Resistance Heating of Surface

[madskier8806]

hi all

I am trying to use a circuit of NiCr wire to heat a surface. I have setup my circuit using parallel 'branches' of NiCr connected to a bus so that voltage is equal across each branch. I am an undergrad EE so I get electrical aspect, but have little knowledge of the thermo.

My problem is spreading out the heat.

My first question is will a larger gauge wire provide better heating over a larger surface?
NiCr wire spec can be found here: http://www.heatersplus.com/nichrome.htm

I have experiemented with 2 gauges: 22 and 18 gauge and I found that the 18 gauge wire provided more heat over a surface than the 22 gauge wire at equal current levels. Does this make sense?

Second question:

I need to cover a large area, have a large number of branches, and have a high enough branch resistance so that the total resistance of my parallel circuit will not be too low. The circuit is setup so that the branches go straight across the surface from bus to bus, like the lines on a sheet of notebook paper.

The area is 8 feet wide. With the 22g wire I used 8 foot long branches from bus to bus, with the 18g wire I need to use 16 foot branches (doubling back, both buses on one side of circuit). The total power in the 22g branch is ~24W (1.724A) and the total power in the 18g branch is ~30W(2.154). Will the fact that the 18g branch is twice the length of the 22g branch reduce its surface heating effieciency?

My thinking is that it should not, because every delta x length along the wire should be disapating ~30W

Thanks for the help!

[mgb_phys]

The limiting step is likely to be coupling the heat from the wire into the surface, thermal conduct across joins is always difficult.
A thin wire might be better able to follow the surface profile.