Pleated Filter Cartridges Research Articles

Study on effects of particle size and maximum pressure drop on the filtration and pulse-jet cleaning performance of pleated cartridge filter

In recent years, pleated cartridge filters have been widely used in the process of industrial production. However, most of the existing studies are focused on the structure optimization design of filters, and there are few studies on the effects of two important factors, namely, particle size and maximum pressure drop, on the performance of filters. So, in this study, the effects of two factors on the filtration and pulse-jet cleaning performance of pleated cartridge filter were investigated through experiments. For the same maximum pressure drop, both average and average residual pressure drops are reduced with the rise of particle size, and meanwhile both the number of pulse-jet cleaning and the average dust emission concentration decrease, which improves the dust collection efficiency. For the same particle size, both average and average residual pressure drops are reduced with the decrease of maximum pressure, but both the number of pulse-jet cleaning and the average dust emission concentration are increased, which lowers the dust collection efficiency.

Design and performance evaluation of novel colliding pulse jet for dust filter cleaning

Pleated filter cartridges with high pleat ratios and large filter surface are found to have great instances of patchy cleaning. In order to improve the intensity and uniformity of filter cleaning, a novel colliding pulse-jet cleaning method was designed and tested in this study. An experimental pulse-jet cleaning dust collector (the filtration chamber is 1225 × 750 × 1000 mm (width × depth × height)) was built with two nozzles installed over the filter cartridge (ϕ320 × ϕ240 × 660 mm) and on the cartridge bottom. The nozzle outlet pressure, pulse jet performance (intensity and uniformity), and compressed air consumption were studied. The effect of the trigger time difference between the top and bottom pulse jets on the performance was researched. This study demonstrated that the non-time-differenced colliding pulse-jet mode increased the pulse-jet intensity obviously to 2.56 times compared with the top-jet-only mode with some more air consumption (about 1.85 times than that in top-jet-only mode), but the pulse-jet uniformity slightly worsened. The pulse-jet intensity could be enhanced remarkably to 5.49 times if the colliding pulse jet was controlled in the strategy of varying trigger time difference, with the uniformity also increased obviously.

Measurement of effective filtration area of pleated bag filter for pulse-jet cleaning

A pleated filter cartridge is a potential component to reduce the installation space required for a bag house dust collection system. However, the optimal pleating method has not been suggested yet, and it has been dependent upon the manufacturer's know-how and experience. In this study, dimensionless parameter, α, which is the ratio of pleat height to pleat width, was introduced to determine the optimal pleat geometry of a pleated filter cartridge. Eight different pleated filters were prepared to determine the effect of α and pleat length, PL, on the filter cleaning efficiency. A lab-scale pulse-jet bag house system which could install four filter bags and to be capable of on-line filter cleaning, was used to perform the filtration tests. Based on experimental data, a pleated cartridge filter with α = 2.21 had the maximum effective filtration area, and filter cleaning efficiency. However, we observed a drastic decrease in filter cleaning efficiency for a filter with an α value higher than 2.21. Therefore, we found that the tested cartridge filter had the optimal filter pleating geometry at α = 2.21, which folds a filter medium as a ratio of pleat height to pleat width, 2.21. In addition, the effective filtration area of a pleated filter cartridge was measured by the relationship between the increase in pressure drop during each filtration cycle, and multiplication of dust concentration and elapsed time. The ratio of the effective filtration area and theoretical filtration area, β, depends on the filtration cycle and the α value at the initial stage; however, it only depends on the α value at a later stage.

Numerical study of the effects of cartridge shape on the reverse pulsed flow cleaning of pleated cartridge filters

Patchy cleaning is one of the principal factors resulting in the reduction of the efficiency and quality of reverse pulse-jet cleaning as well as the service lifetime of filtration units. To resolve the above issues, a new pleated cartridge shape was introduced in this study to improve the cleaning efficiency and quality of pleated filter cartridges. To calculate the transient flow and pressure fields for a simple filtration system with one filter cartridge in the reverse pulse-jet cleaning process, an unsteady computational fluid dynamics model was developed via the commercial computational fluid dynamics software of ANSYS CFX. The transient static pressure fields for filter cartridges under four different pleated cartridge shapes were studied. The conventional cylindrical cartridge was selected as the base-model of filter cartridge and contrasted with other three cartridge shapes. It was found that the convergent–divergent cartridge was able to effectively improve the cleaning performance without the increase of tank pressure. Different pleated cartridge shapes are expected to be able to redistribute the pressure drop across the porous media along the filter height and to improve the flow behavior after pulsing gas releasing from the nozzle. For convergent–divergent cartridge shape, the peak pressure on the inner surface of porous media has an obvious increase and the peak pressure arriving time is earlier than other cases. It shows that the reverse flow has much more competence to remove the dust powder or cake from the porous media. At the same time, the area-averaged pressure drop at the bottom section of the filter has an increase of 50% under the cartridge with a convergent–divergent shape compared to that with a cylindrical shape. It is considered to enhance the cleaning mechanical stress at the bottom section of the filter cartridge. The better cleaning performance was observed in the medium, with 150% increase compared to that with a cylindrical shape. Furthermore, the cleaning performance gets improved because the value enhances on the top section. The redistribution of pressure drop observed is mainly because the special geometric construction of pleated cartridges compresses the flow on the medium and produce higher pressure drop there. Further studies indicate that the improved cleaning performance was observable under the consideration of the tank pressure reduction and variation of media permeability during each cleaning phase, and the change of pleated cartridge shapes can also improve the cleaning performance when combined with other improvement methods.

Influence of injection pipe characteristics on pulse-jet cleaning uniformity in a pleated cartridge filter

Pleated cartridge filters are widely used to remove dust in industrial processes. However, pulse-jet cleaning is not uniform between filter cartridges. This is due to uneven transient pressure below the injection holes leading to the increase of operating resistance and decline in the cleaning cycle, both of which are detrimental to pleated cartridge filter operation. Therefore, the injection pipe plays an important role in pulse-jet cleaning. In order to provide guidance for injection pipe design, a pulse-jet cleaning experimental system was designed. Experiments involved a constant total filtration area under four working conditions; the effects of the injection hole diameter, the number of injection holes, the jet distance, and the tank pressure on pulse-jet cleaning were studied by testing the static pressure on the inner wall of the cartridge. This also allowed optimization of the jet distance, orifice ratio, injection hole diameter, and internal cartridge volume. The results showed that 1) the transient pressure below the injection holes increased gradually along the airflow direction of the injection pipe, and 2) the peak positive pressures on the corresponding cartridge inner surfaces also increased. Both of these pressure values increased with increasing tank pressure. Peak positive pressure on the inner wall of the cartridges first increased, and then decreased with increasing jet distance. The injection hole diameter and the optimum jet distance can be described by mathematical models developed from this study. The optimum jet distance decreased with increasing injection hole diameter. The optimum orifice ratio range was 0.6–0.8 under the optimum jet distance, adoption of which improved the pulse-jet intensity significantly. Injection hole optimization resulted in gradually decreasing injection hole diameter along the airflow direction of the injection pipe and increased the pulse-jet uniformity by a factor of 5–8. The internal volume of the cartridge influenced pulse jet cleaning under constant filtration area.

Cleaning of Filter Cartridges with Convergent Trapezoidal Pleat Shape via Reverse Multi-Pulsing Jet Flow

ABSTRACTPleat structure and tight pleat spacing of pleated filter cartridges often lead to patchy cleaning when applying reverse pulsing technique process to regenerate filter media, consequently resulted in the decrease of the efficiency and quality of reverse pulsed-jet cleaning as well as the service lifetime of filtration units. For improving the non-uniform cleaning or patchy cleaning, a novel convergent trapezoidal pleat shape was used in multi-pulsing reverse flow cleaning. A transient 3D CFD simulation in a simple filtration system with a single filter cartridge was carried out under the four multi-pulsing modes. The effects of multi-pulsing flow cleaning on the cleaning efficiency and quality were systematically investigated. Compared with single-pulsing cleaning mode, the peak pressure differences at the upper regions all became positive because of the increased cleaning frequency, and thus which would be crucially important for improving the local cleaning mechanical stresses and cleaning efficiency. Moreover, the extra peak-pressure augment in the lower regions of filter cartridge also had a positive influence of local cleaning efficiency. For the multi-pulsing scheme of Waveform #4, the peak pressure difference at the section 4 increased by 11.2% than the single-pulsing scheme. The related action mechanism had high correlation with the interaction of residue gas and following jet. Finally, the improvement of the cleaning efficiency and quality are expected to be validated under the decreasing tank pressure and real permeability.

Annular-slit nozzles for reverse flow cleaning of pleated filter cartridges

Abstract Annular-slit nozzles were proposed to reduce the patchy cleaning often encountered in the reserve flow process for regenerating filter media in industrial filtration systems. In this study we investigated the effect of annular-slit nozzles on the efficiency and quality of reverse flow cleaning. A 3-D transient numerical model was developed to model the flow and pressure fields in a simple filtration system having a single pleated filter cartridge. The cleaning performance of three different annular-slit nozzles and paired round nozzles (having the same opening area as that of associated annular one) were analyzed. Compared with paired round nozzles, annular-slit nozzles have favorable effect on the local cleaning efficiency of pleated filter cartridges by significant increasing of local static pressure drop, especially in the upper region of pleated filter cartridges. The uniformity of pressure distribution along the cartridge height is also improved, resulting in the less probability of filter media damage by local mechanical stress developed during reverse flow cleaning when increasing the tank pressure. More, the better cleaning quality of reverse flow cleaning is expected because of the induced gas flow passing through the inner tube of an annular-slit nozzle when the air jetting was initiated from the nozzles. The benefit of applying annular-slit nozzles in the reverse flow cleaning was also observed in the cases taking into the consideration of the dust cake release from the cartridge filter surfaces.

Effect of pleat shape on reverse pulsed-jet cleaning of filter cartridges

The effect of pleat shape on the reverse pulsed-jet cleaning of pleated filter cartridges was investigated in this study with the objective of improving the cleaning efficiency and quality. Pleated filter cartridges have been implemented in continuous particle filtration systems equipped with reverse pulsed-jet cleaning technique for filtration unit regeneration. Previous studies have shown that the local sharp variation and non-uniform distribution of static pressure on the surfaces of pleated filter media often result in the decrease in the efficiency and quality of reverse pulsed-jet cleaning as well as the service lifetime of filtration units. In this study a CFD model to calculate the transient flow and pressure fields in a simple filtration system with one filter cartridge during the reverse pulsed-jet cleaning process was developed via ANSYS CFX R.14. The transient static pressure fields for cartridges with four pleat shapes were studied. Significant non-uniformity of static pressure on the high pressure side of filter media for cartridges with typical V-shaped pleats was observed. Significant reduction in the spatial variation of static pressure on the surfaces of pleated filter media for cartridges with other studied pleat shapes was also observed when compared with those for cartridges having V-shaped pleats. A filter cartridge with pleats in the convergent trapezoidal shape was concluded to achieve the maximum and uniformity of static pressure on the filter surfaces and maximal pressure drop across filter media in the reverse flow cleaning. Significant improvement of cleaning efficiency and quality are expected when using filter cartridges with convergent trapezoidal pleats.

Numerical Study of Reverse Multi-Pulsing Jet Cleaning for Pleated Cartridge Filters

ABSTRACTPatchy cleaning is one of issues often encountered for pleated filter cartridges (in an industrial filtration system) undergoing the reverse flow cleaning for filtration medium regeneration. To improve the cleaning quality for pleated filter cartridges, a novel reverse multi-pulsing jet cleaning was introduced in this study. A CFD modeling, via ANSYS CFX R.14, was applied to study the time-dependent flow and pressure fields in a simple filtration system with one filter cartridge under the proposed reverse flow cleaning. The transient static pressure fields for pleated cartridges under the cleaning with four flow pulsing waveforms and three pulsing frequencies were investigated. Cartridges with triangular pleats were selected as the model cartridge. It was found that the reverse multi-pulsing jet operation was able to effectively improve the cleaning performance without the increase of compressed gas tank pressure. The studied operation increased the number of cleaning action and local acceleration at the top sections of filter cartridges. In addition, the surface-averaged peak pressure drop across pleated filter media at the base section of cartridges was also 6.5% increased when pleated cartridges were cleaned by the proposed scheme as compared to that cleaned by the single-pulsing flow scheme. The peak pressure drop increase enhanced the cleaning mechanical stress at the base section of cartridges. The better performance for reverse flow cleaning was found in the multi-pulsing mode having the rectangular waveform and at high frequency. The observed peak pressure drop increase at the base section of filters was found closely related to the interaction of residual gas from the former pulsing and jet flow from the later pulsing. Further investigation indicated that the observed cleaning performance improvement was also shown under the consideration of the tank pressure reduction and change of media permeability during the removal of dust cake built-up on filter surface.

Effect of cone installation in a pleated filter cartridge during pulse-jet cleaning

This study investigated the pressure inside a pleated filter cartridge and the dust cleaning efficiency when normal and cylindrical cones were installed in a cartridge during a pulse-jet process. An experimental pulse-jet pleated filter dust collector was designed. The static pressures at three points along the length of the pleated filter cartridge were measured and compared before and after the cartridge was installed with cones. Various parameters, including tank pressure, nozzle diameter and jet distance, were investigated. The pressure drop of the filter cartridge and the dust emission concentration were also studied. This study has demonstrated that the increase in tank pressure improves pulse-jet intensity regardless of the presence of cones in the cartridge. Pulse-jet intensity is also enhanced when the cartridge is installed with either type of cone. Pulse-jet uniformity is reduced for normal cone but increased for cylindrical cone. The effect of cones on pulse-jet pressure is verified by operating performance during dust clogging and cleaning in clean-on-demand mode. The residual pressure drop is decreased, and the peak concentration of dust emission is increased when the normal or cylindrical cone is installed in the cartridge. A cylindrical cone extends the cleaning interval and reduces the dust emission, while the normal cone accomplishes the opposite.

The relationship between peak pressure and residual dust of a pulse-jet cartridge filter

To understand the relationship between peak pressure and residual dust of a pulse-jet cartridge filter, the impact of filtration velocity, jetting pressure and nozzle diameter on cleaning effect of the pulse-jet cartridge filter was examined in a semi industrial pulse-jet cartridge filter using several pleated filter cartridges (Φ350×1000mm). The filter was made of polyester and was coated with PTFE (Poly Tetra Fluoro Ethylene) membrane. Results show that filtration velocity could significantly affect the systematic resistance and the residual dust cakes. The smaller the filtration velocity, the less the residual dust cakes and the smaller the systematic resistance. The residual dust cakes are closely related to the peak pressure inside the filter cartridge. After pulse-jet cleaning, the bigger the peak pressures, the less the residual dust is. However, when the peak pressure increases to a certain threshold, the influence of filtration velocity on the dust-cleaning effect is no longer obvious. By curve fitting, the relations between peak pressures and residual dust cakes at a filtration velocity of 0.6, 0.8 and 1.0m/min are: y=1.0715e^(−0.0004x), y=1.4043e^(−0.0005x) and y=1.5476e^(−0.0005x), respectively. Experimental results indicate that the peak pressure is a valid and reliable index for evaluating the dust-cleaning effect of a pulse-jet cartridge filter.

Scale-up of Sterilizing-grade Membrane Filters from Discs to Pleated Cartridges: Effects of Operating Parameters and Solution Properties.

For direct flow sterilizing-grade filtration, a linear scale-up between the performance of discs and pleated filter cartridges has traditionally been assumed. Linear scale-up assumes that the filtration performances, defined here as filter flux and capacity, scale linearly with the membrane area and remains independent of the selected device formats. However, experimental results show that the later assumption does not hold in all cases. In this article, we investigated the effect of solution properties and operating parameters on scale-up with both fouling and non-fouling feeds. For non-fouling solutions, such as buffers, the flux ratio, defined as α, between pleated filter cartridges and disc filters range from 0.5 to 0.85. For complex fouling feeds, such as protein or cell culture media solutions, the ratio of initial flux between pleated filter cartridges and discs was the same as the flux ratio, α. For fouling solutions, the ratio of filtration capacity between pleated cartridges and discs, referred to as capacity ratio, β, was variable. We found that β was sensitive to the particle size distribution of the challenge solution and the mode of filtration operation (constant pressure or constant flux), whereas it was less sensitive to the magnitude of the operating pressure or flux and concentration of the fouling species. For most conditions tested, β among pleated cartridges and discs was within ±20% variation of unity. At the end, we present a modified standard model that accounts for both variations in flux ratio, α, as well as capacity ratios, β, for estimating the requirement for membrane area at manufacturing scale with proteinacious fouling and non-protein/non-fouling feeds. The data show that for cases where filtration is capacity controlled, flux ratios between the pleated filter and disc are not critical. For such cases, the use of a high-area laid-over pleated cartridge construction allows for reducing the number of 10 inch pleated filter cartridges required to process the batch volume. Scale-up remains at the core of a process development. For direct flow sterilizing-grade filtration, a linear scale-up between the performance of discs and pleated filter cartridges has traditionally been assumed. Linear scale-up assumes that the filtration performances, defined here as filter flux and capacity, scale linearly with the membrane area and remains independent of the selected device formats. However, experimental results show that the later assumption does not hold in all cases. We investigated the effect of solution properties and operating parameters on scale-up from membrane disc to pleated filter cartridges. Typical values of flux and capacity ratios and the guidelines on scale-up of direct flow filters from bench-scale to manufacturing-scale are presented. Specifically, we found that the flux ratio for pleated filter and small-scale disc range from 0.5 to 0.85, and capacity ratio for most cases is within ±20% variation of unity, with some exceptions.

On-line pulse-jet cleaning of pleated fabric cartridge filters for collecting pesticides

Cleaning performance of pleated fabric cartridge filters for collecting pesticide particles and the effect of cleaning on system operational process.

Effect of Test Dust on Performance Test for a Pleated Filter Cartridge

This study focuses on the test performance discrepancies for filter cartridges resulting from different kinds of test dust. A comprehensive experimental set-up including pulse-jet cleaning system for cleanable pleated filter cartridges was developed. Then, three identical cartridge samples were tested in this experimental set-up using different synthetic test dust, i.e., 325 mesh talcum powder, ASHRAE dust and ISO A2 dust respectively. Results showed that the type of test dust had significant impacts on dust holding capacity and cleaning effectiveness of pulse-jet cleaned cartridges. Cartridge sample loaded with ASHRAE dust has the smallest dust holding capacity and the worst cleaning effectiveness. However, considering its short experimental period, size distribution and actual simulation effects of atmospheric aerosol, ASHRAE dust is still recommended.

Effect of induced airflow on the surface static pressure of pleated fabric filter cartridges during pulse jet cleaning

Filter cartridges with higher pleat ratios and larger filter surfaces are often cleaned incompletely because of the great variation in the static pressure distribution along the surface of filter cartridges during the pulse jet cleaning process. This study examined the static pressure distribution of filter cartridges and attempted to reduce the incidence of incomplete cleaning, particularly at the top of a filter cartridge, where less static pressure could cause systematic unstable operations. Pressure loss and static pressure behavior were observed across pleated filter cartridges in a dust collector during the pulse jet cleaning process. The instantaneous pressure drops of pleated filters were measured, and filter aging over time was recorded. The pressure drops of pleated filters with induced airflows are less significant than those without induced airflows. The static pressure and the continuous pressure time on the filter cartridges surfaces were obtained using a pressure transducer. The induced airflow was used to alter the static pressure distribution along the filter cartridge surface. The air axial velocity gradually decreased from the supersonic induced nozzle and through the air diffuser. Otherwise, radial velocity increased before encountering the filter cartridge surface, and the dynamic pressure was quickly converted into static pressure at the top of the filter cartridge before being transported to the middle of the filter cartridge and then immediately to the bottom. Sometimes, partial airflow moved into the filter cartridges and rebounded from the bottom of the filter cartridges, thereby forming partial static pressure at the bottom. Thus, the static pressure decreased from the top of the filter cartridge to the bottom. The experimental results show that the static pressure at the top area of the filter cartridges is 23–17kPa and the static pressure at the bottom area of the filter cartridges is 4.7–1.6kPa via the operational time with the 0.6MPa tank pressure in our experiment. The measured results are in good agreement with our photos. This variation resolved the cleaning difficulty at the top of the filter cartridge and maintained the entire systematic sustainable operation.

Study of clogging and cleaning cycles of a pleated cartridge filter used in a thermal spraying process to filter ultrafine particles

Thermal metal spraying or cutting (arc/air) processes produce large quantities of ultrafine particles which cause irreversible clogging of industrial dust collectors in the long-term. This study, conducted on a test system equipped with a pleated filter cartridge confirms the high clogging capacity of these fumes, and also shows that current pulsed-jet cleaning methods are ineffective. The study has shown that the pressure drop across filters rises during filtration primarily due to the presence of ultrafine particles in the aerosol. This explains why cyclone type pre-separation has proved inefficient in preserving filtration capacity. Filter pre-coating could overcome the problem of ineffective cleaning (if used in off-line mode), but this technique generates large quantities of waste requiring specific handling. Future research should be oriented either towards improving filter cleaning or developing alternative separation techniques.

Numerical study of pleated fabric cartridges during pulse-jet cleaning

We established a numerical model and used computational fluid dynamics (CFD) analysis to observe transient flow behavior across pleated filter cartridges in a dust collector during pulse-jet cleaning. The numerical results were in good agreement with the filter-testing data during important periods including during pressure ramp-up and valve opening. Larger errors for predicting overpressure occurred during the pressure ramp-down period likely due to the uniformity of the filters' permeability. This confirmed that the numerical model demonstrated the cleaning efficiency and the local cleaning quality of three different filter cartridges with different filter dimensions and pleat ratios. Data calculated from the average static pressure on the filters' surfaces were more closely correlated to cleaning efficiency than overpressure. The surface static pressure distribution along all filter cartridges showed that the top area of the filter cartridge is difficult to clean because of the lower surface pressure generated by the pulse jet. Filter cartridges with higher pleat ratios were found to have greater instances of incomplete cleaning due to the large variation of static pressure distribution along the filter cartridges. Our results showed that although information such as average pressure and pressure distribution on the filter surface is difficult to obtain by physical measurement, this data is tractable using CFD analysis and is useful for filter design and system optimization.

Experimental study of pleated fabric cartridges in a pulse-jet cleaned dust collector

Six pleated filter cartridges with different base media and geometrical dimensions were tested in a full-size dust collector periodically cleaned by a short burst of pulse-jet. The evaluation was performed under two different cleaning modes called clean-on-demand (to clean the filter once the pressure drop reaches a preset value) and clean-on-time (to clean the filter at a fixed time interval). The filter performance was evaluated by the effective residual pressure drop and downstream particle concentration. The results showed that the pleat ratio, defined as the ratio of pleat height to pleat pitch, had a great influence on the preferred operating mode for cleaning the filter. Clean-on-time mode demonstrated better performance for filters with a high pleat ratio (> 4.0), while clean-on-demand mode performed better for filters with a low pleat ratio (< 4.0). The test results also showed the tank pressure was critical for cleaning the pleated filter cartridges, whereas the pulse duration only had a small effect on the cleaning efficiency. With the same base media, cartridges with surface treatment such as fine fiber were superior to those without surface treatment. Pulse-jet cleaning could also promote particle penetration through filter media. The downstream particle concentration during cleaning was at least twice of that during filtration process for all pleated filter cartridges tested. Further, the downstream particle concentration was independent of the applied cleaning mode and the cleaning intensity in this study.

Membrane pleating effects in 0.2 μm rated microfiltration cartridges

Pleating of membranes allows a larger surface area to be packed into small volume modules and is an integral feature of cartridges used in a range of biotechnology applications. This work investigates the effect that pleating has upon cartridge performance. Using specially fabricated 2.54 cm (1″) sections of a large scale pleated membrane cartridge, together with a full scale 25.4 cm (10″) cartridge, the pleat height ( h P), pleat type, and pleat packing density (PPD), defined as the number of pleats packed around a central core, were systematically varied so as to investigate the subsequent effect upon filtration performance assessed in terms of clean water flux. The normalised clean water flux of a Supor ® UEAV 0.2 μm rated 10″ pleated cartridge filter was 53% lower than that measured for a flat sheet disc of the same membrane material. By reducing both PPD and h P, the measured clean water flux increased, such that a cartridge with a PPD of 0.65 and a h P of 10 mm achieved a comparable clean water flux to that of the flat sheet membrane. The measured variation in flux is attributed to changes in the ease by which the process fluid can access the inner surface of each membrane pleat. This was confirmed by using a dilute 7.7 g l −1 yeast suspension as a probe to investigate the penetration of micron-sized (∼2 μm) particles into the base of the individual membrane pleat. This showed that at PPD values beyond 0.85 and at an h P of 10 mm, areas of the cartridge were largely inaccessible to the yeast cell challenge due to the effects of pleat crowding. As the PPD and h P were reduced, accessibility of the particles to the inner surface of each pleat improved until the whole membrane surface became covered with yeast. Whilst packing more membrane into a cartridge via pleating will improve the overall performance for a given feedstock, these results show that an increase in membrane area may not lead to a proportional increase in membrane performance. The results may provide a basis for the development of models for the prediction of pleated cartridge membrane performance.

Filter Quality of Pleated Filter Cartridges

The performance of dust cartridge filters commonly used in dust masks and in room ventilation depends both on the collection efficiency of the filter material and the pressure drop across the filter. Currently, the optimization of filter design is based only on minimizing the pressure drop at a set velocity chosen by the manufacturer. The collection efficiency, an equally important factor, is rarely considered in the optimization process. In this work, a filter quality factor, which combines the collection efficiency and the pressure drop, is used as the optimization criterion for filter evaluation. Most respirator manufacturers pleat the filter to various extents to increase the filtration area in the limit space within the dust cartridge. Six sizes of filter holders were fabricated to hold just one pleat of filter, simulating six different pleat counts, ranging from 0.5 to 3.33 pleats cm(-1). The possible electrostatic charges on the filter were removed by dipping in isopropyl alcohol, and the air velocity is fixed at 100 cm s(-1). Liquid dicotylphthalate particles generated by a constant output atomizer were used as challenge aerosols to minimize particle loading effects. A scanning mobility particle sizer was used to measure the challenge aerosol number concentrations and size distributions upstream and downstream of the pleated filter. The pressure drop across the filter was monitored by using a calibrated pressure transducer. The results showed that the performance of pleated filters depend not only on the size of the particle but also on the pleat count of the pleated filter. Based on filter quality factor, the optimal pleat count (OPC) is always higher than that based on pressure drop by about 0.3-0.5 pleats cm(-1). For example, the OPC is 2.15 pleats cm(-1) from the standpoint of pressure drop, but for the highest filter quality factor, the pleated filter needed to have a pleat count of 2.65 pleats cm(-1) at particle diameter of 122 nm. From the aspect of filter quality factor, this study suggests that the respirator manufacturers should add approximately 0.5 pleats cm(-1) to the OPC derived from the generalized correlation curve for pleated filter design based on minimum pressure drop.