r/FluidMechanics

For this homework question, I imagined the efficiency contour plots as a mountain and chose the point on the impeller curve that seemed closest to the top of the mountain. However, I don’t think that this is the best way to do it, and I wasn’t able to find a source that explains it. Please help.

Hi everyone, I will start of saying that English isn't my first language so I used AI to sum up my thoughts in terms you will understand.

I’m currently working on a heat exchanger for a fluidized bed boiler and I’m looking for some design insights.

The boiler is burning biomass so there is a lot of stones andother impurities in the fuel. The geometry of the heat exchanger is a bit uncommon: it’s a serpentine path using a rectangular cross-section with a very high aspect ratio 150 mm x 20 mm.

I’m curious about the collective experience here regarding the "ideology" of designing for these types of specific, high-heat-flux environments.

A few points that I'm wondering about:

• The "skinny" channel. The first though that came to my mind was to maximize the surface area to volume of the heat exchanger thus the skinny channels. So that the stones have a free path trough. Is the skinny channel worth it?
• The Serpentine design. The u-bends with the smaller diameter being effectively zero. The flow seperates and creates pressure drops and effectively lowers the area the fluid flows through. Is there a better u-bend design to send the fluid back?
• The fluid speed inside the heat exchanger. Right now I don't have access to current data from the plant so I am stuck guessing numbers and making assumptions. What kind of fluid speed should I expect.

I’m not looking for a specific solution to my problems, but I want to grasp the overall design philosophy. I’ve reviewed Idelchik’s Handbook of Hydraulic Losses, but the bends I’m dealing with don’t match the equations provided there.

Some CFD images.

Again sorry for the AI.