Pressure drop for viscous fluid in conducts with an obstacle at the outlet

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Discussion Overview

The discussion revolves around estimating the pressure drop for a viscous (non-Newtonian) fluid flowing through a tube with an inclined plane at the exit. Participants explore how the angle of the inclined plane influences the pressure drop, considering factors such as viscosity, temperature, and flow conditions.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested
  • Mathematical reasoning

Main Points Raised

  • One participant seeks to understand the influence of an inclined plane on pressure drop for a viscous fluid, specifying the need for calculations based on the angle of the plane.
  • Another participant questions the assumption that viscosity equates to non-Newtonian behavior, suggesting that the behavior of viscous fluids in constricted tubes is generally straightforward.
  • A later reply emphasizes the importance of temperature on viscosity, raising concerns about the effects of temperature variations as the fluid interacts with the inclined plane.
  • One participant proposes to simplify the problem by assuming uniform viscosity, laminar flow, and steady-state conditions, and suggests estimating the drag coefficient for the specific geometry to calculate back pressure.
  • Another participant provides a resource link that may assist in understanding fluid jets and related drag coefficients.

Areas of Agreement / Disagreement

Participants express differing views on the relationship between viscosity and non-Newtonian behavior, and there is no consensus on the best approach to estimate the pressure drop, indicating multiple competing views remain.

Contextual Notes

Participants acknowledge limitations such as the dependence on temperature for viscosity, the assumption of uniform viscosity, and the lack of specific drag coefficients for the described geometry.

pippobaudo
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Hello,

I have the following system (see enclosed figure): A viscous (non Newtonian) fluid at high temperature is going trough a tube at a known mass flow, at the exit there is an inclined plane at a given angle (b).
I would like to estimate in some way how the inclined plane at the exit influences the Pressure drop between the entrance and the tube exit. In addition i'd like to calculate how the pressure drop varies as a function of the angle (b) of the inclined plane.

Any help is appreciated, also If you could suggest some good books on viscous flow hydrodynamics.

Thanks guys,
Pippo
 
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I don't understand why you (apparently) equate viscosity with non-Newtonian behavior.

Your figure is not attached, but the behavior of a viscous fluid leaving a constricted tube (a nozzle) is fairly straightforward in most cases. Streeter's "Fluid Mechanics" is a decent place to start.
 
Hello and thanks for the reply,

well let's say that is a very viscous fluid which, in order to be fluidized, has to be heated to more than 100 Celsius.
I try to enclose again the figure, (I go to "manage Attachments" and upload) I hope It will be attached this time.

 

Attachments

  • B_L_figure.gif
    B_L_figure.gif
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Ok, so the viscosity is a (strong) function of temperature. I wonder if that is more important than whatever nozzle geometry you have- what is the temperature of the fluid as it travels down the pipe and impinges on the plate? If the temperature becomes nonuniform (say the plate is cold but the fluid is hot), I would think the dominant effect would be due to the changes in viscosity.
 
Hi, yes I think you are right, the temperature for fluidizing the medium is 120 Celsius.
However now I'd like to solve the problem assuming uniform viscosity, laminar flow and steady state conditions. In addition the temperature of the tube walls including the external object is assumed equal to that of the fluid.

I am thinking about finding the drag coefficient for this particular geometry and then estimate the force done on the flat surface, from this force will be possible to estimate (in some way...) a back pressure on the fluid so that the pressure drop between the entrance and tube exit will be estimated.

I didnt find yet this geometry among the drag coefficients for immersed bodies...
Thanks
 

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