Jiri Pospisil

Thermoelectric Power Generation Utilizing the Waste Heat from a Biomass Boiler

The objective of the presented work is to test the possibility of using thermoelectric power to convert flue gas waste heat from a small-scale domestic pellet boiler, and to assess the influence of a thermoelectric generator on its function. A prototype of the generator, able to be connected to an existing device, was designed, constructed, and tested. The performance of the generator as well as the impact of the generator on the operation of the boiler was investigated under various operating conditions. The boiler gained auxiliary power and could become a combined heat and power unit allowing self-sufficient operation. The created unit represents an independent source of electricity with effective use of fuel.

Computational modelling of airflow in urban street canyon and comparison with measurements

The main goal of this study was to predict the airflow in a street canyon surrounded by an urban area using CFD modelling. In the street geometry described in the main part, the actual airflow directly influences air infiltration into buildings. Different models of turbulence were tested as well as specific wind boundary conditions. A correct assignment of boundary conditions (i.e., mainly wind conditions) is a very important step to obtain results that are comparable with measurements. Results of 3D airflow in the street canyon were obtained for different velocities and directions of an undisturbed wind above the roof level. Wind conditions were prescribed in two different ways, as a velocity profile on the incoming side of the solution domain, in the other as a fixed velocity in the layer where the wind velocity was measured. Results of calculations are compared with measurements done in the studied street canyon. Individual models of turbulence were tested to obtain the best agreement between predictions and measurements.

MUNICIPAL SOLID WASTE GASIFICATION WITHIN WASTE-TO-ENERGY PROCESSING

This paper discusses theoretical assets and liabilities of a use of advanced thermal technologies within waste-to-energy (WTE) processing. Gasification and pyrolysis are compared to conventional incineration. Major part of the paper deals with results of gasification experiments: various wastes were gasified within a fluid generator with a circulating fluidized bed. The results were later compared. Lower heating value, composition of the syngas and amount of tar within the syngas were the important observed factors. Experiments were performed at a Biofluid, the pilot facility at the Faculty of Mechanical Engineering in Brno.

Particle re-suspension in street canyon with two-way traffic

The paper focuses on determination of the wind threshold velocity of re-suspension (at the height of 10 m) and the near-ground air threshold velocity of re-suspension (at the height of 0.25 m) for particles of size 10 µm in a particular urban street canyon with two-way traffic. The wind threshold velocity of re-suspension is derived from a long-term measurement carried out in the city of Brno. A numerical modelling based on the finite volume method is used for a detail study of the relation between a wind velocity above buildings roofs and a near-ground air velocity in the street canyon.

Dispersion of pollutants in a street canyon and street intersection under traffic-induced flow and turbulence using a low Re κ-ε model

A 3-D Eulerian-Lagrangian approach to moving vehicles is presented that takes into account the traffic-induced flow rate and turbulence. The method is applied to pollutant dispersion in an individual street canyon and a system of two street canyons forming a perpendicular intersection. The approach is based on computational fluid dynamics (CFD) calculations using a Eulerian approach for continuous phase and a Lagrangian approach for moving vehicles. The wind speed was assigned values of 4, 7 and 12 m/s. One-way and two-way traffic with different traffic rates per lane is considered. In the case of the intersection, a longitudinal wind direction was assumed. Predictions show differences in the pollutant dispersion in the case of one-way and two-way traffic.

AUTOMATIC BIOMASS BOILER WITH AN EXTERNAL THERMOELECTRIC GENERATOR

This paper presents the design and test results of an external thermoelectric generator that utilizes the waste heat from a small-scale domestic biomass boiler with nominal rated heat output of 25 kW. The low-temperature Bi2Te3 generator based on thermoelectric modules has the potential to recover waste heat from gas combustion products as effective energy. The small-scale generator is constructed from independent segments. Measurements have shown that up to 11 W of electricity can be generated by one segment. Higher output power can be achieved by linking thermoelectric segments. The maximum output power is given by the dew point of the flue gas. The electrical energy that is generated can be used, e.g., for power supply or for charging batteries. In the near future, thermoelectric generators could completely eliminate the dependence an automated domestic boiler system on the power supply from the electricity grid, and could ensure comfortable operation in the event of an unexpected power grid failure.

Particulate matter dispersion modelling along urban traffic paths

In this paper authors compare two different approaches of 10 μm particles (PM10) dispersion modelling in urban areas. The study is focused on comparison of the Eulerian-Lagrangian approach accurately describing particle aerodynamics and the passive scalar approach representing simplified alternative for description of dispersion processes. CFD code StarCD has been used for this study as appropriate tool capable of correct velocity field prediction and inclusion of both approaches. A street canyon with intensive traffic located in the central part of the city of Brno is used as a convenient study area.

Comparison of Different Turbulence Models Applied to Modelling of Airflow in Urban Street Canyon and Comparison with Measurements

Residential buildings in cities are ventilated using different systems for ventilation. Except for systems that consist in opening windows, there are more sophisticated systems that are controlled by different manners. Among them, hybrid systems are recently gaining more attention as they promise to be energy effective with a good control of indoor air quality. Operation of such ventilation systems can be significantly influenced by airflow in street canyons. Thus, correct prediction of airflow is a prerequisite for efficient functioning of such systems. Authors of this paper choose Agiou Fanouriou street canyon in Athens as a test canyon for comparison of modeling and field measurements.

Threshold velocity of pollination in urban area of the city of Brno

Wind velocity directly influences pollen release rate from mother plants and subsequently, the transport of pollen grains. The threshold velocity of pollination is defined as the lowest wind velocity with evidence of pollen concentration above the threshold pollen concentration. Only a limited number of published papers deal with the relationship between wind velocity and pollen concentration. The results of in situ measurements were used for the analysis of the relation between the wind velocity and pollen concentration in an urban canopy layer. Subsequently, numerical modelling (CFD code StarCD) was used for the parametrical studies that tested the influence of the wind velocity on pollen release from the mother plant and the resulting pollen dispersion in a ground boundary layer.

Pollen dispersion and pollen deposition modelling in micro-scale and regional-scale numerical models

The paper presents part of the research on model development of pollen dispersion and pollen deposition in an urban canopy layer. The CFD code StarCD was used as the basic computational tool for carried out studies. Three different approaches of pollen deposition was tested in two different scale numerical models, namely the regional-scale model covering area of 144 km 2 and the micro-scale model covering area of 1 km 2 . The tested pollen deposition approaches were based on the following assumptions: (i) the deposition velocity prescribed in accordance with the sedimentation velocity; (ii) the zero pollen concentration prescribed on the ground surface; (iii) the deposition considered in accordance with the experimental deposition velocity. The objective of the study is to compare pollen concentration fields obtained from calculations utilising different simplified mathematical descriptions of pollen deposition in a vegetation cover of the ground surface.