Simultaneous measurements of liquid velocity and temperature for high pressure and high temperature liquid single phase flows
Résumé
Forced convective boiling is of great interest for several applications in the power and process industry, particularly in nuclear plants. Under certain nominal, incidental or accidental conditions, boiling crisis (Departure from Nucleate Boiling) may occur resulting in the melting of the heated surface. An accurate prediction of the conditions leading to the occurrence of this phenomenon is then essential. We believe that such an objective unreachable unless one provides a good and accurate description of the associated two-phase flow. To achieve this goal, local parameters e.g. void fraction, vapor and liquid velocities, liquid temperature…, need to be measured within the range of interest, which mainly concerns the high pressure and high temperature convective boiling flows. In this work, we only focus on the liquid velocity and temperature measurements and we propose to use thermal anemometry for performing such measurements. However, due to the high complexity of those flows, we have developed a two-steps strategy. Indeed, before using such an experimental technic for boiling flows, we need first to check the feasibility of this method for characterizing single-phase heated flows. Measurements for boiling flows will be performed in a second step, which is beyond the scope of the present paper. We applied the multiple overheating method for simultaneous measurement of the liquid velocity and the liquid temperature using a single sensor. If this methodology has already been used for gas flows measurements (Bestion et al., 1983; Barre et al., 1992, 1994), as far as we know, this work is the first attempt for liquid flows. We conducted experiments in a circular heated tube whose inner diameter and length are 19.2 mm and 3.5 m, respectively. The sensor (hot wire d~5 µm) has been operated with the Constant Current mode (CCA). To consider for temperature effect on velocity calibration, we proposed a new non-dimensional representation of the calibration curve. We also improve the frequency response of the probe using a digital compensation method. Preliminary tests for single-phase flows confirmed that it was possible to get very accurate measurements of mean and fluctuating liquid velocity profiles as well as mean temperature profiles. We have carefully analyzed the experimental uncertainties, which are close to 0.5 °C for the liquid temperature and ±5% for the liquid velocity.
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