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Drazen: maybe I expressed myself incorrectly, I was not refering to temperature of the duct, but of the air.

I would consider it as a beam, and calculate also the reactions at the supports. May be you can also calculate the deflection in the middle point.

Torque es forcé x distance, if you put a bigger pulley, the toque is the same, but the forcé at the circunference of the pulley will change proportionally.

In my experience there are no standards regarding this topics. I dont remembe NFPA saying something about it. I agree its better to pass the pipe over the dike or Wall, it also permits displacements when temperatura rises. On the other hand you always put a valve at the outlet of the tank...

Thanks HerrKarl, but my doubt was referring to a duct with constant temperature (no variation in density) and considering incompressible flow. In some handbooks I found they add up height pressure, but I think my error was to consider the atmospheric pressure the same at the inlet in the bottom...

I cant imagine a situation where you have constantly a vaccum in the duct, but if fan stops, then air will fill the vacuum. On the othe side if you put the fan at the top you would have a negative pressure inside the pipe, but on the outside you will always have the atmospheric pressure, and...

I was considering no temperature variation, therefore the density remains the same and there is no stack effect. I think HerrKarl example of obtaining potential energy from a duct full of air makes clear that the above reasoning of the Bernoulli ecuation for a non compressible fluid is correct...

If you apply Bernoulli at the inlet, berore the fan, and at the outlet, you will have: v1=0, v2=v (v=velocity inside the duct, suposing air comes out at the same velocity it has inside the duct) p1=p2 + SP(z2-z1) SP: Specific Weight of air Therefore substituting in the Bernoulli formula you...

Thanks all for your answers. If you have a 10m vertical duct with 300m3/hr the height pressure is about 12 mm H2O, this can be important in relation with the friction pressure loss, depending of the type of duct. Is this wrong? If you only have a straight duct, then according to my calculations...

Why is it than in some handbooks for air ventilation, the height pressure (density x height) is not considered for fan pressure calculations?

In all cases we use pipes with angles 35º or more, but in some cases there is no other way than having smaller angles, and it works fine as long as it comes from another pipe with bigger angle and therefore higher velocities.

Berk I understand, but I could fall directly 90º on the belt, I thought that certain angle was needed so as to let the grain have certain velocity in the same direction of the belt, and favor the transition of the falling grain into the belt conveyor. I have seen belts where grain falling...

It means that for a 12º conveyor we would need a 24º degree chute. The angle of the belt conveyor was the same at the entrance?

thank you berkshire: your contribution is very good. I suppose that its smooth belts when you say "with no cleats"? (Forgive me English is not my first language)

Thanks to all that gave interesting ideas. I had already contacted and look about in the bulk-online forum: theoretically speaking nobody has a clear idea of it, and there seems to be several opinions about it. In technical literature it appears 14º as maximun, but there are great discussions...

We are in pre-design phase of a soybeam transportation system. Can anybody recomend the maximun angle for the belt conveyer? Or where can we find literature refering to this subject. thanks

Thanks Greg Locock, we are working for it. In the meantime, is there any rule of thumb for the maximun material to be extracted? alfredo

There is a need to extract material during a turbocompressor dynamic balancing. Is there any limitation to the shape and amount of material to be extracted in a given point? Are there any standards, rules or guidelines regarding this point?

You may estimate by regression analysis coefficients for any type curve with sufficient and reliable data; its very easy with matrix operation in excel. If you find any formula at Nist or Dupont, let me know, I couldnt.

You can also use the churchill equation, its more direct. You still need the rugosity coefficient depending on the type of material.