RU175034U1 - Scheme of a heat-shielding coating of a reusable heat shield of a descent vehicle for returning after a flight to the moon - Google Patents

Abstract

The utility model relates to reusable heat-shielding composite coatings that can be used in space technology. The technical result of the proposed utility model is a heat-shielding coating scheme for the reusable heat shield of the descent spacecraft, optimized for the return of the spacecraft after the flight to the moon. The technical result is achieved by the fact that the heat-shielding coating scheme of the reusable heat shield of the descent spacecraft for returning after the flight to the Moon is characterized by a composition of layers of a non-woven carbon skeleton and a silicon carbide matrix and relates to coatings of substantially anisotropic materials with different physical, mechanical and thermal characteristics as layers and the thickness of the material. Moreover, to return the spacecraft after a flight to the Moon, the coating has four layers: an outer dense layer with a residual porosity of less than 5% of a carbon-ceramic composite material (UKKM) 2 mm thick modified with heat-resistant additives; the second layer of UKKM 30% porosity with a thickness of 7 mm; the third layer of UKKM 50% porosity with a thickness of 10 mm and the fourth layer of high-temperature fiber heat insulator brand Saffil (manufactured by DuPont) with a thickness of 68 mm. 1 s.p. crystals, 4 ill., 1 tab.

Description

Technical field

The utility model relates to reusable heat-shielding composite coatings that can be used in space technology.

State of the art

Known RF patent No. 164403 (IPC F16L 59/02, B32B 18/00, Published: 08/27/2016) for the author's utility model "SCHEME OF HEAT PROTECTIVE COATING BASED ON GRADIENT POROUS CARBON-CERAMIC COMPOSITE MATERIAL" (adopted as the closest). This heat-shielding coating scheme is characterized by the composition of woven and non-woven carbon skeleton layers and a matrix containing carbon and silicon carbide components, and relates to coatings of substantially anisotropic materials with physico-mechanical and thermophysical characteristics of different levels, both layers and material thickness.

However, this coating scheme is unnecessarily complicated, as it consists of five layers arranged in series: the first outer (front) layer of carbon-ceramic composite material (UKKM) based on a woven carbon frame with a residual porosity of less than 5% and a thickness of 3 to 5 mm to ensure thermal and oxidative stability, the second layer under the first layer of at least 5 mm thick of a carbon-ceramic composite material based on a non-woven carbon frame with a residual porosity of at least e 18%, the third layer under the second layer of at least 5 mm thick of a carbon-ceramic composite material based on a non-woven carbon frame with a residual porosity of at least 22%, the fourth layer under the third layer of at least 5 mm thick of a carbon-ceramic composite material based on a non-woven carbon frame with a residual porosity of at least 38%, the fifth layer under the fourth layer with a thickness of at least 5 mm from a carbon-ceramic composite material based on a non-woven carbon frame with a residual porosity of e less than 48%. Such a complex coating structure leads to a significant increase in the duration and cost of manufacture.

Utility Model Disclosure

The technical result of the proposed utility model is a heat-shielding coating scheme for the reusable heat shield of the descent spacecraft, optimized for the return of the spacecraft after the flight to the moon.

The technical result is achieved by the fact that the heat-shielding coating scheme of the reusable heat shield of the descent spacecraft for returning after the flight to the Moon is characterized by a composition of layers of a non-woven carbon skeleton and a silicon carbide matrix and relates to coatings of substantially anisotropic materials with different physical, mechanical and thermal characteristics as layers and the thickness of the material. Moreover, to return the spacecraft after the flight to the Moon, the coating has four layers: an outer dense layer with a residual porosity of less than 5% of a carbon-ceramic composite material (UKKM) 2 mm thick modified with heat-resistant additives (in the prototype: an outer (frontal) layer of UKKM on based on a woven carbon frame with a residual porosity of less than 5% and a thickness of 3 to 5 mm to provide heat and oxidation resistance); the second layer of UKKM 30% porosity of a thickness of 7 mm (in the prototype: the third layer of at least 5 mm thick of UKKM based on a non-woven carbon frame with a residual porosity of at least 22%), the third layer of UKKM 50% porosity with a thickness of 10 mm (in the prototype: a fifth layer of at least 5 mm thick from UKKM on the basis of a non-woven carbon frame with a residual porosity of at least 48%) and a fourth layer of high-temperature fiber insulation Saffil (manufactured by DuPont) with a thickness of 68 mm.

As in the prototype, carbon fibers from artificial cellulose fibers, carbon fibers from PAN fibers and carbon fibers from pitch can be used as a filler for a heat-protective material based on a gradient porous UKCM.

List of drawings

FIG. 1 - A geometric model of an element of a representative volume of UKKM, used to calculate the thermal conductivity of UKKM taking into account radiation heat transfer in the material.

FIG. 2 - The structure of the technical specifications.

FIG. 3 - The density of the heat flux acting on the heat-transfer zone during the descent of the vehicle to the Earth after a flight to the moon.

FIG. 4 - Change in the maximum (on the outer surface of the TZP) and the minimum temperature (on the inner surface of the TZP lying on the surface of the power structure of the spacecraft) as a function of time when it descends in two stages of the spacecraft to Earth after flying to the Moon.

Utility Model Implementation

A feature of the porous UKKM is that two processes of heat transfer simultaneously and interconnected in the bulk of the material proceed - conductive along the solid skeleton and radiation in the space between the fibers. The ratio of conductive and radiation heat fluxes depends on the porosity of the material and temperature. For porous media, the total heat transfer can be characterized by an effective coefficient of thermal conductivity, which is the ratio of the density of the total conductive and radiation heat flux passing through the porous medium to the local temperature gradient. To carry out this calculation, a geometric model of a representative volume element with a size of 100 × 50 × 50 μm was chosen (Fig. 1). A porous UKKM model was placed between the plates. The thermal contact of the plates with the fibers of the porous material was considered ideal. A representative element of the volume was surrounded by a shell of zero thickness, which played the role of a mirror, its reflection coefficient was set to 1. The surfaces of the fibers and outer linings were taken gray, diffusely reflecting and their degree of blackness was adopted 0.8. Further, on the basis of the geometric model thus refined, a finite element model was constructed for computer simulation of temperature fields by the thickness of the representative volume element. As a result of modeling the heat transfer process, the value of the total heat flux passing through both the porous material and through the plates was determined. The thermal conductivity of the representative element of the volume of the system "representative element of the volume-lining" is calculated as the sum of the thermal resistances of a portion of a thermal circuit of constant cross section:

- суммарная толщина и толщина отдельных участков геометрической модели соответственно,

, а λ, λ₁, λ₂, λ₃ - коэффициент теплопроводности всей модели и коэффициент теплопроводности ее отдельных частей соответственно, λ₁=λ₃=λ^*. Тогда теплопроводность представительного элемента объема λ₂ вычисляется как:Where

- the total thickness and thickness of individual sections of the geometric model, respectively,

, and λ, λ ₁ , λ ₂ , λ ₃ - the coefficient of thermal conductivity of the entire model and the coefficient of thermal conductivity of its individual parts, respectively, λ ₁ = λ ₃ = λ ^* . Then the thermal conductivity of the representative element of volume λ _{2 is} calculated as:

The variant of thermal loads on the thermal current transformer was used to launch it to Earth after the spacecraft returned from the moon in two stages (taken from Chen YK, Milos FS Multidimensional Effects on Heatshield Thermal Response for the Orion Crew Module // AIAA 2007-4397. 2007.15 p. ) shown in FIG. 3. During the first stage, the apparatus reaches dense layers of the atmosphere, where it decreases its speed, and the maximum heat flux density reaches 370 W / cm ² . Then the device for some time, about 1000 s, leaves the dense layers of the atmosphere back into space, and then makes a re-entry into the atmosphere. Since the apparatus moves at a much lower speed during the second stage, the maximum heat flux density on the surface of the heat-condensing element in the second stage is approximately 100 W / cm ² . In the simulation, it was believed that after the descent was completed, the thermal current transformer cools down for 5000 s.

For thermal design, a multilayer TZP model was used. The thermal load in the descent section was brought to the frontal surface. The radiation heat removal from the front surface of the heat-condensing element into the surrounding space was taken into account.

The following TZP design was simulated. The outer layer of TZP was a layer of UKKM 2 mm thick with a residual porosity (P) of less than 5%, the role of which is to provide oxidative and erosive protection of the inner porous layers. Beyond it are layers of UKKM of different porosity. Behind the last of the UKKM layers is a layer of high-temperature heat-insulating material of the Saffil brand (manufactured by DuPont, USA), which is located on the power structure of the descent vehicle (SA). The power structure of the SA in computer simulation was a layer of aluminum alloy D16 with a thickness of 2.5 mm. In FIG. 2 numbers indicate: 1 - dense UKKM with residual porosity of less than 5%, 2 - second layer of porous UKKM (P = 30%), 3 - third layer of porous UKKM (P = 50%), 4 - fibrous heat insulator type Saffil, 5 - aluminum alloy D16.

The purpose of thermal design was to determine the thicknesses of the layers of the porous UKKM and Saffil material, which protect the power structure from overheating. The maximum permissible design temperature of the aluminum alloy D16 was set equal to 165 ° C. UKKM temperature should not exceed 2000 ° С. The criterion for optimization was the minimum linear mass of the heat-transfer unit.

The analysis showed that at such a high level of thermal loads (Fig. 3) on the surface of the TZP, it is rational to construct it using UKKM with different porosity. In the temperature range of more than 1800 ° C UKKM with porosity of 30% has the lowest effective thermal conductivity, and at temperatures below 1800 ° C the minimum effective coefficient of thermal conductivity is achieved by UKKM with porosity of 50%. The thicknesses of TZP layers selected as a result of modeling are presented in the table.

An analysis of the temperature state of the thermal current transformer indicates that its surface heats up to a maximum of 2572 ° C (see the graphs of Fig. 4: the upper graph shows the maximum temperature of the outer layer of the thermal resistor, the lower graph shows the minimum temperature on the surface of the power structure CA), which exceeds the permissible operating temperature of the UKKM made of silicon carbide. Thus, the repeated use of this type of TZP without heat-resistant additives is impossible and it is necessary to modify the dense surface protective layer of TZP with heat-resistant additives, for example, by introducing refractory metal compounds into this layer.

The proposed utility model was created and tested during the work under the agreement on the provision of subsidies 14.577.21.0099 between the Ministry of Education and Science of the Russian Federation and MSTU. N.E. Bauman.

Claims (2)

1. The heat-shielding coating of a reusable heat shield of a descent spacecraft, characterized by a composition of layers of a non-woven carbon skeleton and a silicon carbide matrix and relating to coatings of substantially anisotropic materials with different physical, mechanical and thermal characteristics of both layers and material thickness, characterized in that that for the spacecraft descent to Earth after flying to the Moon, the coating has four layers: an outer dense carbon-kera layer with a residual porosity of less than 5% of a composite material (UKKM) with a thickness of 2 mm, modified with heat-resistant additives, a second layer of UKKM with a porosity of 30% and a thickness of 7 mm, a third layer of UKKM with a porosity of 50% and a thickness of 10 mm and a fourth layer of high-temperature fiber heat insulator brand Saffil manufactured by the company Dupont 68 mm thick. 2. The coating according to claim 1, characterized in that carbon fiber from artificial cellulose fiber, carbon fiber from PAN fiber and carbon fiber from the pitch are used as filler of the porous UKKM.

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