Methods and instruments for researching thermophysical properties under heating and cooling

I. Baranov1 and E. Ivashko1

1Saint-Petersburg State University of Refrigeration and Food Engineering, Russia

Keywords: thermal conductivity, thermal capacity, thermal cell, temperature sensor, heat capacity, thermal diffusivity
property: thermal conductivity, thermal capacity, heat capacity, thermal diffusivity
material: thermal insulation, polymers, semiconductors, ceramics, water-containing materials, liquids, pastes

Last 15 years regular thermal methods have several promising directions for further development. These methods were suitable to provide complex measurements of linear thermophysics properties (TPP) of substances at a given temperature (e.g, room). It is possible to use them for a complex study of the temperature dependences of TPP of substances. There was a prospect to implement regular methods in the previously inaccessible region of thermal measurements. It is the study of thermal processes that occur when the temperature changes in structurally complex multicomponent materials. Structural and phase transformations that occur in water-containing materials, particularly, in foods exposed to freezing and defrosting are examples of such processes. The temperature dependence of TPP of these substances increases sharply in the zone of phase transformations. Its effective heat capacity can vary by tens of times in the range of only a few degrees Kelvin temperature scale. There was an opportunity to use patterns of regular thermal methods for creating rapid methods of nondestructive testing of thermal resistance of mechanical joints.

1.Method for determination the linear TPP. With the realization of linear methods for determining TPP of sample pre-aged at a given temperature level, and then located in a thermal block device, which, thermostated at another level of temperature. Additional technical equipments, which complicates the device and reduce its reliability, are required to provide initial and boundary conditions for the experiment. So three regular thermal heat methods have been developed that are based on solving one-dimensional unsteady heat conduction problem. These methods are designed to provide complex measurements of linear TPP of nonmetallic materials (thermal insulation, polymers, semiconductors, and some kinds of ceramics, etc.), liquids and pastes at a constant temperature environment. In practice the using the built-in thermal cell electric heater is an important feature of this group of methods.

2.Method for determination the non-linear TPP. Dynamic methods are used to measure the temperature dependence of TPP of solid and liquid materials. Information about ones is described in many publications. The most interest are methods and automated instrumentation, which enable measurements over a wide temperature range for a small period of time. At the beginning of this work such methods and measuring devices was not enough. And so two dynamic measurement method of TPP for solid, liquid and bulk materials at low temperatures, taking into account their nonlinearity have been developed.

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