MER 439 - Design of Thermal Fluid Systems

Pumps and Fans

Professor AndersonSpring Term 2012

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Hydraulic Turbines (Impulse and Reaction) Gas Turbines (Impulse and Reaction)

◦Pumps, Fans, Blowers, Compressors

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(1) Dynamic Pumps: These pumps use a rotating component to impart energy to the fluid in the form of high velocity, high pressure or high temperature (radial, axial, mixed).

(2) Positive Displacement Pumps: Have a fixed volume chamber that takes in and discharges the pumped fluid.

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http://upload.wikimedia.org/wikipedia/commons/4/4a/Centrifugal_Pump.png

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http://www.lawrencepumps.com/Graphics/Axial1.gif

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Flow Capacity

Pre

ss

ure

Ris

e

Centrifugal

Positive Displacement

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The increase in mechanical energy of the fluid can be found by applying the 1st Law of Thermo across a pump:

suctiondischarge

pump gzVP

gzVP

mW22

22

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suction

pumppump z

g

V

g

Pz

g

V

g

P

gm

WH

22

2

discharge

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When analyzing a piping system which include pipes and the pump we include the head of the pump as a negative loss:

pumpTOTALl Hhzg

V

g

Pz

g

V

g

P

,

2

2

1

2

22

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g

VK

D

Lfh LTOTALl 2

2

,

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The 40 ft long pipeline contains 3 elbows and one ball check valve and is made of 6-nominal schedule 40 PVC pipe. The pump must deliver 250 gpm. Select a pump for this system and calculate the pumping power.

A pipeline that conveys water to an elevated tank at a campsite is shown. The elevated tank supplies water to people taking showers.

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/D = “smooth” ==> f = 0.0165 (Moody Diagram)

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Q = 250 gpm

H = 38.3 ft

A fan from Region 01 will be suitable.

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From our study of pipe flow we know that typically hL varies approximately as the flow rate squared:

Where K depends on the pipe sizes, lengths and types and on the minor loss coefficients.

212 KQzzhP

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Water is to be pumped from one large open tank to another as shown.

The pipe diameter is 6 in and the total length of the pipe between the pipe entrance and exit is 200 ft. Minor loss coefficients for the entrance, exit and the elbow are shown on the figure and the friction factor can be assumed to be 0.02.

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A certain centrifugal pump having the performance characteristics shown is suggested as a good pump for this flow system. With this pump what would be the flow rate between the tanks? Do you think this pump would be a good choice?

We can plot this against the pump curve to locate the operating point.

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Pumps can be arranged in series or parallel to provide additional head or flow capacity.

(a) In Series - add heads at same flow rate(b) In Parallel - add flow rates at same head.

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Do practice problems next week (Quiz on Monday 4/23!)