Can "pipe(G)" block be used to model forced air convection?

Hello,

i am trying to model a battery pack with forced air convection cooling. The pipe(G) block can be used to transfer heat from gas flowing inside a pipe to intended surface geometry. But it is internal flow. My concern is i want to model heat transfer from the surface to the gas(air). But that will become external flow problem. Is it possible to do so?

please help!

thanks.

Answer 1

[Yifeng Tang]

I think it's possible. The combination of cross section and hydraulic diameter will give you a circumference; that multiplied by the pipe length is the total heat transfer area. So I would say it's possible.

[SUDEEP SINGH RAWAT]

Thank you for your feedback. Actually i wanted to model the forced air convection outside the cylindrical battery cell. Hydraulic diameter is Dh=4*A/P. Since the flow is external or outside the surface of pipe(cylindrical battery), should the area(A) be A=2*pi*r*h instead of A=pi*r^2 in this case? Because that will affect the hydraulic diameter and hence the heat transfer area.

Please respond.

Regards,

[Yifeng Tang]

You mentioned "battery pack" in your question and "cylindrical battery cell" in your later comment, which one is it? Is the forced air outside the whole pack or it's in between the cells? The flow cross section will be quite different in each case.

[SUDEEP SINGH RAWAT]

Hi,

I apologize for the confusion. The battery pack will be mode from the series and parallel arrangement of cylindrical lithium ion battery cells. The idea is to model forced air convection inside the battery pack i.e. through the arrangment of battery cells. If the forced air cooling/convection can be done on single cell, it will be easy to replicate for the rest of the arrangments of cells. Should i consider the A=2*pi*r*h instead of A=pi*r^2 in this case?

I have attached the image for your reference. Please suggest your valueable insights.

regards,

Sudeep

[Yifeng Tang]

Like the picture :)

As the air is between the cells, the gap where the air is flowing through is the "cross-section area".

A_pipe_cross_section = gap * h; This is an estimate. You may also consider how much volume is in the gap around each cell and use A = V/length_of_pipe.

Length_pipe = 2*r + gap, the distance from the center of one cell to the next.

Area_surface_heat_transfer = 2*pi*r*h, but the pipe block doesn't ask for this

Circumference_heat_transfer = Area_surface_heat_transfer / Length_pipe;

Hydraulic_diameter = 4 * A_pipe_cross_section / Circumference_heat_transfer

I would expect the final value to be close to the gap size and/or radius.

[SUDEEP SINGH RAWAT]

Thank you.That seems a good explanation. One more doubt in regard to my question. Since the cells are arranged in square topolgy, is there any relation of convective heat transfer coefficient along the length of the battery pack. Obviously the flow become weaker as it moves from inlet to outlet of the pack and so the convective heat transfer coefficient. Any modeling approach or related example in this regard will be of great help.

Regards,

[Yifeng Tang]

No. Simscape components are "lump" models. In general, there isn't any variation along the flow direction within a single block. But you can (1) use a few more blocks in series or (2) modify the convective heat transfer correlation to reflect the overall heat transfer.

[SUDEEP SINGH RAWAT]

Hi,

there is one idea in mind, i would like to seek your input. there is 4 cylindrical cell arrangement having diameter(D), space between cell as (S) and height of cell is (h). The air will be coming from the front i.e. from your viewing angle, and pass through the spacing (S). Please see the attached image. I have calculated hydraulic diameter(Dh) based on this arrangement. Am i correct in this approach?

Regards,

[Yifeng Tang]

If the heat transfer is happening between the air gap and the cell wall, I think the perimeter should be 2*3*h in your equation.

[Yifeng Tang]

But, keep in mind, this is an approximation at best, because I think your formulation is more appropriate for "cubic" shape cells. The gap shown in the picture is really the minimum gap.