Venkatarao Ganni

OPTIMAL DESIGN AND OPERATION OF HELIUM REFRIGERATION SYSTEMS USING THE GANNI CYCLE

The constant pressure ratio process, as implemented in the floating pressure—Ganni cycle, is a new variation to prior cryogenic refrigeration and liquefaction cycle designs that allows for optimal operation and design of helium refrigeration systems. This cycle is based upon the traditional equipment used for helium refrigeration system designs, i.e., constant volume displacement compression and critical flow expansion devices. It takes advantage of the fact that for a given load, the expander sets the compressor discharge pressure and the compressor sets its own suction pressure. This cycle not only provides an essentially constant system Carnot efficiency over a wide load range, but invalidates the traditional philosophy that the (‘TS’) design condition is the optimal operating condition for a given load using the as‐built hardware. As such, the Floating Pressure‐Ganni Cycle is a solution to reduce the energy consumption while increasing the reliability, flexibility and stability of these systems over a...

Spallation neutron source cryomodule heat loads and thermal design

When complete, the Spallation Neutron Source (SNS) will provide a 1 GeV, 2 MW beam for experiments. One portion of the machine’s linac consists of over 80 Superconducting Radio Frequency (SRF) 805 MHz cavities housed in a minimum of 23 cryomodules operating at a saturation temperature of 2.1 K. Minimization of the total heat load is critical to machine performance and for efficient operation of the system. The total heat load of the cryomodules consists of the fixed static load and the dynamic load, which is proportional to the cavity performance. The helium refrigerator supports mainly the cryomodule loads and to a lesser extent the distribution system loads. The estimated heat loads and calculated thermal performance are discussed along with two unique features of this design: the helium heat exchanger housed in the cryomodule return end can and the helium gas cooled fundamental power coupler.

Status of the Cryogenic System Commissioning at SNS

The Spallation Neutron Source (SNS) is under construction at Oak Ridge National Laboratory. The cold section of the Linac consists of 81 superconducting radio frequency cavities cooled to 2.1K by a 2400 Watt cryogenic refrigeration system. The major cryogenic system components include warm helium compressors with associated oil removal and gas management, 4.5K cold box, 7000L liquid helium dewar, 2.1K cold box (consisting of 4 stages of cold compressors), gaseous helium storage, helium purification and gas impurity monitoring system, liquid nitrogen storage and the cryogenic distribution transfer line system. The overall system commissioning strategy and status will be presented.

Application of JLab 12GeV helium refrigeration system for the FRIB accelerator at MSU

The planned approach to have a turnkey helium refrigeration system for the MSU-FRIB accelerator system, encompassing the design, fabrication, installation and commissioning of the 4.5-K refrigerator cold box(es), cold compression system, warm compression system, gas management, oil removal and utility/ancillary systems, was found to be cost prohibitive. Following JLab’s suggestion, MSU-FRIB accelerator management made a formal request to evaluate the applicability of the recently designed 12GeV JLab cryogenic system for this application. The following paper will outline the findings and the planned approach for the FRIB helium refrigeration system.

Simplified Helium Refrigerator Cycle Analysis Using the ‘Carnot Step’

An analysis of the Claude form of an idealized helium liquefier for the minimum input work reveals the ‘Carnot Step’ for helium refrigerator cycles. As the ‘Carnot Step’ for a multi‐stage polytropic compression process consists of equal pressure ratio stages; similarly for an idealized helium liquefier the ‘Carnot Step’ consists of equal temperature ratio stages for a given number of expansion stages. This paper presents the analytical basis and some useful equations for the preliminary examination of existing and new Claude helium refrigeration cycles.

SCREW COMPRESSOR CHARACTERISTICS FOR HELIUM REFRIGERATION SYSTEMS

The oil injected screw compressors have practically replaced all other types of compressors in modern helium refrigeration systems due to their large displacement capacity, minimal vibration, reliability and capability of handling heliums high heat of compression.At the present state of compressor system designs for helium systems, typically two-thirds of the lost input power is due to the compression system. Therefore it is important to understand the isothermal and volumetric efficiencies of these machines to help properly design these compression systems to match the refrigeration process. This presentation summarizes separate tests that have been conducted on Sullair compressors at the Superconducting Super-Collider Laboratory (SSCL) in 1993, Howden compressors at Jefferson Lab (JLab) in 2006 and Howden compressors at the Spallation Neutron Source (SNS) in 2006. This work is part of an ongoing study at JLab to understand the theoretical basis for these efficiencies and their loss mechanisms, as well ...

Capacity Upgrade of the Exell Helium Liquefier Plant by the Addition of a Wet Engine

The capacity of the Bureau of Mines Exell Helium Liquefaction plant near Amarillo, Texas has recently been upgraded by the addition of a reciprocating expander (wet engine) to replace the Joule-Thomson expansion into the two-phase region. The original plant was designed to produce approximately 500 litres per hour of liquid helium from prepurified feed gas using a combination of LN2 precooling, two oil-bearing expansion turbines and the Joule-Thomson effect for refrigeration. The wet engine addition, combined with higher liquid fraction in the precooling nitrogen feed, led to an increase in liquefaction capacity of 38 percent with no increase in the flow of compressed recycle gas to the liquefier. The modification to the plant is described and its observed performance before and after addition of the wet engine is presented and analyzed.

SNS Cryogenic Systems Commissioning

The Spallation Neutron Source (SNS) is under construction at Oak Ridge National Laboratory. The cold section of the Linac consists of 81 superconducting radio frequency cavities cooled to 2.1K by a 2400 watt cryogenic refrigeration system. The major cryogenic system components include warm helium compressors with associated oil removal and gas management, 4.5K cold box, 7000L liquid helium dewar, 2.1K cold box (consisting of 4 stages of cold compressors), gaseous helium storage, helium purification and gas impurity monitoring system, liquid nitrogen storage and the cryogenic distribution transfer line system. The overall system commissioning and future plans will be presented.

Cryogenic System for the Spallation Neutron Source

The Spallation Neutron Source (SNS) is a neutron‐scattering facility being built at Oak Ridge, TN for the US Department of Energy. The SNS accelerator linac consists of superconducting radio‐frequency (SRF) cavities in cryostats (cryomodules). The linac cryomodules are cooled to 2.1 K by a 2300 watt cryogenic refrigeration system. As an SNS partner laboratory, Jefferson Lab is responsible for the installed integrated cryogenic system design for the SNS linac accelerator consisting of major subsystem equipment engineered and procured from industry. Jefferson Lab’s work included developing the major vendor subsystem equipment procurement specifications, equipment procurement, and the integrated system engineering support of the field installation and commissioning. The major cryogenic system components include liquid nitrogen storage, gaseous helium storage, cryogen distribution transfer line system, 2.1‐K cold box consisting of four stages of cold compressors, 4.5‐K cold box, warm helium compressors with i...

Refrigeration Plants for the SSCL

The basic requirements and operating features of the collider cryogenic system have already been described in other publications. The general arrangement of the refrigeration plant and its subsystems is presented, and the issue of how to provide redundancy in the cryogenic system is addressed, and some of the basic features of the refrigeration plants are described. The collider cryogenic system design is not final yet, and this report only reflects the direction and current status of the cryogenic system design.