Airflow mixing

Premix duct based on a lean premixed prevaporised (LPP) concept with a venturi configuration, which has been optimized in order to obtain a good velocity profile at the inlet to the catalytic section. Fuel is injected upstream of the venturi minimum section with injectors angled relative to the airflow. Mixing is achieved with an inlet radial/axial turbulence generator in the venturi inlet. 

When the airflow meets a surface whose temperature is lower than the dewpoint, water vapor from the air condenses on the surface of the cooling coil. If all air comes into contact with the cold surface, the state of the air after the process will be at point 3. Some air always escapes the cold surface, and therefore the state of air after contact with the coil is a mixture of saturated air (3) and escaped air (1). The mixing point (2) lies on the line connecting points 1 and 3, as shown in Example 8. The nearer point 2 is to point 3, the more effective is the cooling coil. 

In rooms where energy is introduced primarily by supply air jets, air distribution methods are referred to as mixing type. With a perfect mixing-type air distribution, airflow pattern and air velocity at any point in the room are... 

Assume the use of mechanical ventilation with full mixing ventilation in the room, and calculate a rough estimate of ventilation airflow found by assuming dilution of contaminants released to the room air to one-third of the TLV level given for the substance in question. 

In order to have effective exchange of air in important locations in a room, the age of the air in those locations should be low. The basis for comparison is the complete mixing scenario. That scenario gives the same age for any air volume selected in the room, identical to the nominal time constant for the ventilation airflow,. A steady-state scenario is assumed. See Sutcliffe for an overview of definitions related to age of air. The various air exchange efficiency indices are presented in Table 8.6. 

German guidelines base the division on the resulting airflow pattern within the room rather than distribution methods. They suggest that airflow patterns be divided into four categories hall-filling mixed flow zonewise mixed flow low-momentum, low-turbulence flow for the air supply in the work region and zonewise displacement ventilation. 

The key flow elements in the zoning strategy arc the supply air jets, plumes of the buoyancy sources, buoyant airflows along the surfaces, and turbulent mixing between the controlled and the uncontrolled zones, as in Fig. 8.32. These flow elements have significant influence on the effectiveness of the system. 

The plume airflows (q ) are determined as described in Section 7.5. The turbulent mixing iqi,) between zones and the penetration of the plume airflows iq, h,n) through the supply airflow patterns must be determined specially for the air distribution method and devices used as well as the locations of plumes and supply air devices. 

The effect of the plume airflow rate and the turbulent mixing airflow rate through the zone boundary is presented in Fig. 8.35. The heat removal effectiveness and contaminant removal effectiveness are presented as functions of the relative airllow rate. 

The influence of airflows from ventilating systems must also be considered. Processes using mediums of different physical qualities when mixed will have separation into different layers. Transmission of energy between molecules in flowing mediums takes place in the direction of the velocity. This strengthens the separation into parallel layers. The level of fluid in containers and tanks is due to stratification of horizontal temperature layers, while airflow after batteries, heat-recovery systems, and humidifiers or dehumidifiers will separate into parallel layers. 

These combinations are possible without too detailed design of the combined jet and exhaust, since the wide jet itself will act as a separator between inside and outside and the consequences of an imbalance of supply and exhaust airflow are small. The relative mixing of outside and inside air into the jet is less than for a thin air jet, which also makes it easier to design fan(s) and ducts. The high velocity needed requires a high airflow rate and, with heating, can be expensive to operate. 

For the models described, the usual assumption for air nodes in regard to the room air distribution is still valid. This means that each air node represents a volume of perfectly mixed air. Thus, the same limitations as for thermal and airflow models apply Local air temperatures and air velocities as well as local contaminant concentrations can he neither considered nor determined. This also means that thermal comfort evaluations in terms of draft risk cannot be performed. 

A common principle for the prt)duction of smoke for this purpose is to cvat>-orate a mineral oil by electrically hearing it and to mix the vapor into air. The oil will then condense and form a mist. Different such apparatus can be found on the market. Some of them are aimed for the visualization t f airflow but others are intended lor special effects in theaters, discotheques, etc. Figure 12.3 shows one such apparatus commonly used for this purpose. 

Dilution ventilation or general exhaust ventilation A mixed airflow designed to dilute the contaminants within a space to required safe concentration... 

Constant flow An assembly within which the primary airflow rate is modulated and mixed with air induced from the surroundings by means of a fan (also known as series type). 

Induction supply ATD An air terminal device in which the primary air from the duct induces secondary airflow from the treated space in such a way that a high rate of mixing between the air from these two sources takes place within the device. 

Mixing actuator Component designed to mix two airflows without controlling the volume. 

Mixing section of an AHU A section where outdoor airflow and the recirculation airflow are mixed in a controlled manner. 

For effective volatilization using an enclosed mechanical aeration system, contaminated soil is mixed in a pug mill or rotary drum. The gasoline components are released from the soil matrix by the churning action of the air/soil contact. The induced airflow within the chamber captures the gasoline emissions and passes them through an air pollution control device (e.g., a water scrubber or vapor-phase carbon adsorption system) before they are discharged through a properly sized stack. 

A new desiccant formulation was prepared from a mixture of submicron-sized silica gel and molecular sieves to achieve the best combination of large water capacity, rapid moisture adsorption and easy regenerability. The formulation also tolerates the presence of VOCs and smokes. Commercial NaX and silica gel were crushed and mixed in the proportion of 1 2 and wash coated on a monolith for testing. The same test cell shown in Fig. 12.7-2 was used. The airflow to the saturator was adjusted to obtain the desired humidity in the feed air. Humidity sensors located at the flow cell inlet and outlet, were used to... 

The compressed, heated air is supplied to the ramburner through the air injection ports. Two types of air-injection ports, forming a so-called multi-port, are shown in Fig. 15.14 the forward port (two ports) and the rear port (two ports). The multi-port is used to distribute the airflow to the ramburner 34% is introduced via the forward port and the remaining 66 % via the rear port. The combustible gas formed by the combustion of the gas-generating pyrolant is injected through the gas injection nozzle and mixed with the air in the ramburner, and the burned gas is expelled form the ramburner exhaust nozzle. The pressures in the gas generator and the ramburner are measured by means of pressure transducers. The temperatures in the gas generator and the ramburner are measured with Pt-Pt/13%Rh thermocouples. 

When the airflow induced from the atmosphere is introduced through the singleport intake, the mixture formed in the forward part of the ramburner is fuel-lean because all the air induced from the single-port air-intake is introduced into the forward part. Thus, an excess-air mixture (fuel-lean mixture) is formed, the temperature of which becomes too low to initiate self-ignition. However, when a multi-port intake is used, the airflow is divided into two separate flows, entering at the forward part and the rear part of the ramburner. At the upstream flow, the air-to-fuel ratio can be made stoichiometric, which allows the mixture to ignite. At the downstream flow, the excess air is mixed with the combustion products and the temperature is lowered to increase the specific impulse. 

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