Intelligent Non-Invasive Thermal Energy Flow Rate Sensor for Laminar and Turbulent Pipe Flows

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Date
2022-03-23
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Virginia Tech
Abstract

This dissertation describes the development of an intelligent non-invasive thermal energy flow rate sensor for laminar and turbulent pipe flows. Energy flow rate is the thermal energy that is carried by a fluid, for example, in a pipe to heat or cool a space in a building. It can be measured by an energy flow rate sensor which consists of a volume flow rate meter and supply and return fluid temperature sensors to bill the users for their energy usage. A non-invasive, low-cost, and easy to install thermal energy flow rate sensor based on thermal interrogation transient heat flux and temperature measurements has been developed to measure fluid velocity and fluid temperature in pipes. This sensor can be used for different pipe diameters, different pipe materials, and different viscous fluids. The transient measurements are made on the outer surface of a pipe by using a heat flux sensor and a thin-film thermocouple which are covered by a thin-film heater. A one-dimensional transient thermal model is applied before and during activation of the external heater along with a parameter estimation code to provide estimates of the fluid heat transfer coefficient and apparent thermal resistance between the thermocouple and the pipe surface. This dissertation contributes to the sensor's development in three ways. First, a new design is developed by using a single layer of Kapton tape with an adhesive (dielectric material) between the thermocouple foils and the pipe wall to isolate the thermocouple electrically from the pipe surface. This new design gives accurate and reliable estimates of the internal mean fluid temperature without environmental interference. Second, this new sensor design is tested for turbulent pipe flows with two different pipe diameters ( = 25.4 mm and = 12.7 mm) and two different viscous fluids (diesel oil and water). Experiments are completed over a large range of fluid velocity from 0.2 m/s to 5.5 m/s and a range of fluid temperature from 20 ℃ to 50 ℃. The estimated parameters, heat transfer coefficient and apparent thermal resistance, are correlated with the fluid velocity and fluid temperature. This sensor gives a good correlation, repeatability, and sensitivity between the estimated parameters and the fluid velocities with an accurate estimation of the fluid temperatures without environmental interference. Third, this sensor is tested for laminar flow in pipes over a range of fluid velocity from 0.049 m/s to 0.45 m/s and a range of fluid temperature from 20 ℃ to 50 ℃. A new empirical correlation between the estimated parameters and the laminar fluid velocity has been developed. The results show that this sensor gives lower sensitivity and accuracy between the estimated parameters and the fluid velocity and fluid temperature for the laminar flow.

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Keywords
non-invasive thermal energy flow rate sensor, heat flux sensor, transient heat flux and temperature measurements, fluid average velocity, fluid temperature, parameter estimation
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