Laminar Flow - Difference Between Helical and the SMX-Types of Mixer

The Helical Mixer is a very simple and versatile static mixer.  Each mixing element of a helical mixer is essentially a plate twisted into a shape of a helix (hence its name) and attached to the next at a 90 degree angle about the axial.

As 2 fluids or more enter a helical mixer, the first element divides the flow into 2 parts.  Along the first element, radial mixing happens.  Then the flow enters the second element, and the flows are further split into 2 and mixed radially.  This continues on and on until full mixing is achieved.

Helical Mixing - Laminar Flow

The mixing is gentle, which is good for fluids that cannot afford to be sheared too much, especially non-Newtonian fluids that need to maintain their physical properties.

One disadvantage however, is that helical mixers may tend to require more elements than other mixers to achieve a good homogeneity, which comes at the cost of real estate or space.

Cross Section Mixing Illustrations After 1 Element, 2 Elements, 3 Elements, and so on. (Taken from http://www.samhwamix.com/)

The diagram above gives a clear indication of visual homogeneity after each element.  Decent mixing probably starts to happen by the 8th element, although streaks can clearly still be seen.


Solution?
An alternative to Helical Mixer could be the SMX-type mixer.  Within a short distance and a smaller number of elements, the mixer is able to thoroughly mix highly viscous fluids as shown in the diagram below:

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The Difference Between ANSI and ASME Flanges

I know, I’ve been confused too.  One moment I see ANSI B16.5, and then a few days later I see ASME B16.5 and I think to myself, “What th–?”

Should I call them ANSI or ASME flanges?  Are they the same? Or are they really different?

The answer is this:  They are the same.

More correctly, ASME should be used, not ANSI.

Apparently, these flanges were initially specified as ANSI B16.5, then they were called ANSI/ASME B16.5.  Today, these flanges are officially categorised under ASME B16.5.  We still see these flanges specified as ANSI, even in large organisations.  Whatever it is, let’s just bear in mind that they are the same and people still use them interchangeably.

Pipe Threads | NPT vs BSP

Threaded connections are one of the common ways of connecting pipes.  Threads are either “male” or “female” and most people (who let’s all hope have enough carnal knowledge) can readily guess which is which.  For the benefit of the rest of the population, it’s like this:  Threads on the outside is male, threads on the inside is female.

Male Threaded Pipe Ends

Female Threaded Pipe Ends

Most of the world will use either NPT (American Standard Pipe Taper Thread, to ASME B1.20.1) or BSP (British Standard Pipe Thread to BS21).   By the way, BSP threads are also interchangeable with ISO, DIN and JIS.  NPT and BSP are not compatible and should not be coupled together (ever).  This is especially true for the smaller threads that are compatible to each other– you will notice a slight resistance when turning them.  Compatible threads should feel easy when you’re turning them during connection.  Having to put a little force to screw them together is a sign that you have incompatible thread standards, and doing so with just damage the threads permanently.

So, NPT or BSP?  It’s really up to you.  Here’s a suggestion:  if you tend to use American standards (for your designs and in your plant) or if your client’s plant is mainly using American standards, then perhaps it’s wise to go for NPT threads.  Likewise, it’s BSP if for example your equipment is already built to BS 2790 (British Standards for welded shell boilers).

But Why Static Mixers?

I’ve recently had a chat with someone and he was curious about static mixers.  As I explained what the static mixer was and what it does, he asked me these questions:

“Erm… so, if you push 2 liquids through a pipe and the flow is turbulent, won’t they both mix eventually anyway?  I mean, I could just put something inside my pipe and eventually get a homogeneous mixture right? ”

Well, the short answer is:  Yes.

But with a fully designed static mixer, you are talking about a predictable homogeneity within a predictable distance.  In other words, with a static mixer, you will get a definitive answer like “a Homogeneity of 96% at the mixer outlet”.

Dye Penetration Test

A Dye Penetration Test, or otherwise known as Dye Penetrant Test, “PT” or Liquid Penetration Test; is one of the most basic Non Destructive Examinations (NDE) or tests that can be performed on a completed weld.  A visual look at a completed weld may not tell if there are defects in a weld.  By performing a dye penetration test, one is able to visually observe imperfections on a welding more easily.  It involves pouring a liquid dye over a weld and letting it seep into any tiny crevice that is present.  The liquid is then washed away and a spray (called a “developer”) is then applied over the weld.  When the developer dries, it pulls out the dye within the crevice and the defect can then be seen where the dye comes out.  However, this method can only detect surface flaws and will not tell you the condition of the weld below the surface.  For that, you will need to use other tests like the Radiography Test or the Ultrasonic Test.  The advantage of this test is that is is cheap and easy to perform.

This short video shows from YouTube shows how a Dye Penetration Test is done.