**3. Methods of conducting experimental research**

The methods of measuring the coefficients of thermal conductivity and heat transfer of material are based on the equation of Fourier's law [33].

$$\frac{Q}{F} = \frac{\lambda}{\delta} (T\_1 - T\_2),\tag{1}$$

The determination of the heat transfer coefficients was carried out in works [27, 28, 34–41]. The main difficulty is that part of the heat flux created by heating is dissipated into the environment, and measuring the heat flux through the structure under study presents a known difficulty. Therefore, it was proposed to use a closed chamber in the form of a parallelepiped with a replaceable top face (cover). It is known that the average heat transfer coefficient of a closed chamber can be calculated by the expression:

$$K\_{av} = \frac{4K\_{sw} \cdot F\_{sw} + K\_{fl} \cdot F\_{fl} + K\_{\text{cov}} \cdot F\_{\text{cov}}}{4F\_{sw} + F\_{fl} + F\_{\text{cov}}},\tag{2}$$

To determine the heat transfer coefficient of the tested structures, it is necessary to know the heat transfer coefficient of the auxiliary elements of the chamber.

Since the bottom and side wall of the test chamber are made of one of the materials, their heat transfer coefficients are equal to *Kfl* = *Ksw* = *K*0,

$$K\_{av} = K\_0 \frac{F\_0}{F\_0 + F\_{\rm cov}} + K\_{\rm cov} \frac{F\_{\rm cov}}{F\_0 + F\_{\rm cov}},\tag{3}$$

With a known thermal conductivity coefficient of the material *λ*, the dimensions of the chamber, from formula (3), according to the experimentally determined average heat transfer coefficient of the chamber, it is possible to find the heat transfer coefficient of the investigated technical solution:

$$K\_{\rm cov} = \frac{K\_{\rm av} \cdot (F\_0 + F\_{\rm cov})}{F\_{\rm cov}} - \frac{K\_0 \cdot F\_0}{F\_{\rm cov}} \,. \tag{4}$$

The values of the thermal conductivity coefficient *λ* of the material may differ depending on its structure. Therefore, to improve accuracy, it was proposed to make *Experimental Research of New Design Solutions for Fencing Refrigerated Wagon Bodies… DOI: http://dx.doi.org/10.5772/intechopen.109744*

two graduated covers from the same material from the same delivery but with different thicknesses: 50 and 100 mm. When the thickness is reduced up to 2 times, the heat transfer coefficient of the cover becomes 1.87 times less.

With the help of the camera calibration data using covers of different thicknesses, we obtain a system of two equations for a more accurate determination of the heat transfer coefficient of the camera:

$$\begin{cases} K\_{av}^{\delta=100} = \frac{K\_0 F\_0 + K\_{\text{cov}100} F\_{\text{cov}}}{F\_0 + F\_{\text{xp}}}\\ K\_{av}^{\delta=50} = \frac{K\_0 F\_0 + \mathbf{1.87} K\_{\text{cov}100} F\_{\text{cov}}}{F\_0 + F\_{\text{cov}}} \end{cases} \tag{5}$$

By solving the system of Eqs. (7) concerning two unknowns, we obtain the refined values of the heat transfer coefficient *K*<sup>0</sup> of the walls and floor of the chamber:

$$K\_0 = \frac{(F\_0 + F\_{\text{cov}}) \cdot \left(1.87 F\_{\text{cov}} \cdot K\_{\text{cov}}^{\delta = 100} - K\_{av}^{\delta = \sharp 0} \cdot F\_{\text{cov}}\right)}{F\_0 - F\_0 \cdot F\_{\text{cov}}}.\tag{6}$$

Thus, the method of experimental determination of the heat transfer coefficient of the tested technical solution, made in the form of a cover to a heat-insulated chamber (HIC), is as follows [32]:


To study the effect of the external temperature, the required temperature of the refrigerating chamber is set, and the experiments are repeated in the same order.

#### **Figure 1.**

*Test chamber TIC-1 for conducting experiments to determine the heat-shielding properties of thermal insulation: 1 – Expanded polystyrene; 2 – Test sample (cover) of the chamber; 3 – Heater; 4 – Test chamber thermostat; 5 – Thermocouples.*
