On Sunday, November 13, 2016, Graham Sortino <dmarc-noreply@xxxxxxxxxxxxx>
wrote:
Chambers tend to be short and fat because it cuts down the total
surface area that needs to be cooled; a sphere is theoretically
optimum. People rarely build spherical liquid rocket chambers any
more, though the advent of single piece additive manufacture will
hopefully lead to reevaluating some of the assumptions for
manufacturability baked in to most engines now. Rectangular channels
in the walls are another such assumption based on what was practical
to machine.
This is an interesting point... I was reading Huzel & Huang the other day
and it mentioned the following with regards to cylindrical chamber shape
(p72 - Chapter 4): *"Compared to a cylindrical chamber of the same
volume, a spherical or near-spherical chamber offers the advantage of less
cooling surface and weight. A sphere has the best surface-to-volume ratio
of all the geometric choices, and for the same material strength and
chamber pressure, the minimum wall thickness required for pressure loads is
about half that of a cylinder. However, the spherical chamber is more
difficult to manufacture and has provided poor performance in other
respects."*
Any idea what the poor performance alluded to could be? One of the
challenges with additive manufacturing is that the build size is limited so
a spherical shape sounds attractive.
