For the calculation of velocities in air-jets behind the ventilating outlets, the constants of ventilating outlets must be known. These constants are specified for each type of ventilating outlets experimentally. They can be usually defined from measured behaviours of axis velocities in the main area of jet, which demands to measure velocity profiles in cross flow section, in several distances from the outlet. The constants of ventilating outlets can be also defined from the air-jet extension in the main jet area behind the ventilating outlet.
Unexpectedly, the indoor-outdoor pressure difference did not affect significantly the moisture content in different layers of two outer walls but the moisture content depended more strongly on the moisture content in outdoor.
When designing the outlets for the ventilation or hot-air heating of particular spaces, we meet usually the problems to specify a form and reach of the air jet and a distribution of velocities and temperatures in the space followed. In practice the calculations of nonisothermal air jets are made using a number of calculation relations to be found e.g. in lit. (1) and other. But when applying the analogical relations derived by different authors we can find out considerable differences in results.
The influence of the electrostatic forces on airborne particles have been known for centuries. These early discoveries have been summarized in several publications including the classical book "Electrostatic Precipitation" by White (1) and many others (e.g. 2, 3, 4). The utilization of the electrostatic force led to the development of electrostatic precipitator (ESP) which has been used for pollution control purposes since the beginning of this century. An excellent historical review about the development of electrostatic gas cleaning has been presented by White (1).
The exterior hood has been used extensively in the local exhaust devices to capture a variety of contaminants generated in a working-site. The performance of a hood can be measured by either how well it captures the contaminants or how far away it can perform an effective capture. It has been known theoretically that in the presence of an uniform cross draft a capture envelope will form in front of an exhausted opening(2, 3). All streamlines inside an envelope will lead into the opening; otherwise, those outside the envelope will lead to infinity downstream.
Occupational hygiene conditions were examined in a welding shop after repairing the air-handling unit. Good indoor air quality was achieved with the new replacement ventilation system. The airborne dust concentrations varied from the detection limit of 0.1 mg/m3 to 0.8 mg/m3 at the stationary sites. Even the breathing zone concentrations of the welders remained below or equal to 2.1 mg/m3. The concentrations of carbon monoxide did not exceed the level of 1 cm3/m3.
It is of prime importance at the design stage that the designer of an industrial ventilation system makes a reasonable assessment as to the owning and operating costs of an Industrial Ventilation System. Armed with these findings the designer must consider what improvements can be made by considering a different approach or by using other types of plant. The designer must inform the owner of the plant of any alternatives.
The owning and operating costs of a system are made up of the following items:
The paper deals with a three dimensional modelling of an experimental device realized in the Department of "Fisica Tecnica" of the University of Rome "La Sapienza" in cooperation with the Italian National Council of Researchers (CNR) in order to investigate the performances of shutter type air curtains as a dynamic barrier against the diffusion of fumes or airborne toxic substances.
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