Research On Temperature Control Characteristics Of Thermostatic Valve

Thermostatic valve is a new type of equipment for controlling fluid temperature. By opening/closing, or the opening size of cold/hot fluid intake which drived by temperature-sensing medium's expansion strength with temperature varying, it can regulating the proper proportion between cool and hot fluid entering the valve, so as to controls exporting temperature of mixed fluid temperature.Because of simple structure, reliable operation, accurate temperature control, without extra power such as electricity or compressed air and automatization, thermostatic valve is widely used for temperature controlling of various kind of heat exchange system such as the civil heating and hot water supply equipment.At the same time, the thermostatic valve study is an important part of energy-saving technology research.The main study includes:(1) The thermostatic valve mathematical model of instantaneous temperature control is deduced.With an integrated test-bed ,which is composed of sensors, smart instrumentation, data collection, computer and industrial control configuration software, experiments of basic temperature control characteristics of thermostatic valve,the influence of major components parameters on the outlet water temperature, and influence significant of major components parameters on the outlet water temperature, are carried out.The results show that: 1) the outlet water temperature change range is±2℃,and the static characteristics of thermostatic valve are linearity and small static deviation. 2) the reset spring preload have a certain impact on the outlet water temperature, so this preload should not be too large or too small, and matched with thermostat temperature control range; greater thermostat expansion coefficient is favorable for preciser temperature control of outlet water temperature; With the largest shutter opening size increasing, thermostatic valve is more vulnerable to cold &hot water pressure,and not conducive to control the outlet water temperature,thus its value should be reduced as much as possible while thermostatic valve meet the circulation ability. 3) The significant influence experiment of major thermostatic valve components provides the selection principle of their parameters, due to produce the minimum temperature deviations.(2) With FLUENT software, the geometric models and physical models of thermostatic valve mixed cabin are established. Under different inlet pressure, the changing trend of pressure distribution, temperature distribution and velocity vector of valve internal flow are simulated, in order to explore the impact of cold&hot water pressure on the outlet water temperature. And influences of shutter's largest opening size on fluid flow are Analyzed, aiming at provide the basis of thermostatic valve structure optimization.The results show that the impact of cold water pressure changes on fluid flow is more significant than hot water pressure, so the structural design of thermostatic valve should focus on the cold water channel for resistance decreased. The shutter largest opening size should not be too large, and minimize its value while thermostatic valve can meet the circulation ability. Based on this principle, the thermostatic valve shutter largest opening size should be 0.65 mm in the paper.(3) Without considering the force of hydraulic pressure, the mathematical model of the Second concussion system, which is composed of shutter, actuator and the reset spring, is established.Through time-domain and frequency-domain analyses, the theorems of improving the dynamic characteristics of thermostatic valve fluid control components are got as following:1) In order to optimize the dynamic system characteristics for optimal damping, the programme that by changing the quality of thermostatic valve flow control components is more effective than that of changing the reset spring stiffness; 2) reduce the quality of flow control components can significantly improve system dynamic characteristics and therefore can explore new materials to achieve; 3) Changing the reset spring stiffness can only optimize the dynamic system indicators partly, as existing correlation between the reset spring stiffness and thermostat, changing spring stiffness should be considered.