Clamp-on measurements of fluid flow in small-diameter metal pipes using ultrasonic guided waves

Clamp-on ultrasonic transit time difference is used extensively to calculate the volumetric flow rate of a fluid through a pipe. The operating principle is that waves traveling along a path that is generally against the flow direction take longer to travel the same path than waves traveling along the same path in the opposite direction. The transit time difference between the waves traveling in opposite directions can be used to calculate the flow rate through the pipe, by applying suitable mathematical correction factors. The approach is non-disruptive and noninvasive and can be retrospectively fit to pipes and easily relocated to different positions. When ultrasonic clamp-on transducers are attached to pipes with diameters of less than 30 mm and a wall thickness of less than a few millimeters, the resulting guided waves can appear confusing and produce very different signals to those observed on larger diameter pipes. The experimentally observed behavior of these guided waves in fluid-filled, small-diameter pipes is analyzed, modeled, and explained. Experiments are performed in copper pipes of sizes that are commonly used in buildings, and accurate measurements of water flow rates are taken down to a few milliliters per second. This technique presents new possibilities for smart metering of water supplies, where the positioning of the small clamp-on transducers is not sensitive to the variations in water temperature, and low-power electronics can be used

Improved HVAC energy throughput system

Currently heating, ventilation and air conditioning (HVAC) systems are difficult and costly to monitor for energy efficiency performance and reliability. As buildings evolve, they will require higher levels of insulation and air tightness which will require ventilation systems to provide the minimum number of air changes and reduced energy usage by recovering heat from the air before it is expelled. This will necessitate the need for monitoring of the operating performance of these systems so that air quality or building energy efficiency is not detrimentally affected. A typical duct airflow monitoring device uses a pressure differential method to determine the airflow rate but they are fragile, expensive and create an additional pressure loss. The monitoring of airflow rates can indicate problems in the design, installation and operation of a HVAC system. One of the possible alternatives to using pressure differential type devices such as Pitot tube/arrays, orifice plates and Venturis is to use an ultrasonic flow rate sensor, but historically their high cost has restricted their use in HVAC systems. This project has looked at improving on existing measuring systems by developing an ultrasonic in-duct flowmeter system to measure the mean airflow, temperature and humidity of a ventilation duct so that a comparative energy level can be accurately deduced. A proof of concept in-duct ultrasonic airflow monitoring device has been developed and has obtained results within ±3.5% RMS of a Venturi airflow measuring device. Matlab code for a Monte Carlo acoustic ray/particle tracing ultrasonic flowmeter simulation has been developed to study the effects of non-ideal installation scenarios. The fully developed centreline computational fluid dynamics (CFD) mean flow velocity to duct total mean flow velocity error can be up to 13%. Analysis of the CFD data for various duct scenarios has shown that this could be reduced to below 5% by using a transducer offset of approximately ±0.25 duct diameters or widths from the centreline at distances as close as one duct hydraulic diameter from an upstream disturbance, such as caused by a bend

State-of-the-Art Measurement Instrumentation and MostRecent Measurement Techniques for Parabolic TroughCollector Fields

The presented review gives reliable information about the currently used measurementinstrumentation in parabolic trough fields and recent monitoring approaches. The usually built-inmeasurement equipment in the solar field, clamp-on systems for flexible measurements of tempera-ture and flow, solar irradiance measurements, standard meteorological equipment, laboratory devicesfor heat transfer fluid analyses and instruments related to the tracking of solar collector assembliesare presented in detail. The measurement systems are reported with their measurement uncertainty,approximate costs and usual installation location for the built-in instrumentation. Specific findingsrelated to the installation and operation of the measurement devices are presented. The usuallyinstalled instrumentation delivers a lot of measurements all over the field at the expense of mea-surement accuracy, compared to special test facility equipment. Recently introduced measurementapproaches can improve the standard instrumentation in terms of accuracy, frequency, spatial distri-bution or can even extend the amount of measurands. The information about available measurandsis the basis for future operation and maintenance solutions based on data-driven approaches