EP2440890A2

EP2440890A2 - Measurement of mass flow

Info

Publication number: EP2440890A2
Application number: EP10737611A
Authority: EP
Inventors: John R. Pugh; Donald Mcglinchey; Elizabeth A. Knight; Paul Mckenna; Yingna Zheng; Qiang Liu
Original assignee: University of Glasgow; Glasgow Caledonian University
Current assignee: University of Glasgow; Glasgow Caledonian University
Priority date: 2009-06-11
Filing date: 2010-06-11
Publication date: 2012-04-18
Also published as: WO2010142999A2; GB0910035D0; GB2470941A; WO2010142999A3

Abstract

A system and method for measuring mass flow of a non-gaseous phase (4) of material such as a solid particulate are described. The material flows through a conduit of which a section (14) is heated or cooled. One temperature sensor (6) is provided upstream of this section and at least another temperature sensor (7, 8) is provided downstream of it. These temperature sensors are adapted to measure the temperature of material in the non-gaseous phase directly. The section is heated or cooled for a first period of time and then neither heated nor cooled for a second period. A third temperature sensor (10) is provided in good thermal contact with the heated or cooled section – this temperature sensor. The temperature sensors measure the temperature of the non-gaseous phase of the material flowing the conduit in at least the second period of time. The mass flow of the non-gaseous phase of the material is calculated from the measurements of temperature.

Description

MEASUREMENT OF MASS FLOW

Field of the Invention

The invention relates to a method and an apparatus for measurement of mass flow In particular, embodiments relate to the measurement of mass flow for a non-gaseous phase, such as a solid phase, in a two-phase flow

Background to the Invention

In a number of contexts, bulk solids are most effectively conveyed by pneumatic conveying through pipelines This is done in power plants (for example, to convey combustible material such as coal to a combustion chamber) and in manufacturing (for example, to convey raw or part-processed materials into manufacturing machinery) Typically, powder or granular solids are added to a moving gas stream, transported through pipes to a desired destination, where the solids are then collected or consumed Transport may be in a dilute phase (in which solids at a concentration of 1 % or less, are suspended in the gas stream and gas velocities are typically above 20 m/s) or a dense phase (in which the solids concentration may be over 30% with gas velocities typically less than 5 m/s and with, for example, a significant pressure drop along the pipeline), or in an intermediate state between the two The mode of solid flow may vary, with a suspension in a dilute phase to plugs, dunes and moving beds in a dense phase In general terms, these systems can be considered to form a gas-solid two-phase mixture

In many applications it is desirable to be able to measure accurately the mass flow through such a system - while this may be possible in many systems in an integrated way (simply by determining the total mass collected at the end of the system at a given time), in others it will not be possible, and even where it is possible, this may not provide an adequate characterisation of the behaviour of the solid material in the pipeline There have therefore been many attempts to provide accurate measurement of mass flow within the system itself

One class of approaches involves indirect measurement of mass flow by measuring volumetric concentration and multiplying it by solids velocity These approaches may be accurate in suitable flow regimes, but are not sufficiently robust to a wide range of flow regimes to be effective in all environments It may be difficult in some flow regimes to achieve effective velocity measurement, and particularly to achieve the mass-weighted average velocity needed for this calculation Volumetric approaches, which also include such approaches as those based on capacitive measurement, are generally found to be very sensitive to extraneous factors such as moisture, particle size and chemical composition

Another class of approaches involves direct sensing of a property of the mass flow One approach uses an appropriately shaped flow line and measurement of Coπolis force - such Coriolis flowmeters are used routinely to measure liquid flows These may be less suitable for the flow of solids, where pipe loops and bends can lead to unwanted effects Abrasion would provide a practical problem that would be difficult to address effectively

Another form of direct measurement uses thermal measurement This approach has apparent advantages, as it appears less likely to be affected by extraneous factors Measurement devices have been developed which operate by injection of heat energy into a fluid field and measuring the resulting heat flow with appropriate sensors

A non-invasive form of thermal measurement was discussed in Moπyama, T et al (1985), "Mass flow meter using heat transfer for dense phase solid gas two-phase flow", Proc lnt Conf on Fluid Control and Measurement, Tokyo, Japan, 795-800 In this system, thermocouples were used to measure the temperatures of a pipe wall at five different detection locations along a pipeline The mass flow rate was calculated through a heat balance approach This approach provided measurement error of less than 10% in the experimental system studied, but a time constant of 1 5 minutes, which is a iimescaJe much longer than that of many flow phenomena, leaving this approach with a time response inappropriate to applications where such phenomena would need to be considered

Other thermal approaches have involved insertion of sensors into the flow Examples are discussed in Kurz J (1992), "Characteristics and applications of industrial thermal mass flow transmitters", in Proceedings of 47^th Annual Symposium on Instrumentation for the Process Industries, USA, and in Li C X et al (2001 ), "Gas-solids mass flow detection based on thermal multi-sensors data fusion techniques", Journal of Huazhong University of Science & Technology, 29, pp 50-52 However, severe wear problems are likely with arrangements of this type, iendermg these approaches unsuitable for the metering of bulk solids flowing in pneumatic pipelines

Thermal approaches generally involve keeping a section of the measurement system at a constant temperature, and establishing stable temperature measurements upstream and downstream of this section and using the temperature difference between these measurements to determine mass flow Variations in flow lead to adjustments to achieve a new equilibrium, in which it is still possible to measure the power supplied to the system, but the time required for the new equilibrium to be established may affect the determination of mass flow

There therefore remains a need for accurate measurement of mass flow of solids in pneumatic conveying systems with measurement systems which are robust and have a time response sufficient to allow real time observation on appropriate timescales, so that flow phenomena (such as the passage of a plug of solids material) can be observed Summary of the Invention

In a first aspect, the invention provides a method of measuring mass flow of a non-gaseous phase of material, the method comprising providing a conduit having a heating or cooling means for changing the temperature of material flowing in the conduit, and providing a first temperature sensor upstream of the heating or cooling means and a second temperature sensor downstream of the heating or cooling means, both the first and the second temperature sensor being adapted to measure directly a temperature of a non-gaseous phase of material flowing in the conduit, heating or cooling a section of the conduit for a first period of time and not heating or cooling the section of the conduit for a second period of time, providing a third temperature sensor in good thermal contact with the section of the conduit, whereby heat transfers between the section of the conduit and the material flowing in the conduit in both the first and the second period of time, and wherein both the first and the second temperature sensor measure the temperature of the non-gaseous phase of the mateπal flowing the conduit in at least the second period of time and the third temperature sensor measures the temperature of the section of the conduit and thereby provides a measure of energy transfer to the material flowing in the conduit, and calculating the mass flow of the non-gaseous phase of the mateπal from the measurements of temperature

This approach allows for mass flow of the non-gaseous phase to be measured accurately, as there is a metered supply of heat into the system - in this approach, mass flow is measured when no heat is provided into the system (and may also be measured when heat is provided too), though heat is transferred through the section of the conduit into the mateπal of the flow during this time Appropriate choice of temperature sensor leads to an extremely responsive system

This arrangement is particularly suitable where the material forms a two phase system comprising a gaseous phase and a non-gaseous phase, and advantageously the contribution of heat lost to the gaseous phase is calculated and allowed for before calculating the mass flow of the non-gaseous phase The method may be adapted in particular for arrangements in which the non-gaseous phase comprises a solid phase particulate

While it is found to be advantageous not to keep the temperature of the heated or cooled section constant as in the prior art, it is found to be desirable that during measurement of the mass flow the temperature of the heated or cooled section of the conduit is kept within a predetermined temperature range This allows certain forms of loss or error — such as loss of heat outside the system - to be kept constant or else easily compensated for Preferably, there is a repeating heating cycle during operation of the method in which the first period is followed by the second period to form one full cycle This allows for effective metering of power The relative length of the two periods or the heating (or cooling) power may be adjusted in order to keep the heated or cooled section within the predetermined temperature range Measurements of temperature, and hence the rate of change of temperature, may advantageously take place throughout the whole cycle

Advantageously, the heated or cooled section is thermally separated from other parts of the conduit, for example by use of insulating gaskets This enables measurement of the change of the heated or cooled section to provide a reliable measure of the power transferred to material within the section of the conduit

In a second aspect, the invention provides a measuring system for measuring mass flow of a non-gaseous phase of material, the measuring system comprising heating or cooling means, a conduit for the material to flow through, including a conduit section adapted for heating or cooling by the cooUng means, a heating controller, adapted to control the heating or cooling means to provide or remove heat to the conduit section in a first period of time but not in a succeeding second period of time, a first temperature sensor upstream of the conduit section and a second temperature sensor downstream of the conduit section, each temperature sensor being adapted to measure directly a temperature of a non-gaseous phase of the material, and a third temperature sensor in good thermal contact with the conduit section to measures the temperature of the conduit section and thereby provide a measure of energy transfer to the material flowing in the conduit, and a system controller, programmed to receive measurements from the temperature sensors in at least the second period of time and to calculate the mass flow of the non-gaseous phase therefrom

This measuring system may further comprise one or more further tempeiature sensors downstream of the heated or cooled section, whereby each of the second and the one or more further temperature sensors are adapted to measure the temperature of non-gaseous material in a different part of the conduit This allows for accurate determination of the mass flow of the non-gaseous phase when there is more than one mode of flow present in the conduit - for example, one temperature sensor could be positioned to detect duno-like movement at the bottom of a conduit, whereas others could be positioned so as to detect suspended particles or plugs of material

Preferably, the first and second temperature sensors comprise IR detectors These offer a particularly good choice for providing direct measurement of the non-gaseous material in the conduit, as they may be recessed within the conduit (so that they will be easier to protect from abrasion) but will still be able to measure temperature directly, rather than indirectly (as would be the case for a thermocouple located outside the conduit itself, even if in good thermal contact with it)

It is also preferred that the conduit section is formed primarily of copper, or a similar material of high thermal conductivity This provides for very good thermal transfer between the heating or cooling means and the material in the conduit, and this enables more accurate measurement of mass flow to be made

Specific Embodiments of the Invention

Specific embodiments of the invention will now be described, by way of example, with reference to the accompanying drawings, of which

Figure 1 shows an embodiment of a system for measuring mass flow of a non-gaseous component in a flow,

Figure 2 illustrates thermal transfer to a non-gaseous component in a two-phase flow in an arrangement of the type shown in Figure 1 ,

Figure 3 illustrates variables in a calculation of heat transfer in a two-phase flow which may be employed in embodiments of the invention,

Figure 4 shows steps performed in an embodiment of a method for measuring mass flow of a non-gaseous component suitable for use for a two phase flow,

Figuies 5A, 5B and 5C illustrate different modes of flow for a solid phase in a two-phase flow, and

Figure 6 illustrates a part of a further embodiment of a system for measuring mass flow using multiple temperature sensors downstream of a heated section

The elements of a system for measuring mass flow of a non-gaseous component suitable for use for a two phase flow will first be described The theoretical basis for measurement of mass flow in this system will then be discussed After this, the measurements of system variables necessary to provide a result for mass flow of a non-gaseous component are considered in further detail Alternative embodiments of the invention suitable for use in measuring specific modes and types of non-gaseous phase flow are then considered Figure 1 shows the elements of an embodiment of a system for measuring mass flow of a non-gaseous component of a flow - this arrangement is particularly suitable for a pneumatic conveying system in which a solid component is transported by a gaseous phase The measurement system 1 is included as a part of a larger materials transport system (not shown) This may be of any type in which two-phase flow is used to transport materials - considerations arising for volatile or sensitive materials are discussed further below The input 2 to the measurement system admits materials from upstream in the materials transport system (and hence from the source of the materials), and the output 3 to the measurement system passes the materials downstream in the materials transport system towards their eventual destination As indicated, the measurement system is adapted for two-phase flow - in the embodiment shown in Figure 1 , this comprises a solid phase 4 and a gas phase 5 As further discussed below, embodiments of the invention are provided which are suitable for mass flow for widely varying flow conditions and flow types for the solid phase 4 and for other non-gaseous phases

The measurement system 1 may therefore form an integrated part of the materials transport system and may be designed to have no significant effect on the overall flow conditions within the materials transport system Alternatively, the materials transport system may be configured to control the flow within the measurement system to some degree - for example, by appropriate geometry upstream (or even downstream) of the measurement system to provide an expected flow speed or flow conditions (such as better mixing of the solid and gas phases) This may only be required for particular materials systems, but such conditioning may improve measurement in such systems

The measurement system comprises a length of conduit which has a heated section 14 between a first unheated section 15 and a second unheated section 16 The conduit in the heated section 14 is designed for rapid thermal transfer, for reasons discussed below Copper is a particularly suitable choice, though other high thermal transfer materials (for example other metals of high thermal conductivity) may be suitable choices - the choice may be to some degiee determined by the materials to be transported in the system (the inner wall of the conduit should not, for example, be made of a material that will be coiroded by or otherwise react with the materials to be transported) The heated section 14 is thermally separated from the unheated sections 15, 16 by thermally insulating gaskets 19 - as will be discussed below, this is desiiable to ensure that the measure of the temperature change in the heated section 14 is a reliable measure of the energy transmitted to the material flowing in the heated section 14 The heated section 14 is in good thermal contact - preferably extended thermal contact along the heated section 14 - with a heater 12 In an alternative to the illustrated embodiment, the heater 12 may be integrated with the heated section 14 of the conduit to provide good and consistent thermal contact between the two The choice of heater 12 will depend on the requirements placed on it, which include the amount of heat transfer required and the geometry of the measurement system 1 For a relatively narrow conduit, a mica nozzle heater will be a suitable choice For a larger conduit, heating tape may provide an alternative choice The heater 12 needs to provide heat in a way which is consistent and easily measured - electrical heating provides easy measurement of the power that is supplied to the measuring system 1 Although this is not shown, the heater 12 and heated section 14 of the measuring system are highly insulated so that much the greater part of the heat supplied passes in to the heated section 14 and so into the materials carried in the conduit Losses outside the system can thus be kept small, and preferably relatively constant, so that they can be compensated for easily These losses can be kept relatively constant by keeping the operating temperature of the heater 12 and heated section 14 reasonably stable (although, as discussed befow, this does not require the heated section 14 to be kept at a fixed temperature)

The temperature of the heated section is measured by a temperature sensor 10 and the power supplied to the heater 12 is determined by a heater controller 9 This temperature sensor 10 does not need as fast a response as the temperature sensors measuring the temperature of the flowing material, but it should have a sufficiently fast response that the change in temperature of the heated section 14 measured reflects the thermal energy transferred fiom the heated section 14 to the material flowing within it The temperature sensor 10 provides its output to a system controller 11 , which may be a suitably programmed computing device This system controller 1 1 also controls and interacts with the heater controllei 9 From these sources the system controller receives or determines two main system variables - the temperature of the heated section 14 and the power supplied to the measurement system by the heater 12 In order to enable mass flow to be calculated, information concerning the temperature of the solid material 4 carried through the measurement system 1 is also required, together with the specific heat capacity and (in determination of temperature by infrared sensing) the emissivity of the solid material itself Alternatively the relevant combination of factors such as specific heat capacity and emissivity can be inferred through calibration

The temperature of the solid material 4 is captured using direct but non-invasive measurement - specifically, by using IR detectors within the conduit of the measurement system 1 to determine the temperature of the non-gaseous phase by direct IR measurement This does not significantly disturb the materials flow, is an accurate measure of the temperature of the phase itself, and allows measurement with a time response period which corresponds to actual flow conditions Tempeiature measurement is required both upstream and downstream of the heated section 14, the key consideration for determination of the mass flow being the difference between the temperature upstream of the heated section 14 and the temperature downstream of the heated section after heat has been transferred to the material but before it has been lost to other system components Upstream temperature sensor 6 is located before the heated section, whereas downstream temperature sensors 7 and 8 are located after the heated section Mass flow measurements may be made in a system with a single downstream temperature sensor, but the use of multiple downstream temperature sensors allows for more sophisticated and more accurate modelling of mass flow in certain materials systems, as will be discussed further below

The temperature sensors 6, 7, 8 should be appropriately constructed for, or protected from, the mass flow conditions to be expected Where the mass flow comprises solid material, there are significant concerns that the sensors could become degraded (for example, by damage to IR detector windows) or clogged (if the sensors are inset into the pipe) For efficient operation of such an arrangement, it may be desirable to take additional measures against such risk The detector positioning may be optimised to minimise the risk of clogging by solids mass flows An IR detector window may be provided with a hard coating to reduce the risk of degradation, and a gas flow may be directed across the window itself to ensure that it remains cleai These, and other known approaches to preventing degradation of windows and direct sensing in a pipe with solid materials flows, may be used

Measurements from the upstream and downstream temperature sensors are received at the system controller 1 1 The system controller 1 1 is programmed to obtain measurements of mass flow from the system variables described above by use of a mathematical model described below The choice of components indicated above enables the measurement system 1 to provide values for mass flow of a non-gaseous phase such as solid phase 4 dynamically at rates appropriate to rates of fluid flow through a system As indicated below, this design of measurement system 1 is sufficiently responsive to perform effectively even if flow is highly variable (for example, for flows which include intermittent appearances of plugs of solid material in the system, and for varying speeds of movement of solid material where more than one flow regime exists)

A significant consideration in the modelling of this system is that of thermal transfer from the heater 12 into the solid material 4 This is illustrated in Figure 2, which shows a cioss- sectional view through the heated section 14 of the measurement system 1 The heater 12 is designed to transfer heat effectively into the conduit of the heated section 14, but the characteristics of the system are affected by how rapidly the heat provided can be transferred into the material within the conduit through the material of the heated section 14 It is found that this may be modelled more effectively if this heat transfer is rapid, and copper (with its uniform structure and high thermal conductivity) is found to be a particularly effective choice of material for the heated section as a result Models have been developed to address the heat flow from a heated wall (such as the inner wall of the conduit in the heated section 14) to a two-phase material flowing within the conduit - these are further discussed below The basis for the mathematical model used to calculate mass flow will now be discussed

In the basic calculation of mass flow, it is taken that the power input to the heated section is essentially transferred to the solid phase in the conduit, and that with knowledge of the specific heat of the solid material and the temperature difference between the temperature of the solid material before heating and the temperature of the solid material after heating, the mass flow can be found

^{( 1 )} '^h" ⁼ -^ CPP - ^AT

Where m_p is the mass flow rate of the solids, Q is the rate of the heat input, c_pp is the specific heat of the solids at constant pressure, and AT is the change in temperature of the solids between the upstream and downstream of the heated region

Prior art systems built to use this approach to mass flow determination have used a fixed temperature heated section As can be seen from Equation 1 above, the determination of the mass flow does not depend on the heated section temperature itself - the benefit of obtaining a constant heated section temperature is that it allows for a steady state measurement for AT This may be necessary if the temperature sensors, or the measurement system as a whole, has a significant delay in its thermal response

The present inventors have appreciated that it is not necessary to keep the temperature of the heated section fixed in this way, and that attempting to do so may lead to very significant disadvantages In particular, it will inevitably result in a slow thermal response - as it requires a feedback loop with slow response components to ensure provision of heat to the heated section to maintain a constant temperature difference Δ T- and will thus be inappropriate to conditions in which the mass flow varies significantly in real time In particular, the presence of irregularly spaced plugs in the solid flow will lead to very inaccurate measurement The present inventors have found that by providing controlled supply of power and allowing the temperature of the conduit section to vary, much more accurate measurements can be achieved provided that the temperature of the material is measured directly (indirect measurements of temperature will lead to a long response time, as they are buffered by the hight thermal mass of the conduit) To do this in a particularly effective way, the temperature sensors should have a sufficiently rapid response to temperature changes that they can adjust to significant changes in the mass flow, which will lead in such an arrangement to significant changes in the temperature sensed downstream of the measurement system The practical consequences of this for control of the measurement system are discussed further below In practice, it is desirable for the heated section to be kept within a controlled temperature range, so that losses outside the system and other factors that may be dependent on the heated section temperature may be kept sufficiently close to constant that they can be approximated without significant effect on mass flow calculations However, this can be achieved without using a feedback loop to keep the heated section at a precise temperature, but by providing metered power and measurement to ensure that the temperature of the heated section remains within a predetermined range - the practical application of this is discussed further below

If the temperature is controlled in this way, losses to the outside can be compensated for without difficulty Of more significance is the proportion of the heat supplied that is lost to the gas phase, as this will clearly affect the amount of heat actually supplied to the solid phase under measurement The loss to the gas phase will need to be considered increasingly for lighter flows With increased concentration of solids in the flow, the loss Io the gaseous phase will in fact be reduced, as there will simply be less volume in the conduit for the gaseous phase Loss to the gas phase may for some embodiments and flow types simply be calibrated out - where compensation is needed, appropriate compensation may be made if the specific heat of the gas is known and a gas flow rate (measured by a standard gas flow means, potentially at another point in the materials transport system separate from the measurement system described here, for example upstream of the mass flow measurement - measurements of change in pressure may also be used) is known by working back from a raw measured mass flow to determine how much of the conduit volume was available for the gaseous phase Although this compensation requires some approximation, as the product of the mass and specific heat for the gaseous phase will generally be very much less than the corresponding product for the solid phase, this approximation may be made without significantly reducing the accuracy of the eventual mass flow measurement Where greater accuracy is required, an iterative approach may be used This may involve making an initial determination of the solids mass flow, determining the gas mass flow contribution, and then refining the determination of each mass flow component iteratively until a sufficient level of accuracy is reached This may be desirable in order to capture significant dynamic variation, such as would be involved in the passage of a plug

To model the mass flow effectively, the thermal transfer characteristics of the system need to be considered This was considered by Avila and Cervantes in "Analysis of the heat transfer coefficient in a turbulent particle pipe flow" in the International Journal of Heat and Mass Transfer, VoI 38, No 11 , 1995, pp 1923-1932, who determined that an average heat transfer coefficient for a solid suspended in a gaseous phase h_susp can be considered as a function of both the heat transported by the suspension Q_susp and the logarithmic mean temperature difference ΔTIm_susp, such that (2) Q,_nιt = K ^• A_an« - ΔTlm_sl

and where

where AT_hιιlι = T_^ - T_httU and ΔT_hllh = T_s - T_huh

The significance of the relevant variables is illustrated in Figure 3, in which the conduit has been presented for convenience in a radial section along the length of the heated conduit. The heat transported by the suspension Q_susp may be evaluated by the following relationship:

(4) Q_sιlψ + m_pc_pp ) ^■ (T_hιιh - T_lwh )

where T_h , = ?!^^^ T₁, , = ^±3

"V>* ^{+ /}Vv*> ' " ^m<^c,>_g ^{+ m}P^CP_P

where A,_ransf is the heat transfer surface area; T_s is the temperature of the pipe surface; T_buι, and T_huio are the suspension bulk temperature at the inlet and the outlet of the heated section; In_g, and T_mgo are the gas phase bulk temperature at the inlet and outlet of the heated section; Tmpi and T_mpo are the solid phase bulk temperature at the inlet and outlet of the heated section; m_χ and m_p are the mass flow rates of the gas and solid phases respectively; and c_pg and Cpp are the specific heat of the gas and the particles respectively.

The heat transfer coefficient h_{w }} can therefore be expressed in terms of measurable quantities in the following way:

u^{ιψ ~} A ( \ A^LλT ¹ImIo - JfAT' hull ))

""^{m/ ' ~} (AT \

In - *^»'"- I This allows for determination of appropriate values of h_sιιs , for calibrating the measurement system for different materials systems and flow regimes This enables appropriate values of h_sιιψ to be applied to actual measurements, allowing the mass flow to be calculated according to equation (2) Certain simplifying assumptions are made in this analysis (that heat is transferred effectively to the material, that there are minimal losses outside the system), but the system is designed so that either these assumptions can reasonably be considered to apply, or else so that simple empirical corrections can be made (for example, by keeping the temperature of the heated section within a sufficiently narrow range that the losses to the outside can justifiably be considered constant)

The practical operation of embodiments of the measurement system shown in Figure 1 to achieve mass flow measurements using the model indicated above will now be discussed further

As indicated previously, it is not necessary for the temperature of the heated section 14 to be maintained at a precise value, but it is desirable for it to be maintained within a range and for the temperature to be measured sufficiently accurately that it can be used to provide a measure of the thermal energy provided to the material flowing in the conduit An effective approach to measurement - which allows controlled heating, maintenance of temperature within a desired range, and effective heat transfer to the transported materials - is to use a heating cycle in which the heater 12 operates for only a part of the heating cycle, and in the othei part of the heating cycle the heater 12 does not provide heat to the heated section Preferably, the heating part of the cycle is shorter than the non-heating part (for example, the cycle could last ten seconds with a two second heating part followed by an eight second non- heating part) The heated section 14 temperature will then cycle around an effective operating temperature (for example, the effective operating temperature may be 373K, and the temperature may rise to 377K just after the heating part ends and falls to 369K just as it starts) The length of the respective parts of the cycle could be adjusted if the temperature would otherwise move outside a predetermined temperature range

It should be noted that throughout the whole cycle heat is being transferred from the heated section 14 to the materials flowing in the conduit - the tempetature of the heated section may be cycling between about 369K and 377K with the materials in the conduit at an original near ambient temperature of 303K, say This approach however allows the heat input to be accurately measured and consistently applied in a short "thermal impulse", allowing measurement to take place over a consistent cycle with no irregularity introduced by the presence of a feedback loop (required if the constant temperature approach is takon) Temperature of the material, and hence mass flow, can be measured throughout the heating cycle, both in the heated and non-heated parts of the cycle - these temperatures can be measured dynamically at a rate equal or greater than normal flow rates, and the mass flow can be obtained at comparable high rates by application of the model

The steps carried out in measuring mass flow are as follows, and are illustrated in Figure 4 First of all, the material related variables (such as the specific heats and emissivities of the materials in the flow) are provided in step 40, so that the measured temperatures will be sufficient to enable the mass flow to be determined The heated section 14 is then brought up to operating temperature in step 42 Once the heated section 14 is in the predetermined operating temperature range, the heating cycle begins in step 44 In step 46, the readings from the upstream and downstream temperature sensors 6, 7, 8 are captured and fed back to the system controller 11 , and the rate of change of temperature of the heated section of the conduit is also determined The system controller 1 1 then calculates (step 48) the instantaneous value of the mass flow from the system variables Temperature readings are taken and mass flow calculated until the measuring system is taken out of operation

As indicated above, the measurement system is adapted to provide a value of the mass flow at a given moment - there will in practice be a sampling rate for measurement, but if the sampling interval is short with respect to the variation in flow, this can effectively be considered a continuous measurement Significant variations in flow can occur in timescales of the order of tenths of a second (to detect the passage of a plug, detection on this scale may be necessary), but sampling can be significantly more rapid than this The mass flow may of course be integrated over time to give a total mass transported in a given time interval (though there may be other ways to measure this quantity in a practical system) What the measurement system can provide is the possibility of observing the flow over any relevant measurement scale, which allows not only the properties of the flow to be measured accurately but also allows phenomena of the flow to be analysed and understood and the effect of changes to the flow to be studied in real time

Modifications to the basic approach set out here can be provided in alternative embodiments of the invention suitable for different materials systems and flow conditions Figures 5A to 5C show different types of solid phase flow Figure 5A shows the solid phase in a distributed suspension, essentially carried along by the gaseous phase Figure 5B shows a "plug" of solid phase material, advancing through the conduit much like a projectile Figure 5C shows an alternative transport mode for a solid phase, in which solid particles advance up an existing slope of material and the solid phase structure as a whole advances in the manner of a sand dune - in this case, the solid phase advances much more slowly than the gaseous phase

The approach to measurement taught above works for all of these flow types, as it is not especially dependent on solid phase velocity (if material moves more slowly, it will heat up more, but the overall relationship to determine mass flow still applies and can be determined from the temperature change) What may cause difficulty is if there are different flows present with different associated temperatures - for example, a suspension together with a dune-like flow - and a single temperature is taken for each flow This may be addressed by using 5 multiple temperature sensors to detect flows in regions of the conduit characteristic to them This is shown in Figure 6 - temperature sensors 61 , 62 and 63 ali observe different parts of the conduit, and from the different temperature readings obtained, inferences may be drawn as to what flows are present and how they should be treated to determine the overall mass flow

I O

The approach to measurement used here is not limited to solid phases It can readily be used for certain forms of liquid phase, such as droplets carried in suspension More modification may be required for modes of flow which vary to some degiee fiom the modes exhibited by solids, but as indicated above, the approach to measurement and models used to determine

15 mass flow are not critically dependent on flow type IR temperature sensors may be used to determine liquid temperatures as effectively as they are used to determine solid temperatures, so the same form of accurate real-time measurement of the temperature of the non-gaseous material in the flow may be made 0 In the embodiments discussed above, a heated section 14 has been provided with a temperature elevated significantly above that of the conduit at a whole, which is considered here to be at an ambient temperature This may not be appropriate for all materials - it may be undesirable to heat volatile materials, or materials which may be damaged by heat (for example, foodstuffs in which a period of time at increased temperature may lead to a growth 5 in bacteria) This may be addressed by providing a cooled section instead of the heated section 14 - heat will be extracted from the flowing material, and its temperature will drop The mass flow may be determined from the drop in temperature in exactly the same way as it is determined from the increase in temperature using the model discussed above In this case it will be important to measure the heat flowing out of the cooled section accurately An0 alternative approach, in which the original approach to heating may be used, is to cool a section of the materials transport system before the measurement system so that the input temperature for the measurement system is lower, though this will need to be done in such a way as not to distort the temperature profile of the materials flow

Claims

1. A method of measuring mass flow of a non-gaseous phase of material, the method comprising:

providing a conduit having a heating or cooling means for changing the temperature of material flowing in the conduit, and providing a first temperature sensor upstream of the heating or cooling means and a second temperature sensor downstream of the heating or cooling means, both the first and the second temperature sensor being adapted to measure directly a temperature of a non-gaseous phase of material flowing in the conduit;

heating or cooling a section of the conduit for a first period of time and not heating or cooling the section of the conduit for a second period of time, whereby heat transfers between the section of the conduit and the material flowing in the conduit in both the first and the second period of time, providing a third temperature sensor in good thermal contact with the section of the conduit, and wherein both the first and the second temperature sensor measure the temperature of the non-gaseous phase of the material flowing the conduit in at least the second period of time and the third temperature sensor measures the temperature of the section of the conduit and thereby provides a measure of energy transfer to the material flowing in the conduit; and

calculating the mass flow of the non-gaseous phase of the material from the measurements of temperature.

2. A method as claimed in claim 1 , wherein the material forms a two phase system comprising a gaseous phase and a non-gaseous phase, further comprising the step of calculating the heat lost to the gaseous phase before calculating the mass flow of the nongaseous phase.

3. A method as claimed in claim 1 or claim 2, wherein the non-gaseous phase comprises a solid phase particulate.

4. A method as claimed in any preceding claim, wherein during measurement of the mass flow the temperature of the heated or cooled section of the conduit is kept within a predetermined temperature range.

5. A method as claimed in any preceding claim, wherein during operation of the method the first period and the second period form one cycle of a repeating heating cycle.

6. A method as claimed in claim 5, wherein the steps of measuring the temperature of the non-gaseous phase and calculating the mass flow of the non-gaseous phase are repeated continuously throughout both the first period and the second period of a heating cycle.

7. A method as claimed in any preceding claim, wherein there are one or more further temperature sensors downstream of the heated or cooled section, whereby each of the second and the one or more further temperature sensors are adapted to measure the temperature of non-gaseous material in a different part of the conduit.

8. A method as claimed in any preceding claim, wherein the heated or cooled section is thermally separated from other parts of the conduit.

9. A method as claimed in any preceding claim, wherein a mass flow of the gaseous phase is initially determined from measurements other than the measurements used to determine the mass flow of the non-gaseous phase.

10. A method as claimed in claim 9, wherein an iterative process is used to modify each of the mass flows of the gaseous phase and the non-gaseous phases to compensate for the other.

11. A measuring system for measuring mass flow of a non-gaseous phase of material, the measuring system comprising:

heating or cooling means;

a conduit for the material to flow through, including a conduit section adapted for heating or cooling by the cooling means;

a heating controller, adapted to control the heating or cooling means to provide or remove heat to the conduit section in a first period of time but not in a succeeding second period of time;

a first temperature sensor upstream of the conduit section and a second temperature sensor downstream of the conduit section, each temperature sensor being adapted to measure directly a temperature of a non-gaseous phase of the material, and a third temperature sensor in good thermal contact with the conduit section to measures the temperature of the conduit section and thereby provide a measure of energy transfer to the material flowing in the conduit; and a system controller, programmed to receive measurements from the temperature sensors in at least the second period of time and to calculate the mass flow of the nongaseous phase therefrom.

12. A measuring system as claimed in claim 11 , further comprising one or more further temperature sensors downstream of the heated or cooled section, whereby each of the second and the one or more further temperature sensors are adapted to measure the temperature of non-gaseous material in a different part of the conduit.

13. A measuring system as claimed in claim 11 or claim 12, wherein each of the first and second temperature sensors comprises an IR detector.

14. A measuring system as claimed in any of claims 11 to 13, wherein the conduit section is formed primarily of high thermal conductivity material.

15. A measuring system as claimed in claim 14, wherein the conduit section is formed primarily of copper.

16. A measuring system as claimed in any of claims 11 to 15, wherein the heating controller is adapted to ensure that the temperature of the conduit section remains within a predetermined range during measurement of the mass flow.

17. A measuring system as claimed in any of claims 11 to 16, further comprising insulating gaskets to provide thermal separation between the heated or cooled section and other parts of the conduit.