Sebnem Tavman

Measurement of thermal conductivity of dairy products

Thermal conductivity of eleven kinds of cheese, four kinds of yogurt and a butter sample has been measured at about 15°C and 30°C. A modified hot wire method was used for thermal conductivity measurements. The effect of the water, fat and protein content on the thermal conductivity has been investigated, the measured thermal conductivity values were linearly dependent on water content, and inversely dependent on fat and protein contents of the various dairy products. A slight increase in the thermal conductivity with temperature has been noticed for four cheese samples studied over a wider range of temperature, between 4°C and 44°C.

Measurement of thermal conductivity of edible oils using transient hot wire method.

Thermal conductivities of three different edible oils, namely sunflower oil, corn oil and olive oil, were measured at temperatures 25, 40, 60, and 80°C. The measurements were carried out using a hot wire probe method. The calibration of the probe was performed using 0.3% agar gel with water and glycerin. In general, thermal conductivities of oils used in this study are found to be decreasing with temperature. The values of thermal conductivity measured are quite near to each other, the highest and the lowest being respectively 0.168 W/m K for sunflower oil at 25°C and 0.152 W/m K for corn oil at 80°C.

Ohmic Heating Behaviour and Rheological Properties of Ice Cream Mixes

Ohmic heating is an alternative heating method for Maras-type ice cream mix, which is a traditional ice cream in Turkey. Fast and uniform heating is necessary for the pre-heating of ice cream mixes. Maras-type ice cream, produced in continuous system, was investigated in this study. The results obtained were compared with those of standard ice cream. The ice cream mix used for this study was supplied before the pasteurization step. A voltage gradient of 10–60 V/cm was used to heat the ice cream mixes ohmically from 4°C to 80°C. Temperature dependent electrical conductivity relations were obtained for different ohmic heating rates. Electrical conductivity of the standard type ice cream mix was lower than that of the Maras type ice cream mix. Fat content and temperature had an effect on the electrical conductivity values. The rheological properties of the ice cream mixes were also measured at 4, 25, 40, 60, 70, and 80°C by a Brookfield viscometer. Experimental data were evaluated according to power the law model—rheological constants (K, n) of Maras type ice cream mix were found to be greater than the standard type ice cream mix and increased with temperature.

Effects Of Spray Drying On Physical Properties, Total Phenolic Content And Antioxidant Activity Of Carob Molasses

Abstract In the present study carob molasses (pekmez) was spray dried to obtain a powder with desired improved handling properties. Maltodextrin with dextrose equivalent (DE) values of 8.6, 15.3 and 18.6 was used as a drying agent. Different molasses to maltodextrin ratios (25:75, 50:50), and dryer air inlet temperatures (160 °C, 210 °C) were additional parameters. The spray dried powders were analyzed for glass transition temperature, moisture content, water activity, wetting behavior, particle size, color, total phenolic content and antioxidant activity. The expected increasing effect of decreasing DE value on the glass transition temperature was obscured by different moisture contents. The glass transition temperature was mainly lowered by increasing the pekmez to maltodextrin ratio but also by increasing the air inlet temperature resulting in increasing moisture content. Wetting behavior was strongly influenced by the DE value. Total phenolic content was reduced in general by about 10 % and antioxidant activity changed by about 20 % independent from the investigated parameters. It can be concluded that spray drying of pekmez with addition of maltodextrin is a suitable method to improve and adjust handling properties of pekmez without loss of its nutritional value.

APPARENT SPECIFIC HEAT CAPACITY OF CHILLED AND FROZEN MEAT PRODUCTS

In this article, apparent specific heat capacities of meat and meat products, minced beef, hamburger patties, soudjouk, minced turkey meat, turkey sausage, and turkey soudjouk, were measured at temperatures ranging from −60°C to +40°C, using a differential scanning calorimeter. Experimental data were compared with values calculated from different predictive models given in the literature. Measured apparent specific heat capacities were also mathematically interpreted as a function of temperature, moisture and fat content by application of nonlinear regression analysis for frozen and unfrozen samples. The developed models were found to be in good agreement with the experimental data.

EXPERIMENTAL STUDY ON THERMAL CONDUCTIVITY AND VISCOSITY OF WATER BASED NANOFLUIDS

nanofluids were investigated for various volumefractions of nanoparticles content and at different temperatures. A 3ωtechnique was developed for measuring thermal conductivity of nano-fluids. The theory and the experimental setup of the 3ω measuringsystem is explained; a conductive wire is used as both heater and sen-sor in this system. At first, the system is calibrated using water withknown thermophysical properties. Measured results showed that theeffective thermal conductivity of nanofluids increases as the concen-tration of the particles increases but not anomalously as indicated inthe majority of the literature and this enhancement is very close tothe Hamilton–Crosser model; also this increase is independent of thetemperature. The effective viscosities of these nanofluids increase by

Thermal Conductivity of Macaroni Products

Thermal properties of agricultural products are important to understand their thermal behaviour. They are also used to model and develop processes, for example drying, sterilization, and freezing, in that mass and energy are exchanged. Proper storage of grains without loosing their quality requires the prediction of their temperature in the stock-pile. The success of the prediction of this temperature also depends on the knowledge of the thermal properties of the agricultural products. The primary thermal properties of agricultural products are thermal conductivity, specific heat and thermal diffiisivity. Although specific heat is the only thermal property needed for estimating the amount of energy required to change the temperature of a product, very often the rate of heat transfer must be known for efficient equipment and process design. Thermal diffiisivity is also required for this case. For agricultural products it is often more simple to calculate thermal diffiisivity from specific heat, thermal conductivity and mass density than to measure thermal diffiisivity directly. Therefore, thermal conductivity data is most frequently used (Wallapan and Sweat, 1982; Chuma et al, 1981).

Production of crispy bread snacks containing chicken meat and chicken meat powder

Chicken meat in two different forms (chicken meat and chicken meat powder) were added into white flour and whole wheat blend baguette bread formulations for protein enrichment and finally developing new and healthy snacks. The chicken meat and powder levels were 10% for white flour baguette, and 15% for whole wheat blend. The dried baguette samples were packaged under 100% N2, and physical, chemical, microbiological and sensorial properties were evaluated during 3 months of storage. Protein content of chicken meat powder added samples were found statistically higher than chicken meat added samples. Hardness of the snacks was significantly affected from type of chicken meat, such as values were higher for chicken meat added samples than chicken meat powder added samples. Lipid oxidation of the snacks was determined by TBA analysis, and TBA value for whole wheat mixture snack with 15% of chicken meat was the highest among all during storage. The highest overall acceptance score was obtained from white flour snack with 10% chicken meat. There was no coliform bacteria detected during storage and the results of yeast-mold count and aerobic plate count of snacks remained between the quantitative ranges.

Assessment of modulated hot wire method for thermophysical characterization of fluid and solid matrices charged with (nano)particle inclusions

Recently we reported on simultaneous thermal conductivity k and thermal diffusivity a measurement of liquids and in particular of nanofluids in a configuration using an ac excited hot wire combined with lock-in detection of the third harmonic (3ω method) [1]. The conductive wire is used as both heater and sensor. The requirements for the asymptotic validity of the line heat source model are fulfilled at low modulation frequencies below a few Hz. The study of the relative sensitivity of signal amplitude and phase to changes in k and a indicates that there is an optimum frequency range for accurate and stable results. We extend by up to two decades the feasible frequency range for 3ω measurements by considering various more elaborate models for the heat transfer between the wire and the fluid. Finally we show that the same ac hot wire method can be applied to soft solid, composite materials. We measured the k enhancement of a poly(ethylene vinyl acetate) EVA polymer matrix charged with various fractions of graphite.

Thermophysical Properties of Foods at Frozen State

In designing food freezing equipment and processes, knowledge of physical and thermal properties of foods is essential. The computation of refrigeration requirements and freezing times can be done only when quantitative information on food properties is available. Considerable research has been done to measure and model properties of foods undergoing various processing treatments. The key properties of interest in food freezing include density, thermal conductivity, specific heat and thermal diffusivity.