Residual Air Research Articles

Water and Air Redistribution within a Dual Permeability Porous System Investigated Using Neutron Imaging

A ponded infiltration experiment was conducted under simultaneous imaging to investigate variations in quasi-saturated hydraulic conductivity a process frequently observed in infiltration experiments in soils with wide grain -size distribution. An artificially prepared heterogeneous sample composed of coarse quartz sand (representing pathways of preferential flow) and fine porous ceramic (representing soil matrix) was investigated. The sample was 34.5mm high and 29.0mm in diameter. Sequences of neutron radiography images (RI) of pixel size 0.045 × 0.045mm were taken at one angle during particular transient phases of the flow process. During quasi-steady state flow stages of the experiment radiography images were acquired in range of angles 0-180° in 0.9° step and. 3D neutron tomograms (TI) were then developed. Using the data a quantitative evaluation of the spatial and temporal distribution of water content within the sample was conducted. For every RI and TI the amount of water in particular pixels and voxels, respectively, was calculated by subtracting the image of dry sample. The accuracy of the water content estimates derived from the images was checked by comparing them to the corresponding gravimetrically determined water content data. Heavy water with equilibrium air saturation was introduced into the sample during two recurrent infiltrations. Thirty five hours later, during second infiltration, the inflow was switched to degassed heavy water in order to remove residual air present in the sample. During the first twelve hours of first infiltration run flow rate through the sample decreased from 3.7cm/hour to 1.0cm/hour at the end of the “steady state flow” stage. The flow rate in second run decreased from 3.6cm/hour to 1.6cm/hour. Comparison of the tomogram of the sample at the beginning and one taken at the end of the steady state flow stage in each run shows an increase of water content in the porous ceramic, while the water content in the coarse sand decreased. On the contrary, during the subsequent infiltration with degassed water the flow rate increased to its maximum value of 10.5cm/hour. The tomograms confirmed removal of the residual air during this stage. Increased water content in the coarse quartz sand was evident on a tomogram made at the end of the degassed water infiltration. The results show that the residual air saturation and its spatial distribution strongly affected the water flow in the quasi-saturated heterogeneous media representing natural soil.

On the mechanism of electrical aging of polymer insulation materials

The results of studies of the intercoupling between the structure and properties of polyvinylidenfluoride (PVDF) samples exposed to glow and torch discharges in an atmosphere of residual atmospheric air gases, argon, and SF6 are detailed. It is demonstrated that the amount of electric charge accumulated in samples exposed to an electric discharge depends on the defects and the degree of imperfection of these samples. The processes of thermally stimulated relaxation of charges from the PVDF samples are studied. This allows one to qualitatively estimate changes in the defect size and the degree of imperfection of the samples in terms of changes in material properties.

Blood-patch pleurodesis for pneumothorax in lung fibrosis due to progressive systemic sclerosis: A case report.

Pneumothorax in patients with progressive systemic sclerosis (PSS) often presents as a difficult-to-treat disease. Autologous blood-patch pleurodesis has previously been used for the treatment of pneumothorax. Blood outside its own environment is an irritant; therefore, chest physicians must watch closely for an allergic reaction. The injection is simple, painless, causes no side effects, is an inexpensive treatment for pneumothorax and is available not only in patients with persistent air leak but also in those with residual air space. A case is reported here of blood-patch pleurodesis for pneumothorax in lung fibrosis due to PSS. As an alternative therapy for difficult-to-treat pneumothorax in patients with PSS with persistent air leak and residual air space, autologous blood-patch pleurodesis would be one of the treatment options.

Рефлектометричні дослідження нанопористих плівок з масивом наночастинок золота

The influence of conditions occurring at the pulsed laser deposition of films with gold nanoparticles on the film porosity has been studied, by using the X-ray reflectometry. The films of two types were obtained by depositing particles (i) from the direct high-energy flow of erosion-torch particles and (ii) from the backward low-energy one. In both cases, the films were deposited either at the residual air pressure p = 10^−2 Pa or in the argon atmosphere with the pressures pAr = 5–100 Pa. In case (i), the film porosity was 0.1% at p = 10^−2 Pa and 1% at pAr ≤ 5 Pa. The plasmon properties of those films are associated with the propagation of surface plasmon-polariton waves. As the argon pressure grew further up to 100 Pa, the porosity increased to approximately 30%. In case (ii), the porosity of films deposited at pAr = 5–100 Pa onto substrates located in the target plane equaled 30 to 70% and depended on the distance from the film to the torch axis. All films with the porosity higher than 20% turned out nanocomposite structures with arrays of gold nanoparticles, which enabled us to observe the excitation of local surface plasmons.

Adsorption cooling utilizing the “LiBr/silica – ethanol” working pair: Dynamic optimization of the adsorber/heat exchanger unit

Owing to encouraging energy saving potential, adsorption heat transformers are considered as promising alternative to compression systems. However the enhancement of their specific power is required for their broader dissemination. This paper aims at the dynamic optimization of the Ad-HEx (adsorber/heat exchanger) unit operating with the novel working pair “LiBr/silica – ethanol”, which is characterized by high sorption difference under typical conditions of ice making and air conditioning cycles. The comparative investigation of various Ad-HEx configurations, namely thin beds of loose sorbent grains located on a flat metal plate and loaded into finned flat-tube heat exchangers was carried out. The effects of the adsorbent grain size, Ad-HEx geometry were explored in detail, and the main factors affecting sorption dynamics were revealed. The intra-particle diffusion of ethanol vapor and heat transfer between the support and the sorbent bed were shown to affect the sorption rate for flat sorbent bed configuration. For the configurations based on finned flat-tube heat exchangers, additional effects of the inter-particle diffusion or/and residual air were detected. On the base of the main findings obtained the practical recommendations on optimization of the Ad-HEx unit were formulated in order to enhance the specific cooling power of the adsorptive chiller.

Changes in residual air saturation after thorough drainage processes in an air–water fine sandy medium

Summary In a previous study we investigated the unstable and stable residual air saturations in an air–water two-phase system in a sand medium during a series of consecutive drainage–imbibition cycles with gradually increasing initial air saturations. In a reciprocal study reported here we extended the previous investigation by determining residual air saturations in consecutive imbibition processes starting from four gradually decreasing levels of initial air saturation (and thus increasing water saturation). Three parallel column tests with 9–12 consecutive drainage–imbibition cycles were performed, in which the first three imbibition processes started from the highest initial air saturation that could be obtained with our experimental system. The results show that all the residual air saturations resulting from the imbibition processes were almost constant after thorough drainage processes (even those following imbibition processes starting from low initial air saturations), and thus independent of the initial air saturation. The results also indicate that once the residual air in interconnected pores at the end of an imbibition process was present in the form of connected, pore network-scale air globules, the residual air remained in this state in subsequent imbibition processes, even if they started from low initial air saturations. It may be deduced that the presence of thin water films on the walls surrounding large pores and large volumes of air in their central parts during an imbibition process resulted in residual air being in the form of connected, pore-network scale air globules in interconnected pores. In contrast, thick water films and small volumes of air in the central parts of the pores resulted in residual air in the form of single pore-scale air globules in interconnected pores. Thus, stronger dynamic flow conditions (e.g., higher capillary numbers) may be required to remobilize connected, pore network-scale air globules than single pore-scale air globules in a forced imbibition process.

P-210 * PEZZER DRAIN VERSUS POLYETHYLENE CHEST TUBE AFTER UPPER LOBECTOMY: A RANDOMIZED PROSPECTIVE STUDY

Objectives: Apical residual air space and prolonged air leak are common complications contributing to prolonged hospitalization following resection of upper lobe of the lung. The objective of the study was to compare, in a prospective randomized fashion, two different management schemes for chest tubes after upper lobectomy: Pezzer drain versus polyethylene chest tube. Methods: Between 2011 and 2013, 50 patients (mean age 48.3 years) with air leaks associated with residual pleural space (3 cm at chest X-ray) persisting over 3 days after upper lobectomy were enrolled in this study. Fifty patients with air leak on the morning of the first postoperative day were randomly assigned to 2 groups: group 1 (Pezzer drain), 25 patients; or group 2 (polyethylene chest tube), 25 patients. The groups were then compared in terms of per and postoperative space, complication, hospitalization days, duration of the chest tubes, age, gender and side of the thoracotomy variables. Results: Postoperative residual space (P = 0.04) showed a significant correlation with apical polyethylene tube insertion. The Pezzer drain average duration of air leak was 3 days, the polyethylene tube average duration of air leak was 5 days. The patients with chronic obstructive pulmonary disease (COPD) in Group 2 had observed prolonged air leaks than the patients with COPD in Group 1 (P = 0.04). Pezzer drain patients showed a reduced incidence of air leak (P = 0.03), and a shorter postoperative hospital stay (P = 0.01), a shorter duration of chest tubes in place (P = 0.02). Age (more than 60 years, P = 0.029) and right thoracotomy (P = 0.01) appeared as significant predictors for apical residual air space. Empyema and pneumonia developed in 2 patients in group 2 after right upper lobectomy. Conclusions: Pezzer drain was superior to polyethylene chest tube alone in reducing the incidence of apical residual air spaces and related complications hospital stay after upper lobectomy. It is a safe, simple, cosmetic and low cost procedure. Disclosure: No significant relationships.

Determination of the optimal impregnation velocity in Resin Transfer Molding by capillary rise experiments and infrared thermography

Abstract Void minimization is an important issue in Resin Transfer Molding (RTM) because concentrated porosity can significantly decrease the quality of final composite parts. The injection stage is critical, since the impregnation of the fibers can generate voids by entrapment of residual air. The optimal velocity of the flow front in RTM injections can be determined by capillary rise experiments carried out through the fibrous reinforcement. Classical wicking investigation techniques are based on the visualization of the liquid front during the capillary rise, which can be enhanced by fluorescence. However, this technique can only be applied to transparent fibers such as glass. For this reason, a new approach based on InfraRed Thermography (IRT) is proposed in this paper for non-transparent carbon fibers. An inverse algorithm is used to estimate the optimal velocity of the flow front during resin injection from the thermal images obtained by IRT. This new experimental method was validated by comparison with capillary rise experiments carried out by fluorescence through glass fibers, after which it was applied to carbon fibers in order to determine the optimal impregnation velocity.

GRUŹLICA PŁUC POCHODZENIA ZAWODOWEGO U PRACOWNIKA DOMU POGRZEBOWEGO - OPIS PRZYPADKU

In Poland the incidence rate of tuberculosis is higher than the average for countries of the European Union, Norway or Iceland. On the other hand, occupational tuberculosis is still rarely recognized in our country. In this paper we present the first in Poland--to our best knowledge--case of pulmonary manifestation of this disease acquired at work in a funeral director. The recognition of the occupational etiology of the discussed illness gave rise to an array of diagnostic problems and became feasible after a thorough analysis of the patient's history and literature data, which allowed finding the relationship between infection and performed job. We speculated that the transfer of the dead body and handling of cadavers may expel residual air from the lungs of the deceased. Although tuberculosis occurs frequently in the general population, the recognition of work-related cases of this disease is still rare, especially among funeral directors.

Purposeful Creation of a Pneumothorax and Chest Tube Placement to Facilitate CT-Guided Coil Localization of Lung Nodules before Video-Assisted Thoracoscopic Surgical Wedge Resection

PurposeTo evaluate the feasibility and efficacy of pneumothorax creation and chest tube insertion before computed tomography (CT)–guided coil localization of small peripheral lung nodules for video-assisted thoracoscopic surgical (VATS) wedge resection. Materials and MethodsFrom May 2011 to October 2013, 21 consecutive patients (seven men; mean age, 62 y; range, 42–76 y) scheduled for VATS wedge resection required CT-guided coil localization for small, likely nonpalpable peripheral lung lesions at a single institution. Outcomes were evaluated retrospectively for technical success and complications. ResultsThere were 12 nodules and nine ground-glass opacities. Mean lesion distance from the pleural surface was 15 mm (range, 5–35 mm), and average size was 13 mm (range, 7–30 mm). A pneumothorax was successfully created in all patients with a Veress needle, and a chest tube was inserted. All target lesions were marked successfully, leaving one end of the coil within/beyond the lesion and the other end of the coil in the pleural space. The inserted chest tube was used to insufflate air to widen the pleural space during coil positioning and to aspirate any residual air before transfer of the patient to the operating room holding area. Intraparenchymal hemorrhages smaller than 7 cm in diameter developed in two patients during coil placement. All lesions were successfully resected with VATS. Histologic examinaiton revealed 13 primary adenocarcinomas, four metastases, and four benign lesions. ConclusionsPneumothorax creation and chest tube placement before CT-guided coil localization of peripheral lung nodules for VATS wedge resection facilitates the deployment of the peripheral end of the coil in the pleural space and provides effective management of procedure-related pneumothorax until surgery.

Estimation of Pore Water Pressure of Soil Using Genetic Programming

Soil–water characteristic curve (SWCC) is one of the input components required for conducting the transient seepage analysis in unsaturated soil for estimating pore water pressure (PWP). SWCC is usually defined by saturated volumetric water content (θs), residual water content (RWC) and air entry value (AEV). Mathematical model of PWP could be useful to unearth the important SWCC components and the physics behind it. Based on authors’ knowledge, rarely any mathematical models describing the relationship between PWP and SWCC components are found. In the present work, an evolutionary approach, namely, multi-gene genetic programming (MGGP) has been applied to formulate the relationship between the PWP profile along soil depth and input variables for SWCC (θs, RWC and AEV) for a given duration of ponding. The PWP predicted using the MGGP model has been compared with those generated using finite element simulations. The results indicate that the MGGP model is able to extrapolate the PWP satisfactory along the soil depth for a given set of boundary conditions. Based on the given AEV and saturated water content, the PWP along the depth can be determined from the newly developed MGGP model, which will be useful for design and analysis of slopes and landfill covers.

Causes of failure in endoscopic frontal sinus surgery in chronic rhinosinusitis patients

The frontal sinus is the most challenging area to address in endoscopic sinus surgery (ESS). Incomplete surgery or iatrogenic injury in the narrow space of the frontal recess with synechia formation can lead to recurrence or persistence of disease. The goal of this study was to identify causes of failure of endoscopic frontal sinus surgery and to determine complication rates. A cross-sectional retrospective study was conducted. Charts and preoperative sinus computed tomography (CT) scans of patients who underwent revision frontal ESS for chronic frontal rhinosinusitis, between 2006 and 2012 were reviewed. Of 829 patients who underwent ESS during the study period, 740 had the frontal recess dissected and frontal sinus opened. Of these, 66 patients had revision surgery of the frontal sinus, with a total of 109 frontal sinuses. The mean ± standard deviation (SD) age was 52 ± 12.9 years. Forty patients were male (59.1%). The most common findings were the following: edematous or hypertrophic mucosa (92.7%); retained agger nasi cell (73.4%); neo-osteogenesis within the frontal recess (45.9%); lateral scarring of the middle turbinate (47.7%); residual anterior ethmoid air cell (32.1.%); and residual frontal cells (24.8%). With the exception of mucosal disease and neo-osteogenesis, all identified causes of failure of frontal sinus surgery are a result of surgical technique. Careful preoperative planning and meticulous and complete surgical execution are therefore critical for a successful surgical outcome in primary frontal sinus surgery.

Paradoxical air embolism to left anterior descending artery during induction of anesthesia in a patient with an atrial septal defect.

Systemic air embolism is a complication after IV injection of air bubbles adhering to IV tubing, 3-way injection ports, and residual air in drug-filled syringes. Paradoxical air embolism across an intracardiac septal defect is a well-known complication, but paradoxical air embolism to the left coronary artery is a rare condition. We report the case of a 50-year-old woman scheduled for elective device closure of an atrial septal defect in whom coronary air embolism to the left anterior descending artery occurred after anesthetic induction.

The Research of On-Line Monitoring System Design for Temperature Distribution in Coalmine Gob Area

With some residual coal and much leaking air in gob area, fire happens frequently in those areas. Thus, it has become one of main factors of restricting mine development. With the technology of optical fiber pyrometer, the monitoring system has been designed for temperature distribution in coalmine gob area. In addition, by combining it with line laying system, power supply system, data collection system and data analysis system, temperature distribution in coalmine gob area could be monitored in time to provide firing warning of the spontaneous fire happening in the residual coal and fire would be reduced effectively. By comparing optical fiber thermometric system with the temperature measurement system, it shows that the former have a clear advantage in the aspects of time, the location of ignition point, reaction speed and costs maintenance.

Thermodynamic analysis of the growth of germanium-containing films from Ge(C2H5)4 + hydrogen mixtures

Low-pressure (1.33 and 13.3 Pa) chemical vapor deposition (CVD) of GeCx from tetraethylger-manium + hydrogen mixtures has been analyzed in a wide range of deposition temperatures, 300–1300 K, using thermodynamic modeling. In low-pressure CVD processes, films can be contaminated with impurities, in particular with oxygen, which may originate in the system in question from the residual air pressure in the reactor. Modeling results for the Ge-C-H and Ge-C-H-O-N systems indicate that the presence of oxygen adds significant complexity to the composition of condensed phases. At sufficiently high temperatures (T > 550 K), one can obtain GeCx films essentially free from oxygen impurities. We have identified deposition conditions (T > 650 K) under which the overall composition of the GeCx carbon-containing germanium layers remains constant. Experimental data are presented on the growth of germanium-containing films from a gas mixture with GeEt4: H2 = 1: 10 in the temperature range 573–823 K by plasma-enhanced CVD. At high deposition temperatures (T > 700 K), the composition of the films was near GeCx, in agreement with thermodynamic analysis results.

Chronic subdural hematoma: complication avoidance

Background and objectiveChronic subdural hematoma (CSDH) is defined as the presence of a typical neomembrane, typical liquefied blood within the hematoma cavity, and 3 weeks of more of acute subdural hematoma. It has been classified into separate, laminar, homogenous, and trabecular types. This study analyzed the complications after burr hole evacuation in CSDHs and the best methods to avoid or at least minimize them.Materials and MethodsA total of 28 patients who were suffering from complications after evacuation of CSDH were analyzed. Data on patients and treatment protocol were collected. Medical problems were also managed. Complications were studied as regards their causes and avoidance.ResultsThe highest incidence of complications is observed in the seventh decade of life. Recurrence was the most common complication especially in the separate type. The recurrence rate was higher among patients operated through a single burr hole. Extradural hematomas, although rare, were observed in three patients. Acute subdural hematoma and cerebral infarction had the worst prognosis.ConclusionSubgaleal dissection and insertion of a subgaleal drain are important for absorption and suction of the residual air and blood. In addition, intraoperative copious saline irrigation and postoperative meticulous follow-up are important for patients with a high risk of recurrence, especially those with hematomas of the separate type. During evacuation of the hematoma, we must avoid sudden decompression of the brain as it leads to cerebral infarction or intracranial hemorrhage. It is important to inform the anesthetist before performing the drainage that the blood pressure should be closely monitored and maintained at normal levels while infusing normal saline during surgery to avoid hypotension, which may lead to infarction. Any source of blood from the extradural space must be adequately dealt with.

Viscoelasticity of Ells River bitumen sand and 4D monitoring of thermal enhanced oil recovery processes

Samples of Ells River bitumen sand from Alberta, Canada were measured at low frequencies (0.2–205 Hz) to determine the temperature and frequency dependence of velocities and attenuations. The samples were first measured “as received” where the pore space is mostly filled with bitumen but also contains small amounts of air and water. With residual air in the pores, at 5°C, there is strong dispersion in the P-wave modulus and a peak in attenuation at seismic frequencies. The frequency-dependent moduli and attenuations shift by three orders of magnitude in frequency as temperature is increased from 5°C to 48°C, consistent with the bitumen viscosity. Samples were then saturated so any empty pore space is filled with water. After saturation, at 1 Hz, increasing temperature from 5°C to 49°C causes a 30% reduction in the saturated P-wave modulus, a 34% reduction in the saturated bulk modulus, and a 6% reduction in the shear modulus. This behavior can only be explained by the temperature-dependent bulk modulus of bitumen. The results enable predictions regarding the P-velocities that can be expected during seismic monitoring of thermal enhanced oil recovery processes. Velocities for cold bitumen sand are near [Formula: see text] at reservoir pressure and temperature. Following steam injection, velocities should be very low (near [Formula: see text]) in heated zones more than 50°C with a free gas phase, which could be steam or gas. There will be a progressive reduction in velocities, i.e., [Formula: see text] at 25°C and [Formula: see text] at 49°C, in areas of formation heating, but without steam or gas in the pores. Albeit smaller than the effect of steam, the effect of formation heating alone is large enough to be easily detected by today’s 4D surveys. With local rock physics calibration, it should be possible to map the areal extent of formation heating using 4D seismic data.

Aluminum toxicity and ecological risk assessment of dried alum residual into surface water disposal

This paper presented a simplified ecological risk assessment of the toxicity of alum residuals from water treatment plants to surface water that is based on the framework recommended by United States Environmental Protection Agency (USEPA). Though few studies have investigated the potential for increased aluminum toxicity with discharge of alum residual streams to the aquatic environment, none have explored the use of ecological risk assessment methodologies to gain additional insight into the potential risk. This systematic approach has been used to elucidate the process of aluminum toxicity from oven-dried alum residuals on aquatic habitats. A laboratory experiment was performed to assess the leaching of dried alum residuals to five lake water samples. The tests were also done to evaluate the effect of pH levels (4, 5·5, and 7) and drying mechanism of alum residual (oven, air or freeze–thaw). Total inorganic aluminum leaching from laboratory analysis was used along with toxicity reference values to determine a risk quotient (RQ) for assessment of risk. Results revealed that alum residuals in surface water could reduce aluminum concentration or potential risk (RQ) for fish in some lake waters at natural pH levels. Surface water pH and drying mechanism of alum residuals did not have considerable effect on leachability of aluminum. Lake waters with and without the addition of alum residual showed a potential risk for chronic sub-lethal toxicity for trout species. Both chronic and acute lethal toxicity was observed in some tests depending on the initial aluminum concentrations in the lake water. A detailed review of toxicological effects of aluminum, its exposure and bioaccumulation was studied for appropriate risk assessment.

Searching for the Ideal Endobronchial Blocker

We read with great interest the editorial in which Edmond Cohen1 extensively reviews the use of endobronchial blockers (BBs) versus double-lumen tubes. We support his message that the anesthesiologist should be familiar with alternative devices for a double-lumen tube. However, some of his comments on our work2 on the EZ-blocker (EZB) deserve our attention.First, Cohen points out that the most important limitation of the EZB is its inability to remove secretions through this blocker or to apply any effective suction. Indeed, the central lumen of the EZB is narrower than that of other BBs. It is, however, doubtful whether thick slimy secretions can be successfully removed through any of the BBs. All BBs are also in a fixed position and cannot be moved forth and back in search of a collection of secretions. Therefore, one needs a larger suction catheter or a flexible bronchoscope that can be used only with a double-lumen tube.There is no immediate need to aspirate air from the lung with our technique of acquiring lung collapse, i.e., 3-min preoxygenation, followed by disconnection of the single-lumen tube from the ventilator for 60 s (starting just before the surgeon opens the pleural space), then insufflation of the cuff of the EZB. In our study, the quality of lung collapse with an EZB was comparable to that with a double-lumen tube, and it was not necessary to aspirate residual air. In cases outside our study, it proved to be possible to remove residual air through the lumen of the EZB by intermittent suction. This practice must be performed with caution because of the risk of negative pressure edema. Oxygen can be administered through the lumen of the EZB to the collapsed lung with a continuous positive airway pressure system because of a low flow suffices, e.g., when hypoxemia occurs during one-lung ventilation.Second, there seems to be confusion about some properties of the EZB versus those of other BBs. As reported,1 BBs such as the Arndt blocker, the Cohen blocker, or the Uniblocker have low-pressure, high-volume cuffs. This does certainly not apply to the EZB, which often needs cuff pressures2 of more than 110 cm H20. Another difference is that the pilot balloons at the proximal end of the EZB are larger. A substantial amount of the volume that is insufflated remains in the pilot balloon and does not contribute to the volume of the distal cuff. Thus, the cuffs of the EZB should rather be classified as high pressure and low volume.

Residual air saturation changes during consecutive drainage–imbibition cycles in an air–water fine sandy medium

Summary To clarify changes of residual air saturation under special (dynamic, nonequilibrium) conditions, the saturation–capillary pressure (S–p) relationship including the residual air saturation under consecutive drainage–imbibition cycles, generated by scheduled water level fluctuations, in an air–water two-phase sandy column was investigated. Water saturation and capillary pressure were measured online and recorded using TDR (Time Domain Reflectometry) probes, T5 tensiometers and a datalogger. The results show that under dynamic flow conditions the residual air saturation changed suddenly from an unstable to a stable state with changes in initial air saturation during the series of imbibition cycles, and stable nonzero residual air saturation only occurred when the initial air saturation of the imbibition process exceeded 0.49, ca. double the value of the main imbibition process. Once stable residual air saturation was obtained, all the subsequent residual air saturations remained stable and constant in the following imbibition cycles. Before this threshold point, the residual air saturation gradually fell given sufficient imbibition time. The results also indicate that the unstable and stable residual air saturations were mainly due to discrete pore-scale air globules trapped in the interiors of pores and pore-network scale globules located in interconnected pores, respectively.