designheatsinkmaterials
I have lot of aluminum sheet 0.5mm thickness at home, normally heat sinks that I have seen had 1mm thickness.
Now I am wondering should I get that sheet welded as heatsink or do I absolutely have to invest in thicker sheet for efficient (at taking away and disposing heat) heat sinks ?
Cutting the Alu in half and sticking it to the back will do almost nothing to help. What you need to do is increase the surface area of the Alu.
If you're stuck for space, then you have a couple of options. If you have space in the vertical direction, you might try just bending the alu so it's not as wide and fits into the shape of the available space. However, you do still need to make sure the heat can get to the outside world. There needs to be some kind of air flow, preferably over the alu.
If there is a fairly constant trickle of water to the plants, then you can use this to extract a lot of heat from the LEDs. Instead of using a sheet of Alu, use some box section. Seal up the ends and attach a push-fit pneumatic connector at each end. Pump the water supply through this, and you should be good to go. Even a tiny flow of water should be enough, but it probably needs to flow fairly constantly, not just once a day.
Typical solutions I've used are either Kapton tape:
Or Sil-Pad:
Sil-Pad 400 is a composite of silicone rubber and fiberglass. The material is flame retardant and is specially formulated for use as a thermally conductive insulator. The primary use for Sil-Pad 400 is to electrically isolate power sources from heat sinks.
If you use a sil-pad the screw will still electrically connect the componet tab with the heat sink. A solution to this is to use a shoulder washer to isolate the screw and the tab:
Best Answer
Rather than ask about how such a heat sink would work, why don't you try actually computing it? http://www.heatsinkcalculator.com/calculator.html will let you design your own.
Note that I entered "heat sink design software" into Google, and that was the third or fourth item on the list.
Let's take your example. You did not specify the number of fins, so I picked 10. The calculator says your 40 x 40 mm, 50 watt Peltiers will operate at about 160 C. Is that a good heat sink or not? Since do not provide a quantified performance goal, there is no way tell for sure, but most likely Not.