## David Steinberg's formula

## David Steinberg's formula

(OP)

Guys:

I'm probably showing my age, but I have this book:

Steinberg, Dave S.,

Any of you out there have ANY OTHER edition of this book?

In my edition his equation for the hydraulic diameter

For years in my career I used this formula in spreadsheet calculations. The natural convection coefficient for that surface is inversely proportional to the fourth root of the hydraulic diameter.

I looked many other places and found that it SHOULD read

I actually used the definition of hydraulic diameter to prove the correction:

I'm probably showing my age, but I have this book:

Steinberg, Dave S.,

*Cooling Techniques for Electronic Equipment 2nd Ed.*; John Wiley & Sons, Inc., 1991.Any of you out there have ANY OTHER edition of this book?

In my edition his equation for the hydraulic diameter

*D*of a*W*X*L*horizontal rectangular surfaces is**. What does your edition say?***D=0.5LW/(L+W)*For years in my career I used this formula in spreadsheet calculations. The natural convection coefficient for that surface is inversely proportional to the fourth root of the hydraulic diameter.

I looked many other places and found that it SHOULD read

**which is four times bigger. So I have been UNDERESTIMATING the natural convection coefficients by a factor of (4)^(-0.25) = .707 for years in my spreadsheet calculations? Do you agree?***D=2LW/(L+W)*I actually used the definition of hydraulic diameter to prove the correction:

*D=4X(cross-sectional area)/(wetted perimeter)=4(LW)/[2L+2W]=2LW/(L+W).*H. Bruce Jackson

ElectroMechanical Product Development

UMD 1984

UCF 1993

## RE: David Steinberg's formula

TTFN (ta ta for now)

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## RE: David Steinberg's formula

## RE: David Steinberg's formula

In the index it lists three places where hydraulic diameter is mentioned. In all three places it is correctly printed:

Dh = 4x area/perimeter (page 170)

for a rectangular duct Dh = 2ad/(a+d)

Can you go back and look at page 170 in your copy of the book? My best guess is that it got copied into the spreadsheet wrong (I do it all the time).

## RE: David Steinberg's formula

Thermal Computations for Electronic Equipmentthat has the wrong formula.Thanks all!

H. Bruce Jackson

ElectroMechanical Product Development

UMD 1984

UCF 1993

## RE: David Steinberg's formula

D = 4 Ac/Pw where Ac is the cross-section area and Pw is the wetted perimeter.

Obviously I can't check every instance in the book, but I think this source also is correct. Maybe it was one of my books that steered you wrong?

## RE: David Steinberg's formula

H. Bruce Jackson

ElectroMechanical Product Development

UMD 1984

UCF 1993

## RE: David Steinberg's formula

Even if you are thinking about natural convection, the concept of hydraulic diameter does not change. Maybe you are thinking of another concept?

## RE: David Steinberg's formula

Now I have searched high and low and cannot find my copy of Ellison's "Thermal Computations for Electronic Equipment" but I DID find a copy of his short course notes where he uses the D=0.5WL/(L+W) formula. I have attached the notes. If you search for the word "characteristic" you'll find it. I can only assume that if he used the wrong formula in his course notes then he must have the wrong formula in his book.

Thanks,

Bruce

H. Bruce Jackson

ElectroMechanical Product Development

UMD 1984

UCF 1993

## RE: David Steinberg's formula

H. Bruce Jackson

ElectroMechanical Product Development

UMD 1984

UCF 1993