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DPM Conjugate Heat Transfer Problem

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Old   June 13, 2018, 22:40
Default DPM Conjugate Heat Transfer Problem
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Hey All,

I am attempting to model a seemingly straight forward problem but am having serious difficulty achieving reasonable results.

The model is based on a pressurized air injection with canola oil droplets. This injection is meant to cool down a solid body with a constant temperature at the tip.

The overall goal is to observe how different flow rates of the canola oil change the temperature propagation throughout the solid body. However, in the numerous methods I have tried, I can't seem to achieve convergence. Below is the outlined model settings.

Steady State, Gravity on.
Energy: on
Viscous: Realizable K-e, scalable wall, viscous heating

DPM: No interaction with continous phase, surface injection (Diameter = 0.0022m), Inert Particle
Example of a flow rate: Velocity= 0.00877m/s, Mass Flow Rate: 3.07e-05 kg/s

-Pressure-Inlet value = 6 Bar
-No slip conditions on the enclosure
-Coupled Solver

Any advice as to how to model the particles heat exchange with the solid domain would be greatly appreciated! I have attached a image of the geometry and what results look like without full convergence.
Attached Images
File Type: jpg 100mlhheat.jpg (52.5 KB, 11 views)
File Type: jpg pathlines-1.jpg (192.6 KB, 9 views)
File Type: jpg contour-2.jpg (55.2 KB, 10 views)
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Old   June 15, 2018, 04:38
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Hi welbouri,

A few thoughts:
-- This does not strike me as a particularly easy problem.
-- You do not need viscous heating here, although it should just be negligible and harmless. (Viscous heating is for situations where the work done to overcome viscous shear is enough to cause a serious temperature change -- for example, extruding molten plastic.)
-- You seem to want the DPM particles to interact with the solid zone, so I think that you will need to activate interaction with the continuous phase. Since you have not done that so far, any strange temperature effects that you currently see in the fluid and solid are probably not due to DPM.
-- It is worth working out what the temperatures look like in the absence of DPM first. (For example, how do you propose to maintain the tip of the body at a constant temperature? I guess one option would be to have the tip as a separate solid cell zone, apply a fixed value of temperature in that zone, and allow conduction to the rest of the solid. How does this happen in reality?)
-- Are you trying to look at a steady-state solution or transient? This is not clear to me, again partly because I do not know what is keeping the solid warm.
-- Now the difficult part: what happens when oil droplets impact with the solid body?
---- We could possibly assume that you want to ignore film formation, drainage, conduction inside the oil, etc -- if you need all that, then you could embark on the Wall Film model(s), and good luck to you.
---- So maybe you want to have an instant effect in heat terms, then kill the particle. What is the heat consequence of a droplet hitting the body? -- Suppose the drop represents a mass m_p of fluid (or a continuous mass flowrate, in a steady-state simulation) and a temperature T_p, and the neighbouring solid cell has a temperature T_s, and the neighbouring fluid cell has a temperature T_f. What do you want to happen next? You need to have a clear answer to this, or else you do not know what you are trying to simulate.
---- Unfortunately, whatever your answer is, I cannot see an easy way to explain it to Fluent. [[There might be some convoluted bodge using Evaporating droplets, trapped by walls.]] In particular, it is not easy to assign heat effects to the solid zone, rather than the fluid cell containing the particle. You might need to go quite deep into User-Defined Functions here.
Hmm, this is getting more difficult than I thought. I'll see if anyone else comes up with easy (or even medium-level) approaches.
Good luck!
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compressible flow, conjugate heat transfer, dpm fluent model, two-phase flow

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