Steam Engine: Basic & advanced features: Pts. One & Two
This is going long... so get comfortable, and I'll try and make it as painless as possible.
Update: On 5/24/15 I discovered that the new forum software allows far more than the old vBulletin limit of 10,000 characters per posting, so I've combined what was originally a two part series into a single article.
More so than any other element of the Steam Engine modeling program, the variable of "heat flux", is the most difficult to understand. Along with questions about wire gauge, surface area, net resistance/parallel coil count (or why anyone in their right mind would want a 300 plus watt APV)... that I wonder just how many folks there are out there who may be avoiding 'SE' completely... perhaps because they feel a bit technically overwhelmed by the multitude of input options.
(Note: Things advance and improve rapidly in the vaping world. 200+ watt mods are now common place, as is temperature control - making some of the more critical tuning options, er... less critical. If you run a modern device, it still doesn't hurt to build an efficient atomizer, and if you run an unregulated (mech) mod, this article is still highly applicable)
In the next few several paragraphs, I will endeavor to explain how to use specific elements of SE... to the users best advantage.
First, lets give credit where it is definitely due. Steam Engine was created (and is continuously upgraded since it's introduction) by ECF member - and an extremely clever and generous fellow - by the name of "Dampmaskin" (AKA, Lars Simonsen). I'm honored that Lars has read both parts of this article, and approves them for content and accuracy.
The word 'Dampmaskin', as it turns out, is Norwegian for 'steam engine'... and Lars lives in Norway. Now it all makes sense, yes?
And for even more reading (as if this isn't enough already), here's Dampmaskin's blog and his FB page, on the subject of Steam Engine.
To begin, lets visit the often overlooked variables... variables in which you, the vapist must enter appropriate values. Viewing from top left, our first variable is "metric units/imperial/USCS units"
(top left hand corner). Use which ever method of measurement you're more comfortable with. I prefer metric, and/or decimal inch.
Certain aspects of the program, like "Inner diameter of coil" (top right hand) has a default of 1.3mm. If you use metric units, and click on the x/y" (top far right, lower corner of Inner diameter of coil)... a drop down will list values in fraction, and the display will indicate a metric conversion - i.e. 1/16" will show as 1.59mm.
If you chose "imperial units", the drop down will still be fractional, but will convert to decimal - i.e. 1/16" will be displayed as 0.0625".
Coil inner diameter (ID) is based on the outer diameter (OD) of the mandrel you use - be it a toothpick, a drill bit, the shaft of a micro screwdriver - all are considered, for our purposes, a mandrel.
If you use unmarked mandrels, a good investment will be a digital or dial type caliper, which will allow you to accurately measure your mandrel OD.
Our next variable will be "Advanced and Reset" (upper mid left hand). 'Advanced' will show more detail of your build model, and 'Reset' is just that... erasing all user loaded data, and returning you to a program baseline.
Want to play with braided or twisted coils? In the box for "Material and profile" the default profile is "Round"... as in round wire. If you click on the drop down menu on the right of that box, you'll see "Round, twisted/parallel".
Clicking on that, two new windows will open... "Twist pitch" and "Number of strands". You can use up to 4 separate strands of wire... and pay particular attention to the twist pitch value where you measure the distance between wire ridges... and insert that value into the twist pitch box.
Here is a re-print what Dampmaskin has written regarding twist pitch:
"The distance between each "ridge" on the twisted wire. Use 0 (mm) for non-twisted wire (parallel strands). For improved accuracy: Count 10 ridges, measure their total width, and divide by 10."
A bit of critical info for multi-strand users... if you have two strands per coil, even though they alone technically qualify as dual parallel coils, the program considers it a single coil, when you click the "round, twisted/parallel option. It's not a dual parallel build.
If you have four strands making up two coils... then it's considered a dual parallel build.
A thread from 6/18/15, where a more extensive explanation of the variables in twist pitch can be found here.
Next is perhaps the most valuable reference you can click on... "How it Works" (bottom lower left)... which extends the page (don't forget to scroll down a bit) and provides an overview of the program details, and how to interpret those details.
Quick note - The only thing that determines resistance is the wire length and thickness. Example: A 72.6mm length of 28 gauge Kanthal A1 wire (call it as you wish, terminal to terminal - post to post or positive to negative) will always have a resistance of 2.6Ω.
The wrap count, coil ID, leg lengths... any and all physical changes you make to the wire (aside from stretching it with high tension, or cutting it to a shorter length), have no effect on resistance.
Let's look next at "Setup". Setup is a drop-down option of the physical elements, for the determination of net resistance ('net' being the combined resistance value), of your build.
Individual lengths of wire have a singular resistance value - adding additional lengths of wire will alter the net resistance - dividing the value of one wires resistance by the total number of wires used. This is called a "Parallel" build.
Example: If you have 2 individual coils (dual parallel), the net resistance will be the resistance of one coil, divided by 2. Five coils... divide the resistance of one wire by 5, and so on. An example of this would be a penta (5) parallel build, where it would require five 3.5Ω coils to produce a 0.7Ω net resistance.
The "Serial" build option is when coils are end to end... like one piece of wire used to make two or more coils. Basically, regardless of the number of individual coils made in a length of wire, you are using the resistance value of that length of wire for the total resistance value.
So... four coils made using one length of wire (and ending in one pair of +/- terminals) has the same resistance as one coil, made from the same length of wire... and a whole lot of leg length.
Jumping ahead to some additional less than obvious elements of SE...
"Leg length"... is the approximate length of the wire "leads" at the ends of your coil. Call them legs, tails or pains in the backside... this is something that can be measured accurately, but typically only after the coil has been installed in the atty. Long legs waste available energy... keep 'em as short, within the limits of RBA physical properties and placement relative to air flow.
I tend to use 5mm (or 10mm for 2 parallel coils) as a general purpose length (2.5mm length X 2 legs per coil)... because it takes a substantial change in leg length - unless you're on the ragged edge of a "Number of wraps" - to have any effect on the finished wrap count.
There... that didn't hurt too bad, did it? Good... the next bit might.
Heat Flux... and you.
Lets look at perhaps the most ignored, misused and/or misunderstood option in SE... and the reason I wrote all this in the first place. "Heat Flux" (HF).
Heat flux (HF) is a measurement of radiant heat our resistance wire coil generates, measured in milliwatts per millimeter squared, or mW/mm2.
Dampmaskin has provided, along with actual numeric values, a color code range that runs from a cold blue to a flaming hot, deep red... so you can, by calculating your current build and PV power output, create a baseline reference, or optimal HF to suit your personal preference.
The easiest way to view heat flux is as the radiant heat potential of an atomizer - not a specific, Fahrenheit or Celsius value. Even with an infrared, laser aimed thermometer, the variables that effect
temperature are too many and too inconsistent to be remotely relatable.
The way heat flux works... you can approach it from more than one direction.
You can use it to determine the optimal wattage value for a given build, or the optimal build for a given wattage. With the latter, a single change to one element, will affect all other elements.
In practical (and overly simplistic) terms, the lower the peak wattage output of your device, the thinner the wire must be... and of course the higher the current output, the thicker the wire gauge you can adequately support.
Let me offer an example. You are a mech user, and are - like most RDA fans - of the opinion that thicker wire is always a good thing. You build a dual coil RDA with a 28 gauge, dual parallel build at 1.0Ω. You're using an 18350 mech with an Efest "Purple" 10.5a rated battery.
So... why the hell is my vape so darn cold, or why does my wick and coil "gunk up" so quickly, you ask? Heat, or rather... a lack of it.
You may think that because your battery is rated for 10.5 amps continuous discharge, that you're getting a full 42 watts of power and your heat flux is around 186 mW/mm2, right?
Recalling Ohm's law... your resistance dictates how much current is being discharged, which in the case of a 1.0Ω net resistance and a 4.2v battery... that's only about 17 watts. Your HF is a chilly 75 mW/mm2.
To "push" your unregulated 18350 battery mod to it's maximum continuous discharge, you'd need to run at least 30 gauge wire for a 1.0Ω net resistance, dual parallel build, and preferably 31 or 32 gauge, to obtain a warmer heat flux.
Other options are a lower resistance, or build a single coil with your 28 gauge... any of these, or a combination will increase your HF temperature.
Watch the HF values change - sometimes dramatically - as you change just one variable.
If you're a unregulated mod user (mech), you can't "force" wattage as you would with a regulated APV. You'll need to use Ohm's law formula to calculate wattage discharge for your resistance and battery. Same goes for APVs that are voltage controllable only... to obtain a wattage value SE will accept.
Another example, is with a 100 watt VW APV. Because you can, you want to run the full hundred watts, to see what it's like... right? What can you build that won't turn your mod into a Tiki torch?
First, set your wattage value at 100 (or what ever you want to start with), then on to your "Setup".
For setup, we're using a dual parallel coil RTA, like an Orchid. Next set your target or desired resistance... lets try a net resistance of 0.6Ω.
OK... based on past experience, we don't want our heat flux higher than 375.
Now... start to adjust the size of your wire, while you watch the HF values.
Click, clickity... click. 28 gauge is too hot and 24 gauge is a bit too cool... but 26 gauge, with a HF of 369 is (well, if you're into pretty darn warm) just right.
Let's run a popular low powered example... for an MVP2, at it's limit of 11 watts, 1.3Ω+/- and 3 amps. You may have already guessed that we might need thin wire for this one... but as a single coil build, we can do better than you might expect.
Using 28 gauge wire at 8 wraps (on a 2mm mandrel), we get a "green zone" HF of 163 mW/mm2, and if we go with a 30 gauge wire at 5 wraps... a very nicely warm HF of 326 mW/mm2.
The only down side here is the coil surface area... but as all we have is 11 watts to work with, not to mention that 1.2Ω limit, it's the best we can do.
If we had a lower resistance limit, say enough current output for 0.8Ω... we could get a warm 244 mW/mm2 with a 28 gauge 5 wrap build.
So, is there an "optimal heat flux"? Good question.
Although one might consider something in the green to yellow as an optimal value, I continue to run into individuals who prefer a heat flux in the blue / green range... and some into the deeper red zone. It's a highly subjective value, and one that drawing comparisons of - unlike wire gauge, juice blend or net resistance - offers only limited value to the individual.
What you like, is... what you like. If you like a warm 356 mW/mm2 in December, and a cooler 189 mW/mm2 (or less) in August... that makes all the sense in the world, don't it?
Perhaps the easiest way to determine your best heat flux is to run the numbers of what you are currently happy with. If you're somewhere in the 150 to 400 mW/mm2 range... it's a wide range, but surprisingly, fairly normal.
The more experienced RDA users tend to run the hottest, then, due to their limited coil chamber space - RTAs, with clearos glassos and cartos usually running a bit cooler. The latter vapists are frequently beginners - and having read all the scary ECF warnings - are a bit paranoid about things exploding, or being rendered unconscious from the massive vapor hit.
The text book optimal or perfect build would have a user preferred HF... along with the more universally desirable low HC for a rapid heating time, a low leg power loss, so you're not wasting energy to heat legs... while we're at it, and if that's not enough, a terrific surface area - more area - so more juice gets vaporized.
Does that exist? Absolutely, but only within certain parameters - a parameter target you can hit squarely... or miss by a mile.
Based on what I read in the vape forums on a near daily basis... there are far more builds that miss the target by varying degrees, than are direct bullseyes. Seriously.
Don't believe me? Run someone else's numbers. You might be surprised (as in builds that are far too hot or cold, with terrible temperature lag, and/or high heat capacity values)... at what you discover.
Speaking of heat capacity...
Another ignored and misunderstood reference value (even more so than HF) is heat capacity (HC). It's important... but not as user critical as heat flux.
This is a representation of time-to-temperature efficiency... or how fast a coil will heat up - to the heat flux value. Time is directly relatable to the coil(s) mass.
The value - mJ K-1 - is measured in millijoules (time) to Kelvin (temperature per mass). The higher the mJ/K value, the longer it takes for the coil(s) in question to reach peak temperature (HC).
(After spending a good bit of time researching reference material, converting Kelvin to C° and F°, converting millijoules to BTUs and watt-seconds, making pages of notes, discussing it with Lars and "readeuler", (both of whom did meaningful research - and the vast majority of "hardcore" mathematics) about alternate references - until further notice, it shall remain as stated... or simplified to just mJ/K.)
In atomizer heating elements, a clear example would be... a pair of thinner gauge parallel coils are more efficient than a single thicker gauge coil - at the same resistance and wattage input - due to the greater net mass of the single coil.
The net mass value can be found by clicking on the "Advanced" button (upper mid left hand) and scrolling to those coil physical dimension values.
Examples: (where a lower HC value is preferred)
Example 1. Is our baseline... the most efficient, with the highest peak temperature.
- 30 gauge dual parallel build at 1.0Ω/24 watts. HF is 214, HC is 12, net coil mass is 25 mg.
- 28 gauge dual parallel build at 1.0Ω/24 watts. HF is 107, HC is 30, net coil mass is 64 mg.
- 24 gauge single build at 1.0Ω/24 watts.......... HF is 106, HC is 94, coil mass is 205 mg.
- 22 gauge single build at 1.0Ω/24 watts.......... HF is 53, HC is 239, coil mass is 519 mg.
Example 2. Efficiency decreases 2.5 times that of example 1. Peak temperature decreases to 1/2 of example 1.
Example 3. Efficiency decreases 3 times that of example 2, and nearly 8 times that of example 1. peak temperature remains constant from sample 2.
Example 4. Efficiency decreases 2.5 times that of example 3 and 20 times that of example 1. Peak temperature rises to 1/2 of example 3 and 1/4th that of example 1.
What you can take from this is that - for a desired resistance (wire gauge and length to produce a specific resistance) along with coil count and wattage - coil mass can have a substantive effect on the efficiency of your build.
There will be an optimal value for a given set of elements, where you can have the desired high HF, with a fairly low HC.
The way I see it... coil net surface area comes first (or not... because many will limit surface area because of power or lower resistance limits,) desired HF, then the lowest HC I can produce for that desired resistance and surface area. I'm willing to tolerate a few extra seconds of time to get the HF and surface area I want.
5-23-2015 Addendum: Having read this through a few times, I've decided to re-write it in it's entirety... with a more "step-by-step" process suitable for brandy new Steam Engine users.
I'll save this old version when I post the re-edited, "new and improved" version... for those that have it linked as a reference source.
10-18-2015 Addendum: I am a lazy ........ I will write something soon. This year... promise. No, really. Honest.
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