Heat load budgeting of a superconducting induction heater‘s commercial cryocooler-based cryostat

Within a project funded by the German Federal Ministry for Economic Affairs and Energy (BMWI), the Karlsruhe Institute of Technology (KIT) collaborates with the Theva GmbH and Bültmann GmbH to develop a superconduct-ing magnetic heater. The Theva GmbH designs and supplies the high-temperature superconducting (HTS) coil. It will be integrated in a cryostat designed and supplied by KIT and cooled to ca. 25 K via a GM-cryocooler. Granted successful test results at KIT, the cryostat with the superconducting coil will serve to operate an induction heater at the Bültmann GmbH and be assessed there under industrial conditions. The challenge within the cryogenic design lies in the simultaneous requirement of relatively low production costs, robustness and extremely limited operation downtimes to form a competitive product. This contribution presents aspects of the cryogenic system’s conceptional design, with a focus on its heat load budgeting. Due to the limited cooling capacities of cryocoolers on each stage, the main aim of the design is to distribute the estimated heat loads as suitably as possible between the cryocooler stages. In the cryostat we designed, the total heat loads on both cryocooler stages will have three significant contributions: heat conduc-tion along connected components, Joule heating and thermal radiation. The respective estimation methods for these heat loads and their results are briefly shown and evaluated in this contribution. In this context, specific examples for the results‘ influence on the cryostat design within the scope of thermal and economical design are given. The heat load approximations’ eligibility to serve as a determination basis of an appropriate cryocooler model is discussed as well. On this basis, finally, we give suggestions for specific cryocooler models currently on the market

Stabilized nanoparticles of phytosterol by rapid expansion from supercritical solution into aqueous solution

The basic objective of this work was to form stable suspensions of submicron particles of phytosterol, a water-insoluble drug, by rapid expansion of supercritical solution into aqueous solution (RESSAS). A supercritical phytosterol/CO2 mixture was expanded into an aqueous surfactant solution. In these experiments 4 different surfactants were used to impede growth and agglomeration of the submicron particles resulting from collisions in the free jet. The concentration of the drug in the aqueous surfactant solution was determined by high-performance liquid chromatography, while the size of the stabilized particles was measured by dynamic light scattering. Submicron phytosterol particles (<500 nm) were stabilized and in most cases a bimodal particle size distribution was obtained. Depending on surfactant and concentration of the surfactant solution, suspensions with drug concentrations up to 17 g/dm3 could be achieved, which is 2 orders of magnitude higher than the equilibrium solubility of phytosterol. Long-term stability studies indicate modest particle growth over 12 months. Thus, the results demonstrate that RESSAS can be a promising process for stabilizing submicron particles in aqueous solutions