Contact US

Log In

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips Forums!
  • Talk With Other Members
  • Be Notified Of Responses
    To Your Posts
  • Keyword Search
  • One-Click Access To Your
    Favorite Forums
  • Automated Signatures
    On Your Posts
  • Best Of All, It's Free!

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

Students Click Here




Hello All.

How do I solve the power of e , I circled in image below? what is Xdx?

Thank you.

RE: Derivatives

Sorry I meant Ddx (not Xdx)

RE: Derivatives

The "…al Profile" in the top LH corner of your image is consistent with Greg's impression of what the formula is for.  However several things about that formula seem a bit odd, not just the dx.  Could you please give us an explanation of what it is supposed to be for, and where it comes from.  Plus full definitions of all the terms, and the units in which the terms are to be expressed.

RE: Derivatives

This formula is for steady state thermal profile of a subsea pipe. I know the units are mismatch.I was looking to understand dx to solve the exponential value but I only had pipe length and no other varying parameter for x. But I believe GregLocock is right and I will proceed on my calcs with that. Thank you so much.

RE: Derivatives

The fact that the exponent is not non-dimensional is what I was hinting at with my "several things about that formula seem a bit odd".  "A bit odd" is a massive understatement:  be VERY careful if you intend to proceed without digging further into the formula's provenance.

RE: Derivatives

Looks like a really good problem for SMath... units and derivative... maybe try coding it up...


RE: Derivatives

Actually the units look ok to me assuming (dx) has units of length (maybe it is shorthand for a small delta-X as opposed to a calculus symbol which would not be properly applied without another differential or integral symbol somewhere). I don't know what the physical problem is - I'm just looking at the units.

The numerator and denominator of the exponential argument both have units of watts per degrees Kelvin (W/K), so the argument ends up dimensionless.
Numerator = U D dx = (W/m^2*k) * (m) *(m) = W / K
Denominator = m-dot * cp = (kg/sec) * (Joule/[kg*K]) = Joule / [sec*K]) = W / K

(2B)+(2B)' ?

RE: Derivatives

So Cp is not a dimensionless coefficient (despite being presented as such in the hand annotations)?

RE: Derivatives

Oh, I see what you're saying. Yes, the handwriter apparently forgot to label those units. I missed that he missed that. That's a good thing to question / clarify.

Cp is apparently referring to specific heat capacity (at a constant pressure) which would have SI units J/[kg*K] (I don't know what specific units were intended to accompany the value listed 1800)

(2B)+(2B)' ?

Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

Reply To This Thread

Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members! Already a Member? Login


Low-Volume Rapid Injection Molding With 3D Printed Molds
Learn methods and guidelines for using stereolithography (SLA) 3D printed molds in the injection molding process to lower costs and lead time. Discover how this hybrid manufacturing process enables on-demand mold fabrication to quickly produce small batches of thermoplastic parts. Download Now
Design for Additive Manufacturing (DfAM)
Examine how the principles of DfAM upend many of the long-standing rules around manufacturability - allowing engineers and designers to place a part’s function at the center of their design considerations. Download Now
Taking Control of Engineering Documents
This ebook covers tips for creating and managing workflows, security best practices and protection of intellectual property, Cloud vs. on-premise software solutions, CAD file management, compliance, and more. Download Now

Close Box

Join Eng-Tips® Today!

Join your peers on the Internet's largest technical engineering professional community.
It's easy to join and it's free.

Here's Why Members Love Eng-Tips Forums:

Register now while it's still free!

Already a member? Close this window and log in.

Join Us             Close