Hydraulic Diameter Explained: 4.4 vs 4.5

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Homework Help Overview

The discussion revolves around the definitions and calculations of hydraulic diameter in different contexts, specifically comparing the equations presented in sections 4.4 and 4.5 of a text. Participants are examining the differences in the definitions of hydraulic radius and equivalent diameter.

Discussion Character

  • Conceptual clarification, Assumption checking

Approaches and Questions Raised

  • Participants are questioning the rationale behind the different definitions of diameter in the two sections, specifically why D is defined as 4Rh in 4.4 and 2Rh in 4.5. There is an attempt to clarify the definitions of hydraulic radius and equivalent diameter.

Discussion Status

The discussion is active, with participants providing insights into the definitions used in the text. Some participants suggest that there may be a mistake in the terminology used in section 4.5, while others are seeking further clarification on the definitions and their implications.

Contextual Notes

There appears to be confusion regarding the notation used for hydraulic radius and its application in different scenarios, particularly in relation to cylindrical shapes. The original poster's inquiry highlights a potential inconsistency in the text's definitions.

foo9008
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Homework Statement


why in 4.4 the author gave D =4Rh? in 4.5, D= 2Rh ?

Homework Equations

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In some developments, the hydraulic radius is defined as the area divided by the wetted perimeter. Get used to the idea.
 
Chestermiller said:
In some developments, the hydraulic radius is defined as the area divided by the wetted perimeter. Get used to the idea.
why in 4.4 the author gave D =4Rh? in 4.5, D= 2Rh ? can you explain?
 
foo9008 said:
why in 4.4 the author gave D =4Rh? in 4.5, D= 2Rh ? can you explain?
Yes. He is consistent in defining the hydraulic radius as S/Lp, and the equivalent diameter as 4S/Lp. However, in 4.5, he makes the mistake of calling the radius of the cylinder RH. The term in brackets should not have a subscript H. It should just have an R. And, for a cylinder, RH=R/2.
 

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