Heat transfer of thermal protective fabrics under deformation and prediction method of skin burns

Abstract

The present application discloses a method for predicting heat transfer and skin burns of thermal protective fabrics under deformation, comprising the following steps: establishing a fitting equation for fabric thickness under deformation to obtain fabric thickness; establishing a method for calculating fabric density under deformation to obtain fabric density; establishing a method for calculating thermal conductivity under deformation to obtain thermal conductivity, wherein the thermal conductivity is respectively related to the air content in the fabric after deformation and the air content in the fabric before deformation; establishing a heat transfer equation through a single layer of thermal protective fabric in the heat exposure and cooling stages and its corresponding boundary conditions and initial conditions to obtain fabric temperature; establishing a heat transfer equation through an air layer and its corresponding boundary conditions and initial conditions to obtain air layer temperature; establishing a heat transfer equation through a simulated skin sensor and its corresponding boundary conditions and initial conditions to obtain skin temperature field. Due to the adoption of the above technical scheme, the present invention has the following advantages and positive effects compared with the prior art: the present invention can estimate the temperature distribution of the fabric layer under deformation, and predict the skin burn grade in combination with the skin heat transfer model and the skin burn integral model.

Description

Technical Field

[0001] The invention relates to the field of thermal protection clothing, in particular to a method for predicting heat transfer and skin burns of thermal protection fabrics in a deformed state. Background Art

[0002] Firefighters are usually exposed to heat hazards from the environment when they are fighting fires and rescuing people. Thermal protective clothing, as a good barrier to isolate the human body from the thermal environment, can reduce heat transfer and delay the time of skin burns. Its performance directly affects the life safety and work efficiency of firefighters. When firefighters are working, they are exposed to the hot environment for a long time, and the heat is stored in the protective clothing. When the human body leaves the hot environment, the thermal protective clothing, as a passive heat source, releases the stored heat naturally or forcibly to the human skin, thereby aggravating the skin burns. At the same time, due to changes in limb movements and mechanical loads, the fabric will be stretched or squeezed. Studies have shown that from 2007 to 2011, 15% of the burns among American firefighters came from contact and compression burns. Therefore, the study of heat transfer of thermal protective clothing under stretching and squeezing deformation is crucial. Since the laboratory simulation method of thermal protection performance is dangerous and has low repeatability, a numerical simulation method is used to establish a heat transfer model of thermal protection fabrics under deformation state to explore the overall heat transfer mechanism between environment-fabric-skin and predict skin burns, providing appropriate guidance for contact and compression burns. Summary of the invention

[0003] The technical problem to be solved by the present invention is to provide a method for predicting heat transfer and skin burns of thermal protective fabrics in a deformed state. The method is suitable for simulating a human body wearing thermal protective clothing, and the heat flux transferred to the surface of a simulated skin sensor is obtained by a fabric-air layer heat transfer model. The heat flux is used as the skin heat transfer boundary condition to obtain the skin temperature field, and the skin base temperature and the skin burn integral model are combined to predict skin burns.

[0004] The present application embodiment discloses a method for predicting heat transfer and skin burns of a thermal protective fabric in a deformed state, comprising the following steps:

[0005] (1) Establishing a fitting equation for fabric thickness under deformation to obtain fabric thickness;

[0006] (2) Establish a calculation method for fabric density under deformation to obtain fabric density;

[0007] (3) Establishing a calculation method for thermal conductivity under deformation to obtain thermal conductivity, wherein the thermal conductivity is related to the air content in the fabric after deformation and the air content in the fabric before deformation, respectively;

[0008] (4) establishing a heat transfer equation through a single-layer thermal protective fabric during heat exposure and cooling stages and its corresponding boundary conditions and initial conditions to obtain the fabric temperature field, wherein the heat transfer equation involves the fabric thickness, the fabric density, and the thermal conductivity;

[0009] (5) establishing a heat transfer equation through the air layer and its corresponding boundary conditions and initial conditions to obtain the temperature field of the air layer, wherein the boundary conditions involve the thickness of the fabric;

[0010] (6) establishing a heat transfer equation and its corresponding boundary conditions and initial conditions by simulating the skin sensor to obtain the skin temperature field, wherein the boundary conditions involve the thickness of the fabric;

[0011] (7) The quantitative value of skin burn degree is obtained based on the Henriques skin burn scoring model.

[0012] Preferably, in the step (1), a fitting equation of fabric thickness and stretch rate is established based on the experimental data of fabric thickness after deformation, and a fitting equation of fabric thickness, stretch rate and pressure is established. The fitting equation of fabric thickness is:

[0013] When the fabric is only stretched, the fitting equation of fabric thickness and stretch rate is:

[0014] L fab =ax c

[0015] When the fabric is stretched and squeezed at the same time, the fitting equation of fabric thickness, stretch rate and pressure is:

[0016] L fab =dx e +fx 1 g

[0017] Among them, L fab is the thickness of the fabric after deformation; x is the stretching rate; x 1 is pressure; a, c, d, e, f, and g are all constants and can be obtained through experiments.

[0018] Preferably, in step (2), according to the law of conservation of mass, a method for calculating the fabric density is established as follows:

[0019] When the fabric is deformed, the fitting equation of fabric area and stretch rate obtained by the "photographic method" is:

[0020] S fab =hx+i

[0021] When the fabric is only stretched, according to the law of conservation of mass, the calculation method of fabric density and stretch rate is established as follows:

[0022]

[0023] When the fabric is stretched and squeezed at the same time, according to the law of conservation of mass, the calculation method of fabric density, stretch rate and pressure is established as follows:

[0024]

[0025] Among them, S 0 is the fabric area before deformation; S fab is the area of ​​the fabric after deformation. The area of ​​the fabric in this deformed state is obtained by photographing the fabric before and after deformation under the same external conditions, and the photograph is imported into CAD to calculate its accurate area; ρ 0 is the fabric density before deformation; ρ fab is the fabric density after deformation; L 0 is the fabric thickness before deformation; L fab is the thickness of the fabric after deformation; x is the stretching rate; x 1 is pressure; h, i, j, k, l, m, n, o, p, q, and r are all constants.

[0026] Preferably, in the step (3), a method for calculating the thermal conductivity of the fabric is established according to the different air contents in the fabric after deformation, and the method for calculating the thermal conductivity of the fabric after deformation is:

[0027]

[0028] Among them, V air is the air content in the fabric before deformation; L 0 is the fabric thickness before deformation; L fab is the thickness of the fabric after deformation; k air k is the thermal conductivity of air; fiber k is the thermal conductivity of the fiber; fab is the thermal conductivity of the fabric after deformation.

[0029] Preferably, in step (4), the one-dimensional heat transfer differential equation of the fabric is obtained according to Fourier's law and the law of conservation of energy. The source term in the differential equation in the heat exposure stage is part of the heat absorbed by the fabric. In the cooling stage, the fabric is subjected to contact compression by the compression block, so only heat conduction exists. The heat transfer equation of the fabric is:

[0030] When in the heat exposure stage, the heat transfer equation through the fabric is:

[0031]

[0032] When in the cooling stage, the heat transfer equation through the fabric is:

[0033]

[0034] When in the heat exposure stage, the left and right boundary conditions of fabric heat transfer are:

[0035]

[0036]

[0037] When in the cooling stage, the left and right boundary conditions of fabric heat transfer are:

[0038]

[0039]

[0040] The initial condition of fabric temperature is:

[0041] T fab =T amb =300K

[0042] Among them, ρ fab is the fabric density; (cp) fab k is the specific heat capacity of the fabric; fab (T) is the thermal conductivity of the fabric at T; q rad-absorb is the radiant heat absorbed from the heat source to the fabric; rad-tran It is the part of radiant heat transfer in fabric; h conv1 is the convective heat transfer coefficient between the heat source and the outer surface of the fabric during the heat exposure stage; T fab is the fabric temperature; T amb is the ambient temperature q fab-sen k is the radiant heat transferred from the back of the fabric to the simulated skin sensor; air k is the thermal conductivity of air; block k is the thermal conductivity of the compressed block; epi is the thermal conductivity of the epidermis of the skin; where L in this step fab , fab , k fab Obtained by the above steps (1)(2)(3) respectively.

[0043] Preferably, in step (5), the one-dimensional heat transfer differential equation of the air layer is obtained according to Fourier's law and the law of conservation of energy. The air layer, as a radiation participating medium, only absorbs thermal radiation but does not reflect thermal radiation. The source term is the radiant heat transferred from the back of the fabric layer to the skin simulation sensor through the air layer. The heat transfer equation of the air layer is:

[0044]

[0045] The left and right boundary conditions for air layer heat transfer are:

[0046]

[0047]

[0048] The initial condition of air layer temperature is:

[0049] T air =T amb =300K

[0050] Among them, ρ air is the air density; (c p ) air is the specific heat capacity of air; k air (T) is the thermal conductivity of air at T; q rad-absorb2 is the radiant heat absorbed from the back of the fabric to the simulated skin sensor; T air is the air layer temperature; L fab is the fabric thickness; L air is the thickness of the air layer.

[0051] Preferably, in step (6), the one-dimensional heat transfer differential equation obtained by simulating the skin sensor according to Fourier's law and the law of conservation of energy is:

[0052]

[0053]

[0054]

[0055] The left and right boundary conditions for heat transfer in the skin layer are:

[0056]

[0057]

[0058] Among them, ρ epi is the skin density of the epidermis; ρ der is the dermis skin density; ρ sub is the density of the subcutaneous tissue layer; (c p ) epi is the specific heat capacity of the epidermis; (c p ) der is the specific heat capacity of the dermis; (c p ) sub is the specific heat capacity of the subcutaneous tissue layer; k epi k is the thermal conductivity of the epidermis; der k is the thermal conductivity of the dermis; sub is the thermal conductivity of the subcutaneous tissue layer; q rad-tran2is the transfer part of radiant heat in the air layer; k air is the thermal conductivity of air.

[0059] Preferably, in step (7), the quantitative value of the skin burn degree obtained according to the Henriques skin burn score model is:

[0060]

[0061] Among them, Ω is the quantitative value of the degree of skin burns; P is the skin tissue frequency factor; △E is the skin activation energy; R is the molar gas constant; T is the temperature at 80μm from the skin surface; and t is the time the skin is heated.

[0062] The technical solution of this application has at least the following advantages:

[0063] Due to the adoption of the above technical solution, the present invention has the following advantages and positive effects compared with the prior art: the present invention can estimate the temperature distribution of the fabric layer under the deformation state, and predict the skin burn grade in combination with the skin heat transfer model and the skin burn integral model. BRIEF DESCRIPTION OF THE DRAWINGS

[0064] In order to more clearly illustrate the specific implementation methods of the present application or the technical solutions in the prior art, the drawings required for use in the specific implementation methods or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are some implementation methods of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0065] Figure 1 It is a schematic diagram of heat transfer from a radiation heat source to a simulated skin sensor in the present invention. DETAILED DESCRIPTION

[0066] The following will be combined with the accompanying drawings to clearly and completely describe the technical solutions in this application. Obviously, the described embodiments are part of the embodiments of this application, rather than all of the embodiments. Based on the embodiments in this application, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of this application.

[0067] The present application embodiment discloses a method for predicting heat transfer and skin burns of a thermal protective fabric in a deformed state, comprising the following steps:

[0068] (1) Establish a fitting equation for the fabric thickness under deformation, including the fitting equation for the fabric thickness and stretch rate and the fitting equation for the fabric thickness and stretch rate and pressure.

[0069] Among them, according to the experimental data of fabric thickness after deformation, the fitting equation of fabric thickness and stretch rate is established, and the fitting equation of fabric thickness, stretch rate and pressure is established. The fitting equation of fabric thickness is:

[0070] When the fabric is only stretched, the fitting equation of fabric thickness and stretch rate is:

[0071] L fab =ax c

[0072] When the fabric is stretched and squeezed at the same time, the fitting equation of fabric thickness, stretch rate and pressure is:

[0073] L fab =dx e +fx 1 g

[0074] Among them, L fab is the thickness of the fabric after deformation; x is the stretching rate, which is a variable and can be set independently; x 1 is the pressure, which is a variable and can be set independently; a, c, d, e, f, and g are all constants and can be obtained through experiments.

[0075] (2) A method for calculating the density of fabric under deformation is established, wherein the fabric area under deformation is obtained by the “photography method”, that is, taking photos of the fabric before and after deformation under the same external conditions, and importing the photos into CAD to calculate its accurate area.

[0076] According to the law of conservation of mass, the calculation method of fabric density is established as:

[0077] When the fabric is deformed, the fitting equation of fabric area and stretch rate obtained by the "photographic method" is:

[0078] S fab =hx+i

[0079] When the fabric is only stretched, according to the law of conservation of mass, the calculation method of fabric density and stretch rate is established as follows:

[0080]

[0081] When the fabric is stretched and squeezed at the same time, according to the law of conservation of mass, the calculation method of fabric density, stretch rate and pressure is established as follows:

[0082]

[0083] Among them, S 0 is the fabric area before deformation; S fab is the fabric area after deformation; ρ0 is the fabric density before deformation; ρ fab is the fabric density after deformation; L 0 is the fabric thickness before deformation; L fab is the thickness of the fabric after deformation; x is the stretching rate, which is a variable and can be set independently; x 1 is pressure, which is a variable and can be set independently; h, i, j, k, l, m, n,

[0084] o, p, q, and r are all constants and can be obtained through experiments.

[0085] (3) A method for calculating the thermal conductivity under deformation is established, wherein the air content in the fabric after deformation is related to the air content in the fabric before deformation.

[0086] According to the different air contents in the fabric after deformation, a calculation method for the thermal conductivity of the fabric is established. The calculation method for the thermal conductivity of the fabric after deformation is:

[0087]

[0088] Among them, V air is the air content in the fabric before deformation, which can be obtained by measurement or by calculation formula; L 0 is the fabric thickness before deformation; L fab is the thickness of the fabric after deformation; k air is the thermal conductivity of air, which can be obtained by consulting references or inputting; k fiber is the thermal conductivity of the fiber, which can be obtained by querying or inputting the calculation formula; k fab is the thermal conductivity of the fabric after deformation.

[0089] (4) Establish a heat transfer equation through a single layer of thermal protection fabric during heat exposure and cooling stages and its corresponding boundary conditions and initial conditions to obtain the fabric temperature field, wherein the heat transfer equation involves the fabric thickness, the fabric density and the thermal conductivity. Among them, the heat transfer inside the fabric includes heat radiation and heat conduction, wherein the radiant heat is partially reflected from the fabric surface to the environment, partially penetrates the fabric layer, and partially is absorbed by the fabric layer and this part of the heat is expressed by the source term in the differential equation. The heat incident on the fabric surface includes natural convection between the heat source and the fabric surface and the radiant heat and conduction heat transferred from the heat source to the fabric surface.

[0090] According to Fourier's law and the law of conservation of energy, the one-dimensional heat transfer differential equation of the fabric is obtained. The source term in the differential equation during the heat exposure stage is the partial heat absorbed by the fabric. During the cooling stage, the fabric is subjected to contact compression by the compression block, so only heat conduction exists. The heat transfer equation of the fabric is:

[0091] When in the heat exposure stage, the heat transfer equation through the fabric is:

[0092]

[0093] When in the cooling stage, the heat transfer equation through the fabric is:

[0094]

[0095] When in the heat exposure stage, the left and right boundary conditions of fabric heat transfer are:

[0096]

[0097]

[0098] When in the cooling stage, the left and right boundary conditions of fabric heat transfer are:

[0099]

[0100]

[0101] The initial condition of fabric temperature is:

[0102] T fab =T amb =300K

[0103] Among them, (cp) fab k is the specific heat capacity of the fabric, which can be obtained by experimental measurement or by referring to references; fab (T) is the thermal conductivity of the fabric at T; q rad-absorb is the radiant heat absorbed from the heat source to the fabric; rad-tran It is the part of radiant heat transfer in fabric; h conv1 is the convective heat transfer coefficient between the heat source and the outer surface of the fabric during the heat exposure stage, which can be obtained by the calculation formula; T fab is the fabric temperature; T amb is the ambient temperature q fab-sen k is the radiant heat transferred from the back of the fabric to the simulated skin sensor; air is the thermal conductivity of air, which can be obtained by referring to references; k block k is the thermal conductivity of the compressed block, which can be obtained by consulting references; epi is the thermal conductivity of the epidermis, which can be obtained by consulting references, where L in this step fab , fab , k fab Obtained by the above steps (1)(2)(3) respectively.

[0104] Among them, the heat transfer of the fabric system does not take into account the influencing factors such as moisture, so the heat convection only occurs on the outer surface of the fabric, and the radiant heat generated by the radiant heat source can penetrate into the fabric. And because the thickness of the fabric layer and the air layer is small, only heat conduction and heat radiation occur between them, and there is no heat convection.

[0105] The source term of the differential equation for heat transfer of fabrics is radiant heat, which penetrates into the fabric only during the heat exposure stage. According to Beer's law, the radiant heat absorbed by the fabric during this stage is calculated by the following formula:

[0106] q rad-absorb =q rad (1-exp(-γ fab x))

[0107]

[0108] γ fab =-ln(τ) / L fab

[0109]

[0110]

[0111] Among them, q rad-absorb is the radiant heat absorbed from the heat source to the fabric (W / m 2 );q rad is the incident radiation heat reaching the fabric surface (w / m 2 );γ is the extinction coefficient of the fabric; F hs-fab is the angular coefficient of radiation heat source and fabric; F fab-amb is the angular coefficient between fabric and environment; σ is the Stefan-Boltzmann constant 5.67×10 -8 W / (m K 4 ); hs is the radiation coefficient of the heat source; ε fab is the fabric radiation coefficient; ε g is the thermal gas radiation coefficient; T hs is the heat source temperature (K); T fab is fabric temperature (K); T amb is the ambient temperature (K); A hs is the heat source area (m 2 );A fab is the fabric area (m 2 ), τ is the radiation transmission coefficient, L fabl is the fabric thickness (m); d is the distance from the heat source to the fabric (m); r 1 is the radius of the heat source (m); r 2 is the fabric radius (m).

[0112] When the fabric is deformed, the air content in the fabric changes, which in turn affects the thermal conductivity k of the fabric. At temperature T, the thermal conductivity k of the fabric is fab (T) is determined by the fiber and air content in the fabric and can be calculated according to the following formula:

[0113] k fab (T) = V air,com %k air (T)+(1-V air,com %)k fiber (T)

[0114]

[0115]

[0116]

[0117]

[0118] Among them, V air,com % is the air content in the fabric after deformation (%); L fab2 is the thickness of the fabric after deformation; V air % is the air content in the fabric (%); k air (T) is the thermal conductivity of air at temperature T W / (m·K); k fiber (T) is the thermal conductivity of the fiber at temperature T (W / (m·K)); ρ fiber is the fiber density (kg / m 3 );ρ fab is the fabric density (kg / m 3 );ρ air is the air density (kg / m 3 ).

[0119] Natural convection occurs between the outer surface of the fabric and the environment. The air heat transfer coefficient h in the fabric heat transfer boundary condition is conv It can be calculated according to the following formula:

[0120]

[0121]

[0122]

[0123] Where, Nu is the Nusselt number; l fab is the characteristic length of the fabric m; Ra is the Rayleigh number; Pr is the Prandtl number; g is the gravitational acceleration m / s 2 ; β is the volume expansion coefficient of the fluid; α is the thermal diffusion coefficient m 2 / s; v is the kinematic viscosity m2 / s.

[0124] The radiant heat emitted by the heat source will penetrate into the fabric. The radiant heat transmitted through the fabric can be calculated according to the following formula:

[0125] q rad-tran =q rad (exp(-γ fab x))

[0126] Among them, q rad The incident radiation heat absorbed by the fabric w / m 2 ; γ fab is the extinction coefficient of the fabric.

[0127] (5) A heat transfer equation through the air layer and its corresponding boundary conditions and initial conditions are established to obtain the temperature field of the air layer, wherein the boundary conditions involve the thickness of the fabric, wherein the heat transfer inside the air layer includes thermal radiation and heat conduction, wherein heat conduction is the conductive heat exchange between the fabric and the simulated skin sensor; and thermal radiation is the radiant heat from the back of the fabric that is conducted to the simulated skin sensor after passing through the air layer.

[0128] According to Fourier's law and the law of conservation of energy, the one-dimensional heat transfer differential equation of the air layer is obtained. The air layer, as a radiation participating medium, only absorbs thermal radiation but does not reflect thermal radiation. The source term is the radiant heat transferred from the back of the fabric layer to the skin simulation sensor through the air layer. The heat transfer equation of the air layer is:

[0129]

[0130] The left and right boundary conditions for air layer heat transfer are:

[0131]

[0132]

[0133] The initial condition of air layer temperature is:

[0134] T air =T amb =300K

[0135] Among them, ρ air is the air density, which can be obtained by consulting references; (c p ) air is the specific heat capacity of air, which can be obtained by referring to references; k air (T) is the thermal conductivity of air at T, which can be obtained by the calculation formula; q rad-absorb2 is the radiant heat absorbed from the back of the fabric to the simulated skin sensor; T air is the air layer temperature; Lfab is the fabric thickness; L air is the thickness of the air layer, which can be obtained through experimental measurement.

[0136] The air layer acts as a radiation participating medium and can absorb radiation heat. When the thickness of the air layer is less than 6.4 mm, the convection heat transfer can be ignored. rad-absorb2 is the radiant heat absorbed from the back of the fabric to the simulated skin sensor W / m 2 , can be calculated according to the following formula:

[0137] q rad-absorb2 =q fab-sen (1-exp(-κ air x))

[0138]

[0139] Among them, q fab-sen The radiant heat transferred from the back of the fabric to the skin simulation sensor W / m 2 κ air is the air layer absorption coefficient.

[0140] (6) Establishing a heat transfer equation through a simulated skin sensor and its corresponding boundary conditions and initial conditions to obtain the skin temperature field, wherein the boundary conditions involve the thickness of the fabric, wherein the heat transfer inside the skin is heat conduction, and the heat incident on the skin surface is the radiant heat and conductive heat that reaches the skin simulation sensor from the back of the fabric layer through the air layer.

[0141] According to Fourier's law and the law of conservation of energy, the one-dimensional heat transfer differential equation obtained by simulating the skin sensor is:

[0142]

[0143]

[0144]

[0145] The left and right boundary conditions for heat transfer in the skin layer are:

[0146]

[0147]

[0148] Among them, ρ epi is the epidermal skin density, which can be obtained by referring to references; ρ der is the dermis skin density, which can be obtained by referring to references; ρ sub is the density of the subcutaneous tissue layer, which can be obtained by referring to references; (c p )epi is the specific heat capacity of the epidermis; (c p ) der is the specific heat capacity of the dermis; (c p ) sub is the specific heat capacity of the subcutaneous tissue layer; k epi is the thermal conductivity of the epidermis, which can be obtained by referring to references; k der is the thermal conductivity of the dermis, which can be obtained by referring to references; k sub is the thermal conductivity of the subcutaneous tissue layer, which can be obtained by referring to references; q rad-tran2 is the transfer part of radiant heat in the air layer; k air is the thermal conductivity of air, which can be obtained by referring to references.

[0149] The heat absorbed by the simulated skin sensor surface is used as the boundary condition of skin heat transfer, and the skin temperature field is obtained based on the skin heat transfer model to predict the skin burn grade.

[0150] Preferably, the method may further include step (7) of obtaining the time when the skin reaches second-degree burns and third-degree burns according to the Henriques skin burn score model.

[0151] In the step (7), the quantitative value of the skin burn degree obtained according to the Henriques skin burn score model is:

[0152]

[0153] Among them, Ω is the quantitative value of the degree of skin burns; P is the skin tissue frequency factor; △E is the skin activation energy; R is the molar gas constant; T is the temperature at 80μm from the skin surface; and t is the time the skin is heated.

[0154] 2. Skin burn score model

[0155] According to the Henriques skin burn scoring model, the quantitative value Ω of the skin burn degree is obtained. When the skin temperature T>44℃ and Ω=0.53 at the junction of the epidermis and dermis, the skin reaches first-degree burns; when the skin temperature T>44℃ and Ω=1 at the junction of the epidermis and dermis, the skin reaches second-degree burns; when the skin temperature T>44℃ and Ω=1 at the junction of the dermis and subcutaneous tissue, the skin reaches third-degree burns.

[0156] 3. Model Solution

[0157] The differential equations and boundary conditions are discretized using the finite difference method based on the Crank–Nicholson implicit format to obtain a nonlinear tridiagonal system. The discrete equations are solved using the Gauss–Seidel point-by-point iteration method. Matlab software is mainly used for programming and solving.

[0158] When discretizing the heat transfer differential equation and its boundary conditions, the forward difference method is used for time coordinates and the central difference method is used for space coordinates.

[0159]

[0160] The discrete equations for the fabric layer, air layer, and skin layer are as follows:

[0161]

[0162] The present invention is further described below with reference to a specific embodiment.

[0163] When the simulated stretching rate is 3% and the pressure is 0 kPa, a single-layer fabric is exposed to low-radiant heat for 600 seconds and then moved to a place without a radiant heat source to cool for 300 seconds. The heat flux reaching the skin simulation sensor is calculated based on the fabric-air layer-skin simulation sensor, and this heat flux is used as the skin heat transfer boundary condition to obtain the skin temperature field. The skin burn grade is predicted by combining the skin base temperature and the skin burn integral model.

[0164] The input parameters required by the model are as follows:

[0165] (1)Thickness m: L fab =0.45*10 -3 ; L air =0.6*10 -3 ; L epi =75*10 -6 ; L der =1125*10 -6 ;

[0166] L sub =3885*10 -6 ;

[0167] (2) Volume heat capacity J / (m 3 K): (ρc) fab =342*1570;(ρc) air =1.2*1005;(ρc) epi =4.4*10 6 ; (ρc) der =4.186*10 6 ; (ρc) sub =2.6*10 6;

[0168] (3) Time s: T exp =600; T cool =600;

[0169] (4) Radiation coefficient: ε fab =0.9; ε g =0.02; ε sen =0.9;

[0170] By bringing the input parameters into the model for solution, the temperature field distribution of fabric-air layer-skin can be obtained, thereby predicting the skin burn grade and the time to reach second-degree burns.

[0171] Table 1 Temperature distribution of fabric-air layer-skin system

[0172]

[0173] Table 2 Prediction of skin burn grade

[0174] Ω 2.13 Second degree burn time / s 466.3

[0175] Obviously, the above embodiments are merely examples for the purpose of clear explanation, and are not intended to limit the implementation methods. For those skilled in the art, other different forms of changes or modifications can be made based on the above description. It is not necessary and impossible to list all the implementation methods here. The obvious changes or modifications derived therefrom are still within the scope of protection created by this application.

Claims

1. A method for predicting heat transfer and skin burns of thermal protective fabrics in a deformed state, characterized in that: The following steps are involved: (1) Establishing a fitting equation for fabric thickness under deformation to obtain fabric thickness; (2) Establish a calculation method for fabric density under deformation to obtain fabric density; (3) Establishing a calculation method for thermal conductivity under deformation to obtain thermal conductivity, wherein the thermal conductivity is related to the air content in the fabric after deformation and the air content in the fabric before deformation, respectively; (4) establishing a heat transfer equation through a single-layer thermal protective fabric during heat exposure and cooling stages and its corresponding boundary conditions and initial conditions to obtain the fabric temperature field, wherein the heat transfer equation involves the fabric thickness, the fabric density, and the thermal conductivity; (5) establishing a heat transfer equation through the air layer and its corresponding boundary conditions and initial conditions to obtain the temperature field of the air layer, wherein the boundary conditions involve the thickness of the fabric; (6) establishing a heat transfer equation and its corresponding boundary conditions and initial conditions by simulating the skin sensor to obtain the skin temperature field, wherein the boundary conditions involve the thickness of the fabric; (7) The quantitative value of skin burn degree is obtained according to the Henriques skin burn scoring model: Among them, Ω is the quantitative value of the degree of skin burn; P is the skin tissue frequency factor; △E is the skin activation energy; R is the molar gas constant; T is the temperature at 80μm from the skin surface; t is the skin heating time; The area of ​​the fabric in the deformed state is obtained by a photographic method, in which the fabric before and after deformation is photographed under the same external conditions, and the photograph is imported into CAD to calculate its accurate area.

2. The method for predicting heat transfer and skin burns of thermal protective fabrics under deformation according to claim 1, characterized in that: In the step (1), a fitting equation of fabric thickness and stretch rate is established based on the experimental data of fabric thickness after deformation, and a fitting equation of fabric thickness, stretch rate and pressure is established. The fitting equation of fabric thickness is: When the fabric is only stretched, the fitting equation of fabric thickness and stretch rate is: L fab =ax c When the fabric is stretched and squeezed at the same time, the fitting equation of fabric thickness, stretch rate and pressure is: L fab =dx e +fx1 g Among them, L fab is the thickness of the fabric after deformation; x is the elongation rate; x1 is the pressure; a, c, d, e, f, and g are all constants and can be obtained through experiments.

3. The method for predicting heat transfer and skin burns of thermal protective fabrics under deformation according to claim 2, characterized in that: In the step (2), according to the law of conservation of mass, the calculation method of fabric density is established as follows: When the fabric is deformed, the fitting equation of fabric area and stretch rate obtained by the "photographic method" is: S fab =hx+i When the fabric is only stretched, according to the law of conservation of mass, the calculation method of fabric density and stretch rate is established as follows: When the fabric is stretched and squeezed at the same time, according to the law of conservation of mass, the calculation method of fabric density, stretch rate and pressure is established as follows: Where S0 is the fabric area before deformation; S fab is the fabric area after deformation, ρ0 is the fabric density before deformation; ρ fab is the density of fabric after deformation; L0 is the thickness of fabric before deformation; L fab is the thickness of the fabric after deformation; x is the elongation rate; x1 is the pressure; h, i, j, k, l, m, n, o, p, q, and r are all constants.

4. The method for predicting heat transfer and skin burns of thermal protective fabrics under deformation according to claim 1, characterized in that: In the step (3), a method for calculating the thermal conductivity of the fabric is established according to the different air contents in the fabric after deformation. The method for calculating the thermal conductivity of the fabric after deformation is: Among them, V air is the air content in the fabric before deformation; L0 is the thickness of the fabric before deformation; L fab is the thickness of the fabric after deformation; k air k is the thermal conductivity of air; fiber k is the thermal conductivity of the fiber; fab is the thermal conductivity of the fabric after deformation.

5. The method for predicting heat transfer and skin burns of thermal protective fabrics under deformation according to claim 1, characterized in that: In the step (4), the one-dimensional heat transfer differential equation of the fabric is obtained according to Fourier's law and the law of conservation of energy. The source term in the differential equation during the heat exposure stage is the part of the heat absorbed by the fabric. During the cooling stage, the fabric is subjected to contact compression by the compression block, so only heat conduction exists. The heat transfer equation of the fabric is: When in the heat exposure stage, the heat transfer equation through the fabric is: When in the cooling stage, the heat transfer equation through the fabric is: When in the heat exposure stage, the left and right boundary conditions of fabric heat transfer are: When in the cooling stage, the left and right boundary conditions of fabric heat transfer are: The initial condition of fabric temperature is: T fab =T amb =300K Among them, ρ fab is the fabric density; (c p ) fab k is the specific heat capacity of fabric; fab (T) is the thermal conductivity of the fabric at T; q rad-absorb is the radiant heat absorbed from the heat source to the fabric; rad-tran It is the part of radiant heat transfer in fabric; h conv1 is the convective heat transfer coefficient between the heat source and the outer surface of the fabric during the heat exposure stage; T fab is the fabric temperature; T amb is the ambient temperature q fab-sen k is the radiant heat transferred from the back of the fabric to the simulated skin sensor; air k is the thermal conductivity of air; block k is the thermal conductivity of the compressed block; epi is the thermal conductivity of the epidermis of the skin; where L in this step fab , fab , k fab Obtained by the above steps (1)(2)(3) respectively.

6. The method for predicting heat transfer and skin burns of thermal protective fabrics under deformation according to claim 1, characterized in that: In step (5), the one-dimensional heat transfer differential equation of the air layer is obtained according to Fourier's law and the law of conservation of energy. The air layer, as a radiation participating medium, only absorbs thermal radiation but does not reflect thermal radiation. The source term is the radiant heat transferred from the back of the fabric layer to the skin simulation sensor through the air layer. The heat transfer equation of the air layer is: The left and right boundary conditions for air layer heat transfer are: The initial condition of air layer temperature is: T air =T amb =300K Among them, ρ air is the air density; (c p ) air is the specific heat capacity of air; k air (T) is the thermal conductivity of air at T; q rad-absorb2 is the radiant heat absorbed from the back of the fabric to the simulated skin sensor; T air is the air layer temperature; L fab is the fabric thickness; L air is the thickness of the air layer.

7. The method for predicting heat transfer and skin burns of thermal protective fabrics under deformation according to claim 1, characterized in that: In step (6), the one-dimensional heat transfer differential equation obtained by simulating the skin sensor according to Fourier's law and the law of conservation of energy is: The left and right boundary conditions for heat transfer in the skin layer are: Among them, ρ epi is the skin density of the epidermis; ρ der is the dermis skin density; ρ sub is the density of the subcutaneous tissue layer; (c p ) epi is the specific heat capacity of the epidermis; (c p ) der is the specific heat capacity of the dermis; (c p ) sub is the specific heat capacity of the subcutaneous tissue layer; k epi k is the thermal conductivity of the epidermis; der k is the thermal conductivity of the dermis; sub is the thermal conductivity of the subcutaneous tissue layer; q rad-tran2 is the transfer part of radiant heat in the air layer; k air is the thermal conductivity of air.

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