Characterization of residential chimney conditions for flue gas flow measurements

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.

Strategisk utveckling och ekonomistyrning : Ett livscykelperspektiv

This dissertation synthesizes previous research and develops a model for the study of strategic development, strategic congruence and management control. The model is used to analyze a longitudinal case study of the Swedish engineering company Atlas Copco. Employing contingency theory, the study confirms that long-term survival of a company requires adaption to contingencies. Three levels of strategy are examined: corporate, business and functional. Previous research suggests that consistency between these levels (strategic congruence) is necessary for a company to be competitive. The dissertation challenges this proposition by using a life-cycle perspective and analyzes strategic congruence in the different phases of a life cycle. It also studies management control from a life-cycle perspective. In this context, two types of management control are examined: formal and informal. From a longitudinal perspective, the study further discusses how these types interact during organizational life cycles. The dissertation shows that strategic development is more complex than previous studies have indicated. It is a long, complex and non-linear process, the results of which cannot always be predicted. Previous models for strategy and management control are based on simple relationships and rarely take into account the fact that companies often go through different phases of strategic development. The case study shows that strategic incongruence may occur at times during organizational life cycles. Furthermore, the use of management control varies over time. In the maturity phase, formal control is in focus, while the use of informal control has a bigger role in both the introduction and decline phases. Research on strategy and management control has intensified in recent years. Still there is a gap regarding the coordination of complex corporate structures. The present study contributes with further knowledge on how companies manage long-term strategic development. Few studies deal with more than two levels of strategy. Moreover, the present study addresses the need to understand strategic congruence from a life-cycle perspective. This is particularly relevant in practice, when management in large companies face difficult issues for which they expect business research to assist them in the decision-making process.