Previous studies have shown that poorly ventilated classrooms can have negative impact on the health of children and school staff. In most cases, schools in Serbia are ventilated naturally. Considering their high occupancy, classroom air quality test determines the level of air pollution, after which it is possible to implement corrective measures. The research presented in this study was conducted in four schools which are located in different areas and have different architecture designs. Measurements in these schools have been performed during the winter (heating season) and spring (non-heating season) and the following results were presented: indoor air temperature, relative humidity and carbon dioxide concentration. These results show that the classroom average concentration of carbon dioxide often exceeds the value of 1500 ppm, during its full occupancy, which indicates inadequate ventilation. Measurement campaigns show that carbon dioxide concentration increased significantly from non-heating to heating season in three of the four schools. Analysis of measurements also determined high correlation between relative humidity and carbon dioxide concentration in all schools in winter season. This fact may constitute a solid basis for the fresh air supply strategy. [Projekat Ministarstva nauke Republike Srbije, br. III42008: SINPHONIE - Schools Indoor Pollution and Health: Observatory Network in Europe]

-The paper addresses numerical simulation for the case of convective drying of hygroscopic material in a packed bed, analyzing agreement between the simulated and the corresponding experimental results. In the simulation model of unsteady simultaneous one-dimensional heat and mass transfer between gas phase and dried material, it is assumed that the gas-solid interface is at thermodynamic equilibrium, while the drying rate of the specific product is calculated by applying the concept of a "drying coefficient". Model validation was done on the basis of the experimental data obtained with potato cubes. The obtained drying kinetics, both experimental and numerical, show that higher gas (drying agent) velocities (flow-rates), as well as lower equivalent grain diameters, induce faster drying. This effect is more pronounced for deeper beds, because of the larger amount of wet material to be dried using the same drying agent capacity.

ALEKSANDAR VENCL, MIHAILO MRDAK, and MILOSˇBANJACThe microstructure and tribological properties of ferrous coatings applicable to cylinder bores were investigated in this study. Two kinds of ferrous powders were sprayed on Al-Si cast alloy (EN AlSi10Mg) substrate by atmospheric plasma spraying. Microstructural analysis showed that various Fe oxides were formed in the coatings. The presence of pores, unmelted particles, and Fe precipitates was also noticed. The pin-on-ring tribometer was used to carry out tribological tests under lubricated sliding conditions: sliding speed of 0.5 m/s, sliding distance of 5000 m, and normal load of 450 N. High porosity and the presence of larger and irregularly shaped pores as well as the amount of oxides were the controlling factors for the crack initiations and, consequently, the wear rate. Tribological properties of the coatings were compared with gray cast iron as a standard material for cylinder blocks and showed that, for the investigated conditions, both coatings could be an adequate substitution.

The paper presents an experimental analysis of the relationship between local thermal comfort and productivity loss in classrooms. The experimental investigation was performed in a real university classroom during the winter semester in city of Belgrade. Measurements were taken for four scenarios, with different indoor comfort conditions. Variations were made by setting the central heating system on/off, adding an additional heat source to provoke higher indoor temperatures, and measuring the radiant asymmetry impact. Innovative questionnaires were developed especially for the research, in order to investigate students' subjective feelings about local thermal comfort and indoor environmental quality. Local predicted mean vote and predicted percentage dissatisfied indices were calculated using data measured in situ. The results were compared to existing models recommended in literature and European and ASHRAE standards. Student productivity was evaluated using novel tests, designed to fit the purposes of the research. Surveys were conducted for 19 days under different thermal conditions, during lectures in a real classroom, using a sample of 240 productivity test results in total. Using the measured data, new correlations between the predicted mean vote, CO 2 , personal factor and productivity loss were developed. The research findings imply that local thermal comfort is an important factor that can impact productivity, but the impact of the personal factor is of tremendous importance, together with CO 2 concentration in the classroom.

With the aim of evaluating capabilities of a ventilation system to control the spread of smoke in the emergency operating mode, thereby providing conditions for safe evacuation of people from a fire-struck area, computational fluid dynamics simulation of a fire in a semi-bedded garage was conducted. Using the experimental results of combustion dynamics of a passenger car on fire, optimal positions of ventilation openings were determined. According to recommendations by DIN EN 12101 standard, the operating modes of a ventilation system were verified and optimal start time of the smoke extraction system was defined.