H. Quack

Further Development of a Mixed Gas Joule Thomson Refrigerator

A mixed gas Joule Thomson refrigerator has distinct advantages over other cryocooler for certain applications. The system is compact, has good thermodynamic efficiency and low levels of vibration and noise. Further development of this refrigeration machine is possible by optimization of the gas mixture composition. A method was developed which permits a reduction by a large factor in the number of simulation calculations and thus shortens the optimization time considerably.

Low Cost Mixture Joule Thomson Refrigerator

Publisher Summary This chapter focuses on the development of the closed cycle Joule Thomson Refrigerator for cooling electronic devices, which operates in the temperature range from 70 K to 95 K, which uses refrigerant mixtures and a single stage oil lubricated compressor. It provides high reliability and no maintenance. It describes the system and its performance characteristics. This system is compact, has a good thermodynamic efficiency and low levels of vibration and noise. The system and its performance characteristics is addressed in the chapter.

Mixed Gas J-T Cryocooler with Precooling Stage

A mixed gas Joule Thomson refrigerator offers decisive advantages for several applications. Requirements such as an extreme long MTBF and long life, low levels of vibration and noise can be satisfied by such a refrigerator. However, the known coolers of this type have a relative low thermodynamic efficiency. An improvement of the efficiency is possible by introducing a precooling stage. This method will be discussed in the paper. A mixed gas JT refrigerator with precooling stage has been tested. The efficiency proved to be 1.5 times better compared with a Gifford-McMahon refrigerator.

Cryogenic Concept for the Low-energy Electrostatic Cryogenic Storage Ring (CSR) at MPI-K in Heidelberg

At the Max‐Planck‐Institut fur Kernphysik in Heidelberg a next generation electrostatic storage ring for cryogenic temperatures is under development. The main focus of this unique machine is the research on ions, molecules and clusters up to bio molecules in the energy range of 20–300 keV at low temperatures down to 2 Kelvin. The achievement of this low temperature for all material walls seen by the ions in the storage ring will allow novel experiments to be performed, such as rotational and vibrational state control of molecular ions and their interaction with ultra‐low energy electrons and laser radiation. The low temperature of the storage ring not only causes a strong reduction of black body radiation incident onto the stored particles, but also acts as a large cryopump, expected to lead to a vacuum in the 10–15 mbar range. In this paper the cryogenic concept of the storage ring and the related vacuum design will be presented.

Experimental Observation and Empirical Estimation of Formation of Solid Carbon Dioxide in Safety Valves for Refrigerating System

Safety valves are used to guarantee refrigeration system safety under abnormal overpressure. For the safety valve of a CO2 refrigeration system, the tendency to form solid CO2 and to block the release path of the safety valve during release may endanger the entire system. This problem is unique for CO2 refrigeration systems and has never been studied before. In order to fill in the blank, the blockage characteristics of the different types of safety valves were experimentally studied by constructing glass tubes with different geometries similar to the flow channel in safety valves and building them into an experimental rig. And the effect of other parameters on the formation of solid CO2 was studied by theoretical analysis of the pressures along the release path based on a much simplified model. These studies showed that severe blockage will occur in the downstream line and endanger the protected system after the valve house is partly blocked by solid CO2. To avoid the blockage of solid CO2 in safety valves, a simple structure of the safety valve, high fluid velocity, and long downstream pipe are preferred. But this preference will cause high pressure in the downstream line and might further lead to blockage in the downstream line. So the downstream line should be able to tolerate high pressure, and measures such as heating or blowing should be simultaneously taken to prevent the blockage in the downstream line.

Heat transfer in gas filled pipes with closed warm end under different orientations

Publisher Summary In cryogenics it is a standard arrangement, that pipes filled with a stagnant gas, which lead from a high temperature to a low temperature, are installed with the warm end up. But sometimes the overall configuration does not allow this and pipes have to be arranged, for example, horizontally or even with the warm end down. Based on a straight pipe with a closed warm end and an open cold end, a model for a CFD-simulation is created. The model contains the fluid region as well as the solid walls. The warm and cold temperatures are applied to the pipe ends. A structured grid is applied to the model and the basic parameters are set. The warm end is connected to the surrounding temperature at 298 K, the cold end corresponds to a liquid hydrogen tank at 28 K and 6 bar absolute pressure. The pipe is filled with gaseous para-hydrogen and the wall consists of stainless steel. CFD simulations show that the heat flux through pipes by convection compared to conduction can be up to 30 times higher. A doubling of the wall thickness increases the heat flux for positive inclinations. The cross section for heat conduction becomes higher. A doubling of the gas cross section gives a more than 4 times higher heat flux if convection occurs. As a result from these CFD-simulations more detailed hints for construction can be deduced. Usual design rules can be optimized more precisely. Moreover the influence of the inclination can be taken into account.

Dynamic Characteristics of a Simple Brayton Cryocycle

The goal of the overall program is to develop a dynamic numerical model of helium refrigerators and the associated cooling systems based on commercial simulation software. The aim is to give system designers a tool to search for optimum control strategies during the construction phase of the refrigerator with the help of a plant “simulator”.In a first step, a simple Brayton refrigerator has been investigated, which consists of a compressor, an after‐cooler, a counter‐current heat exchanger, a turboexpander and a heat source. Operating modes are “refrigeration” and “liquefaction”. Whereas for the steady state design only component efficiencies are needed and mass and energy balances have to be calculated, for the dynamic calculation one needs also the thermal masses and the helium inventory. Transient mass and energy balances have to be formulated for many small elements and then solved simultaneously for all elements.Starting point of the simulation of the Brayton cycle is the steady state operation at de...

Options for the Cryogenic System for the BESSY‐FEL

The Berliner Elektronenspeicherring‐Gesellschaft fur Synchrotronstrahlung (BESSY GmbH), in January 1999, started operation of BESSY II, a third‐generation synchrotron light source delivering world‐class, high‐brilliance photon beams in the VUV to XUV spectral range. Based on this experience, BESSY has recently proposed the construction of a free‐electron laser (FEL), covering a photon‐energy range from 20 eV to 1 keV.To reduce the development time and cost, BESSY intends to use proven cavity and cryostat technology developed for the TESLA linear collider. However, the cryogenic load per cavity is approximately 15 to 20 times higher than that anticipated for the (pulsed) TESLA operation. This paper describes possible modifications of the cryostat design to accommodate these additional losses.Superconducting RF cavities are the basis of the FEL accelerator providing the driving electron beam with 2.25 GeV. The accelerator consists of five cold sections separated by warm sections reserved for bunch compressi...

European Large Scale Helium Refrigeration

The largest installations for operation at liquid helium temperatures are presently being built in support of research in high energy physics or nuclear fusion. The associated refrigerators are normally being specified for peak refrigeration requirements. So they have spare capacity, which could be used for other investigations, e.g. for High Reynolds or Rayleigh Number research. Details are being presented of 7 systems, which are in operation or are in the planning stage in Europe. In the process of the design of these refrigerators, special machines had to be developed, which operate at low temperatures: high speed turbo expanders, liquid helium pumps and so called cold compressors. Some of the features of these machines could be used to develop circulation blowers for cryogenic wind tunnels.

Mixed refrigerant cycle with neon, hydrogen, and helium for cooling sc power transmission lines

The use of superconductors in very long power transmission lines requires a reliable and effective cooling. Since the use of cryocoolers does not appear feasible for very long distances, a cryogenic refrigeration cycle needs to be developed. For cooling superconducting cables based on MgB2 (T c = 39 K), liquid hydrogen (LH2) is the obvious cooling agent. For recooling LH2, one would need a refrigeration cycle providing temperatures at around 20 K. For this purpose, one could propose the use of a helium refrigeration cycle. But the very low molecular weight of helium restricts the use of turbo compressors, which limits the overall efficiency. In order to increase the molecular weight of the refrigerant a mixture of cryogens could be used, allowing the use of a turbo compressor. Temperatures below the triple point of neon are achieved by phase separation. This paper presents a possible layout of a refrigeration cycle utilizing a three component mixture of neon, hydrogen, and helium.