Experimental Research of New Design Solutions for Fencing Refrigerated Wagon Bodies and Containers

Abstract

In this chapter, in order to select the directions of development and develop scientifically based technical solutions to improve the thermal parameters of the bodies of refrigerated wagons and containers for the transportation of perishable goods in the conditions of the Republic of Uzbekistan, experimental studies of new design solutions for fencing refrigerator bodies and containers have been carried out. For conducting experimental research a method of experimental determination of the body heat transfer coefficient using a closed thermally insulated chamber in the form of a parallelepiped with a replaceable upper face (cover) has been developed. As a result of comprehensive research using analytical calculations and field experiments, it was found that a promising option for thermal body fencing is a technical solution where polyurethane foam and “Corundum” are used as thermal insulation. The use of these technical solutions in the fences of refrigerated wagons bodies and containers will reduce the heat transfer coefficient by up to 20% and, accordingly, reduce the thickness of the fence by 20–30%, which will lead to an increase in the internal useful volume of the body, a decrease in its mass and consumption of materials used, and an improvement in the thermal state of the body.

1. Introduction

Effective functioning of railway transport in the Republic of Uzbekistan plays a significant role in creating conditions for modernization, transition to an innovative path of development and sustainable growth of the national economy of the country [1, 2]. By their geographical location, the railways of Uzbekistan are an integral part of the Eurasian Railway Network and are also the largest transport and logistics facility of national importance [3]. Throughout the existence and functioning of railway transport works in close relationship with other sectors of the national economy of the Republic of Uzbekistan. One of its main tasks is to meet the needs of the economy by providing timely cargo and passenger transportation. The work in this direction is carried out in various aspects and is aimed at ensuring the safe maximum possible throughput and carrying capacity of the railway network of the Republic of Uzbekistan [4, 5].

The location and peculiarity of the climate of the Republic of Uzbekistan – aridity, a large amount of solar heat, continentality contribute to the mass cultivation of fruit and vegetable products and allow sufficiently high yields of fruits, berries and vegetable products, to provide not only domestic needs but also to supply products to the markets of the near and far abroad [6, 7, 8, 9, 10, 11, 12].

For the export of fruits and vegetables, a sufficiently large number of vehicles equipped with thermal insulation and refrigeration and heating installations are needed. However, at present, the fleet of refrigerated rolling stock, as well as the entire fleet of freight wagons of the railways of Uzbekistan, is experiencing a shortage of serviceable vehicles [4, 13, 14, 15, 16, 17, 18, 19, 20, 21]. The current state of the fleet of refrigerated rolling stock does not allow to supply of a large number of perishable goods to other countries, which negatively affects the development of perishable traffic in the Republic of Uzbekistan.

The thermal engineering properties of the thermal insulation material play an essential role in the design of the thermal fencing of the bodies of refrigerated vehicles [21, 22]. Various materials are used for the thermal insulation of wagons and containers: mineral wool, foams and polyurethanes, characterized by low values of thermal conductivity coefficients [14, 18, 20, 23, 24]. However, due to the presence of thermal bridges, moisture and deterioration of thermal insulation properties during operation in refrigerated wagons and containers, the thickness of body fences (walls, roof and floor) usually exceeds 160–200 mm and reaches 250 mm, which leads to a decrease in the internal useful volume of the body and an increase in the weight of the container. The reason for this is the imperfection of technical solutions for the construction of body fencing structures and thermal insulation materials. During operation, the insulation of the body fence ages and wears out due to the effects of vibration, temperature and humidity changes. Deterioration of the insulation quality of fences leads to fuel overspending and an increase in financial costs, and the volume of work increases with planned types of repairs.

At the same time, new materials are being used in related branches of technology [22, 25, 26], having the lowest coefficient of thermal conductivity and greater strength, which makes it possible to create solid bearing structures of smaller size and weight. Therefore, the development of new technical solutions and the search for promising thermal insulation materials for fencing bodies of refrigerated wagons and containers are relevant. In this regard, the main purpose of this research is to select areas of development and develop scientifically sound technical solutions to improve the thermal parameters of the bodies of refrigerated wagons and containers for the transportation of perishable goods in the conditions of the Republic of Uzbekistan.

2. Analysis of thermal insulation materials for fencing bodies of refrigerated wagons and containers

In recent years, the most commonly used insulation is made of polyurethane foam, which is applied to finished surfaces by spraying [21, 22]. Table 1 shows some characteristics of the materials used.

Name of the material	Coefficient of thermal conductivity, λ, W/m·°C	Specific weight, ρ, kg/m^3
Foam PCV-1	0.035	70–100
Foam PCV-2	0.047	100–130
Foam resin phenolformal FRP-1	0.058	70
Foam resin phenolformal FRP-2	0.058	100
Mineral plate	0.075–0.08	300–350
Mipor	0.035–0.045	12–15
Expanded polystyrene PSBS	0.038–0.041	25–40
Polyurethane foam PPU-36	0.04–0.046	25–40
Fiber glass	0.058	170
Wood	0.14–0.23	500–600
Dry air	0.023	—

Table 1.

Characteristics of insulation materials.

To ensure a low value of the heat transfer coefficient, the dimensions of the thickness of the body fence with these materials are in the range of 160–240 mm. The fences of the vehicle body with the specified materials do not protect against the formation of fogging of the body fence elements and the formation of moisture inside the body, which is harmful to the transported goods.

When repairing refrigerated wagons and containers, it is necessary to replace almost all the elements of the body fence due to moisture damage [13, 21].

The consumption of materials for body fencing is quite high, which undoubtedly affects the cost of vehicles. The search for materials for thermal insulation of the body of vehicles that could become ideal continues [27, 28, 29].

To protect building structures from moisture and heat preservation indoors at low temperatures, the thermal insulation material “Corundum” [30], created in 2008, and produced by Russian manufacturers, is used. This material is a one-component polymer suspension, to which the smallest ceramic heat-sealed granules are added, which are characterized by the physical principle of reflection and heat transfer. The content of such granules (microspheres) in the suspension reaches 70%. Depending on the intended purpose, pigmenting fire-resistant, anticorrosive and inhibitory components are added to the composition. All this makes it possible to obtain thermal insulation with high adhesion and elasticity, which does not change under the influence of external factors: humidity, ultraviolet rays, temperature changes, mold and fungi. The basis of corundum is an Aqueous-F acrylic solution, to which the above components are added [31]. In addition, a number of new materials have appeared. Basic information about these materials is given in Table 2. Therefore, the task arises to assess the possibility of using these materials in the construction of fencing of wagons and containers [32].

Indicators	Traditional thermal insulation		Corundum	Manufactured by LLC “Regent Baltika” and LLC “BALTMASH”
	Mipora TU 6-05-1112-92	Foamed polystyrene		Foamed polystyrene reinforced in volume with fiberglass (RZhD – 1)	Honeycomb panel and foamed polystyrene reinforced in volume	Honeycomb panel
Thermal conductivity, W/°C	0.034-0.052	0.025–0.03	0.001	0.026	0.007	0.032
Labor costs for installation, person⸱h/m2	10	1–2	1–2	0.5–1
Service life, years	Up to 5	From 10	From 10	30–50

Table 2.

Comparison of technical characteristics of traditional and new thermal insulation.

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].

$$\frac{Q}{F}=\frac{\lambda }{\delta }\left(T_1-T_2\right),$$E1

The determination of the heat transfer coefficients was carried out in works [27, 28, 34, 35, 36, 37, 38, 39, 40, 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:

$$K_{\mathit{av}}=\frac{4K_{\mathit{sw}}\cdot F_{\mathit{sw}}+K_{\mathit{fl}}\cdot F_{\mathit{fl}}+K_{\mathrm{cov}}\cdot F_{\mathrm{cov}}}{4F_{\mathit{sw}}+F_{\mathit{fl}}+F_{\mathrm{cov}}},$$E2

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 K_fl = K_sw = K₀,

$${К}_{\mathit{av}}={К}_0\frac{F_0}{F_0+F_{\mathrm{cov}}}+{К}_{\mathrm{cov}}\frac{F_{\mathrm{cov}}}{F_0+F_{\mathrm{cov}}},$$E3

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:

$$K_{\mathrm{cov}}=\frac{K_{\mathit{av}}\cdot \left(F_0+F_{\mathrm{cov}}\right)}{F_{\mathrm{cov}}}-\frac{{К}_0\cdot F_0}{F_{\mathrm{cov}}}.$$E4

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 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:

$$\left\{\begin{array}{l}{K}_{\mathit{av}}^{\delta =100}=\frac{K_0{F}_0+K_{cov100}{F}_{\mathrm{cov}}}{F_0+F_{\mathit{кр}}}\\ K_{\mathit{av}}^{\delta =50}=\frac{K_0{F}_0+1.87K_{cov100}{F}_{\mathrm{cov}}}{F_0+F_{\mathrm{cov}}}\end{array}\right..$$E5

By solving the system of Eqs. (7) concerning two unknowns, we obtain the refined values of the heat transfer coefficient K₀ of the walls and floor of the chamber:

$${К}_0=\frac{\left(F_0+F_{\mathrm{cov}}\right)\cdot \left(1.87F_{\mathrm{cov}}\cdot K_{\mathrm{cov}}^{\delta =100}-K_{\mathit{av}}^{\delta =50}\cdot F_{\mathrm{cov}}\right)}{F_0-F_0\cdot F_{\mathrm{cov}}}.$$E6

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]:

• the area of the enclosing surfaces of the chamber and the cover is calculated;

• the chamber is installed in a heat-insulated room or a refrigerating chamber;

• the temperature difference is measured outside and inside the chamber;

• the air inside the chamber is heated by an electrical device connected to an electricity meter;

• upon reaching a conditionally stationary mode with a constant temperature difference outside and inside the chamber, the average heat transfer coefficient is calculated;

• using the obtained average heat transfer coefficient, the heat transfer coefficient of the lower enclosures of chamber K₀ is calculated according to the formula (5) (performed only when the chamber is calibrated);

• with the help of the value of the coefficient K_av, the heat transfer coefficient of the investigated technical solution of thermal insulation is found according to (4).

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.

4. Experimental setup and calibration

A general view of the thermally insulated chamber (TIC-1) in Figure 1 and the geometric mean areas of the chamber elements are given in Table 3.

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.

Chamber elements names	The area of the elements outside, m^2	The area of the elements inside, m^2	The average area of elements, m^2
Side wall, Fsw	0.8064	0.2464	0.4457
Floor, Ffl	0.1764	0.0484	0.092
Cover, Fcov	0.1024	0.1024	0.1024
Total average chamber area, ∑ F			0.6401

Table 3.

Geometric average areas of the chamber elements.

The test chamber is made of 100 mm thick expanded polystyrene, the inner dimension of which is 220 × 220 × 280 mm. The top of the test chamber (cover) is a test piece of thermal insulation (fence). Samples for the calibration of the test chamber were designed in the form of a cover measuring 320 × 320 mm and a thickness of 50 and 100 mm.

The geometric mean areas of the fence elements of the test chamber (Table 3) were determined by the formula:

$$F_{\mathit{av}}=\sqrt{F_{\mathit{\text{out}}}\cdot F_{\mathit{\text{in}}}},$$E7

The TIC-1 chamber is equipped with a heating element (electric lamp 25 W), connected through a meter to an electric source, and MS-227R4 thermocouples, as well as a W1209 thermostat for temperature control. The heating element is installed so that it evenly heats the inside of the test chamber.

The test chamber was placed in a special climatic chamber of the (CHALLENGE CH600C) series equipped with the necessary measurement and monitoring means, where the temperature can be maintained in the range from −75 to +180°C. When calibrating, the test chamber was placed inside the climatic chamber, and the temperature was maintained at 40°C inside and −20°C outside. The correlation between electricity consumption and temperature inside and outside is shown in Figure 2. It can be seen from it that the temperature remained practically constant, and the power consumption linearly depended on the time of the experiment. The results of processing the experimental data are shown in Table 4.

Figure 2.

Dependence of power consumption on the time of the experiment at a temperature outside −20°C (2) and inside the test chamber +40°C (3).

Test parameters	δ = 100 mm	δ = 50 mm
Holding time of samples, h	22
Electricity consumption, W⸱h	220	255
Internal temperature of the test chamber, °C	40.1	40.486
Internal temperature of the climatic chamber, °C	−19.9	−19.52
Temperature difference, °C	60	59.71
Average heat transfer coefficient of the chamber, W/m^2⸱K	0.260	0.304
Average heat transfer coefficient of the graduation cover Kcov, W/m^2⸱K	0.263	0.537
Average heat transfer coefficient of side walls and floor Ksw and Kfl, W/m^2⸱K	0.259

Table 4.

Experimental data and results of determining the heat transfer coefficient of the TIC-1 test chamber.

5. Heat-protective fence design

To assess the effectiveness of various technical solutions for the fence, the following samples were made (Table 5).

• Sample 1 is a typical fragment of the thermal insulation of refrigerated wagons and containers. It consists of a steel sheet with a thickness of 2 mm, a U-shaped frame with dimensions of 30 × 30 × 2 mm, expanded polystyrene with a thickness of 60 mm, an inner lining of plywood with a thickness of 4 mm, an aluminum sheet with a thickness of 2 mm;

• Sample 2 is similar to Sample 1, but layers of “Corundum” 1 mm thick are applied between the steel sheet and expanded polystyrene, expanded polystyrene and plywood, plywood and aluminum sheet, as well as along the perimeter of the U-shaped frame;

• Sample 3 is similar to Sample 1, but instead of an aluminum sheet with a thickness of 2 mm, a sheet of vinyl plastic with a thickness of 3 mm is installed; a layer of “Corundum” with a thickness of 2 mm is applied between the plywood and vinyl plastic, and layers of “Corundum” with a thickness of 1 mm are applied between expanded polystyrene and plywood, as well as along the perimeter of the U-shaped frame;

• Sample 4 – in this sample, reinforced polyurethane foam with fiberglass, manufactured by “Regent Baltika”, with a thickness of 80 mm, was used as a fragment of thermal insulation;

• Sample 5 – a combination of reinforced polyurethane with a thickness of 100 mm and honeycomb insulation with a thickness of 35 mm was used as a promising fragment of thermal insulation;

• Sample 6 – a honeycomb panel, 35 mm thick, was used as a fragment of thermal insulation.

Table 5.

Technical solutions for the experimental determination of the heat transfer coefficient.

6. Results of experimental studies of thermophysical properties of fences

In the first stage, Samples 1–3 were tested in the CHALLENGE CH600C (Figure 3) climatic chamber. The holding time of the samples was 22 hours; inside the TIC-1 chamber, the temperature was maintained at 40°C, outside −20°C (Figure 4). The average heat transfer coefficients of the cover and chamber are given in Table 6. The thermal insulation properties of Samples 2 and 3, containing thermal insulation “Corundum”, were almost 2 times better. In Sample 3, the thickness of the layers of “Corundum” was 1.5 times thicker, but the heat transfer coefficient of the sample decreased by less than 3% compared to Sample 2. This requires further research to select the optimal thickness of insulation of the “Corundum” type.

Figure 3.

General view of the CHALLENGE CH600C climatic chamber and the TIC-1 test chamber.

Figure 4.

Dependence of power consumption at the time of the experiment at a temperature outside −20°C (2) and inside the test chamber +40°C (3).

Test parameters	Sample no.
	1	2	3
Holding time of samples, h	22
Power consumption, W h	273	228	226
Internal temperature of the test chamber, °C	40.009	40.066	40.1
Internal temperature of the climatic chamber, °C	−19.73	−19.49	-19.56
Temperature difference, °C	59.73	59.56	59.66
Average heat transfer coefficient of the chamber, W/m^2 K	0.325	0.272	0.270
Average heat transfer coefficient of the cover, W/m^2 K	0.673	0.341	0.332

Table 6.

Data obtained from experimental studies using a climatic chamber.

In the second stage, the determination of the heat transfer coefficients was carried out at the testing ground of the Scientific-Implementation Center “Wagons” in a room at an outside air temperature of 18–20°C without using a climatic chamber. Inside the test chamber, heating was carried out to 60–70°C. In this case, the power of the heating element – an electric lamp (25 W) – was reduced by means of a power regulator to 8.8 W.

Six prototype chamber covers were tested for 18 hours each. All parameters – power consumption, air temperature outside and inside the chamber and test duration were recorded. As a result of the experiment, the dependences of the external and internal temperatures and the average heat transfer coefficient on the experiment’s time were determined, as shown in Figure 4. The results of the statistical analysis of the data obtained in experimental studies are shown in Table 7.

Test parameters	Sample No.
	1	2	3	4	5	6
Holding time of samples, h	160	160	160	160	160	160
Power consumption, W h	19.2	19.2	19.3	18.9	17.4	17.4
External temperature, °C	62	70.2	71	70	72.4	58.2
Internal temperature of the test chamber, °C	42.8	51	51.7	51.1	55	40.8
Temperature difference, °C	0.324	0.272	0.269	0.271	0.252	0.340
Average heat transfer coefficient of the chamber, W/m^2 K	0.664	0.341	0.322	0.332	0.220	0.761

Table 7.

Data obtained in experimental studies without a climatic chamber.

In Figure 5a, it can be seen that the air temperature in the test chamber increases during 5–6 hours, and then it stabilizes at the level of 58–75°C due to the transfer of heat from the test chamber to the outside. From Figure 5b, it follows: at the beginning of the experiment, during 5 h, the heat transfer coefficient of the test chamber drops sharply, which can be explained by an increase in the temperature difference between the outside and inside air (t_in – t_ex). Then the heat transfer coefficient is stabilized and takes on a constant value. The heat transfer coefficients of the chamber covers are shown in Figure 6.

Figure 5.

Dependences of the internal temperature (a) and the heat transfer coefficient of the test chamber (b) on the time of the experiment: 1 – Sample No. 1, 2 – Sample No. 2, 3 – Sample No. 3, 4 – Sample No. 4, 5 – Sample No. 5, 6 – Sample No. 6, 7 – Outside the test chamber.

Figure 6.

Average heat transfer coefficients of cover samples No. 1–6.

The heat transfer coefficients with and without a climatic chamber practically did not change. Their difference does not exceed 3%, which indicates a small dependence of the thermal conductivity coefficients of Samples 1–3 on temperature.

Repeated tests of Samples 1–3 confirmed (Figure 6) that the application of thermal insulation “Corundum” reduced the heat transfer coefficient almost twice. Thus, using “Corundum” as a layer of thermal insulation, it is possible to reduce the side wall thickness of refrigerated wagons and containers. For real wagons and containers, it is possible to reduce the insulation thickness by 20–30%. Insulation Samples 5 manufactured by “Regent Baltika” have the lowest heat transfer coefficients, but their thickness was significantly greater (135 mm) than Samples 1–3. Their application is promising, but it is necessary to develop technical solutions for their implementation.

7. Conclusions and recommendations

This chapter presents a set of theoretical and experimental research on the choice of development directions and the development of scientifically sound technical solutions to improve the thermal parameters of the bodies of refrigerated wagons and containers for the transportation of perishable traffic in the conditions of the Republic of Uzbekistan.

1. Based on the analysis of the designs of vehicles for the transportation of perishable goods and their thermal insulation materials, the main problems and prospects for the development of transportation of perishable goods in the conditions of the Republic of Uzbekistan are determined.

2. A method of experimental determination of the body heat transfer coefficient using a closed thermally insulated chamber in the form of a parallelepiped with a replaceable upper face (cover) has been developed.

3. A heat-insulated chamber has been developed that allows experimentally determining the coefficients of heat transfer and thermal conductivity of model thermal insulation samples with sufficient accuracy (error no more than 3%).

4. As a result of comprehensive research using analytical calculations and field experiments, it was found that a promising option for thermal body fencing is a technical solution where polyurethane foam and “Corundum” are used as thermal insulation.

5. The minimum value of the heat transfer coefficient from the materials studied was provided by the option of RZhD-1 thermal insulation (manufactured by “Regent Baltika”), which combines reinforced polyurethane and a honeycomb structure on a paper base.

6. The use of these technical solutions in the fences of refrigerated wagons bodies and containers will reduce the heat transfer coefficient by up to 20% and, accordingly, reduce the thickness of the fence by 20–30%, which will lead to an increase in the internal useful volume of the body, a decrease in its mass and consumption of materials used, and an improvement in the thermal state of the body.

7. The comparison of the calculation data using analytical formulas with the experimental results showed satisfactory accuracy in determining the average value of the heat transfer coefficient (the error is not more than 9%).

Thus, as a result of comprehensive studies using analytical calculations and field experiments, it was found that a promising option for thermal body fencing is a technical solution where polyurethane foam and “Corundum” are used as thermal insulation. The minimum value of the heat transfer coefficient from the studied materials was provided by the option of thermal insulation of RZhD-1 (produced by “Regent Baltika”), combining reinforced polyurethane and a honeycomb structure on a paper base. The use of these technical solutions in the fences of the bodies of refrigerated wagons and containers will reduce the heat transfer coefficient to 20% and, accordingly, reduce the thickness of the fence by 20–30%, which will lead to an increase in the internal useful volume of the body, reduce its weight and consumption of materials used, improve the thermal condition of the body. Theoretically and experimentally, the possibility of piecewise continuous recording of vertical and lateral forces from the wheel/rail interaction was achieved by measuring the stresses in two rail sections on a significant part of the sleeper gap.