Lithographically Micromachined Si/Glass Heat Exchangers for Joule-Thomson Coolers.

Heat Exchanger;Joule-Thomson Cooler;MEMS;Cryosurgery;In-Situ Temperature Sensing;Flow Modulation;Electrical Engineering;Mechanical Engineering;Engineering;Mechanical Engineering

Zhu, WeibinYoon, Euisik ;

University of Michigan

关键词: Heat Exchanger;    Joule-Thomson Cooler;    MEMS;    Cryosurgery;    In-Situ Temperature Sensing;    Flow Modulation;    Electrical Engineering;    Mechanical Engineering;    Engineering;    Mechanical Engineering;   

Others  :  https://deepblue.lib.umich.edu/bitstream/handle/2027.42/62436/zhuwb_1.pdf?sequence=1&isAllowed=y

瑞士|英语

来源: The Illinois Digital Environment for Access to Learning and Scholarship

【 摘 要 】

Micromachined Joule-Thomson (J-T) coolers have applications ranging from cryosurgery to cooling infrared detectors.With the absence of cold moving parts, the J-T coolers can be implemented with simple structures that are suitable for silicon/glass microfabrication.The investigation proposed in this thesis focuses on the development of micromachined Si/glass heat exchangers used in the J-T coolers that operate at 200-225K when the gas pressure is 1-2MPa.The heat exchangers must maintain good stream-to-stream heat conductance between the high- and low-pressure streams while restricting stream-wise conduction to achieve a high effectiveness.Two heat exchangers were designed, fabricated and tested.The first, a planar design, uses rows of high-conductivity silicon fins bonded onto a 100µm thick low-conductivity glass base plate.It was fabricated using a five-mask process including Si/glass/Si anodic bonding, two-step DRIE, and HF glass etching, etc.The second, a perforated-plate design, uses numerous silicon plates alternated with glass spacers.It was fabricated using a four-mask process including KOH on (110) silicon wafers, HF glass etching and anodic bonding.Platinum resistance temperature detectors were integrated into the heat exchanger for in-situ temperature sensing.Whereas the performance of the planar heat exchanger was limited by its ability to accommodate a pressure differential across the base plate, the perforated-plate heat exchangers demonstrated a high effectiveness (0.912) in at 237-252K in effectiveness tests and good robustness at high pressures (1MPa) in J-T self-cooling tests.The temperature distribution along the heat exchanger was measured by integrated resistance temperature detectors with sensitivities of 0.26-0.30%/K at 205-296K.A J-T system using the perforated-plate heat exchanger achieved 218.7K at steady state and 200.3K in a transient state.The system provided 200mW cooling power at 228K and 1W at 239K with an estimated parasitic heat load of 300-500mW.Finally, a flow-controlled J-T system using a perforated-plate heat exchanger and a piezoelectric microvalve was demonstrated.By modulating the flow, the microvalve could vary the cooling temperature by 5-8K around the operating points, which were 254.5K at 430kPa pressure difference in steady state, and 234K at 710kPa in transient state, without an added heat load.