The Combined Use of a Gas-Controlled Heat Pipe and a Copper Point to Improve the Calibration of Thermocouples up to 1100 ˚C

Abstract

The calibration of platinum-based thermocouples from 420 • C to 1,100 • C is currently carried out at INRIM making use of two different apparatus: for temperatures below 930 • C, a potassium gas-controlled heat pipe (GCHP) is used, whereas a metal-block furnace is adopted for higher temperatures. The standard uncertainty of the reference temperature obtained in the lower temperature range is almost one order of magnitude better than in the higher temperature range. A sealed copper cell was investigated to see if it could be used to calibrate thermocouples above 930 • C with a lower uncertainty than our current procedures allowed. The cell was characterized with Type S and Pt/Pd thermocouples and with an HTPRT. The freezing plateaux were flat within 0.01 • C and lasted up to 1 h with a repeatability of 0.02 • C. The temperature of the cell was determined with a standard uncertainty of 0.04 • C. Hence, the copper cell was found to be superior to the comparator furnace for the calibration of platinum-based thermocouples because of the significant decrease in the uncertainty that it provides. An analysis was also carried out on the calibration of Pt/Pd thermocouples, and it was found that the combined use of the potassium GCHP and the Cu fixed-point cell is adequate to exploit the potential of these sensors in the range from 420 • C to 1,084 • C. A comparison with a fixed-point calibration was also made which gave rise to agreement within 0.07 • C between the two approaches.

Sodium-Potassium Alloy Heat Pipe under Geyser Boiling Experimental Study: Heat Transfer Analysis

“…The working temperature of high temperature heat pipes is higher than 750 K. Sodium, potassium and other alkali metals are often used as working fluid for high temperature heat pipe because of their high boiling temperature, low saturation pressure, high latent heat of vaporization and high heat transfer performance. Alkali metal heat pipes have been used in many high temperature applications such as high temperature isothermal heater [4], thermometric calibration system [5,6], solar energy utilization system [7,8], residual heat removal system [9][10][11][12], high temperature thermal management [13][14][15] and so on. The alloy of suitable ratio of sodium and potassium is liquid at room temperature, so the sodium-potassium (Na-K) alloy heat pipe has great advantages in cold-start and working fluid filling.…”

Isothermal performance of a temperature comparison source using potassium concentric annular heat pipe

“…Figure 3B presents the size and structure of heating furnace. The potassium CAHP was placed horizontally in the middle of the heating furnace, and other places in the furnace were filled with insulation The operating temperature range of potassium heat pipe is about 400 C to 1000 C, 9,18 and depends on the temperature required for thermocouple calibration, the heating temperatures in this study were set at 400 C, 500 C and 600 C. The temperature distribution at 0 to 16 cm from the bottom of four metering wells was measured. One thermometer as a reference thermometer is always placed at the bottom of the metering well, and the other as a measuring thermometer to measure the temperature at different positions.…”

“…The operating temperature range of potassium heat pipe is about 400°C to 1000°C, 9,18 and depends on the temperature required for thermocouple calibration, the heating temperatures in this study were set at 400°C, 500°C and 600°C. The temperature distribution at 0 to 16 cm from the bottom of four metering wells was measured.…”

“…And the temperature stability of water GCHP could also reach ±1 mK. Astrua et al 18 studied the calibration using potassium GCHPs and copper point cell. The temperature uniformity of this device was 0.01 K and the temperature stability within 1 h was ±0.02 K. McAllan and Bassani 19 studied the working fluid flow fluctuation at the connection between the pressure controller and the heat pipe condenser.…”

NIM gas controlled sodium heat pipe

“…As a result, these heat pipes can be maintained isothermally. These heat pipes are also called variable conductance heat pipes (VCHPs) and are applied to precision spacecraft thermal control [2], electronics temperature control, and accurate temperature measurements [3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20][21][22].…”