Simultaneous Determination Of Thermal Diffusivity Research Articles

Dental Plating Efficiency of Metal Base Dental Alloys by Thermal Diffusivity Study

The need for reliable data on thermophysical properties of materials has increased continuously in the last period. The existing data, except for some pure elements or alloys and compounds, often unreliable, and in many cases the need for accurate and acceptable data, can only be achieved by measuring a given property. This paper focuses on elements of the used test methods associated with the description of the newly introduced parameter (effectiveness of dental coating). The selected method was the “pulse method” for determining thermal diffusivity (the method allows simultaneous determination of thermal diffusivity, specific heat capacity and thermal conductivity) directly applicable in the study of the thermal compatibility of metal-ceramic systems in dental applications.

A review on simultaneous determination of thermal diffusivity and heat transfer coefficient

Mathematical simulation studies for thermal food processes require knowledge of thermal diffusivity and convective heat transfer coefficient. There have been different experimental and empirical approaches reported in the literature for determination of these parameters where different approximations were applied. One of the most applied approaches is to assume an infinite convective heat transfer coefficient at the surface boundary when analytical solutions for infinite slab, infinite cylinder and sphere are used for further determinations. Since this approach results in certain errors in results, it would be an important task to determine thermal diffusivity and convective heat transfer coefficient simultaneously. Therefore, the objective of this study was to review the literature for determination of thermal diffusivity and mathematically apply optimization methodologies for simultaneous determination of heat transfer coefficient. For this purpose, constrained optimization methodologies, based on analytical solutions of infinite slab, infinite cylinder and sphere were defined, and results were discussed intensively. The results showed that a precise determination of thermal diffusivity and convective heat transfer coefficient is a difficult task, but knowing the location where the experimental time–temperature was obtained would really simplify this problem.

Measurement of thermophysical properties of polyester cured with styrene in the range 300–450 K

AbstractA pulse method for the simultaneous determination of thermal diffusivity, α, specific heat capacity, Cp, and thermal conductivity, λ, are measured for a series of curing of polyester and styrene in the presence of 10, 20, and 30% carbon black in the temperature range 300–450 K. The results show a dependence of the above‐mentioned properties on temperature and composition. The mechanism of heat transfer through the specimens is also discussed. © 1993 John Wiley & Sons, Inc.

Simultaneous determination of thermal diffusivity and thermal conductivity of liquids by the Laplace transform method.

A new unsteady-state method for measuring simultaneously the thermal dilfusivity and the thermal conductivity of liquids is presented. The method utilizes the principle of the Laplace transform and has the advantage of measuring these two properties under arbitrary heating or cooling conditions imposed on the test liquid, where unidirectional heat flow and a uniform temperature profile at the initial stage are conditions of testing. A measuring theory is developed for a measuring system wherein test liquid is intruded between a pair of flat reference samples whose properties are known. The characteristics and measuring errors of the method are discussed. An apparatus in which low-expansion borosilicate glass is used as the reference sample is made on an experimental basis. The method is verified by measuring both the thermal diffusivity and the thermal conductivity of water, toluene and NaCl solution.

Simultaneous Determination of Thermal Diffusivity and Heat Transfer Coefficient during Sterilization of Carrot Dices in a Packed Bed

ABSTRACTCarrot dices were heated under ultra‐high temperature sterilization conditions in a packed bed to quantify the effect of superficial fluid velocities on heat transfer coefficient (h) and obtain a value for thermal diffusivity (α). h and α were determined simultaneously under non‐constant heating fluid temperatures using a finite difference technique. Temperature profiles calculated using assumed h and α were matched with measured temperature at two points in a cube. Using best fit value for α of 1.94 × 10−7 m2/sec, mean h ranged from 600 to 1533 and 359 to 735 W/m2K for 0 and 1.58 cm/sec fluid velocity and 1 and 2 cm cubes, respectively. At 15.2 cm/sec, when a controlled heat transfer, calculated α was 1.86 ± 0.044 × 10−7 m2/sec.

Method of Simultaneous Measurement of Radiative and Lattice Thermal Conductivity

A new technique of high-temperature thermal-conductivity measurement is described. A CO2 gas laser is used to generate a low-frequency temperature wave at one face of a small disk-shaped sample, and an infrared detector views the opposite face to detect the phase of the emerging radiation. A mathematical expression is derived which enables phase data at several frequencies to be used for the simultaneous determination of thermal diffusivity and mean extinction coefficient. Lattice and radiative thermal conductivities are then calculated. Test results for sintered aluminum oxide at temperatures from 530 to 1924 °K are within the range of error of previously existing data.

Simultaneous determination of overall thermal diffusivity and conductivity of composite building elements in situ

A method has been developed for the simultaneous determination of thermal diffusivity and conductivity of enclosing fabrics of an unconditioned enclosure exposed to outdoor periodic excitations. These fabrics may be homogeneous or multilayered. It is only necessary to make measurements over a complete period of 24 h of the external and internal surface temperatures and of the heat flow rates at the internal surface. The observed surface temperatures and heat flow rates are represented by series of complex harmonic terms of which these were the real part. For any particular harmonic, the argument of the resulting complex expression representing the heat flux in terms of the two surface temperatures and the material properties could be equated with the argument of the complex expression, representing the observed heat flux, giving the value of thermal diffusivity. Having determined the thermal diffusivity, the thermal conductivity could be obtained by equating their modulii. The thermophysical coefficients, thus obtained, were more realistic in connection with the precise prediction of indoor climate of an unconditioned enclosure exposed outdoors and this method has been found to be sufficiently accurate for similar applications.