# Flow Network model - missing some heat **URL:** \ **Category:** Uncategorized\ **Created:** [December 1, 2022, 9:14pm UTC](https://calculix.discourse.group/t/flow-network-model-missing-some-heat/1360 "2022-12-01T21:14:23Z")\ **Posts on this page:** 9\ **Page:** 1
**Author:** ![JohnM](https://avatars.discourse-cdn.com/v4/letter/j/848f3c/32.png) [@JohnM](https://calculix.discourse.group/u/JohnM)\ **Post date:** [December 1, 2022, 9:14pm UTC](https://calculix.discourse.group/t/flow-network-model-missing-some-heat/1360/1 "2022-12-01T21:14:23Z")
![image](https://global.discourse-cdn.com/free1/uploads/calculix/original/2X/e/e56e18757d52f53212e07e41aac3a3f4d5ff2792.png) I have a test problem that uses heat transfer with a pipe flow network. There is no pressure drop calculation, only mass flow and capacitance are considered (test model below). The figure shows the issue. I apply a convection on the base, a mass flow and inlet temperature to the pipe. I expected the convection, conduction and thermal mass transport to all be the same, but the pipe flow “cool down” is about 30% too low. Any help would be appreciated! ---------------- pipetest.inp \*NODE 1,0,0,0 2,0.01,0,0 3,0.01,0.01,0 4,0,0.01,0 5,0,0,0.01 6,0.01,0,0.01 7,0.01,0.01,0.01 8,0,0.01,0.01 9,0,0,0.02 10,0,0,0.03 11,0,0,0.04 12,0,0,0.05 13,0,0,0.06 14,0,0,0.07 15,0,0,0.08 16,0,0,0.09 17,0,0,0.1 18,0.01,0,0.02 19,0.01,0,0.03 20,0.01,0,0.04 21,0.01,0,0.05 22,0.01,0,0.06 23,0.01,0,0.07 24,0.01,0,0.08 25,0.01,0,0.09 26,0.01,0,0.1 27,0.01,0.01,0.02 28,0.01,0.01,0.03 29,0.01,0.01,0.04 30,0.01,0.01,0.05 31,0.01,0.01,0.06 32,0.01,0.01,0.07 33,0.01,0.01,0.08 34,0.01,0.01,0.09 35,0.01,0.01,0.1 36,0,0.01,0.02 37,0,0.01,0.03 38,0,0.01,0.04 39,0,0.01,0.05 40,0,0.01,0.06 41,0,0.01,0.07 42,0,0.01,0.08 43,0,0.01,0.09 44,0,0.01,0.1 45,0,0.02,0 46,0,0.02,0.05 47,0,0.02,0.1 48,0,0.02,0.025 49,0,0.02,0.075 \*ELEMENT,TYPE=DC3D8 1,1,2,3,4,5,6,7,8 2,5,6,7,8,9,18,27,36 3,9,18,27,36,10,19,28,37 4,10,19,28,37,11,20,29,38 5,11,20,29,38,12,21,30,39 6,12,21,30,39,13,22,31,40 7,13,22,31,40,14,23,32,41 8,14,23,32,41,15,24,33,42 9,15,24,33,42,16,25,34,43 10,16,25,34,43,17,26,35,44 \*ELEMENT,TYPE=D 11,45,48,46 12,46,49,47 \*NSET,NSET=pipe\_flow\_mdot 48 49 \*NSET,NSET=temp\_inlet 45 \*NSET,NSET=pipe\_flow 45 46 47 \*ELSET,ELSET=wpipe 11 12 \*ELSET,ELSET=solid 1 2 3 4 5 6 7 8 9 10 \*MATERIAL,NAME=dummy\_thermal \*DENSITY 7700 \*CONDUCTIVITY,TYPE=ISO 0.001,0 \*SPECIFIC HEAT 3850 \*SOLID SECTION,ELSET=solid,MATERIAL=dummy\_thermal \*FLUID SECTION,MATERIAL=WATER,ELSET=wpipe \*MATERIAL,NAME=water \*FLUID CONSTANTS 4186,8.9E-4,310 \*STEP \*HEAT TRANSFER,STEADYSTATE,SOLVER=SPOOLES 1,1,0,0 \*BOUNDARY temp\_inlet,11,373.15 \*FILM 2,F3,293.15,1 1,F3,293.15,1 3,F3,293.15,1 4,F3,293.15,1 5,F3,293.15,1 6,F3,293.15,1 7,F3,293.15,1 8,F3,293.15,1 9,F3,293.15,1 10,F3,293.15,1 \*NODE FILE,GLOBAL=YES NT \*EL FILE HFL \*BOUNDARY pipe\_flow\_mdot,1,1e-5 \*\*\* pipe \*FILM 7 ,F5FC, 46,70.123 6 ,F5FC, 46,70.123 8 ,F5FC, 47,70.123 5 ,F5FC, 46,70.123 9 ,F5FC, 47,70.123 4 ,F5FC, 46,70.123 10 ,F5FC, 47,70.123 3 ,F5FC, 45,70.123 2 ,F5FC, 45,70.123 1 ,F5FC, 45,70.123 \*END STEP ---
**Author:** ![Disla](https://yyz2.discourse-cdn.com/free1/user_avatar/calculix.discourse.group/disla/32/3548_2.png) [@Disla](https://calculix.discourse.group/u/Disla)\ **Post date:** [December 2, 2022, 7:10pm UTC](https://calculix.discourse.group/t/flow-network-model-missing-some-heat/1360/2 "2022-12-02T19:10:46Z")
Hi John, How cool is this.!!!. Thanks for sharing. It’s kind of an HEX tube temperature profile. I’m obtaining similar result but would like to comment some points with you. -I have noticed that the final temperature depends on how many surfaces are assigned to each Temperature node. ¿Could this be the source of discrepancy? You are assigning (3,4,3). I have refined and discrepancy has drop to 20% which is still large. Each node has two surfaces now. By other hand, if we compare Q’s assuming the same temperature on top and bottom of the solid bar , we are indirectly assuming perfectly homogeneous transverse heat transfer in the equilibrium.Not sure about that considering the nature of the heat flow on the source (longitudinal) and the small number of elements. I keep investigating. Maybe it is a bug, we never know. ![screenshot.42](https://global.discourse-cdn.com/free1/uploads/calculix/original/2X/0/0e7ca86e9b7f0f7bbe6ed416d08a660b9bf24d1f.png) ![screenshot.41](https://global.discourse-cdn.com/free1/uploads/calculix/original/2X/9/98b1c96a34b211103e6e02ec5cd3e2f7baf6ae37.png) ---
**Author:** ![JohnM](https://avatars.discourse-cdn.com/v4/letter/j/848f3c/32.png) [@JohnM](https://calculix.discourse.group/u/JohnM)\ **Post date:** [December 2, 2022, 8:52pm UTC](https://calculix.discourse.group/t/flow-network-model-missing-some-heat/1360/3 "2022-12-02T20:52:19Z")
@Disla thanks for taking a look, and yes this stuff is cool. This method is used by aerospace to model bypass cooling air in turbine blades, disks and ducts, and since Guido works at MTU Aero it’s no surprise that this is part of the Calculix tool set. We use this a lot as a “poor man’s conjugate heat transfer”. At some point I will share the python API scripts that generate the network and I’m hoping to get our friend Victor to build this in as a command set. But in the mean time I would like to minimize the heat balance discrepancy. As you say, the error gets reduced a bit with mesh density, but I was hoping to get better than 20%. If you make any discoveries, let me know. Thanks! ---
**Author:** ![Calc\_em](https://avatars.discourse-cdn.com/v4/letter/c/43a26b/32.png) [@Calc\_em](https://calculix.discourse.group/u/Calc_em)\ **Post date:** [December 2, 2022, 9:37pm UTC](https://calculix.discourse.group/t/flow-network-model-missing-some-heat/1360/4 "2022-12-02T21:37:50Z")
> [@JohnM](#): > > We use this a lot as a “poor man’s conjugate heat transfer”. Can’t you use CalculiX + OpenFOAM with preCICE for CHT ? > **[Heat exchanger | preCICE - The Coupling Library](https://precice.org/tutorials-heat-exchanger.html)** > > Tutorial for a shell-and-tube heat exchanger, using OpenFOAM and CalculiX ---
**Author:** ![JohnM](https://avatars.discourse-cdn.com/v4/letter/j/848f3c/32.png) [@JohnM](https://calculix.discourse.group/u/JohnM)\ **Post date:** [December 2, 2022, 9:42pm UTC](https://calculix.discourse.group/t/flow-network-model-missing-some-heat/1360/5 "2022-12-02T21:42:12Z")
I have always found preCICE interesting, and may find a use for it, but the pipe network approach is very effective and very fast for what we need. When you understand the flow side well (i.e. know the heat transfer coefficients) and only need to consider the energy transfer to/from the fluid, the network is a great tool. ---
**Author:** ![Disla](https://yyz2.discourse-cdn.com/free1/user_avatar/calculix.discourse.group/disla/32/3548_2.png) [@Disla](https://calculix.discourse.group/u/Disla)\ **Post date:** [December 2, 2022, 10:14pm UTC](https://calculix.discourse.group/t/flow-network-model-missing-some-heat/1360/6 "2022-12-02T22:14:05Z")
HI John I have obtained a 0.17% of deviation with the following distribution: Use the same number of elements than surfaces and two nodes for each surface . 1,F5FC,45,70.123 1,F5FC,93,70.123 2,F5FC,93,70.123 2,F5FC,95,70.123 3,F5FC,95,70.123 3,F5FC,97,70.123 4,F5FC,97,70.123 4,F5FC,99,70.123 5,F5FC,99,70.123 5,F5FC,101,70.123 6,F5FC,101,70.123 6,F5FC,103,70.123 7,F5FC,103,70.123 7,F5FC,105,70.123 8,F5FC,105,70.123 8,F5FC,107,70.123 9,F5FC,107,70.123 9,F5FC,109,70.123 10,F5FC,109,70.123 10,F5FC,47,70.123 Mdot 1.00E-05 Kg/s Cp 4186 AT 0.173 ºC 100.000 ºC 99.827 ºC Q 0.007242 W Surface Integral Top - 0.007254 In Surface Integral Bottom 0.007254 Out Deviation 0.17 % ![screenshot.45](https://global.discourse-cdn.com/free1/uploads/calculix/original/2X/7/77668b93830af98464ecfb5a696ef0f332667287.png) ![screenshot.44](https://global.discourse-cdn.com/free1/uploads/calculix/original/2X/e/e302ed99d0ec1ac777c141ecef4a1148b6d1480c.png) ---
**Author:** ![JohnM](https://avatars.discourse-cdn.com/v4/letter/j/848f3c/32.png) [@JohnM](https://calculix.discourse.group/u/JohnM)\ **Post date:** [December 2, 2022, 10:41pm UTC](https://calculix.discourse.group/t/flow-network-model-missing-some-heat/1360/7 "2022-12-02T22:41:07Z")
Nice! I’ll give that a try, sounds like you have the handle on it! Have a great weekend. ---
**Author:** ![ceanwang](https://avatars.discourse-cdn.com/v4/letter/c/4da419/32.png) [@ceanwang](https://calculix.discourse.group/u/ceanwang)\ **Post date:** [April 16, 2025, 1:16am UTC](https://calculix.discourse.group/t/flow-network-model-missing-some-heat/1360/8 "2025-04-16T01:16:37Z")
```auto *ERROR reading *BOUNDARY. Card image: TEMP_INLET,11,373.15 ``` ---
**Author:** ![Calc\_em](https://avatars.discourse-cdn.com/v4/letter/c/43a26b/32.png) [@Calc\_em](https://calculix.discourse.group/u/Calc_em)\ **Post date:** [April 16, 2025, 12:40pm UTC](https://calculix.discourse.group/t/flow-network-model-missing-some-heat/1360/9 "2025-04-16T12:40:42Z")
CalculiX is expecting a range of DOFs: ![image](https://global.discourse-cdn.com/free1/uploads/calculix/original/2X/2/26e7e662c52d66b93c7f0aa5d952dfac9b52a86f.png) So change it to: ```auto *BOUNDARY temp_inlet,11,11,373.15 ``` and also change the other BC accordingly.