Characterizing Drift Behavior in Type K and N Thermocouples After High Temperature Thermal Exposures

Abstract

Although of the widespread use of base metal thermocouples in the industry, many previous relevant researches have shown that the accuracy and stability of thermocouples are clearly influenced by any physical or chemical changes in their thermoelements. Among the most important of these changes are the inhomogeneity, pollution, oxidation and microstructure changes of the thermoelements, all of these changes and more leads to thermocouples drift after a prolonged thermal exposure. To study how these changes affect the drift and thermoelectric properties of thermocouples, in this work we subjected the base metal thermocouples of types K and N to successive thermal exposure periods at their maximum temperatures. Scanning electron microscopy (SEM) and Energy Dispersive X-ray (EDX) systems were used to monitor the change in the crystal structure and chemical composition of the thermocouple wires after each stage of the thermal heating, and then we studied the changes in the thermoelectric properties of thermocouple wires. The results showed type N thermocouples are more stable at high temperatures (up to 1050 ͦ C), even if used for long periods (for more than 1200 hours) at those temperatures, but K type thermocouples showed a rapid drift with first exposure to high temperatures and completely failed after 600 hours due to devastating corrosion.

Mesh Independence Study on CFD for Cryo-CO2 Cooling Strategy

“…The cryo-CO2, which was supplied from a compressed cylinder of LCO2 was injected through a nozzle with an inner diameter of 1.3 mm to the open air. The flow temperature was measured using a K-type thermometer [26]. The test bench setup, as shown in Figure 4, consisted of a board divided into quadratic sectors measuring 18 × 18 mm, along with a high-speed digital camera Olympus i-speed LT and five tungsten spotlights with power outputs set at 1000 W each to measure and record variations in cryo-CO2 flow temperatures at different distances.…”

Investigation of Temperature Drift with Thermocyclic Oxidation on K-Type Bare Thermocouples

“…This research examined the degeneration of thermocouple material using SEM-EDAX analyses method, induced by continuous contact to high temperatures, which causes surface oxidation. SEM is an effective technology for investigating a materialꞌs surface and cross-section and EDAX provides SEMꞌs chemical components [25]. Several studies discuss thermocouple drift and temporal stabilities [26], with one study stating that a large degree of long-term stability of chromel-alumel based thermocouples is a problem that warrants more investigation.…”