Cryogenic insulation standard data and methodologies

CEC Netherlands, 2015

The close relationship between industrial energy use and cryogenics drives the need for optimized thermal insulation systems. Emerging cryofuels usage is enabled by adequate isolation of the liquid hydrogen or liquefied natural gas from the ambient environment. Thermal performance data for the total insulation system, as rendered, are essential for both engineering designs and cost-benefit decisions involving comparisons among alternatives. These data are obtained through rigorous testing with suitable apparatus and repeatable methods. Properly defined terminology, analysis, and reporting are also vital. Advances in cryogenic insulation test apparatus and methods have led to the recent addition of two new technical standards of ASTM International: C1774-Standard Guide for Thermal Performance Testing of Cryogenic Insulation Systems and C740-Standard Guide for Evacuated Reflective Cryogenic Insulation. Among the different techniques described in the new standards is the cylindrical boiloff calorimeter for absolute heat measurement over the full range of vacuum pressure conditions. The details of this apparatus, test method, and data analysis are given. Benchmark thermal performance data, including effective thermal conductivity (k e) and heat flux (q) for the boundary temperatures of 293 K and 77 K, are given for a number of different multilayer insulation (MLI) systems in comparison with data for other commonly-used insulation systems including perlite powder, fiberglass, polyurethane foam, and aerogels.

International Thermal Conductivity Conference, 2008

Efficient ways to characterize thermal performance of materials under cryogenic and vacuum conditions have been developed. These methods provide thermal conductivity data on materials under actual-use conditions and complement established methods. The actual-use environment of a large temperature difference across the insulation in combination with vacuum pressure is essential for understanding how insulation systems perform. Test articles include solids, foams, powders, layered blankets, and composite panels. Test methodology and apparatus design for several insulation test cryostats are discussed. The measurement principle is liquid nitrogen boiloff calorimetry. Heat flux capability ranges from about 0.5 to 500 W/m 2 ; corresponding apparent thermal conductivity values range from below 0.01 up to about 60 mW/m-K. Example data for different insulation materials are also presented. After further work to standardize test methods, these patented insulation test cryostats can be used in a wide range of industrial applications.

International Congress of Refrigeration, 2000

The results of a comparative study of cryogenic insulation systems performed are presented. The key aspects of thermal insulation relative to cryogenic system design, testing, manufacturing, and maintenance are discussed. An overview of insulation development from an energy conservation perspective is given. Conventional insulation materi-als for cryogenic applications provide three levels of thermal conductivity. Actual thermal performance of standard multilayer insulation (MLI) is several times less than laboratory performance and often 10 times worse than ideal per-formance. The cost-effectiveness of the insulation system depends on thermal performance; flexibility and durability; ease of use in handling, installation, and maintenance; and overall cost including operations, maintenance, and life cy-cle. Results of comprehensive testing of both conventional and novel materials such as aerogel composites using cry-ostat boil-off methods are given. The development of efficient, robust cryogenic insulation systems that operate at a soft vacuum level is the primary focus of this paper.

Cryogenics Test Laboratory NASA Kennedy Space Center, 2019

New materials in recent decades have enabled advances in thermal insulation systems for storage and transfer of cryogens. To preserve the cold and achieve efficient cryogenic systems, a combination of materials, testing, and engineering is required. The total heat leak into any cryogenic assembly is comprised of three main parts: 1) heat leak through the insulation, 2) heat leak through the support structures, and 3) heat leak attributed to piping penetrations and feedthroughs (and their negative effects on the insulation). This "cold triangle" approach provides a basis for evaluating performance benefits of new materials and analyzing the cost effectiveness in overall system design. Provided are thermophysical data for aerogels, aerogel composites, novel multilayered composites, and glass bubbles for standard test conditions of 293 K and 78 K under conditions from high vacuum to ambient pressure. Examples of cryogenic storage tanks show the relative importance of both insulation and structural materials for achieving designs of highest energy efficiency.

Standards for thermal insulation used in applications between ambient and low temperatures, below 100 K, require test data under relevant conditions and by different laboratories to develop data sets for the proper comparisons of materials. This critically important technology is needed to provide reliable data and methodologies for industrial energy efficiency and energy conservation. Under ASTM International's Committee C16 on Thermal Insulation, two standards have been issued on cryogenic thermal insulation systems. Thermal conductivity data sets have been taken using identical flat-plate boiloff calorimeter instruments independently operated at the Cryogenics Test Laboratory of NASA Kennedy Space Center (KSC) and the Thermal Energy Laboratory of LeTourneau University (LETU). Precision specimens of cellular glass insulation were produced for both laboratories to provide the necessary comparisons to validate the thermal measurements and test methodologies. Additional specimens of commercial cellular glass pipe insulation were tested at LETU to compare with the flat plate results. The test data are discussed in relation to the experimental approach, test methods, and manner of reporting the thermal performance data. This initial Inter-Laboratory Study (ILS) of insulation materials for sub-ambient temperature applications provides a foundation for further ILS work to produce standard data sets for several key commercial materials. 1. Introduction There is a need for standard thermal data for cryogenic insulation materials or standard test methods and instrumentation in this area. Standard test methods are needed to produce standard data for conduction of heat by materials in the sub-ambient temperature range. An initial step has been taken for producing standard thermal data through a preliminary Inter-Laboratory Study (ILS) initiated by NASA Kennedy Space Center and LeTourneau University. A major objective of this initial research is to explore the suitability of new methodologies for producing standard data for effective thermal conductivity (ke(T)) and heat flux (q(T)) for commonly used cryogenic insulation materials. Other objectives of this effort are to pave the way for establishing standard data sets for use by engineers, to develop accepted baselines for the performance of novel materials under development, and to provide technical insight on the nature of low heat flows through low-density materials. Knowledge of the dependence of heat transfer related properties on temperature for materials is extremely important because even materials that are considered homogenous may be complicated when applied in systems having temperature differences of several hundred degrees imposed across its thickness.

AIP Conference Proceedings, 2008

Thermal isolation of low-temperature systems from ambient environments is a constant issue faced by practitioners of cryogenics. For energy-efficient systems and processes to be realized, thermal insulation must be considered as an integrated system, not merely an add-on element. A design tool to determine the performance of insulation systems for comparative trade-off studies of different available material options was developed. The approach is to apply thermal analysis to standard shapes (plane walls, cylinders, spheres) that are relatively simple to characterize with a one-dimensional analytical or numerical model. The user describes the system hot and cold boundary geometry and the operating environment. Basic outputs such as heat load and temperature profiles are determined. The user can select from a built-in insulation material database or input user defined materials. Existing information has been combined with the new experimental thermal conductivity data produced by the Cryogenics Test Laboratory for cryogenic and vacuum environments, including high vacuum, soft vacuum, and no vacuum. Materials in the design tool include multilayer insulation, aerogel blankets, aerogel bulk-fill, foams, powders, composites, and other insulation system constructions. A comparison of the design tool to a specific composite thermal insulation system is given.

AIP Conference Proceedings, 2004

The study and evaluation of cryogenic thermal insulation materials and systems is atechnology focus area of the Cryogenics Testbed at NASA Kennedy Space Center. The liquidnitrogen evaporation method is used between boundary temperatures of about 300 kelvin (K)and 77 K to make accurate measurements of the heat transfer rates and apparent thermalconductivity values (k-values) through different insulation systems. The methods includethermal performance characterization over the full range of pressures from high vacuum to novacuum. Innovations include the design and development of three types of research testcryostats. The novel cryostats include absolute k-value for cylindrical specimens, comparativek-value for cylindrical specimens, and comparative k-value for flat specimens (includingcompressive loading). The material specimens may be in forms such as bulk fill, flat panel,multilayer, or continuously rolled. These new test methods are shown to be complementary toother established test methods.

Cryogenics Test Laboratory NASA Kennedy Space Center, 2018

Extensive cryogenic thermal testing of more than 100 different multilayer insulation (MLI) specimens was performed over the last 20 years for the research and development of evacuated reflective thermal insulation systems. From this data library, 26 MLI systems plus several vacuum-only systems are selected for analysis and comparison. The test apparatus, methods, and results enabled the adoption of two new technical consensus standards under ASTM International. Materials tested include reflectors of aluminum foil or double-aluminized Mylar and spacers of fiberglass paper, polyester netting, silk netting, polyester fabric, or discrete polymer standoffs. The six types of MLI systems tested are listed as follows: Mylar/Paper, Foil/Paper, Mylar/Net, Mylar/ Blanket, Mylar/Fabric, Mylar/Discrete. Also tested are vacuum-only systems with different cold surface materials/finishes including stainless steel, black, copper, and aluminum. Testing was performed between the boundary temperatures of 78 K and 293 K (and up to 350 K) using a thermally guarded one-meter-long cylindrical calorimeter (Cryostat-100) for absolute heat flow measurement. Cold vacuum pressures include the full range from 1 × 10 −6 torr to 760 torr with nitrogen as the residual gas. System variations include number of layers from one to 80 layers, layer densities from 0.5 to 5 layers per millimeter, and installation techniques such layer-by-layer, blankets (multi-layer assemblies), sub-blankets, seaming, butt-joining, spiral wrapping, and rollwrapping. Experimental thermal performance data for the different MLI systems are presented in terms of heat flux and effective thermal conductivity. Benchmark cryogenic-vacuum thermal performance curves for MLI are given for comparison with different insulation approaches for storage and transfer equipment, cryostats, launch vehicles, spacecraft, or science instruments.

Supercollider 4, 1992

Cryogenics Test Laboratory NASA Kennedy Space Center, 2015

A problem common to both space launch applications and cryogenic propulsion test facilities is providing suitable thermal insulation for complex cryogenic piping, tanks, and components that cannot be vacuumjacketed or otherwise be broad-area-covered. To meet such requirements and provide a practical solution to the problem, a layered composite insulation system has been developed for nonvacuum applications and extreme environmental exposure conditions. Layered composite insulation system for extreme conditions (or LCX) is particularly suited for complex piping or tank systems that are difficult or practically impossible to insulate by conventional means. Consisting of several functional layers, the aerogel blanket-based system can be tailored to specific thermal and mechanical performance requirements. The operational principle of the system is layer-pairs working in combination. Each layer pair is comprised of a primary insulation layer and a compressible radiant barrier layer. Vacuum-jacketed piping systems, whether part of the ground equipment or the flight vehicle, typically include numerous terminations, disconnects, umbilical connections, or branches that must be insulated by nonvacuum means. Broad-area insulation systems, such as spray foam or rigid foam panels, are often the lightweight materials of choice for vehicle tanks, but the plumbing elements, feedthroughs, appurtenances, and structural supports all create ''hot spot" areas that are not readily insulated by similar means. Finally, the design layouts of valve control skids used for launch pads and test stands can be nearly impossible to insulate because of their complexity and high density of components and instrumentation. Primary requirements for such nonvacuum thermal insulation systems include the combination of harsh conditions, including full weather exposure, vibration, and structural loads. Further requirements include reliability and the right level of system breathability for thermal cycling. The LCX system is suitable for temperatures from approximately 4 K to 400 K and can be designed to insulate liquid hydrogen, liquid nitrogen, liquid oxygen, or liquid methane equipment. Laboratory test data for thermal and mechanical performance are presented. Field demonstration cases and examples in operational cryogenic systems are also given.