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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 163 records · Page 9
All sourcesNASA NTRSDOE OSTI
NASA NTRS1943

Operating Temperatures of a Sodium-Cooled Exhaust Valve as Measured by a Thermocouple

A thermocouple was installed in the crown of a sodium-cooled exhaust valve. The valve was then tested in an air-cooled engine cylinder and valve temperatures under various engine operating conditions were determined. A temperature of 1337 F was observed at a fuel-air ratio of 0.064, a brake mean effective pressure of 179 pounds per square inch, and an engine speed of 2000 rpm. Fuel-air ratio was found to have a large influence on valve temperature, but cooling-air pressure and variation in spark advance had little effect. An increase in engine power by change of speed or mean effective pressure increased the valve temperature. It was found that the temperature of the rear spark-plug bushing was not a satisfactory indication of the temperature of the exhaust valve.

FUEL-AIR MIXTURES↗
NASA NTRS2018

Uncertainty Analysis of Coaxial Thermocouple Calorimeters Used in Arc Jets

Recent introduction of Coaxial Thermocouple type calorimeters into the NASA Ames arc jet facilities has inspired an analysis of 2D conduction effects internal to this type of calorimeter. Lateral conduction effects violate the 1D finite slab inverse analysis which is typically used to deduce the heat transfer to such calorimeters. The spherical shaped nose associated with most calorimeters (rather than flat) leads to a bias error that over-estimates the stagnation heating. Non-uniform heating on the face of spherically shaped calorimeters leads to conduction losses to the colder rim of the calorimeter which causes an underestimate of the stagnation heating. These two effects come into play at different times of the calorimeter's exposure to the arc jet, so they do not cancel. The spherical body effects come into play in the early stages of exposure, while the non-uniform heating effect becomes most severe at the later stages of exposure. The bias associated with spherical effects can be avoided by rewriting the 1D finite slab inverse analysis code to solve for 1D conduction in spherical coordinates. However, reducing the bias error associated non-uniform heating requires a somewhat ad hoc modification to the 1D finite element inverse analysis.

Isotherms↗
NASA NTRSDate not supplied

A survey of thermocouple anomalies: mechanisms, interpretation, and mitigation

Thermocouples (TCs) are a critical diagnostic sensor for high enthalpy environments including thermal protection systems (TPS) for atmospheric re-entry, hypersonic wind tunnels, and arc jet test facilities. They are used for both evaluating facility environmental conditions (enthalpy, heat flux) as well as for measuring in-situ material thermal response under test conditions (thermal conductivity, heat capacity, B’, etc.). Consequently, accurate TC measurements are fundamental for both material and facility verification and validation (V&V). However, a number of TC anomalies have been observed in both ground tests and flight instrumentation. These anomalies are caused via various coupling mechanisms: electrostatic gradients, temperature-dependent electrical shorts, radio pickup, magnetic induction, and pressure-dependent leaks. All of these mechanisms can, if unaddressed, result in obviously compromised results or worse, non-physical measurements which appear reasonable. This work will survey known anomaly mechanisms and discuss ongoing efforts to quantify and mitigate anomaly mechanisms including anomaly modeling, diagnostics, and new TC designs/development.

thermocouple anomalies↗
NASA NTRSDate not supplied

A Survey of Thermocouple Anomalies: Mechanisms, Interpretation, and Mitigation

Thermocouples (TCs) are a critical diagnostic sensor for high enthalpy environments including thermal protection systems (TPS) for atmospheric re-entry, hypersonic wind tunnels, and arc jet test facilities. They are used for both evaluating facility environmental conditions (enthalpy, heat flux) as well as for measuring in-situ material thermal response under test conditions (thermal conductivity, heat capacity, B’, etc.). Consequently, accurate TC measurements are fundamental for both material and facility verification and validation (V&V). However, a number of TC anomalies have been observed in both ground tests and flight instrumentation. These anomalies are caused via various coupling mechanisms: electrostatic gradients, temperature-dependent electrical shorts, radio pickup, magnetic induction, and pressure-dependent leaks. All of these mechanisms can, if unaddressed, result in obviously compromised results or worse, non-physical measurements which appear reasonable. This work will survey known anomaly mechanisms and discuss ongoing efforts to quantify and mitigate anomaly mechanisms including anomaly modeling, diagnostics, and new TC designs/development.

Thermocouple Anomalies↗
NASA NTRS2022

Thermocouple Temperature Measurements in Selective Laser Melting Additive Manufacturing

The extreme thermal history resulting from selective laser melting leads to microstructural characteristics and residual stresses that have considerable impact on the mechanical behavior of the printed part. Accurate measurements of the temperature combined with thermal models are needed to better understand and control the thermal history to optimize mechanical properties. In order to calibrate and validate models, experimental temperature data must be accurately measured in a rapid fashion due to the high speeds of the laser. In this work, a novel method to read data from thermocouples is created with enhanced circuitry that achieves a sampling rate of 10 kHz. This data acquisition rate allows for high precision sampling of SLM heating and cooling cycles.

additive manufacturing↗
DOE OSTI2024

Enhancing the cooling performance of thermocouples: a power-constrained topology optimization procedure

Abstract Heat pumping through thermoelectric devices has many advantages over traditional cooling. However, their current efficiency is a limiting factor in their implementation. In this paper, we approach the non-convex topology optimization of thermoelectrical elements for cooling applications through the method of moving asymptotes (MMA) to improve their cooling capabilities per watt usage. The optimization problem is defined for a given power budget, aiming for the minimum temperature with a known heat pumping need. The introduction of power as a constraint justifies the introduction of the voltage gradient across the thermocouple as a design variable to maintain the thermoelectrical device in its optimum power-to-heat extraction ratio. To better understand the convergence of this non-convex problem, we present a two-variable analytical thermoelectric optimization model. This example provides information on how to select the penalty parameters used to scale the three material coefficients involved in the problem to obtain lower objective values and better convergence using MMA. The analytical model shows the non-convexity of the problem and provides the recommendation to use penalization coefficients of the form $$p_k=p_{\sigma }>p_{\alpha }=1$$ p k = p σ > p α = 1 for the thermal conductivity, electrical conductivity, and Seebeck coefficients. We tested these penalization coefficients through optimizations of a model based on the 1MC10-031 commercial thermoelectric-cooler (TEC) using the finite element method (FEM). These penalization coefficients provided local minima without the need for volume constraints. With this procedure, we found designs that provided temperatures close to 10 degrees lower using 60% less semiconductor material volume compared to the initial design.

Gutiérrez, G. Reales↗
DOE OSTI2025

Thermocouples in Resistive and Induction Furnaces Operated in Strong Magnetic Fields

The thermomagnetic processing methods require an understanding of the in situ temperatures experienced by the workpieces. When commonly used thermocouples (TCs) are employed in induction furnaces, RF fields can contribute additional temperature uncertainties to the ones arising from the use of strong magnetic fields. Focusing on temperatures between 300 ° C and 1000 ° C produced by induction and resistive furnaces, the readings generated by Type-K TCs were contrasted to the ones produced by Type-S and Type-N sensors for magnetic fields up to 9 T. Overall, when comparing Type-K response to temperatures above 700 ° C in both zero field and high field ( ≤9 T), the differences amounted to less than 1% and when continuously measured has a linear relationship to the strength of the applied field. The relative invariance of Type-N and Type-S TCs was confirmed. In conclusion, these findings suggest that the use of TCs in high magnetic fields remains a viable option for applications, although the precision depends on the type used.

Tener, Zachary P. [Oak Ridge National Laboratory (↗
NASA NTRS1967

Thoriated tungsten tube provides improved high temperature thermocouple sheath

Thermocouple tubing of thoriated tungsten with a very fine grain structure produces a small-diameter sheath capable of operating up to 5000 degrees R in a hydrogen and graphite environment. This tubing remains ductile and resists both grain growth and carbiding even after prolonged exposure to temperature.

Zellner, G. J.↗