RU2809939C1 - Method for determining reduced cooled mass of ir receivers and their thermal models - Google Patents

Abstract

FIELD: thermophysical measurements.

SUBSTANCE: invention relates to a method of thermophysical measurements, namely to a method for measuring the reduced cooled mass of photodetectors (PD) of infrared radiation and their thermal models in laboratory and production conditions. The problem solved by the proposed invention is the development of a method for determining the reduced cooled mass of IR photodetectors and their thermal models. A method is proposed for determining the reduced cooled mass of IR photodetectors and their thermal models, which includes the process of measuring the flow rate of liquid nitrogen evaporating from the well of the receiver cryostat, the process of measuring the temperature of the bottom of the well, and calculating the heat flow from the flow rate of evaporated nitrogen. Moreover, the change in heat flow to the photodetectors from the environment and the change in the temperature of the bottom of the well of the photodetector holder for two subsequent measurements, as well as the time between measurements, are determined, after which the value of the reduced cooled mass of the photodetectors is calculated.

EFFECT: increasing the accuracy of determining the cooled mass by directly measuring it.

1 cl, 1 tbl

Description

The invention relates to a method of thermophysical measurements, namely to a method for measuring the reduced cooled mass of infrared radiation receivers and their thermal models.

When working with cooled IR photodetectors (PDs), it is necessary to know its main parameters, namely, the heat flow from the environment to the PD cryostat and the reduced cooled mass of the PD. These parameters are used to select the appropriate microcryogenic system (MCS), which should cool the photosensitive element (PSE) of the receiver to specified temperatures. The heat flow to the FP cryostat is the thermal load for the ISS, and therefore determines its required cooling capacity, and the reduced cooled mass of the FP determines the time for the FP to reach operating mode.

The reduced cooled mass of the FP characterizes the amount of heat that must be removed from the FP when it is transferred from a state of equilibrium with the environment (for example, under normal climatic conditions) to a state corresponding to the operating mode of the PSE receiver at cryogenic temperatures.

Since the FP structurally consists of parts and assemblies made of various materials, it is customary to express the reduced mass of the FP in equivalent. This equivalent is numerically equal to such a mass of copper, for cooling which from the ambient temperature to the operating temperature of the FP (cryostatic temperature), it is necessary to remove the same amount of heat Q _0TB as from the FP when it is cooled to the same temperature (MROM-110-89).

The reduced cooled mass of the FP is determined by calculation in accordance with the instructions of document MPOM-110-89. The accuracy of the calculations is low, the reason for this is the approximation of the main assumptions embedded in the methodology. In addition, in the manufacture of the structure of FP elements and assemblies, substitute materials are often used, the thermophysical properties of which are either not studied or differ from the properties of the materials specified in the design documentation. Thus, the main problem of this technique is the approximate determination of the amount of heat removed from the FP elements during its cooling, based on the use of reference data on materials.

The issue of determining the amount of heat removed from the FP elements is solved by measuring the heat flow to the FP from the environment. There is a known method for measuring the heat flow of IR photodetectors, which includes the process of measuring the flow rate of liquid nitrogen evaporating from the well of the FP cryostat, the process of monitoring the temperature of the bottom of the well and calculating the heat flow to the FP cryostat based on the flow rate of evaporated nitrogen (invention patent RU No. 2791432, IPC G01K 17/ 00, G01F 5/00). The disadvantage of this known method is the impossibility of directly measuring the reduced cooled mass of the FP.

The problem solved by the proposed invention is the development of a method for determining the reduced cooled mass of IR receivers and their thermal modules, the technical result of which is to increase the accuracy of determining the cooled mass by directly measuring it.

The proposed method includes the process of measuring the flow rate of liquid nitrogen evaporating from the well of the cryostat of the receiver, the process of measuring the temperature of the bottom of the well, calculating the heat flow from the flow rate of evaporated nitrogen, characterized in that they determine the change in heat flow to the FP from the environment and the change in the temperature of the bottom of the well of the FP holder for two subsequent measurements, as well as the time between measurements, after which the value of the reduced cooled mass of the FP is calculated.

The essence of the proposed invention is as follows. As is known, the amount of heat ΔQ received (given) by a body of mass M with an increase (decrease) in its temperature by ΔT is equal to (see, for example, Handbook of Elementary Physics. M., “Nauka”, 1976, p. 60, equation 2.1):

Where

ΔQ - amount of heat, J;

C is the specific heat capacity of the body material, J/kg⋅K;

M - body weight, kg;

ΔT - change in body temperature, K.

Transforming equation (1), we obtain the dependence for determining body mass M:

Using equation (2), it is possible to determine the reduced cooled mass of the receiver M _pr by measuring the amount of heat ΔQ _pr removed from the FP during its cooling and the corresponding change in its temperature ΔT _pr :

The amount of heat ΔQ _pr can be determined using the results of measurements of heat inflows to the FP:

Where

- change in the amount of heat flow to the FP from the environment during its cooling from τ _i to τ _i+1 , W;

- measured heat inflows at times τ _i and τ _i+1 , W;

- time between two measurements, s;

- change in the temperature of the bottom of the well during the measurement time from τ _i to τ _i+1 , K;

C _pr - average specific heat capacity reduced to the equivalent of copper (Table 2 MPOM-110-89 regulates the value of C _pr = 360 J/kg⋅K).

From here equation (3) can be reduced to the form

The measurement of the reduced cooled mass of the IR photodetector is carried out as follows. Liquid nitrogen is poured into the well of the FP cryostat, after which the heat influx q _i is determined in the stabilized evaporation section for any moment of time τ _i . according to the measured volumetric flow rate of evaporated nitrogen in accordance, for example, with the methodology of the invention patent RU No. 2791432. At the same time, for each τ _i, the readings of a temperature sensor installed at the bottom of the cryostat well are measured. Then the change in the amount of heat inflow Δq to the FP from the environment is determined during its cooling from τ _i to τ _i+1 , the time Δτ and the change in the temperature of the bottom of the well ΔT _pr during the time between two measurements are determined. The values Δq, ΔT _pr and Δτ obtained as a result of measurements are substituted into equation (4) and the reduced cooled mass of the receiver M _pr is determined.

As an example, we will show how the value of the reduced cooled mass of the receiver is experimentally determined and subsequently used. Let the following values be obtained for the last two measurements before the complete boiling away of liquid nitrogen in the FP well: Δτ = 10 s, ΔT _pr = 0.4 K, Δq = 0.326 - 0.254 = 0.072 W. Then from equation (4) we get:

The obtained value of the reduced cooled mass of the receiver in copper equivalent M _pr = 5.4 g is used to select the appropriate ISS parameters, for example, produced by JSC NTK Cryogenic Technology (MSMG) or the company RICOR (K508 and K548) (Table 1 ).

Analysis of the data presented in the table shows that the following ISSs are suitable for the FP with a reduced cooled mass of 5.4 g:

- MSMG-5A-1.3/80 and MSMG-3V-1/80 developed by JSC NTK Cryogenic Technology;

- K548 developed by RICOR.

Thus, the measured value of the reduced cooled mass of the FP using the proposed method is a real value that can be used to clarify the calculations performed according to MPOM-110-89, and allows you to select for the FP (even if the user does not have design documentation for it) the appropriate ISS parameters.

Claims (6)

A method for determining the reduced cooled mass of IR receivers and their thermal models, including the process of measuring the flow rate of liquid nitrogen evaporating from the receiver cryostat well, the process of measuring the temperature of the bottom of the well, calculating the heat flow from the flow rate of evaporated nitrogen, characterized in that the change in heat flow to the photodetectors is determined from the environment and the change in temperature of the bottom of the well of the photodetector holder for two subsequent measurements, as well as the time between measurements, after which the value of the reduced cooled mass of the receiver is calculated using the formula where M _pr is the reduced cooled mass of photodetectors, g; - change in heat flow to photodetectors from the environment during the measurement from τ _i to τ _i+1 , W; Δτ=(τ _i+1 -τ _i ) - time between two subsequent measurements, s; - T _i - change in temperature of the bottom of the well of the photodetector holder during the measurement time from τ _i to τ _i+1 , K.