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Schodel R.,Physikalisch - Technische Bundesanstalt | Thummes G.,Trans Center for Adaptive Cryotechnology and Sensors | Heltzel S.,European Space Agency
European Space Agency, (Special Publication) ESA SP | Year: 2012

Various ESA projects have identified the need for materials with very high thermal stability down to 4 K. For the design of ultra stable structures it is necessary to characterize the thermal expansion coefficient (CTE) of these materials within their entire in-service temperature range with a maximum uncertainty of 3×10-9 K-1. This paper describes the enhancement of PTB's Ultra Precision Interferometer (UPI) by an external measurement pathway (EMP) and appropriate cooling equipment which enables, for the first time ever, absolute length measurements of prismatic bodies to be performed down to cryogenic temperatures. The performance of the enhanced UPI is demonstrated for two materials that are relevant for space applications From the absolute length measurements, performed in a temperature range from 7 K to 320 K, the CTE and its uncertainty is extracted from a mathematical analysis. Source

Schodel R.,Physikalisch - Technische Bundesanstalt | Walkov A.,Physikalisch - Technische Bundesanstalt | Zenker M.,Physikalisch - Technische Bundesanstalt | Bartl G.,Physikalisch - Technische Bundesanstalt | And 5 more authors.
Measurement Science and Technology | Year: 2012

A new Ultra Precision Interferometer (UPI) was built at Physikalisch-Technische Bundesanstalt. As its precursor, the precision interferometer, it was designed for highly precise absolute length measurements of prismatic bodies, e.g. gauge blocks, under well-defined temperature conditions and pressure, making use of phase stepping imaging interferometry. The UPI enables a number of enhanced features, e.g. it is designed for a much better lateral resolution and better temperature stability. In addition to the original concept, the UPI is equipped with an external measurement pathway (EMP) in which a prismatic body can be placed alternatively. The temperature of the EMP can be controlled in a much wider range compared to the temperature of the interferometer's main chamber. An appropriate cryostat system, a precision temperature measurement system and improved imaging interferometry were established to permit absolute length measurements down to cryogenic temperature, demonstrated for the first time ever. Results of such measurements are important for studying thermal expansion of materials from room temperature towards less than 10 K. © 2012 IOP Publishing Ltd. Source

Sun J.,Justus Liebig University | Sun J.,Trans Center for Adaptive Cryotechnology and Sensors | Sun J.,Zhejiang University | Dietrich M.,Justus Liebig University | And 3 more authors.
Refrigeration Science and Technology | Year: 2012

High-power cryocoolers are used in many superconductor and gas liquefying applications. Stirling-type pulse-tube cryocoolers (PTCs) offer the advantage of high reliability, high efficiency and low maintenance compared to other cooler types. An in-house made single-stage Stirling-type pulse-tube cryocooler with inline configuration of regenerator and pulse tube was optimized for high cooling power near 80 K. The cooler is driven by a 10 kW-class linear compressor with dual opposed pistons (QDrive model 42SM-2S297W PWG). In order to reduce losses from pressure drop, the regenerator is designed with a small length to diameter ratio, thus making it susceptible to internal streaming losses. These losses manifest themselves in a measureable temperature inhomogeneity around the circumference of the regenerator and in a low cooling performance. To overcome these losses, the transverse heat conductance in the regenerator was increased by use of sandwich type fillings, where a part of the original stainless wire mesh was replaced by materials with higher thermal conductance, such as copper and brass mesh. Several types of sandwich fillings were experimentally investigated. Using these types of regenerator fillings, the losses from streaming were significantly reduced and the minimum no-load temperature was lowered from 54 to 47.5 K. The mean pressure and frequency of the pressure oscillation were also optimized. Up to now, a cooling power of 413 W at 80 K is available with an acoustic power (pV-power) of 7.8 kW at a frequency of 56 Hz. Source

Dietrich M.,Justus Liebig University | Euler A.,Trans Center for Adaptive Cryotechnology and Sensors | Thummes G.,Trans Center for Adaptive Cryotechnology and Sensors
Cryogenics | Year: 2014

A thermal heat switch has been developed intended for cryogenic space applications operating around 100 K. The switch was designed to separate two pulse tube cold heads that cool a common focal plane array. Two cold heads are used for redundancy reasons, while the switch is used to reduce the thermal heat loss of the stand-by cold head, thus limiting the required input power, weight and dimensions of the cooler assembly. After initial evaluation of possible switching technologies, a construction based on the difference in the linear thermal expansion coefficients (CTE) of different materials was chosen. A simple design is proposed based on thermoplastics which have one of the highest CTE known permitting a relative large gap width in the open state. Furthermore, the switch requires no power neither during normal operation nor for switching. This enhances reliability and allows for a simple mechanical design. After a single switch was successfully built, a second double-switch configuration was designed and tested. The long term performance of the chosen thermoplastic (ultra-high molecular weight polyethylene) under cryogenic load is also analysed. © 2013 Elsevier Ltd. All rights reserved. Source

Sun J.-C.,Zhejiang University | Sun J.-C.,Justus Liebig University | Sun J.-C.,Trans Center for Adaptive Cryotechnology and Sensors | Dietrich M.,Justus Liebig University | And 4 more authors.
Journal of Zhejiang University: Science A | Year: 2015

The operating characteristics are important for design and optimization of pulse tube cryocoolers, in particular for those with high cooling power, which up to now have been seldom extensively investigated. In this study, the dependence of cooling performance on the charge pressure and operating frequency has been investigated, both numerically and experimentally. A numerical model based on Sage software was established. Experiments were performed on a home-made single-stage high power Stirling-type pulse tube cryocooler (SPTC) working at liquid nitrogen temperatures. The results revealed that each charge pressure corresponds to an optimum frequency with respect to compressor and regenerator efficiency. A lower charge pressure results in a higher cryocooler efficiency, but the delivered maximum pV power is significantly reduced due to the stroke limit of the pistons in the linear compressor. The influence of operating characteristics on the temperature non-uniformity in the regenerator was also investigated. By optimizing the charge pressure and frequency, the minimum no-load temperature was decreased to 46.9 K at 56.5 Hz and 2.0 MPa. A cooling power of 300 W at 71.8 K was measured with an electrical input power of 8.9 kW. © 2015, Zhejiang University and Springer-Verlag Berlin Heidelberg. Source

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