Precise thermodynamic control of high pressure jet expansions

Abstract

We describe an experimental setup for supersonic jet expansions of supercritical fluids. It is characterized by well-defined thermodynamic values to allow systematic investigations of pressure and temperature effects on molecular beam parameters. The design permits stagnation temperatures T(0)=225-425 K with a thermal stability DeltaT(0)<30 mK and stagnation pressures p(0)=0.2-12 MPa that are measured with 0.05% precision. For optimum stability, gas reservoir, pressure transducer, and gauge amplifier are temperature-controlled, and a feedback loop permits active pressure stabilization using a pulseless syringe pump. With this approach stagnation pressures can be reproduced and kept constant to Deltap(0)<2.9 kPa. As a result, flow velocity and kinetic energy of molecular beams can be controlled with maximum accuracy.

Stationary flow conditions in pulsed supersonic beams

“…[118][119][120][121] In short, it consists of a differentially pumped ultrahigh vacuum set-up with a customer-specific version of the Even-Lavie pulsed valve. The valve control 122 provides two complementary means for adjusting the opening behavior, namely, the maximum solenoid current, I v , and the pulse width of the valve control signal, δt 0 .…”

Probing Phase Transitions with Supersonic Beams – A Joint Experimental and Theoretical Study

“…Although these observations have been routinely ascribed to the formation of clusters in the expanding jet, the opposite behavior, a reduced flow velocity at higher source pressures, has been reported, too [9,35,42,69,71]. Clearly, the ideal gas description is insufficient as it does not provide any pressure dependence of the terminal flow velocity, see references [72,73]; it does also not consider particle interactions that might form the physical basis of nucleation and condensation in the jet or in the stagnation reservoir.…”

“…The experimental design has been described in detail in references [41][42][43][44]. Briefly, it consists of a differentially pumped ultra-high vacuum apparatus with a pulsed jet expansion.…”

Ultra-precise particle velocities in pulsed supersonic beams

“…67 Thanks to the vanishingly small volume flow rate of less than 100 μLh −1 , pressure gradients between manometer and valve are negligible. In consequence, constant pressure within recipient, supply line, and valve is guaranteed.…”