Abstract
The new 4.5 K refrigerator system at the Jefferson Lab (JLab) Central Helium Liquefier (CHL-2) for the 12 GeV upgrade was commissioned in late spring of 2013, following the commissioning of the new compressor system, and has been supporting 12 GeV LINAC commissioning since that time. Six design modes were tested during commissioning, consisting of a maximum capacity, nominal capacity, maximum liquefaction, maximum refrigeration, maximum fill and a stand-by/reduced load condition. The maximum capacity was designed to support a 238 g/s, 30 K and 1.16 bar cold compressor return flow, a 15 g/s, 4.5 K liquefaction load and a 12.6 kW, 35-55 K shield load. The other modes were selected to ensure proper component sizing and selection to allow the cold box to operate over a wide range of conditions and capacities. The cold box system is comprised of two physically independent cold boxes with interconnecting transfer-lines. The outside (upper) 300-60 K vertical cold box has no turbines and incorporates a liquid nitrogen pre-cooler and 80-K beds. The inside (lower) 60-4.5 K horizontal cold box houses seven turbines that are configured in four expansion stages including one Joule-Thompson expander and a 20-K bed. The helium compression system has five compressors to support three pressure levels in the cold box. This paper will summarize the analysis of the test data obtained over the wide range of operating conditions and capacities which were tested.
Highlights
IntroductionThe new 12 GeV helium refrigerator has three pressure levels (high, medium and low pressure; High pressure (HP), MP and LP, respectively) and uses a liquid nitrogen (LN) pre-cooler and four expansion stages with three turbine strings and one Joule-Thompson (JT) expander
The new 12 GeV helium refrigerator has three pressure levels and uses a liquid nitrogen (LN) pre-cooler and four expansion stages with three turbine strings and one Joule-Thompson (JT) expander
The cold box system is well matched to the compressor system which is entirely designed by Jefferson Lab (JLab) and built-to-print by industry [4]
Summary
The new 12 GeV helium refrigerator has three pressure levels (high, medium and low pressure; HP, MP and LP, respectively) and uses a liquid nitrogen (LN) pre-cooler and four expansion stages with three turbine strings and one Joule-Thompson (JT) expander. As an example, referring to table 4, the increased LN consumption (2.7 times greater than the design for mode-1) could be accounted for by losing the cooling to ~6% of the HP stream passes (or an equivalent improper flow distribution), which would only increase the pressure drop in the HP stream by ~12% if they were blocked. The purpose of this example is to emphasize the effect of the flow distribution using a simple calculation.
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