Week 1 Unit Conversions Mass and Volume Flow Ideal Gas Newtonian Fluids, Reynolds No . Week 2

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Week 1 Unit Conversions Mass and Volume Flow Ideal Gas Newtonian Fluids, Reynolds No . Week 2 Pressure Loss in Pipe Flow Pressure Loss Examples Flow Measurement and Valves Pump Calcs and Sizing.

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Presentation Transcript

Week 1

Unit Conversions

Mass and Volume Flow

Ideal Gas

Newtonian Fluids, Reynolds No.

Week 2

Pressure Loss in Pipe Flow

Pressure Loss Examples

Flow Measurement and Valves

Pump Calcsand Sizing

1000 gallons of wortis transferred from a kettle through a 100 m long, 4 cm diameter pipe with a roughness of 0.01 mm. The wort flows at an average velocity of 1.2 m/s and assume that its physical properties are the same as those of water (μ = 0.001 Pa.s).

• Determine the time required to transfer all of the wort to the boil kettle, in min.
• Determine the Reynolds Number.
• Determine the pressure drop in the pipe.

Friction Losses in Pipes

found on Moody Chart handout

Determine the pressure drop of water, moving through a 5 cm diameter, 100 m long pipe at an average velocity of 5 m/s. The density of the water is 1000 kg/m3 and the viscosity is 0.001 Pa.s. The pipe roughness is 0.05 mm.

Valves – Globe Valve

Single Seat

- Good general purpose

- Good seal at shutoff

Double Seat

- Higher flow rates

- Poor shutoff (2 ports)

Three-way

- Mixing or diverting

- As disc adjusted, flow to one channel increased, flow to other decreased

Valves – Butterfly Valve

Low Cost

Poor flow control

Can be automated

Valves – Mix-proof Double Seat

Two separate sealing elements keeping the two fluids separated.

Keeps fluids from mixing

Immediate indication of failure

Automated, Sanitary apps

Easier and Cheaper than

using manyseparate valves

Valves – Gate Valve

Little flow control, simple, reliable

Valves – Ball Valve

Very little pressure loss, little flow control

Valves – Brewery Applications

Product Routing – Tight shutoff, material compatibility, CIP critical

Butterfly and mixproof

Service Routing – Tight shutoff and high temperature and pressure

Ball, Gate, Globe

Flow Control – Precise control of passage area

Globe (and needle), Butterfly

Pressure Relief – Control a downstream pressure

Flow Measurement Principle:

• Bernoulli Equation
• Notice how this works for static fluids.

Flow Measurement – Orifice Meter

• Cd accounts for frictional loss,  0.65
• Simple design, fabrication
• High turbulence, significant uncertainty

P1

P2

Flow Meas. – Venturi Meter

• Less frictional losses, Cd 0.95
• Low pressure drop, but expensive
• Higher accuracy than orifice plate

P1

P2

Flow Meas. – Variable Area/Rotameter

Inexpensive, good flow rate indicator

Good for liquids or gases

No remote sensing, limited accuracy

Flow Measurement - Pitot Tube

• Direct velocity measurement (not flow rate)
• Measure P with gauge, transducer, or manometer

P1

P2

1 2

v

Flow Measurement – Weir

Open channel flow, height determines flow

Inexpensive, good flow rate indicator

Good for estimating flow to sewer

Can measure height using ultrasonic meter

Flow Measurement – Thermal Mass

Measure gas or liquid temperature upstream and downstream of heater

Must know specific heat of fluid

Know power going to heater

Calculate flow rate

Flow Measurement – Magnetic

Magnetic field applied to the tube

Voltage created proportional to velocity

Requires a conducting fluid (non-DI water)

Pumps

hf = head loss due to friction

Suction

Pump

Delivery

Pumps

Calculate the theoretical pump power required to raise 1000 m3 per day of water from 1 bar to 16 bar pressure.

If the pump efficiency is 55%, calculate the shaft power required.

Denisityof Water = 1000 kg/m3

1 bar = 100 kPa

Pumps

A pump, located at the outlet of tank A,

must transfer 10 m3 of fluid into tank B

in 20 minutes or less. The water level in

tank A is 3 m above the pump, the pipe

roughness is 0.05 mm, and the pump

efficiency is 55%. The fluid density is

975 kg/m3 and the viscosity is 0.00045

Pa.s. Both tanks are at atmospheric

pressure. Determine the total head and

pump input and output power.

4 m

Tank B

15 m

Pipe Diameter, 50 mm

Fittings =

5 m

Tank A

8 m

Pumps

Need Available NPSH > Pump Required NPSH

Avoid Cavitation

hf = head loss due to friction

Pumps

A pump, located at the outlet of tank A,

must transfer 10 m3 of fluid into tank B

in 20 minutes or less. The water level in

tank A is 3 m above the pump, the pipe

roughness is 0.05 mm, and the pump

efficiency is 55%. The fluid density is

975 kg/m3 and the viscosity is 0.00045

Pa.s. The vapor pressure is 50 kPa and

the tank is at atmospheric pressure.

Determine the available NPSH.

4 m

Tank B

15 m

Pipe Diameter, 50 mm

Fittings =

5 m

Tank A

8 m

Pump Sizing

• Volume Flow Rate (m3/hr or gpm)
• Total Head, h (m or ft)
• 2a. P (bar, kPa, psi)
• Power Output (kW or hp)
• NPSH Required

Pumps

Centrifugal

Impeller spinning inside fluid

Kinetic energy to pressure

Flow controlled by Pdelivery

Positive Displacement

Flow independent of Pdelivery

Many configurations

Centrifugal Pumps

Delivery

Impeller

Volute Casting

Suction

Centrifugal Pumps

Flow accelerated (forced by impeller)

Then, flow decelerated (pressure increases)

Low pressure at center “draws” in fluid

Pump should be full of liquid at all times

Flow controlled by delivery side valve

May operate against closed valve

Seal between rotating shaft and casing

Centrifugal Pumps

Simple construction, many materials

No valves, can be cleaned in place

Relatively inexpensive, low maintenance

Operates at high speed (electric motor)

Wide operating range (flow and head)

Multiple stages needed for high pressures

Poor efficiency for high viscosity fluids

Must prime pump

Centrifugal Pumps

H-V Chart

Increasing Impeller Diameter

(or P)

A B C

Volume Flow Rate

Centrifugal Pumps

H-Q Chart

Increasing Efficiency

(or P)

Required NPSH

A B C

Volume Flow Rate

Centrifugal Pumps

H-Q Chart

(or P)

A B C

Volume Flow Rate

Centrifugal Pumps

H-Q Chart

Required Flow Capacity

(or P)

Actual Flow Capacity

Required Power

Volume Flow Rate

Pump Sizing Example

Requirements

100 gpm

Choose the proper impeller

Determine the power input to the pump

Pressure Drop Example

Water flows through a 10 cm diameter, 300 m long pipe at a velocity of 2 m/s. The density is 1000 kg/m3, the viscosity is 0.001 Pa.s and the pipe roughness is 0.01 mm. Determine:

a. Volume flow rate, in m3/s

b. Mass flow rate in kg/s

c. Pressure loss through the pipe, in Pa

d. Head loss through the pipe meters