Heat Island Technology

[Alan]

There have been some questions as to how the new style log vaporizers operate. I am posting this in the vaporization discussion section since it is not model specific. There are multiple vaporizers that use this technology.

The following diagram illustrates how this new technology works. It also provides terminology for each of the parts.

There are three main parts. The core outer tube, the core center tube, and the heating element.

The roasting tubes can be placed over the core center tube or into the core center tube to draw hot air through the herbal mass. Room air enters into the space between the core outer and center tubes traveling down to the bottom. The air passes through holes drilled into the center tube and makes a 180 degree turn passing between the center tube and the heating element.

The heart of the system is a heating element. The HI uses a vitrious enamel coated resistor that is identical to those found in the heart of all 12 volt log vaporizers. It is about 5mm in diameter and 23mm in length. The temperature measured 450F with a probe in contact with both the center tube and heating element with 12 volts applied. Since the HI is able to cause combustion at 12 volts and combustion occurs at around 450F, therefore the temperature of the air leaving the center tube is approximately the same as the temperature of the heating element. If the heating element can reach 700F, then the air coming out will be 700F. The reason for this is the holes drilled into the center tube. They provide a physical break in the metal which significantly reduces the metal conduction path. They are the real key to the design. The holes eliminate 2/3 of the metal conduction path with the HI. The heat is mostly trapped in the center tube. The total area of all the holes (6) in the HI center tube is equivalent to the area of the center tube so the holes do not provide any additional resistance to air flow. The only air flow resistance is from the heating element in the center tube. The longer the heating element and center tube, the more air resistance. Only the portion of the heating element in the air stream will transfer heat to the air. Having a heating element with 4 times more surface area stuck into the core will not transfer more heat since only the portion in the air stream can transfer heat to the air stream. The distance from the holes in the center tube to the top of the center tube will determine both the air resistance and how much heat can be transferred to the air. This distance is 30mm with the HI.
The HI center tube is made from stainless steel which has a thermal conductivity of about 20 (Btu/(hr oF ft)). The HI outer tube is also made from stainless steel. I had considered using aluminum since it is easier to work, but it has a thermal conductivity of about 120 (Btu/(hr oF ft)) which is 6 times higher than stainless steel. I want the heat to stay at the center tube so that it is available to heat the air rather than conducting the heat away and into the wood. Bare aluminum also has a nasty habit of forming an oxide layer which could make the outer tube larger in diameter and crack the wood over time. Stainless steel remains very stable and is much stronger.
I also measured a surface contact temperature of 285F at the core outer tube with 12 volts applied to the HI. Since the heat conduction path is severely limited, there will be much less heat transferred to the wood which will eliminate any charring concerns.

 

[fubar]

There have been some questions as to how the new style log vaporizers operate. I am posting this in the vaporization discussion section since it is not model specific. There are multiple vaporizers that use this technology.

The following diagram illustrates how this new technology works. It also provides terminology for each of the parts.
.

Interesting. Looks to me like it kind of starts to get at the physics of http://en.wikipedia.org/wiki/Countercurrent_exchange ?
An old idea but a good one to make heat transfer more efficient - why not make the path longer for even more surface between incoming and outgoing air for countercurrent heat exchange?

 

[stickstones]

thanks alan...I love learning this shit!

 

[Alan]

Interesting. Looks to me like it kind of starts to get at the physics of http://en.wikipedia.org/wiki/Countercurrent_exchange ?
An old idea but a good one to make heat transfer more efficient - why not make the path longer for even more surface between incoming and outgoing air for countercurrent heat exchange?

A longer path will definitely increase the heat transfer since it provides more surface area. The trade off is that there is more air flow resistance with a longer path. The current length is able to provide more heat energy to the air than necessary, so a longer path is really not needed.

You are welcome stickstones. I love discovering this stuff so that everyone can enjoy the benefits.

 

[nopartofme]

What other logs use this technology?

 

[Squonk]

Hi Alan,

Is the core outer tube closed at the bottom ?... meaning that air can only enter inside the core center tube via the 6 holes.

Also I want to say that I really appreciate your expertise and know how on the subject of log vape.

 

[Alan]

What other logs use this technology?

The Wychwood and e-nano are the other log vaporizers using this technology.

Hi Alan,

Is the core outer tube closed at the bottom ?... meaning that air can only enter inside the core center tube via the 6 holes.

Also I want to say that I really appreciate your expertise and know how on the subject of log vape.

Thanks Squonk. The core outer tube is closed at the bottom by a stainless steel washer that connects the outer and center tubes together. The core is pressed into a hole bored into the wood body. Air can only enter from the open end of the outer tube since the power socket of the heating element closes the hole in the bottom of the wood body when it is threaded in.

 

[stickstones]

alan...doesn't the UD vegan use this design? or is he not offering those anymore?

 

[EveryDayAmnesiac]

alan...doesn't the UD vegan use this design? or is he not offering those anymore?

I don't know about the technology part, but I inquired about a Vegan Dog not long ago and he said he'd make me one if I decided I wanted one.

Just sayin'.

 

[stickstones]

cool...im pretty sure it is the same design, he just probably isn't marketing it...just special orders.

 

[kingofnull]

Wow, real nice Alan. I figured this was pretty much how all heat island style vapes worked.

 

[Alan]

alan...doesn't the UD vegan use this design? or is he not offering those anymore?

I believe the core of a vegan UD is the same as a regular UD.

The core of the PD, WZ, UD, TT, and Pod all connect at the top (and some the full length of the core) which transfers more heat energy to the wood and makes less available for heating the air at a given voltage. More heat energy can be made available by simply increasing the voltage which increases the temperature. All log style vaporizers are capable of very good efficiency.

 

[Tweek]

Thanks for taking the time to share this info. Very generous and much appreciated.

 

[OO]

I believe the core of a vegan UD is the same as a regular UD.

The core of the PD, WZ, UD, TT, and Pod all connect at the top (and some the full length of the core) which transfers more heat energy to the wood and makes less available for heating the air at a given voltage. More heat energy can be made available by simply increasing the voltage which increases the temperature. All log style vaporizers are capable of very good efficiency.

How do you rate the thermal conductivity, and by the inverse, thermal insulating ability of different woods?

Ideally I think you're looking for a wood that is hard enough to not char, yet Light enough to not conduct too much heat out correct?

Probably something high in lignin?

 

[Hippie Dickie]

i think minimizing contact of the heater with the wood would be preferred. a dead air space is a great insulator without adding mass. then the wood type is totally arbitrary ... well, some soft woods may not mill well enough.

 

[ACE OF VAPE]

I would like to address these 3 statements made by Alan in this post.

There have been some questions as to how the new style log vaporizers operate. I am posting this in the vaporization discussion section since it is not model specific. There are multiple vaporizers that use this technology.


1) If the heating element can reach 700F, then the air coming out will be 700F.

2) Only the portion of the heating element in the air stream will transfer heat to the air. Having a heating element with 4 times more surface area stuck into the core will not transfer more heat since only the portion in the air stream can transfer heat to the air stream.

3) Bare aluminum also has a nasty habit of forming an oxide layer which could make the outer tube larger in diameter and crack the wood over time.

1) The 700F degree temp produced by a heating element is only 700F at the surface or contact point of the element itself. As soon as this thermal energy leaves the heating element it is immediately mixed with the ambient air coming in through the holes in the heater core. The resulting temperature leaving the top of the heater core is a result of the volume and temperature of the air it is mixed with as well as the heat produced by the element.

2) If you have 4 times more surface area in the airstream you naturally transfer more heat into the airstream. Perhaps Alan was confusing surface area with volume?

3) 'By rusting, aluminum is forming a protective coating that’s chemically identical to sapphire—transparent, impervious to air and many chemicals, and able to protect the surface from further rusting: As soon as a microscopically thin layer has formed, the rusting stops.' (“Anodized” aluminum has been treated with acid and electricity to force it to grow an extra-thick layer of rust, because the more you have on the surface, the stronger and more scratch-resistant it is.) http://www.popsci.com/scitech/article/2004-09/amazing-rusting-aluminum

why not make the path longer for even more surface between incoming and outgoing air for countercurrent heat exchange?

That is why I used a much larger heating element in the E-Nano.

 

[Hippie Dickie]

so your longer heater fills more of the Core Center Tube (in the diagram)?

also, is there a heat gradient along the ceramic heater? i see this in a nichrome coil: hottest in the middle loops of the coil and cooler toward the end loops.

 

[ACE OF VAPE]

so your longer heater fills more of the Core Center Tube (in the diagram)?

also, is there a heat gradient along the ceramic heater? i see this in a nichrome coil: hottest in the middle loops of the coil and cooler toward the end loops.

Yes, much more. As such you can pull much more air volume past the core without cooling the element. My heater also plugs the bottom of the heater core with the ceramic flange, which completely isolates the air path from any wires, etc. i will post a drawing later.
Yes there is a heat gradient, and you can specify to the manufacturer where you want it to be. I placed the hottest part about 1/3 of the way down from the tip, so it is deep in the airflow.

 

[Hippie Dickie]

and you can specify to the manufacturer where you want it to be

nice! i had never thought about that.

 

[tepictoton]

thanks for sharing all this, really nice information

 

[Alan]

I would like to address these 3 statements made by Alan in this post.




1) The 700F degree temp produced by a heating element is only 700F at the surface or contact point of the element itself. As soon as this thermal energy leaves the heating element it is immediately mixed with the ambient air coming in through the holes in the heater core. The resulting temperature leaving the top of the heater core is a result of the volume and temperature of the air it is mixed with as well as the heat produced by the element.

2) If you have 4 times more surface area in the airstream you naturally transfer more heat into the airstream. Perhaps Alan was confusing surface area with volume?

3) 'By rusting, aluminum is forming a protective coating that’s chemically identical to sapphire—transparent, impervious to air and many chemicals, and able to protect the surface from further rusting: As soon as a microscopically thin layer has formed, the rusting stops.' (“Anodized” aluminum has been treated with acid and electricity to force it to grow an extra-thick layer of rust, because the more you have on the surface, the stronger and more scratch-resistant it is.) http://www.popsci.com/scitech/article/2004-09/amazing-rusting-aluminum

I was going to wait until after you had posted a diagram to post a response, but it might not ever get posted.

The temperature of the air leaving the center tube will be very close to the temperature of the heating element. Especially at lower flow rates. That is just the physics of heat exchangers. You can't change it. I would imagine your leaving air temperature is around 460 with the dial at around 5.5 and a normal draw speed.

I'm not confused about anything Andy and please don't presume that I am. You do not have 4 times more hot surface area in the air stream. I have seen one first hand. With the heating wires only in a part of the heating element, this makes for even less surface area available for heating.

Aluminum has twice the capacity for holding / storing heat by weight than does stainless steel. However, aluminum is also three times lighter in weight per volume than stainless steel so overall it has less capacity for storing heat than an equivalent sized piece of stainless steel.
I had the opportunity to measure the temperature of the aluminum outer sleeve with the dial at about 5.5. It was a relatively cool 185F. The aluminum doesn't have the capacity to transfer heat to the wood as does stainless steel. The wood should see less heat with the aluminum outer core as compared with stainless steel.

I did enjoy using the e-nano. It does a very good job of producing lots of hot air for roasting.

 

[Tweak]

The temperature of the air leaving the center tube will be very close to the temperature of the heating element. Especially at lower flow rates.

Excuse my ignorance, but wouldn't heat, much like light, follow the inverse-square law?

At least in my very limited experiences with vaporizers, the farther from the heat source, the lower the temperature gets.

Nice diagram btw, really helps my understandings. Wish we could have a sticky thread with basic diagrams like this for every vaporizer on the market, .

 

[OO]

Excuse my ignorance, but wouldn't heat, much like light, follow the inverse-square law?

At least in my very limited experiences with vaporizers, the farther from the heat source, the lower the temperature gets.

Nice diagram btw, really helps my understandings. Wish we could have a sticky thread with basic diagrams like this for every vaporizer on the market, .

I think he meant that the air remains in contact with the heating element for a longer amount of time, therefore will have more heat transferred into it, and therefore a higher temperature than air drawn over the element at a higher velocity.

 

[momofthegoons]

And I'm thinking he's talking about draw speed. Like the LB, log vapes can be affected by the draw speed. Faster draw speed will bring more air past the resister and would be cooler. Conversely, a slow draw is a hotter one.

I'm sure Alan will chime in here and clear things up though.

 

[rayski]

If the air travels a long enough path wouldn't it reach the heaters temperature and remain that temperature regardless of the velocity. Would a corkscrew air path work well?