Robert Type Evaporator Design Calculation Sheet




INPUT DATA to be give in Yellow colour cells



Heating surface


m^{2}

Inlet vapour
temperature


oC



Tube OD


mm

outlet vapour
temperature


^{o}C



Tube thickness


mm

Velocity of inlet
vapour


m/sec



Tube Length


mm

velocity of outlet
vapour


m/sec



Tube plate thickness


mm

Velocity of
condensate


m/sec



Tube expansion allowance


mm

Evaporation rate of
the body


Kgs/m^{2} /hr



Legment


mm

Inlet vapour specific
volume


M^{3}/kg



Tube clearance


mm

outlet vapour
specific volume


m^{3}/kg



Tube plate hole clearance


mm



proportional factor(β)





Percentage of
downtake Dia on tube plate area of tubes


%


S.No

Description

UOM

Value

Formula


1

Number of tubes



Mean dia of the tube
( Dm)

mtr


Tube OD Tube Thickness



Effective Length of
the tube ( L )

m


Tube
lg  2(Tube plate thk)2(Tube expansion allowance)



No. of tubes

no.s


Heating Surface = π D L N


2

Tube plate &
Downtake dia


a

Area occupied for
tube plate



Tube Pitch (P )

mtr


OD+legment+tube
clearance+hole clearance



Taken
extra dia for stay roads arrangement or multiple down take arrangement

%





Tube plate area required for tubes
only

m^{2}


(0.866 x P^{2} x N /β) x %extra



Tube plate Dia
required for tubes only

mtrs


SQRT ( A x 4/π )




mm



b

Dia of the single down take



Dia of the down take

mm


Tube plate dia for tubes x % of downtake on tube
plate



Area of the downtake

m^{2}


π r^{2}



Total area of the
tube plate

m^{2}


Area of the Tube plate for
tubes + Downtake area


c

Final Dia of the tube
plate

mtr


SQRT ( A x 4/π )




mm



d

Dia of the multiple down takes





Consider each
peripheral down take dia

mm




Consider number of
peripheral down takes

no.s




Total area of
peripheral down takes

mm^{2}


π r^{2} x number of peripheral
down takes (r = radious of each peripheral down take



Available area for
central down take

mm^{2}


Area of the single
downtake  Total area of peripheral down takes



Dia of the central
down take

mm


SQRT ( A x 4/π )


3

Dia required for vapour
inlet and Dia of the Calendria in
radial steam/ vapour entry



Number of steam/ vapour entries

no.s




Evaporation rate of
the body

Kgs/m^{2} /hr




Vapour required for
calendria

Kgs/hr


Heating surface x Evap.
Rate




m^{3}/sec


Multiptiplyed by specific
volume of vapour



Total area for vapour
entry ( A )

m^{2}


A = Q/ V


a

Dia of the each
steam entry

mm


SQRT [ (A / Number of
steam/ vapour entries) x (4/π ) ]



Say

mm



b

Calendria dia at the entry of the steam/vapour jocket





Area of each steam
entry

mm^{2}


π r^{2}



Height of the steam
entry

mm


Take Effective Length of
the tube



Width of the steam
entry

mm


A = L x W


c

Dia
of calendria at the point of radial steam entry

mm


It
is to be maintained at the vapour entry side
later it may reduced in vapour travel direction.


4

Vapour outlet pipe
dia





Vapour volume

m^{3}/sec


Heating surface X Evap.
Rate x Specific volume of vapour/3600



Vapour outlet pipe
dia

mtr


SQRT [vapour vol./(0.785 x
velocity of vapour)]



Say

mm



5

Dia of the
condensate line






Volume of the
condensate

kgs/hr


Heating surface X Evap.
Rate




m^{3}/sec


Here
considered density of water as 1 and also consider 10% extra for free removal
of condensate



No. of condensate
withdrawals

no.s




Condensate pipe dia each

mtr


SQRT (vapour vol./(0.785 x
velocity of condensate))




mm



6

Noxious gases






Cross section area of non condensable
gases

cm^{2}





No. of NCG withdrawal points








Dia of the each non condensable gases
line

cm


SQRT( 4*area./3.14*no. of
points)



Say

mm






7

Vapour space height

Take


Generally for Robert
type bodies taken for lost effect 2.5 times on calendria tube height and for remaining bodies take 2 tmes on
Calendria tube height




mm



8

Velocity in vapour space
of body (Cross checking of the system )



Vapour volume

m^{3}/sec


Heating surface X Evap.
Rate



Crossectional area of
the body

m^{2}




Velocity in vapour
space of body

m/sec


The
velocity of vapour leaving the liquid surface would then be approximately 10
cm/sec




Ft/sec



9

Calendria shell
thickness


(P* Di / (2*F*J  P) )
+ C




P = Maximum allowable
pressure

kg/cm^{2}




Di = ID of the
Calendria

mm




F = Allowable stress

kg/cm^{2}




J = Joint efficiency





C= corrosion
allowance

mm




Calendria shell
thickness

mm




Say

mm



10

Vapour shell
thickness


(P* Di / (2*F*J  P) )
+ C



P = Maximum allowable
pressure

kg/cm^{2}




F = Allowable stress

kg/cm^{2}




J = Joint efficiency





C= corrosion allowance

mm




Di = ID of the Calendria

mm


OD  2 x Calendria shell
thickness



Vapour shell thickness

mm




Say

mm



11

Tube plate
thickness



C= corrosion
allowance

mm




F = Allowable stress

kg/cm^{2}






P = Maximum allowable
pressure

kg/cm^{2}




E_{s} = Modulus factor for MS sheet

kg/cm^{2}




E_{t} = Modulus factor for SS sheet

kg/cm^{2}




G = ID of the shell

mm


OD  2 x Calendria shell
thickness



t_{ts} = Thickness of the shell

mm




t_{t} = Thickness of tube

mm




d_{o}= OD of the tube

mm




D_{o} = OD of the calendria sheet

mm




N_{t
}= Number of tubes

no.s




K



K =( E_{s} x t_{s} x (D_{o} t_{s})) /(N_{t} x E_{t} x t_{t} x(d_{o} t_{t}))



f = safety factor



f = SQRT ( K / (2 + 3K))



Tube plate
thickness

mm


f x G x SQRT((0.25 x P)/F) + C


12

Vapour doom dia

On vapour outlet line area


Generally
for Robert type bodies vapour doom dia taken 2 to 2.5 times for vapour outlet
pipe area



Cross sectional area
of the vapour doom

mm^{2}




Vapour doom dia





Say

mm




Top cone angle (φ)

Deg




Top cone height



Tan φ( (ID of body ID of doom)/2)


13

Center Umbrella area


a

Case
1 (cross sectional Area of the body 
cross sectional area of the doom = area of Umbrella

mm







mm


Here Case 2 considered



Gap
between Umbrella to top cone at entry H

mm


π * Dia of Umbrella*
H = Area of vapour doom



Gap between
Umbrella to top cone at exist H

mm


π * ID of doom* H =
Area of vapour doom



