Technical Page
Black Painted Barrels
Black Paint & Cooling.

As part of my final year thesis, me and my friends built a test rig to test the effects of black paint on cylinder cooling,...

So the thing we did was build a test rig. A test rig designed by poverterty stricken uni students must have the following properties;
* be really cheap to build
* Ugly is OK, looks are not important
* Must produce accurate results, wouldn't have been much use building it otherwise
* Must use as much cool University equipment as possible.

We fell short on the using cool uni equipment department. All we used for this one was (1) a thermal couple reader and (2) a small fan air speed meter.

The barrel test rig.
The finished test rig is shown below. Ugly? sure. Functional? Definitely

The thingy on the left, is a squirrel cage fan. The bit in the middle is the thermocouple reader and the hole where the cylinder goes. The bit on the right is where the air goes out.

Basically, air goes in the fan on the right. It is blown along a duct to the center where the barrel is located. The air cools the barrel and continues along the duct to the right where it exits.
The barrel is enclosed in the duct, and filled with boiling hot water. We monitor the water temp until it gets to a set start point, then we turn the fan on. The barrel is then cooled by the incoming air. As it cools we took temperature readings every 30 seconds for the first 5 minutes, and then every minute until 10 minutes. This allowed us to plot temperature vs time graphs for our three different barrel surfaces. The barrel surfaces are shown below.

Bare metal barrel.
The photo on the left shows a new (newish anyway) bare metal barrel. Virtually rust free. It is an old barrel out of my old 1835cc engine. After having an 1835 I'll never build one again. I've never seen so much blow by in my life, those thin walls don't keep their shape when warm which cause the rings to lose their seal. But's that's another story for later.

Oily/dirty fouled barrel.
The photo on the right shows a fouled barrel, which simulates an old engine which has been in service quite a while and received little attention or love.

The yellow wires (yellow in the first photo anyway) coming off the barrel are thermocouples, or in simpler terms, temperature probes. We put some in the barrel, on the longest fin, on the shortest fin, basically anywhere we thought we should take a temperature reading.

Black painted barrel.
The photo on the right shows a barrel with a coat of black paint. This was tested to dispel the theory that you should paint you cylinders black.

Fin temp vs internal temperature.
The chart below shows of plot of fin tip temperature vs internal water temperature. The upper curves are for the short base fin at the bottom of the barrel. The lower curves are for the longer fin near the top of the cylinder.
The three colours are the three cylinder coatings. The lower the fin temperature is for any given water temperature, the better the cooling is. As you can see, the bare barrel is the best, black barrel a close second, and the fouled barrel dead last.
I'll add reasons why the black is worse than the bare when I get a chance..........