II ococ ? Optimisation of ABBs Wind Turbine Generator Performance by Installing A Heat Pipe Heat...

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?Optimisation of ABB’s Wind Turbine Optimisation of ABB’s Wind Turbine Generator Performance by InstallingGenerator Performance by Installing

AA

Heat PipeHeat PipeHeat ExchangerHeat Exchanger

Presented by: Haytham AbdulwahabThe United Arab Emirates University

What?

Selection

- Increase in the temperature difference safety margin, which allows increasing the loading.- extending the life of the insulation, and thus the life of the generator.

OverviewOverview

Internal circulating Internal circulating hot air closed cycle hot air closed cycle

Cold ambient air Cold ambient air dragged by fan dragged by fan

Cold air Cold air outlet outlet

Internal air Internal air entres closed entres closed cycle again cycle again

Internal air is Internal air is beeing cooled by beeing cooled by cold ambient air cold ambient air after it absorbed after it absorbed heat from generator heat from generator

- Increase in the temperature difference safety margin, which allows increasing the loading.- extending the life of the insulation, and thus the life of the generator.

What

What?What’s a heat pipe?

What reasons behind choosing a heat pipe to solve the problem

What consideration should be taken in designing a heat pipe?

What could limit the operation of a heat pipe?

What procedures are taken to design a heat pipe?

What other things should we be awared of?

What do you need to ask more?

What?What?

What?

?

Why a heat pipe was considered?Why a heat pipe was considered?

1.1. A heat pipe will transport the heat to a location where it can be effectively dissipated by natural or forced convection.

2.2. The heat pipe provides a thermal path through the enclosure wall, while the internal air cycle is kept close.

3.3. There will be no need for extra cooling fan that would consume extra power; since the original cooling fan used to drag cooling air for the primary cooling unit is the one to be used in the cooling of the heat sink by forced convection.

4.4. The product maintenance requirements are eliminated or reduced. And no noise source does exist.

Heat Pipe Fundamentals:Heat Pipe Fundamentals:

Thermal Design:

- Evaporator

- Adiabatic

- Condenser( Heat Sink)

Manufacturer:

- Container

- Working Fluid

- Wick Structure (operation

against gravity)

Selection

Materials Selection Creteria:Materials Selection Creteria:

Container Material:

1.1. The container should isolate the working fluid from the outside environment.

2.2. The container should also enable heat transfer to take place from and into the working fluid.

3.3. The container material should be compatible with both the working fluid and external environment.

4.4. A material with good fabrication properties including weldibility, machineability and ductility, is preferable.

Selection

SelectionSelection


Working Fluid Material:

1.1. Compatibality of the working fluid with the container material.

2.2. The thermal stability of the working fluid.

3.3. High latent heat a high latent heat of vaporization and high thermal conductivity.

4.4. Low values of vapor and liquid viscosities to minimize the resistance to fluid flow.

5.5. Acceptable freezing point in comparison to the operating temperature range.

Methanol has a boiling point of 46oc

Temperature Range (oC)

Working FluidVessel

Material

-200 to -80 Liquid NitrogenStainless

Steel

-70 to 60 Liquid Ammonia

Nicker, Aluminum, Stainless

Steel

-45 to 120 Methanol

Copper, Nicker,

Stainless Steel

5 to 230 WaterCopper, Nickel

190 to 550Mercury,

MagnesiumStainless

Steel

400 to 800 PotassiumNickel,

Stainless Steel

500 to 900 SodiumNickel,

Stainless Steel

900 to 1,500 LithiumNiobium,

+15 Zirconium

SelectionSelection


- - Methanol was fluid of choice.Methanol was fluid of choice.

Methanol would provide a temperature potential capable of driving the required amount of heat because of its low value of boiling point Tsat.

Since methanol freezes at a very low temperature, -97C, it is useful in gravity-aided, pool boiling applications where water heat pipes would be subject to freezing.

- Copper for evaporator tubes, and aluminum for - Copper for evaporator tubes, and aluminum for condenser fins.condenser fins.

materials with good fabrication properties and good thermal properties in addition to compatability with working fluid of choice.

Description Cause Potential Solution

Viscosity Viscous forces hinder vapor flow in the heat pipe

Heat pipe operating below recommended operating

temperature

Increase heat pipe operating temperature

or find alternative working fluid

Sonic

Vapor flow reaches sonic velocity when exiting heat

pipe evaporator resulting in a constant heat pipe transport power and large temperature

gradients

Power/temperature combination, too much power at low operating

temperature

This is typically only a problem at start-up. large temperature

gradient will be reduced as the heat

pipe warms up

Entrainment/Flooding High velocity vapor flow

prevents condensate from returning to evaporator

Heat pipe operating above designed power input or at

too low operating temperature

Increase vapor space diameter or operating

temperature

Capillary

Sum of gravitational, liquid and vapor flow pressure

drops exceed the capillary pumping head of the heat

pipe wick structure

Heat pipe input power exceeds the design heat transport capacity of the

heat pipe

Modify heat pipe wick structure design or reduce power input

Boiling Film boiling in heat pipe evaporator would initiate

High radial heat flux causes film boiling resulting in heat

pipe dry-out and large thermal resistances

Use a wick with a higher heat flux

capacity or spread out the heat load

Limits to Heat Pipe OperationLimits to Heat Pipe Operation

airair

ostator

airair

radevaporatorair outair instatorostatorair in

air out

Cpu

hACpu

QQ) / T (T -ThAT

T

.

.

21

)2(

NuD = 1.13C1C2 Remmax Pr 1/3

ST/D

1.25 1.5 2 3

SL /D C1 m C1 m C1 m C1 M

0.6 - - - - - - 0.213 0.636 0.9 - - - - 0.446 0.571 0.401 0.581 1 - - 0.497 0.558 - - - -

1.125 - - - - 0.478 0.565 0.518 0.56 1.25 0.518 0.556 0.505 0.554 0.519 0.556 0.522 0.562 1.5 0.451 0.568 0.46 0.562 0.452 0.568 0.488 0.568 2 0.404 0.572 0.416 0.568 0.482 0.556 0.449 0.57 3 0.31 0.592 0.356 0.58 0.44 0.562 0.428 0.574

NL 1 2 3 4 5 6 7 8 9

0.68 0.75 0.83 0.89 0.92 0.95 0.97 0.98 0.99

Δp=NLχ(χρairV2

max/2)f

Evaporator DesignEvaporator Design

All the dimensions and geometry details are shown in the figure beside

18 circular pipes of 25mm. The cross section of the pipe array is cantered a distance of 237.5mm from the axis of the generator.

Each pipe is made of copper and has a wall thickness of 2mm.

The average convection heat transfer coefficient based on the velocity of air at the centre of the array is equal to 47.5 W/m2.oC

The total heat transfer to the evaporator tubes is equal to 1692W

The total weigh of evaporator tubes filled with methanol is 42kg. The empty tubes weigh 35kg.

The time required for the heat pipe to start working is 8 minutes.

Evaporator Tubes Design Summery:

Condenser DesignCondenser Design

2

27/816/9

6/1

Pr559.01

387.06.0

air

air

NCRa

kDhNu

Low velocity areaLow velocity area

High velocity areaHigh velocity area

AverageAveragevelocityvelocity14.8m/s14.8m/s


High velocity areaHigh velocity areaAverageAveragevelocityvelocity12.1m/s12.1m/s


wall.theofetemperaturtheatwasfin

entiretheiffinthefromratetransferheat

finthefromratetransferheatactualη

4/13

)(

)(68,0)(729.0

DTTu

kTwallTsatCphgh

wallsatl

llfgvllo

unfinwww

f

iGfff

ii

AAN

N

hRAN

hR

1/1

Side Front

Fin DimensionsN = 49

All the dimensions and geometry details are shown in the figure above. 49 L-shaped rectangular aluminium fins will be attached on the inner surface of the air duct using a glue material that has a thermal conductivity of 0.95 W/m.oC. The methanol vapor will be contained between this surface and a 510mm diameter concentric cylindrical surface forming the heat pipe heat sink.

Heat Sink Design Summery:

Side Front


The natural convection heat transfer coefficient on the outer surface of the heat sink was found to be 4.77 W/m2.oC. The emmisivity ε of paint material on the outer surface was taken to be 0.85

This gives us a total of heat transfer to the outside equal to 309W.


Side Front


Based on an average air velocity inside the duct of 13.443 m/s, the forced convection heat transfer coefficient on the inner surface of the heat sink was found to be 33.3kW/m2.oC


Side Front


And thus the heat emitted by the fins is equal to 687W. While the heat emitted by the wings is equal to 103W. The rest unfinned area emits 551W. A total amount of heat transfer to the air driven by the duct fan equal to 1341W

The total amount of heat emitted by the heat sink is equal to 1650W. The temperature of the inner surface of the heat sink is equal to 63.6 oC.


Alternative Design

[Acetone Heat Pipe][Acetone Heat Pipe]

IIJust 12 evaporator tubes!

But we will need more than 40 extra fins.

It is highly recommended to check a safety data sheet or a hazard sheet that provides information about safety about dealing with methanol.

Recommendations!Recommendations!

Since the wind turbine will be used in a marine environment, a surface coating is required to protect the heat sink assembly, where dissimilar materials are being attached to each other (aluminum fins on steel wall), from galvanic corrosion.


When monitoring heat pipe performance, the key parameter is the temperature difference between the surfaces of the evaporator and the condenser.


Don’t use the same heat pipe design for two different working fluids.


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??Thanks for Listening!Thanks for Listening!

What questions do you have?

II ococ ? Optimisation of ABBs Wind Turbine Generator Performance by Installing A Heat Pipe Heat...

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