Project tri duct

A
Project Report on
Tri Duct Heat Exchanger
Submitted in partial fulfillment of
The requirement for the award from
DEPARTMENT OF CHEMICAL ENGINEERING
Submitted by
HARISH K
Under the guidance of
Smt. J. Gouthami, (H.O.D)
Sri. S. Vijay Kumar (Sr.Lecturer)
DEPARTMENT OF CHEMICAL
ENGINEERING

DEPARTMENT OF CHEMICAL ENGI-
NEERING
Approved by
Andhra University, Hyderabad
CERTIFICATE
This is to certify that the project entitled, Tri Duct Heat Ex-
changer is the bonafied work of Mr. K HARISH bearing PIN No: 09096 -
CH - 006 from Department of chemical engineering 7th semester (2012),
submitted in the partial fulfillment of his course period.
J.Gouthami S. Vijay Kumar
(Head of the Department) (Guide)

Contents
 List of Figures
 List of Tables
 List of symbols
 INTRODUCTION
 Heat Transfer
 Project Background
 Functions of Heat exchanger
 Flow arrangements of Heat Exchanger
 Types of Heat Exchanger
 TRI DUCT HEAT EXCHANGER
 Introduction
 Construction
 Flow arrangements
 TDHE Fig.

 THEORY PART
 Overall resistance
 Dimensionless values
 Forced & Natural Convection
 Film Co-efficient
 PROBLEMATIC PART
 Introduction
 Assumptions
 Calculation
 Results

List of Figures
Figure No. Title
1.1. Co-Current (or) Parallel flow
1.2. Counter flow
1.3. Cross flow
2.1. Double pipe heat exchanger
3.1. Heat transfer through boundary layer
List of Tables
Table No. Title
2.2. Table of Diameters of duct according to TEMA
4.2. Table of Properties of fluids

List of Symbols
Ai --------Area of the inner duct
Am --------Area of the middle duct
Ao --------Area of the Outer duct
CP --------Specific heat
D1 --------Outer diameter of inner duct
D2 --------Inner diameter of middle duct
D3 --------Inner diameter of Outer duct
Di --------Inner diameter of inner duct
Dm --------Inner diameter of middle duct
Do --------Inner diameter of Outer duct
Doi --------Outer diameter of inner duct
Dom --------Outer diameter of middle duct
DoO --------Outer diameter of Outer duct
Dii --------Inner diameter of inner duct
Dim --------Inner diameter of middle duct
DiO --------Inner diameter of Outer duct
Dwi --------Log mean diameter of inner duct
Dwm --------Log mean diameter of middle duct
DwO --------Log mean diameter of Outer duct

Gi --------Mass velocity through inner duct
Gm --------Mass velocity through middle duct
GO --------Mass velocity through Outer duct
hi --------Heat transfer coefficient of inner duct
hm --------Heat transfer coefficient of middle duct
hO --------Heat transfer coefficient of Outer duct
k --------Thermal conductivity
mi --------Mass flow rate of inner duct
mm --------Mass flow rate of middle duct
mO --------Mass flow rate of Outer duct
NRe --------Reynolds’s number
NPr --------Prandtl’s number
NNu --------Nusselt’s number
u --------Velocity
Uoi --------Over all heat transfer coefficient of inner duct
Uom --------Over all heat transfer coefficient of middle duct
UoO --------Over all heat transfer coefficient of Outer duct
x --------Thickness of the duct
ρ --------Density of fluids
µ --------Viscosity of fluids

INTRODUCTION
1.1 HEAT TRANSFER
It is well established fact that if two bodies of different temperatures
are brought into thermal contact, heat flows from a body at high tempera-
ture to that at lower temperature [second law of thermodynamics]. The net
flow of heat is always in the direction of temperature decrease. Thus, heat is
defined as a form of energy which is in transit between a hot source and
cold receiver. The transfer of heat solely depends on the temperature of the
two parts of the system. In other words, temperature can be termed as a lev-
el of thermal energy i.e., high temperature of the body is the indication of
high level of heat energy content of the body.
Whenever the temperature difference (driving force for heat transfer) exists
between two parts of the system, the heat may flow by one or more of the
three basis mechanisms, namely, conduction, convection, and radiation.
Conduction
It is the transfer of heat from one part of the body to the another part
of the body or from one body to another which is in physical contact to it,
without appreciable displacement of particles of the body. In metallic solids
, thermal conduction results from the motion of unbound electrons. It is re-
stricted to flow of heat in solids.
Convection
It is the transfer of heat from one point to another point within a fluid
(gas or liquid) by mixing of hot and cold portions of the fluid. It is attribut-
ed to the macroscopic motion of the fluid. Convection is restricted to flow
of heat in fluids and closely associated with the fluid mechanics.
Radiation
Radiation refers to the transfer of heat energy from one body to an-
other, not in contact with it, by electromagnetic waves through space.

Boundary layers
Since for every fluid flowing with low flow rates there will be a re-
sistance offered to the transfer of heat due to the formation of a static layer
of that fluid around the walls. This layer is called boundary layer. Being a
static layer it offers resistance to the flow of heat through the wall. And this
resistance can be overcome by increasing the flow rate of the passing fluid.
This results to the decrease of the thickness of the boundary layer.
If the resistance to heat transfer is considered as lying within the film cover-
ing the surface, the rate of heat transfer Q is given as
Q = kA ΔT/x
The effective thickness x is not generally known and therefore the
equation is usually re-written in the form :
Q = hA ΔT
This is the basic equation for the rate of heat transfer by convection
under steady state conditions.
Where ‘h’ is called as film heat transfer co-efficient or surface co-efficient
or simply film co-efficient.
Numerically, heat transfer co-efficient (h) is the quantity of heat
transferred in unit time through unit area at a temperature difference of one
degree between the surface and surrounding.

PROJECT BACKROUND :
The heat exchanger is a device which transferred the heat from hot medium
to cold medium without mixed both of medium since both mediums are
separated with a solid wall generally. There are many types of heat ex-
changer that used based on the application. For example, double pipe heat
exchanger is used in chemical process like condensing the vapor to the liq-
uid. When to construct this type of heat exchanger, the size of material that
want to uses must be considered since it affected the overall heat transfer
coefficient. For this type of heat exchanger, the outlet temperature for both
hot and cold fluids that produced is estimated by using the best design of
this type of heat exchanger.
HEAT EXCHANGER :
Heat exchanger is a device, such as an automobile radiator, used to transfer
heat from a fluid on one side of a barrier to a fluid on the other side without
bringing the fluid into direct contact (Fogies, 1999). Usually, this barrier is
made from metal which has good thermal conductivity in order to transfer
heat effectively from one fluid to another fluid. Besides that, heat exchanger
can be defined as any of several devices that transfer heat from a hot to a
cold fluid. In engineering practical, generally, the hot fluid is needed to cool
by the cold fluid. For example, the hot vapor is needed to be cool by water
in condenser practical. Moreover, heat exchanger is defined as a device
used to exchange heat from one medium to another often through metal
walls, usually to extract heat from a medium flowing between two surfaces.
In automotive practice, radiator is used as heat exchanger to cool hot water
from engine by air surrounding same like intercooler which used as heat
exchanger to cool hot air for engine intake manifold by 4 air surrounding.
Usually, this device is made from aluminum since it is lightweight and good
thermal conductivity.

1.3 FUNCTIONS OF HEAT EXCHANGER :
Heat exchanger is a special equipment type because when heat exchanger is
directly fired by a combustion process, it becomes furnace, boiler, heater,
tube-still heater and engine. Vice versa, when heat exchanger make a
change in phase in one of flowing fluid such as condensation of steam to
water, it becomes a chiller, evaporator, sublimated, distillation-column re-
boiler, still, condenser or cooler-condenser. Heat exchanger may be de-
signed for chemical reactions or energy-generation processes which become
an integral part of reaction system such as a nuclear reactor, catalytic reac-
tor or polymer (Fogiel, 1999). Normally, heat exchanger is used only for the
transfer and useful elimination or recovery of heat without changed in
phase. The fluids on either side of the barrier usually liquids but they can be
gasses such as steam, air and hydrocarbon vapor or can be liquid metals
such as sodium or mercury. In some application, heat exchanger fluids may
use fused salts.

1.4 FLOW ARRANGEMENTS OF HEAT EXCHANGER :
There are three basic flow arrangements,
1. Parallel flow/Co-current flow
2. Counter current flow and
3. Cross flow.
Consider a double pipe heat exchanger wherein hot fluid is flowing through
inside pipe and cold fluid is flowing through annular space for explanation
of parallel and counter current flow.
When both the fluids flow in same direction from one end of the heat ex-
changer to the other end, then the flow is called co-current (or) parallel
flow.
Such flow is shown in Fig. 1.1.

When the fluids are flowing through the heat exchanger in opposite direc-
tions with respect to each other (i.e. one fluid enters at one end of heat ex-
changer and other fluid enters at opposite end of the heat exchanger), then
the flow is termed as counter current flow.
It is shown on Fig. 1.2.
When the fluids are directed at the right angles to each other through heat
exchanger, then the flow arrangement is called cross flow.
It is show in Fig. 1.3.

1.5 CLASSIFICATION OF HEAT EXCHANGERS :
There are mainly three types of Heat exchangers which are most used in
industries.
1. Double pipe Heat Exchanger
2. Shell and tube Heat Exchanger and
3. Plate-type Heat Exchanger.

2 TRI - DUCT HEAT EXCHANGER
2.1 INTRODUCTION :
It is one type of heat exchanger which is a combination of double pipe heat
exchanger and shell and tube heat exchanger. It is mainly associated to in-
crease the surface contact to the hot fluid to the cold fluid more than that of
double pipe heat exchanger and occupying the almost same space as the
double pipe heat exchanger does.
Finally it can be employed in those industries where :-
1) the heat transfer rate should be more than that of double
pipe heat exchanger and
2) the occupying space of the instrument should be less than that of shell
and tube heat exchanger.
Hence, the main purpose of the Tri - Duct Heat Exchanger is to removing
(or) transferring the heat in the center of the hot fluid flowing in the duct.
Demonstration of the above statement :-
Let us consider a hot fluid flowing in the tube of an double pipe heat
exchanger and a cold fluid which is passing counter currently between the
annular space of the double pipe heat exchanger,
as shown in the Fig. 2.1.
If we observe it according to the rate of heat transfer, there will be
two main resistance offered to the heat transfer.
1) Resistance offered by the tube wall (metal wall)
2) Resistance offered by the boundary layer.

Hence, the first resistance which is due to the tube wall can be re-
duced by decreasing the thickness(x) of the metal wall.
And the second one is caused by the friction offered by the inside
wall of the tube which causes to static arrangement of water molecules and
forms a layer which causes resistance. Well this problem can be overcome
by increasing the flow rate of the fluid which produces the turbulence and
eddies in the fluid. These eddies will create some disturbance in the static
layer and make the molecules in that layer to flow with them.
But here the main thing we have to consider is that “As the liquid flows, the
flow rate increases from the boundary layer to the center point of the liq-
uid”.
This notifies us that the fluid which is flowing in contact with the boundary
layer will have much more heat transfer rate than the fluid flowing in the
center of the pipe.
To overcome this problem within a given space Tri - Duct Heat Exchanger
is introduced.
2.2 CONTRUCTION OF TRI-DUCT HEAT EXCHANGER
Tri - Duct Heat Exchange is almost similar to double pipe heat ex-
changer. It consists of concentric pipes, connecting tees, return heads, and
return bends. The packing glands will support the inner, middle and outer
pipes. The tees are provided with nozzles or screwed connections for per-
mitting the entry and exit of the annular fluid which crosses from one leg to
the other through the return head. The return bend connects two legs of in-
ner pipes to each other. This exchanger can be very easily assembled in any
pipe fitting shop as it consists of standard parts and it provides inexpensive
heat transfer surface. In this exchanger, one of the fluids flow through the
middle duct and other fluid flows through the inner and outer pipes either in
co-current or in counter current fashion.
The tri-duct heat exchanger is very attractive where the total heat transfer
surface required is small, 9.29 m2
to 14 m2
or less. This is simple in con-
struction, cheap and easy to clean.
The major difference according to the double pipe heat exchanger is that it
consists of another pipe embedded within the inner tube, making the inner
tube as middle one.

And here, hot fluid flows within the middle pipe counter currently to the
cold fluid which flows in the inner tube and annular space (or) outer tube.
This type of construction makes the hot fluid to transfer higher rates of heat
to the cold fluid.
Outer diameter, inches Inner diameter, inches
2 1 1/4
2 1/2 1 1/4
3 2
4 3
2.2 Table of Diameters of ducts according to TEMA :-
2.3 FLOW ARRANGEMENTS :-
In this heat exchanger according to the three types of flows the coun-
ter current flow will be good to achieve higher heat transfer rates.

3 THEORY PART
3.1. OVERALL RESISTANCE :-
Q = hA ΔT
This is the basic equation for the rate of heat transfer by convection
under steady state conditions.
Where ‘h’ is called as film heat transfer co-efficient or surface co-efficient
or simply film co-efficient.
Numerically, heat transfer co-efficient (h) is the quantity of heat transferred
in unit time through unit area at a temperature difference of one degree be-
tween the surface and surrounding.
As shown in the Fig.3.1.
The temperature change from T1 to T2 is taking place in a hot fluid
film of thickness x1. The rate of heat transfer through this film by conduc-
tion is given by :
Q = k1 A1 (T1 -T2) / x1
The effective film thickness x1 depends upon the nature of flow and
nature of surface, and is generally not known. Therefore the equation is
usually rewritten as :
Q = hi Ai (T1 -T2)

where hi is known as inside heat transfer co-efficient or surface co-
efficient or simply film co-efficient.
As seen from the above equation, the film co-efficient is the measure
of rate of heat transfer for unit temperature difference and unit surface of
heat transfer and it indicates the rate or speed of transfer of heat by a fluid
having variety of physical properties under varying degrees of agitation. In
SI system, it has units of W/(m2
.K).
The overall resistance to heat flow from hot fluid to cold fluid is
made up of three resistances in series. they are :
1. Resistance offered by film of hot fluid
2. Resistance offered by the metal wall and
3. Resistance offered by film of cold fluid.
Rate of heat transfer through the metal wall is given by equation :
Q = kAw (T2 -T3) / xw
here, Aw - log mean area of pipe
xw - thickness of wall pipe
k - thermal conductivity of material of pipe.
The rate of heat transfer through cold fluid film is given by
Q = hoAo (T3 -T4)
here, ho is the outside film co-efficient (or) individual heat transfer co-
efficient.
therefore the equation can be written as (T1 -T2) = Q / hiAi
Similarly the equation for the metal wall can be written as
(T2 -T3) = Q / (kAw/xw)

and
(T3 -T4) = Q / hoAo
Adding the above all equations, we get :
(T1 -T2) + (T2 -T3) + (T3 -T4) = Q [1/ hiAi + 1/ (kAw/xw) + 1/ hoAo]
Therefore, (T1 -T4) = Q [1/ hiAi + 1/ (kAw/xw) + 1/ hoAo]
here, T1 and T4 are the average temperatures of hot and cold fluids respec-
tively.
Therefore equation similar to above equation in terms of overall heat
transfer co-efficient can be written as :
Q = Ui Ai (T1 -T4) (or) Q = UoAo (T1 -T4)
here, Ui or Uo are the overall heat transfer co-efficient based on inside and
outside area respectively.
Resistance form of overall coefficient :-
Reciprocal of the overall heat transfer co-efficient can be considered
as the overall resistance and it may be given by equation :
1/Uo = 1/hi (Do/Di) + xw/k (Do/Dw) + 1/ho
The individual terms on R.H.S. of the above equation represents the
individual resistances of the two fluids and a metal wall.
The overall temperature drop is proportional to 1/U. Similarly, indi-
vidual temperature drops in the two fluids and metal wall are proportional
to individual resistance.

3.2 DIMENSIONLESS QUANTITIES :-
Reynolds’s number = Duρ/µ
Nusselt’s number = hL/k
Prandtl’s number = Cpµ/k
3.3 FORCED AND NATURAL CONVECTION :-
For natural convection :-
NNu = f(NPr, NGr)
For forced convection, Reynolds’s number influences the heat trans-
fer characteristics and the Grashof’s number may be omitted. Thus for
forced convection
NNu = f(NRe, NPr)

3.4 HEAT TRANSFER CO-EFFICIENTS :-
In laminar flow
The sider- tate equation for the calculation of heat transfer coefficient
for laminar flow in horizontal ducts is—
NNu = 1.86 [(NRe)(NPr)(D/L)]1/3
[µ/µw]0.14
In turbulent flow
The Dittus-Boelter equation for the calculation of heat transfer coef-
ficient for turbulent flow in horizontal ducts is—
For heating :
NNu = 0.023 (NRe)0.8
(NPr)0.4
For cooling :
NNu = 0.023 (NRe)0.8
(NPr)0.3
In transition flow
For transition region i.e. for 2100 < NRe <10000, the following empirical
equation can be used.
NNu = 0.116 [(NRe)2/3
-125] (NPr)1/3
[1+(D/L)2/3
] [µ/µw]0.14

4 PROBLEMATIC PART
4.1. INTRODUCTION :
Being our equipment is a Tri Duct Heat Exchanger, the hot fluid
should be flowing through the middle pipe and the cold fluid which is used
to absorb the heat from the hot fluid should be flowing through the inner
and outer ducts.
Hence, the ducts should be made up of Stainless Steel and the flow is
counter current.
Other moulding like fines on the tubes can be used to increase the
heat transfer rate. When these are attested there will be a negligible loss inn
flow rate but being negligible they are not taken into account.
4.2. ASSUMPTIONS :
Let,
the hot fluid (middle) be ethylene glycol
the cold fluid (inner, outer) be toluene
the entering temperature of the hot fluid be 85 C
the entering temperature of the cold fluid be 30 C
the outside diameter of the outer pipe be 90mm
the outside diameter of the middle pipe be 75mm
the outside diameter of the inner pipe be 30mm
the wall thickness of all the pipes be 3mm
the flow rates of all the fluids be 5000kg/h

Property Ethylene glycol Toluene
Density
Specific heat
Thermal con-
ductivity
Viscosity
1080 kg/m3
2.680 kJ/(kg.K)
0.248 W/(m.K)
3.4 x 10-3
Pa.s
840 kg/m3
1.80 kJ/(kg.K)
0.146 W/(m.K)
4.4 x 10-4
Pa.s
Table :- 4.2. Properties of fluids
Thermal conductivity of metal pipes is 46.52 W/(m.K), ethylene gly-
col is flowing through the middle and toluene is flowing through the inner
and outer pipes counter current to each other.

4.3. CALCULATION :
For toluene flowing through the inner pipe :
mass flow rate of toluene = mi
= 5000 kg/h
= 1.388 kg/s
Outer diameter of inner pipe = 30 mm
Inner diameter of inner pipe = 30 - 2x3
= 24 mm
= 0.024 m
Area of inner pipe = A i
= (π/4) D2
i
= (π/4) (0.024)2
A I = 0.000452 m2
Mass velocity G = m i/A i
= 1.388/0.000452
= 3070.7 kg/(m2
.s)
NR = D iuρ/µ
= D iG/µ
Since,
Viscosity of the toluene µ = 4.4 x 10-4
Pa.s
= 4.4 x 10-4
kg/(m.s)
Specific heat of toluene Cp = 1800 J/(kg.K)
Thermal conductivity of toluene k = 0.146 W/(m.K)

NRe= (0.024 x 3070.7)/ 4.4 x 10-4
= 1,67,492
NPr= Cpµ/k
= 1800 x 4.4 x 10-4
/ 0.146
= 5.42
As NRe > 10,000 we can use the Dittus - Boelter equation [for heating]
NNu= 0.023 (NRe)0.8
(NPr)0.4
= 0.023 (167492) 0.8
(5.42) 0.4
= 683.1
Since NNu = hiDi/ k
hiDi/ k = 683.1
= 683.1 x 0.146 /0.024
hi = 4155 W/(m2
.K)
-------------------------------------------------------------------------------------------

For Ethylene glycol flowing through the middle pipe :
mass flow rate of ethylene glycol = mm
= 5000 kg/h
= 1.388 kg/s
Outer diameter of middle pipe = 75 mm
Inner diameter of middle pipe = 75 - 2x3
= 69 mm
= 0.069 m
Equivalent diameter of middle pipe = Dm
= D2
2
- D1
2
/ D1
= (0.0692
- 0.032
) /0.03
= 0.128 m
Area of cross section for flow = A m
= (π/4) [D2
2
- D1
2
]
=(π/4)[(0.0692
- 0.032
)]
= 0.00303 m2
Mass velocity Gm = m m
/Am
= 1.388/0.00303
= 458.08 kg/(m2
.K)
NRe = D muρ/µ
= D mGm/µ

Since,
Viscosity of the ethylene glycol µ = 3.4 x 10-3
Pa.s
= 3.4 x 10-3
kg/(m.s)
Specific heat of ethylene glycol Cp = 2680 J/(kg.K)
Thermal conductivity of ethylene glycol k = 0.248 W/(m.K)
NRe = (0.128 x 458.08)/ 3.4 x 10-3
= 17,245
NPr = Cpµ/k
= 2680 x 3.4 x 10-3
/ 0.248
= 36.74
As NRe > 10,000 we can use the Dittus - Boelter equation [for cooling]
NNu = 0.023 (NRe) 0.8
(NPr) 0.3
=0.023 (17245)0.8
(36.74)0.3
= 166.18
Since NNu = hmDm/ k
hmDm/ = 166.18
= 166.18 x 0.248 /0.128
hm = 321.97 W/(m2
.K)
-------------------------------------------------------------------------------------------

For toluene flowing through the outer pipe :
mass flow rate of toluene = mo
= 5000 kg/h
= 1.388 kg/s
Outer diameter of outer pipe = 90 mm
Inner diameter of outer pipe = 90 - 2x3
= 84 mm
= 0.084 m
Equivalent diameter of outer pipe = Do
= D3
2
- D2
2
/ D2
= (0.0842
- 0.0692
) /0.069
= 0.033 m
Area of cross section for flow = A o
= (π/4) [D3
2
- D2
2
]
= (π/4) [(0.0842
- 0.0692
)]
= 0.0018 m2
Mass velocity Go= mo
/Ao
= 1.388/0.0018
= 771.1 kg/(m2
.s)
NRe = D ouρ/µ
= D oGo/µ
Since, Viscosity of the toluene µ = 4.4 x 10-4
Pa.s

= 4.4 x 10-4
kg/(m.s)
Specific heat of toluene Cp = 1800 J/(kg.K)
Thermal conductivity of toluene
k = 0.146 W/(m.K)
NRe = (0.033 x 771.1)/ 4.4 x 10-4
= 57,832
NPr = Cpµ/k
= 1800 x 4.4 x 10-4
/ 0.146
= 5.42
As NRe > 10,000 we can use the Dittus - Boelter equation [for heating]
NNu = 0.023 (NRe)0.8
(NPr)0.4
=0.023 (57,832)0.8
(5.42)0.4
= 291.78
Since NNu = hoDo/ k
hoDo/ k = 291.78
= 291.78 x 0.146 /0.033
ho = 1,290.9 W/(m2
.K)
-------------------------------------------------------------------------------------------

Over all heat transfer co-efficient :-
Log mean diameter of inner pipe = Dwi
=(0.03-0.024)/[ln (0.03/0.024)]
= 0.0246 m
Over all heat transfer co-efficient based on the outside area of
inner pipe
(UOi )
1/UOi = [(1/hO) + (1/hm) + (1/hi)] [(DOi/Dii) + (x/k)] [DOi/Dwi]
= [(1/1290.9) + (1/321.97) + (1/4155)] + [(0.03/0.024) +
(0.003/46.52)] + [(0.03/0.0246)]
= (4.119 x 10-3
) (1.25) (1.2195)
= 6.278 x 10-3
1/UOi = 6.278 x 10-3
UOi = 159.28 W/(m2.
K)

Log mean diameter of middle pipe = Dwm
=(0.075-0.069)/[ln
(0.075/0.069)]
= 0.0719 m
Over all heat transfer co-efficient based on the outside area
of middle pipe
(UOm)
1/UOm = [(1/hO) + (1/hm) + (1/hi)] [(DOm/Dim) + (x/k)] [DOm/Dwm]
= [(1/1290.9) + (1/321.97) + (1/4155)] + [(0.075/0.069) +
(0.003/46.52)] + [(0.075/0.071)]
= (4.119 x 10-3
) (1.153) (1.056)
= 5.015 x 10-3
1/UOm = 5.015 x 10-3
UOm = 199.4 W/(m2.
K)

Log mean diameter of outer pipe = Dwo
=(0.09-0.084) /[ln (0.09/0.084)
= 0.086 m
Over all heat transfer co-efficient based on the outside area of
outer pipe
(UoO)
1/UoO = [(1/hO) + (1/hm) + (1/hi)] [(DoO/DiO) + (x/k)] [DoO/DwO]
= [(1/1290.9) + (1/321.97) + (1/4155)] + [(0.09/0.084) +
(0.003/46.52)] + [(0.09/0.086)]
= (4.119 x 10-3
) (1.071) (1.046)
= 4.6143 x 10-3
1/UoO = 4.6143 x 10-3
UoO = 216.7 W/(m2.
K).
-------------------------------------------------------------------------------------------

APPENDICES
Transfer of heat from one place to another with or without any medium is
called heat transfer.
Conduction
It is the transfer of heat from one part of the body to the another part of the
body or from one body to another which is in physical contact to it, without
appreciable displacement of particles of the body.
Convection
It is the transfer of heat from one point to another point within a fluid (gas
or liquid) by mixing of hot and cold portions of the fluid. It is attributed to
the macroscopic motion of the fluid.
Radiation
Radiation refers to the transfer of heat energy from one body to another,
not in contact with it, by electromagnetic waves through space.
Boundary layers
Since for every fluid flowing with low flow rates there will be a resistance
offered to the transfer of heat due to the formation of a static layer of that
fluid around the walls. This layer is called boundary layer.
Parallel flow
When both the fluids flow in same direction from one end of the heat ex-
changer to the other end, then the flow is called co-current (or) parallel
flow.
Counter flow
When the fluids are flowing through the heat exchanger in opposite direc-
tions with respect to each other (i.e. one fluid enters at one end of heat ex-
changer and other fluid enters at opposite end of the heat exchanger), then

the flow is termed as counter current flow.
Cross flow
When the fluids are directed at the right angles to each other through heat
exchanger, then the flow arrangement is called cross flow.
Thermal conductivity
It is the quantity of heat passing through a quantity of material at unit thick-
ness with unit heat flow area in unit time when temperature difference of
maintained across the opposite faces of material.

Project tri duct

Recommended

Recommended

More Related Content

What's hot

What's hot (20)

Similar to Project tri duct

Similar to Project tri duct (20)

Recently uploaded

Recently uploaded (20)

Project tri duct