Design of Heat Exchanger Engr. Rey F. Fiedacan, MEP - ME
DEVELOPED IN EXCEL BY: REY FIEDACAN - MECHANICAL ENGINEER ,11.07.2010
ENGINEERING CALCULATION THERMAL DESIGN OF HEAT EXCHANGER Project Title Part Prepared by Date Doc. No. Revision No.
APPLIED LIMITATION: SENSIBLE COOLING or SENSIBLE HEATING ONLY : HEAT EXCHANGER FOR CHILLED WATER
: : : : :
Horizontal Shell Rey Fiedacan 11.07.2010 HX - 01 -09 1
Key in value in blue color only TUBE SIDE:
SHELL SIDE: COLD SIDE [Fluid medium] WATER
HOT SIDE
[Fluid medium] WATER [Mass flowrate] 150 [Inlet temperature] 20 [Density] 998.2 [Specific heat] 4181.6 [Thermal conductivity] 0.6 [Dynamic Viscosity] 0
[Mass flowrate] 50 [Inlet temperature] 32 [Density] kg/m3 996.4 [Specific heat] J/Kg-K 4178.7 [Thermal conductivity] 0.61 W/m-K N.s/m2 , kg/m-s [Dynamic Viscosity] 0 Kg/s C
Kg/s C kg/m3 J/Kg-K W/m-K N.s/m2 , kg/m-s
FLOW CONDITION [Type of flow]
Counter flow
[Design Fouling Factor]
0
m2- K/W
ESSENTIAL VARIABLES [Tube materials]
WATER
[Velocity of fluid inside Tubes]
2
m/s
[Tube Outside Diameter]
19
mm
[Tube Inside Diameter]
16
mm
[Thermal Conductivity of Tubes] 42.3
W/m-K
TUBE ORIENTATION & GEOMETRY [Number of Passes] [Tube Pitch]
3 0.03
[Tube layout]
mm
Square Layout
[Tube Count Layout]
45 deg.
[Baffle Spacing - baffle cut at 25%]0.5
m
FINAL DECIDING VALUES BASED ON CORRELATED INPUTS ABOVE Step #1: Evaluate the LMTD correction factor given the value of P and R ( Computed ) P = 0.19 R = 3 From this set of conditions, See Table on LMTD correction factor to determine the factor F corresponding to type of flow ( Parallel or counterflow) and number of passes Enter correction Factor, F 0.94 Step #2: Check the value of overall conductance, U against the recommend values 1,869.27 W/m2-K Computed value of U = Based on the correlation of Reynolds number, flow condition and thermal conductivity, Check this value against permissible range from table of overall conductance U,
Enter value of U if the computed value is within the range
2263.20
Step #3: Check the % surface design of heat exchanger due to fouling effects 61% Computed value of = If the value is too high , Set value for desired surface design then enter
30%
Step #4: Evaluate computed length of tube of heat exchanger, Note that standard length is in 20 ft and it is recommended to use it out of the its length 1.89 m Computed Length = Enter, the effective length of tubes should not < computed length 4.00 Step #5: Evaluate the re-calculated shell diameter on the new length of HX, Inside diameter should referred to available shell to be used ( can be pipe or rolled plate) 0.68 m Computed Shell ID = Enter new shell ID,must be available size 0.80 Step #6: Enter the absolute viscosity at wall temperature, Evaluate at reference temperature T = 24.83 oC Reference Temp. Enter absolute viscosity,kg/m - s at reference Temp. 0
FINISH Check the result in the next sheet, Carefully evaluate and proceed next iteration if needed. The areas for iteration will be size, tube layout, flow conditions, geometry length of tubes ,baffle spacing and tube materials. DEVELOPED IN EXCEL BY: REY FIEDACAN - MECHANICAL ENGINEER ,11.07.2010
1
ENGINEERING CALCULATION
Designed by
Rey Fiedacan
THERMAL CALCULATION OF HEAT EXCHANGER TYPE: SHELL & TUBES
Date
11.07.2010
Doc. No.
HX - 01 -09
DEVELOPED USING EXCEL BY REY FIEDACAN,MECHANICAL ENGINEER, 11.07.2010
[email protected]
Revision
1
Project Title
:
HEAT EXCHANGER FOR CHILLED WATER
Part
:
Horizontal Shell
HEAT EXCHANGER THERMAL CALCULATION BY REY FIEDACAN, MEP - ME
Sketch :
I.HEAT & MASS BALANCE 1.0 Temperature of outlet fluid - Cold fluid ( Predicted from energy and mass balance) msCps(Ts1-Ts2) = ### K mtCpct 2.0 Log mean temperature difference across the heat exchanger (LMTD) Ts2 =
Δtmax - Δtmin Δtmax ln Δtmin P = 0.19 R = 3 F = 0.9400
LMTD =
= 7.1 K
where: LMTD= ### for parallel flow LMTD= ### for counterflow
3.0 LMTD Calculation ( Corrected ) where : ΔTm = F(LMTD) = ### K for Counter flowheat transfer between shell & tubes 4.0 HEAT DUTY OF HEAT EXCHANGER based on the temperature difference between hot fluids inlet and outlet condition. Q =(mscps)(Ts1 -Ts2) =
###
KW
5.0 NUMBER OF TUBES- based on the mass flowrate of cold fluid inside the tubes and recommended velocity on the specified number of passes. Nt = 4mtNp/ρtvtπdi2 =
### tubes 374 per pass
II. TUBE SIDE CALCULATION: 1.0 TUBE SIDE HEAT TRANSFER ht =
Nutkt
where:
di
Nut Kt di
= Nusselt number of fluid inside the tubes = Thermal conductivity of fluid inside the tubes = Inside diameter of tubes
2.0 NUSSELT NUMBER ( CORRELATION FROM Petukhov - Kirililov for Turbulent flows ) which predicts results in the range of 104< Ret < 5 x106 and 0.5 < Prt < 200 Nut =
(f/2)RetPrt 1.07+12.7(f/2)1/2(Prt2/3 -1)
HEAT
ENGINEERING CALCULATION
Designed by
Rey Fiedacan
THERMAL CALCULATION OF HEAT EXCHANGER TYPE: SHELL & TUBES
Date
11.07.2010
Doc. No.
HX - 01 -09
DEVELOPED USING EXCEL BY REY FIEDACAN,MECHANICAL ENGINEER, 11.07.2010
[email protected]
Revision
1
Prt
2.1
Prandtl number
2.2
Ret = ρtvtdi/µt Reynold number at tube side
2.3
Friction factor at given Re Ft Nut =
ht =
=
6.8 =
the flow is turbulent
###
-2 = (1.58lnRet - 3.28) =
(f/2)RetPrt 1.07+12.7(f/2)1/2(Prt2/3 -1) Nutkt
0.01
=
225.72
=
###
di
W/m2-K
( This correlated heat transfer coefficient at tube s condition of flow )
III.SHELL SIDE CALCULATION 1.0 SHELL SIDE HEAT TRANSFER BY KERN CORRELATION which predicts results in the range of 2x103< Res = GsDe/µ< 1 x106 0.55 1/3 ht = 0.36ks Res Prs De
where: Nus Ks de Res Prs
2.1
Reynolds Number
Res = (ms/As)(De/µs) =
2.2
Equivalent Diameter
De
= = = = =
Nusselt number of fluid outsidethe tubes Thermal conductivity of fluid outside the tubes Equivalent diameter of shell Reynold number flow outside the tubes Prandtl number of flow outside the tunes ###
the flow is turbulent
= f(Square,Triangular layout) do
De of square pitch in tube layout Flow
PT
DeΠ =
4(PT -πdo /4) De 2
2
S
= ### m2 s
De of triangular pitch in tube layoutFlow
PT do
4(PT2(3)1/2/4-πdo2/8) = ### m2 πdo/2 0 s Use: Square Pitch ; De =0.024234
DeΔ =
2.3
Bundle Crossflow
As
= f(Clearance, Baffle spacing)
2.4
Total flow area of tubes
As
DsCB PT
= ### m2 0 s = f(Clearance, Baffle spacing) =
Estimated Shell Diameter Ds
πdiNt = ### m2 4 0 s = f(Clearance, Baffle spacing)
Tube Pitch Ratio
2 2 t 1/2 = = 0.637(CL/CTP)(πdo PR N ) 0 s = f(Clearance, Baffle spacing)
= 2.5
2.6
PR
= PT/do 2.7
Tube Layout Constant
=
0.996
m
1.337
m
= f(Clearance, Baffle spacing) for 90o and 45o CL = 1 for 30o and 60o CL = 0.87 one tube pass CTP = 0.93
ENGINEERING CALCULATION
Designed by
Rey Fiedacan
THERMAL CALCULATION OF HEAT EXCHANGER TYPE: SHELL & TUBES
Date
11.07.2010
Doc. No.
HX - 01 -09
DEVELOPED USING EXCEL BY REY FIEDACAN,MECHANICAL ENGINEER, 11.07.2010
[email protected]
Revision
1
two tube pass CTP = three tube pass CTP = Use: CL = 1.0 CTP =0.930 0.55 1/3 ht = 0.36ks Res Prs De
=
###
0.9 0.85
W/m2-K
( This correlated heat transfer coefficient at shell side condition of flow )
IV. OVERALL HEAT TRANSFER COEFFICIENT 1.0 Outer surface area - Clean heat transfer coefficient do do 1 do ln(di ) 1 Uc = kt ho + di hi + 2
1.1
-1 =
###
W/m2-K
Surface area of heat exchanger for clean condition ( No fouling Effect )
Q = 97.11 UcΔTm Use: Uc = 2263.2 2.0 Outer surface area - Fouled heat transfer coefficient Ac =
do -1 do 1 do ln(di ) 1 Uf = + Rft = kt ho + di hi + 2
2.1
2.2
m2
###
W/m2-K
Surface area of heat exchanger for clean condition ( with fouling Effect ) Af =
Q UfΔTm
Os =
Af Ac
=
156.25
m2
Check for % surface design
Use:
= 61% Os = ###
2.3
Surface design area of heat exchanger at### certain more allowance for fouling effect 2 A' = 126.24 m
2.4
Effective length of tube for area in heat transfer A' L = N πd = 1.89 m t o Use:
2.5
New Shell Diameter
Ds'
L = ### m
= f(Clearance, Baffle spacing) = 0.637(CL/CTP)1/2(A'PR2do/L)1/2 = 0.68 m corrected shell diameter at the given length however, the actual diameter shall be the nearest available size either seamless pipe or fabricated as rolled plate Use: Ds' = ### m
V. PRESSURE DROP- This is used to determined the pumping power required to handle the fluid in tubes and shell 1.0 TUBE SIDE PRESSURE DROP
ENGINEERING CALCULATION
Designed by
Rey Fiedacan
THERMAL CALCULATION OF HEAT EXCHANGER TYPE: SHELL & TUBES
Date
11.07.2010
Doc. No.
HX - 01 -09
DEVELOPED USING EXCEL BY REY FIEDACAN,MECHANICAL ENGINEER, 11.07.2010
[email protected]
Revision
1
1.1
Tube side friction factor
1.2
Tube side friction factor
ft
-2 = (1.5ln(Ret) - 3.28) =
ΔPt =
###
ftLNp µc2 + 4Np ρc di 2
= 58.68 Kpa , head required to pump the fluid into the tubes = 8.5 psi
2.0 SHELL PRESSURE DROPThe shell-side fluid experiences a pressure drop as it passes through the exchange over the tubes, and around the baffles. f G2 (N +1)D's ΔPs = s s b 2ρsDeΦs 2.1 Shell side friction factor fs = exp(0.576 -0.19ln(Res)) = 0.300
2.2
2.3
Bundle crossflow area
Wall temperature
2.4
Correction Factor
2.5
Number of Baffles
2.6
Number of Baffles
therefore:
As
=
Tw
=
DsCB PT Tt1+Tt2
= ### m2 , based on corrected shell Φ, clearance of tubes and baffle spacing. +
Ts1+Ts2 1
2 2 = ### K , average temperature between cold and hot fluid across the tube length therefore: the absolute viscosity and wall temperature 24.8 of oC = 0 kg/m - s
2
Φs =
µs µw
Nb =
L B
Gs =
Ms As
ΔPs = = =
0.14
-1
= 0.989
=
7
=
### kg/m2-s
fsG2s(Nb+1)D's 2ρsDeΦs 6.4 0.9
Kpa , head required to pump the fluid into the shell psi
ENGINEERING CALCULATION
Designed by
Rey Fiedacan
THERMAL CALCULATION OF HEAT EXCHANGER TYPE: SHELL & TUBES
Date
11.07.2010
Doc. No.
HX - 01 -09
DEVELOPED USING EXCEL BY REY FIEDACAN,MECHANICAL ENGINEER, 11.07.2010
[email protected]
Revision
1
Summary of THERMAL DESIGN OF HEAT EXCHANGER TUBE SIDE : HOT SIDE o 20 1 Inlet temperature C 150 2 Mass flowrate kg/s 998.2 kg/m3 3 Density 0.6 4 Thermal Conductivity W/m - K 0 5 Dynamic viscocity N.s/m2 4181.6 J/kg - K 6 Specific Heat 6.8 7 Prandtl number 2 8 Velocity of fluid inside the tubes m/s 0 9 Total fouling factor m2 - K/W SHELL SIDE: COLD SIDE o 32 1 Inlet temperature C o 25 2 Outlet temperature C o 28.5 3 Average temperature C 50 4 Mass flowrate kg/s 996.4 kg/m3 5 Density 0.61 6 Thermal Conductivity W/m - K 0 7 Dynamic viscocity N.s/m2 4178.7 J/kg - K 9 Specific Heat 5.64 10 Prandtl number CONSTRUCTIONAL DATA OF THE PROPOSED SHELL AND TUBE HX 0.800 m 1 Shell diameter 1121.07 2 Number of tubes 4.000 m 3 Length of tubes(Allowancefor tubesheet not included) 0.019 m 4 Tube outside diameter 0.016 m 5 Tube inside diameter 0.500 m 6 Baffle spacing ( baffle cut at 25%) 0.025 7 Tube pitch 3.000 8 Number of passes 42.300 W/m - K 9 Thermal Conductivity of tubes 8526.66 W/m2 - K 10 Tube side heat transfer coefficient 2800.32 W/m2 - K 11 Shell side heat transfer coefficient 1869.27 W/m2 - K 12 Clean overall heat transfer coefficient 1406.54 W/m2 - K 13 Fouled overall heat transfer coefficient 58.68 Kpa 14 Tube side pressure drop 6.40 15 Shell side pressure drop Kpa
ENGINEERING CALCULATION
Designed by
Rey Fiedacan
THERMAL CALCULATION OF HEAT EXCHANGER TYPE: SHELL & TUBES
Date
11.07.2010
Doc. No.
HX - 01 -09
DEVELOPED USING EXCEL BY REY FIEDACAN,MECHANICAL ENGINEER, 11.07.2010
[email protected]
Revision
1
