeller velocity of 875 rpm. Due to brewery expansion, a new, larger, heat exchanger is installed which increases the total system pressure head to 150 ftH2O. To what velocity must the pump impeller be increased in order to overcome the new higher system backpressure? Brewery Engineering Lecture 1- P 22

23. Pumps - Centrifugal • Solution: Write down the information in the problem statement: • Q1 = 100 gpm • H1 = 100 ftH2O • H2 = 150 ftH2O • P1 = 8 h.p. • N1 = 875 rpm • N2 = ? rpm • Then algebraically rearrange the relevant Affinity Law equation: Brewery Engineering Lecture 1- P 23

24. Pumps - Centrifugal • Then substitute in the appropriate values from the problem statement: • H1 = 100 ftH2O • H2 = 150 ftH2O • N1 = 875 rpm • And solve: Impeller velocity must be increased from 875 rpm to 1072 rpm, an increase of approximately 23%

25. Pumps - Centrifugal • In order for a pump to move liquid, it must do work on the liquid, and work requires energy. Doing more work requires more energy. • The rate at which energy is used and work is done (work per unit time) is the definition of power. • The amount of power required to move a liquid is dependent upon the liquid flow rate, the back pressure within the system and the efficiency of the motor. • For a centrifugal pump, the (hopefully familiar) equation that describes the relationship is: Where: P = Power (h.p.) Q = Flow rate (gallons/minute or gpm) DPtotal = total system pressure (pounds/in2 or psi) h = overall pump efficiency Brewery Engineering Lecture 1- P 25

26. Pumps - Centrifugal • Centrifugal pump manufacturers typically supply performance curves for each of their pumps. • These are normally referred to as “pump curves”, and are generally developed using water as the reference fluid. • Most centrifugal pump curves allow for direct reading or easy determination of: • System pressure (head) vs. flow rate for any fluid • Pump efficiency for any fluid • Pump energy (horsepower) requirements for a system pumping water Brewery Engineering Lecture 1- P 26

27. Pumps - Centrifugal • Here is an example of a pump curve provided by a manufacturer: Efficiency NPSH Impeller Diameter Developed Head Horsepower Flow Rate Brewery Engineering Lecture 1- P 27

28. Pumps - Centrifugal • Net Positive Suction Head (NPSH) • Net positive suction head (NPSH) is the pushing force at the intake of a pump. It is the force of the liquid pushing into the pump due to gravity, plus other head pressures • It can be thought of as the net positive pressure of the liquid entering the pump intake, and is determined by liquid head height or liquid head pressure + gravity pressure, minus friction loss. • NPSH is the head (pressure and gravity head) of liquid in the suction line of the pump that will overcome the friction resistive forces. Brewery Engineering Lecture 1- P 28

29. Pumps - Centrifugal • Net Positive Suction Head Required (NPSHR) • NPSHR is the minimum amount of liquid pressure required at the intake port of a pump • Net Positive Suction Head Available (NPSHA) • is the amount of positive pressure head available at the pump intake after pipe friction losses and head pressure contribution has been accounted for • It is very important that NPSHA > NPSHR • Why…..? Brewery Engineering Lecture 1- P 29

30. Pumps - Centrifugal • When a centrifugal pump is pulling liquid in through the suction side of the impeller it is creating a large low-pressure situation immediately upstream of the impeller • If liquid is unable to flow into the pump intake fast enough, this low-pressure situation can become a VERY low-pressure situation. • If the pump suction is strong enough, a pump can create a vacuum that is so strong that the pressure within the pipe immediately upstream of the impeller is low enough for the liquid to begin to boil • This situation is given the name “cavitation” • Cavitation decreases pump performance and can cause damage to the pump. Brewery Engineering Lecture 1- P 30

31. Pumps - Centrifugal • To avoid this situation, ensure that centrifugal pumps are properly specified and installed in a location that maximizes available suction head (i.e. near the low-point within the piping system). ü Tank #1 Tank #2 Pump Pump X Tank #1 Tank #2 Brewery Engineering Lecture 1- P 31

32. Pumps – Air Operated Diaphragm • Another kind of pump that is often found in breweries is an Air Operated Diaphragm (AOD) pump. • An Air Operated Diaphragm pump uses a combination of the reciprocating action of one or more diaphragms and internal inlet and outlet check valves to move fluid. • AOD pumps use compressed air to provide the energy needed to move fluids. • Air supply is shifted from one internal chamber to another to cause the diaphragm(s) to flex back and forth. Check valves open and close as internal pressure pushes the liquid through the pump. Brewery Engineering Lecture 1- P 32

33. Pumps – Air Operated Diaphragm • Here are some examples of AOD pumps ……. Brewery Engineering Lecture 1- P 33

34. Pumps – Air Operated Diaphragm • ……… and a view of the internals………….. Discharge Manifold Air Chamber Air Distribution System Liquid Chamber Outer Diaphragm Inner Diaphragm Diaphragm Check-Valve Ball Intake Manifold Check-Valve Seat Brewery Engineering Lecture 1- P 34

35. Pumps – Air Operated Diaphragm • ……… and a view of the internals Brewery Engineering Lecture 1- P 35

36. 1 2 3 NM NM NM NM NM NM 4 5 NM NM GIF Animation of AOD Pump NM = No Movement Liquid Flow Direction Air Flow Direction NM NM

37. Pumps – Air Operated Diaphragm • AOD pumps differ from centrifugal pumps in several important ways: • Energy source: • Centrifugal: Electric motor • AOD: Compressed air • Effect of system head pressure • Centrifugal: flow varies with system head pressure • AOD: flow remains constant with changing system pressure • Inlet Condition Requirements • Centrifugal: Liquid must be in pump head; not self-priming • AOD: Liquid not needed at inlet; self priming Brewery Engineering Lecture 1- P 37

38. Pumps – Air Operated Diaphragm • Like centrifugal pumps, AOD pumps also have performance curves, but the things that AOD pump performance curves describe are different • The physical parameters that affect AOD pump performance are • Compressed air inlet pressure • Compressed air consumption rate • These parameters affect AOD pump performance and determine the output parameters for the pump. • AOD pump output parameters are: • Discharge pressure • Liquid flow rate Brewery Engineering Lecture 1- P 38

39. Whirlpools • What, exactly is a whirlpool? • The first thing that I think of is the appliance manufacturer……….. Brewery Engineering Lecture 1- P 39

40. Whirlpools • ….but that’s not really exactly what we are talking about today. Brewery Engineering Lecture 1- P 40

41. Whirlpools • Here are several definitions of a Whirlpool: • a swirling body of water that is produced by the meeting of currents flowing in opposite directions • water in swift, circular motion, as that produced by the meeting of opposing currents, often causing a downward spiraling action • a vortex, spinning around a central point • It seems that most people can agree that a whirlpool is “swirling water” Brewery Engineering Lecture 1- P 41

42. Whirlpools • A whirlpool occurs when two currents are moving in opposing directions, or at an angle to each other in such a way as to allow friction between the two currents to cause the water to spin, creating the whirlpool. 3 1 2 Brewery Engineering Lecture 1- P 42 4 5

43. Whirlpools • A whirlpool can also be generated by inducing a liquid to swirl around, either from mechanical agitation (stirring): • or by tangentially directing the flow of a fast-moving stream within the bulk of the liquid: Side Top Side Top Brewery Engineering Lecture 1- P 43

44. Whirlpools • In many breweries, “whirlpooling” is a specific step in the brewing process. • Whirlpooling is done in order to help separate suspended solids (hop particles, hot-break material, trub etc.) from the liquid wort • Whirlpooling, if performed, is done right after the boil: Brewery Engineering Lecture 1- P 44

45. Barley Water Yeast Hops Adjuncts Energy Milling Ground Barley Yeast Starter Grind Settings Strain More Yeast Amount Mashing Temp. Wort Water to Grist Ratio Temp. Sparging Rate Wort Water to Grist Ratio Boiled Wort Boil Temp. Isomerized a-acids Time Maillard Reaction Products Type Finings Addition / Whirl pooling Hot Break Amount Time Wort Cooling Method Cooled Wort Temp. Time Wort Aeration Method Oxygenated Wort Amount Transfer to Fermenter Method Wort in Fermenter Transfer Rate Yeast Pitching Fermentation Temp. CO2 Time Beer Dry Hopping Time Conditioning Temp. CO2 Secondary Ferment Beer Lagering Packaging & Carbonating Packaged Beer Keg Finished Beer Carbonated Beer Bottle Time Storage Temp. Finished Beer (ageing) Light Exposure Consumption Temp. Joy ! Amount

46. Whirlpools • Breweries sometimes even have tanks that are specifically designated for whirlpooling. Here’s a PFD to illustrate this: Brewery Engineering Lecture 1- P 46

47. Whirlpools • The moving liquid in a whirlpool causes suspended particulate matter to move to the center of the tank and form a cone: Brewery Engineering Lecture 1- P 47

48. Whirlpools • But why does this happen? • Why does rotating liquid within a tank cause suspended particulate matter to move inward? • Shouldn’t centrifugal force cause the particulate matter to be slung outward toward the tank wall? • What’s going on…….? Brewery Engineering Lecture 1- P 48

49. Whirlpools • First of all, lets talk through a simple, representative physical system (one that has been extensively analyzed) and discuss the forces at work within it. Let’s talk about tea in a teacup. Specifically, loose leaves being stirred in a teacup. • When the tea leaves are being stirred, they are rotating around the bottom of a cup, following the motion of the water that is induced by stirring. When the spoon is removed, the leaves begin to move towards the center and collect on the bottom of the cup (just like our trub collects in the center of the whirlpool). Brewery Engineering Lecture 1- P 49

50. Whirlpools • This can be explained by the fact that the pressure (and water level) near the side walls of the cup is higher than the pressure in the center when the water is rotating. • Note that the shape of the surface of the water, while the tea is rotating, is concave from the viewpoint of the drinker. • This pressure variation is the result of the centripetal acceleration that balances the centrifugal acceleration of the rotating liquid water. • It is this pressure gradient that induces a vortex effect within the system • But why does this pressure gradient exist? Brewery Engineering Lecture 1- P 50