Heat conductivity of some food products: theoretical models and practical measurements

Thermo-physical properties are necessary for the design and prediction of heat transfer operation during handling, processing, canning, and distribution of foods. Thermal conductivity is defined as the ability of a material to conduct heat. There are steady-state and transient-state methods for measurement of thermal conductivity. The most commonly used transient methods are the thermal conductivity probe method, transient hot wire method, modified Fitch method, point heat source method, and comparative method. In this paper the modified Fitch method was used in order to measure thermal conductivity; the results were compared with the one predicted by some heat conductivity models: series model, parallel model, the weighted geometric mean method. Experimental tests and calculations were applied to the following food items: dry salami (salam uscat CrisTim); Transylvanian salami (salam ardelenesc); rustic sausage (parizer ţărănesc Caroli). The experimental tests were performed immediately after the products were purchased and then repeated after they were stored for one week, at 6°C. The results show that the series model adequately describes the heat conductivity for dry salami and rustic sausage, while the weighted geometric mean model is more appropriate Transylvanian salami, which has the lowest water content and the highest fat content

Researches regarding the aggresiveness of the active parts over the soil

Researches aiming to establish the effect of the active parts of the agricultural units over the soil’s physical degradation were developed; several variants regarding the machinery used for soil tillage, for maize growth, were taken into account (including hoeing). For each variant the bulk density and soil penetration resistance were measured, as well as the average weighted diameter and the water stability of the soil el

Research on the operation of an innovative equipment hybrid drying

The study of the operating parameters of an innovative equipment hybrid drying for cereal seeds is important for drying technology. An optimal operation of the hybrid dryer model requires the monitoring of essential technological parameters such as the velocity, temperature and humidity of the drying agent at the entrance to the dryer, as well as the temperature plus humidity of the drying agent at its exit. The energy consumption of the hybrid drying equipment is also monitored. Equipping the hybrid dryer with sensors to track these technological parameters is important, and knowing the accuracy of their measurement both in stationary and non-stationary regimes, leads to the evaluation of the degree of variability of the acquired numerical data. An important role in the evaluation of the technological parameters of the installation is also given by the mounting position of the sensors in the hybrid drying installation. The innovative equipment hybrid drying has both a convective pre-drying component and a final drying component through high frequency currents (microwaves). In the convective drying component, the cold air is heated in a heating battery with electrical resistances to a maximum of 44.9°C at an average dryer air inlet velocity of 16.54 m/s. In the final part of the drying plant, after passing through the microwave component, the maximum temperature reaches 39.3°C. The average energy consumed in idle operation of the hybrid dryer is 1.52 kWh

Studies on the Physical Changes in Corn Seeds during Hybrid Drying (Convection and Microwave)

Hybrid seed drying technology, based on convection and microwave drying, is a modern method, and the research on the physical changes in cereal seed resulting from hybrid drying is still in its infancy. The aim of the present paper is to study the uniformity of the drying process by examining the physical changes occurring in corn seeds. An innovative drying equipment, combining convective and microwave drying, was used to dry corn seeds (variety DKC5068). The convective drying was performed during the pneumatic transport of the seeds, using hot air at a maximum temperature of 50 °C; the microwave-based drying was performed using 2.45 GHz microwaves. Thus, the seeds were volumetrically heated at a temperature which does not exceed 44 °C. The physical changes in corn seeds were measured in terms of moisture, volume, cracking and color. The results regarding the moisture and volume changes in the seeds during the drying process proved that moist seeds are more homogeneous than dry seeds. The change in volume also changed the stiffness of the seeds, which showed greater homogeneity after drying compared to wet seeds. Hybrid drying led to an average shrinkage of 8.76% compared with the original seed volume, while the percentage of seeds showing cracks after drying increased by 22%. Generally, the drying process also led to color changes, but in the case of hybrid drying the results were inconclusive. Hybrid drying of corn seeds requires a shorter time and does not significantly influence physical characteristics, compared to other drying technologies

Research on the physical changes of cereal seeds dried in the innovative equipment hybrid drying

Hybrid drying of cereal seeds is a modern drying method. Over time, more research has been carried out in the field of grain drying, moving from convective drying as the commonly used method, to hybrid drying that combines the convective phenomenon with that of thermal conduction or radiation. Current technology offers the possibility of using hybrid methods of drying cereal seeds, which have the advantage of lower energy consumption and shorter drying time compared to the convective drying method. The paper proposes the analysis of the physical changes that occur after the hybrid drying of cereal seeds. The research was carried out by drying cereal seeds on an innovative hybrid drying facility that uses both convection and microwaves. In this sense, the physical changes that occur in corn seeds were studied, through determinations of humidity, changes in color, dimension, as well as changes related to the mechanical resistance of the seeds. The maximum drying temperatures inside the dryer were between 48 and 50 °C, obtained at a maximum microwave power of 2400 W, and a drying time of 3 seconds

Assessment of the quality of secondary production from different agricultural crops used as primary material for densified solid biofuels

The quality of densified solid biofuels is directly influenced by the biomass characteristics used as feedstock. Under the conditions of the Republic of Moldova, the main source of raw material used in the production of briquettes and pellets is represented by agricultural residues and those from the food industry. For this reason, it is important to know the qualitative characteristics of these residues. The purpose of this study is to highlight the main qualitative parameters of agricultural residues used as energy sources specific for the Republic of Moldova. The issue of research refers to the estimation of the possibilities of using indigenous agricultural residues as a raw material for the production of densified solid biofuels with ENPlus 3 characteristics. The investigative methodology is based on a complex study, organized and realized in the Solid Biofuels Laboratory of the State Agrarian University of Moldova. The paper presents the results of the research regarding the estimation of the calorific value, the moisture content, the ash content and the chemical analysis of the main agricultural residues from the agrarian sector depending on their origin and specificity, emphasizing on herbaceous, arboreal and vines residues. The study showed that only about 10% of the residues from agricultural activities can be used directly to produce bio briquettes and pellets with qualitative indicators according to the requirements of ENPlus 3. It should be noted that practically, all agricultural and vineyard residues can be used as a raw material to the production of ENPlus certified densified solid biofuels, and herbaceous residues can only be used in mixtures with other types of vegetable biomass or require pre-treatment before densification, for example, by torrefaction

The improvement of a traction model for agricultural tire–soil interaction

The goodness-of-fit analysis performed over the results provided by a model presented in a previous paper proved that the theoretical data were very well correlated with the experimental data with regard to the traction force (with Pearson coefficient r2 over 0.9); however, the model was less accurate in predicting traction efficiency, with r2 = 0.203. In order improve the model and obtain a better fit between the theoretical and experimental data (especially for the traction efficiency), the model was updated and modified by taking into account the geometry of the tire cross section, which was considered to be a deformable ellipse. Due to the deformable cross section, the minor axis of the tire–ground contact super ellipse decreased compared with the previous model (from 0.367 m to 0.222 m), while the major axis increased (from 0.530 m to 0.534 m). As a result, different data for the traction force and traction efficiency were obtained. The effect of the wheel travel reduction (wheel slip) over the tire–soil shear area was also investigated, and the hypothesis of a constant shear area (independent of wheel slip) provided the most accurate results. The goodness-of-fit analysis performed using the data predicted by the modified model showed that the Pearson coefficient increased significantly with regard to the traction efficiency (from 0.203 to 0.838), while it decreased by only 2.7% with regard to the data for the traction force, still preserving a high value (r2 = 0.896)