Abstract
Compact high-effectiveness Counter Flow Heat EXchangers (CFHEX) are crucial components of recuperative coolers, such as Joule-Thomson and Turbo-Brayton coolers and of remote cooling systems realised by a convective loop. This paper presents a design and analysis of a cryocooler-based remote cooling system that extends the cooling capabilities of a two-stage cryocooler. Increased heat exchange between high- and low-pressure channels is established by adding copper mesh material. A compact effective mesh-based CFHEX design covering the 4.5-290 K temperature and 1–10 bar pressure operation ranges is presented. The discretised numerical model of the CFHEX is also presented and covers a wide field of parameters, including axial conduction, variable material and fluid properties based on experimental and theoretical data and wall-mesh thermal contact conductance. In our design the latter has shown to have a significant influence on the effectiveness of the CFHEX based on the analysis of a range of inner tube materials. The sizing of a high-performance CFHEX with a predicted effectiveness of 96.5 % (number of transfer units (NTU)=27.6) and an accumulated pressure drop of 15 mbar using the model is demonstrated. The outlook for future work and experimental measurements of the parameters to complete the numerical model is presented.
Highlights
A large number of ultra-sensitive instruments require cryogenic cooling to be provided in a minimised-disturbance and remote manner
For remote-cooling systems that apply a convective cooling loop and recuperative coolers like Turbo-Brayton [7,18,19], Counter-Flow Heat EXchangers (CFHEXs) form crucial components and their effectiveness can be a cornerstone for the system performance
The proposed mesh-based CFHEX design consists of two concentric tubes filled with layers of woven mesh screens that act as fins maximising the heat transfer area
Summary
A large number of ultra-sensitive instruments require cryogenic cooling to be provided in a minimised-disturbance and remote manner. The currently existing Stirling and pulse-tube cryocoolers have residual exported vibrations in the 30 Hz - 1000 Hz bandwidth [7] and typical vibration amplitudes of 1–10 μm depending on direction [8] leading to complex systems being needed to provide mechanical damping In installations such as the CERN HiRadMat facility [9,10,11,12], the remote cooling would be very beneficial to protect the cryocoolers from the high radiation levels. One example of a high-effectiveness meshbased CFHEX design reaching an NTU of 15.7 was presented by Zhao et al [27], who used stainless steel spacers to reduce the axial thermal conduction The latter aspect is crucial for cryogenic CFHEX design as the temperature differences can go up to ≈ 220 K. The cooling system analysis and its predicted performance with the designed CFHEX is presented
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