Perforated Liners Research Articles

Effect of nonlinear flame response on the design of perforated liners in suppression of combustion instability

This paper aims at investigating how to suppress combustion instability using perforated liners under nonlinear flame response. A theoretical model is thus presented to describe the interaction between the unsteady heat release, acoustics, and fluid fields, which takes both perforated liner and flame nonlinearity into account. To establish an eigenvalue problem to evaluate combustion instability, appropriate matching and boundary conditions are set up by applying conservation laws across the interfaces, consequently deriving the dispersion relation equation in the form of a matrix. In view of the nonlinearity of flame response function, it is found that the control strategy of combustion instability should be devoted to the reduction of the limit cycle amplitude to an acceptable level rather than the complete elimination of its onset. Based on the present model, we have studied the first longitudinal mode of a Rijke tube equipped with perforated liners. It is noted that the change of combustion instability evolution is sensitive to the design parameters of perforated liners, including cavity depth, installation position, and bias flow velocity. On the one hand, it is indeed possible to suppress the onset of combustion instability with elaborately designed parameters of the perforated liners. On the other hand, the limit cycle amplitude can be reduced as small as possible under various design restrictions of perforated liners in practice. Therefore, this study presents an alternative design criteria of perforated liners for the control of combustion instability.

A Porous Media Model for the Numerical Simulation of Acoustic Attenuation by Perforated Liners in the Presence of Grazing Flows

In this paper, a novel model is proposed for the numerical simulation of noise-attenuating perforated liners. Effusion cooling liners offer the potential of being able to attenuate combustion instabilities in gas turbine engines. However, the acoustic attenuation of a perforated liner is a combination of a number of interacting factors, resulting in the traditional approach of designing perforated combustor liners relying heavily on combustor rig tests. On the other hand, direct computation of thousands of small-scale holes is too expensive to be employed as an engineering design tool. In recognition of this, a novel physical velocity porous media (PVPM) model was recently proposed by the authors as a computationally less demanding approach to represent the acoustic attenuation of perforated liners. The model was previously validated for the normal incidence of a sound wave by comparison with experimental data from impedance tubes. In this paper, the model is further developed for configurations where the noise signal propagates in parallel with the perforated liners, both in the presence and absence of a mean flow. The model is significantly improved and successfully validated within coexisting grazing and bias flow scenarios, with reference to a series of well-recognized experimental data.

Improvement of loads calculation of the perforated liner in a geothermal production well

The integrity of perforated liners is crucial in geothermal production wells and this should be well designed according to correct standards. The available geothermal standards, such as the New Zealand Standard, NZS2403:2015, provides a general but less detailed discussion of geothermal perforated liner system design considerations.This research aimed to improve the limitations of NZS2403:2015 by calculating and evaluating the dynamic loads of perforated liner during four phases: borehole drilling and liner installation, flow testing, stand-alone production, and production during the injection operation. The data from production well HCE29 and injection well HCE29A, Dieng Field, Indonesia, were used in this research. In every phase, perforated liner yield strength changed, and load mechanisms varied between 1.3-2.7 and 1.6–4.6 times of the actual liner burst and collapse strength, respectively, and these lead to perforated liner failure and its lifetime reduction. The calculation results, combined with the significant production decline and production casing failure, indicated the perforated liner failure. The results also showed when it was mandatory to revise operation at later phases and to conduct appropriate maintenance according to actual perforated liner condition. Furthermore, this study can be used as a basis of future wells design and operation related to perforated liner.

Numerical investigation on the porosity effect of a bias-flow perforated liner on attenuating self-excited thermoacoustic oscillations

Self-excited thermoacoustic oscillations are unwanted in propulsion and stationary gas turbines due to the undesirable structural and heating damage to the engine systems. To prevent overheating and damping noise, perforated liners are widely applied in engines. It is a cylindrical metal sheet perforated with a number of millimetre-size circle orifices. In this work, numerical studies are conducted on an acoustically open-open thermoacoustic combustor with premixed propane and air fuelled and burnt. A perforated liner with a porosity σ is implemented downstream of the combustor in the presence of a cooling flow (also known as bias flow). The effects of (1) the cooling mass flow rate ṁb and (2) the porosity σp are examined one at a time. It is found that in the absence of the cooling flow, i.e., ṁb = 0, the perforated liner’s acoustic damping effect is quite small. Increasing is found to increase the liners damping performance in terms of attenuating the thermoacoustic oscillations, due to the enhanced vortex shedding generated over the rims of the perforated holes. In addition, there is an optimum cooling flow rate corresponding to the maximum acoustic damping effect of the liner. Furthermore, for a given mass flow rate, there is an optimum porosity.

Using a Sweating Residuum/socket Interface Simulator for the Evaluation of Sweat Management Liners in Lower Limb Prosthetics.

Lab-based simulators can help to reduce variability in prosthetics research. However, they have not yet been used to investigate the effects of sweating at the residuum-liner interface. This work sought to create and validate a simulator to replicate the mechanics of residual limb perspiration. The developed apparatus was used to assess the effects of perspiration and different liner designs. By scanning a cast, an artificial residuum was manufactured using a 3D-printed, transtibial bone model encased in silicone, moulded with pores. The pores allowed water to emit from the residuum surface, simulating sweating. Dry and sweating cyclic tests were performed by applying compressive and tensile loading, while measuring the displacement of the residuum relative to the socket. Tests were conducted using standard and perforated liners. Although maximum displacement varied between test setups, its variance was low (coefficient of variation <1%) and consistent between dry tests. For unperforated liners, sweating increased the standard deviation of maximum displacement approximately threefold (0.04mm v 0.12mm, p<0.001). However, with the perforated liner, sweating had little effect on standard deviation compared to dry tests (0.04mm v 0.04mm, p=0.497). The test apparatus was effective at simulating the effect of perspiration at the residual limb. Moisture at the skin-liner interface can lead to inconsistent mechanics. Perforated liners help to remove sweat from the skin-liner interface, thereby mitigating these effects.

Numerical simulations of perforated plate liners: Analysis of the visco-thermal dissipation mechanisms.

In the linear regime and in the absence of mean flow, the impedance of perforated liners is driven by visco-thermal effects. In this paper, two numerical models are employed for predicting these visco-thermal losses. The first model is the linearized compressible Navier-Stokes equations (LNSE), solved in the frequency domain. The second model is the Helmholtz equation with a visco-thermal boundary condition, accounting for the influence of the acoustic boundary layers. These models are compared and validated against measurements. The quantitative analysis of the dissipation rate due to viscosity, computed from the LNSE solutions of four perforated plates, highlights significant differences between the edge effects of a macro- and a micro-perforated plate. In the latter case, a jet is present at the entrances of the perforation. In contrast, the proposed numerical method to calculate the impedance of perforated liners, based on the Helmholtz equation and a visco-thermal boundary condition, is found to be computationally cheaper and to provide reliable predictions.

Experimental Evaluation of Using Silica Aerogels as the Thermal Insulator for Combustor Liners

An experimental study was conducted for evaluating the feasibility of using silica aerogel as thermal insulator for combustor liners. Aerogels are a superior material for minimizing heat flux to the metal structure of the combustion liner due to their low thermal conductivity. In this study, a conical natural gas fired swirling-flame combustor was utilized for reproducing the combustion environment. The silica aerogel blanket was attached to the inner side of a perforated combustor liner. Temperature distribution on the outer side of the combustion liner was measured using a calibrated IR camera. To create a protective cooling film over the aerogel surface, cooling air was supplied from the back side of the perforated metal liner and was allowed to penetrate the silica aerogel blanket to be discharged to the combustor. As the combustor was operated at a fixed equivalence ratio of 0.83, cooling air flow rates were varied to evaluate the effectiveness of transpiration cooling on the aerogel blanket as various cooling flow rates. The measured evolution of temperature distribution confirmed thermal equilibriums for every test condition with transpiration cooling. The measured temperature distribution of metal liner demonstrated superior thermal insulation of aerogel blanket under the protection of cooling film with a temperature difference as high as 1580 K between combustion products temperature and the metal liner temperature on the back side. In addition, silica aerogel samples were examined before and after the combustion tests to understand their material degradation exposing to a typical gas turbine combustor environment using high-resolution scanning electron microscope (SEM). Test results suggest multiple degradation mechanisms to the silica aerogel blanket samples from the combustion tests. Improvements can be made to the silica aerogel blankets for a more resilient thermal insulator, for example, by replacing glass fibers in silica aerogels.

Impact of using Double Layers Perforated Liners on the Acoustic Treatments of the Combustor Systems

The response of the combustor’s liner to the air-flow that passes through it is the key reason for the combustion chambers noise, hence the instabilities of those chambers that decreases the mechanical efficiency of such sections, by increased its mechanical vibrations, which increases the failure rate created during originating of the cracks spreading by the shakes producing by the series of high-level frequencies. Accordingly, any work debating the impact of the context of liners in the combustion chamber can provide grasping for the combustion noise generated by the undesirable vibrations, and benefits the industrial firms to design an ideal production procedure which increases the lifespan of the combustor. The goal of this work is to examine the influence of the acoustic treatment using a double layers cylindrical perforated liner on the acoustic transmission loss of gas turbines. The liners layout influences on this acoustic parameter was examined using an experimental data gained by the insertion of a full scale single and double patterns of perforated liners into the unique large scale acoustic wind tunnel at the acoustic research center at Hull University. The experimental tests under-designed acoustic signals were established firstly using 0m/s air cross-flow velocity, then by changed velocities with interval 5m/s ranging between 10m/s to 25m/s. MATLAB script was used to simulate, analyze, and figure out the data collected the insertion of single and double layer patterns of the perforated liner. The experiments demonstrated that, if the perforation acoustic treatments are applied, the acoustic transmission loss will decrease, particularly obvious at higher level frequencies. Further, the results exposed that the air tunnel with the insertion of the liner with double layers reveals an improved perforation acoustic treatment.

Evaluation of the airflow characteristics, cooling kinetics and quality keeping performances of various internal plastic liners in pomegranate fruit packaging

Abstract There is a trade-off to be optimised carefully as plastic liners deal with postharvest cooling processes as well as the produce quality and sustainability requirements. Understanding the implementation of plastic liners in the fresh fruit cold chain is required to reconcile the opposing roles. In this paper, the performances of four types of internal packaging plastic liners were studied. The airflow characteristics, cooling rate, cooling uniformity and quality keeping performances were measured. Cases: no liner, non-perforated liner, micro-perforated liner, macro perforated liner with 2 mm diameter holes, macro perforated liner 4 mm diameter holes were investigated. Generally, the liners delayed the cooling rate significantly. Non-perforated and micro-perforated liners are similar in terms of airflow resistance and cooling rate, both delayed the optimum cooling time by 5 h compared to the plastic-free case. On the other hand, macro-perforated liners cause a delay of only 3 h.

Experimental studies on sound absorption coefficients of perforated pipes with bias-grazing flows at low Mach and Strouhal number

This work considers the sound absorption characteristics of acoustic absorbers through which acoustical energy is absorbed partially by a number of circular orifices perforated on a cylindrical pipe (i.e. a perforated liner) in the presence of a mean flow. Sound absorption coefficient Δa is used to characterize the noise damping performance. It describes the fraction of incident acoustical energy being absorbed. To protect such liner in gas turbines and aero-engines, it is subjected to a range of joined grazing-bias flows. The bias flow passes through each orifice to create a cooling flow. Another stream of either cold/hot air flow grazes the same edge side of each orifice. The grazing and bias flow velocities are characterized by Mach number Mg and Mb respectively. Experimental measurements of Δa are conducted on 7 perforated pipes with different porosity δp but implemented in a single-layer configuration, over Strouhal number St ranged from 0.27 to 1.1. It is found that decreasing the grazing flow Mg leads to the liner's damping performance being improved over the interested St range. However, it is shown that when the bias flow Mb is increased, Δa is enhanced. The porosity δp is found to affect Δa and the optimum δp corresponding to max⁡{Δa} is found to be 1.84%. Finally, further comparison study is conducted on single- and double-layer perforated liners. In general, the present work shed lights on aeroacoustics damping characteristics of single-layer liners in the presence of both bias and grazing flow over the low Mach and St ranges.

Optimization of perforated liner parameters in horizontal oil wells

Nowadays, horizontal wells play a vital role in the production from thin heavy oil reservoirs. Designing a suitable completion for this kind of reservoirs is a decisive factor to boost the efficiency of durable production. This study deals with the optimization of perforated liner design for horizontal wells in Sarvak oil reservoir, which is located in the southwest of Iran. Sarvak is a carbonate oil reservoir, but it contains shale and mudstone. To avoid solid production and formation collapse, the screen liner was selected as a cost-effective solution. There were two choices, either perforated liner or slotted liner. The perforated liner was selected by finite element analysis and strength checking, which was proven by laboratory experiments. Sensitivity analysis was performed on various perforated parameters such as phase angle, hole density, hole diameter and hole distribution to determine the pattern of the holes so that enough strength of the liner was maintained while maintaining the maximum hole density. Then, parameters of perforated liner were determined by calculated loss of the flowing path, collapse resistance strength and tensile strength of casing pipes after perforated. As a result, hole density, hole size and perforated pattern were selected 100 HPM, 10 mm and 4-thread-line, respectively, in 4 ½” liner with 13.5 ppf. The ratio of the strength of the optimized perforated liner was less than 8% for collapse and 5% for tensile compared to the same specification casing.

Using Perforated Liners to Combat the Detrimental Effects of Excessive Sweating in Lower Limb Prosthesis Users.

Excessive sweating of the residual limb has a substantial effect on the daily activities of people with lower limb amputation. Prosthetic liners offer protection and comfort to sensitive areas but often exacerbate perspiration. They act as insulators, trapping sweat on the skin's surface to the detriment of skin health. Recently, liners with perforations have been developed, allowing the moisture to escape. The goal of this study was to assess the impact of such liners. A sample group of 13 patients with unilateral transtibial amputation, who wore a perforated liner (PL) as part of their current prescription, was compared to 20 control patients who wore non-perforated liners (NPL). During their routine appointments, they completed a survey of scientifically validated outcome measures relating to their limb health, pain and the impact on daily life over a 12-month period. Patients using the PL had healthier residual limbs, reporting higher scores on questions relating to limb health, experiencing fewer skin issues (p<0.001) and estimating a 61.8% lower rating in perceived sweat (p=0.004). Perhaps consequentially, there was a lower incidence of residual (p=0.012) and phantom (p=0.001) limb pain when compared to the control group. The prevalence of individual issues affecting the residual limbs of PL users was also lower. Of the issues that remained, only 23% were attributed to sweating in PL users, compared to 49% for the NPL group (p=0.066). PL users missed fewer days of work in the year (2.4 vs 11.6, p=0.267) and were also limited on fewer days (1.4 vs 75.4, p=0.009). The use of perforated liners shows much promise within prosthetic care, significantly improving the health of the residual limb. The observed effects on perceived sweat reduction, residual skin health, pain levels and patient limitation suggest that perforated liners are highly beneficial to patients.

Effects of Perforated Liners on Controlling Combustion Instabilities in Annular Combustors

This paper investigates the effects of two perforated liners on controlling combustion instabilities in a simplified annular combustor using a three-dimensional modeling approach. With this approach, the effects of radial modal coupling caused by the impedance jump across the connection interface between the rigid wall and perforated liner in the combustor are studied. The eigenfrequencies of the first longitudinal mode, the second longitudinal mode, and the first azimuthal mode are examined. The results show that the radial modal coupling is crucial to the prediction of the stability. It is also found that the absorption of the perforated liners is directly determined by the integrated effect of the local fluctuating pressure differences across the perforated plates. The integrated effect is influenced by both the position and length of the perforated liners. Effective control is achieved when the liners are placed at the pressure antinode of the combustion chamber, whereas ineffective control is achieved when they are placed at the pressure node of the combustion chamber. Also compared is the effectiveness of the outer and inner liners, and it is found that it is essential to consider the coupled system of the two liners when checking the overall control effects.

Control of Gray Mold on Clamshell-Packaged 'Benitaka' Table Grapes Using Sulphur Dioxide Pads and Perforated Liners.

The use of vented clamshells has become popular in the packaging of grapes for local and international markets. The aim of this study is to evaluate the postharvest preservation of ‘Benitaka’ table grapes individually packaged in vented clamshells using different types of SO2-generating pads and perforated plastic liners during cold storage. A completely randomized design with four replications in a two-factor arrangement with an additional treatment [(4 × 3) + 1] was used. The trials were carried out under two situations: Artificial or natural infections with Botrytis cinerea, which is the causal agent of gray mold on table grapes. The incidence of gray mold, shattered berries, and stem browning were evaluated at 30 and 45 days of cold storage at 1 ± 1 °C and 3 days of shelf-life at 22 ± 1 °C after the period of cold storage. Mass loss and berry firmness were also examined at the end of the cold storage period. The use of dual-release SO2-generating pads containing 5 or 8 g of a.i. and slow-release pads with 7 g of a.i. was effective in controlling the incidence of gray mold in grapes packaged in vented clamshells and kept under cold storage for up to 45 days. Under these storage conditions, perforated plastic liners with 0.3% ventilation area or micro-perforated liners with 1.0% ventilation area reduced the percentage of mass loss and shattered berries.

Ethyl formate fumigation: Its effect on stone and pome fruit quality, and grain chinch bug (Macchiademus diplopterus) mortality

The grain chinch bug, Macchiademus diplopterus (Distant) (Hemiptera: Lygaeidae), is a key phytosanitary pest requiring postharvest mitigation control for successful export of South African deciduous fruit. The main aims of the present investigation was to examine, firstly, the potential of ethyl formate as a fumigant to control the grain chinch bug and secondly, the effect of ethyl formate on the fruit quality of selected stone and pome fruit cultivars. The preliminary trial indicated a minimum concentration of 50 g/m3 (or 50 mg/L) ethyl formate for 1 h was required to obtain 100% mortality of the grain chinch bug. Building on those findings, phytotoxic trials assessed the effect of applying a dose range of 50–150 g/m3 ethyl formate for 1 h in desiccators at ambient temperature on various pome and stone fruit cultivars. No internal or external phytotoxic damage was observed on the various cultivars. An informal tasting panel could not distinguish between treated and untreated fruit. The effect of packaging (cartons with perforated bags or liners as per commercial use for each product) on the ability of ethyl formate to control the grain chinch bug was assessed after the phytotoxic susceptibility trials. The introduction of packaging confirmed that a higher concentration of ethyl formate (85 g/m3) was required for packaged fruit compared to the 50 g/m3 required for open crates or lugs. Higher ethyl formate concentrations enabled the fumigant to diffuse and penetrate the different packaging types without a dilution effect, effectively controlling the grain chinch bug embedded inside the cartons while maintaining fruit quality.

Demonstration study of applying bias-flow perforated liner on damping self-excited thermoacoustic oscillations in T-shaped thermoacoustic combustor

Self-excited thermoacoustic instability is undesirable in propulsion and power generation systems due to its detrimental effects. In this work, we conducted experimental demonstration study of applying bias-flow perforated liners on attenuating self-excited thermoacoustic oscillations in a premixed T-shaped combustor. For this, two perforated liners with different porosities and variable bias flow rate are experimentally tested and compared. It is found that in the absence of bias flow (cooling flow), the premixed flame can produce and sustain limit cycle oscillations. The amplitude and frequency of the dominant thermoacoustic mode are approximately 215 Hz and 140 dB. However, as the cooling flow velocity is increased to 5.5 m/s, the limit cycle oscillations are completely attenuated. More than 50 dB sound pressure level reduction is achieved. High-frequency modes are dampen by more than 25 dB. Further experimental test is conducted on the perforated liner with a porosity of 2.9%. Similar attenuation effect is achieved. Finally, during the transient growth process, dominant mode switching from high (non-harmonic) to low frequency is observed. The present work shed lights on the optimum design of perforated liner on attenuating thermoacoustic instability and the dynamic behaviours of the transient growth process.

Acoustic performance of a resonating perforated liner with incident axial and circumferential acoustic modes

Perforated liners are a common form of passive damping device used in engineering applications to damp acoustic pressure fluctuations. The liner has many orifices arranged over the surface with a rear cavity, where the liner can be designed to resonate akin to an array of Helmholtz resonators in parallel. However, whilst a Helmholtz resonator is insensitive to the incident mode, the large surface area and rear cavity of a perforated liner can generate internal mode shapes that affect the acoustic performance. This paper presents a quasi-one-dimensional analytical model capable of capturing the variation in acoustic performance as the internal cavity segmentation is altered with incident higher-order acoustic modes in a narrow annular duct. Thus, the model can allow the generation of circumferential mode shapes. The model shows, when the liner is highly segmented circumferentially, the liner behaviour is akin to that with an incident axial wave. The segmentation causes the internal cavity pressure to fluctuate uniformly at a similar frequency to a Helmholtz resonator with the same effective cavity dimensions. When the cavity length is significant relative to the wavelength, circumferential mode shapes are generated within the cavity and the frequency of resonance increases based on the circumferential frequency component. The model is then compared to an example experimental data set obtained from a facility designed to allow circumferential modes to cut-on simultaneously with an axial mode. A description of the facility and the multi-microphone decomposition method applied to decompose simultaneous modes of unknown orders and relative magnitudes is presented. The model has good agreement with the experimental results for a small cavity segmentation, although there is deviation observed at high frequencies when the cavity length becomes significant relative to the circumferential wavelength.

Acoustic damping characterization of a double-perforated liner in an aero-engine combustor

Double-perforated liners are widely used in gas turbine combustors because of their improved thermal load characteristics and broader acoustic damping compared with single-layer perforations. The present study examines the absorption of normal-incidence acoustic waves by double perforated liner, and provides quantitative analysis results on the effects of key liner parameters on the acoustic damping characteristics using the electro-acoustic analogy method. The developed impedance model is successfully validated against the measured data in the literature. Then, the impedance model is applied to the design of a double-perforated liner in the aero-engine combustor under development and the optimal liner design results are shown in terms of acoustic damping. It is found that the dome plate porosity and the plate gap, which is the space between the dome and splash plate, have a major impact on acoustic absorption for a given combustor geometry and flow condition. In contrasts, the splash porosity and plate thickness have minor significance over frequency range of interest. Thus, the optimized liner configurations are proposed from the viewpoint of acoustic damping.

Mitigating self-excited flame pulsating and thermoacoustic oscillations using perforated liners

Open-loop control of self-excited flame pulsating oscillations and thermo-acoustic instability is considered in this work. The performance of the control strategy is numerically evaluated in a 2D Rijke-type combustor with a perforated pipe implemented. It is found that approximately 38 dB sound pressure level (SPL) reduction can be achieved by actively tuning the cooling flow through the perforated pipe. Furthermore, the vorticity-induced damping performance is contributing to the breaking up of flame-acoustics coupling. However, the shedding of vortices is not uniformly distributed along the perforated pipe. To apply the control strategy in practice and to validate the findings, experimental studies are performed on a customer-designed Rijke-type combustor with a perforated liner implemented. To mimic practical engines, a cooling flow generated by a centrifugal pump is provided to pass through the perforated pipe. Properly tuning the cooling flow rate is found to lead to the unstable combustor being successfully stabilized. SPL is reduced by approximately 35 dB at ω1/2π≈245 Hz, and harmonic thermoacoustic modes are completely attenuating. Further study is conducted by suddenly removing the perforated pipe section. The combustion system is found to be associated with not only classical thermo-acoustic limit cycle oscillations with a dominant mode at 2.45×102 Hz, but also beating oscillations at 1.4×100 Hz. It is revealed that increasing acoustic losses by implementing the perforated pipe is another critical mechanism contributing to attenuating flame pulsating instability. The present work opens up an applicable means to attenuate both self-excited high-frequency thermoacoustic and low-frequency flame pulsating oscillations.

Post-harvest conservation of “Benitaka” table grapes with different SO2−generating pads and plastic liners under cold storage

This work aimed at evaluating the post-harvest conservation of “Benitaka” table grape by using different types of SO2-generating pads and perforated plastic liners under cold storage. The grapes were harvested from off-season crop 2018 in a commercial vineyard located at Cambira, PR, Brazil. The completely randomized design was used with four replications in a 2-factor arrangement with an additional treatment [(4 × 3) + 1], and the following factors were evaluated: a) SO2-generating pads (slow release containing 7 g of active ingredient – a.i.; slow release containing 4 g of a.i.; dual release containing 5 g of a.i.; and dual release containing 8 g of a.i.); and b) perforated plastic liners (0.3%, 0.9% and 1.0% of ventilation areas). The additional treatment did not contain any type of SO2-generating pad, only standard microperforated plastic liner (1% of ventilation area). The bunches were packed in 0.5 kg-capacity plastic clamshells, which were placed in a corrugated carton box with the different combinations of SO2-generating pads and plastic liners under cold storage at 1 ∘C with high relative humidity (&gt;90%). The treatments were evaluated at 30 and 45 days after the beginning of the cold storage, recording the incidence of gray mold, shattered berries, stem browning, mass loss and berry firmness. The data were submitted to analysis of variance and the means were compared by Tukey's test at 5%. The use of dual release SO2-generating pads containing 5 g or 8 g of a.i., as well the slow release pads with 7 g of a.i., are efficient to control the incidence of gray mold in “Benitaka” table grapes packaged in plastic clamshells and kept under cold storage at 1 ∘C up to 45 days. In these storage conditions, the use of perforated plastic liners with 0.3% of ventilation area or the micro perforated with 1.0% of ventilation area, result in the lowest bunch mass loss and shattered berries.