D. E. Daney

Nitrogen heat pipe for cryocooler thermal shunt

A nitrogen heat pipe was designed, built and tested for the purpose of providing a thermal shunt between the two stages of a Gifford-McMahan (GM) cryocooler during cooldown. The nitrogen heat pipe has an operating temperature range between 63 and 123 K. While the heat pipe is in this temperature range during the system cooldown, it acts as a thermal shunt between the first and second stage of the cryocooler. The heat pipe increases the heat transfer to the first stage of the cryocooler, thereby reducing the cooldown time of the system. When the heat pipe temperature drops below the triple point, the nitrogen working fluid freezes, effectively stopping the heat pipe operation. A small heat leak between cryocooler stages remains because of axial conduction along the heat pipe wall. As long as the heat pipe remains below 63 K, the heat pipe remains inactive. Heat pipe performance limits were measured and the optimum fluid charge was determined.

HTS high gradient magnetic separation system

We report on the assembly, characterization and operation of a high temperature superconducting (HTS) magnetic separator. The magnet is made of 624 m of Silver/BSCCO superconducting wire and has overall dimensions of 18 cm OD, 15.5 cm height and 5 cm ID. The HTS current leads are designed to operate with the warm end at 75 K and the cold end at 27 K. The system operates in a vacuum and is cooled by a two stage Gifford-McMahon cryocooler. The upper stage of the cryocooler cools the thermal shield and two heat pipe thermal intercepts. The lower stage of the cryocooler cools the HTS magnet and the bottom end of the HTS current leads. The HTS magnet was initially characterized in liquid cryogens. We report the current-voltage (I-V) on characteristics of the HTS magnet at temperatures ranging from 15 to 45 K. At 40 K the magnet can generate a central field of 2.0 T at a current of 120 A.

Calorimeter for measuring AC losses in HTS cables for superconducting power transmission lines

We have developed a calorimeter with a sensitivity of better than 1 mW/m for measuring AC losses in HTS multi-strand conductors for superconducting power transmission lines over a temperature range of 64 K to 80 K. By choosing a temperature difference technique we eliminate the need for corrections due to heating at the cable end connections. Use of a three-phase configuration allows measurement of single-phase, three-phase, and coupling losses. The 60 Hz calorimeter power supply has a capacity of 2500 A rms.

HYDROGEN VEHICLE FUELING STATION.

We describe a hydrogen vehicle fueling station that receives and stores hydrogen in liquid form and dispenses it either as a liquid or compressed gas. The economics of distribution that accrue from the favorable weight and volume advantages of liquid hydrogen support this concept both now and for some time to come. Our model for liquid transfer to a 120 L vehicle tank shows that tank filling times under five minutes are feasible with pump-assisted transfer, or for pressure transfer with subcooling greater than 1 K. Our model for compressed gas transfer shows that vehicle tank underfilling of nearly 30 percent can occur during rapid refueling. Cooling the fill gas to 214 K completely eliminates the underfilling problem.

HTS current lead using a composite heat pipe

This paper discusses the design and fabrication of HTS current leads being built by Los Alamos to supply power to a demonstration HTS coil which will operate in a vacuum cooled by a cryocooler. Because vapor cooling is not an option for this application the leads must be entirely conductively cooled. In the design of HTS current leads for this type of application, it is desirable to intercept part of the heat load at an intermediate temperature. This thermal intercept or connection must be electrically insulating but thermally conductive, two mutually exclusive properties of most candidate solid materials. To achieve this end we incorporate a composite nitrogen heat pipe, constructed of conducting and nonconducting materials, to provide efficient thermal communication and simultaneously, electrical isolation between the lead and the intermediate temperature heat sink. Another important feature of the current lead design is the use of high Jc thick film superconductors deposited on a nonconducting substrate to reduce the conductive heat leak through the lower portion of the lead. Two flexible electrical conductors are incorporated to accommodate handling, assembly and the dissimilar expansion coefficients of the various materials.<<ETX>>

Heat pipes for enhanced cooldown of cyrogenic systems

In many important cryogenic applications the use of liquid cryogens for system cooling are either not feasible or are unsuitable. In such cases a cryogenic refrigeration system or multi stage cryocooler must be employed to provide the necessary cooling. To shorten cooldown time for such a system, especially if the thermal mass is large, a thermal shunt directly connecting the first stage of the cryocooler to the load during cooldown is desirable. This thermal shunt allows effective utilization of the greater cooling power available from the first stage of the cryocooler early in the cooldown. Upon reaching operating temperature, the thermal shunt must exhibit a high resistance to thermally isolate the first stage of the cryocooler from the load. Heat pipes are well suited to achieve these objectives. The Advanced Lightweight Influence Sweep System (ALISS), under development by the U. S. Navy for shallow water magnetic mine countermeasures, employs a large, conductively cooled, superconducting magnet that must be cooled from 300 to 4.2 K. Cryogenic heat pipes acting as cryocooler thermal shunts are used to shorten the cooldown time. Ethane, nitrogen and oxygen were evaluated as possible working fluids. A thermal model of the ALISS was developed to evaluate the cooldown performance of various heat pipe combinations. In conjunction with heat pipe performance tests, this model was used to select a suitable design for the heat pipe thermal shunts.

Performance of Crycooler Shunt Heat Pipes

In many important cryogenic applications the use of liquid cryogens for system cooling is either not feasible or is unsuitable. In such cases a cryogenic refrigeration system or multi stage cryocooler must be employed to provide the necessary cooling. To shorten cooldown time for such a system, especially if the thermal mass is large, a thermal shunt directly connecting the first stage of the cryocooler to the load during cooldown is desirable. This thermal shunt allows effective utilization of the greater cooling power available from the first stage of the cryocooler early in the cooldown. Upon reaching operating temperature, the thermal shunt must exhibit a high resistance to thermally isolate the first stage of the cryocooler from the load. Heat pipes are well suited to achieve these objectives. The Advanced Lightweight Influence Sweep System (ALISS), under development by the U. S. Navy for shallow water magnetic mine countermeasures, employs a large, conductively cooled, superconducting magnet that must be cooled from 300 to 4.2 K. Cryogenic heat pipes acting as cryocooler thermal shunts are used to shorten the cooldown time. Ethane, nitrogen and oxygen were evaluated as possible working fluids. A thermal model of the ALISS was developed to evaluate the cooldown performance of various heat pipe combinations. In conjunction with heat pipe performance tests, this model was used to select a suitable design for the heat pipe thermal shunts.

Assembly and testing of a composite heat pipe thermal intercept for HTS current leads

We are building high temperature superconducting (HTS) current leads for a demonstration HTS high gradient magnetic separation (HGMS) system cooled by a cryocooler. The current leads are entirely conductively cooled. A composite nitrogen heat pipe provides efficient thermal communication, and simultaneously electrical isolation, between the lead and an intermediate temperature heat sink. Data on the thermal and electrical performance of the heat pipe thermal intercept are presented. The electrical isolation of the heat pipe was measured as a function of applied voltage with and without a thermal load across the heat pipe. The results show the electrical isolation with evaporation, condensation and internal circulation taking place in the heat pipe.

A Comparison of Hydrogen Vehicle Storage Options Using the EPA Urban Driving Schedule

The three standard options for the storage of hydrogen fuel on passenger vehicles are compressed gas, metal hydride and cryogenic liquid storage. The weight of the hydrogen storage system affects the performance of the vehicle. We examine vehicle performance as a function of hydrogen storage system type and capacity. Three vehicles are modeled, a metro commuter, a mid size sedan and a full size van. All vehicles are powered by a fuel cell and an electric drive train. The impact of auxiliary power requirements for air conditioning is also examined. In making these comparisons it is necessary to assume a driving cycle. We use the United States Environmental Protection Agency (EPA) urban dynamometer driving schedule in all simulations to represent typical urban driving conditions.

Thermal analysis of the APT power coupler and similarities to superconducting magnet current leads

A detailed thermal analysis has been performed on the 210 kW, 700 MHz RF power coupler (PC) which transfers microwave energy from high power klystrons to the superconducting (SC) resonant cavities for the acceleration of protons. The work is part of the design for Accelerator Production of Tritium funded by the US Department of Energy. The PC is a co-axial design with the RF power transmitted in the annular region between two concentric cylinders. The PC provides a thermal connection from room temperature to superconducting niobium operating at 2.15 K. Heat transfer mechanisms considered are conduction, infra-red radiation, RF joule heating in normal and superconducting materials, and, forced and natural convection cooling. The objective of the thermal analysis is to minimize the required refrigeration power subject to manufacturability and reliability concerns. The problem is reminiscent of the optimization of superconducting magnet leads. The similarities and differences in the results between SC leads and PCs are discussed as well as the critical parameters in the PC optimization.