Fluid System
Technologies

Research and Technology
2002

Performance Characterization of
Perforated Multilayer Insulation (MLI) Blanket

A perforated MLI
blanket system is targeted for a number of large-scale cryogenic
facilities. Space applications and particle accelerators are two fields
concerned with the thermal shielding of devices used at cryogenic
temperatures. Because radiation heat transfer varies with T4
insulation, systems operating between the boundary temperatures of 300 and
77 kelvin (K) are of prime importance. The heat transfer in this range is
the dominant portion of the total heat transfer, even for devices
operating with a cold boundary temperature as low as 2 K. Systems
operating under conditions of degraded vacuum levels are also a key
consideration because of heat transfer by residual gas
conduction.

An experimental
study of a perforated MLI blanket was performed in 2001. The blanket,
manufactured by Jehier (Chemille, France), is a cryogenic thermal
insulation system composed of perforated double-aluminized Mylar separated
by polyester net spacers. Two blankets of 15 layers each were installed on
the cylindrical cold mass of the research cryostat as shown in figure 1.
The total thickness of the 30 layers was 7 millimeters (mm). Complete
characterization of the blanket thermal performance between 300 and 77 K
using a steady-state liquid nitrogen evaporation method was produced using
Cryostat-1.

A summary graph of
the variation of apparent thermal conductivity (k-value) with cold vacuum
pressure (CVP) is given in figure 2. The k-value at the high vacuum
condition of 0.01 millitorr was measured to be 0.029 milliwatt per
meter-kelvin (mW/m-K). (The equivalent R-value per inch is 5,000.)
Comparison of experimental data for other types of MLI systems is also
presented. Layer temperature profiles for the different vacuum levels are
presented in figure 3.

The testing was
performed at the Cryogenics Test Laboratory of NASA Kennedy Space Center
as part of a comparative study of cryogenic vacuum insulation systems.
Basic heat transfer questions and practical methods of application
regarding the performance of high-performance MLI blankets continue to be
addressed. A target is to develop thermal insulation systems that can
operate effectively for large-scale, energy-efficient industrial
application on Earth and in space.

Contact: J.E. Fesmire (mailto:[email-masked]),
YA-C2, (321) 867-7557
Participating Organizations: Dynacs Inc. (Dr.
S.D. Augustynowicz) and Fermi National Accelerator Laboratory (C.
Darve)

Figure 1a. Installation of MLI
Blanket

Figure 1b. Completed Installation
Showing Lower Closeout of Cold Mass

Figure 2. Variation of k-Value
With CVP’s for Different MLI Systems

Figure 3. Layer Temperature
Profiles as a Function of Blanket
Thickness for Different
CVP’s

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