mixing

The mixing system (even called the dilution system) is normally used throughout the world to supply air to a premises. In the mixing system you blow air at high velocity into the room at a temperature which gives you the wanted room temperature. If the system works perfectly, you will have the same temperature and concentration of contamination in the whole room. That is because the supplied air and the air in the room is mixed due to induction.

Ventilation systems perform a number of tasks. They must remove contamination/pollution, they act as heat/cold transporters and they must create a satisfactory room climate without causing draughts. States that users must be aware of the limitations of ventilation systems and that ventilation systems are not able to carry out all tasks completely satisfactorily. Compares the efficiencies of displacement and mixing systems and gives guide values for temperature differences between room air and supply air for office and industrial applications.

The sink or removal rates for two reactive indoor air contaminants (NO2 and SO2) were evaluated in an environmental chamber as a function of material type (painted sheetrock, wallpaper and carpeting), variable surface area of the material, relative humidity and air mixing. Sink rates for SO2 are generally higher than those for NO2. The sink rates for NO2 and SO2 were found to increase with material surface roughness and material surface area. Increases in relative humidity had a pronounced positive impact on SO2 sink rates and a smaller but significant impact on NO2 sink rates.

This article examines a solution procedure which can determine the flow in an air-conditioned room. The method is based on the solution of a group of equations for the flow (four non-linear partial differential equations) by means of a numerical method. Comparison with test results indicates that the method studied is suitable for prediction of air movement in an air-conditioned room when the flow is steady and two-dimensional. The method can be extended to give the required information for the evaluation of thermal comfort in the room.

Models are defined for various mixing conditions, in continuous flow systems. Differential equations are derived which take into account aneffective volume of mixing, possible short-circuiting, hold-up time of the system, partial displacement or piston flow. The values of the different factors contained in the integrated equations can be determined experimentally by the particular response of a given system to a sudden change in composition of the feed. A correlation of the effective volume of mixing and the agitator r.p.m. is presented.

The problem of describing quantitatively the effective ventilation in a room when the air within the room is imperfectly mixed is discussed. It is suggested that the protection afforded by the ventilation to any given position against air