Description of the Ortho-Para Convertor and internal plumbing of the Hydrogen target
1. Scope
This document addresses the design of the ortho-para convertor and internal hydrogen target plumbing that connects to the hydrogen fill/vent line which is part of the safety hydrogen relief system of the NPDGamma liquid hydrogen target.
2. Components covered
The documents covers the ortho-para convertor, the hydrogen liquefaction chamber, and the plumbing connections of the target vessel to the fill/vent line. see Fig. 1.
Figure 1. Hydrogen target plumbing and OPC
3. Description
The hydrogen gas enters the system through the 1.5” OD stainless steel fill/vent line connection. After the tube bends it forks into 2 paths. One path takes the gas directly into the top of the aluminum target vessel with a 1.5” OD stainless line connected using a friction weld. The other goes through a ¼” OD stainless tube into a copper hydrogen liquefaction chamber. Figure 1 shows the tube between the fill/vent line and the Conflat flange. This tube has a 1.33” Conflat joint in the middle with a strengthening ring to increase the sealing force on the joint. The SS tube is soldered into the copper liquefaction chamberusing Castolin silver solder: all other SS tube joints are welded. The liquefaction chamber is directly attached to the upper cryorefrigerator and possesses internal grooves (see Figure 3) to increase the surface area of contact for the cold H2 gas, The liquid hydrogen drips down a 3/8” OD stainless tube (also soldered into the chamber)soldered into the bottom of the liquefaction chamber (see Fig. 4) and flows into the copper ortho-para convertor. The ortho-para convertor (OPC, Figure 5) contains iron oxide catalyst powder confined inside the copper chamber using stainless steel mesh wire on the inlet and outlets. The ortho-para convertor employs brazed connections and its outlet is a ½” OD stainless tube connected to an ¾” OD aluminum tube at the bottom of the target vessel through another friction weld joint.
Figure 2: Part of connection path of fill/vent line to the hydrogen liquefaction chamber.
Figure 3: Top piece of the hydrogen liquefaction chamber.
Figure 4: Bottom portion of the hydrogen liquefaction chamber.
Figure 5: Vertical slice through the ortho/para convertor volume.
Testing
In addition to the general requirements, this section of the fill/vent line must in addition be able to withstand several thermal cycles over the course of the experiment between room temperature and 17K. Extensive testing has been conducted on the friction weld joints, the conflat flanges, the brazed joints of the ortho/para convertor and the soldered joints of the hydrogen liquefaction chamber. These tests are described in other documents listed in the design and safety document. The hydrogen liquefaction chamber and the tubing that connects it to the OPC and the fill/vent line were used in the LANSCE experiment.