how much w/cm²

[Fredistiller]

Hi,

I run with gas in the garage but want to go electric for my new still. Heating elements are hard to find in my country. I can find one completely SS with 12.5W/cm² (for water). If I want lower like 5w/cm² they make it with brass screw plug and I don't want brass. If I want one with SS screwplug they ask me more than three time the price!! .

So my question is: is 12.5W/cm² OK for a boiler I would use only for spirit run? or is it too much and is there an security issue? Security is one of the reason I want to quit gas. And as I would, in a close future, have a room inside the house, I want to be sure about safety.

Thanks!

Fred.

[still_stirrin]

Here's a guideline:
A ULWD 5.5kW 240VAC wavy element has a watt density of 50W/sq.in. (7.8W/sq.cm)
A LWD 4.5kW 240VAC foldback element has a watt density of 150W/sq.in. (23.25W/sq.cm)

Either of those would be good choices for a boiler. So, a 12.5W/sq.cm element would be great.
ss

[Kareltje]

I just measured my element: radius is 8,5 mm, length is 90 cm, so in total 24 cm2. According to the friend that built the still, it is 2,1 kW, so 87,4 W/cm2. But while running I measured an uptake of about 3,3 kW per hour. The other element is a bit smaller, both in size and in power.
I stripped some birdwatchers with them without any problem.

By the way: I did not ask my friend how he built his still, some 20 years ago. But knowing his style of working I guess he used a second hand element from a washing machine or something like that. Or he asked a friend mechanic for some spare ones.
(Hij en ik wonen in het noordelijke van de twee kleine koninkrijken.)

Edit: compared to the figures of still_stirrin these calculation seems 10-fold too high. What am I missing??

[Odin]

Kareltje, your wattage per cm2 is quite high. OP, you will be more than fine.

Regards, Odin.

[Kareltje]

Kareltje, your wattage per cm2 is quite high.

Clearly. But what did I do wrong????
Luckily I get corrected.

[BugHunter]

Let's see, the circumference is 8.5mm * 3.14 = 26.69mm or 2.669 cm

2.669cm * 90cm = 240.21 cm^2

So it looks like you multiplied mm times cm to get cm^2, which got you off by a factor of 10.

2100W / 240.21cm^2 = 8.74 w/cm^2 which sounds pretty reasonable.

[Odin]

If it is that close to 8 w/cm it is perfectly fine.

Regards, Odin.

[Kareltje]

Let's see, the circumference is 8.5mm * 3.14 = 26.69mm or 2.669 cm

2.669cm * 90cm = 240.21 cm^2

So it looks like you multiplied mm times cm to get cm^2, which got you off by a factor of 10.

2100W / 240.21cm^2 = 8.74 w/cm^2 which sounds pretty reasonable.

Oh fuck!! That is the problem!!

I found 8.5 mm makes 26.69 mm circumference but took it for mm2, so made it 0.2669 cm2.
How stupid!
Thanks BugHunter, you honour your name!

[Kareltje]

But then again: I trusted my friends build, so I did not question his choice of element. But why is this parameter of interest?

I had to clean the elements when I bought the still, but is this not more caused by the contents of the still than by the power?

[Odin]

If you run dirty washes, sugar rich washes, or do on the grain distilling (very) high w/cm2 can give you scorching easier.

Odin.

[Kareltje]

OK, I see. Haven't done that yet with my elements, so did not think of it.

[Fredistiller]

Nice to see how you can calculate it. Never thought about it....

We always talk about W/cm² for dirty wash and scorching. But if I understand well, there is no issue using a higher one for a spirit run then. Is that right?

Kareltje, your wattage per cm2 is quite high. OP, you will be more than fine.

Regards, Odin.

What do you mean by OP please?

(kareltje: ik las je zinnetje in het nederlands en mijn grijze cellen waren zoals: bergepen vs klopt hier iets niet...zeer grappig!)

[Odin]

Original Poster.

Odin.

[Fredistiller]

Original Poster.

Odin.

Thanks Odin

And so it answer my question as well

[still_stirrin]

...if I understand well, there is no issue using a higher one for a spirit run then. Is that right?

Yes and no. Theoretically as the watt density increases, you get more and more like a point source of heat. That can cause localized boiling points on the element (or in the boiler). The result could reduce the life of the electric element (resistive element burnout).

To decrease boil time, more heating element surface area is desireable over a higher watt density. It would have more element surface area to transfer heat to the liquid it’s immersed in. Bubbles will form along the element, coalesce and rise to the surface.

So, the “issues” with higher watt density elements are: 1) usually they have a lower wattage rating, 2) usually they have less surface in contact with the conducting liquid, 3) usually the internal resistance per lineal inch of the element is higher (conducts less current at rated voltage), and 4) with a higher rsistance per linear inch/cm of length they will get hotter along the length and this leads to burnout.

But....your 12.5 W/sq.cm element is very appropriate for a boiler.
ss

[Fredistiller]

Thanks for the replies everyone!

This forum is and stays a very good community...

[Fredistiller]

HI,

So my element is in my possession. But there is something that I don't like: they put some synthetic resin in the screw cap. Yet I asked the salesman if it was only SS when I ordered .

He said it was ok for the food industry but he would search if it is safe for reactions with alcohol and let me know. So in the meanwhile I would like to have the opinion of the people of this forum ( because I am not sure I can 100% trust him).
Nothing is paid already so I can force him to take the element back...if I have good arguments!

But maybe it is okay to use, I am really carefull to use only safe materials but I don't want to think short-sighted either. So do someone know more about this problem?

(When I know which resin they used I can come with more details of course)

Thanks in advance....

Fred.

[Danespirit]

Could you post a picture Fred...?
I had mine delivered with some sort of what I think would be a silicone gasket as a seal.
I threw it away and gave the threads a couple of wraps PTFE tape, seals well and can be easily replaced if I'm taking the whole element out for a cleaning.
Sounds a bit weird with that resin in your element...

[Fredistiller]

here the pic

[Fredistiller]

(was little bit too fast)

for me it looks like silicone, it is also "soft" like silicone when you push on it. Resin would be hard I think....

[Danespirit]

I'm sorry to write it...but I'm afraid your element ain't suitable for distilling.
My expectation is that a spirit run is going to dissolve some of the material used..
I'd rather buy another one.
There are plenty of them on eBay.
Just an example: https://www.ebay.com/p/Dernord-Heating- ... 0005.m1851" onclick="window.open(this.href);return false;" rel="nofollow

[zapata]

I wouldn't use it either for what it's worth. Regardless of what the seller says, I habe higher standards than commercial producers or equipment salesmen.

[Fredistiller]

Thanks,

I will wait for his answer but I don't have a good feeling either.
And keep on searching... The problem is that it is really difficult to find an element 3kw were I live...

[sw_reijnders]

what you can do is buy a 9000w 3-phase element and connect the 3 elements is parallel as a single phase element.
https://www.ebay.nl/itm/Mutilpe-220V-38 ... zGtqS6oSRA" onclick="window.open(this.href);return false;" rel="nofollow

this will give you a large element with only 3,6kw.
large surface / low wattage

I do use the 9000w elements with brass base, and they have an internal length of 29cm.

quick calculation pi * 0.8cm * (6*29) = 437 cm2
3600w / 437 = 8,2 w/cm2

[Fredistiller]

what you can do is buy a 9000w 3-phase element and connect the 3 elements is parallel as a single phase element.
https://www.ebay.nl/itm/Mutilpe-220V-38 ... zGtqS6oSRA" onclick="window.open(this.href);return false;" rel="nofollow

this will give you a large element with only 3,6kw.
large surface / low wattage

I do use the 9000w elements with brass base, and they have an internal length of 29cm.

quick calculation pi * 0.8cm * (6*29) = 437 cm2
3600w / 437 = 8,2 w/cm2

Never thought about that, thanks!...but I would like to avoid brass as well...