Design Procedure for Fixed Tubesheet Heat Exchanger

SHELL SIDE :-

Note :- For Shell Side J = 0.85

1)Shell Diameter :-

a)Area occupied by each tube (a) = (S_T)²(for square pitch)

= 0.866 (S_T)²(for triangular pitch)

Here S_T is the pitch of tube.

b) Area occupied by ‘n’ tubes (a_n) = n x (S_T)²(for square pitch)

= n x 0.866 (S_T)²(for triangular pitch)

c) Area of shell (A_s) = a_n/β

Here β is the proportionality factor whose value is,

0.8 - For single pass

0.7 - For double pass

0.6 - For multiple pass

d) Also, Area of shell (A_s) = π/4 Di²

Here Di is the Shell inside diameter.

Therefore from c) and d) we can say that,

a_n/β = π/4 Di²

From the above equation we can calculate Di ,Which should be a multiple of 50.

2)Shell Thickness :-

t = (PDi / 2fJ – P) = (PDo / 2fJ + P) = (PD / 2fJ)

P = Design Pressure

Di = Inner diameter of shell as calculated above

Do = Outer diameter of shell

D = Mean diameter of shell = Do + Di /2

f = Allowable stress of shell material

The calculated value of ‘t’ must be greater than 8mm,if it is less than 8mm than take t = 8mm.

3)Nozzle (Inlet & Outlet) :-

Nozzle Thickness (tn) = (PDi / 2fJ – P)

Here, Di = Nozzle Inlet & Outlet Diameter

After adding corrosion allowance to the above calculated value of tn it must be greater than 4mm,if it is less than 4mm than take tn = 4mm.

4)Head Thickness :-

For a Fixed Tubesheet Heat Exchanger the head used is always a Torispherical Head.

Therefore,

Head thickness(th) = (PRcW/2fJ) + c

Here,

Rc = Crown Radius

Rk = Knuckle Radius

W = 1/4 ( 3+ (Rc /Rk)^1/2)

If Rc is not given then take shell Inside Diameter as Rc .

Also Rk = 6% of Rc

If it is mentioned in question that, U- tube type horizontal heat exchanger head is joined to the shell with the help of flanges which are cold, then, For cold forming calculate

5 x t(shell thickness) and take it as Rk .

5) Baffles :-

The baffles used will be of the Transverse type with spacing = Di / 5

Thickness of baffles will be = 6mm

The baffles are 25% cut

Therefore, Baffle length = 0.75 x Di

6) Tie Rods :-

No. of Tie rods = 6

Dia. Of tie rod = 10mm

7) Flange Joint Between Shell & Tubesheet :-

Note:- Some times G is taken same as calculated for Tube Side.

a) Design of Gasket :-

i)Gasket inside diameter (G_i)= Do + 10

ii)G_o/ G_i = ( y – pm / y – p(m+1) )^1/2

Now, After calculating the ratio G_o/ G_i substitute the value of G_i and calculate

iii) G_oi.e Gasket outside diameter_.

Then calculate,

iv) Mean Gasket Diameter(G) = G_o+ G_i/ 2

v) Width of Gasket ( N ) = G_o- G_i/ 2

vi) Basic Gasket seating width b_o= N/2

Now,

If b_o< 6.3 then b = b_o&

If b_o> 6.3 then b = 2.5(b_o)^1/2

Here, b is Effective gasket seating width

b) Design of Bolt :-

i) W_m1 = π b G Y_b

ii) W_m2 = π (2b) G m p + π/4 G² P

Consider the greater value from W_m1and W_m2for all the further calculations.

iii) Bolt Area (A) = W_m(max)/ f

iv) No. of Bolts(n) = G / 25 (should be a factor of 4)

v) Bolt circle Diameter (B) = G_o+ 2 d_b

c) Design of Flange :-

Flange thickness( t_f) = G ( P/ kf )^1/2

k = 1 / ( 0.3 +( 1.5 W_m(max)h_G/H x G ))

H = π/4 G² P

h_G= B – G / 2

TUBE SIDE :-

Note :- For Tube Side J = 1

1)Tube Thickness :-

t = (PDi / 2fJ – P) = (PDo / 2fJ + P)

If t is less than 2mm then take t = 2mm.

2)Tubesheet Thickness :-

t = FG ( 0.25P/f )

For Fixed Tubesheet Heat Exchanger

F = ( 2+k / 2+3k )^1/2 &

F = ( k / 2+3k )^1/2

K = ( Es ts (D_o- ts ) ) / ( Et N tt (d_o- tt ) )

Take that F whose value is greater & take G = 380 if not given.

3)Channel & Channel Cover :-

It is proposed to make the channel & channel cover out of a single plate.

Therefore,

Thickness of Channel Plate( t ) = G_c( kp/f )^1/2

For Ring type gasket or gasket bolted with narrow faced k = 0.3

For cover bolted with full faced gasket k = 0.25

4) Flange joint between Tubesheet and Channel :-

a) Design of Gasket :-

If G is assumed 380 then take Ring Gasket width(w) =

22mm & bo = w/8

Y_a= 126.6 N/mm²

m = Gasket Factor = 5.5

And if G is to calculated then calculate G by the method as given below.