Modeling air exchange in office premises using a microperforated fabric air duct

Summary

The issues of improving the quality of the internal environment of an office building using an advanced air dispersion device – a fabric air duct with micro-orifices are considered. The advantage of this device is supplying the incoming air by jets with a low impulse allowing to locate the devices near the working space in offices eliminating the risk of drafts at the working places. The purpose of the work is a comparative numerical calculation of the efficiency of arranging the air exchange in an office building with two air supply schemes: through supply grilles and through a fabric air duct with microperforation. Modeling was carried out using the commercial STAR-CCM + software package. The system of Reynolds equations with closure using the k-ω SST turbulence model (Mentor) is used to describe the air movement. As part of the study, data on the nature of the change in temperature and air speed along the height of the working area of the office were obtained. It has been determined that while air is supplied through the supply grilles, the temperature (23.3–27.2 °C) and air speed (0.06–0.22 m/s) meet the permissible microclimate standards (GOST 30494-2011); while arranging the air exchange with the use of a microperforated air duct they correspond to the optimal parameters (temperature 23.1–25.4 °С, air speed 0.09–0.13 m/s) that are comfortable for the human body. Thus, the use of a microperforated air duct enhances the efficiency of heat surplus assimilation in comparison with traditional air distribution devices (ventilation grilles).

Key words

numerical simulation , ventilation , control volume approach CFD , air distribution , heat-mass exchange , microperforated fabric air duct

Heat exchange processes in open wastewater treatment facilities

Summary

The paper dwells upon studying heat and mass transfer processes between waste liquid passing through open wastewater treatment complexes and the environment. Under the conditions of operating facilities heat and mass transfer results in the waste liquid temperature increase or decrease depending on the time of year; and that leads, provided other things equal, to a change in the quality of treatment. The possibility of using mathematical models for open wastewater structures that describe heat and mass transfer processes used in heating engineering is considered. The study was carried out by analyzing domestic and foreign sources on heat and mass transfer. Changes in the temperature of waste liquid in open facilities were determined by calculation for a specific facility and compared with actual measurement data at the same facility. During the study, items of heat loss and input were established for the winter and summer periods of the year in three open structures: primary settling tanks, aeration tanks and secondary settling tanks. A mathematical model has been tested that determines the change in the temperature of the waste liquid depending on the residence period in the structures. The method for calculating primary settling tanks, aeration tanks and secondary settling tanks has been improved that provides for accounting at the design stage of the treatment facilities of the changes in the temperature of waste liquid during treatment, which eliminates deterioration in the quality of waste water treatment at any time of the year.

Key words

heat-mass exchange , aeration tanks , heat loss and input , primary and secondary settling tanks , wastewater quality , temperature variation