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Experimental validation of a CFD model of a ground heat exchanger with slinky coils

Grzywacz Robert, Teper Mikołaj

Polish Journal of Chemical Technology

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2024

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Vol. 26, nr 2

86--91

EN

Rising energy prices have increased the popularity of many renewable energy sources including heat pumps. In the case of ground heat pumps research related to the analysis of the operation and selection of ground heat exchangers as a heat source are insufficient. With this in mind, on the operation of the horizontal slinky coil heat exchanger research work has been undertaken. As a research tool, the Computational Fluid Dynamics has been used. To check the adequacy of the CFD model, a validation of the model was carried out using the results of research on a real heat exchanger. Comparison was made: values of ground temperatures, outlet temperatures from the exchanger, and heat flux exchanged by the heat exchanger. In the opinion of the authors, the validation of the CFD model was successful.

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The dumping of oscillatory phenomena in the process of bioethanol production by continuous fermentation

Ciesielski Adrian, Grzywacz Robert

Technical Transactions

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2019

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Vol. 116, iss. 3

119--132

EN

This article presents the results of numerical research on the dumping of oscillatory phenomena occurring in the continuous bioethanol production process. Proportional and proportional-integral types of controllers were tested for this purpose. Numerical analysis showed that the appropriate selection of the Kc value makes it possible to suppress the oscillations in the system. The introduction of the integral term improves the performance of control system. Using numerical calculations, it was shown that the PI controller is effective at dumping the occurring oscillations. The presence of the integral term allows the reduction of the gain coefficient value. After the proper selection of parameters, the PI controller effectively supresses the oscillations present in the system.

PL

W niniejszym artykule zaprezentowano wyniki badań numerycznych, dotyczących tłumienia zjawisk oscylacyjnych występujących w procesie produkcji bioetanolu metodą ciągłą. Przebadano w tym celu regulator typu proporcjonalnego oraz proporcjonalno-całkującego. Analiza numeryczna wykazała, iż odpowiedni dobór wartości współczynnika wzmocnienia Kc umożliwia tłumienie zjawisk oscylacyjnych w układzie. Wykazano także, iż wprowadzenie członu całkującego poprawia jego działanie. Za pomocą obliczeń symulacyjnych wykazano, że regulator proporcjonalno-całkujący dobrze radzi sobie z tłumieniem występujących oscylacji. Obecność członu całkującego pozwala na zredukowanie wartości współczynnika wzmocnienia. Po odpowiednim doborze parametrów, regulator PI skutecznie tłumi obecne w układzie oscylacje.

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Models of airlift bioreactors for double-substrate kinetics. The analysis of sufficient oxygenation conditions with a view of mathematical model choice

Grzywacz Robert

Chemical and Process Engineering

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2019

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Vol. 40, nr 1

3--19

EN

The quantitative description of an airlift bioreactor, in which aerobic biodegradation limited by carbonaceous substrate and oxygen dissolved in a liquid takes place, is presented. This process is described by the double-substrate kinetics. Mathematical models based on the assumption of plug flow and dispersion flow of liquid through the riser and the downcomer in the reactor were proposed. Calculations were performed for two representative hydrodynamic regimes of reactor operation, i.e. with the presence of gas bubbles only within the riser and for complete gas circulation. The analysis aimed at how the choice of a mathematical model of the process would enable detecting the theoretical occurrence of oxygen deficiency in the airlift reactor. It was demonstrated that the simplification of numerical calculations by assuming the “plug flow” model instead of dispersion with high Péclet numbers posed a risk of improper evaluation of the presence of oxygen deficiency zones. Conclusions related to apparatus modelling and process design were drawn on the basis of the results obtained. The paper is a continuation of an earlier publication (Grzywacz, 2012a) where an analysis of single-substrate models of the airlift reactor was presented.