Publish Time: 2023-09-04 Origin: Site
Energy conservation and environmental protection is a major project. In order to reduce building heating energy consumption and promote heating energy conservation, many countries and regions have introduced charging based on heat consumption, thereby using economic leverage to encourage users to save energy. This article will introduce the working principle of ultrasonic heat meter, which are widely used in the heating industry.
1、 The working principle of the ultrasonic heat meter from the perspective of construction.
The smart ultrasonic heat meter is composed of several parts, including flow sensors, microprocessors, paired temperature sensors, display and communication. Paired temperature sensors are used to measure water temperature, and ultrasonic flow sensors are used to measure the volume of fluid flowing through. Among them, the flow measurement system composed of ultrasonic flow sensors and microprocessors is the core of the ultrasonic heat meter. The microprocessor is equivalent to the "brain" of an ultrasonic heat meter, whether it is integrating flow signals and temperature signals, or controlling the entire measurement process in a sequential manner, all of which are thanks to the microprocessor. The LCD screen on ultrasonic heat meters is mainly used to display data, and many ultrasonic heat meters can choose to be equipped with communication modules and remote meter reading devices for data communication.
2、 The working principle and derived calculation formula of ultrasonic heat meter.
Taking the time difference method as an example, in general, a pair of ultrasonic transducers are installed directly at both ends of the pipeline channel during measurement. The mirror surface of the reflection column inside the pipeline is fixed at a 45 ° angle to the axis of the pipeline. The inner diameter of the pipeline section is D, and the length of the ultrasonic path is L total (L total=D/2+L+D/2). The propagation speed of ultrasound in static water is c, the water flow speed is V0, the propagation time along the flow is t1, and the propagation time against the flow is t2, so there are:
In practice, we need to correct V by multiplying it by the correction factor K. The actual flow field of liquid velocity in pipelines can be divided into laminar flow, excessive flow, and turbulent flow, and the state of these three flow fields is determined by Reynolds number. The calculation formula for Reynolds number Re is:
Dynamic viscosity coefficient of liquid μ and the density of the liquid ρ. It is also related to the pressure and temperature of the liquid in the pipeline. Once the pressure and temperature of the liquid in the pipeline are known, the dynamic viscosity coefficient of the liquid can be obtained by looking up a table μ and the density of the liquid ρ. Therefore, the magnitude of the correction coefficient K must also be determined by the Reynolds number Re.
3、 The Working Principle and Compensation Setting of the high accuracy ultrasonic heat meter.
(1)Flow compensation
Each caliber of heat meter undergoes full range flow compensation to ensure the accuracy of the meter at different temperatures. The flow accuracy of an ultrasonic heat meter is greatly affected by the base meter, and the flow field curve does not change linearly. When measuring and calculating, piecewise linear fitting is required, and strict matching of the parameters of the base meter and the transducer is required to compensate for the full range flow of the heat meter.
(2)Temperature compensation
Temperature is the main factor affecting the flow measurement of ultrasonic heat meters. The water temperature will affect the changes in ultrasonic sound velocity, causing the water meter to expand and affect cross-sectional area, sound path, etc. To compensate for these changes, temperature compensation will also be added in the design and manufacturing of ultrasonic heat meters.
Compared with mechanical heat meters, the ultrasonic heat meter do not have movable mechanical components, and in principle, their pressure loss is smaller than that of mechanical heat meters. As a measuring instrument, ultrasonic heat meters have high requirements for each individual item such as machining error, component error, and manual assembly error.