Presented by

THANT ZIN WIN

Department of Mechanical EngineeringTechnological University (Kyaukse)

Mandalay Division, Myanmar

thantm7@gmail.com

2

Presentation Outlines

1. Introduction2. Operating Principle of Coreless Induction Furnace3. Important Role of Water Cooling4. Types of Water Cooling System5. Layout Description6. Design Parameters of Cooling Pond7. Pond Design Model Consideration8. Equilibrium Temperature and Surface Heat Flux9. Pond Design Calculation10. Case Study11. Cooling Pond Performance12. Conclusion13. Further Suggestions

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Introduction

Core Type Coreless Type

Fig 1 – Core and Coreless Type of Induction Furnace

Electric Induction Furnace

4

Operating Principle of Coreless Induction Furnace

Electromagnetic induction Connect to a source of AC Create thermal energy Melt the charge Stirring action caused by molten metal

Fig 2 - Simplified Cross Section of Coreless Induction Furnace

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Important Role of Water Cooling

Fig 3 - A Sample Induction Coil with Cooling Water

Water is vital to be success. Need high water quality. Flow velocity of all water

circuit should be monitored.

Cooling water supply temperature should not be below 25°C.

Upper limit of leaving the coil should be no more than 70°C.

If too cold water is allowed, condensation may be formed.

Fig 4 - Sample of the Damaging Induction Coil

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Types of Water Cooling System

The types of water cooling system are as follow: Cooling Pond System Spray Pond System Evaporative Cooling Tower – Open-circuit System Fan-radiator Closed-circuit System Water/water Heat Exchanger Dual System Dual System with Closed-circuit Cooling Tower

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Cooling Pond System

Fig 5 – Sketch of Typical Cooling Pond System

Large ground area Small investment

Hot water inlet Cool water outlet

Water surface

Pond

Process Description

24.33 ft3/min Cool water inlet

Pumps

Hot water outlet

Control panel

Capacitor bank

Furnace 2

Furnace 1

Cooling pond(8,000 ft3)

Fig 6 – Schematic Diagram of Cooling Pond Model

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Layout Description of 0.16 ton Coreless Induction Furnace

Fig 7 - Functional Layout of 0.16 ton Coreless Induction Furnace

Pump

Discharge Pipeline

Suction Pipeline

Capacitor Bank

Furnace No. 1

Cooling Pond

Control Panel

Furnace No. 2

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Design Parameters of Cooling Pond

The hot water or inlet temperature into the pond The cool water or outlet temperature from the pond The operating time occupied in melting The solar heat flux or solar energy identified as the

main heating mechanisms The pond volume and size corresponding to the

equilibrium temperature

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Pond Design Model Consideration

HcQTRTcTVcdt

di ˆˆ)ˆ(

Fig 8 - Illustrative Diagram of Cooling Pond Model

V = volumeT = temperatureA = area

Induction Furnaces

Cooling Pond

V, T

Q, T Ti, R

H

Interchange with Atmosphere

Q =

Out

flow

rat

e

R =

inflo

w r

ate

TE

Tb

Ta

Td

Ts

W

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Equilibrium Temperature and Surface Heat Flux

Windspeed

sc

s

a

ar

br e c

Ground

Subsurfaceconduction

Hot waterinlet

Cool wateroutlet

srR, ToQ, Ti Tsw

W2

Ta

Td

TE

sn anTb

T

Sun

)255.0)((23

1600]255.0)[(

Wf

TTWfT adscE

Fig 9 – Heat Transfer Mechanisms in Cooling Pond

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Pond Design CalculationKnown Data◙ Relative humidity, RH = 62%◙ Ambient air, Ta = 88ºF◙ Dew point, Td = 72ºF◙ Hot water, Ti = 91.4ºF◙ Cold water, To = 82.4ºF◙ Latitude of Yangon, = 16.45 N◙ Wind speed, W = 4 mph◙ Flow rate, Q = 24.37 ft3/min

Assumptions◙ Steady-state (Completely mixed Pond)◙ Inflow rate is equal to outflow rate◙ Ts = T (Completely well-mixed pond)◙ No seepage into or from groundwater◙ Neglect heat conduction between the surrounding soil◙ Heat exchange occurs near the pond surface only◙ Volume, V = constant◙ Density, ρ = constant◙ At time t = 0, T = 28ºC

)Tk(kk.k.dt

dTTrTr 5962491 where,

kr = water retention ratekT = thermal rate

ftftftftV 62050 6000 3 210002050 ftftftA

Pond volume

Pond surface area

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Case StudyData for the Example

Parameter Specified Value

Capacity 0.16 ton

Current frequency 1,000 Hz

Metal overheating temperature 2.912°F

Consumed power 16 kW

Dry bulb temperature 88°F

Relative humidity 62%

Wind speed 4 mph

Entering water temperature 82.4°F

Leaving water temperature 91.4°F

Latitude of Yangon 16.45 N

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Cooling Pond Performance

0

1

2

3

4

5

6

7

8

7000 8000 9000 10000 11000

Pond Area (ft2)

(Fixed on 8 ft depth)

All

owab

le O

pera

ting

Tim

e (h

r)

The results corroborate the fact that the most important variable oncooling pond performance is pond surface area itself, but not is volume.

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Conclusion Cooling system is the important part of coreless

induction furnace.

Cooling ponds are one of the economically competitive alternatives for removing of heat from induction furnaces.

The most important influence factor on the cooling pond configurations is pond surface area.

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Further Suggestions

◙ Extending the baffles in the pond.

◙ Using the heat exchangers.

Highly baffled pond, longitudinal baffles, rectangular dischargeHighly baffled pond, lateral baffles, rectangular discharge

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Spray Pond System

Fig - Sample Spray Pond System Use a number of nozzles Depend on relative humidity

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Fan-radiator Closed-circuit System

Fig - Fan-radiator (closed-circuit) System

Completely enclosed Loss of water is slight

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Water/water Heat Exchanger Dual System

Fig - Dual System with Water/water Heat Exchanger More compact Easier to clean and maintain

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Dual System with Closed-circuit Cooling Tower

Fig - Dual System with Closed-circuit Cooling Tower

Slightly more expensive Lower Piping and pumping costs

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Types of Cooling Tower

Fig - Mechanical Draft Cooling Towers Fig - Natural Draft Cooling Towers

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By using the following equations, 25.04.824.91

4.8265.84

o

v

T

T

)3.0( IPThe type of pond is shallow

51.10)74264(365

360sin45.23

rads 5159.185.86)51.10tan45.16tan(cos 1

hrSo 58.1185.8615

2

)/( 62.34233 ))85.86sin()51.10cos()45.16cos()51.10sin()45.16sin(52.1(

75365

360cos033.015141

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2daymkJ

osc

Declination angle,

The hour angle,

Maximum possible sunshine duration,

The extraterrestrial solar radiation ,

Ref: Magal, B. S. (1999), Solar Power Engineering, Fourth reprint, TATA McGraw Hill Publishing Company Limited, Bombay.

Cooling Pond Area and Volume Calculation

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) /( 62.2034)/( 25.23106 9.11

5.962.018.0

62.3423322 ftdayBtudaymkJsc

sc

FTE59.625917.62

) /( 1060 2ftdayBtue

) /( 73 2ftdayBtuc

) /( 18215100

1217 2ftdayBtusn

) /( 50815100

3386 2ftdayBtuan

) /( 3519 2ftdayBtubr

) /( 38167310603519508182 2ftdayBtun

Clear sky solar radiation,

Equilibrium temperature by using the iterative method,

The net heat flux,

25

) /( 173)59.6265.84(

3816 2 FftdayBtuK

6876.059.624.91

59.624.82

iT

rTi

1

1

4543.0 1

16876.0

rr

Qc

KAr

ˆ

2 5768 )37.24003.14.62(

)1440/173(4543.0

ftA

A

The net heat exchange coefficient,

Normalized intake temperature,

Pond cooling capacity,

Required cooling pond area,

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ftftftftV 62049 5768 3

By implementing to unit depth, the volume of cooling pond is

ftftftft 62050 6000 3 Approximately, the volume is used in the construction.

210002050 ftftftA

)Tk(k62.59k91.4kdt

dTTrTr

From the above volume and area, the relationship between the temperature and operating time is obtained as follows:

Where, kr = water retention rate kT = thermal rate

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Solar Heat Flux

cebransnn

sc

s

a ar

e c

sn an

br

srCloud

Sun

Water surface

Fig – Components of Surface Heat Transfer

where, n = the net heat flux into the water surfacesn = the net solar (short-wave) radiation into the water surface an = the net atmospheric (long-wave) radiation from the water surface br = the back (long-wave) radiation from the water surface e = the evaporative heat flux from the water surface c = the conductive heat flux from the water surface s = the solar radiation at water surfacesr = the reflected solar radiationa = the atmospheric (long-wave) radiation ar = the reflected atmospheric radiation