9 replies to this topic

[techno_chrat]

Hello, I have recently started designing cooling system, having experience in manufacturing and maintenance area. We have got analysis done for a recent project for a air cooled heat exchanger. I am sharing the report as follows. Kindly interpret the runtime message and errors.

Process Conditions
Outside
Tubeside
Fluid name
CHARGE AIR
20% RPAM700AF fluid + 80% water
Fluid condition
Sens. Gas
Sens. Liquid
Total flow rate
(1000-kg/hr)
6.150
52.000
Weight fraction vapor, In/Out
1.0000
1.0000
0.0000
0.0000
Temperature, In/Out
(Deg C)
350.00
45.00
25.00
45.00
Skin temperature, Min/Max
(Deg C)
32.65
141.08
27.39
66.17
Pressure, Inlet/Outlet
(kgf/cm2A)
6.118
6.114
4.079
2.904
Pressure drop, Total/Allow
(kgf/cm2) (kgf/cm2)
3.93e-3
5.10e-3
1.175
0.510
Midpoint velocity
(m/s)
2.35
3.63
- In/Out
(m/s)
2.21
3.65
Heat transfer safety factor
(--)
1.0000
1.0000
Fouling
(m2-hr-C/kcal)
0.000349
0.000116
Exchanger Performance
Outside film coef
(kcal/m2-hr-C)
96.98
Actual U
(kcal/m2-hr-C)
63.759
Tubeside film coef
(kcal/m2-hr-C)
9276.6
Required U
(kcal/m2-hr-C)
63.510
Clean coef
(kcal/m2-hr-C)
72.021
Area
(m2)
70.737
Hot regime
Sens. Gas
Overdesign
(%)
0.39
Cold regime
Sens. Liquid
Tube Geometry
EMTD
(Deg C)
105.3
Tube type
Continuous Fin
Total duty
(MM kcal/hr)
0.708
Tube OD
(mm)
12.000
Unit Geometry
Tube ID
(mm)
10.000
Bays in parallel per unit
1
Length
(mm)
850.000
Bundles parallel per bay
1
Area ratio(out/in)
(--)
12.473
Extended area
(m2)
70.737
Layout
Staggered
Bare area
(m2)
6.775
Trans pitch
(mm)
24.000
Bundle width
(mm)
404.
Long pitch
(mm)
20.784
Nozzle
Inlet
Outlet
Number of passes
(--)
4
Number
(--)
1
1
Number of rows
(--)
14
Diameter
(mm)
77.927
77.927
Tubecount
(--)
231
Velocity
(m/s)
2.98
3.01
Tubecount Odd/Even
(--)
16 /
17
R-V-SQ
(kg/m-s2)
9025.0
9103.2
Material
Copper/nickel 70/30
Pressure drop
(kgf/cm2)
0.051
0.032
Fin Geometry
Fan Geometry
Type
None
No/bay
(--)
0
Fins/length
(fin/meter)
472.4
Fan ring type
Fin root
(mm)
12.500
Diameter
(mm)
0.
Height
(mm)
Ratio, Fan/bundle face area
(--)
0.0000
Avg. thickness
(mm)
0.150
Driver
(kW)
-
/
-
Over fin
(mm)
0.000
Tip clearance
(mm)
0.000
Efficiency
(%)
85.0
Efficiency
(%)
0.0000
Area ratio (fin/bare)
(--)
10.4
Fans turned-down
(--)
No Fans
Material
Copper
Airside Velocities
Actual
Standard
Thermal Resistance, %
Face
(m/s)
1.49
Air
65.74
Maximum
(m/s)
3.83
Tube
8.57
Flow
(100 m3/min)
0.306
Fouling
11.47
Velocity pressure
(mmH2O)
0.000
Metal
14.21
Bundle pressure drop
(mmH2O)
39.329
Bond
0.00
Bundle flow fraction
(--)
1.000
Bundle
100.00
Airside Pressure Drop, %
Louvers
0.00
Ground clearance
0.00
Fan guard
0.00
Hail screen
0.00
Fan ring
0.00
Fan area blockage
0.00
Steam coil
0.00

Simulation-Vertical economizer countercurrent to crossflow
Unit ID 100 - WARNING MESSAGES (CALCULATIONS CONTINUE)
General
The hot and cold fluid duties differ by 69.2793 percent. (MN 4087)
The heat duty calculated from the process conditions differs from the specified value by 49.71 percent. Check the
specified process conditions and physical properties. (MN 4000)
The duty calculated from the hot fluid process conditions is 5.382E11 MW ( 1836 M Btu/hr). (MN 4075)
The duty calculated from the cold fluid process conditions is 1.109E12 MW ( 3783 M Btu/hr). (MN 4073)
The specified heat duty is 5.500E11 MW ( 1877 M Btu/hr). (MN 4088)
The required heat duty is 5.500E11 MW ( 1877 M Btu/hr). The percent overdesign is based on this value. (MN
4089)
Thermal & Hydraulic
The calculated pressure drop for the cold fluid exceeds the allowable pressure drop by 130.5276%. (MN 8017)
Geometry, Mechanical Design, and Vibration
The specified bundle width is 87. percent of the minimum bundle width calculated based on the tube pitch and the
number of tubes in each row. The bundle width entered was ignored. Check the number of tubes per row and the
bundle width entered. If necessary, correct the values and rerun the case. (MN 3123)
The specified ground clearance is less than the recommended minimum per API 661, Section 7.2.1. For this case, the
recommended minimum is .05659 m. (MN 3512)
Fluid Properties
The HTRI property correlations used for the cold fluid are being accessed at temperatures beyond the valid
temperature range of the correlations. (MN 5085)
The maximum process temperature is outside the correlational range of the thermal conductivity correlation. The
thermal conductivity was calculated at the temperature limit. For tube metal number 34 this temperature limit is 391.7
F. (MN 5088)
The physical properties of the cold fluid have been extrapolated beyond the valid temperature range. Check the
calculated values. The thermal analysis requires properties at bulk and skin/wall temperatures. (MN 5033)

[latexman]

First, I've never run HTRI, but I've had lots of experience calculating HXs and analyzing other systems that calculate HXs.  Second, be sure you and your company's input to this analysis is not the source of all the errors and messages!  If not, I would throw this report in the dust bin, and get a different contractor to work on it.  There are a lot of BIG red flags.  "The hot and cold fluid duties differ by 69.2793 percent" - way off!  Danger, Will Robinson!  "The heat duty calculated from the process conditions differs from the specified value by 49.71 percent. Check the specified process conditions and physical properties" - again, way off!  "The HTRI property correlations used for the cold fluid are being accessed at temperatures beyond the valid temperature range of the correlations" - physical properties are being EXTRAPOLATED, that may not be good!

 

If you proceed with this, the RISK is on YOU.  Don't let others substandard work put you at risk.

 

Next time just attach the PDF or DOC file.  I bet the formatting on that was more intuitive.

[techno_chrat]

First, I've never run HTRI, but I've had lots of experience calculating HXs and analyzing other systems that calculate HXs.  Second, be sure you and your company's input to this analysis is not the source of all the errors and messages!  If not, I would throw this report in the dust bin, and get a different contractor to work on it.  There are a lot of BIG red flags.  "The hot and cold fluid duties differ by 69.2793 percent" - way off!  Danger, Will Robinson!  "The heat duty calculated from the process conditions differs from the specified value by 49.71 percent. Check the specified process conditions and physical properties" - again, way off!  "The HTRI property correlations used for the cold fluid are being accessed at temperatures beyond the valid temperature range of the correlations" - physical properties are being EXTRAPOLATED, that may not be good!

 

If you proceed with this, the RISK is on YOU.  Don't let others substandard work put you at risk.

 

Next time just attach the PDF or DOC file.  I bet the formatting on that was more intuitive.

Hello, I appreciate the reply. My thoughts were similar after seeing the report. However from where I am there are not many options in person who will provide this service. My company doesn't prefer services provided online from elsewhere. This cac I am working on is a replacement (service maintanence) job and the geometry is 90% similar to the one in service. The one is service is giving satisfactory performance duty wise and delta pressure. The major issues faced is with leakages on the air side which we have addressed. I did speak to analysis service provider, he informed me that the cold side coolant is custom and is unable to find relevant data to input for the fluid properties which is causing the error. We are confident with the performance as it's based on a field proven cac.The number of tubes, fpi, core lenght etc have been kept similar. Any insights and comments would be really appreciated here. I have asked for a rerun and will share the pdf of the analysis here soon. Also we have done preliminary manual calculations which seem good for the cooler. Thanks.

Edited by techno_chrat, 08 November 2025 - 07:03 AM.

[deft clay]

Are you in Design, Rating, or Simulation mode?

 

You need to check your inputs. If the duties differ by this amount then the trouble is this:

• Your inputs are wrong... make sure you aren't putting things in the wrong unit
• The design is too restrictive, so HTRI is trying to do something absurd to compensate.

[techno_chrat]

 

Are you in Design, Rating, or Simulation mode?

 

You need to check your inputs. If the duties differ by this amount then the trouble is this:

• Your inputs are wrong... make sure you aren't putting things in the wrong unit
• The design is too restrictive, so HTRI is trying to do something absurd to compensate.

 

its done in the rating mode. I have a copy of the rerun and uploading it here.

 

1) The in puts have been double checked. No problems there.

2) Analysis was also done in the simulation mode, but still the problem persists. It will be helpful if you could shed some light on this.

Thanks.

[techno_chrat]

Hello, I have the rerun results. It will be really helpful if someone could help interpret it.

 

Thanks.

Attached Files

•  1.png   167.84KB   0 downloads
•  2.jpg   115.34KB   0 downloads
•  3.jpg   196.57KB   0 downloads

[breizh]

Hi,

Make sure you have all the fluid properties well defined, same for operation conditions within the correlation limits.

 

Garbage in =garbage out!

 

This is your responsibility.

 

I've attached a brochure about air cooler from a reputable company .

 

Breizh

Attached Files

•  Air cooler Hudson.pdf   528.27KB   6 downloads
•  air cooler design Sheiko.pdf   1.64MB   4 downloads

[latexman]

I like to see the heat duty difference under 5%.

 

Drill down and figure out which component(s) has the correlation temperature limit issue. 

[techno_chrat]

I like to see the heat duty difference under 5%.

Drill down and figure out which component(s) has the correlation temperature limit issue.

We have eliminated the general warning by adjusting the coolant flow. I am unable to comprehend how htri is assessing this. The new coolant flow 25000 kg/hr gives no general warning. Even a slight change there again difference in hot and cold duties appear. Still stuck with fluid properties error.

[techno_chrat]

Hi,
Make sure you have all the fluid properties well defined, same for operation conditions within the correlation limits.

Garbage in =garbage out!

This is your responsibility.

I've attached a brochure about air cooler from a reputable company .

Breizh

Thanks a lot. Any other resource specifically for design calculation of air coolers, intercooler, charge air cooler would be really helpful.