Thomas G. Kollie

The thermal conductivity of AISI 304L stainless steel

A compilation and critical analysis of the thermal conductivity (γ) of AISI 304 stainless steel (SS) between 100 and 1707 K has been given in the literature. The author represented his “recommended” values of λ by an inflection in the A versus temperature relationship between 300 and 500 K. Because a physical mechanism had not been identified that would produce such a temperature dependence in γ of 304 SS, interest was generated in the possible existence of an as yet undiscovered phenomenon that might cause such an inflection. Consequently, experimental verification of the inflection was sought. The present paper presents recent measurements of λ, the electrical resistivity, and the absolute Seebeck coefficient of 304L SS from 300 to 1000 K and of the thermal diffusivity (α) from 297 to 423 K. The λ values computed from the a measurements were within ± 1.6% of the directly measured λ An inflection was not observed in the temperature dependence of λ between 300 and 500 K. After careful evaluation and because a physical mechanism still has not been identified which would produce such an inflection, the authors conclude that the inflection in the λ vs T relationship reported in the literature was caused by the data analysis technique.

Large thermocouple thermometry errors caused by magnetic fields

Chromel/Alumel thermocouples used in a magnetic field indicated temperatures in error by about ±150% at 100 °C. Diagnostic tests showed that the errors were caused by the Ettingshausen–Nernst (EN) effect. The EN effect produces an emf in a conductor, such as a thermocouple, placed in a magnetic field and temperature gradient which are both transverse to the length of the conductor. The heat transfer experiment at the Oak Ridge National Laboratory in which the temperature measurement errors were encountered is described, and the results of diagnostic tests performed in this experimental apparatus and in auxiliary lab‐bench experiments to identify the EN effect are presented. Sources of error, other than the EN effect, for thermocouples used in a magnetic field are discussed.

Temperature measurement errors with type K (Chromel vs Alumel) thermocouples due to short‐ranged ordering in Chromel

After annealed, type K (Chromel vs Alumel) thermocouples were heated above 200 °C, their temperature measurements were in error up to 1.3%, as determined by comparison calibrations to working standard 90% Pt–10% Rh/Pt thermocouples or platinum resistance thermometers. Reannealing the type K thermocouples removed the errors. The errors were due to changes in the thermal emf vs temperature relationship of the type K thermocouples, which from previous work of others can be attributed to short‐ranged ordering of the Chromel thermoelements. Reannealing the thermocouples removed the errors because the order–disorder transformation is reversible; that is, short‐ranged ordering of the Ni and Cr atoms of the Chromel alloy occurs between 200° and 600 °C, and disordering occurs above 600 °C. The traveling gradient method was used to determine the effects of heat treatment on the thermal emf of type K thermocouples, to investigate the kinetics of ordering of Chromel, and to determine the amount of order produced by h...

Physical contributions to the heat capacity of nickel

Abstract Heat capacity data for solid nickel have been re-evaluated and analyzed into physical contributions, 0–1726 K. Two new sets of measurements of C p (Ni), 333–1500 K, have been combined with literature data to produce an evaluated data set with uncertainty ⩽ ± 2%. These smoothed data have been analyzed into vibrational harmonic, electronic, magnetic and dilatational contributions with the aid of auxiliary measurements of expansion coefficient, compressibility, vibrational and electronic densities of states, elastic constants, and magnetic exchange integral and susceptibility obtained from the literature. The vibrational harmonic term is interpreted in terms of a θ D -vs- T curve in accord with predictions of the density-of-states distribution. The electronic contribution is smaller than predicted by free-electron theory due to a large electron-phonon effect. The electronic term for paramagnetic nickel is in good agreement with that predicted from band calculations. The magnetic contribution yields a magnetic entropy in accord with theoretical predictions, and a magnetic internal energy and critical-point behavior in agreement with the isotropic Heisenberg model. The experimental heat capacity can be accounted for without reference to vibrational anharmonic and vacancy contributions, in accord with recent calculations.

Thermal Transport Properties of Ordered and Disordered Ni3Fe

Thermal conductivity λ, electrical resistivity ρ, and Seebeck coefficient S measurements have been made from 80 to 400 K on a Ni3Fe alloy (74.77‐at. % Ni and 25.33‐at. % Fe) in both disordered and highly ordered states. The effect of lattice disorder is to lower λ and S and increase ρ. Although λ and ρ for the three states studied differ by about 50%, the Lorenz ratios λρ/T are the same to within the combined uncertainty of the measurements. This ratio is near the Sommerfeld value Lo from 200 to 400 K, and the positive deviation from Lo below 200 K indicates a significant lattice component to λ in all states of disorder. The thermal conductivities of the three states of Ni3Fe exhibit peaks between 142 and 175 K. The unusual relative shift of the temperatures of the maximum conductivities is related directly to the large deviation of the electrical resistivity differences from Matthiessens rule.

Evaluation of a commercial, portable, ambient‐temperature emissometer

The DevicesS an uncertainty of ±0.014 units was determined. These repeatability and accuracy values were confirmed by a round‐robin investigation using two working standards whose e’s were measured by three independent laboratories using model AE emissometers and by four laboratories that used absolute methods. The instrument was shown to measure the total hemispherical e, not the total normal e. Experimental difficulties were encountered during measurements on a very anisotropic material and in determinations of e’s of materials with transpare...

Measurement of B versus H of Alumel from 25 to 180 °C

The relationship between the magnetic induction B and the magnetic field H in Alumel was measured by the ring method for temperatures T between 25 and 180 °C. These data were needed to correct for large temperature measurement errors that occurred when Chromel‐vs‐Alumel thermocouples were used in a magnetic field. Through application of the Weiss equation, the saturation value of the intrinsic magnetic induction Bs was calculated as a function of T from the experimental B‐vs‐T data. Weiss’s method was used to determine the Curie temperature of Alumel, Tc?152 °C, from a plot of B2s versus T near Tc. The experimental values of Bs versus T were in good agreement with those obtained from the Brillouin function with quantum number J=1/2.

Specific Heat Determinations by Pulse Calorimetry Utilizing a Digital Voltmeter for Data Acquisition

A pulse calorimeter for measuring the specific heat of electrical conductors from 25 to 900°C is described. The technique employed was unique in that a digital voltmeter, which was capable of recording 400 readings per second to a readability of 0.1% of full scale, was utilized to measure the transient temperature and power signals requisite to the method. Using this technique, a calculated determinate accuracy of 99% was achieved. Measurements of the specific heat of high‐purity iron from 25 to 900°C confirmed this calculated accuracy and were repeatable to within ±0.5%. The calorimeter was capable of measuring the specific heat rapidly at temperature intervals as small as 0.1 C°. Modifications are suggested to decrease the measurement errors to 0.5% and to increase the temperature range from −190 to 1400°C.

Derivation and testing of a model to calculate electrical shunting and leakage errors in sheathed thermocouples

A three‐wire transmission line model was derived to calculate temperature measurement errors caused by electrical shunting and leakage in metal sheathed, oxide insulated, compacted thermocouple assemblies. Input parameters for the model were measured and used to verify experimentally the validity of the model on a 0.5‐mm‐diam stainless steel sheathed, MgO insulated, Chromel/Alumel thermocouple assembly. When a 1.27‐m length of the assembly was heated to 1274 K, the errors due to shunting, calculated using the model, were 6.4% and 9.4% lower than the experimentally measured errors for theromocouple measuring junction temperatures of 273.2 and 371.5 K, respectively. With the 1.27‐m length heated to 1373 K, the errors due to shunting, calculated using the model, were 12.6% and 14.9% lower than the experimentally measured errors for measuring junction temperatures of 273.2 and 371.5 K, respectively. For a 1.27‐m length of the thermocouple assembly at 1274 K, the measuring junction at 273.2 K, and sheath curre...

Evaluation of a commercial, computer-operated heat flow meter apparatus

A Holometrix, Inc., R‐Matic model R‐41 Heat Flow Meter Apparatus (HFMA) is evaluated by measurements on homogeneous materials and anisotropic composite materials. The former class of materials includes: foams, calcium silicate boards, fiberglass batts, and loose‐fill fiberglass. Materials in the latter class are polystyrene with gas‐filled panels and batts with powder‐filled evacuated panels. Thermal models of the anisotropic composite materials allow design of composite test specimens and help in the interpretation of test results by computation of apparent thermal conductivities (k). The HFMA includes a dedicated computer for test control, data acquisition, and data analysis. Thus, the computer helps obtain the conditions needed to conduct accurate and repeatable steady‐state tests to meet ASTM C 518 with minimum operator involvement. The k values from this HFMA and three other HFMAs (model R‐20 and R‐21 units) exhibit imprecisions of 2.2% (two standard deviations) for specimens of foam insulation. Such...