Deicing performances of a road unit driven by a hydronic heating system in severely cold regions of China

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Abstract

The deicing performances of a road unit driven by a hydronic heating system in severely cold regions of China were investigated by using the Open Source Lattice Boltzmann Code. The model used the enthalpy-based method and double distribution functions for the velocity and temperature fields to solve the ice melting problem. The average road surface temperatures and melting conditions (melting ratio and mass) as affected by ice thickness (3 20 mm), pipe spacing (80 240 mm), and air temperature (252 268 K) were detailed, and the parameters were analyzed by the orthogonal test method. The results show that for the ice thickness increasing from 3 mm to 20 mm, the heating rate was slightly increased from 6.3 K/h to 6.45 K/h in the preheating and initial melting stages, and from 1.32 K/h to 2.06 K/h in the rapid melting stage, the melting mass was increased from 360 g/m to 762.06 g/m whereas the melting ratio was decreased from 1.00 to 0.32. The pipe spacing of 120 mm was suitable for the road heating whereas 160 mm was not feasible in the severely cold regions. For the air temperature was increased from 252 K to 268 K, the preheating time was decreased from 3.02 h to 0.82 h, the heating rate in the melting stages was increased from 0.68 K/h to 2.94 K/h and the melting ratio was linearly increased. The parameter analysis reveals that the air temperature had the most important influence on the melting ratio whereas the pipe spacing had the most significant impact on the average road surface temperature, and the ice thickness had a slight influence on the melting ratio and average road surface temperature.

Introduction

The ice formation on the road significantly affects transportation safety [1]. To resolve these problems, road heating systems have been widely investigated due to their advantages: (a) operationally effective, and (b) environmentally friendly [2]. Such road heating systems include the electric heating system [3], the heat pipe system [4] and the hydronic heating system [5]. Lai et al. [3] validated that the electric airport pavement heating system was feasible in Beijing. Wang et al. [4] proposed the finite volume model of the heat pipe to optimize the design of heat pipes in an assumed ice and snow melting system. Seo et al. [5] reported an application of hydronic highway heating system in South Korea. Among the three deicing methods, the hydronic heating system has many advantages: (a) heat supply is more reliable than the heat pipe system, and (b) heat source is more flexible than the electric heating system and heat pipe system. For the aims of improving system efficiency and reducing initial cost, it is essential to establish the melting model for the hydronic heating system to analyze the heating performance and optimize the system design.

Mathematical models have been developed for the road heating system because the models can reduce time and money in comparison to experiments [6], and provide detailed information on the spatiotemporal variations in parameters such as temperature and velocity [7]. Chapman et al. [8] proposed a one-dimensional steady-state equation to calculate the total heating load. Schnurr et al. [9] developed a steady-state two-dimensional finite-difference model for the system without snow. Kilkis [10] proposed a simplified steady-state model to calculate the heating load for various road surface conditions. Chiasson et al. [11] described a transient two-dimensional finite difference model for a heating slab. Rees et al. [12] proposed a three-node snow melting model and Liu et al. [13] simplified it into a two-node model to reduce the computation time. Xu et al. [14] presented a heat and mass coupled model for road heating system. However, most models assumed that the snow and ice layer as one-dimensional by mainly considering the energy and mass conservation. Liu et al. [15] proposed a two-dimensional snow heating model for the compacted snow layer, whereas the phase change in the melting process was also not considered. Therefore, it is crucial to develop a two-dimensional melting model to evolve the phase-change process.

The modeling of the phase-change process is a challenging problem due to the nonlinearity at the moving solid–liquid interface [16]. The lattice Boltzmann method (LBM) has many advantages [17], [18], such as the easy boundary treatment, simple algorithm background and parallelizable computation property [19], [20]. Huang et al. [20] proposed a new phase-change model using enthalpy-based LBM. Wu et al. [21] studied the fourth-order analysis of force terms in a pseudopotential lattice Boltzmann model for multiphase flow. Lin et al. [22] investigated the melting process in the encapsulated phase change materials by LBM. Li et al. [23] presented the lattice Boltzmann models for axisymmetric solid–liquid phase change. Then, it is possible to evolve the ice melting process of a hydronic road unit heating system by using the LBM. There are two major methods to address the solid–liquid phase-change problems by lattice Boltzmann model: (a) phase-field method, and (b) enthalpy-based method. The phase-field method needs extremely thin grids to resolve the interfacial region, however, the enthalpy-based method traces the phase interface by updating the total enthalpy [20]. Therefore, the enthalpy-based LBM was adopted in the ice melting model.

In this study, a two-dimensional ice melting model was implemented by Open Source Lattice Boltzmann Code, using enthalpy-based LBM and double distribution functions for the velocity and temperature fields to obtain the accurate temperature field. The road surface temperature and ice melting conditions (melting ratio and mass) as affected by the ice thickness, pipe spacing, and air temperature were analyzed. Additionally, the parameter analysis by the orthogonal test method was conducted to evaluate the influence degree of different parameters.

Section snippets

Geometry model

The geometry model is a part of the road unit center cross-section (in Fig. 1), which consists of concrete, hydronic heating pipe, air and ice (as shown in Fig. 2). The diameter of the embedded pipes is 16 mm, and the letters of d and s denote the pipe depth and spacing of the embedded pipes, respectively. The model is carried out under the following assumptions:

  • (1)

    The right and left boundaries are adopted the periodic boundary conditions, the bottom boundary is adiabatic and the ice surface is

Results and discussion

The base case was the same as the experimental case, and other variable parameters were presented in Table 1. The ice thickness, pipe spacing, and air temperature fluctuated in the ranges of 320 mm, 80240 mm and 252268 K, respectively.

Conclusions

Open Source Lattice Boltzmann Code was used to study the deicing performances of a road unit driven by a hydronic heating system in severely cold regions of China. Some conclusions were obtained.

When the ice thickness was increased from 3 mm to 20 mm, the heating rate was slightly increased from 6.3 K/h to 6.45 K/h in the preheating and initial melting stages, and from 1.32 K/h to 2.06 K/h in the rapid melting stage, the melting mass was increased from 360 g/m to 762.06 g/m whereas the melting

Acknowledgments

The authors are extremely grateful to the financial supports for this study by the Special Foundation for Major Program of Civil Aviation Administration of China (Grant No. MB20140066), Fundamental Research Funds for the Central Universities (HIT. NSRIF. 2019062) and National Natural Science Foundation of China (Grant No. 51606050).

References (31)

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