- #1
Kara386
- 208
- 2
I'm looking into how cryostats are designed. There's an absolute wealth of information on how they work; less about how design choices are made. So I'm giving it a go myself, but I'm stuck on pretty much the first hurdle. I'd like the cryostat to have a boil off rate of helium of ##50##ml/hr max, but this could be a very complicated calculation if I try and work out the heat from individual sources like radiation and residual gas conduction. Instead I'd like to work out the total heat input that leads to the ##50##ml/hr figure. But I'm not sure that's possible.
Instead, my thoughts were that I can find the rate of heat flow into the cryostat from an insert using Fourier's law:
##\dot{Q} = \frac{A}{L}(T_2-T_1) \bar{K}##
Then do similar calculations for what I consider to be the other important sources to try and get a total heat flow into the cryostat, .
And then use this equation: for heat input ##\frac{dQ}{dT}## the evaporation rate is ##\frac{1}{L} \frac{dQ}{dT}##
I found that second equation in some obscure textbook and I can't derive it. I don't want to use it if I can't derive it, so could anyone point me in the direction of some resources on the subject or show me how to derive this? Thanks for any help! :)
Instead, my thoughts were that I can find the rate of heat flow into the cryostat from an insert using Fourier's law:
##\dot{Q} = \frac{A}{L}(T_2-T_1) \bar{K}##
Then do similar calculations for what I consider to be the other important sources to try and get a total heat flow into the cryostat, .
And then use this equation: for heat input ##\frac{dQ}{dT}## the evaporation rate is ##\frac{1}{L} \frac{dQ}{dT}##
I found that second equation in some obscure textbook and I can't derive it. I don't want to use it if I can't derive it, so could anyone point me in the direction of some resources on the subject or show me how to derive this? Thanks for any help! :)