On 2/15/2018 12:09 PM, Norman Yarvin wrote:
On Wed, Feb 14, 2018 at 01:39:29PM -0800, Keith Henson wrote:
Norman Yarvin <yarvin@xxxxxxxxxxxx> wrote:
I don't think either of those examples fully captures the glory of an
aircraft whose essential centerpiece would be a super-high-performance,
super-delicate heat exchanger filled with hydrogen and exposed to
incoming airflow.
It's helium in the fine tubes. Otherwise, you would have hydrogen
embrittlement. But you are close to the initial reason I rejected the
concept. Thousands of brazed joints and it's not going to leak? But
they built some furnace brazed test articles and they did not leak.
That's when I started to take them seriously.
There's a long way between "we made one and it works in the lab" and
"it survives the chicken cannon".
By the way, the engine for the Suntan project used a somewhat similar
heat exchanger, with no intermediate helium stage and "four and one
half miles of 3/16-inch diameter tubing... Hasteloy R because of its
compatibility with hot hydrogen." (quote from Dick Mulready, in
_Advanced Engine Development at Pratt & Whitney_.) The engine was
built and tested, albeit only on the ground.
(Its concept was that rather than using the normal turbine stage to
extract energy from the exhaust gases, they used the exhaust gases to
gasify and heat up the hydrogen fuel in the heat exchanger and then
ran the turbine off the hydrogen. I'm not sure what the attractions
of that arrangement were: did they think it was necessary to gasify
the hydrogen before injecting it? Or is hydrogen that much better of
a working fluid for a turbine?)