Thermal performance analysis and prediction of a circumferential serpentine tube for high-power motor cooling

The servo motor in the actuator of flight vehicles suffers both a high-power loss and a harsh thermal environment, which lead to a risk of overheating failure. To address this issue, the liquid cooling device is employed on the flight vehicle to remove heat from the motor, using the onboard cryogenic fuel (supercritical methane, S-CH4) as the coolant. To improve the applicability and versatility, a circumferential serpentine tube (CST) encircled the motor as the cooling jacket is proposed. This configuration has a compact structure as well as a large heat exchange area, and the inlet and outlet of the cooling tube locate adjacently, which is convenient to arrange and install the coolant pipeline. With this in mind, a three-dimensional numerical model of CST is established based on the shear stress transport k–ω turbulent model, and the flow and heat transfer of S-CH4 in CST are explored. The effects of operating parameters, such as pressure, heat flux, and mass flux, on the heat transfer are analyzed. The results present that the heat dissipation performance of motor is improved significantly, owing to the combined effect of the thermophysical properties of S-CH4 and the geometric structure of CST. Furthermore, the heat transfer prediction of CST is investigated by comparing various heat transfer correlations, and an improved one is proposed furtherly based on the Ornatsky's correlation owing to its better prediction relatively. Thereinto, the geometric parameters of CST, the thermophysical properties of supercritical coolant, and the flow regime of convection are considered. The average error is 8.66% under various operating conditions and improved by 40.73% compared with that of the Ornatsky's correlation, indicating a superior prediction accuracy.