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Sulaiman

Sat Jul 07 2018, 01:15PM

Registered Member #162 Joined: Mon Feb 13 2006, 10:25AM
Location: United Kingdom
Posts: 3140

This is my TEC test rig (not in use) using CPU heatsink/fan for outsides
and 40mm water block inside for hot/cold or heated/cooled water

1530969134 162 FT182521 Techeatsinksfans

A car radiator is more efficient than a domestic radiator,
but it uses a lot of power for the fan.
A domestic radiator is much larger for a given power and temperature,
but no fan is required.
The power output of your system is (ideally) proportional to temperature difference,
so the cold side needs to be as cold as practicable.
Your TEG should at least be able to power its own fans and pumps :)

Based on my very limited experience, I guess that an average size (used/free) domestic radiator would be a good start for your 1 kW system,
and could be improved by a couple of low power fans.

Overall, I'd start with whichever was easiest to obtain as there is always something not considered that often requires a re-build

(or two, or .... I'll finish it after I retire

I'm sure that you will discover all of the above and more once you actually start experimenting with your test setup.

hen918

Sun Jul 08 2018, 07:56PM

Registered Member #11591 Joined: Wed Mar 20 2013, 08:20PM
Location: UK
Posts: 556

The issue with using TEG is their low efficiency; over 10% is pretty much impossible without using fancy materials and manufacturing techniques.

Plasma

Sun Jul 08 2018, 11:03PM

Registered Member #61406 Joined: Thu Jan 05 2017, 11:31PM
Location:
Posts: 268

Yeah the efficiency is low but they still have good points, no moving parts, operating at low temperature, and modular, can slowly keep increasing the output.
still wondering how the parrellel set up is going to work with, but instead of one meter, will have 450mm and ten, sealed in a insultor.

Plasma

Fri Jul 20 2018, 09:21PM

Registered Member #61406 Joined: Thu Jan 05 2017, 11:31PM
Location:
Posts: 268

I've drawn a picture of what I type of want to do. I'm hoping the water will self limit the temperature to 100degrees, will that happen? Thinking of using passive cooling from CPU heatsink, without the fan will it work if the temperature is 100 degrees about what temperature do you think the cold side be.
Thanks

2Spoons

Sat Jul 21 2018, 03:26AM

Registered Member #2939 Joined: Fri Jun 25 2010, 04:25AM
Location:
Posts: 615

CPU heatsinks will work badly without forced air flow - the fins are too close for effective natural convection. You need a fin spacing of at least 10mm for good natural convection flow.

Using water as a heat transfer medium will definitely limit the hot side to 100C.

You say one benefit is "no moving parts" - isn't the pump a moving part?

I'm guessing your overall efficiency from wood to electricity is going to be under 1%.

The other thing you really should use with each module is a MPPT controller - that will extract maximum power from each TEG and convert to whatever your desired output voltage is. That will also allow you to parallel as many modules as you want - the MPPT controllers will do the load matching for you.

Plasma

Sat Jul 21 2018, 01:36PM

Registered Member #61406 Joined: Thu Jan 05 2017, 11:31PM
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Posts: 268

Thanks 2spoons
sorry for the confusion but in the picture it's a single ended box section, was going to relie on convection. Would still like to use air cooling as would need to cool water like that anyway.
1%is a bit crap 50watts a kg of wood isn't that great.
I've ordered another 10,so have 20 at the moment, but slowly build them up.
at 20 degrees they have 4ohms internal resistance, makes 0.5volt 0.125amp.

Can you connect two or more mppt in parallel with out effecting the controllers?

2Spoons

Sat Jul 21 2018, 07:58PM

Registered Member #2939 Joined: Fri Jun 25 2010, 04:25AM
Location:
Posts: 615

Some of the MPPT controller chips are designed with load sharing in mind. ST used to have ones that could operate either parallel or series. Cant find it now, but have a look around.

1% is a guess - but getting electricity from low-grade heat sources has always been difficult. Look at coal fire power generation - they go to a lot of effort to burn the coal completely (its powdered and blown into the furnace) and they use multi-stage steam turbines operating at over 500C. And they manage to get ~35% efficiency.

TEGs are better for situations where you have a lot of low grade heat available - eg geothermal steam or waste heat from some industrial process. Or if you want to power a space probe for decades from a chunk of plutonium.

Burning wood just isn't an efficient process - quite a bit of heat simply disappears up the chimney. And getting complete combustion is also not the easiest thing.

Conundrum

Mon Jul 23 2018, 05:12AM

Registered Member #96 Joined: Thu Feb 09 2006, 05:37PM
Location: CI, Earth
Posts: 4062

Thanks, very useful.
Wonder if I can recycle waste heat from my SDR to reduce its poiwer consumption for mobile use?
Have some micro peltiers on order (0.7V 3W)

Plasma

Fri Jul 27 2018, 02:31AM

Registered Member #61406 Joined: Thu Jan 05 2017, 11:31PM
Location:
Posts: 268

I've found these heatsink and fan, was thinking about putting ten in series, would the fan do much with these heatsink

2Spoons

Sat Jul 28 2018, 08:45PM

Registered Member #2939 Joined: Fri Jun 25 2010, 04:25AM
Location:
Posts: 615

No idea. There's no datasheet I can find for that heatsink that states its thermal resistance under forced airflow.

I think you need to sit down with a calculator and design this thing properly.

Determine your heat source temperature (100C wasn't it?) and your cold sink temperature (ambient air? 20C?)

Determine what the heat flow through 1 TEG will be, what power you want out of it, and from that the delta T across it.

Now you know the heat flow and the TEG cold side temp you can work out what the thermal resistance of the heatsink needs to be.

Decide what kind of heatsink system you need, based on those numbers

Now you can go shopping for parts

All this should have been done before you spent any money on hardware, including TEGs.
Engineering is 10% inspiration , 90% maths.

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