PSI - Issue 36

Anatolii Pavlenko et al. / Procedia Structural Integrity 36 (2022) 3–9 Anatolii Pavlenko, Andrii Cheilytko, Serhii Ilin, et al. / Structural Integrity Procedia 00 (2021) 000 – 000

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2

porous materials depends on the coefficient of thermal transmittance and geometric characteristics of the porous structure. It was also proved that knowing the geometric characteristic of the porous structure of thermal insulation materials, it is possible to calculate the thermal conductivity of this material. Below are the main points by which you can calculate the effective thermal conductivity of porous structures. For a macroporous body, energy transfer will be characterized by an effective thermal conductivity or thermal resistance. Let's represent thermal energy as a fluid. So, the heat flux through the porous body can be divided into many heat pipes, the lateral boundaries of which are formed by the projection of the lateral surface of the pores with a diameter d 2 . The diameter d 2 corresponds to the largest diameter of the pores that form the conditional tube. The pore itself is located in the heat pipe and has the dimensions shown in Fig. 1. For a stationary flow through each section of the tube heat flow flows per unit time specific heat flow in the amount, W/m 2 :

(1)

,

i q Q =

2 1 d d   

where: Q i is the heat flow through the tube, W; d 2 – diameter of the lateral surface of the pores, m; d 1 – the pore size, m.

Fig. 1. Steam heat pipe.

Heat flux through closed porous constructions is assumed to be the product of the heat transfer coefficient of the material without pores, the thermal permeability of the material, the geometric characteristic of the porous structure and the temperature gradient: ( ) , =    tr Q G H grad T  (2) where H tr - heat transfer coefficient;  - thermal permeability of the porous material, showing the distribution of the porosity of the material per pore in the heat pipe:

П n

(3)

 =

b

i

b