Research On The Measurement Of Temperature About The Standard Positive Nozzle Device

Sonic nozzle, also known as the Venturi nozzle, is widely used in various fields,like petroleum, chemical, natural gas, energy saving, environmental protection, andaerospace. It’s also used as gas flow transfer standard, and can be directly used forflow measurement. The standard device based on sonic nozzle is currently dividedinto two kinds, positive pressure method and negative pressure method. There aremany scholars at home and abroad have research on negative pressure method, whilethe positive pressure method is less studied due to high cost and complexity of thefront system. The positive pressure method can be used for flow-meter test at differentpressure conditions, and it’s easy to reach a large flow range, so research on it is veryvaluable.The flow-rate of nozzle is related to upstream stagnation pressure andtemperature according to the nozzle theory, accurate measurement of them is essentialfor calibration. A large stagnation tank is often placed in the upstream of the nozzle,the pressure of the tank changed rapidly at pressure regulating period, and can beaccurately measured, but the temperature changes slowly and there is a rapid declineand then increase of it, this process involves complex knowledge of heat transfer.During the calibration process, only when the temperature is stabled and you can startthe experiment. Now the Pt platinum resistance sensor used for temperaturemeasurement in the standard device has a long response time, it is difficult to track therapid temperature changes accurately, and we couldn’t know the exact temperaturestabilization time. This article based on the positive pressure method Standard deviceof Tianjin University, a temperature change model was established through theoreticalanalysis. The theoretical model was verified by experiment and simulation methods,and proved its correctness, then the real temperature change process was estimated,the temperature stabilization time, and the error of Pt resistance sensor were obtained.Finally, according to uncertainty analysis of the standard device, the error range oftemperature measurement was calculated, if we begin the experiment when the truetemperature stabilized, at low flow-rate the device precision can be ensured, but atlarge flow-rate, the device precision will be out of range, so a real-time dynamictemperature compensation model was designed to compensate the sensor output, reducing the dynamic measurement error. Fluent simulation was also done to analysestagnation temperature distribution of the tank. The result proved that the temperaturedistribution has small influence on temperature measurement and can be ignored.Finally, we also designed a method for temperature pre-estimation, given thestagnation container specifications, the initial pressure and temperature and theself-regulator value adjustment range, then the temperature change process can beestimated through experiments and theoretical models The method can be used fortemperature and pressure estimation on most positive Pressure Method nozzlestandard device and have practical significance.