INFLUENCE OF STORING AND TEMPERATURE ON RHEOLOGIC AND THERMOPHYSICAL PROPERTIES OF WHISKY SAMPLES

Temperature and storing time can be included between the most significant parameters that influence physical properties of food. This article deals with selected rheologic and thermophysical properties of alcohol drink whisky. Our research was oriented on measuring of rheologic and thermophysical characteristics of whisky. There were measured two types of whisky – Grant’s and Jim Beam from two different producers, both samples had 40 % of alcohol content. During the experiments were analyzed rheologic parameters as: dynamic viscosity, kinematic viscosity and fluidity and thermophysical parameters as: thermal conductivity, thermal diffusivity and volume specific heat. Selected parameters were measured in temperature range (-5 – 27) °C. Measurements were done on whisky samples in different days during the storage. Measuring of dynamic viscosity was performed by digital rotational viscometer Anton Paar (DV-3P). Principle of measuring is based on dependency of sample resistance against the probe rotation. Density of whisky samples was determined by pycnometric method. Average density at given temperature along with dynamic viscosity value was used at calculation of kinematic viscosity and fluidity was also determined. Measuring of thermophysical parameters was performed by instrument Isomet 2104. Measurement by Isomet is based on analysis of the temperature response of the measured sample to heat flow impulses. Relations of rheologic and thermophysical parameters to the temperature were made and influence of storing time was discussed. From obtained results is clear that dynamic and kinematic viscosity is decreasing exponentially with temperature and fluidity has increasing exponential progress. We found out that both whisky samples had at the beginning and after one week of storage very similar values of rheologic parameters. Very small difference in rheologic parameters of whisky samples was found after two weeks of storing. Values of dynamic and kinematic viscosity were a bit higher and values of fluidity were a bit smaller after storing, that can be caused by loosening of the water during storage. Thermophysical parameters are increasing linearly with temperature for both whisky samples. Higher values of thermophysical parameters were in all cases obtained for whisky Grant’s

THERMOPHYSICAL AND RHEOLOGIC PROPERTIES OF BIOOIL SAMPLES

This article deals with thermal properties of selected biooils (Plahyd S – biooil No1 and Plahyd N – biooil No2) and rheologic properties of rapeseed oil. Plahyd S is a synthetic, rapidly biodegradable fluid which is based on sustainable raw materials. It is exceptionally suitable for applications in mobile and stationary hydraulic systems. Plahyd N is multigrade hydraulic oil based on rapeseed oil used in agricultural and construction machinery. For thermal parameters measurements was used Hot wire method. The experiment is based on measuring of the temperature rise vs. time evaluation of an electrically heated wire embedded in the tested material. The thermal conductivity is derived from the resulting change in temperature over a known time interval. Dependency of material resistance against the probe rotation was used at measurement of rheologic properties with instrument viscometer Anton Paar DV-3P. For two samples of biooils – Plahyd N and Plahyd S were determined basic thermophysical parameters – thermal conductivity, thermal diffusivity and volume specific heat. For each biooil samples were made two series of measurements. In the first series were measured thermal conductivity and thermal diffusivity at constant room temperature 20 °C. Every thermophysical parameter was measured 10 times for each sample. The results were statistically processed. For biooil No1 thermal conductivity was 0.325 W*m -1 .K-1 , it was higher value than we obtained for biooil No2 – 0.224 W*m -1 .K-1 . The similar results were obtained for thermal diffusivity of biooil No1 2.140.10-7 m 2 *s -1 and biooil No2 2.604.10-7 m 2* s -1 . For samples with constant temperature were calculated basic statistical characteristics as: standard deviation for ? – biooil No1 (±0.056 W*m -1*K -1 ) and biooil No2 (± 0.054 W*m -1*K -1 ); probable error of the arithmetic average for ? – biooil No 1 (±0.012 W*m - 1*K -1 ) and biooil No 2 (±0.005 W*m -1*K -1 ); relative probable error in % for ? – biooil No1 (±3.69 %) and biooil No2 (±2.23 %). The same statistical characteristics were calculated for thermal diffusivity. In the second series of measurements were measured relations of thermal conductivity and thermal diffusivity to the temperature in temperature range (20 – 29) °C. From results was evident that all measured dependencies are nonlinear. For both thermophysical parameters were obtained polynomial functions of the second degree described by the polynomial coefficients. Type of function was selected according to statistical evaluation based on the coefficient of determination for every thermophysical parameter graphical dependency. In temperature dependency of rapeseed oil dynamic viscosity was used decreasing exponential function, which is in accordance with Arrhenius equation. The results obtained by the implementation of thermophysical and rheologic measurements on samples of biooils could be compared with the values presented in the literature

Tepelné vlastnosti vybraných vzoriek syrov

The thermophysical parameters of selected cheeses (processed cheese and half hard cheese) are presented in the article. Cheese is a generic term for a diversegroup of milk-based food products. Cheese is produced throughout the world in wide-ranging flavors, textures, and forms. Cheese goes during processing through the thermal and mechanical manipulation, so thermal properties are one of the most important. Knowledge about thermal parameters of cheeses could be used in the process of quality evaluation. Based on the presented facts thermal properties of selected cheeses which are produced by Slovak producers were measured. Theoretical part of article contains description of cheese and description of plane source method which was used for thermal parameters detection. Thermophysical parameters as thermal conductivity, thermal diffusivity and volume specific heat were measured during the temperature stabilisation. The results are presented as relations of thermophysical parameters to the temperature in temperature range from 13.5°C to 24°C. Every point of graphic relation was obtained as arithmetic average from measured values for the same temperature. Obtained results were statistically processed. Presented graphical relations were chosen according to the results of statistical evaluation and also according to the coefficients of determination for every relation. The results of thermal parameters are in good agreement with values measured by other authors for similar types of cheeses.Článok sa zaoberá vybranými tepelnými vlastnosťami syrov (taveného syra a polotvrdého syra). Syr je všeobecný pojem používaný pre rôznorodé skupiny mliečnych potravín. Syry sa vyrábajú po celom svete v rôznych príchutiach, textúrach a formách. V priebehu spracovania syry prechádzajú tepelnou a mechanickou manipuláciou a preto tepelné vlastnosti sú u syrov jednými z najdôležitejších. Poznatky o tepelných vlastnostiach syrov môžu byť využité pri procese hodnotenia ich kvality. Na základe prezentovaných faktov boli realizované merania termofyzikálnych parametrov vybraných syrov vyrobených slovenskými výrobcami. V teoretickej časti článku je uvedená všeobecná charakteristika syra a popis metódy plošného zdroja, ktorá bola použitá pri experimentoch. V rámci merania boli zisťované: tepelná vodivosť, teplotná vodivosť a objemová tepelná kapacity v priebehu teplotnej stabilizácie. Výsledky meraní sú prezentované ako závislosti termofyzikálnych parametrov od teploty, v teplotnom intervale od 13,5°C do 24°C. Každý bod prezentovaných grafických závislostí je aritmetickým priemerom 50-tich nameraných hodnôt pre jednu teplotu. Získané výsledky boli štatisticky spracované a prezentované závislosti boli vybrané na základe štatistického vyhodnotenia výsledkov a tiež na základe hodnôt koeficientov determinácie pre každú grafickú závislosť. Výsledky meraní termofyzikálnych parametrov sú v dobrej zhode s meraniami prezentovanými inými autormi pre podobné druhy syrov

Thermal properties of selected bee products

Knowledge of bee products’ physical properties has a decisive importance for the monitoring of their quality. Thermophysical parameters are very important properties. Thermal conductivity and thermal diffusivity of selected bee products (honey, bee pollen and perga) were measured by two different methods. For identification of thermal conductivity and thermal diffusivity transient methods were used: Hot Wire (HW) and Dynamic Plane Source (DPS) method with an instrument Isomet 2104. The principle of measuring process is based on the analysis of timetemperature relation. In the first series of measurements thermal conductivity and diffusivity at constant laboratory temperature of 20 °C were measured. The second series was focused on identification of the changes in the thermophysical parameters during temperature stabilisation in the temperature range of 5–25 °C. For samples with constant temperature standard deviations and probable errors in % were calculated. For relations of thermal parameters to temperature graphical dependencies were obtained. Two different thermophysical methods were used for improvement of data reliability and data statistics

Temperature and storing time influence on selected physical properties of milk and acidophilus milk

This article deals with thermophysical parameters as: temperature, thermal conductivity, diffusivity and rheologic parameters as: dynamic, kinematic viscosity and fluidity of milk and acidophilus milk. For thermophysical parameters measurements was used Hot Wire method and for rheologic parameters measurements was used single – spindle viscometer. In the first series of measurements we measured relations between thermophysical and rheologic parameters in temperature range (5–25) °C for milk and acidophilus milk. Relations of all physical parameters of milk to the temperature showed influence of relative fat content. Effect of storage on milk and acidophilus milk is shown in the text. All measured relations for milk and acidophilus milk during temperature stabilisation had linear increasing progress with high coefficients of determination in the range (0.991–0.998). It was shown that increasing relative fat content has decreasing influence on milk thermal conductivity. Relations of rheologic parameters as dynamic and kinematic viscosity to the temperature had decreasing exponential progress, while relation of fluidity to the temperature had increasing exponential shape with high coefficients of determination in the range (0.985–0.994).. Mathematical description of the dependencies is summarised by regression equations and all coefficients are in presented tables

Temperature Relations of Selected Engine Oils Dynamic Viscosity

This article focuses on temperature relations of dynamic viscosity for selected engine oils. The effect of temperature on new and used oil dynamic viscosity was investigated. Measurements were performed on three different motor oil samples. All the three motor oil samples were synthetic. The first oil sample was new, the second sample was used for 15,000 km, and the third sample was used for 30,000 km. There were made two measurements of samples in one week. Dynamic viscosity was measured using a digital rotational viscometer Anton Paar DV-3P. The principle of measurement is based on the dependence of sample resistance to probe rotation. The results of measurements are shown as graphical relationships between dynamic viscosity and temperature. Decreasing exponential functions in temperature relationships were used for all the samples. The highest difference between the first and second measurement was observed in the new oil, and very small differences were found in other oils. Due to different types of oils and different stage of usage, the results could not be compared

Influence of Roof Installation of PV Modules on the Microclimate Conditions of Cattle Breeding Objects

This paper is focused on the temperature measurements which can detected the influence of temperature changes on the microclimate in animal production building after the installation of photovoltaic (PV) modules. The first series of experiments were performed on a specially designed model cowshed. For the data comparison and verification, the same measurements were realized in real conditions of the animal production object. The temperature balance was identified by measurements of the temperatures in the different parts of roof, PV modules, and the most important were measurements of the ambient temperature and temperatures in three levels of the cowshed interior. For the confirmation of results, measurements were done in two cowsheds, which had the same azimuth orientation and roof slope. The first cowshed was without installation of the PV modules on the roof and the second building had installed PV modules. By the data analyzed from experimentally obtained time-temperature dependencies, it was found that the installation of PV modules on the cowshed roof had a positive influence on the interior temperature balance. The installation of PV also had a positive effect on the cowshed microclimate, which was declared by calculation of the Temperature—Humidity—Index

Dynamic Viscosity and Activation Energy of Wort During Fermentation and Storing

This paper presents the results of wort dynamic viscosity and activation energy during fermentation. The effect of temperature and storing time on both parameters was investigated. Measurements were performed on two wort samples. The first sample was taken at the beginning of fermentation, and the second sample after three hours of fermentation. Both samples were also measured after three weeks of storing. Dynamic viscosity measurements were performed with a digital rotational viscometer Anton Paar DV-3P, the principle of which is based on the dependency of sample resistance to probe rotation. Results of measurements are shown as graphical dependencies of both analysed parameters on temperature. The temperature dependence of dynamic viscosity can be characterised by a decreasing exponential function, while in case of activation energy linear increasing characters were obtained. Longer fermentation and storing period caused a decrease in both analysed parameters, due to the structural changes in wort samples during fermentation and storing

Selected Physical Properties Assessment of Sunflower and Olive Oils

Presented paper is focused on comparison of certain physical properties of selected vegetable oils. Physical properties, such as density, dynamic, kinematic viscosity and fluidity, were experimentally determined. All experiments were conducted on two samples of vegetable oils: sunflower and extra virgin olive oils with approximate temperature range of 5–32 °C. Density of oils was determined by oscillation method utilizing digital densimeter Anton Paar DMA 4500M at different temperatures. Dynamic viscosity was measured by means of rotational viscometer Anton Paar DV-3P. The rest of rheological parameters were determined on the basis of their definitions. Obtained results are depicted as graphical dependencies of rheological parameters and density on temperature. These dependencies of vegetable oils on dynamic and kinematic viscosity showed decreasing exponential shape, which is in compliance with Arrhenius equation; temperature dependencies on fluidity showed an increasing exponential shape for both samples. Density dependencies of samples on temperature were characteristic with decreasing linear function within measured temperature range. Similar results were achieved by other researchers. On the basis of measured values, it is evident that dynamic viscosity of extra virgin olive oil shows higher values than sunflower oil viscosity, which is a result of different composition of oils

Influence of Temperature and Storing Time on Selected Red Wine Physical Properties

Presented article is focused on red wine rheological and thermal properties. Effects of temperature and short term storage on density, rheological parameters and thermal parameters were investigated. First measurement was done at the beginning of storage and then the same sample was measured again after one week of storing. Density was measured by densimeter Mettler Toledo DM 40 at different temperatures. For dynamic viscosity measurement was used rotational viscometer Anton Paar DV-3P. The kinematic viscosity and fluidity were determined according to the definitions. Thermal parameters were measured by instrument Isomet 2104. Temperature dependencies of wine dynamic and kinematic viscosity had decreasing exponential shape and temperature dependencies of fluidity had an increasing exponential shape. Temperature dependencies of red wine thermal conductivity and diffusivity had increasing linear character. Decreasing polynomial functions were obtained for temperature dependencies of red wine density. The values of dynamic and kinematic viscosity, thermal conductivity and diffusivity, and density of red wine were a little bit higher after short term storing, which can be expressed by changed amount of water caused by evaporation. Due to the same reasons were values of fluidity little bit lower after storage