Vertical Wall Surface Research Articles

Calculation of Natural Ventilation in Large Enclosures

There is a need for a good analytical model of natural ventilation of large enclosures. This study describes a multi-layer pattern of thermal stratification in high and large spaces driven by natural ventilation. The pattern is then used to construct an analytical model for natural ventilation of large enclosures. A thermal plume developed in the multi-layer environment is investigated based on its development across each density interface. This kind of plume and the airflows along vertical wall surfaces are combined to establish the heat and mass balances in each thermally stratified layer. Two different mathematical models that model the airflows along vertical wall surfaces are presented. These two models are compared for their predictions of the ventilation flow rate and vertical temperature profiles. Results of both present models are also compared with those calculated by computational fluid dynamics (CFD). It is shown from the comparisons that both models predict reasonably the thermal stratification in the large enclosure but only the one that considers continuous airflow along the whole wallsurface gives reliable predictions which agree well with results from the CFD study.

Resilient ceiling construction in residential buildings

In multifamily buildings, the floor/ceiling assembly between living units needs to be sound rated. In North America, a common light-frame floor construction involves wood or cold-formed metal joists spaced at 400 mm. The typical practice is to attach a gypsum board ceiling to the underside of the floor framing using narrow strips of ‘‘Z’’-shaped thin metal called ‘‘resilient channels.’’ If the resilient channels or the ceiling are installed incorrectly, the low-frequency sound insulation of the assembly can be seriously degraded. Based on our experience with resilient ceiling construction, there are two significant factors that have not yet been documented in an acoustical laboratory. One factor is to maintain a small separation around the entire perimeter of the ceiling where it intersects vertical wall surfaces (this void is later sealed airtight with a flexible caulking material). A second is the particular design of the Z-shaped resilient channel. The paper will discuss findings from two acoustical test series of floor/ceiling assemblies in wood-frame buildings. In both cases, the assembly was tested before and after modifications to the perimeter of the existing resilient ceiling. Each of the series also included tests of a complete ceiling reconstruction using an improved resilient channel design.

A parametric model for predicting wind-induced pressures on low-rise vertical surfaces in shielded environments

This paper describes the development of a parametric mathematical model to predict wind-induced surface pressures on exterior vertical wall surfaces on a single model block in shielded environments. The first phase of the project focused on the development of a parametric model to determine the average pressure coefficients on exterior building surfaces shielded by a single windward obstruction model block. A pressure modification coefficient was defined to estimate the shielding effect based on the angular relationship between, the shielding block and the surface for which average pressure is to be computed, and the wind direction. The second phase involved expanding the scope of the prediction model to account for the various arrangement possibilities of the shielding blocks relative to the surfaces under investigation. The predicted pressure modification coefficient may be used to estimate average pressure coefficients taking into account the indoor velocity coefficients, surface porosity, window design, and interior partition types. The prediction model considers the effect of multiple shielding blocks, and the gaps between them on a vertical surface relative to wind direction. Wind tunnel verification of the model showed robust estimation of surface pressures in complex urban configurations.

New Convection Correlations for Cooled Ceiling Panels in Room with Mixed and Stratified Airflow

Models for buildings' surface convective boundary conditions are important components of building design and simulation programs. This is especially true for cooled ceiling (CC) panels, which extract major cooling loads from rooms. This paper introduces new convection correlations for rooms with CC panels, developed from laboratory measurements conducted in a full-scale experimental facility. The new convection correlations were developed for CC panels used with or without a ventilation system. When the ventilation system was used, the air was supplied through a high aspiration diffuser. High aspiration diffusers, recommended for use with CC systems, create a specific airflow pattern characterized by narrow and directional jets with a large entrainment of surrounding air. To account for the forced airflow and local buoyancy effects, new convection correlations for CC surfaces were developed as functions of temperature difference and normalized volume flow rate, i.e., the number of air changes per hour (ACH) in the room. Results show that the high aspiration diffuser, even though installed at the ceiling, produces enough air motion in the vicinity of the floor and vertical wall surfaces to affect the convective heat transfer at these surfaces as well. In fact, the effect of forced convection due to the presence of a high aspiration diffuser increases the total convection coefficient at CC surfaces by 4% to 17%.

Vertical wall surface forming of rectangular shell using multistage incremental forming with spherical and cylindrical rollers

A multistage incremental sheet metal bulging machine using spherical and cylindrical rollers has been developed for vertical wall surface forming of rectangular shallow shells. The multistage incremental forming comprises three operations: bulging with a spherical roller, right-angle forming and flattening with cylindrical rollers. The hand-operated bulging machine formed a vertical wall surface, which is highly precise and preferred by designers. A method of calculating for the approximate distribution of thickness strain and the maximum bulging height of the rectangular panel was proposed using the deformation limit diagram obtained from the incremental bulging test with a ball roller and a geometrical plane-strain deformation model with a constant strain gradient. The predictions for the rectangular shell were reasonably in good agreement with experimental values for the annealed aluminum sheet.

Development of advanced plasma process with an optical emission spectroscopy-based end-point technique for etching of AlGaAs over GaAs in manufacture of heterojunction bipolar transistors

We demonstrated an advanced plasma etching technology for AlGaAs over GaAs in a BCl 3/N 2 inductively coupled plasma using an optical emission spectroscopy. The process results showed that etch rate of GaAs and Al x Ga 1− x As ( x=0.2) was equal in the condition, which means that selectivity of AlGaAs over GaAs was 1:1. The process also provided very smooth surface morphology, vertical side wall and residue-free surface. All the results indicated that the process would significantly improve reproducibility and reliability for the plasma process in advanced manufacturing of AlGaAs/GaAs-based semiconductor devices, such as heterojunction bipolar transistors.

Convective Heat Transfer from the Wall Surface of a Cavity to the External Stream(Effects of Temperature Nonuniformity on the Wall Surface for Correlations of Heat Transfer Model).

Convective heat transfer from the wall surface of a cavity to the external stream is experimentally studied in the Reynolds number range from 10000 to 100000. Temperature distribution of the fluid in the cavity is almost uniform, except in the thin region immediately adjacent to the wall surface of the cavity. The temperature of the fluid in the cavity is represented by the average temperature of the fluid in the cavity. Namely, convective heat transfer from the wall surface of the cavity to the external stream is treated with the heat transfer model comprising the following two phenomena: one is the heat transfer from the wall surface to the fluid in the cavity, and the other is the heat transfer from the fluid in the cavity to the external stream. The vertical wall surface temperature of the cavity decreases from the bottom to the opening of the cavity. The effects of temperature nonuniformity on the wall surface of the cavity for convective heat transfer are also reported.

On the thermal field of a wall plume (The response to artificial disturbances)

Experimental investigations were carried out on the characteristics of the thermal field of a wall plume ascending from a horizontal line heat source embedded on the low part of a vertical wall surface. For the stability analysis of the present wall plume field, a vibrating copper wire was set horizontally near the line heat source in the field and the wall plume field was disturbed by the vibrating wire. Some two-dimensional sinusoidal thermal disturbances were introduced into the wall plume field and the growth or diminution of the amplitude of temperature fluctuations by the artificial disturbance were measured in the wall plume field with a thermal probe. The response characteristics of the wall plume field to the disturbance frequency were also examined. As a result, it was ascertained that the frequency response of a wall plume field could be predicted by linear stability analysis

C303 トンボの自由飛行と流れ

The flapping styles of dragonflies in horizontal free flight and at take-off from a vertical wall surface were observed and analyzed with a high-speed video camera. Also, a dragonfly was set in a wind tunnel and flow states generated by flapping of wings were visualized by smoke flow. The results represented the facts that when the wings were flapping with amplitude of about 50-80 degrees, the flow upstream of the body was sucked into the lower pressure region around the body, and in the wake, convex protuberance and concave depressions are brought about on its boundary of the wake. Moreover, when the wings are flapping with amplitude of 3-5 degrees, a mushroom type of vortex was brought forth behind the wings.

On the thermal field of a wall plume (The response to artificial disturbances)

Experimental investigations were carried out on the characteristics of the thermal field of a wall plume ascending from a horizontal line heat source embedded on the low part of a vertical wall surface. For the stability analysis of the present wall plume field, a vibrating copper wire was set horizontally near the line heat source in the field and the wall plume field was disturbed by the vibrating wire. Some two-dimensional sinusoidal thermal disturbances were introduced into the wall plume field and the growth or diminution of the amplitude of temperature fluctuations by the artificial disturbance were measured in the wall plume field with a thermal probe. The response characteristics of the wall plume field to the disturbance frequency were also examined. As a result, it was ascertained that the frequency response of a wall plume field could be predicted by linear stability analysis. © 1999 Scripta Technica, Heat Trans Asian Res, 28(7): 559–572, 1999

On the Thermal Field of a Wall Plume. On the Responce to Artificial Disturbances.

Experimental investigations were carried out on the characteristics of the thermal field of a wall plume arising from a horizontal line heat source embedded on the low part of a vertical wall surface. For the stability analysis of the present wall plume field, a vibrating copper wire was set horizontally near the line heat source in the field. The wall plume field was disturbed by the wire, and some two-dimensional sinusoidal thermal disturbances were introduced into the wall plume field. The growth or diminution of the thermal amplitude of disturbance was measured in the wall plume field with a thermal probe. The frequency response of the disturbance in the wall plume field was also examined. As a result, it was ascertained that the frequency response of the wall plume field was fit well with the prediction of the linear stability analysis.

Flexible and Incremental Sheet Metal Bulging using a Path-Controlled Spherical Roller. 2nd Report. Vertical Wall Surface Forming of Rectangular Shell Using Multistage Incremental Forming with Spherical and Cylindrical Rollers.

A multistage incremental sheet metal bulging machine using spherical and cylindrical rollers has been developed for vertical wall surface forming of rectangular shallow shells. Multistage incremental forming comprises three operations : bulging with a spherical roller, right-angle forming and flattening with cylindrical rollers. The hand-operated bulging machine formed a vertical wall surface which is highly precise and preferred by designers. A method of calculating for the approximate distribution of thickness strain and the maximum bulging height of the rectangular panel was proposed using the fracture limit obtained from the incremental bulging test with a ball roller and a geometrical plane-strain deformation model with a constant strain gradient. The predictions for the rectangular shell were in reasonably good agreement with experimental values for the annealed aluminum sheet.

Wall temperature and the soiling of murals

A balance is made here of the intensities of the main deposition mechanisms (i.e. Brownian diffusion, thermophoresis, inertial impaction, gravitational settling and Stefan flow) in the case of vertical wall surfaces, and thus frescoes or other murals. When the wall is colder than the air, the temperature gradient forces negative thermophoresis and develops a downward free-convection layer. This generates inertial impaction and increases gravitational settling. A further contribution due to the Stefan flow may be generated. When the wall is warmer, thermophoresis partially counteracts other deposition mechanisms for fine particles, but the temperature gradient generates an uprising flow, and inertial impaction of the largest particles occurs. The deposition rate is reduced for fine particles, but increased for the largest ones. As the mass of the suspended paniculate matter is concentrated in the coarsest particles, the net effect is a heavy soiling. Up-rising flows transport upwards the majority of particles, causing soiling also of the ‘downward facing’ parts of the surface irregularities. Warm floor or cold ceiling may cause atmospheric instability and convective motions, with the above mentioned negative effects. Cold floor and warm ceiling form stable temperature profiles and attenuation of turbulence. Under the warm ceiling a cushion of stable air forms without motion (and inertial deposition) and with thermophoresis (partially) counteracting Brownian diffusion. The best situation appears to be offered by cold floor, warm ceiling, walls in thermal equilibrium with ambient air, and air with stable temperature gradient.

Ablauf fördernde Trichterkonstraktionen von S'dozeHen

The following article describes how it is possible to discharge bulk materials from silo bins by suitable constructive measures of the bin bottom, even without the aid of mechanical discharging devices. The proper design of hopper surfaces is particularly important; they must be smooth and steep enough to effect mass flow. In rectangular and square bins the hopper surfaces must be arranged in such a way that they always intersect only with a vertical wall surface. The best flow-promoting measure is the loosening of the bulk material in the lower region of the silo bin. The hopper bottom constructions described here have been specially developed for this purpose. However, it is to be expected that in the future further ingenious hopper constructions will be invented to facilitate the discharge of difficult-flowing bulk materials.

Coagulation and scavenging of radioactive aerosols

The coagulation constant of nonradioactive and radioactive metallic aerosols produced by an exploding-wire technique was determined experimentally. At early stages of coagulation the coagulation constant of radioactive gold aerosols (2 to 3.5 c./g.) was approximately twenty times the mean value of slightly radioactive aerosols (50 to 900 mc./g.). The values of the coagulation constant were corrected for deposition on vertical wall surfaces by means of a derived equation. Scavenging of radioactive aerosols was divided into three groups based upon the mechanism of coalescence: ( 1) dry particulate matter mixed with an aerosol, ( 2) dry particulate matter formed in the aerosol atmosphere, and ( 3) hygroscopic and liquid particulate matter formed in the aerosol atmosphere. Brownian motion in the presence of a water vapor concentration gradient around condensing droplets was found to be the most effective scavenging mechanism for slightly radioactive aerosols.