SU1160291A1 - Device for determining material thermal diffusivity coefficient - Google Patents

Abstract

A DEVICE FOR DETERMINATION OF THE MATERIAL TEMPERATURE CONDUCTIVENESS COEFFICIENT, containing a series-connected measuring and regulating unit, a thyristor unit and a transformer, in the secondary circuit of which a flat nag rewel is connected and the contact is in contact with the sample, characterized in that it is out of contact with the pattern, characterized in that it is out of contact with a specimen which is in contact with the sample, in order to reduce the error in determining materials. additionally contains a rectifier with a smoothing filter, a voltage divider and a generator of sinusoidal signals of infra-low frequencies, When this heater is connected in parallel with a rectifier smoothing filter, which is included in parallel voltage divider whose output is connected to a first input measuring (LS regulating unit, the second input of which is coupled to the output of the generator sinusoidal signals infralow frequencies.

Description

The invention relates to the field of determining the thermophysical properties of nonmetallic materials, in particular, to devices for determining the thermal diffusivity of nonmetallic materials, and can be used in chemical, electronic, electrical and other industries. A device for determining the thermal diffusivity of materials containing a tungsten helical cathode is known. located parallel to the PLO (to whom the sample of the material under study, and the photoelectric block from temperature measurement is established from the side of the non-heated surface of the sample 1. The disadvantage of this device for determining the thermal and thermal conductivity of materials is that the determination of the desired value is carried out with great error, since in practical implementation of the device the theoretical model is not fully implemented task. The closest to the invention to the technical essence and the achieved result is a device for determining the temperature coefficient conductivity of nonmetallic materials containing a series-connected measuring-regulating unit, a thyristor unit and a transformer, in the secondary circuit of which a flat heater is connected, contacted during the measurement process with a sample of the material under study. In the course of the experiment, the temperature of the heater and the temperature difference on the sample of the test material of known thickness are measured. After that, information on the refractive indices and absorption indices of the heater – sample – cooler system is attracted, the inverse heat conduction problem is solved, and the required value is determined by the formula “. , Ср where a is the thermal diffusivity coefficient Л - thermal conductivity coefficient с - the specific heat capacity; f is the density of the material C2. The main disadvantage of the known device is that the determination of the thermal diffusivity of nonmetallic materials is carried out with a large error, which greatly affects the accuracy, of determining the desired quantity. For example, a 3% error in determining the emissivity of a heater results in a 25% error in determining the coefficient of thermal diffusivity. The purpose of the invention is to reduce the error in determining the coefficient of thermal diffusivity of materials. The goal is achieved by the fact that the device for determining the thermal diffusivity of materials, containing a series-connected measuring and regulating unit, a thyristor unit and a transformer, in the secondary circuit of which a flat heater is connected, which is in contact with the sample of the material under study, is additionally equipped with a straightener with a smoothing filter, a voltage divider and a generator of sinusoidal signals of infra-low frequencies, while parallel to the heater A rectifier is connected with a smoothing filter, in parallel with which a voltage divider is connected, the output of which is connected to the first input of the measuring regulating unit, the second input of which is connected to the output of a sine wave generator of infrasonic frequencies. An additional introduction to the known device is a mittel with a smoothing filter, a voltage divider, a generator of sinusoidal signals of infra-low frequencies and their corresponding connection allows you to implement an automatic feedback system that reduces the error in determining the thermal diffusivity of nonmetallic materials. Thanks to sinusoidal form (with high accuracy) of the heat flux heating the sample with a period of the order of (5-100) s. There are means that are widely used in the study of the properties of high-conductive materials, such as metals and their alloys, the principle of zero-sin heating according to a sinusoidal law with a period of more than 1 s is practically impossible.

The use of mechanical modulation techniques leads to a distortion of the sinusoidal shape of the supply voltage and, as a consequence, the need to isolate the main harmonic component with temperature measurements.

The drawing shows a diagram of the device.

A device for determining the thermal diffusivity of nonmetallic materials consists of series-connected measuring unit 1, thyristor unit 2, transformer 3, into the secondary circuit of which a flat heater 4 is connected, which comes in contact with two samples 5 of the material under test, rectifier 6, the input of which is connected parallel to the heater, and the output is connected through a smoothing filter 7 and a voltage divider 8 to the first input of the measuring and regulating block ka 1, the second input of which is coupled to the output of the generator 9.

The device works as follows.

Using measuring and regulating 1 and thyristor 2 blocks, the supply voltage is fed with a frequency f to a transformer 3, in the secondary circuit of which a flat heater 4 is turned on, which is in thermal contact with two samples 5 of the material under study. To conduct an automatic adjustment of a predetermined thermal mode, the voltage from heater 4 is supplied to rectifier b, after which the voltage pulsations of filter 7 are smoothed and the first input of measuring-regulating unit 1 is fed from one of the divider 8 resistors to the second input which provides a sinusoidal voltage of the infralow frequency from the generator 9. After the establishment of the thermal regime, the phase difference between the onset of the supply and the temperature of the sample is measured on the heated surface of the sample. th surface, and then thermal diffusivity is determined from the relationship

.i

01

X X X Sb; j cos; -ch: s, -n; j :.

where Ch. is the phase difference between the supply voltage and the temperature of the unheated sample surface; .

About at cf Wee) / ";

сГ - sample thickness} w.

PRI im p A strip zigzag heater made of 50 µm nichrome foil is installed between two flat samples of the material under investigation, on which unheated surfaces there are chromel alumel thermocouples. The high-precision temperature regulator VRT-2 is used as the measuring and regulating unit, and the thyristor amplifier U-252 with the thyristor device BT-01 and the transformer OSU-20 are used as the thyristor unit. The transformer serves to reduce the supply voltage,

0 as well as for electrical wiring of power and measuring circuits. The constant voltage of the negative feedback with the voltage divider is fed to the measuring and regulating unit. A variable voltage of an infra-low frequency is supplied to the same block from a generator of the type G6-15. In the variable-regulating unit, the alternating voltage of the generator is added to the internal unit setpoint voltage. The constant voltage set by the setting unit of the measuring and regulating unit gives an average level of the supply

5, and the alternating voltage of the generator sets the modulation depth.

The device has sufficient speed to create a modulation with a period of the order of tens of seconds and a high accuracy of voltage maintenance on the heater. The voltage on the heater is maintained 5 with an error not exceeding 0, t / J, the harmonic coefficient of the modulated voltage does not exceed 1-2%. The temperature drift of the sample swarm missing

Claims (1)

A DEVICE FOR DETERMINING THE MATERIAL TEMPERATURE CONDUCTIVITY COEFFICIENT, containing a series-connected measuring and regulating unit, a thyristor unit and a transformer, in the secondary circuit of which is included a flat nugget which is in contact with the sample, which differs in that, in order to reduce the error in the determination of materials thermal conductivity, the device further comprises a rectifier with a smoothing filter, a voltage divider and a generator of sinusoidal signals of infra-low frequencies, at m heater is connected in parallel with the rectifier smoothing filter, which is included in parallel voltage divider whose output is connected to the first input izmeritelnoreguliruyuschego unit, the second input of which is connected to the output of the generator sinusoidal signals infralow frequencies.