ESA Document - Emits - ESA

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HMM
Assessment Study
Report: CDF-20(A)
February 2004
page 243 of 422
3.4.3.4.3 Regenerative and thermoelectric coolers
These systems are not considered for such volume (above 10 m3) being poorly efficient when
high refrigeration loads are required in the case of regenerative system (Stirling for example), or
to low temperatures with thermo-electric cooling (above 140K).
3.4.3.4.4 Recuperative coolers
Among possible recuperative systems, the Turbo-Brayton (TB) cycle presents a relatively high
thermodynamic efficiency at 20K and appears to be a good candidate today for this range of
cooling power (5-15W). Available for ground applications (100 watts, 4K), the challenge is to
downsize the cooling power and miniaturize elements to fit space-related requirements, which
was done in particular for NICMOS (5W@65K) and MELFI projects (47Wat190K).
Developments are ongoing in U.S. and in Europe (ESA TRP on a compressor 50mWat6K, 300W
input power).
Expected efficiency of a TB is about 10 to 15% Carnot at 35K today (an equivalent efficiency
can be reasonably projected in the coming years for 20K), which would require an input power
of the order of 950W.
Figure 3-79: COP efficiency and input power as function of Tc
A higher boiling temperature allows significant reduction of the cooler input power: having a
subcritical liquid reduces input power by 55%. The primary objective however is densification of
the hydrogen to reduce the total amount at launch. Increasing the fluid temperature is therefore
secondary and only possible if the launcher capability on the volume is reached.
Figure 3-80: TB schematic (1 stage)