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Abstract

There exist numerous modelling techniques and representation methods for digital control algorithms, aimed to achieve required system or process parameters, e.g. precision of process modelling, control quality, fulfilling the time constrains, optimisation of consumption of system resources, or achieving a trade-off between number of parameters. This work illustrates usage of Finite State Machines (FSM) modelling technique to solve a control problem with parameterized external variables. The structure of this work comprises six elements. The FSM is presented in brief and discrete control algorithm modelling is discussed. The modelled object and control problem is described and variables are identified. The FSM model is presented and control algorithm is described. The parameterization problem is identified and addressed, and the implementation in PLC programming LAD language is presented. Finally, the conclusion is given and future work areas are identified.
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Abstract

Plate fin-tube heat exchangers fins are bonded with tubes by means of brazing or by mechanical expansion of tubes. Various errors made in the process of expansion can result in formation of an air gap between tube and fin. A number of numerical simulations was carried out for symmetric section of plate fin-tube heat exchanger to study the influence of air gap on heat transfer in forced convection conditions. Different locations of air gap spanning 1/2 circumference of the tube were considered, relatively to air flow direction. Inlet velocities were a variable parameter in the simulations (1– 5 m/s). Velocity and temperature fields for cases with air gap were compared with cases without it (ideal thermal contact). For the case of gap in the back of the tube (in recirculation zone) the lowest reduction (relatively to the case without gap) of heat transfer rate was obtained (average of 11%). The worst performance was obtained for the gap in the front (reduction relatively to full thermal contact in the average of 16%).
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Abstract

Costs of Spatial Disorder for the Real Estate Market. The article discusses the problem of costs which the spatial disorder in Poland causes in the real estate market. It also draws attention to the likely future consequences of the current lack of spatial order for the domestic real estate market. The impact of spatial chaos on the functioning of this market was considered in terms of economic, social and environmental costs. In the empirical part of the paper, analyzing land turnover in the Poznań agglomeration, the characteristics of the undeveloped real estate market in metropolitan areas in Poland were presented. At the same time, the negative effects of land trading in the situation of a flawed spatial planning system were emphasized. In addition, particular attention was paid to the common practice in Poland of excluding only part of the investment plots from agricultural use. At the same time, the urgent need to create the mechanisms of the actual protection of agricultural land within the agglomeration is emphasized.
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