NOTE

Every effort has been made to ensure that the information contained in this manual is accurate. Should an error be discovered please inform the company in writing, giving full details. Any experimental results given are for guidance only and are not guaranteed as exact answers that can be obtained for a given apparatus.

Sample calculations are just for the teacher guidance and are not suppose to be necessarily remains the same.

If there is any slip up in readings, formulation and apparatus or you need any modification in Current apparatus EES is warmly welcome your opinions and implications

Table of Contents1. INTRODUCTION...................................................................................................................................3

2. DESCRIPTION.......................................................................................................................................4

3. EXPERIMENTAL CAPABILITIES..............................................................................................................5

4. THEORY................................................................................................................................................6

4.1.1. Heat Exchangers..................................................................................................................6

4.1.2. Types of Heat Exchanger......................................................................................................6

4.1.3. Co-current (Parallel) flow.....................................................................................................7

4.1.4. Counter current flow...........................................................................................................7

4.1.5. Crossed flow........................................................................................................................7

4.1.6. Design and Construction......................................................................................................7

4.2. Shell and Tube Heat Exchanger:..................................................................................................7

4.3. Heat Balance................................................................................................................................8

4.4. Heat Transfer...............................................................................................................................9

4.5. Shell-side Heat-transfer Coefficient, hs and Pressure Drop, Ps (Kern’s Method).......................11

5. Procedure..........................................................................................................................................14

5.1. General Operating Procedure....................................................................................................14

5.2. General Shut-down Procedure..................................................................................................14

6. CALCULATION DATA..........................................................................................................................15

7. SPECIMEN CALCULATIONS:................................................................................................................23

1. INTRODUCTIONA heat exchanger is a piece of equipment built for efficient heat transfer from one medium to another. The media may be separated by a solid wall to prevent mixing or they may be in direct contact. They are widely used in space heating, refrigeration, air-conditioning, power plants, chemical plants, petrochemical plants, petroleum refineries, natural gas processing, and sewage treatment. The classic example of a heat exchanger is found in an internal combustion engine in which a circulating fluid known as engine coolant flows through radiator coils and air flows past the coils, which cools the coolant and heats the incoming air.

2. DESCRIPTION

3. EXPERIMENTAL CAPABILITIESEnergy balance determinationTemperature profile in counter current flowLog mean temperature differenceHeat transfer coefficientFlow rate effects on heat transfer rateHeat loss estimation

Specificationsa) Shell & Tube Heat Exchanger:Tube O.D. (do): 10.0 mmTube I.D. (di): 8.0 mmTube Length (L): 500.0 mmTube Count (Nt): 13 (single pass)Tube Pitch (pt): 18.2 mmTube arrangement: non-cumulative triangularShell O.D.: 123.9 mmShell I.D. (Ds): 116.06 mmBaffle Count: 8Baffle Cut (Bc): 40%Baffle Distance (lB): 53.3 mmTube-to-Baffle Clearance (ct): 0 in. (0 mm)Material of Construction: stainless steelNumber of tube Rows 3

a) Instrumentations:Measurements of inlet and outlet temperatures for hot water and cold water streams Measurements of flow rates for the hot water and cold water circuits Measurements of pressure drops across the heat exchangers

b) Control Panel:To mount all the necessary digital indicators, temperature controller, selector switches, on/off switches, etc.

General RequirementsCooling water: Laboratory tap water,

Drainage point

4. THEORY

4.1.1. Heat Exchangers

Heat exchangers are devices designed to transfer heat from one fluid to another without the fluids coming into contact.

4.1.2. Types of Heat Exchanger

Shell-and-tube heat exchanger: The most common type of heat exchanger in industrial applications.

They contain a large number of tubes (sometimes several hundred) packed in a shell with their axes parallel to that of the shell. Heat transfer takes place as one fluid flows inside the tubes while the other fluid flows outside the tubes through the shell.

4.1.3. Co-current (Parallel) flow

As the name suggests, the flow of the hot and the cold fluid is taking place in the same direction in this case. As the graph shows, the temperature difference between the hot and the cold fluid keeps on decreasing from one end to the other.

4.1.4. Counter current flow

In this setup, the hot fluid enters from one end of the exchanger and the cold from the opposite end. This results in nearly constant temperature difference between the hot and the cold fluid. This is a significant aspect and makes counter current exchangers preferable over co-current exchangers. We will discuss this point later when we talk about LMTD.

4.1.5. Crossed flow

The cold and the hot fluid flow axis is at an angle to each other and hence, the fluids cross each other in this arrangement. The most common type of crossed flow exchanges has the angle between axes as 90 degrees.

4.1.6. Design and Construction

Shell and heat tube exchangers-It finds application in a variety of industries and is, without doubt, one of the most widely used exchangers. It has a series of tubes which is enclosed by a shell. One fluid flows inside the tubes while the other liquid flows over the outside walls of the tubes which, basically, is the shell. It's highly recommended for places where there's a need for high heat transfer coefficient as the number of tubes can be increased depending on the need. Due to its unique shape, it finds use in high pressure applications.

Plate and frame heat exchanger-This exchanger consists of a series of thin plates normal to the direction of flow of the fluids. The plates provide a large surface area for heat exchange and are, at some places, more convenient than the shell and heat tube exchanger primarily because of its unique shape.

4.2. Shell and Tube Heat Exchanger: ConstructionTubes-The tubes provide the heat transfer area in a shell and tube heat exchanger. The tubes in a shell and tube heat exchanger are arranged in various arrangements. They are enclosed by a shell around them. They are available in various sizes and shapes according to B.W.G

(Birmingham wire gauge) system. The selection of wall thickness of tube depends on maximum operating pressure and corrosion characteristics.

Tube Pitch-Various aspects have to be kept in mind while designing a shell and heat tube exchanger. The tubes cannot be made very close to each other as that would then leave very less amount of metal between the drilled tubes holes in tube sheets attached at the ends of the exchanger. And if the space between the tubes is very high, it would result in less surface area which in turn, would affect the efficiency of the exchanger. Hence, an optimum distance should be maintained. The shortest distance between centers of two adjacent tubes is called the tube pitch, should not be less than 1.25 times the tube diameter.

Shell- As shown in the figure, the shell is the outer casing of the heat exchanger. One fluid flows between the outer wall of the heat exchanger and inner wall of the shell while the other flows inside the tube. Shell has a circular cross section and selection of material of the shell depends upon the corrosiveness of the fluid and the working temperature and pressure. Carbon steel is a common material for the shell under moderate working conditions.

Baffles-These are panels responsible for obstructing and redirecting the flow of fluid in the shell side of an exchanger. They are situated normal to the walls of the shell and force the liquid to flow at right angles to the axis of the tubes. This increases turbulence resulting in greater heat transfer. Also, the baffles help in keeping the tubes from sagging and increase the strength of the tubes by preventing their vibration.

4.3. Heat BalanceFor a parallel-flow shell and tube heat exchanger with one tube pass and one shell pass shown in Figure 2a, the heat balance is given as:mt Cpt (t2 - t1) = ms Cps(T1 - T2) = q (Eq.1a)Similarly, for the counter flow shell and tube heat exchanger with one tube pass and one shell pass shown in Figure 2b, the heat balance is given as:mt Cpt (t2 - t1) = ms Cps(T1 - T2) = q (Eq.1b)

Where,mt = mass flow rate of cold fluid in the tube (kg.s-1)ms = mass flow rate of hot fluid in the shell (kg.s-1)Cpt = specific heat of cold fluid in the tube (kJ.kg-1.°C-1)Cps = specific heat of hot fluid in the shell (kJ.kg-1.°C-1)t1, t2 = temperature of cold fluid entering/leaving the tube (°C)T1, T2 = temperature of hot fluid entering/leaving the shell (°C)

q = heat exchange rate between fluid (kW)

4.4. Heat TransferThe general equation for heat transfer across the tube surface in a shell and tube heat exchanger is given by:q = Uo Ao Tm = Ui Ai Tm (Eq. 2)

Where,Ao = outside area of the tube (m2)Ai = inside area of the tube (m2)Tm = mean temperature difference (°C)Uo = overall heat transfer coefficient based on the outside area of the tube (kW.m-2.°C-1)Ui = overall heat transfer coefficient based on the inside area of the tube (kW.m-2.°C-1)

The coefficients Uo is given by:

Where,ho = outside fluid film coefficient (kW.m-2.°C-1)hi = inside fluid film coefficient (kW.m-2.°C-1)hod = outside dirt coefficient (fouling factor) (kW.m-2.°C-1)hid = inside dirt coefficient (kW.m-2.°C-1)Kw = thermal conductivity of tube wall material (kW.m-1. °C-1)do = tube outside diameter (m)di = tube inside diameter (m)

The mean temperature difference for both parallel and counter flow shell and tube heat exchanger with single shell pass and single tube pass is normally expressed in terms of log-mean temperature difference,

)(

)(ln

)()(

)/ln(

42

31

4231

21

21

TT

TT

TTTT

TT

TTTlm

For a more complex heat exchanger, such as 1:2 heat exchangers an estimate of the true temperature difference for Eq. 2 is given by

Tm = Ft Tlm

Where Ft is the temperature correction factor as a function of two dimensionless temperature ratios R and S:

Having calculated R and S, then Ft is determined from the standard correction factor figures.

Tube-side Heat-transfer Coefficient, hi and Pressure Drop, PtFor turbulent flow, Sieder-Tate equation can be used:

14.0

33.08.0 Pr

weu CRN

de

KCRh f

wei

14.0

33.08.0 Pr

Re = Reynolds Number = f

etf du

Nu = Nusselt Number = f

ei

k

dh

Pr = Prandtl Number = f

fp

k

C

de = equivalent (or hydraulic) diameter (m) = 4 x (cross-sectional area of flow) / wetted perimeter

= di for tubesGt = mass velocity, mass flow per unit area (kg/ s.m2)Viscosity of fluid=μf

µf = fluid density (kg.m-3)ut = fluid velocity in tube (m.s-1)Cp = fluid specific heat, heat capacity (J/kg. °C)C = 0.023 for non-viscous liquids = 0.027 for viscous liquidsFor laminar flow (Re < 2000), the following correlation is used:

14.033.033.0Pr)(Re*86.1

wL

deNu

Where, L = the tube length (m)The tube-side pressure drop is given by:

25.28

2tf

m

wifpt

u

d

LJNP

Pt = tube pressure drop (N/m2)Np = number of tube-side passesjf = tube dimensionless friction factor from Figure L = length of one tube, (m)ut = tube-side velocity (m/s)m = 0.25 for laminar, Re < 2100 = 0.14 for turbulent, Re > 2100

4.5. Shell-side Heat-transfer Coefficient, hs and Pressure Drop, Ps (Kern’s Method)

In order to determine the heat transfer coefficient for fluid film in shell, first calculate the cross-sectional area of flow As for tube rows in the middle of the shell as follows:

t

bsts p

lDdpA

Where, do = tube outside diameter (m)pt = tube pitch (m)Ds = shell inside diameter (m)lb = distance between baffle (m)Then, the fluid velocity in shell is calculated from:us = Vs /A s (Eq. 11)Where Vs = fluid volumetric flow rate on the shell side, m3/s.The shell equivalent diameter, De is given by:

22 785.027.1

dpd

De t

(For square pitch arrangement)

22 917.010.1

dpd

De t

(For equivalent triangular arrangement)

Thus Reynolds number in shell is given by:

Re = esDu

Baffle cut, Bc, is used to specify the dimensions of a segmental baffle. It is the height of the segment removed to form the baffle, expressed as a percentage of the baffle disc diameter.

Using this Reynolds number and given Bc value, the heat transfer factor, jh value is determined from Figure B4. Then, the heat transfer coefficient for fluid film in shell is calculated from:

The shell-side pressure drop is given by:

Where, Ps = shell pressure drop (N/m2)jf = shell dimensionless friction factor from Figure B5lB = distance between baffle (m)us = shell-side velocity (m/s)

5. Procedure

5.1. General Operating Procedure 1. Perform a quick inspection to make sure that the equipment is in a proper working

condition.2. Be sure that all valves are initially closed.3. Connect the cold water tank or reservoir to fill up the hot water tank and also this water

is used to passes through the shell side4. Switch on main power. Switch on the heater in the hot water tank and make sure that

the set point on the temperature controller is set to 60 C.5. Solenoid valve controls the level of water in hot water tank. If the water level is below

the selected level then it will allow the water to enter into the tank and keep the level high.

6. Turn on the hot water pump for circulation in tubes7. Operate the system for 10 mints to achieve the stable temperature readings.8. Control the flow by flow meter both in hot and cold side9. For Co-Current heat exchanger. Open valves 1 and 3 10. For counter current heat exchanger, open valves 2 and 411. Note down the cold and hot water temperature gauges

5.2. General Shut-down Procedure1. Switch off the heater and allow the water to cool down.2. Switch off both pumps and the stirrer.3. Switch off main power.4. Drain off all liquids in the process lines. Retain the water inside the hot water tank and

cold water tank for next laboratory sessions.5. Close all valves.

Note: If the equipment is not to be run for a long period, drain off all liquids completely.

6. CALCULATION DATA

Hot Fluid (Tube): Water Cold Fluid (Shell): WaterGiven To Find Given To Find

Vol. Flow rate(L/min)

Cross section area

Vol. Flow rate(L/min)

Cross flow area, Asm 2

Mass flow rate(kg/s)

Total cross section area

Mass flow rate(kg/s)

Linear velocity, usm/s

Inlet Temp(k)

Linear velocity

Inlet Temp(k)

Equivalent diameter, de(m)

Outlet Temp(k)

Reynolds Outlet Temp(k)

Reynolds Number, Re

Internal Dia Prandtl Density(kg/m3)

Prandtl

Outer Dia Type of flow

Heat Capacity(J/kg.K)

Type of flow

Heat Transfer(J/s)

Nusselt Thermal Conductivity(W/m.K)

Baffle cut %

Density(kg/m3)

Tube coeff, hi

Viscosity(Pa.s)

Heat transfer factor, jh

Heat Capacity(J/kg.K)

Friction Factor, jf

Nusselt Number, Nu

Thermal Conductivity(W/m.K)

Tube Side Pressure Drop (Calculated)

Shell coeff, hs

Viscosity(Pa.s)

Friction Factor, jf

Heat Transfer(J/s)

Shell Side Pressure Drop (Calculated)mH20

7. SPECIMEN CALCULATIONS:Tube Side Calculations

Tin=25.1+273= 298.1K

Tout= 24.3+273 = 297.3K

Outer Dia = 10x10-3

Internal Dia = 8 x10-3

Density of water at 20c

Area= A = pi*r2 = 3.14*(4 x10-3)2= 5x10-4m2

Vol. Flow Rate = = 2LPM = 0.033x10-3m3/s

Mass Flow Rate= = 0.4 kg/s

Ut= /A = 0.033x10-3/5 m/s

= (997*0.066*0.008)/.798 x10-3

Re = 577.21

As Re<2100 so Flow is Turbulent

=4186*7.98-4/0.6

Pr =5.56

Is neglected

= 1.86*{(577.21*5.56)

Nu = 6.31

Tube Co-efficient

6.31= hi*.008/.6

hi =540.85

Tube Side Pressure Drop

is neglected

Np = no of tube passes =1

Jf = tube dimensionless friction factor =1.5*10-2

Jf is calculated from chart. As we already calculated Reynolds no = 577.21 so corresponding value of jf is calculated

= 25.3 Pa

=.0025 mH2O

Shell Side Calculations:

In order to determine the heat transfer coefficient for fluid film in shell, first calculate the cross-sectional area of flow As for tube rows in the middle of the shell as follows:

= 0.033x10-3/2.75x10-3

= 0.011 m/sAs the arrangement is triangular so use the below formula to find equivalent diameter of shell

As Re<2100 so flow is turbulent

Find the value of Jh and Jf corresponding to the Reynolds no in the respective charts

Jh = 2.5x10-2

Jf = 7x10-2

Now Find the Predntle No

Nu =2.5x10-2 *283.24*(6.99)0.33(1)0.14

Nu = 13.45

Find the Pressure drop for shell side

= 1.43kPa

= 0.45 mH2O

Heat Transfer

= 3.3x10-5*4186*5.5

=757.47 J/s

=0.0329*4186*10.6 =1459.82 J/s

Heat Loss = -

=1459.82 - 757.47 = 702.355 J/s

% age = 757*100/1459 =51.88%

Total Exchange area

Ignoring &

Total Exchange Area:Outer area of tube = WhereTotal N is no of tubes =2*3.14*5x10-3*13 = 0.4086

= (1/405.13) +

=4.840x10-3

= 206.611