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desA
26-06-2010, 05:09 AM
Multi-port copper tubes have been developed over the past few years.

These can come in a number of variants:
1. Formed-then-finished all-in-one construction;
2. Composite construction - internal insert fitted inside tube & joined.

The type2 construction has pressure capability typically of up to around 38bar(g) & can be constructed from copper & its alloys (brass). The typical joining method for the internal insert is generally brazing.

The type1 construction has been tested to 320 bar(g), where the test pump failed. These tubes can be used in CO2 applications, with ease, due the typically small grain size of copper & its alloys. Examples of shapes vary from a series of tubes joined side-by-side, to a flat 16x1.5mm 4-port multiport tube, to junctions of tubes of different diameters.

I'm very interested in getting these type2 tubes moving in the RHVAC industry & would like to brainstorm uses for these tubes in the current RHVAC industry. I'd really value comments & suggestions, wish-lists. Wherever an aluminium multiport tube enters the RHVAC industry, it can be out-performed by these new copper-based tubes. I understand copper to be the natural material of choice for the RHVAC industry.

An application for the use of a flat multiport tube could be in condensers, or evaporators, for example.

Tesla
26-06-2010, 10:15 AM
Thanks dESA
How about a heat exchanger for hot water heatpump or water to water exchanger. Provided pressures are not to different a very thin wall could be used - How thin is the wall thickness of these tubes? and what is their U value? Could you please give us some specks and maybe some pics.

al
26-06-2010, 12:11 PM
Desa

If the tube is only rated to 38B how would it be suitable for RHVAC?

al

desA
27-06-2010, 02:41 AM
If the tube is only rated to 38B how would it be suitable for RHVAC?


There are two types of tube:

Type1 - burst pressure ~ 38bar(g)
Type2 - burst pressure > 320bar(g).

These tubes are of totally different construction. The type1 tube is what we call a composite tube, where an insert is placed inside a thin-walled tube, then the whole composite tube fused together.

38bar would be sufficient for a heat-pump system running on R134a, R407c, R290 for instance.

For cases where higher pressures are required eg. R410A, R744, then the type2 tube - with burst pressure in excess of 320bar(g) should be used.

desA
27-06-2010, 03:14 AM
How about a heat exchanger for hot water heatpump or water to water exchanger. Provided pressures are not to different a very thin wall could be used -

Good ideas, Tesla. Thank you.


How thin is the wall thickness of these tubes?

A typical lower limit wall thickness for the type 1 tube is ~ 0.1mm, with the type2 tube ~ .15mm.

For comparison purposes, the multiport tube construction used in typical aluminium automotive condensers (R134a) has a wall thickness of ~ 0.2mm - 0.3mm - due to the large aluminium grain size. With copper, or brass tubes, the grain size is very refined, allowing greatly reduced wall thicknesses, for similar, or better corrosion resistance.


and what is their U value?

Since the tubes are generally of flat construction (although edge-wise connected round tubes are also available), the thermal resistance would be:

R,th = dx/k

where : dx = material thickness [m] / k = thermal conductivity [W/m.K]

U,th = 1/R,th = k/dx

Example : copper k ~ 380 W/m.k ; dx = 0.1e-3 m
U,th = 380/0.1e-3 = 3,800,000 W/m2.K !!!

In other words - negligible thermal resistance. :)


Could you please give us some specks and maybe some pics.

I'll do that. Let me pull out some of my files & extract some pics.