RU2763917C1 - Apparatus for heat protection of an aircraft - Google Patents

Abstract

FIELD: rocket and space technology.SUBSTANCE: invention relates to the field of rocket and space technology, more specifically, to cooling. The apparatus for heat protection of an aircraft is made in the form of external and internal shells. The refrigerating agent is located in capsule-type modules made of capillary-porous mesh material lined with foil on all sides. The modules are rigidly fixed over the entire area of the outer surface of the inner shell, forming a gap for release of the refrigerating agent vapours between the outer surface of the modules and the inner surface of the outer shell ring. The outer surface of the modules is covered with foil with a low degree of blackness, wherein the thickness of the foil is determined from the ratio identified by the authors.EFFECT: durability is increased.1 cl, 2 dwg

Description

The proposed technical solution relates to heat engineering and can be used mainly in the cooling systems of on-board equipment of various compartments of high-speed aircraft (LA).

The requirements for such systems include: minimum volume, simplicity and reliability of the design, maintenance of performance after long-term storage, efficient heat removal under external mechanical influences at any orientation in the gravitational field.

The flight of an aircraft at supersonic speeds is accompanied by an increase in aerodynamic heating of the compartment structure, including the instrument compartments. Acceptable temperature conditions for the functioning of the equipment are provided both by protecting the compartment structure from external heat inflows by insulating it, and by using other methods and means based, for example, on heat and mass transfer by evaporation.

A device for thermal protection of an object is known (RF patent No. 2269170, January 27, 2006), containing sequentially arranged layers: outer, intermediate and inner. On the outer surface of the outer shock-resistant layer made of heat-resistant metal and perforated with drainage holes, a bimorph heat-shielding coating of a heat-insulating composite material is formed. The intermediate heat-shielding layer is made of refractory dry material and is designed for passive heat protection of the stored object. The inner heat-shielding layer, intended for active protection of the stored object, is formed from a material, which includes compounds containing crystallization water. This layer is enclosed between the outer and inner heat-reflecting pads.

The known invention makes it possible to protect the stored object when exposed to mechanical and thermal loads when exposed to a temperature of 1100°C for 1 hour, and also when exposed to a temperature of 260°C for 10 hours.

However, this technical solution, namely, the inner heat-shielding layer containing crystalline hydrates, intended for active protection of the stored object, is not operable under conditions of a significant external aerodynamic flow that counteracts the drainage of water vapor through holes in the outer heat-shielding layers. Without the removal of water vapor, the inner layer is not operational, because. with external heating, the pressure inside the active protection will increase significantly and, accordingly, the evaporation temperature of the refrigerant and the protected object will increase significantly.

The closest in essence to the proposed technical solution is a thermal protection device for an aircraft (RF patent No. 2657614, 06/14/2017), made in the form of outer and inner shells and containing a cooling porous material impregnated with a refrigerant, fixed on the outer surface of the inner shell and made in the form segments fixed over the entire surface of the shell with certain gaps. At the rear end of the device in the direction of flight of the aircraft, holes are made to drain the refrigerant vapor through the steam lines into the cavity of the unpressurized compartment of the aircraft, which is not subject to external aerodynamic pressure. In this case, the shells are made coaxially and equidistantly relative to each other, and an additional layer of thermal insulation in the form of a heat-shielding screen made of heat-resistant material can be installed on the outer surface of the outer shell.

The advantages of the known thermal protection device are the simplicity of the design, operable under conditions of high external aerodynamic pressure.

The disadvantages of this solution include the instability of the cooling material during a long period of storage. The cooling material must be a capillary-porous non-metal, for example, made of polyvinylformal, capable of holding in the pores a significant proportion by weight of a liquid substance - a refrigerant, which can be used as water, water-alcohol solutions, etc. The capillary-porous material impregnated with refrigerant during a long period of storage (more than 10-20 years) loses its shape and loses its ability to hold the working substance. As a result, the capillary-porous material and the refrigerant are converted into a homogeneous substance.

The proposed technical solution is based on the technical problem of increasing the efficiency and reliability of the thermal protection of aircraft compartments with on-board equipment operating under high ambient temperatures.

The technical result of the proposed technical solution is to create a device with the functions of thermal protection and removal of external heat flux by evaporation, operating at any orientation in space under the influence of external mechanical loads and high ambient temperatures and capable of maintaining characteristics after a long period of storage.

This technical result is achieved by the fact that in the thermal protection device of the aircraft, made in the form of external and internal coaxially and equidistant shells located relative to each other with holes made on the rear end of the device in the direction of flight of the aircraft for the removal of refrigerant vapor, the device is equipped with capsule modules filled with refrigerant type, made of a capillary-porous mesh metal material, lined with foil on all sides, the modules are rigidly fixed over the entire area with the outer surface of the inner shell with the formation of a gap for the release of refrigerant vapor between the outer surface of the modules and the inner surface of the outer shell, while the foil, covering the outer surface of the modules, has a low degree of blackness, and the thickness of the foil is selected from the ratio:

where δ - foil thickness, m;

Ro - refrigerant charge pressure, Pa;

β - degree of module filling with refrigerant;

α - coefficient of thermal expansion of the refrigerant, 1/K;

ΔT - temperature difference between the refrigerant charge temperature and the allowable temperature of the instrument compartment equipment, K;

D _equiv - equivalent size (diameter) of the outer surface of the module, m;

S - relative elongation of the foil;

σ - foil strength, Pa.

The design features of the new proposed technical solution determine the achievement of the claimed result.

Capsule-type modules with a refrigerant contained in them, made of a capillary-porous mesh material lined with foil on all sides, at the beginning of the working process (aircraft flight at high speed) function as a thermal resistance. The foil sealing the volume of the modules, the outer surface of which has a low degree of blackness, is necessary to reduce the heat flux by radiation from the outer shell to the refrigerant.

After heating (ΔT) of the refrigerant to the permissible temperature of the equipment, accompanied by an increase in the volume of the refrigerant, the foil breaks and the modules are depressurized. The refrigerant heats up, boils and evaporates with the absorption of a significant portion of the heat flux. This reduces the temperature of the inner shell, thereby protecting the equipment of the instrument compartment from overheating.

The gap between the outer surface of the modules and the inner surface of the outer shell is necessary to remove the refrigerant vapors that enter the rear end of the device and pass through the holes through the steam lines into the cavity of the unpressurized aircraft compartment, from where they are discharged into the surrounding space.

The capillary-porous mesh material retains the refrigerant (liquid phase) in the volume of the modules at any location in space and, at the same time, due to the mesh structure, passes the refrigerant vapor.

The degree of filling of the volume of the modules with the refrigerant is selected from the condition of ensuring the rupture of the foil on the surface of the modules from the side of the gap when the temperature of the refrigerant is equal to the allowable temperature of the instrument compartment equipment.

According to the ratio revealed by the authors as a result of the research, an important parameter is determined in advance - the thickness of the foil 5. After calculating the thickness of the foil according to the above formula, a specific value is chosen as the closest value from a number of ranges of foil thicknesses produced by the industry, for example, 0.05 mm, etc.

Rupture of the foil at a certain point in time of the flight of the aircraft is necessary to prevent the increase in pressure in the volume of the modules and the decrease in the boiling point of the refrigerant and, accordingly, not to exceed the temperature of the inner shell over the permissible temperature of the protected equipment.

The essence of the proposed technical solution is illustrated in Fig. 1 and 2, which schematically show an aircraft thermal protection device.

The figure has the following designations:

1 - protected aircraft equipment;

2 - thermal protection device (capsule-type modules with refrigerant);

3 - inner shell;

4 - outer shell;

5 - steam pipelines;

6 - additional thermal protection;

7 - cavity of an unpressurized compartment;

8 - foil;

9 - capillary-porous mesh material;

10 - refrigerant;

11 - gap.

The proposed thermal protection device LA works as follows.

During the flight of an aircraft at supersonic and hypersonic speeds, under the influence of an external aerodynamic flow, additional thermal protection 6 and outer shell 4 are heated.

Through the gap 11 from the outer shell 4, the heat flow acts on the capsule-type modules of the thermal protection device 2, the outer surface of which is formed by a capillary-porous mesh material 9, covered on the outside with a foil 8, which, while performing the functions of sealing, at the same time, due to the low degree of blackness of the surface, significantly reduces the radiative heat flux from the outer shell 4.

As a result, the temperature of the refrigerant 10 rises, its volume increases, and when the temperature of the refrigerant reaches the permissible temperature of the instrument compartment equipment, the foil 8 breaks on the surface of the module from the side of the gap 11. The foil breaks precisely on this surface, because the remaining surfaces of capsule-type modules are in close contact with each other and with the inner shell 3.

The foil thickness δ is determined in advance according to the above relation, which takes into account the values of the design parameters of the modules.

After the rupture of the foil 8, the refrigerant 10 located in the modules of the capsule type begins to boil and evaporate, the refrigerant vapor through the gap 11 through the steam lines 5 is sent to the cavity of the leaky compartment 7.

The driving force for the removal of refrigerant vapors is the gradient between the pressure in the modules and the pressure in the cavity of the non-pressurized compartment 7, in which the pressure of the gaseous medium is much lower and is determined by the pressure outside the aircraft.

During the operation of the proposed thermal protection device as a result of the evaporation of the refrigerant in capsule-type modules, the temperature of the inner shell 3 and, accordingly, the temperature of the protected equipment of the aircraft 1 is at the required level, depending on the boiling (evaporation) temperature of the refrigerant, the value of which is determined by the pressure in the modules.

If the thermal protection device 2 is exposed to external heat fluxes that are insignificant in terms of power or a short time of exposure to the outer shell 4, there is no need to install a heat shield 6.

The capillary-porous mesh material 9 consists of several sintered layers of a thin metal mesh made, for example, of stainless steel. The thickness of the material is selected taking into account the external loads acting in the flight of the aircraft and, as a rule, does not exceed 1-2 mm.

The low emissivity foil ε<0.05 - 0.10 used in the device can also be made of stainless steel.

In the proposed device, water, water-alcohol solutions, alcohol, etc. can be used as a coolant 10.

The implementation of the main working parts of the device - hermetic capsule-type modules from foil-lined metal meshes and the use of refrigerant meshes compatible with the material determines the ability of the device to maintain characteristics after a long period of storage (10-20 years or more).

The totality of the proposed new features of the technical solution is the implementation of the evaporator device in the form of two shells with the placement of sealed capsule-type modules on the inner shell, made of a shell of capillary-porous mesh material, lined on all sides with foil, with the location of the refrigerant in the internal volumes of the modules and with the formation of a gap for the release of refrigerant vapor between the outer surface of the modules and the inner surface of the outer shell, - allows you to get an effective, due to the relationship of features, technical result - a new device with the functions of heat protection and evaporation, operating at any orientation in space under high ambient temperatures and able to save characteristics after a long period of storage.

Claims (10)

Aircraft thermal protection device, made in the form of external and internal coaxially and equidistant shells located relative to each other with holes made on the rear end of the device in the direction of flight of the aircraft for the removal of refrigerant vapor, characterized in that the device is equipped with capsule-type modules filled with refrigerant, made of capillary-porous mesh metal material lined with foil on all sides, the modules are rigidly fixed on the entire area of the outer surface of the inner shell with the formation of a gap for the release of refrigerant vapor between the outer surface of the modules and the inner surface of the outer shell, while the foil covering the outer surface of the modules has a low degree of emissivity, and the foil thickness is selected from the ratio:

where δ - foil thickness, m; R _o - refrigerant charge pressure, N/m ² ; β - degree of module filling with refrigerant; α - coefficient of thermal expansion of the refrigerant, 1/K; ΔT - temperature difference between the refrigerant charge temperature and the allowable temperature of the instrument compartment equipment, K; D _equiv - equivalent size (diameter) of the outer surface of the module, m; S - relative elongation of the foil; σ is the tensile strength of the foil, N/m ² .

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