Plate heat exchangers are often required for high performance during secondary energy utilization in recent years. The efficiency of energy utilization can greatly contribute to sustainable development, in response to the increasingly severe energy crises and environmental challenges. In this study, the numerical analysis was conducted on the flow and heat transfer in a gas-to-gas plate heat exchanger. The dimensions of the heat exchange plate were 1 530 mm in length and 750 mm in width, with a spacing of 12 mm between the plates. The cold and hot fluids were exchanged in the form of cross flow. The dimpled plate of the heat exchanger shared two dimpled heights of 6.0 and 3.5 mm. The structural parameters of the dimpled plate were then optimized for the high efficiency of heat exchange. Among them, the 6.0 mm concave pits and convex cells were the supporting contacts of the cold and hot fluid channels, respectively. Simulation analysis was conducted to take the high-temperature flue gas and air as the media of heat exchange. The better performance of heat transfer was achieved in the 6.0 mm concave pits and convex cells, compared with the 3.5 mm ones. Therefore, all 3.5 mm dimples were replaced with 6.0 mm dimples in the plates of heat exchange. Furthermore, the number of dimples of 6.0 mm increased from the original 42 to 189. The longitudinal, herring bone, and transverse arrangement were also optimized on the support contact of the hot fluid channel. Some parameters were calculated under different flow rates of flue gas, including the Nussel number, the flow resistance of the channel, the Performance Evaluation Criterion (PEC) of heat transfer performance, and the pressure difference between the two sides of the plate. The results indicate that better performance was achieved in the longitudinal arrangement of the improved dimpled plate in the heat exchanger under the design condition, compared with the original plate structure. Specifically, the PEC of heat transfer was 1.25, the pressure dropped from 277.02 Pa to 308.31 Pa, the increase rate was 11%, the Nu increased from 11.48 to 15.21, and the performance of heat transfer increased by 32%. The longitudinal arrangement shared the smallest values of the maximum pressure, compared with the rest heat exchangers. The best scheme was then obtained for the improved design. The key factors were also optimized after simulation, such as the heat transfer, flow, and pressure. The dimpled arrangement has significantly improved the performance of the plate heat exchanger. The practical significance and application were provided for the dimpled plate of the heat exchanger.

In order to study the influence of thermal insulation layer thickness and carbon fiber heating wire temperature on the snow and ice melting of the pavement under pavement daily cycle thermal boundary conditions, the heat conduction equation of the conventional asphalt pavement structure is built when the heating wire is laid horizontally, and the numerical solution of the temperature field is obtained by solving the partial differential equation using MATLAB PDE toolbox. The example chooses the freezing meteorological conditions on a certain winter day in Hunan Province, the temperature of the constrained pavement is above 4.8 ℃, and the temperature of the heating wire is 30-50 ℃. The temperature rise rates of the pavement are calculated when the thickness range of the thermal insulation layer is 5-40 mm. Results showed that in the hot summer and cold winter areas represented by Hunan Province, the average temperature rise rate of road surface with a thermal insulation layer thickness of 5mm is about 3.5-9 times higher than that without thermal insulation layer; while that with a thermal insulation layer thickness of 10 mm is increased by 3.55-9.5 times. After the thickness of the thermal insulation layer exceeds 10 mm, the increase trend of the average temperature rise rate of road surface is not obvious. At the same time, the temperature rise rate of the road surface is not only nonlinear with the thickness of the thermal insulation layer but also nonlinear with the temperature of the heating wire. Therefore, it is not that the thicker the thermal insulation layer, the better the temperature rise and defrosting effect of the road surface. In addition, the additional heat insulation layer prevents most of the heat generated by the heating wire from flowing underground, so that the temperature distribution of the road surface is more uniform. The pavement temperatures with insulation are also higher than those without insulation. The simulation results for the cold and harsh places reveal that the heating wire temperature should be increased to 50-70 ℃ when the limited road temperature is likewise over 4.8 ℃, and the effect of insulation layer thickness is still consistent with the example. Theoretically, considering the road surface heating performance and the engineering costs, it is considered that the hot wire temperature of 30-70 ℃ and the thermal insulation layer of 5-10 mm are more suitable. The conclusions are also applicable to cold and severe regions and can provide a reference for choosing the optimum economical thickness of the insulation layer when the heating wire assists the deicing or snow-melting on the road surface with the periodic thermal boundary condition.