I can obtain a large batch of 0.8mm I.D., 1.2mm O.D. (.031" I.D. / .047" O.D.) brass pipe. Now, this seems quite ideal stuff to construct low power shell-tube heat exchangers with. Many thin strands provide a very large surface area.

But, how many of these pipes do I need to put parallel to equal the pressure drop of an 1/4" pipe?

One could simply say: divide the cross-section surface area of both pipes. This would equal to about 40 parallel strands needed to equal the cross-section surface area of a 1/4" pipe.

But with multiple parallel pipes the wall surface area is greatly increased, increasing friction.

I ran a few calculations with the Gas Pipes module of Coolpack, and if Coolpack is right, I would need 80-90 strands in parallel to equal 1/4" pipe pressure drop.

But, I cannot use Coolpack for ethane (R170) at real temperatures, so I used propane (R290) at -30C evaporation instead, to provide Coolpack with density and viscosity information matching ethane as close as possible within the limits of the software.

I don't really thrust Coolpack with these small pipes, since I expect these small pipes to behave different from larger ones.

Can anyone verify this information?

If anyone needs design parameters, use R170 vapour at -100C, mass flow 1.8kg/hr.