2016 Scientific Ballooning Technologies Workshop Title Liquid Cooling of High Power Dissipation Electronics Author Andrei L. Korotkov (Brown University) Abstract Bolometer Readout (BRO) system for the EBEX2013 kilo-pixel array of transition-edge sensors dissipated about 600 W by the 28 digital frequency domain multiplexer (DfMUX) boards. The DfMUX boadrs were divided between four separate BRO crates, containing six or eight boards. Inside the crates each DfMUX board was heatsunk to the heat-exchanger panel on the crate top wall with two Nanospreaders - proprietary copper heat pipes made by Celsia Technologies. The crates were located in the vicinity of the receiver cryostat, in the well screened area of the instrument gondola with very limited possibility for direct radiative heat exchange with the deep sky. A Liquid cooling system (LCS) was developed to transfer heat from the BRO top plate to the radiator at the front of the telescope inner frame. The LCS consisted of two independent closed loops of 4.75 mm inner-diameter copper, Teflon and aluminum tubes. Dynalene HC-40 was used as liquid agent due to its good heat transfer characteristics and low freezing point of -40°C. A 20 W, 80 PSI differential pressure pump (Micropump GJ Series) circulated Dynalene at at 32 mL/s through each loop. Aluminum radiator panels of total area of 4.16 m2 were attached to the inner frame with an electrically insulating fixture. They dissipated the heat to space with an average view factor of 0.52. The radiator surfaces were covered with Sheldahl 250 μm thick Fluorinated Ethylene Propylene (FEP) tape with a 150 nm silver layer to improve infrared emissivity while keeping absorption of visible light low. During flight, the LCS kept the BRO heat exchangers below the 25 °C required to maintain the DfMUX board components below 70 °C. The details of the design as well as the performance of the LCS will be presented.

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