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A desktop fume hood installed with an innovative design of flow boundary-layer separation controllers on the leading edges of the side plates, work surface, and corners was developed and characterized for its flow and containment leakage characteristics. The geometric features of the developed desktop fume hood included a rearward offset suction slot, two side plates, two side-plate boundary-layer separation controllers on the leading edges of the side plates, a slanted surface on the leading edge of the work surface, and two small triangular plates on the upper left and right corners of the hood face. The flow characteristics were examined using the laser-assisted smoke flow visualization technique. The containment leakages were measured by the tracer gas (sulphur hexafluoride) detection method on the hood face plane with a mannequin installed in front of the hood. The results of flow visualization showed that the smoke dispersions induced by the boundary-layer separations on the leading edges of the side plates and work surface, as well as the three-dimensional complex flows on the upper-left and -right corners of the hood face, were effectively alleviated by the boundary-layer separation controllers. The results of the tracer gas detection method with a mannequin standing in front of the hood showed that the leakage levels were negligibly small (≤0.003 ppm) at low face velocities (≥0.19 m/s).

A conventional box-type commercial kitchen hood and its improved version (termed the "IQV commercial kitchen hood") were studied using the laser-assisted smoke flow visualization technique and tracer-gas (sulfur hexafluoride) detection methods. The laser-assisted smoke flow visualization technique qualitatively revealed the flow field of the hood and the areas apt for leakages of hood containment. The tracer-gas concentration detection method measured the quantitative leakage levels of the hood containment. The oil mists that were generated in the conventional box-type commercial kitchen hood leaked significantly into the environment from the areas near the front edges of ceiling and side walls. Around these areas, the boundary-layer separation occurred, inducing highly unsteady and turbulent recirculating flow, and leading to spillages of hood containment due to inappropriate aerodynamic design at the front edges of the ceiling and side walls. The tracer-gas concentration measurements on the conventional box-type commercial kitchen hood showed that the sulfur hexafluoride concentrations detected at the hood face attained very large values on an order of magnitude about 10(3)-10(4) ppb. By combining the backward-offset narrow suction slot, deflection plates, and quarter-circular arcs at the hood entrance, the IQV commercial kitchen hood presented a flow field containing four backward-inclined cyclone flow structures. The oil mists generated by cooking were coherently confined in these upward-rising cyclone flow structures and finally exhausted through the narrow suction slot. The tracer-gas concentration measurements on the IQV commercial kitchen hood showed that the order of magnitude of the sulfur hexafluoride concentrations detected at the hood face is negligibly small--only about 10(0) ppb across the whole hood face.

To increase containment efficiency and reduce energy consumption, a sash-less, variable-height inclined air-curtain fume hood (sIAC hood) was developed and tested by a laser-assisted flow visualization technique and tracer-gas detection method. This novel design requires neither sash nor baffle. The sIAC hood employed the inclined push-pull air-curtain technique and two deflection plates installed on the side walls of the hood to induce a tetra-vortex flow structure. The results of flow visualization showed that the slot for suction flow, offset from the slot for the up-blowing jet, caused the air curtain to incline towards the rear wall, thus enhancing the robustness of the tetra-vortex flow structure. Such a flow structure could reduce the influence of draught and human walk-by across the hood face. The containment around the central area of the hood was isolated by the inclined push-pull air curtain. The pollutants carried by the reverse flow induced by the flow separation were guided by the deflection plates from the side walls towards the rear, thus contributing to the formation of the tetra-vortex flow structure. The up/down movable ceiling positioned the suction slot close to the device's pollutant emission opening, but left room (less than 50 cm) for unrestricted hand movement. Testing was carried out based on the methodology described in EN14175. The results of a static test showed that small face velocities of 0.25 and 0.16 m s(-1) were enough to obtain nearly null leakage levels for low and tall pollutant sources. The results of a traversing plate test showed that the face velocity, 0.32 m s(-1), would cause negligibly small leakage levels. The sIAC hood could obtain significantly higher containment efficiency than a conventional hood by operating at a face velocity significantly lower than that of conventional hoods.

The effects of draft on the flow and spillage characteristics of wall-mounted and jet-isolated range hoods were investigated. A specially designed draft generator that could supply low-swirl air current was used to provide "cross draft" from three directions, lateral (θ = 0(o)), oblique (θ = 45(o)), and front (θ = 90(o)), with respect to the center point of the range hoods. Flow characteristics of oil mist were inspected through visualization of smoke flows with light scattering (laser light sheet-assisted visualization of smoke flow). The leakage mechanisms, which were closely related to the flow features, were studied by examining both movies and still pictures showing smoke-flow evolution. The sulfur hexafluoride tracer gas concentration detection method was employed to measure the capture indices. The results showed that the lateral draft pushed the pollutants generated under the hood in the opposite direction and induced serious spillage. The oblique draft pushed the pollutants toward both the rear wall and opposite side and induced more serious spillage than did the lateral draft. The frontal draft forced the pollutants to bifurcate into streams moving toward the left and the right, and induced the most serious pollutant spillage among the three tested drafts. Pollutant spillage became critically significant as the cross draft velocity was increased to greater than 0.2 m/sec. Spillage of pollutants increased as the velocity of the cross draft was increased. Increasing the suction flow rate of the range hood may increase resistance to the draft, but the benefits were limited at draft velocities greater than 0.2 m/sec. Both range hoods had a similarly low capture index under the influence of the lateral draft. For the oblique and frontal drafts, the jet-isolated range hood demonstrated a higher capture index than did the wall-mounted range hood.

The flow and leakage characteristics of the air-curtain fume hood under high temperature operation (between 100°C and 250°C) were studied. Laser-assisted flow visualization technique was used to reveal the hot plume movements in the cabinet and the critical conditions for the hood-top leakage. The sulfur hexafluoride tracer-gas concentration test method was employed to examine the containment spillages from the sash opening and the hood top. It was found that the primary parameters dominating the behavior of the flow field and hood performance are the sash height and the suction velocity as an air-curtain hood is operated at high temperatures. At large sash height and low suction velocity, the air curtain broke down and accompanied with three-dimensional flow in the cabinet. Since the suction velocity was low and the sash opening was large, the makeup air drawn down from the hood top became insufficient to counter act the rising hot plume. Under this situation, containment leakage from the sash opening and the hood top was observed. At small sash opening and high suction velocity, the air curtain presented robust characteristics and the makeup air flow from the hood top was sufficiently large. Therefore the containment leakages from the sash opening and the hood top were not observed. According to the results of experiments, quantitative operation sash height and suction velocity corresponding to the operation temperatures were suggested.

This study focused on the leakage characteristics of the air-curtain fume hood that are subject to the influences of sash movement and walk-by motion while a high temperature heat source was operated in the hood. The flow visualization and trace gas test method were used to investigate the performance of the air-curtain fume hood. An electric heater was placed in the hood to simulate the heat source. The temperature of the heat source installed inside the air-curtain fume hood varied between 180°C and 300°C. Trace gas tests following the dynamic test methods of EN-14175 protocol were employed to measure the spillages of sulfur hexafluoride gas that were released in the hood. When subject to the influence of sash movement at a heat source temperature lower than 260°C, the leakage level was high at the suction velocity V(s) < 8 m/sec but was negligibly small at V(s) > 10 m/sec. When subject to the influence of people walk-by, the leakage level was relatively low at the suction velocity larger than 8 m/sec at sash height H = 50 cm. The height of the sash opening was a crucial parameter for the containment of the air-curtain fume hood. At the sash opening lower than about 25 cm, suction velocity less than or equal to 6 m/sec was enough to make the sulfur hexafluoride leakage less than the threshold value, 0.65 ppm, suggested by the BG Chemie. The air-curtain fume hood presented a great performance to resist the effect of drafts even though there was a high temperature heat source working in the hood.

The current study developed a new type of range hood, which was termed an 'inclined air-curtain range hood', in order to improve the flow and performance of the conventionally used wall-mounted range hood. The flow characteristics and oil mist spillages of air-curtain and conventional range hoods under the influences of both a mannequin presence and a simulated walk-by motion were experimentally examined. The study examined flow patterns by using a laser-light-sheet-assisted smoke-flow visualization technique and diagnosed spillages by using the tracer gas concentration test method. A mannequin presented in front of the conventional hood induced turbulent dispersion of oil mists toward the chest and nose of the mannequin owing to the complex interaction among the suction, wake, and wall effect, while the inclined air-curtain hood presented excellent hood performance by isolating the oil mists from the mannequin with an air curtain and therefore could reduce spillages out into the atmosphere and the mannequin's breathing zone. Both flow visualization and the tracer gas test indicated that the air-curtain hood had excellent 'robustness' over the conventional hood in resisting the influence of walk-by motion. The air-curtain technique could drastically improve the flow characteristics and performance of the range hood by consuming less energy.

The flow characteristics and oil mist spillages of wall-mounted and jet-isolated range hoods were studied experimentally. Flow patterns were examined using a laser-light, sheet-assisted, smoke flow visualization technique. Spillages were diagnosed by the locally averaged tracer gas concentration test method. Tracer gas concentration test results correlated well with those of flow visualizations. For the wall-mounted hood, primary leakages occur around the region near the front edge of a countertop due to boundary layer separation, as well as the region just below the lower edge of the side panels of the hood due to the expansion effect of plumes. Increasing the suction flow rate above some critical values may help to reduce leakages out of the lateral planes but would increase spillages around the front edge of the countertop. For the jet-isolated range hood, oil mists spread widely and present unsteady motions with a high degree of turbulence because insufficient free air is allowed to enter the space enclosed by the jets and rear wall. Spillages across the jets into the environment due to turbulent dispersion become significant. Increasing the suction flow rate above some critical values may help to reduce spillages, while increasing the jet velocity would increase turbulent dispersion and thus lead to larger leakages.

Laser-assisted flow-visualization experiments and tracer gas concentration tests were conducted for the wall-mounted and jet-isolated range hoods to examine the physical mechanisms and relative magnitudes of hood spillages. The effects of a mannequin standing in front of the test rig and walk-by motions (which are situations always encountered in kitchens) were emphasized. The results showed that a mannequin (or a cook) standing in front of the counter would attract oil fumes toward the mannequin's body, induce large turbulent flows, and cause a significant dispersion of oil fumes into the environment through the front edge of the hood. Very high tracer gas concentrations were detected around the breathing zone of the mannequin. Increasing the suction flow rate did not reduce the spillage levels of the wall-mounted range hood but could moderately lower those of the jet-isolated hood. Serious spillages from both the wall-mounted and jet-isolated range hoods were detected as the simulated walk-by motion was performed. The jet-isolated range hood presented a much lower robustness in resisting the influence of people's walk-bys than did the wall-mounted range hood. In summary, both the wall-mounted and jet-isolated range hoods were vulnerable to the influences of a cook's presence and a cook's walk-by motions. Increasing the suction flow rate might not obtain satisfactorily low spillages of pollutants but might increase noise level and energy consumption.

Tsai et al. (Airborne nanoparticle exposures associated with the manual handling of nanoalumina and nanosilver in fume hoods. J Nanopart Res 2009; 11: 147-61) found that the handling of dry nanoalumina and nanosilver inside laboratory fume hoods can cause a significant release of airborne nanoparticles from the hood. Hood design affects the magnitude of release. With traditionally designed fume hoods, the airflow moves horizontally toward the hood cupboard; the turbulent airflow formed in the worker wake region interacts with the vortex in the constant-flow fume hood and this can cause nanoparticles to be carried out with the circulating airflow. Airborne particle concentrations were measured for three hood designs (constant-flow, constant-velocity, and air-curtain hoods) using manual handling of nanoalumina particles. The hood operator's airborne nanoparticle breathing zone exposure was measured over the size range from 5 nm to 20 mum. Experiments showed that the exposure magnitude for a constant-flow hood had high variability. The results for the constant-velocity hood varied by operating conditions, but were usually very low. The performance of the air-curtain hood, a new design with significantly different airflow pattern from traditional hoods, was consistent under all operating conditions and release was barely detected. Fog tests showed more intense turbulent airflow in traditional hoods and that the downward airflow from the double-layered sash to the suction slot of the air-curtain hood did not cause turbulence seen in other hoods.

In order to recognize the problems associated with the transport mechanism of containment during the ventilation process of a laboratory fume hood, a transparent, full scale chemical fume hood is constructed for experimental studies. Distributions of mean velocity and velocity fluctuation in the sash plane are measured using a thermal anemometer. Flow patterns and tracer-gas concentration leakages are respectively diagnosed via the laser-assisted flow visualization method and the EN 14175-3 test protocol. The magnitudes of measured velocity fluctuations exhibit a sharp peak along the perimeter of the sash opening. The results of flow visualization verify that the elevated turbulence fluctuations are induced by the boundary-layer separation when the flow passes over the edges of sash perimeter. The tracer gas experiment shows that the regions where high degree containment leakages detected are located along the perimeter of hood aperture. Eleven commercial hoods which are claimed with fine aerodynamic design are further tested for confirmation of these observations. The results show similar correlations. Conclusions thus are made that large-scale vortex structures occurring around the perimeters of hood aperture due to the boundary-layer separation could induce strong turbulence, and therefore enhance dispersion of the hood containment.

The flow separation and its accompanied recirculation induced when the airflow passes over the inappropriately designed doorsill of a chemical fume cupboard are the key factors which would lead to deterioration of the cupboard performance. In order to alleviate the contaminant leakage of the fume cupboard induced by inherent aerodynamic deficiency, a technique using doorsill jet injection is developed and validated. A planar jet is ejected upward through a slot located across the inner surface of the doorsill of a full-scale, transparent fume cupboard and is ejected upward. The laser-light-sheet-assisted smoke flow visualization is performed to explore the physical mechanism of changing and controlling the flow structure. It is found that the upward injected jet is curved by the airflow drawn into the sash opening and forms a layer of clean air which can isolate the contaminant and alleviate the diffusion through the recirculating vortex on the doorsill, if the jet velocity is properly adjusted. The tracer gas concentration measurements present extraordinarily satisfactory results--the order of magnitude of the leakage of tracer gas near the doorsill may be reduced from original levels of approximately 10(2) to approximately 10(-2) p.p.m. Except for the experimental fume cupboard used for development of technique, two commercial fume cupboards are employed for verifications and comparisons on the proposed method. Tests about the two modified commercial fume cupboards demonstrate good agreement to those of the model fume cupboard.

In order to speculate the physical mechanisms of contaminant leakage during sash movement and walk-bys through a laboratory fume cupboard, the complicated three-dimensional flow patterns and the real-time tracer gas leakage are studied via the laser-assisted flow visualization method and the standard gas sampling technique, respectively, over a transparent, full scale chemical fume cupboard. Through the flow visualization, the evolution of drastic changes of the flow pattern is demonstrated. The highly turbulent jet-like currents are induced by the unsteady flow motion near the cupboard face. Large-scale turbulent eddies accompanied with the jet-like currents obviously bring large amount of in-cupboard smoke out to the atmosphere. The turbulent mixing extends the size and the strength of the large-scale eddy circulations, and predominantly contributes to the mechanism that causes the severe spread of contaminant leakage in few seconds. The tracer gas tests that are conducted by employing pr-EN 14175:2003 method show consistent containment results with the flow visualization findings. The temporally evolving large-scale turbulent eddies induced by the sash movement and the walk-bys cause substantially high contaminant leakage to the environment and the breathing zone of the operator.