Precise determination of the thermal conductivity of fluids using absolute transient hot-wire technique
Creators: name: Mani, Narayanaswamy
Publisher: name: University of Calgary
Year: 1971
Subjects: subject: QC 323 M35 1971 Microfilm
subject: Heat - Conduction
subject: Thermodynamics

description: Bibliography: p. 210-216.
description: The knowledge of accurate data on the transport properties of fluids is not only demanded by theoreticians to predict accurately the basic molecular mechanisms involved in the transport phenomena in fluids and fluid mixtures but is equally important to the engineer in order to design advanced heat transfer elements such as in nuclear and rocket technology. But disparities of± SO per cent are not uncommon in the existing data for the transport properties. This uncertainty in the property values can result in considerable over or under design, The fact that our analytical ability and phenomenological knowledge concerning heat transfer mechanisms far outstrips our design and technological ability can thus be attributed to some extent to a lack of sufficiently precise property data for most fluids. An apparatus was, therefore, developed using an ab~olu;te · br.arlJ.&gt;ient hot-w)Jz,e technique to measure aeewr.a.,te and p~ewe values of the theJt.mal eonduetivity, one of the transport properties, of liquids and dense gases over a wide range of temperature from 100°K to 400°K and of pressure up to 700 bar. An analysis for heat transfer by simultaneous conduction and radiation in a radiation participating medium surrounding the hot-wire in a cylindrical enclosure was carried out to account for the radiative component of the thermal conductivity. The transient response of the hot-wire in the surrounding medium was also studied to determine the onset of convection and the consequent termination of the pseudoconduction regime so as to ensure convection free measurements. The effect of non-constant heat generation from the hot-wire on measurements was also examined and accounted for so that the results, independent of the heat flux from the wire, were obtained . From an analysis of all possible errors, corrections and t heir minimization, a system with measurement reproducibility and accuracy of better than 0.5 per cent was designed using a computerized data acquisition system. Measurements were carried out on liquid and dense gaseous methane over the entire design temperature and pressure range and the results compared with the correlations obtained for the existing data, The accuracy of the measurements and the reliability of the apparatus were also checked by measurements on toluene, one of the suggested standard reference materials for thermal conductivity measurements, in the temperature range from - 90 to 110°C at atmospheric pressure. The measured conductivity value of 129.16 mW/m°K at 25°C for toluene agrees favourably with recent Jz.a.d,,,la,u,on component n~ee values reported using steady state methods. The measurement results on toluene indicate a distinct region of p~e-6~eezing anomaly which may be attributed to cluster formation in the liquid as the solid-liquid phase boundary is approached. This pre-freezing anomaly is likely in most liquids , An anomalous enhancement. in the thermal conductivity of methane is suspected in the vicinity of its thermodynamic critical point.