Presented by
THANT ZIN WIN
Department of Mechanical Engineering
Technological University (Kyaukse)
Mandalay Division, Myanmar
thantm7@gmail.com
Presentation Outlines
1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
11.
12.
13.
Introduction
Operating Principle of Coreless Induction Furnace
Important Role of Water Cooling
Types of Water Cooling System
Layout Description
Design Parameters of Cooling Pond
Pond Design Model Consideration
Equilibrium Temperature and Surface Heat Flux
Pond Design Calculation
Case Study
Cooling Pond Performance
Conclusion
Further Suggestions
2
Introduction
Electric Induction Furnace
Core Type
Coreless Type
Fig 1 – Core and Coreless Type of Induction Furnace
3
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
4
Important Role of Water Cooling



Water is vital to be success.
Need high water quality.
Flow velocity of all water
circuit should be monitored.
Fig 3 - A Sample Induction Coil with Cooling Water



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
5
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
6
Cooling Pond System
Hot water inlet
Cool water outlet
Water surface

Large ground area
 Small investment
Pond
Fig 5 – Sketch of Typical Cooling Pond System
Process Description
Hot water outlet
Furnace 1
Capacitor bank
Cooling pond
(8,000 ft3)
Furnace 2
Control panel
Fig 6 – Schematic Diagram of
Cooling Pond Model
Pumps
24.33 ft3/min
Cool water inlet
7
Layout Description of 0.16 ton Coreless Induction Furnace
Suction Pipeline
Discharge Pipeline
Cooling Pond
Furnace No. 1
Furnace No. 2
Control Panel
Capacitor Bank
Pump
Fig 7 - Functional Layout of 0.16 ton Coreless Induction Furnace
8
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
9
Pond Design Model Consideration
V = volume
T = temperature
A = area
W
R = inflow rate
Q = Outflow rate
Cooling Pond
Interchange with Atmosphere
Ta
H
Td
Q, T
Ti, R
Ts
TE
V, T
Tb
Induction Furnaces
Fig 8 - Illustrative Diagram of Cooling Pond Model
d
( cˆTV )  cˆTi R  QT cˆ  H
dt
10
Equilibrium Temperature and
Surface Heat Flux
Sun
Ta
sc
Td
a
Wind
W
speed 2
s
br
e
c
ar
sr
R, To
Q, Ti
Tsw
Hot water
inlet
sn
Cool water
outlet
TE
an
T
Tb
Subsurface
conduction
Ground
Fig 9 – Heat Transfer Mechanisms in Cooling Pond
sc  f (W )[ Td  0.255Ta ]  1600
TE 
23  f (W )(   0.255)
11
Pond Design Calculation
Known 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
Pond volume
V  6000 ft 3  50 ft  20 ft  6 ft
Pond surface area
A  50 ft  20 ft  1000ft 2
dT

 91.4k r  62.59 kT  (kr  kT )T
dt
where,
kr = water retention rate
kT = thermal rate
12
Case Study
Data 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
Wind speed
62%
4 mph
Entering water temperature
82.4°F
Leaving water temperature
91.4°F
Latitude of Yangon
16.45 N
13
Cooling Pond Performance
Allowable Operating Time (hr)
8
7
6
5
4
3
2
1
0
7000
8000
9000
10000
11000
Pond Area (ft2)
(Fixed on 8 ft depth)
The results corroborate the fact that the most important variable on
cooling pond performance is pond surface area itself, but not is volume.
14
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.
15
Further Suggestions
◙
Extending the baffles in
the pond.
Highly
baffled
pond,
longitudinal
baffles,
rectangular
discharge
Highly
baffled
pond,
lateral baffles,
rectangular
discharge
◙
Using the heat exchangers.
16
17
Spray Pond System
Fig - Sample Spray Pond System
 Use a number of nozzles
 Depend on relative humidity
18
Fan-radiator Closed-circuit System
Fig - Fan-radiator (closed-circuit) System


Completely enclosed
Loss of water is slight
19
Water/water Heat Exchanger
Dual System
Fig - Dual System with Water/water Heat Exchanger


More compact
Easier to clean and maintain
20
Dual System with Closedcircuit Cooling Tower
Fig - Dual System with Closed-circuit Cooling Tower


Slightly more expensive
Lower Piping and pumping costs
21
Types of Cooling Tower
Fig - Mechanical Draft Cooling Towers
Fig - Natural Draft Cooling Towers
22
Cooling Pond Area and Volume Calculation
By using the following equations,
T v 84.65  82.4

 0.25
To
91.4  82.4
( IP  0.3)
The type of pond is shallow
Declination angle,
 360

  23.45sin 
(264  74)  10.51
 365

s  cos1 ( tan16.45tan 10.51)  86.85  1.5159rad
The hour angle,
Maximum possible sunshine duration, S o 
2
 86 .85  11.58hr
15
The extraterrestrial solar radiation ,
360


 51411  0.033cos
 75 

365


(1.52sin(16.45) sin(10.51)  cos(16.45) cos(10.51) sin(86.85))
 34233.62 kJ /(m 2 day)
 sc 
o
24
Ref: Magal, B. S. (1999), Solar Power Engineering, Fourth reprint, TATA McGraw Hill Publishing Company Limited, Bombay.
23
 sc
 9.5 
 0.18  0.62

34233.62
11
.
9


 sc  23106.25 kJ /(m 2 day)  2034.62 Btu /(day ft 2 )
Clear sky solar radiation,
Equilibrium temperature by
using the iterative method,
TE  62.5917  62.59 F
  sn 
  an 
1217
 15  182 Btu /(day ft 2 )
100
3386
 15  508 Btu /(day ft 2 )
100
br  3519Btu /(day ft 2 )
e  1060Btu /(day ft 2 )
c  73 Btu /(day ft 2 )
The net heat flux,
n  182 508 3519 1060 73  3816Btu /(day ft 2 )
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The net heat exchange coefficient,
Normalized intake temperature,
K
3816
 173 Btu /(day ft 2  F )
(84.65  62.59)
82.4  62.59
Ti 
 0.6876
91.4  62.59


Ti 
Pond cooling capacity,
1
1 r
1
0.6876
1 r
r  0.4543
KA
r
cˆQ
(173/ 1440) A
(62.4  1.003 24.37)
 A  5768 ft 2
0.4543
Required cooling pond area,
25
By implementing to unit depth, the volume of cooling pond is
V  5768 ft 3  49 ft  20 ft  6 ft
Approximately, the volume
6000 ft 3  50 ft  20 ft  6 ft
is used in the construction.
A  50 ft  20 ft  1000ft 2
From the above volume and area, the relationship between the
temperature and operating time is obtained as follows:
dT

 91.4k r  62.59k T  (k r  k T )T
dt
Where, kr = water retention rate
kT = thermal rate
26
Solar Heat Flux
Sun
sc
br
Cloud
s
sr
a
e
c
ar
Water surface
sn
an
n  sn  an  br e  c
Fig – Components of Surface Heat Transfer
where,
n = the net heat flux into the water surface
sn = 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 surface
sr = the reflected solar radiation
a = the atmospheric (long-wave) radiation
ar = the reflected atmospheric radiation
27