The use of the capacitive sensors for the study of condensation processes in the short low-temperature range heat pipes. Calibration and measurement
DOI: 10.21047/1606-4313-2017-16-2-57-65
UDC 681.3:536.24.08
Seryakov A. V., Mikhailov Y.E., Shakshin S.L.
Keywords: low-temperature heat pipe, capacitive sensor, dielectric fluid, electrode.
UDC 681.3:536.24.08
The use of the capacitive sensors for the study of condensation processes in the short low-temperature range heat pipes. Calibration and measurement
For citation: Seryakov A.V., Mikhailov Y.E., Shakshin S.L. The use of the capacitive sensors for the study of condensation processes in the short low-temperature range heat pipes. Calibration and measurement. Vestnik Mezhdunarodnoi akademii kholoda. 2017. No 2. p. 57-65
Abstract
The description of the automated capacitive meter of local thickness of the of condensate film of working fluid in a short low-temperature range heat pipes are presented . Presents design, calculation of the capacitance of the open compact capacitive sensors, the calibration results, as well as electronic equipment, allowing us to carry out measurements of local thickness of the working fluid film on the condensation surface within heat pipes (HPs). With the aim of improving the accuracy of calibration the sensors and capacitance meter were generally carried out in a fragment of HPs, in which the distribution of metal and electrical fields around the measuring electrodes of the sensors are identical to the measurement conditions that employed in the regular HPs. To measure the thickness of the liquid film condensate inside the HP was applied the method of registration of changes in the electrical capacitance ΔС of the capacitive sensor when changing the thickness of the liquid film condensate on its surface. Due to the very small changes in capacitance of the sensor with film condensation of vapour inside the HP, the determination of the thickness of the formed liquid film was carried out by measuring the change in the frequency of high frequency generator, in an oscillating circuit of which includes a measuring capacitive sensor, relative to the same reference generator, the resonant circuit of which includes similar reference capacitive sensor in the reference HP. We used two identical HPs, measurement and reference with the same capacitive sensors in each of them, the measuring one was filled with diethyl ether, and the reference one was filled with dry air with a dew point temperature below 233.15 K (–40 °C). Electronics capacitance meter consists of two high-frequency generators 33 MHz placed directly on the upper lids of both HPs, mixer and low pass filter. The lead wires of the capacitive sensors are soldered in generators mounting boards, surrounded by the metal shielding screens, sealed and placed in a flow calorimeter at a stable temperature of T = 298±0.03 K . The measured average time values of the condensate film thickness is depending on the heat load on the capillary-porous evaporator. The measurement error does not exceed 2·10-3mm. It was shown that the condensate film thickness of the working fluid decreases sharply with increase of heat load on the evaporator in the short low-temperature range HPs.
Abstract
The description of the automated capacitive meter of local thickness of the of condensate film of working fluid in a short low-temperature range heat pipes are presented . Presents design, calculation of the capacitance of the open compact capacitive sensors, the calibration results, as well as electronic equipment, allowing us to carry out measurements of local thickness of the working fluid film on the condensation surface within heat pipes (HPs). With the aim of improving the accuracy of calibration the sensors and capacitance meter were generally carried out in a fragment of HPs, in which the distribution of metal and electrical fields around the measuring electrodes of the sensors are identical to the measurement conditions that employed in the regular HPs. To measure the thickness of the liquid film condensate inside the HP was applied the method of registration of changes in the electrical capacitance ΔС of the capacitive sensor when changing the thickness of the liquid film condensate on its surface. Due to the very small changes in capacitance of the sensor with film condensation of vapour inside the HP, the determination of the thickness of the formed liquid film was carried out by measuring the change in the frequency of high frequency generator, in an oscillating circuit of which includes a measuring capacitive sensor, relative to the same reference generator, the resonant circuit of which includes similar reference capacitive sensor in the reference HP. We used two identical HPs, measurement and reference with the same capacitive sensors in each of them, the measuring one was filled with diethyl ether, and the reference one was filled with dry air with a dew point temperature below 233.15 K (–40 °C). Electronics capacitance meter consists of two high-frequency generators 33 MHz placed directly on the upper lids of both HPs, mixer and low pass filter. The lead wires of the capacitive sensors are soldered in generators mounting boards, surrounded by the metal shielding screens, sealed and placed in a flow calorimeter at a stable temperature of T = 298±0.03 K . The measured average time values of the condensate film thickness is depending on the heat load on the capillary-porous evaporator. The measurement error does not exceed 2·10-3mm. It was shown that the condensate film thickness of the working fluid decreases sharply with increase of heat load on the evaporator in the short low-temperature range HPs.
Keywords: low-temperature heat pipe, capacitive sensor, dielectric fluid, electrode.
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