Impact forces in pneumatic conveying bends are becoming more significant in industry, and in research centres, as the size of pneumatic conveying pipeline bores increase to achieve high product throughput with the greater efficiency possible from a dense phase conveying system. This paper continues the authors' work in investigating this issue by undertaking a detailed comparison of the equations given for contact time and maximum contact force, from a range of literature with applications to various impact events both practical and theoretical. These predictions are also compared: to experimental results presented previously by the authors, to further results from an electrical resistance measurement system, and to a limited extent to experimental results from existing literature. The equations that are most reliable consider the elasticity of the particle and the elasticity of the impact surface, as well as the particle size, and also reflect a weak dependence on impact velocity. Whilst the electrical resistance measurement method has provided a useful verification of a number of theoretical predictions, its application is limited and is not suitable for the majority of particles that are conveyed pneumatically. Future work will expand on the particles tested using this method, and will also work on understanding better the influence of the force sensor on contact time and maximum force measurement.

•Using a transducer to measure impact force is often not ideal.•Using the impacting particle and surface as the transducer may be better.•Electrical conductance may provide a suitable means.•It was found that the technique was not suitable – due to low repeatability.

Experiments with a gas–solids dense phase pneumatic pipe flow have been undertaken: (1) to determine the average heat transfer coefficient between a heated wall and a gas–solids dense phase flow; (2) to investigate the heat transfer mechanisms of pneumatically conveyed dense phase flow in detail as the system operates by injecting heat energy into the pipeline to heat the pipe section, as a result, to heat the dense phase gas–solids׳ plugs, and measuring the resultant change in solids׳ plug and heated wall׳s temperatures. The experimental results suggest that the average heat transfer coefficient between the heated wall and the gas–solids dense flow displays an approximately linear relationship with the solids loading ratio. A larger solids׳ loading ratio results in a higher average heat transfer coefficient. The results have been compared with those of Moriyama et al. although the overlap of data ranges is limited. Experimental results also indicate that the inner wall temperature is able to reflect the energy change when each solids׳ plug is being through the heated region. The calculated gradient change of the outer wall temperature–time history T1 measured is consistent with the fluctuation of the wavering of the inner wall temperature along with the present of solids׳ plugs in the heated region.

An ideal mass low meter should have the following properties: it should be non-invasive so as not to disrupt the low profile; it should be easily installed on the conveying line to provide on-line and continuous measurements; it should be able to provide an accurate indication of the mass flow rate regardless of the orientation of the measurement section, inhomogeneities in the solids' distribution, irregularities in the velocity profile, or variations in particle size, moisture content and material properties. A mass flow meter as described in this paper has been developed which uses a thermal method, a direct, non-invasive approach to measuring the mass flow rate. The thermal method uses the principle of heat transfer to solid particles in a flowing fluid to determine the mass low rate of particles. The mass flow meter is designed such that temperature sensors are located at two ends of a heated pipe section. In the experiments carried out, measurements of gas and solids' temperature were taken and used to calculate the heat transferred to the solids. The mass flow rate obtained using the thermal mass flow meter was compared to that using load cells. The results obtained are analysed and presented in this paper.

The in-line measurement of solids mass flow rate in a prototype industrial scale pneumatic conveying pipeline by a thermal method has been investigated over a range of dilute conveying conditions. A thermal method of determining solids mass flow rate should, in principle, be capable of achieving a reliable measurement regardless of; inhomogeneities in solids' distribution, irregularities in velocity profile and variations in particle size or shape. The instrument described in this article operates by the injection of heat energy into the pipeline by way of a heated section and measuring the resultant change in solids' temperature using infrared sensors. Initial results from the thermal instrument are compared with measurements from a gain in weight system showing good correlation. The importance of sensor window condition and temperature on measurement is discussed.

Thermal mass flow meters can, in theory, be used in pneumatic conveying applications to provide a reliable monitoring of the mass flow rate of solids being transported in a stream of gas. Accurate measurement of temperature is necessary for the mass flow rate to be reliably determined. Direct measurement of temperature of particulate solids being conveyed pneumatically can be achieved, in principle, with the use of infra-red (IR) detectors. This has been done in previous work for the measurement of solids’ temperatures in a pneumatic conveying line where windows were employed. This paper investigates the influence of windows on the temperature measurement process. We investigate specifically the effect of dust deposited on the window surface in conjunction with the window temperature. The results show that if the window is not ideal, measurements of temperatures above the temperature of the window will be below actual, and measurement of target temperatures below the window temperature will be higher than actual. A simple assumption that a non-ideal window would attenuate the IR signal and result in lower temperature measurements is therefore, not valid. An analysis is offered that explains the results obtained.

Mass and energy balances are required in power generation, chemical, pharmaceutical, food and commodity transfer processes in order to achieve efficient utilization of energy and raw materials. There is a need for accurate, reliable, on-line, continuous and non-invasive measurement of solids' mass flow rate in many industrial processes mentioned above. Thermal flowmeters, in theory, provide a true indication of the mass flow of solids in pneumatic conveying pipelines.A complicated heat transfer between a pipe wall and a gas-solid flow in a conveying pipeline inevitably takes place in a thermal solids' mass flow measurement process. A study of heat transfer mechanisms to pneumatically conveyed gas-solid dense phase flow as a means to mass flow rate measurement has been conducted experimentally and numerically to evaluate the heat transfer coefficient between the hot wall and the gas-solid dense phase flow. The prediction of the heat transfer coefficient is compared with the experimental findings. It was found that the heat transfer coefficient between the pipe wall and the gas-solid dense flow is a function of solids loading ratio. Increasing the gas stream velocity significantly augments the heat transfer between the hot wall and the gas-solid dense phase flow. (C) 2010 Elsevier B.V. All rights reserved.

The flexibility of routing offered by pneumatic conveying systems allows pipelines to fit into a minimal plant footprint. Current trends in the reduction of energy costs and regulatory drivers on waste and the environment, as well as process demands, require pneumatic conveying systems to operate efficiently with low product damage. A resulting increase in the number of dense phase (low velocity) systems has led to greater interest in the analysis of forces at the bends of these pipelines. In dense phase systems the material may move along the pipeline in plugs and these plugs cause contact forces at bends that need to be considered in the design. Despite the increased interest in the analysis of these forces, there is no standard method of determining them. In order to understand better the interaction of the particles with the bend, an investigation of the interaction between solid particles and an impact surface is to be undertaken, primarily the measurement of impact force. The aim is to use these data to inform better computational models and engineering practice. This paper reports on the work completed to date in the development of an experimental rig and the initial results from these developments.

Thermal flowmeters based on the heat transfer principle can, in theory, provide direct mass flow measurement of gas-solids two-phase flow. They are applicable to a wide range of industrial process, where there is a need for accurate, reliable, on-line, continuous and non-invasive measurement of solids' mass flow rate. A non-invasive thermal system has been proposed. The key issues have been highlighted and the results from initial simulations and experiments have indicated that the technique is worthy of further and more detailed investigation.This paper concentrates on: (i) measuring the temperature of a single particle both before and after passage through a heated region; (ii) describing the transient thermal characteristics of the gas and the single particle in the heated region; and (iii) characterizing the heat transfer from the hot pipe wall to the gas and from the gas to the single particle. (C) 2007 Elsevier Ltd. All rights reserved.

Pneumatic conveying of powdered and granular materials is a very common transport technology across a broad range of industries, for example, chemicals, cosmetics, pharmaceuticals, and power generation. As the demands of these industries for greater efficiency increases and to comply with environmental regulations there is a need for a more fundamental understanding of the behavior of materials in pneumatic conveying systems. The approach presented in this article is to develop a model of a section of pneumatic conveying line, a horizontal or vertical 90 degrees bend, in the commercial CFD software package FLUENT and to describe the multiphase flow behavior by the mixture or Eulerian method. Models of this type have been used in the past to show qualitative and quantitative agreement between model and experiment. The model results presented were compared with experimental data gathered from an industrial-scale pneumatic conveying test system. Broad qualitative agreement in trends and flow patterns were found. Quantitative comparisons were less uniform, with predictions from around 10% to 90% different from experimental results, depending on conveying conditions and bend orientation.

An experimental technique to measure various characteristics of plug flow in dense phase pneumatic conveying systems based on the unique characteristics of plug flow, i.e., the fluctuation of axial pressure drop along a pipeline and pressure difference in the radial direction at the back of a plug, was developed by Li et al. (2002). Based on this work, a further experimental study combined with numerical modeling was carried out to describe the structure of plugs through the analysis of the measurements of pressure difference in both axial and radial directions. A theoretical explanation of these pressure differences was proposed and agrees very well with the recorded signals of pressure difference from differential transducers. This explanation will prove useful in understanding plug structures in industrial applications.