Abstract:In order to predict long-term changes in the temperature of the ground in which a horizontal ground heat exchanger has been installed, it is beneficial to implement simplified mathematical models of heat transfer. The possibility of using a one-dimensional equation of heat conduction while modelling heat transfer in a ground heat exchanger with horizontal pipes has been demonstrated in the work. A theoretical analysis based on the linear heat source model as well as experimental research works have been carried out. It has been concluded that the temperature profiles of the ground in which parallel pipes of the heat exchanger are placed do not significantly differ from the profiles for the heat exchanger in the form of a plate; in particular, this refers to large distances from the level in which the pipes are positioned, small distances between pipes axes and the long duration of the process. Discrepancies between the calculated temperature increases for pipe and plate exchangers varied significantly in the individual time intervals, and were approx. 20-30%. The conducted experiments have demonstrated that the temperature field around parallel pipes of the heat exchanger may be described by the linear heat source model. The compatibility of temperature maps that were determined theoretically and experimentally was satisfactory with a good degree of accuracy.

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The paper presents the effect of the addition of hydrocolloids-xanthan gum and guar gum-on the rheological properties of ovoalbumin-based food foams, produced by continuous method. The foaming was carried out in a column apparatus with additional aeration equipped with a paddle stirrer. In order to determine the rheological parameters, a hysteresis loop test was carried out. The results of the study were described using the Ostwald-de Waele equation. The effect of the addition of hydrocolloid on the rheological properties of the obtained foams was characterized, and the synergistic effects between the hydrocolloids used were described.

Heat transfer during storage of hot liquid in the tankPrzenoszenie ciepła podczas magazynowania gorącej cieczy w zbiorniku AbstractIn the article, a mathematical model of heat transfer in a storage tank for hot water with a non-uniform initial temperature is presented. The influence of the initial temperature distribution of the liquid in the tank and the influence of thermal resistance of the tank' s walls, bottom and cover on temperature profiles of the liquid in the tank and changes of these profiles in time were analysed. A good conformity of the results obtained based on the process model with the results of measurements of water temperatures carried out under laboratory conditions was obtained.Keywords: thermal stratification, thermal energy storage, renewable energy sources Streszczenie W artykule przedstawiono model matematyczny przenoszenia ciepła w zbiorniku magazynującym gorącą ciecz o niejednorodnej temperaturze początkowej. Przeanalizowano wpływ początkowego rozkładu temperatury cieczy w zbiorniku oraz wpływ oporu cieplnego ścian, dna oraz pokrywy zbiornika na profile temperatur cieczy w zbiorniku, a także czasowe zmiany tych profili. Uzyskano dobrą zgodność wyników otrzymanych na podstawie modelu procesu z wynikami pomiarów temperatur wody przeprowadzonych w warunkach laboratoryjnych.