Nghiên cứu xác định các thông số làm việc hợp lý của máy đốt nóng mặt đường bê tông nhựa cỡ nhỏ khi sửa chữa đường ô tô ở Việt Nam

Nghiên cứu xác định các thông số làm việc hợp lý của máy đốt nóng mặt đường bê tông nhựa cỡ nhỏ khi sửa chữa đường ô tô ở Việt NamNghiên cứu xác định các thông số làm việc hợp lý của máy đốt nóng mặt đường bê tông nhựa cỡ nhỏ khi sửa chữa đường ô tô ở Việt NamNghiên cứu xác định các thông số làm việc hợp lý của máy đốt nóng mặt đường bê tông nhựa cỡ nhỏ khi sửa chữa đường ô tô ở Việt NamNghiên cứu xác định các thông số làm việc hợp lý của máy đốt nóng mặt đường bê tông nhựa cỡ nhỏ khi sửa chữa đường ô tô ở Việt NamNghiên cứu xác định các thông số làm việc hợp lý của máy đốt nóng mặt đường bê tông nhựa cỡ nhỏ khi sửa chữa đường ô tô ở Việt NamNghiên cứu xác định các thông số làm việc hợp lý của máy đốt nóng mặt đường bê tông nhựa cỡ nhỏ khi sửa chữa đường ô tô ở Việt NamNghiên cứu xác định các thông số làm việc hợp lý của máy đốt nóng mặt đường bê tông nhựa cỡ nhỏ khi sửa chữa đường ô tô ở Việt NamNghiên cứu xác định các thông số làm việc hợp lý của máy đốt nóng mặt đường bê tông nhựa cỡ nhỏ khi sửa chữa đường ô tô ở Việt NamNghiên cứu xác định các thông số làm việc hợp lý của máy đốt nóng mặt đường bê tông nhựa cỡ nhỏ khi sửa chữa đường ô tô ở Việt NamNghiên cứu xác định các thông số làm việc hợp lý của máy đốt nóng mặt đường bê tông nhựa cỡ nhỏ khi sửa chữa đường ô tô ở Việt NamNghiên cứu xác định các thông số làm việc hợp lý của máy đốt nóng mặt đường bê tông nhựa cỡ nhỏ khi sửa chữa đường ô tô ở Việt NamNghiên cứu xác định các thông số làm việc hợp lý của máy đốt nóng mặt đường bê tông nhựa cỡ nhỏ khi sửa chữa đường ô tô ở Việt NamNghiên cứu xác định các thông số làm việc hợp lý của máy đốt nóng mặt đường bê tông nhựa cỡ nhỏ khi sửa chữa đường ô tô ở Việt NamNghiên cứu xác định các thông số làm việc hợp lý của máy đốt nóng mặt đường bê tông nhựa cỡ nhỏ khi sửa chữa đường ô tô ở Việt NamNghiên cứu xác định các thông số làm việc hợp lý của máy đốt nóng mặt đường bê tông nhựa cỡ nhỏ khi sửa chữa đường ô tô ở Việt NamNghiên cứu xác định các thông số làm việc hợp lý của máy đốt nóng mặt đường bê tông nhựa cỡ nhỏ khi sửa chữa đường ô tô ở Việt NamNghiên cứu xác định các thông số làm việc hợp lý của máy đốt nóng mặt đường bê tông nhựa cỡ nhỏ khi sửa chữa đường ô tô ở Việt NamNghiên cứu xác định các thông số làm việc hợp lý của máy đốt nóng mặt đường bê tông nhựa cỡ nhỏ khi sửa chữa đường ô tô ở Việt NamNghiên cứu xác định các thông số làm việc hợp lý của máy đốt nóng mặt đường bê tông nhựa cỡ nhỏ khi sửa chữa đường ô tô ở Việt NamNghiên cứu xác định các thông số làm việc hợp lý của máy đốt nóng mặt đường bê tông nhựa cỡ nhỏ khi sửa chữa đường ô tô ở Việt NamNghiên cứu xác định các thông số làm việc hợp lý của máy đốt nóng mặt đường bê tông nhựa cỡ nhỏ khi sửa chữa đường ô tô ở Việt NamNghiên cứu xác định các thông số làm việc hợp lý của máy đốt nóng mặt đường bê tông nhựa cỡ nhỏ khi sửa chữa đường ô tô ở Việt NamNghiên cứu xác định các thông số làm việc hợp lý của máy đốt nóng mặt đường bê tông nhựa cỡ nhỏ khi sửa chữa đường ô tô ở Việt NamNghiên cứu xác định các thông số làm việc hợp lý của máy đốt nóng mặt đường bê tông nhựa cỡ nhỏ khi sửa chữa đường ô tô ở Việt NamNghiên cứu xác định các thông số làm việc hợp lý của máy đốt nóng mặt đường bê tông nhựa cỡ nhỏ khi sửa chữa đường ô tô ở Việt NamNghiên cứu xác định các thông số làm việc hợp lý của máy đốt nóng mặt đường bê tông nhựa cỡ nhỏ khi sửa chữa đường ô tô ở Việt NamNghiên cứu xác định các thông số làm việc hợp lý của máy đốt nóng mặt đường bê tông nhựa cỡ nhỏ khi sửa chữa đường ô tô ở Việt Nam

MINISTRY OF EDUCATION AND TRAINING UNIVERSITY OF TRANSPORT AND COMMUNICATIONS

-o0o -

NGUYEN VAN DUNG

RESEARCH TO DETERMINE REASONABLE WORKING PARAMETERS OF SMALL-SIZED ASPHALT CONCRETE PAVEMENT

HEATERS WHEN REPAIRING HIGHWAY IN VIETNAM

Major in: DYNAMIC MECHANICAL ENGINEERING Code: 9520116

SUMMARY

ENGINEERING DOCTORAL THESIS

Hanoi –2024

Thesis completed at:

UNIVERSITY OF TRANSPORT AND COMMUNICATIONS

Scientific supervisor: 1 Associate Prof., Dr Nguyen Binh 2 Dr Nguyen Huu Chi

This thesis may be learnt at:

1 Library of University of Transport and Communications 2 National Library of Vietnam

INTRODUCTION1 Urgency of the thesis

Road maintenance, repair, and maintenance work is extremely important in exploiting roads and ensuring traffic safety According to the basic standards 07.2013 of the General Department of Roads on the maintenance, repair and maintenance of asphalt concrete pavement, regular repair work of the road surface accounts for a large proportion, including tasks such as: Patching potholes, repairing cracks, ruts Road surface repair using the on-site heating method has many advantages, so it is very suitable for minor road surface maintenance and repairs In the hot repair method of pavement, the operation of a heater needs to transfer heat to the asphalt concrete pavement to the necessary temperature to ensure the quality of the recycled asphalt layer Therefore, it is necessary to research and determine the reasonable working parameters of small-sized pavement heaters under actual operating conditions in Vietnam, as a basis for operating the machine effectively and saving fuel, construction time while ensuring road surface quality after repair Therefore,

the thesis "Research to determine reasonable working parameters of

small-sized infrared asphalt heaters machine when repairing motorways in Vietnam"

is urgent and highly practical

2 Objective of the thesis

Determine the working parameters of infrared asphalt heaters machine such as: required heating temperature, heating time, heating distance and structural parameters to ensure the quality of repaired and consumed pavement smallest fuel Build a scientific basis for effective operation and design and manufacture of heating machines to replace imported equipment

3 Object and scope of research

a) Research object

Small-sized infrared asphalt heaters machine with heating plate size ≤ 1 m2, moving and pushing by hand by worker, heating by infrared radiation principle using gas fuel, serving minor repair working asphalt pavement

b) Research scope

The machine is used to repair cracks and damages with a size of ≤ 0.5 m2 on asphalt pavement The heating target is asphalt pavement of 60/70 degree C12.5 granularity with minor damage and the ability to be hot recycled

4 Research content

- Overview of the issues related to the thesis

- Research on the scientific basis of the heat transfer process and flame characteristics in the combustion chamber

- Determine the operating parameters of the infrared asphalt heaters machine through the study of heat transfer theory and combustion theory

- Experimental research and determination of reasonable operating parameters by means of multi-objective experimental planning method

5 Scientific and practical significance of the thesis

a) Scientific significance

Determining the necessary heating temperature when repairing the road surface is a condition for studying the problem of unstable heat transfer from the machine to the road surface using the finite element method (FEM) and flame combustion theory in the combustion chamber, from which the range of working parameter values of the machine can be determined, which is the scientific basis for manufacturing heating machines

Field experiments and the use of experimental planning methods to optimize target surfaces to build regression equations of objective functions and multi-objective simultaneous surveys are the scientific basis for determining The machine's working parameters satisfy the requirements of the objective function

b Practical significance

The research results of the thesis are documents that guide the operation of heaters when performing minor road surface repairs and also provide a scientific basis for the design and manufacture of infrared asphalt heaters machine in Vietnam

6 New points of the thesis

a) Research theoretical

Use the FEM to solve the heat transfer problem for infrared asphalt heaters machine with the boundary conditions of the environment and construction objects Research combustion theory to determine the structural

parameters of the combustion chamber of the heater

b) Research experimental

Build an experimental matrix, apply a multi-objective optimization

experimental planning problem model for the infrared asphalt heaters machine to determine the reasonable working parameters of the machine

c) Results application

- Determining a reasonable set of working parameters for pavement heaters is the scientific basis for the process of operating, designing and manufacturing infrared asphalt heaters machine in Vietnam

CHAPTER 1: OVERVIEW OF RESEARCH ISSUES

1.1 Introduction to manufactured pavement heaters in Vietnam

1.1.1 Structural characteristics of infrared asphalt heaters machine

- The infrared asphalt heaters machine is coded as IHM.01 IHM.01 is a product of a key university-level scientific research project conducted by the doctoral student during the thesis process The IHM.01 machine was designed, manufactured and its technical parameters were completed during the research process The IHM.01 machine is the research object of the thesis

- The machine has a compact structure, the heating plate has an area of ≤ 1 m2, the fuel tank uses gas, the machine is equipped with 4 metal wheels, and is moved by workers during construction To ensure flexibility during construction, the PhD-Student proposed a machine design consisting of 2 heating blocks joined together, including basic components: heating plate, fuel supply system, moving system, and control system The structure of the IHM.01 machine is described in Figure 1.1

Figure 1.1 Image of The pavement heating machine IHM.01 1 Moving wheel, 2 Combustion chamber, 3 Fuel injector, 4 Seal, 5 Gas tank holder, 6 Gas tank, 7 Control cabinet, 8 Solenoid valve, 9 Push handle

1.2 Overview of research works at home and abroad related to the thesi

1.2.1 Research works on heat transfer process in asphalt concrete

Many scientists in China, Russia, European countries and Vietnam have studied the heat transfer process in asphalt concrete materials, which has been presented in the documents: [23], [32], [40], [45], [47], [51], [62], [65], The authors use the Fourier heat transfer equation theory, use the PTHH method to simulate the heat transfer process, describe the law of temperature distribution according to the depth of the road surface, thereby finding the road surface temperature at different depths However, the research works have not mentioned the unstable heat transfer process from IHM.01 to the road surface

1.2.2 Research works on characteristic parameters of gas flame in combustion chamber

Scientists in China, Russia, the United States, and European countries have studied the characteristic parameters of the flame in the combustion chamber, which have been presented in the documents: [35], [36], [41]… These studies have determined the characteristic thermal parameters of the gas flame in natural conditions based on the combustion theory However, these documents have not mentioned the flame in the combustion chamber of IHM.01

1.2.3 Research works on determining the working parameters of infrared asphalt heaters machine

Research works related to determining the operating parameters of pavement heating machines carried out by many scientists in China, Russia, European countries and Vietnam are presented in the documents: [8], [37], [38], [42], [46], [50], [53], [54] The studies focus on building theoretical or experimental heat transfer models from which the authors determine the operating temperature parameter values of the machine suitable for construction conditions These documents have not mentioned the experimental process of the influence of multiple factors on the heat transfer process of the machine to determine the operating parameters

CONCLUSION OF CHAPTER 1 AND RESEARCH ORIENTATION

1 Researching the overview of published works, the PhD student found that a number of remaining issues need to be developed and researched to clarify as follows:

- A number of foreign and domestic authors have studied the heat transfer process in asphalt layers using common analytical methods, empirical formulas or using the FEM However, these studies have not mentioned in detail the

simultaneous effects of boundary conditions such as: environmental conditions (temperature, radiation, humidity and wind), asphalt pavement conditions - Determining the characteristic parameters of gas flames has also been researched by some authors However, studies have not mentioned determining the parameters of the fire in a limited combustion environment to determine the structural parameters of the combustion chamber whose radiant surface is a thermal ceramic plate

- Research projects on determining parameters of heating machines have also been carried out by some authors However, the studies either focus on pure theory, or mainly on experimental measurements of road surface temperature through temperature probes Research projects have also not mentioned determining the operating parameters of the heater using the experimental planning method to complete theoretical calculation results

2 The thesis identifies the research objectives and content, which are: studying the unsteady heat transfer process from the heater to the road surface using the FEM considering the simultaneous influence of boundary conditions; Study the characteristics of the fire in the combustion chamber From there, we can roughly determine the value range of the machine's working parameters such as: heat transfer distance; heating temperature of the machine; heating time and structural parameters of the combustion chamber From the results of theoretical research, the researcher built a heater and tested it using the multi-objective optimization experimental planning method From there, determining the reasonable working parameters of the heating machine is the scientific basis for manufacturing and perfecting the machine right in the process of theoretical research and machine experimentation Detailed content will be presented in the next chapters of the thesis

CHAPTER 2: RESEARCH ON THE SCIENTIFIC BASIS OF HEAT TRANSFER PROCESS AND FLAME CHARACTERISTICS IN THE

COMBUSTION COMPARTMENT 2.1 Heat transfer problem model

2.1.1 Heat transferred to the road surface

The heat flow affecting the asphalt layer of the road surface is q, including: q = qbx + qđl ( W/m2) (2.1)

where qbx is the radiant heat flow, W/m2; qdl is the convective heat flow in a narrow space The amount of heat exchanged by radiation between surfaces 1 and 2 is determined according to Stefan Boltzomann [25]:

Q = Ft.FG.σ0.(𝑇1-𝑇2) (2.2)

where Ft is a factor that considers the nature of the two surfaces, FG is a factor that considers the geometric orientation of the two radiating surfaces With 2 radiant heat transfer surfaces are thermal ceramic plates; and the road surface in the middle is the air environment

- Radiant heat flow density: qbx = 5,67∗10

1,15 = 4,93.10-8 (Tm4 ÷ 354), W/m2 (2.3) where Tm is the temperature of the heating plate on the machine Equation (2.3) is the equation that describes the value of the radiant heat of the heating plate according to temperature

- Calculate the heat transmitted through both surfaces of the object, [26]: qđl = 𝜆𝑡đ

𝑎 (T𝑚− T0) (2.4) Where q is the heat between two surfaces (W/m2); λtd is the equivalent thermal conductivity coefficient, λtd = λ.εtđ, tđ - thermal conductivity coefficient of the liquid, tđ - correction coefficient

Calculating the parameters instead of (2.4) gives the result: qđl = 0,208

𝑎 (𝑇𝑚− 308) = 0,208

𝑎 (W/m2) - Total useful heat transferred to the road surface:

q = 4,93.10-8 T4

𝑎 + 443.65 (2.5)

2.1.2 Heat transfer in asphalt concrete layers

The heat transfer model in asphalt concrete layers is an unstable heat transfer process through asphalt pavement layers The heating plate is placed a centimeter away from the road surface, transferring heat to the road surface (Figure 2.6) Survey the road surface temperature within range A (m2), the heat transfer depth is considered for a 5 cm thick layer of smooth asphalt

Figure 2.1 Overall discretization of the heat transfer medium

The thesis chose the heat transfer element as a bar element with 2 nodes, with A1

121113Tấm đốt nóng bức xạ

a thickness of the surface asphalt layer of 5 cm to facilitate solving the problem The author chose each element to have a length of 1 cm The temperature at the nodes and the load vector can be written at time m or p+1, which means they can be different by one time step Δτ Solve the characteristic equation to determine the temperature parameter at time p+1:

{𝑇}𝑝+1 = {[𝐶] + ∆𝜏 [𝐾]}−1∗ ([𝐶] {𝑇}𝑝+ ∆𝜏 {𝑓}𝑝+1) (2.6) Equation (2.6) is the heat transfer matrix equation of the problem, determining the coefficient matrix values

- Heat capacity matrix:

[𝐶] =[

2.4 Model for calculating the fire in the combustion chamber

2.4.2 Calculate the length of the burning gas flame

The length of the pure mixed-flow diffusion flame is determined based on the concentration distribution of fuel and oxygen in the spray stream as follows, [43]:

𝐿𝑓+ 𝑎

1 + 2 𝑆𝑐𝑡32 𝑍̃𝑠𝑡 (

) 𝜌𝑜𝜌∞ 𝐶

With: Lf is the flame length, cm; a is the spray pipe length, cm; d is the nozzle diameter, cm; 𝑢̃𝑧 average value of combustion gas velocity, cm/s; 𝑍̃𝑠𝑡coordinates of the end point of the flame, cm; 𝜌𝑜 density of the combustion gas mixture at the nozzle face, kg/cm3; 𝜌∞ is the density of the combustion gas at the farthest part of the combustion chamber, kg/cm3

With u0/ν0 = 70 and Sct = 0.72; Constant value C = (ρ0 ρst)1/2/ρ∞ Then we have: 𝐿𝑓+𝑎

where d is the diameter of the gas nozzle, cm; Q is the heat of the flame, kW The gas flow velocity at the nozzle is determined according to [52]: u0 = 𝜌0.𝜋𝑑2𝑄𝑜

, According to [52], the flame length is determined according to the combustion gas pressure as follows: Lf = α* P-2/3, with α being the influence coefficient of the combustion gas pressure; P being the combustion gas pressure, kg/cm2 The temperature and velocity of the combustion gas flame are determined:

H5/3 corresponding to structure of the flame r/H ≤ 0,1 (2.8) From solving the matrix equation (2.7), we can determine the solution sets (T1, T2, T3, T4, T5) with appropriate temperature conditions, this is the basis for determining technical parameters of the machine in chapter 3.

2.7

T-T∞ = 5,38∗(Qr)5/3

H corresponding to structure of the flame r/H > (2.9) u = 0,96*(Q

H)1/3 corresponding to structure of the flame r/H ≤ 0,15 (2.10)

𝑟5/6 corresponding to structure of the flame r/H > 0,15 (2.11) where: T is the temperature at the center of the flame, oC; T∞ is the temperature at the farthest position of the combustion space, oC; Q is the heat supplied from the flame, kW; H is the impact distance of the flame, cm; r is the diffusion radius of the flame, cm; u is the velocity of the flame, cm

CONCLUSION OF CHAPTER 2

Chapter 2 has solved the following specific problems:

1 Radiative and convective heat transfer from the heating plate to the road surface according to the Stefan Boltzomann law and the Newton - Richman law determined by equation (2.5)

2 Heat transfer between asphalt layers, using the FEM to write the heat transfer equation with the following contents:1 Discretize the heat transfer space and heat transfer time, build the heat transfer equation in matrix form (T1 ÷ T5); 2 Use the matrix algorithm program to solve the solution sets, thereby building the relationship between the temperature of the heating plate and the temperature in the road surface layers corresponding to the heating time periods at times P = 1÷15

3 Investigate the dependence between the temperature of the asphalt layer and the temperature of the heating plate Tm From there, it is possible to determine the temperature zone suitable for the asphalt heating process corresponding to the appropriate value of Tm, this is the basis for determining the technical parameters of the machine in chapter 3

4 Through the study of the combustion theory of the flame, it is possible to determine the equations describing the dependence of the flame length on the combustion pressure P, the gas flow rate (𝑚̇ ) ̇ and the temperature of the gas 𝐹flame by equations (2.43), (2.44), (2.45), (2.46) this is the basis for determining the structural parameters of the burning mineral so that the flame burning the ceramic plate reaches the temperature Tm, oC

CHAPTER 3: DETERMINING THE WORKING PARAMETERS OF THE PADDLE HEATING MACHINE THROUGH THE STUDY OF

HEAT TRANSFER THEORY AND COMBUSTION THEORY 3.1 Determining the size of the heating plate

The basis for determining the size of the heating plate is determined through the heating object, which is the damaged area of the road surface The size of the heating plate must ensure that it can cover the most common cracks and damage At the same time, it must be flexible and can be assembled when repairing large damages The damage sizes are surveyed as follows:

Table 3.1 Damage dimensions of the road surface

1 Polygonal Crack 0,5 ÷ 1 m2 0,6÷ 1,2 m22 Longitudinal Crack 0,75 ÷ 1,25 m 1 ÷ 2 m 3 Horizontal Crack 0,45 ÷ 1 m 0,6÷ 1,2 m

From the size values in table 3.1, determine that the heating plate with the size: L x B = 1 x 0.6 (meters) is suitable

3.2 Effect of heating plate temperature and heat transfer time

With the temperature requirement of the asphalt layers that need to be heated determined from chapter 1, item (1.3) is 104 oC ÷ 177 oC achieved with the required heat transfer depth of 5 cm Investigate the heat transfer process (2.6) with a heating time step Δτ = 30 s, run the results of heat output and heating plate temperature according to heating time using the program We have, the value of q is shown in the graph in figure 3.1 as follows:

Figure 3.1 Graph depicting the value of radiant heat flow

The temperature of the heated asphalt layer needs to reach 104 oC ÷ 177 oC Therefore, the range of heat values considered in graph 3.1 is in the

temperature range T1 ≤ 177 oC and T5 ≥ 104 oC

- Determine the temperature range of the surface asphalt layer T1, oC

From the table of temperature values at different times and nodes corresponding to different depths, replacing the heat value q, we can calculate the temperature values corresponding to different heat transfer times Temperature T1 is described in Figure 3.2

Figure 3.2 Surface temperature and radiant heat flux over heating timeComment: From the graph in Figure 3.2, we see that starting from the

heating time P=3 (t = 3*30 = 90 s) with the radiant heat flow at the surface of 4738 W/m2; up to time P14 (t = 12*30 = 420 s) = 7 minutes, at this time the surface temperature of the road surface is from 104.3 oC to 175.2 oC, this is the temperature range that satisfies the allowable temperature range of the asphalt *

- Determine the temperature range of the bottom asphalt concrete layer T5, oC

Figure 3.3 Temperature of the bottom asphalt layer and radiant heat flow over time

Upper limit temperature heat flow density

Upper limit temperature