Stratification temperature

Plumes are influenced by the temperature stratification. The driving force of the plume is the temperature difference between the plume and the surroundings. When this difference diminishes, the plumes will disintegrate and spread horizonraliy in the room see Fig. 7.77. 

We now put the cylinder of Example 7.5.4 inside a room with a vertical temperature gradient of 1.5 C/m (see Fig. 7,78). In this case we assume that there are other heat sources in the room. We want to Investigate how this temperature stratification influences the volume flow in the plume above the cylinder, and at what height the plume stops. 

Aksenov, A.A., A.V. Gudzovski, E.O. Shilkrot, and A.M. Zhivov. 1998. Thermal plumes above heat sources in rooms with a temperature stratification. In Roomvent 98. 

The use of a natural ventilation system assumes temperature stratification throughout the room height. Air close to heat sources is heated and rises as a thermal plume (Fig. 7.105). Part of this heated air is evacuated through air outlets in the upper zone, and part of it remains in the upper zone, in the so-called heat cushion. The separation level between the upper and lower zones is defined in terms of the equality of and G, which are the airflow rate in thermal plumes above heat sources and the airflow supplied to the occupied zone, respectively. It is assumed that the air temperature in the lower zone is equal to that in the occupied zone, and that the air temperature in the upper zone is equal to that of the evacuated air,... 

Natural or displacement ventilation systems creating temperature stratification (Fig. 7.109(i)... 

The mechanism of turbulent heat exchange between tbe upper and lower zones in the case of ventilation system design with temperature stratification is described in Section 7.3. 

A characteristic of many industrial halls is that zones of occupancy take up only a small portion of the room volume and height. In addition, the flows are normally buoyancy dominated. This results in a vertical temperature stratification that can be utilized for room air conditioning design in order to achieve effective climatization along with low energy consumption. 

Outside air entering the space through openings near the ground spreads over the floor and absorbs energy from the floor surface. The resulting air temperature increase leads to buoyancy and forces the air up into the upper hall zone. This results in a temperature stratification in the hall. Due to this vertical temperature gradient, the air in the occupied zone does not reach the exhaust air temperature (see Fig. 11.37). 

Due to the methods and limitations outlined in Section 11.3..3, in thermal comfort analysis, draft risk evaluations cannot be performed using this type of room model. Analysis of air temperature stratification and thermal comfort for the occupant zone can be achieved only by using multi-air-node room models. 

Turbulence is generated by wind shear in the surface layer and in the wake of obstacles and structures present on the earth s surface. Another powerful source of turbulent motion is an unstable temperature stratification in the atmosphere. The earth s surface, heated by sunshine, may generate buoyant motion of very large scale (thermals). 

The temperature stratification is used to avoid mixing in a water storage tank. These tanks are not only deep ones but also shallow ones as shown in Figure 184. The degree of stratification depends on momentum of water and density or temperature difference at inlet. The appropriate condition at inlet can stratify water in a tank whatever the depth of a tank is. As the deep tank has difficulties of construction, the shallow tanks in basement are often applied. 

The pressure difference promoting vertical vent flows are solely due to temperature stratification, and conform to a hydrostatic approximation. In other words, the momentum equation in the vertical direction is essentially, due to the low flows ... 

Diesel fuel and kerosene alone are not effective solvents for use in solubilizing most WCMs for low-temperature application. The low KB value of diesel fuel and kerosene makes these fuels ineffective at holding the WCM in solution for extended periods of time at low temperatures. Stratification and separation of the WCM from solution can lead to application problems such as filter plugging and inaccurate WCM treatment. 

The Influence of Temperature Stratification on the Thermal Performance of a Natural Draft, Dry Cooling Tower Buxmann, J. 

Although much work has been performed to improve and develop other methods of sterilization, very little has been accomplished in the field of dry-heat sterilization. The process is time consuming and difficult to control because of the temperature stratification and slow heating rate. Dry heat is still the agent of choice for sterilizing items that might not be adequately penetrated by steam and that will tolerate high temperatures, such as oils, petrolatum, and closed containers. ... 

Lakes Closed system. Are subject to evaporative effects. Assumes poor mixing within the lake (temperature stratification with depth). 

The effect of temperature stratification on the atmosphere can be illustrated by considering the different forms a plume may assume. The form of a plume is determined essentially by the relation of the plume release point to any stable, neutral, and unstable layers that may be present the basic forms have been summarized by Slade (1968) and Arya (1999). In a stable layer, vertical mixing of the plume will be limited, and the plume will fan out in the horizontal plane. If a plume is released into a neutral layer capped by a stable layer, the plume will mix vertically throughout the entire depth of the neutral layer. If a plume is released into a neutral layer... 

Hydrology Seepage Water level Water level dynamics Rate of flow Barriers Flood Temperature stratification Drainage dynamics... 

At low airflows, temperature stratification in the vertical direction would be a problem both upstream and downstream of the test core. Thus it becomes difficult to obtain true bulk mean temperatures Taj and T . 

TABLE 18.5 Relationship between Pasquill-Gifford Stability Classes and Temperature Stratification... 

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