Supply Air Velocity Research Articles

Effect of ventilation pattern on room air and contaminant distribution

The ventilation efficiency of different ventilation patterns arranged by two inlet and two outlet diffusers at different locations is investigated. The numerical simulation was first adopted to predict airflow pattern and ventilation performance. Then, a laboratory experiment at room air and contaminant distribution in a full-scale test chamber was conducted to validate the simulation results. Applied the tracer-gas techniques to the experimental program, a concentration decay of CO 2 is used to calculate the ventilation efficiency and air change rate of the test chamber. The distribution of supply/exhaust air in the study characterized by ventilation efficiency, was investigated in isothermal conditions using different supply air velocities. The results indicate that the ventilation efficiency might be dominantly influenced by location of diffuser rather than air change rate.

Experimental study on the performance of a compact heat sink for LSI packages

The cooling performance of compact heat sinks composed of small fins, investigated in conditions of both natural and forced air convection, should also be explored in designing the heat sink on an LSI package. An experimental study was performed with respect to natural air convection and forced air convection. Several kinds of compact heat sink which have different base areas, fin intervals and fin heights were heated by an attached electrical heater, which could supply a specific heat flux. The increase in fin temperature was measured by small thermocouples. In natural air convection experiments, the effect of the supplied wattage on the temperature rise of the heat sink was examined for different fin intervals and fin heights. In forced air convection experiments, a wind tunnel was used. The heat sink was set downstream in the wind tunnel and a specific heat flux was applied to it. The correlation between supplied air velocity and temperature rise in the heat sinks was explored. Furthermore, from these results, non-dimensional expressions to evaluate the cooling performance of compact heat sinks were examined.

清浄度立ち上がり特性によるクリーンルームの性能評価に関する研究 : 一方向流方式の場合

The air cleaning ability of a unidirectional flow cleanroom system is examined experimentally in regard to various air-supply velocities, the size of the vent of the ceiling and of the floor and the relations between them. The change of particle concentration is referred to as the 'decay of particle concentration' judged from the point when the system begins operation. The pattern and the time of this decay indicates the system's air cleaning ability. The experiment shows that although the configuration of the cleanroom is a unidirectional flow, the property of controlling contamination is in three degrees, namely, unidirectional flow, 'perfect diffusion', and 'imperfect discharge' according to the velocity. The latter two are referred to as non-unidirectional. Clean-up time is calculated using two kind of equations. The lower limit of the vent's size is obtained. For the ceiling inlet, 50% of the size ratio constitutes the lower limit necessary to maintain the cleanliness class 5 in JIS B 9920, to the contrary to the limit of 14% for the floor outlet.

Influence of the boundary thermal conditions on the air change efficiency indexes.

The influence of a thermal heterogeneity boundary conditions on the air change efficiency (ACE) of a mechanical ventilation system in a test room was experimentally evaluated by means of the "step-down" tracer gas technique in 24 different experimental conditions. The experiments were performed under isothermal condition, varying the air supply temperature with respect to the walls and varying the surface temperature of a wall with respect to the other walls and the supply air, simulating both heating and cooling situations. Changing the position of the outlet grid two different configurations of the ventilation system were tested. The nominal supply air velocity varied between 0.04 and 0.11 m/s, corresponding to a range from 1 to 3 ach, and the temperature differences varied from 0 to 5 degrees C. Results are reported in terms of air change efficiency indexes, both local and global. The global air change efficiency (ACE), values are presented as a function of the Archimedes number (Ar), whose values were in the range 0 to 181. The reported results suggest that the Ar number may be used to organize the ACE values when in the presence of thermal heterogeneity, both in the external envelope and in the supplied air. The obtained results show that there is a logarithmic relation between Ar and ACE. In particular, for both ventilation strategies tested, the increase of the absolute value of Ar leads to an increase of ACE when the supply air is warmer than the walls, and to a decrease of ACE when the supply air is colder than the walls. Under isothermal conditions the Reynolds number (Re) fairly correlates the experimental results.

Mixing characteristics in a ventilated room with non-isothermal ceiling air supply

A two-dimensional turbulence k–ε model is used to predict distribution of air velocity, temperature and turbulence kinetic energy in an air-conditioned room using ceiling air supply. Mixing characteristics of the airflow are analyzed under different air supply velocities and temperatures. A modified Archimedes number is correlated with the parameters characterizing heat transfer, ventilation system, and turbulence kinetic energy of room air flow. Significant correlations have been shown. It is found that the linear ceiling air supply air-conditioning system with a high level return air provides excellent air mixing across a wide range of Archimedes numbers. The results are useful for air-conditioning design and thermal comfort study.

Numerical investigation of local thermal discomfort in offices with displacement ventilation

Local thermal discomfort in offices with displacement ventilation is investigated using computational fluid dynamics. The standard κ-ϵ turbulence model is used for the prediction of indoor air flow patterns, temperature and moisture distributions, taking account of heat transfer by conduction, convection and radiation. The thermal comfort level and draught risk are predicted by incorporating Fanger's comfort equations in the airflow model. It has been found that for sedentary occupants with summer clothing common complaints of discomfort in offices ventilated with displacement systems result more often from an unsatisfactory thermal sensation level than from draught alone. It is shown that thermal discomfort in the displacement-ventilated offices can be avoided by optimizing the supply air velocity and temperature. It is also shown that optimal supply air conditions of a displacement system depend on the distance between the occupant and air diffuser.

Control of Airborne Particle Concentration and Draught Risk in an Operating Room

The influence of location of airborne particle source, ventilation rate, air inlet size, supply air velocity, air outlet location, and heat source on the distributions of airborne particle concentration and draught risk in an operating room is investigated. The investigation is carried out by using flow program with the k-e model of turbulence. Based on a standard case, five cases, each with one changed parameter, are computed, and the detailed field distributions of air velocity, temperature, airborne particle concentration, and draught risk are presented. The parametric study concludes that, for a better air quality and thermal comfort, it is desirable to use a higher inflow rate, a larger inlet area, and a uniform velocity profile of supply air. Outlet location and heat source have little influence on the distributions ofthe particle concentration in the room. It has also been found that the distributions of particle concentration in the recirculating zone are very sensitive to the location of the particle sources.

A114 空調機吹出噴流の室内気流分布に及ぼす影響の評価

Experiments were performed to evaluate the air flow and air temperature distributions in a model room heated by both blown hot air from the lower supply air opening and blown room temperature air from the upper one in case of a model of an indoor ceiling-suspended system air conditioner having two supply air openings. Measurements were made of the local air velocities and local air temperatures in the room by varying the supply air temperatures, the supply air velocities and supply air jet angles of two supply air jets from the model indoor unit. The local air velocities in the room were determined by means of a particle image tracing technique. The obtained results indicated that two supply air jets formed a flow that circulated in the large part of the room. It was also found that difference in vertical air temperature became small.

Hydrogen combustion tests simulating a subsonic ram-combustor for a hypersonic plane.

To obtain design data of a subsonic ram.combustor for a hypersonic plane, hydrogen combustion tests were were made by an approximately one-tenth scale model. It was composed of a constant area combustion duct, a flame holder and a center body which simulate the turbofan engine to be used as a booster for the take-off mode. The conditions of supplied air velocity, air temperature and mixture strength were equivalent to those of the combustor inlet at flight speeds ranging from take.off to Mach 3. Gas velocity and temperature distributions along the axis and the values of total pressure loss were obtained by measurements of total and static pressures. Combustion efficiency was derived from gas analysis of the sampled gas at the exit. It was found that the fuel distribution in the combustor makes significant effects on the combustion efficiency near stoichiometric mixture condition.