Subway operations generate substantial heat, and inadequate dissipation can progressively degrade tunnel thermal conditions. The thermal distribution within the surrounding rock is critical for calculating the load on subway environmental control systems. However, the heat transfer patterns in the surrounding rock for intersecting tunnels remain poorly understood. Therefore, this study employs COMSOL software to numerically analyze the impact of intersecting line layouts on the temperature field distribution within the surrounding rock. Results indicate that when tunnels intersect, heat accumulates in the surrounding rock near the intersection. Compared to the single-tunnel structure, intersecting tunnels exhibit higher peak temperature when reaching dynamic thermal equilibrium, and the time required to achieve equilibrium is longer. Reducing the vertical spacing between intersecting tunnels concentrates heat within the intersection zone, leading to elevated temperature in that area. However, when the vertical spacing exceeds 12 m, the numerical value no longer exhibits significant variation with vertical spacing. The intersection angle also influences the temperature distribution characteristic and numerical value. The smaller intersection angle causes heat to concentrate within the crossing zone, leading to an overall increase in surrounding rock temperature within that area. Additionally, the rate of temperature increase in the rock mass at the intersection zone and the magnitude of temperature at dynamic equilibrium are significantly influenced by geographical factors. The lower the ambient temperature in the climate zone where the intersecting subway tunnels are located, the faster the temperature rise rate at the intersection zone. When heat transfer in the rock mass reaches dynamic equilibrium, the temperature difference at the same monitoring point can reach approximately 10°C between severely cold and temperate regions.

The probe calibration wind tunnel of IFA300 hot-wire anemometer system cannot complete the probe calibration at a given temperature and low flow rate, because the side wall of the calibration wind tunnel has high thermal conductivity. That is to say, when the air flows through the calibration wind tunnel, its temperature will decrease sharply. In view of this structural defect, a measure method is put forward to maintain the temperature of the calibrated airflow by heating the side wall of the calibrated wind tunnel, which greatly widens the temperature range of the calibrated low-speed airflow. This measure adopts repetitive experimental methods to effectively improve the accuracy of the calibration results. The relative error of the test is controlled under 1% for the calibration airflow with temperature from 20 ℃ to 58 ℃, which is much higher than the design accuracy of the IFA300 hot-wire anemometer. In order to adapt to the test of the flow parameters in an enclosed cavity, a set of probe anti-collision control system is designed and manufactured, and the hot-wire probe has been protected well. The temperature and average velocity in the outer normal direction at different heights of the hot wall of the enclosed cavity are measured, which is in good agreement with the literature results.

To evaluate the contribution of a built-in fin-type Trombe wall to reducing indoor heating energy consumption, this study takes a typical residential building in Lanzhou as the research object. Fins are installed on the heat-absorbing surface of the Trombe wall to enhance heat transfer and thereby improve the indoor thermal environment. The results show that the isosceles right-triangle fins with a height of 20 mm, a transverse spacing of 0.20 m, a longitudinal spacing of 0.533 m, and an in-line configuration provide the greatest improvement in heat transfer performance and indoor thermal conditions. Over the entire simulation period, the average Nusselt number (Nu) of the fin-type Trombe wall is 21.28 higher than that of the finless wall. Compared with a conventional room, the energy-saving rates of the finless Trombe wall and fin-type Trombe wall rooms are 36.38% and 44.63% respectively, meaning the fin-type Trombe wall yields an additional 8.25% energy-saving improvement.

Proper orthogonal decomposition (POD) reduced-order model can save computing time by reducing the dimension of physical problems and reconstructing physical fields. It is especially suitable for large-scale complex problems in engineering, such as ground heat utilization, sea energy development, mineral exploitation, multiphase flow and flow and heat transfer with complex structure. In this paper, the POD reduced-order model was used to calculate the heat transfer in a flat tube bank fin heat exchanger. The calculating results of the finite volume method (FVM) were adopted as the snapshot samples. Singular value decomposition method was used to decompose the samples to obtain a series of bases and corresponding coefficients on sampling conditions. With these coefficients, interpolation method was used to calculate the coefficients on predicting conditions. And the physical field has been reconstructed using the bases and the interpolated coefficients directly.

In the calculation of heat transfer unit of flat tube fin heat exchanger, air-side Reynolds number, transverse tube spacing and the fin spacing were chosen as the variables. The results obtained by the POD method are in good agreement with the results calculated by the FVM. Moreover, the POD reduced-order model presented in this paper is more advantageous in comparison with the FVM in terms of accuracy, suitability, and computational speed.