Abstract
Forced convective heat transfer from three horizontally inclined rectangular-based cylinders (rods) has been studied experimentally under representative Martian near-surface air flows in the Aarhus Wind Tunnel Simulator (AWTS), Denmark. The testing campaign was developed for the HABIT (Habitability: Brines, Irradiation and Temperature) instrument, European payload on board the ExoMars 2022 Kazachok surface platform. The average heat transfer coefficient was determined from steady CO2 flows at a pressure of 9.9 mbar, an ambient temperature of ∼25 °C, and for horizontal free-stream velocities between 0.8 and 12 m/s. A retrieval algorithm to derive the wind speed from the average heat transfer coefficient estimated at each of the three HABIT Air Temperature Sensors (ATS) rods was calibrated within the AWTS. The ATS rods are placed one at the front of the instrument structure (ATS2) and two on the sides (ATS1 and ATS3); and under Martian atmospheric conditions these rods serve as cooling fins. Several relationships between the Nusselt number and the Reynolds and Prandtl numbers reported in the literature were evaluated to model convective heat transfer from the ATS rods. Where needed, corrections to account for radiative heat transfer within the AWTS were implemented. The final retrieval method demonstrated that wind speed can be retrieved for frontal winds in the range of 0–10 m/s, with an error of ±0.3 m/s, using the cooling profile of the ATS rod 3, and for lateral winds in the range of 0–6 m/s, with an error of ±0.3 m/s, using the ATS rod 2 cooling profile.
Highlights
Many engineering applications require fluid flow velocity to be measured
The capabilities of wind speed retrieval algorithm for ExoMars have been experimentally assessed under representative near-surface
The retrieval is based on modelling forced convection around the three rectangularbased Air Temperature Sensors (ATS) rods of the HabitAbility: Brines Irradiation and Temperature (HABIT) instrument
Summary
Many engineering applications require fluid flow velocity to be measured. The retrieval of low speeds is interesting in a wide range of scenarios, such as the controlled flow in a cleanroom or the ventilation systems. HABIT flight model (FM) is shown in Fig. 1-left, including the three air temperature sensors (ATS) of the instrument designed to provide the air temperature in the vicinity of the SP. These ATS consists of three thin rectangular-based rods, whereby the temperature is monitored along their axis at three points to the REMS and TWINS ATS rods. The retrieval is based on the modelling of convective heat transfer around the HABIT ATS rods when immersed in a cross-flow. The calibration of the retrieval was performed for the expected range of wind speeds on the surface of Mars and, limited by the AWTS testing capabilities, at ambient temperature. The retrieval developed in this research work is limited to horizontal winds
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