Determining the thermal conductivity of liquids using the transient hot disk method. Part II: Establishing an accurate and repeatable experimental methodology (original) (raw)
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International Journal of Heat and Mass Transfer
Methods to determine the thermal conductivity of liquids have come under increased scrutiny recently due to their relative importance in determining the precise physical mechanisms responsible for heat flow in different materials and at multiple length scales. In transient-based systems, one important but often overlooked parameter is the onset of natural convection. In the first part of this study, the transient effects of natural convection are analyzed numerically for a relatively new transient thermal characterization system (transient hot disk) in order to determine when they begin to affect the calculation of a surrounding fluid's thermal conductivity. A comprehensive analysis of the effect of a fluid's pertinent thermophysical properties, Rayleigh number and Prandtl number on the sensor temperature response during testing is completed. Subsequently, a correlation is developed to determine the onset of natural convection during testing for fluids having a wide range of Prandtl numbers. The solution is verified using experimentation with multiple fluids having known, temperature-dependent volumetric heat capacities. The correlation is used as part of a new method to accurately calculate the thermal conductivity of different Newtonian fluids in Part II of this study, which is published separately.
Correct Use of the Transient Hot-Wire Technique for Thermal Conductivity Measurements on Fluids
International Journal of Thermophysics
The paper summarizes the conditions that are necessary to secure accurate measurements of the thermal conductivity of fluids using the transient hot-wire technique. The paper draws upon the development of the method over five decades to produce a prescription for its use. The purpose is to provide guidance on the implementation of the method to those who wish to make use of it for the first time. It is shown that instruments of the transient hot-wire type can produce measurements of the thermal conductivity with the smallest uncertainty yet achieved (± 0.2%). This can be achieved either when a finite element method (FEM) is employed to solve the relevant heat transfer equations for the instrument or when an approximate analytic solution is used to describe it over a limited range of experimental times from 0.1 s to 1 s. As well as establishing the constraints for the proper operation of the instrument we consider the means that should be employed to demonstrate that the experiment o...
Thermal Science, 2017
Transient hot wire method is considered a reliable and precise technique for measuring the thermal conductivity of liquids. The present paper describes a new transient hot wire experimental set-up and its initial testing. The new apparatus was tested by performing thermal conductivity measurements on substances whose reference thermophysical properties data existed in literature, namely on pure toluene and double distilled deionized water. The values of thermal conductivity measured in the temperature range 25 to 45 ?C deviated +2.2% to +3% from the literature data, while the expanded measurement uncertainty was estimated to be ?4%.
A New Instrument for the Measurement of the Thermal Conductivity of Fluids
International Journal of Thermophysics, 2006
The transient hot-wire technique is at present the best technique for obtaining standard reference data for the thermal conductivity of fluids. It is an absolute technique, with a working equation and a complete set of corrections reflecting departures from the ideal model, where the principal variables are measured with a high degree of accuracy. It is possible to evaluate the uncertainty of the experimental thermal conductivity data obtained using the best metrological recommendations. The liquids proposed by IUPAC (toluene, benzene, and water) as primary standards were measured with this technique with an uncertainty of 1% or better (95% confidence level). Pure gases and gaseous mixtures were also extensively studied. It is the purpose of this paper to report on a new instrument, developed in Lisbon, for the measurement of the thermal conductivity of gases and liquids, covering temperature and pressure ranges that contain the near-critical region. The performance of the instrument for pressures up to 15 MPa was tested with gaseous argon, and measurements on dry air (Synthetic gas mixture, with molar composition certified by Linde AG, Wiesbaden, Germany, Ar-0.00920; O 2-0.20966; N 2-0.78114), from room temperature to 473 K and pressures up to 10 MPa are also reported. The estimated uncertainty is 1%.
18th International Congress of Metrology
This work concerns the characterization of the thermal conductivity of liquids by hot wire method. A measuring cell has been specially developed for this study. The method of analysing the transient response makes it possible to obtain values of conductivity close to those expected (deviations <4%) for two reference fluids and measurement uncertainties in the order of 5%. The use of the so-called steady state method (ASTM D 2717) leads to relative deviations and uncertainties of the measurements about 3 times higher.
Thermal Conductivity Measurements of Liquids with Transient Hot-Bridge Method
Instrumentation Mesure Métrologie
In this paper an electro-thermal method is used for measuring the thermal conductivity of liquids. This technique is based on eight heat sensing resistors which are connected to form a Wheatstone bridge. Measurements performed on several liquids covering a wide range of thermal properties validate the method. The total standard uncertainty of the experimental results was estimated to be less than 3.8 %. Good agreement is found between the measured values of the thermal properties and previously reported values in literature. Moreover, measurements using this method are less time consuming than using the classical methods. This technique may find practical application for the thermal characterization of complex fluids even when applying external electric or magnetic fields.
International Journal of Energy Research, 1994
Simultaneous measurements of thermal conductivity and thermal diffusivity of composite red-sand bricks, glycerine and mercury have been made at room temperature by the recently developed transient plane source (TPS) technique. This paper describes, in brief, the theory and the experimental conditions for the simultaneous measurements of thermal conductivity and thermal diffusivity of insulators, fluids and metals. The source of heat is a hot disc made out of bifilar spirals. The disc also serves as a sensor of temperature increase in the sample. The measured values of the thermal conductivity and thermal diffusivity of these samples are in agreement with the values reported earlier using other methods. The advantage of the TPS technique is the simplicity of the equipment, simultaneous information on thermal conductivity and thermal diffusivity, and also the applicability of the technique to insulators, fluids and metals.
Thermal diffusivity measurement by the transient hot-wire technique: A reappraisal
International Journal of Thermophysics, 1988
The theory of the transient hot-wire technique for thermal conductivity measurements is reassessed in the special context of thermal diffusivity measurements. A careful examination of the working equation and an error analysis are employed to identify the principal sources of error. Notwithstanding earlier claims to the contrary, the best precision that can be attained in thermal diffusivity measurements is of the order of +3%, while the accuracy is inevitably poorer. Experimental evidence is adduced from two different instruments that supports the analysis given here. Although the technique cannot yield values of the thermal diffusivity, K, as accurate as can be achieved by the use of the best possible individual values of 2, p, and Cp in the relation K = ~/pCp, the simplicity of the technique makes it attractive for many purposes. It is even possible to derive values of the isobaric heat capacity Cp for many fluids not available from other methods.
Measurement of thermal conductivity of fluid using single and dual wire transient techniques
Measurement, 2013
A modified measurement device to measure thermal conductivity of fluids using transient hot-wire technique has been designed, developed, tested and presented in this paper. The equipment is designed such that the thermal conductivity could be measured using both single wire sensor of different length and dual wire sensor. The sensor, which is also a heater, is a platinum micro-wire of 50 lm diameter. The influence of wire length on the measurement of thermal conductivity of fluids is tested using two single wires of length 50 mm and 100 mm. The thermal conductivity is also measured using a dual hot wire arrangement; which is achieved by placing the 100 mm and 50 mm wires in a Wheatstone bridge with the 100 mm wire as the sensor and 50 mm wire as a compensation wire. The apparatus requires a 100 ml of test fluid to perform the experiment. The testing temperature of the test fluid during the experimentation can be suitably varied by the choice of heat exchange fluid used in the apparatus. Water is chosen as testing fluids for primary standards. When compared to single wires, the thermal conductivity of the fluids measured is consistent with dual-wire method with an uncertainty of ±0.25%.