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  • 1.
    Paavilainen, Janne
    Dalarna University, School of Technology and Business Studies, Energy Technology. Chalmers.
    Characterization of Chimney Flue Gas Flows: Flow Rate Measurements with Averaging Pitot Probes2016Licentiate thesis, monograph (Other academic)
    Abstract [en]

    Performance testing methods of boilers in transient operating conditions (start, stop and combustion power modulation sequences) need the combustion rate quantified to allow for the emissions to be quantified. One way of quantifying the combustion rate of a boiler during transient operating conditions is by measuring the flue gas flow rate. The flow conditions in chimneys of single family house boilers pose a challenge however, mainly because of the low flow velocity. The main objectives of the work were to characterize the flow conditions in residential chimneys, to evaluate the use of the Pitot-static method and the averaging Pitot method, and to develop and test a calibration method for averaging Pitot probes for low 𝑅𝑅𝑅𝑅.A literature survey and a theoretical study were performed to characterize the flow conditions in in single family house boiler chimneys. The flow velocities under normal boiler operating conditions are often below the requirements for the assumptions of non-viscous fluid justifying the use of the quadratic Bernoulli equation. A non-linear calibration coefficient is required to correct for these viscous effects in order to avoid significant measurement errors. The flow type in the studied conditions changes from laminar, across the transition regime, to fully turbulent flow, resulting in significant changes of the velocity profile during transient boiler operation. Due to geometrical settings occurring in practice measurements are often done in the hydrodynamic entrance region, where the velocity profiles are neither fully developed nor symmetrical. The predicted changes in velocity profiles are also confirmed experimentally in two chimneys.Several requirements set in ISO 10780 and ISO 3966 for Pitot-static probes are either met questionably or not met at all, meaning that the methods cannot be used as such. The main issues are the low flow velocity, viscous effects, and velocity profiles that change significantly during normal boiler operation. The Pitot-static probe can be calibrated for low 𝑅𝑅𝑅𝑅, but is not reliable because of the changing velocity profiles.The pressure averaging probe is a simple remedy to overcome the problems with asymmetric and changing velocity profiles, but still keeping low the irrecoverable pressure drop caused by the probe. However, commercial averaging probes are not calibrated for the characterized chimney conditions and the information available on the performance of averaging probes at low 𝑅𝑅𝑅𝑅 is scarce. A literature survey and a theoretical study were done to develop a method for calibrating pressure averaging probes for low 𝑅𝑅𝑒 flue gas flows in residential chimneys.The experimental part consists of constructing a calibration rig, testing the performance of differential pressure transducers, and testing a prototype pressure averaging probe. The results show good correlation over a wide operation range, but the low 𝑅𝑅𝑅𝑅 characteristics of the probe could not be identified due to instability in the chosen pressure transducer, and temperature correlation for one of the probes while not for the other. The differential pressures produced are close to the performance limitations of readily available transducers and it should be possible to improve the method by focusing on finding or building a suitable pressure transducer. The performance of the averaging method can be improved further by optimizing the geometry of the probe. Another way of reducing the uncertainty would be to increase the probe size relative to the conduit diameter to produce a higher differential pressure, at the expense of increasing the irrecoverable pressure drop.

  • 2.
    Paavilainen, Janne
    Dalarna University, School of Technology and Business Studies, Energy and Environmental Technology.
    Characterization of residential chimney conditions for flue gas flow measurements2012Report (Other academic)
    Abstract [en]

    A literature survey and a theoretical study were performed to characterize residential chimney conditions for flue gas flow measurements. The focus is on Pitot-static probes to give sufficient basis for the development and calibration of a velocity pressure averaging probe suitable for the continuous dynamic (i.e. non steady state) measurement of the low flow velocities present in residential chimneys. The flow conditions do not meet the requirements set in ISO 10780 and ISO 3966 for Pitot-static probe measurements, and the methods and their uncertainties are not valid. The flow velocities in residential chimneys from a heating boiler under normal operating condi-tions are shown to be so low that they in some conditions result in voiding the assumptions of non-viscous fluid justifying the use of the quadratic Bernoulli equation. A non-linear Reynolds number dependent calibration coefficient that is correcting for the viscous effects is needed to avoid significant measurement errors. The wide range of flow velocity during normal boiler operation also results in the flow type changing from laminar, across the laminar to turbulent transition region, to fully turbulent flow, resulting in significant changes of the velocity profile during dynamic measurements. In addition, the short duct lengths (and changes of flow direction and duct shape) used in practice are shown to result in that the measurements are done in the hydrodynamic entrance region where the flow velocity profiles most likely are neither symmetrical nor fully developed. A measurement method insensitive to velocity profile changes is thus needed, if the flow velocity profile cannot otherwise be determined or predicted with reasonable accuracy for the whole measurement range. Because of particulate matter and condensing fluids in the flue gas it is beneficial if the probe can be constructed so that it can easily be taken out for cleaning, and equipped with a locking mechanism to always ensure the same alignment in the duct without affecting the calibration. The literature implies that there may be a significant time lag in the measurements of low flow rates due to viscous effects in the internal impact pressure passages of Pitot probes, and the significance in the discussed application should be studied experimentally. The measured differential pressures from Pitot-static probes in residential chimney flows are so low that the calibration and given uncertainties of commercially available pressure transducers are not adequate. The pressure transducers should be calibrated specifically for the application, preferably in combination with the probe, and the significance of all different error sources should be investigated carefully. Care should be taken also with the temperature measurement, e.g. with averaging of several sensors, as significant temperature gradients may be present in flue gas ducts.

  • 3.
    Paavilainen, Janne
    et al.
    Dalarna University, School of Technology and Business Studies, Energy and Environmental Technology.
    Bales, Chris
    Dalarna University, School of Technology and Business Studies, Energy and Environmental Technology.
    Feasibility of Solar Thermal Assisted Small Scale District Heating in Nordic Countries2008In: Eurosun 2008, Lisbon, 2008Conference paper (Other academic)
    Abstract [en]

    A feasibility study for combining solar thermal plants with small scale 0.5-2 MWth mobile district heating plants under north European conditions was done. The study was done from a heat service company point of view, trying to come up with generally applicable scenarios rather than case studies. It was found that if the saved fuel is mainly pellets, without subsidies it is difficult to find economically feasible payback periods within the plants estimated lifetime, even with moderate pellet price increases. With oil as saved fuel the feasible payback periods range between 10-20 years with an estimated 5% annual oil price increase. The costs of moving the solar plant to another locations were also considered. A rough estimation of these costs resulted in a prolonged payback period of 3-6 years, which is considered too long regarding the general plant payback periods.

  • 4.
    Persson, Tomas
    et al.
    Dalarna University, School of Technology and Business Studies, Energy and Environmental Technology.
    Fiedler, Frank
    Dalarna University, School of Technology and Business Studies, Energy and Environmental Technology.
    Nordlander, Svante
    Bales, Chris
    Dalarna University, School of Technology and Business Studies, Energy and Environmental Technology.
    Paavilainen, Janne
    Dalarna University, School of Technology and Business Studies, Energy and Environmental Technology.
    Validation of a dynamic model for wood pellet boilers and stoves2009In: Applied Energy, ISSN 0306-2619, E-ISSN 1872-9118, no 86Article in journal (Refereed)
    Abstract [en]

    Optimising systems with wood pellet boilers or stoves using simulations requires realistic computer models. The objective of this work was to develop and verify a mathematical model for wood pellet boilers and stoves for use in system simulations with the dynamic simulation programme TRNSYS, calculating both the energy balance and the CO-emissions (carbon monoxide emissions). Laboratory measurements have been carried out and a mathematical two-node model was developed and implemented as a TRNSYS component. Parameters were identified and the model has been compared with measurements. The model shows in general good agreement with measured data, however there are details that could be improved. This involves improved modelling of the dynamic response for boilers with large water volumes and improved modelling of the air factor and the CO-emissions, especially during start and stop conditions. Further improved methodology and accuracy for measuring and parameter identification is recommended.

  • 5.
    Win, Kaung Myat
    et al.
    Dalarna University, School of Technology and Business Studies, Energy and Environmental Technology.
    Paavilainen, Janne
    Dalarna University, School of Technology and Business Studies, Energy and Environmental Technology.
    Persson, Tomas
    Dalarna University, School of Technology and Business Studies, Energy and Environmental Technology.
    Emissions Characterisation of residential pellet boilers during start-up and stop periods2010In: 3rd International Scientific Conference on “Energy systems with IT”, Älvsjö, Stockholm, Sweden, 2010Conference paper (Refereed)
    Abstract [en]

    In this study, gaseous emissions and particles are measured during start-up and stop periods for an over-fed boiler and an under-fed boiler. Both gaseous and particulate matter emissions are continuously measured in the laboratory. The measurement of gaseous emissions includes oxygen (O2), carbon dioxide (CO2), carbon monoxide (CO), nitrogen oxide and (NO). The emissions rates are calculated from measured emissions concentrations and flue gas flow. The behaviours of the boilers during start-up and stop periods are analysed and the emissions are characterised in terms of CO, NO, TOC and particles (PM2.5 mass and number). The duration of the characterised periods vary between two boilers due to the difference in type of ignition and combustion control. The under-fed boiler B produces higher emissions during start-up periods than the over-fed boiler A. More hydrocarbon and particles are emitted by the under-fed boiler during stop periods. Accumulated mass of CO and TOC during start-up and stop periods contribute a major portion of the total mass emitted during whole operation. However, accumulated mass of NO and PM during start-up and stop periods are not significant as the duration of emission peak is relatively short.

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