## 5 Conclusions  
A heat exchanger was designed to achieve heat exchange between the hot gas and the cold gas of a temperature control valve system without mixing, effectively improving the cold gas and the hot gas of the original temperature control system. A disadvantage was the unstable flow from the back to the outlet. Through CAD modeling of the temperature control value system, an Ansys simulation was designed to qualitatively analyze the influence of the temperature at the outlet of the hot path on the temperature control value system. Then, a characteristics test experiment for the temperature control valve and heat exchanger was designed. A current was used to control the torque motor, a series of data were collected, the simulation conclusion was verified, and the possible reasons for the temperature control valve system's effect on the change of the temperature at the outlet of the hot path were analyzed based on the two aspects of simulation and experiment. Based on the affecting factor, a four-segment identification experiment was designed to analyze the dynamic characteristics of the heat exchanger. According to the experimental data, a steady-state model of the heat exchanger was obtained by a 25-point orthogonal experiment. Taking the predicted hot-side flow rate of the heat exchanger under different flow conditions as input, the heat exchanger model was fitted and dynamically analyzed, obtaining the transfer function of heat exchanger under different working conditions.  
A mathematical model of the temperature control system was established for the temperature control system. Dynamic simulation of the temperature control valve was carried out by Ansys. The factors affecting the temperature changing of the hot-side outlet were the flow rate of the cold-side gas, the flow rate of the hot-side gas, heat exchanger efficiency and the NTU coefficients. Controlling the butterfly valve rotation could effectively control the cold-side of the gas flow to achieve the hot-side of the gas temperature control. The dynamic time constant of heat exchanger, combined with the given phase margin and current phase angle, could be used to calculate the maximum lead angle to calculate the real-time PID parameters of the control system and realize the adaptive control of the temperature valve motor.  
Compared with the current temperature control strategies based on the mixing of hot-side and cold-side gases in the air mixing chamber, the control strategy proposed in this paper can be used without hot and cold mixing directly. Therefore, the hot-side gas can be directly controlled, the control efficiency can be improved, and the energy consumption generated by the air mixing chamber temperature difference can be reduced.  
Future work will include fit the experimental dynamic time constant of the heat exchanger. According to the given phase margin and the current angle of the system, the cutoff frequency, open-loop transfer function, and maximum advance angle of the system can be calculated. The real-time PID parameters of the temperature control valve can be calculated to realize the adaptive control of the temperature control system under different working conditions.  
Data curation, Z.S.; formal analysis, X.Q.; investigation, Q.L.; methodology, Q.L.; project administration, Z.S. and Z.W.; resources, Z.S.; supervision, X.Q. and Z.W.; validation, M.D.; writing--original draft, Z.S., M.D. and Q.L.; writing--review & editing, M.D. and Z.W. All authors have read and agreed to the published version of the manuscript.  
This work was funded by Shaanxi province Major Science and Technology projects (No. 2019 zdzx01-01-02) and the key research and development program of Shaanxi province (No. 2020 ZDLGY06-10, No. 2021 GY-302, No. 2022 ZDLGY03-06).  
Not applicable.  
The data that support the findings of the study are available from the corresponding author, Z.W., upon reasonable request.  
The authors declare no conflict of interest.