EXACTLY how low is "low power density"?

Just a quick question gentlemen...

What exactly is low power density?
I don't mean definition, I mean numbers.

Like, 20W per 1 square cm - is it low density? (I believe it is not).
10W/cm^2? 5? 2?
At exactly how many watts per square cm or inch do we agree it is a low power density heater?

And does it in any way depend on the vessel volume?
(like, 10W/cm^2 would be low for 40L kettle but is quite high for 5L)

Thank you!

GQT said:

Just a quick question gentlemen...

What exactly is low power density?
I don't mean definition, I mean numbers.

Like, 20W per 1 square cm - is it low density? (I believe it is not).
10W/cm^2? 5? 2?
At exactly how many watts per square cm or inch do we agree it is a low power density heater?

And does it in any way depend on the vessel volume?
(like, 10W/cm^2 would be low for 40L kettle but is quite high for 5L)

Thank you!

Click to expand...

I dont really know as far as metric but Bobby at brewhardware had the definition threshold posted on brewhardware.com under the elements. Theres high density, low density and then the best for brewing which is ULWD...(ultra low watt...)

augiedoggy said:

Bobby at brewhardware had the definition threshold posted

Click to expand...

Thanks a lot, it does shed some light (although the answer is still not clear).

Let's see:
Roughly 6.45 cm^2 in a square inch.
Hence, 30W/inch^2 makes 4.65W/cm^2 - which Bobby defines as Insanely Low Watt Density.
However talking in terms of numbers and wort safety rather than sanity it'd be better to understand what exactly watt density is safe.
Not "stay as low as you can", but "starting from XX W/inch^2 down you don't have to worry about scorching your brew".

GQT said:

Thanks a lot, it does shed some light (although the answer is still not clear).

Let's see:
Roughly 6.45 cm^2 in a square inch.
Hence, 30W/inch^2 makes 4.65W/cm^2 - which Bobby defines as Insanely Low Watt Density.
However talking in terms of numbers and wort safety rather than sanity it'd be better to understand what exactly watt density is safe.
Not "stay as low as you can", but "starting from XX W/inch^2 down you don't have to worry about scorching your brew".

Click to expand...

Well we know that its very difficult to scorch with regular ripple elements which are ULWD (both 5500w and the lower WD 4500w versions... the only way to scorch with these it to literally let proteins settle on top of the element prior to turing it on usually done by accident when someone turns the element off during a boil for a bit and then back on without stirring first.
We also know that LWD works with minimal carmelization and some scorching reported on bigger gravity beers. (straight 11- 12" long foldback 4500w and 5500w elements are an example of these...

I thought I remember reading that under 80w per square inch was ideal. I thought my 4500w element was 63w per sq inch for some reason but could
be wrong.

On a side note.. I use a very long 1800w cartridge heater in my rims... its 36" log and 5/8" diameter.... it is extremely low watt density and I get absolutely no carmelization or buildup on it after brewing ...it stays completely clean. and the long length ensures longer contact time with the gentler heat so it works perfect without any negative effects gaining my a rise of 2 degrees per minute if needed. on 5 gallons of liquid.

augiedoggy said:

I remember reading that under 80w per square inch was ideal. I thought my 4500w element was 63w per sq inch for some reason but could be wrong.

Click to expand...

Now THIS really helps, thank you!
Any scorching issues, ever?

GQT said:

Now THIS really helps, thank you!
Any scorching issues, ever?

Click to expand...

yes but only with a much shorter (10") 1000w cartridge heater in a very small copper rims setup I made... the end where it was mounted had a narrow area of dead space where proteins would sit and not recirculate well which caused it to burn to the end of the element... I had to dump two batches of beer from it.. live and learn.(which is why I use the 36" long element now) in reality the original would have worked fine if the rims diameter was bigger.

The residue left on my boil kettle element today from brewing (all stainless 4500w ULWD ripple one I ordered from the electricbrewery.com) wiped right off with my finger.. Absolutely no scorching

ULWD = 50W per square inch or 7.8W per square centimeter or lower

It greatly reduces the chance of scorching or caramelizing the boiling wort.

Kal