SU813219A1 - Method of measuring thermal-physical characteristics of grain materials - Google Patents

Description

The invention relates to thermophysical measurements, and in particular to methods for determining the thermophysical characteristics of grain materials. The known method for determining the thermophysical characteristics of granular materials, involves placing the sample and the floor of the same thickness between the heaters and the cooler with respectively equal temperatures. In this case, the densities established through the sample and the standard of heat fluxes are determined by their thermal conductivities 11. However, this method is suitable only if the thermal resistances of the contact between the sample and the standard with heating surfaces are equal. In addition, the temperature control system is complex, which makes it difficult to carry out the experiment. The method allows only the coefficient of thermal conductivity of the samples to be determined. The closest to the technical solution is the method of alternately determining the thermal conductivity and volumetric heat capacity of materials in a flat layer in stationary and transient thermal conditions. Information continuously obtained with the help of temperature and heat flux density sensors placed in the contact planes of the sample with the heater and cooler is sufficient to determine the desired characteristics 121. However, due to the inconsistency of contact thermal resistance in the study of granular materials, finds uses. In addition, ballast thermal resistances and capacitances must be taken into account. The purpose of the invention is to improve the measurement accuracy by eliminating the influence of contact and ballast thermal resistances and capacitances. This goal is achieved by the fact that the heat flux simultaneously affects two samples of the test material of different thickness, placed between one isothermal heater and two isothermal refrigerators, while maintaining the same temperature of the heater, as well as equal and constant temperatures of refrigerators, i .e. the same temperature difference in the samples, a stationary thermal regime is obtained; these temperatures and densities of heat fluxes penetrating each sample are measured; the calculated thermal conductivity coefficient of the material under investigation is calculated. By changing the temperature of the heater: l of the refrigerator to one and the same predetermined time interval, e. producing a transient thermal regime and measuring the heat accumulation during each breakdown, the volumetric heat capacity is determined.

Figure 1 shows the layout of the sample, heater and cooler; Fig. 2 is a graph showing the changes in thermophysical characteristics.

Between the heater 1 and two stockpiles 2 place samples of sample 3 and 4 of different thickness. On the working surfaces of the heater 1 and coolers 2 in the form of plates 5, or in some other way, heat flow and temperature sensors 6 are mounted.

The measurements are carried out as follows.

Place samples of sample 3 and 4 in the cells of the device. The heater 1 and refrigerators 2 are thermostatically controlled at given temperatures t and tj, and a steady-state thermal regime is established, which is characteristic of the fact that the density of the heat flow for each sample is constant in thickness and in time. The signals of all sensors are recorded as a function of time. The view of the graph is shown in FIG. 2, where 1 is the heater temperature, 2 is the temperature of the coolers, 3 is the average temperature of both PSBs, 4 is the heat flux density through the larger sample, 5 is the heat flux density through the smaller sample. The amounts of heat accumulated by the larger and smaller samples are designated b and 7, respectively.

According to the data of the initial stationary mode (period 1, figure 2) we make the system of equations

a.t and.,. "

rit "about 1.

where q and q are the densities of heat flows through the larger and smaller samples; h and h are sample thicknesses; At - temperature difference

between the heater and

KHBLAUTILNIK1MI.

The total contact and ballast thermal resistances for both cells are the same (R Rj). The system solution gives the following formula for determining the sample thermal conductivity.

(hh)

(2) At CI /

Thus, the values of contact and ballast thermal resistances are excluded from the calculation.

Then (period P, Fig. 2), the temperatures of the heater and the cooler are changed by the same interval. In this case, the samples begin to absorb heat, which is expressed by an increase in the density of the heat flux at the heat input to the layer and a decrease in the output. When the heater and the cooler reach the set temperatures, the thermal conditions stabilize (period, figure 2). The heat flux densities on the layer level off, and a final steady-state thermal regime sets in (period y, Fig. 2), according to which the thermal conductivity coefficient is calculated. The heat flux density lines at the heat inlet and outlet describe closed figures 6 and 7, the areas of which are proportional to the amount of heat absorbed by each breakdown for the transition mode.

0 According to the data of the transient regime we make up the system of equations

-one

-P

Wed

where Q and the amount of heat accumulated. probes for the transitional regime with an increase in their temperature by ft ft. As in the previous case, the ballast 0 heat capacities of the cells are equal (Pg P). The system solution provides the formula for determining the volumetric heat capacity of the sample.

; -Q-Q

(four)

P S-t (h-H)

Thus, the ballast heat capacities are also excluded from the calculation.

The thermal diffusivity coefficient is calculated using the known formula, using the obtained values of the thermal conductivity coefficient and the volumetric heat capacity.

The proposed method is intended

for complex determination of such thermophysical properties of materials as thermal conductivity, heat capacity and thermal diffusivity during heating or cooling of the sample. is he

allows to increase the accuracy and reliability of the results of TFH studies of granular materials by eliminating the influence of contact and ballast thermal resistances and capacities, and is practically the first method specifically designed for this purpose. The method allows for studies to simulate various heat loads, approaching them to, production, high speed

measurement makes it possible to avoid the effect of moisture transfer in the study of wet materials.

Claims (2)

The invention is most expediently used to study the temperature and humidity dependences of the TPC of grain, bulk and granulated materials of the food, chemical and other industries. It is also suitable for studying soils, especially when it is frozen or defrosted. Claims The method for determining the thermophysical characteristics of grain materials in a flat layer placed between an isothermal heater and a cooler consists in one-dimensional heat transfer by alternating stationary and transient thermal conditions, characterized in that, in order to improve the measurement accuracy, by eliminating the influence of and thermal thermal resistances and capacitances, which are simultaneously affected by a heat flow on two samples of the material under study of different thicknesses, while maintaining This constant temperature of the heater, as well as equal and unchanged temperatures of the refrigerators, measures the indicated temperatures and densities of heat fluxes that penetrate each load, and calculate the coefficient of heat conduction aV (hh) u, -ti) ((j,) The amount of heat that is accumulated by each breakdown for the transient mode determines the volumetric heat capacity g -QO.,, "t {hh-) e q, and q is the heat density at the same specified time interval. current, respectively, through the first and second samples, nor h the thickness of the samples; Oi O the amount of heat accumulated by the first and second samples; tj - temperature of the heater and refrigerator; - temperature increment for the transitional mode. Sources of information that are considered in the examination in examination 1, Authors of the USSR certificate 542945, class C 01 N 25 / 18,1977. 2. Authors certificate of the USSR 347643 C. C 01 N 25/18, 1972 rototype).