Hoping to make a wax melter

[oliver90owner]

Is there any reason why twin walled polycarbonate won't work?

It will work, but one needs to know the spectral response for the material. Some materials work better than others because they allow passage of near IR, in sunlight, through into the receptacle, but are more opaque to the longer IR re-radiated by the cooler bodies within the structure (think here difference of black body radiation between 'Earth items', at around 300-400K and the spectral output from the Sun at around 6000K). Glass is very good in this respect, which is why a double glazed unit works well.

In addition, one needs to vector in the coefficient of conduction for the material. One millimetre of polycarbonate will conduct more thermal energy than eight millimetres of glass, I would guess.

So, the term 'work' is not a straightforward comparison of the construction (ie both are effectively double skinned).

The problem of the inner leaf cracking is a function of thermal expansion, I would suggest. If both sheets were able to move relatively freely, instead of being constrained, the inner glass leaf would withstand the elevated temperature. After all, they do not often crack when fitted to our houses (which do not reach that range of thermal gradient).

On the point about flat plate solar thermal collectors, we again have cherry picked data. Yes, flat plate collectors are both cheaper and as good as (or better than) evacuated tube technology in bright direct sunlight at higher ambient temperatures. It is not the case for all conditions which actually translates to evavuated tubes are far better collectors,for the UK climate, when evaluated over the whole year. Ie flat plate collectors are pretty poor in comparison to evacuated tubes, when in less bright light and at low ambient temperatures - like we get in the winter months. Now think when that improved thermal gain is more valuable - in the winter months, I would suggest!

So don't believe all you are told on a non-technical forum like this one! If you don't believe my points above, go and look it up on some technical/scientific websites, where you would be able to find the real truth in peer-appraised papers and not just the cherry picked points put forward by persons with rose tinted spectacles or wearing blinkers!

RAB

 

[Tom Bick]

Double Glazed Units in Solar Wax Melter

Been there. Done that. I found that the inner sheet always cracks in strong sunlight. Stresses.

Did you break the airtight seal by drilling a small hole through the spacer as this is recommended to reduce the chance of the panel breaking.

 

[Tom Bick]

Is there any reason why twin walled polycarbonate won't work?

It works a treat but it warps so needs to be held in place and you have to seal the ends otherwise it will draw air up through the gaps acting as a cooling effect.

 

[Little John]

Ok - here's my experience with making an ad hoc wax melter.

First try was using a 'brood box' simply nailed together from scrap wood. This had four very carefully made plates of aluminium angled downwards from the sides, such that a rectangular slot was formed at their lower edges. Beneath this slot was a channel, sloping downwards and out through a slot cut in the side of the box.
Above this box was placed an eke which already had plastic screen stapled across it, from a much earlier experiment. Below the box was placed an unwanted electric kettle, with it's bimetallic strip cut-out 'over-ruled'.

Results: the planks from which the wooden box was made curled-up alarmingly from the steam. The plastic screen sagged dramatically, and the wax which dripped through the mesh was cooled by the aluminium such that much of it hardened on it's way out of the box. The aluminium and kettle went for recycling, and the box burned well, once dried.


Second try was using a plastic swing-top bin 'on the tilt' with one bottom corner cut away. An old pillow-case was filled with unwanted combs and scraps of wax, and suspended inside the bin, near the the top. A wallpaper stripper was connected to a hole near the base of the bin, and a short length of wooden plank placed on top to keep the steam in.

Results: wax duly emerged from the hole at the base, and into a waiting bowl of water. The only negatives were that the plastic bin distorted a little, and the pillow-case can best be considered as a 'one-off' disposable item. So it worked, but I'm not impressed.


This year I'll be trying a solar melter - after all it's a method which has been employed by beekeepers since the 1920's, if not earlier.

I've also got a spare hot-water/tea-urn which I'll be playing with - might come in handy if I run out of wax and the sun ain't shining.

LJ

 

[For want of a better word]

Did you break the airtight seal by drilling a small hole through the spacer as this is recommended to reduce the chance of the panel breaking.

Very good point for a solar wax melter..... some argon or nitrogen filled double glazed panels are manufactureed to keep heat inside the house and reflect heating Sun rays out...
which is why I suggested a single pain of glass would be just as effective.

Agree that probably the work that was undertaken by The Department of Environmental Science at The University of Plymouth was too technical for the less well read to comprehend... Solar tracking flat plate single glazed devices that could also automatically tilt between 49 degrees and 52 degrees for this latitude produced the best results...

There is a description of a simple motorised solar tracker utilising four PV plane cells somewhere on Youtube.https://www.youtube.com/watch?v=HkhVomoD47g

A simple black painted box with a bit of insulation and a metal inner tray... with a simple single glass cover , tilted at about 50 degrees towards the South West will suffice for the average hobby beekeeper to melt a bit of wax in!!

Mytten da

 

[Poly Hive]

A simple black painted box with a bit of insulation and a metal inner tray... with a simple single glass cover , tilted at about 50 degrees towards the South West will suffice for the average hobby beekeeper to melt a bit of wax in!!


Precisely!

KISS

PH

 

[BeeJayBee]

Is there any reason why twin walled polycarbonate won't work?

It will work, but one needs to know the spectral response for the material. Some materials work better than others because they allow passage of near IR, in sunlight, through into the receptacle, but are more opaque to the longer IR re-radiated by the cooler bodies within the structure (think here difference of black body radiation between 'Earth items', at around 300-400K and the spectral output from the Sun at around 6000K). Glass is very good in this respect, which is why a double glazed unit works well.

In addition, one needs to vector in the coefficient of conduction for the material. One millimetre of polycarbonate will conduct more thermal energy than eight millimetres of glass, I would guess.

So, the term 'work' is not a straightforward comparison of the construction (ie both are effectively double skinned).

Thanks RAB, I had no idea it could be so technical! I was just thinking of using some I've been given, seems a pity to waste it.

It works a treat but it warps so needs to be held in place and you have to seal the ends otherwise it will draw air up through the gaps acting as a cooling effect.

I was thinking of holding it in place with some cuphooks or similar. What's the best way to seal the cut ends?

We spend time every year taking shards of glass out of flowerbeds and the veg patch, presumably from shattered greenhouse or cold frame panes, hence the reluctance to use glass.

 

[pargyle]

A simple black painted box with a bit of insulation and a metal inner tray... with a simple single glass cover , tilted at about 50 degrees towards the South West will suffice for the average hobby beekeeper to melt a bit of wax in!!

Precisely!

KISS

PH

Post #3 & Post #6 ... Got there in the end via a torturous route !

 

[Tom Bick]

Is there any reason why twin walled polycarbonate won't work?



I was thinking of holding it in place with some cuphooks or similar. What's the best way to seal the cut ends?

We spend time every year taking shards of glass out of flowerbeds and the veg patch, presumably from shattered greenhouse or cold frame panes, hence the reluctance to use glass.

Gaffer tape worked for me but anything will do providing you seal the ends

 

[oliver90owner]

Tobe honest, if there is a reasonable slope, only tne top end needs sealing completely, as the air flow would always be towards that end. Simple practical physics principle of convection. Depends on the orientation, of course - horizontal v vertical.

A bit like the practical issues of evacuated tube technology overflat plates. Think, in this case, that to collect sufficient energy during the winter months one may need double, or more, flat plate area for the same thermal collection which practically means tha the summer output would be far in excess of requirements (needing a large heat dump to be put in place?). There are more considerations than simple ''efficiency'' results may reveal. Of course, neither technology is normally installed at a size sufficient for full winter heat demand.

A bit like solar electric panels - one would need about eight(?) times the area to provide all winter requirements, than for summer. Impractical in most situations for several reasons.

One needs to review the practical issues, not blindly over engineer for the worst possible scenarios (which may need taking into account for many situations).

Double glazed solar wax melters are better than single glazed items, for many periods in the fickle UK weather patterns. Not absolutely necessary, but a definite advantage if that option is available.

 

[For want of a better word]

Very good point for a solar wax melter..... some argon or nitrogen filled double glazed panels are manufactureed to keep heat inside the house and reflect heating Sun rays out...
which is why I suggested a single pain of glass would be just as effective.

Agree that probably the work that was undertaken by The Department of Environmental Science at The University of Plymouth was too technical for the less well read to comprehend... Solar tracking flat plate single glazed devices that could also automatically tilt between 49 degrees and 52 degrees for this latitude produced the best results...

There is a description of a simple motorised solar tracker utilising four PV plane cells somewhere on Youtube.https://www.youtube.com/watch?v=HkhVomoD47g

Double glazed solar wax melters are better than single glazed items
A simple black painted box with a bit of insulation and a metal inner tray... with a simple single glass cover , tilted at about 50 degrees towards the South West will suffice for the average hobby beekeeper to melt a bit of wax in!!

Mytten da

Double glazed solar wax melters are better than single glazed items

But the bottom panel fractures, due to stresses in this application that it is NOT designed for!

Mytten sa

 

[oliver90owner]

But the bottom panel fractures, due to stresses in this application that it is NOT designed for!

Do keep up! Do read my post on constrained or free floating panes!

Do think here of household double glazing - there to prevent heat loss from inside to outside. Double glazing is better. Indeed, some of my house has triple glazed windows, which is common building practice in several other countries.

 

[Tom Bick]

A good tip and not looking it's best at this time of year but if any of you want to increase heat and productivity during days when it's just not right for melting wax you can simply knock up some sort of reflective board to direct more of the available sun into the extractor.
This one is some old insulation I had laying around but kitchen foil on some cardboard would do the job and probably a better reflective material.
I will leave it to the boy scouts amongst us to sharpen their pencils and calculate the optimum angles

 

[BeeJayBee]

I've seen pictures of online of solar wax melters lined with car window protectors, the cheap shiny silvery ones. No idea if they're any good though.