Cyclic Fluid Flow Research Articles

Particle transport during asymmetric net-zero cyclic fluid flow: Flow in tubes and radial flow in fractures

Cyclic fluid flow enhances transport in porous media. We study particle transport during asymmetric net-zero cyclic fluid flow where the fluid injection rate is higher than the withdrawal rate. Inside a tube, the threshold fluid velocity required to mobilize a particle depends on the relative particle size: larger particles obstruct flow more effectively than small particles and require a smaller velocity to be transported. Then, flow rates can be selected so particles move forward during the injection phase and remain stationary during withdrawal. Similarly, asymmetric cyclic fluid flow transports particles radially along fractures despite the net-zero fluid flow. The flow velocity decreases away from the injection point and particles migrate to a characteristic “terminal radial distance”. Unlike tube flow, a grain has a diminishing obstructing effect on the radial flow field, and the threshold flow rate required to mobilize grains increases with increasing particle size during radial flow.

Scheelite, apatite, calcite and tourmaline compositions from the late Archean Hutti orogenic gold deposit: Implications for analogous two stage ore fluids

Gold mineralization at Hutti, southern India has occurred in two stages. Stage-1 mineral assemblage comprises biotite, chlorite, plagioclase, calcite, epidote, actinolite, tourmaline, arsenopyrite, pyrite, pyrrhotite and gold, whereas the stage-2 mineral assemblage is represented by sericite, chlorite, calcite, scheelite, tourmaline, apatite, titanite, pyrrhotite, arsenopyrite and gold. We report here the occurrence of scheelite from the stage-1 assemblage and compare major and trace element compositions of scheelite, fluorapatite (F≈4wt.%), calcite and tourmaline from the two stages with an emphasis on the second stage in which they are best represented. Scheelite displays three types of REE patterns. These are the type-I middle REE (MREE)-enriched with negative Eu-anomaly, type-II heavy REE (HREE)-enriched with minor positive/negative Eu-anomaly, and type-III that varies from slightly MREE-enriched to MREE-depleted with correspondingly increasing positive Eu-anomaly. The stage-1 scheelites display type-I pattern, while stage-2 scheelites display type-II and type-III patterns. Textural and compositional evidence suggest asynchronous precipitation of scheelite, fluorapatite and calcite in the stage-2 mineralization, indicating precipitation from cyclic fluid flow. The occurrence of rare minute scheelite grains in the stage-1 mineralization assemblage is most likely because of prevalent high temperature (350–477°C), whereas during the stage-2 mineralization abundant scheelite precipitation, evidenced by the presence of scheelite-rich carbonate-quartz veins, was favored by the decrease in temperature (~300°C). Additionally, repeated fluid pressure fluctuations due to fault-valve mechanism would have further enhanced precipitation of scheelite in stage-2. The fewer scheelites in stage-1 mineralization resulted in their MREE-enriched pattern with high ΣREE. The MREE-depleted patterns of stage-2 scheelites, on the other hand, do not necessarily indicate a compositionally different fluid, but are due to rapid removal of MREE in early formed MREE-enriched scheelites making them less and less available in the fluid for later crystallizing scheelites. This is supported by the observation that except for the slight remobilization of LREE, the REEs are conserved in the altered rocks. Trace element ratios (Y/Ho, Zr/Hf, Nb/Ta) in fluorapatite and calcite are chondritic indicating little fractionation of these element pairs and cannot be diagnostic of fluid composition. Tourmalines from both the stages record equally low contents of Na, LILEs, and HFSEs and comparably low Fe3+/Fe2+ ratios, suggesting very similar nature of the two fluids which were low in salinity, trace element poor and reducing in nature, indicating a metamorphic parentage.

Multiphysics modeling of magnetorheological dampers

The dynamics of a small scale magnetorheological damper were modeled and analyzed using multiphysics commercial finite element software to couple the electromagnetic field distribution with the non-Newtonian fluid flow. The magnetic flux lines and field intensity generated within the damper and cyclic fluid flow in the damper under harmonic motion were simulated with the AC/DC and CFD physics modules of COMSOL Multiphysics, respectively. Coupling of the physics is achieved through a modified Bingham plastic definition, relating the fluid’s dynamic viscosity to the intensity of the induced magnetic field. Good agreement is confirmed between simulation results and experimentally observed resistance forces in the damper. This study was conducted to determine the feasibility of utilizing magnetorheological dampers in a medical orthosis for pathological tremor attenuation. The implemented models are thus dimensioned on a relatively small scale. The method used, however, is not specific to the damper’s size or geometry and can be extended to larger-scale devices with little or no complication.

AC Diffusion: Transport in Porous Networks Subjected to Zero-Time-Average Advective Flow

Diffusion is a slow transport mechanism and advective transport tends to dominate in large-size systems. An alternative transport mechanism is explored herein, whereby zero time-average cyclic fluid flow is compounded with pore-scale mixing to render effective transport. Two one-dimensional cyclic flow cases are analyzed: a rigid porous network with two open boundaries subjected to cyclic flow through, and a compressible porous network with only one open boundary subjected to cyclic compression. The corresponding analytical models predict diffusion-like macroscale response and provide explicit expressions for the effective diffusion coefficients in terms of the microstructure of the porous medium and flow conditions. A parallel experimental study is conducted to corroborate analytical predictions. Results confirm the relevance of pore-scale mixing in cyclic flow as a transport mechanism in porous networks.

Cyclic fluid shear stress promotes osteoblastic cells proliferation through ERK5 signaling pathway

Fluid shear stress plays an important role in bone remodeling, however, the mechanism of mechanotransduction in bone tissue remains unclear. Recently, ERK5 has been found to be involved in multiple cellular processes. This study was designed to investigate the potential involvement of ERK5 in the proliferative response of osteoblastic cells to cyclic fluid shear stress. We reported here that cyclic fluid shear stress promoted ERK5 phosphorylation in MC3T3-E1 cells. Inhibition of ERK5 phosphorylation attenuated the increased expression of AP-1 and cyclin D1 and cell proliferation induced by cyclic fluid flow, but promoted p-16 expression. Further more, we found that cyclic fluid shear stress was a better stimuli for ERK5 activation and cyclin D1 expression compared with continuous fluid shear stress. Moreover, the pharmacological ERK5 inhibitor, BIX02189, which inhibited ERK5 phosphorylation in a time-dependent manner and the suppression lasted for at least 4 h. Taken together, we demonstrate that ERK5/AP-1/cyclin D1 pathway is involved in the mechanism of osteoblasts proliferation induced by cyclic fluid shear stress, which is superior in promoting cellular proliferation compared with continuous fluid shear stress.

Fluid flow within the damage zone of the Boccheggiano extensional fault (Larderello–Travale geothermal field, central Italy): structures, alteration and implications for hydrothermal mineralization in extensional settings

AbstractThe Neogene extensional province of southern Tuscany in central Italy provides an outstanding example of fossil and active structurally controlled fluid flow and epithermal ore mineralization associated with post-orogenic silicic magmatism. Characterization of the hydrodynamic regime leading to the genesis of the polysulphide deposit (known as Filone di Boccheggiano) hosted within the damage zone of the Boccheggiano Fault is a key target to assess modes of fossil hydrothermal fluid circulation in the region and, more generally, to provide inferences on fault-controlled hydrothermal fluid flow in extensional settings. We provide a detailed description of the fault zone architecture and alteration/mineralization associated with the Boccheggiano ore deposit and report the results of fluid inclusion and stable oxygen isotope studies. This investigation shows that the Boccheggiano ore consists of an adularia/illite-type epithermal deposit and that sulphide ore deposition was controlled by channelling of hydrothermal fluids of dominantly meteoric origin within the highly anisotropic permeability structure of the Boccheggiano Fault. The low permeability structure of the fault core compartmentalized the fluid outflow preventing substantial cross-fault flow, with focused fluid flow occurring at the hangingwall of the fault controlled by fracture permeability. Fluid inclusion characteristics indicate that ore minerals were deposited between 280° and 350°C in the upper levels of the brittle extending crust (lithostatic pressure in the order of 0.1 GPa). Abundant vapour-rich inclusions in ore-stage quartz are consistent with fluid immiscibility and boiling, and quartz ore vein textures suggest that mineralization in the Boccheggiano ore deposit occurred during cyclic fluid flow in a deformation regime regulated by transient and fluctuating fluid pressure conditions. Results from this study (i) predict a strongly anisotropic permeability structure of the fault damage zone during crustal extension, and (ii) indicate the rate of secondary (structural) permeability creation and maintenance by active deformation in the hangingwall of extensional faults as the major factor leading to effective hydraulic transmissivity in extensional terranes. These features intimately link ore-grade mineralization in extensional settings to telescoping of hydrothermal flow along the hangingwall block(s) of major extensional fault zones.

Heat transport in granular materials during cyclic fluid flow

Heat transfer takes place between grains and the fluids that saturate the pore space in granular materials, when the fluid is static or moving. This study explores effective heat transport in granular materials during cyclic fluid flow. Controlled particle-scale experiments, complementary analyses and numerical simulations help us identify the governing variables and ensuing time scales. We show that fluid-grain heat transfer leads to effective heat transport along the granular medium during cyclic fluid flow. At the macro-scale, the process resembles diffusion where the effective diffusion coefficient is proportional to the square of the fluid invasion length in each cycle and inversely proportional to the cycle period. Both experimental and numerical results confirm improved heat transfer by cyclic fluid flow over thermal diffusion under hydrostatic conditions. The formulation can be used to identify optimal operation conditions for maximum transport.

Response of human osteoblast-like cells to fluid flow shear: A potential role for the microtubule network and primary ciliums

Introduction: A limited understanding of the cellular mechanisms governing bone mechanotransduction has inhibited the development of clinical treatments for a variety of bone disorders, including osteoporosis, osteoarthritis and microgravity-associated bone atrophy. The cytoskeleton is thought to play a role in cellular mechanotransduction, however the exact mechanism in bone cells has not yet been clearly elucidated. Studies involving cytoskeletal inhibitors have not generally considered secondary effects on cellular organelles such as the primary cilia. These cellular projections could account for the disparity between shear stresses predicted to occur in vivo and the minimum threshold of membrane deformation required to elicit a cellular response in vitro.
 Methods: MG-63 (human osteoblast-like) cells were cultured in vitro. Cultures were exposed to intermittent cyclic fluid flow shear stress (1 Pa amplitude), for 8 or 12 hrs. Some cultures were loaded in the presence of nocodazole (a microtubule inhibitor) or cytochalasin D (an actin filament inhibitor). The cellular response was analyzed through RT-PCR assessment of messenger RNA levels for specific molecules related to matrix metabolism. The effects of drug treatments on cytoskeletal disorganization and the primary cilia were assessed with immunocytochemistry and electron microscopy.
 Results: In untreated cultures, shear stress was associated with significant increases in mRNA levels for collagen I and matrix metalloproteinases 1 and 3, for both time points assessed. These increases were maintained in cultures loaded in the presence of cytochalasin D, but were almost completely abrogated in nocodazole-treated cultures. Cytoskeletal inhibitors exerted some dose-dependent effects on length and structure of primary cilia in MG-63 cells.
 Conclusions: The microtubule network appears to be necessary for some shear-induced responses of osteoblast-like cells. MG-63 cells possess primary cilia, organelles that could amplify fluid flow shear, accounting for some apparent contradictions between studies related to osteoblast mechanosensitivity. Since these structures are composed of microtubules, the observation that microtubule disruptors inhibit the shear response of osteoblast-like cells suggests the primary cilium may have a role in osteoblast mechanotransduction. The effects of cytoskeletal inhibitors on cilium structure may explain the conflicting results of earlier mechanotransduction studies.

Cyclic fluid flow through a regionally extensive fracture network within the Kodiak accretionary prism

Two types of periodic textures observed in veins from the Kodiak accretionary prism attest to cyclic fluid flow through a regionally extensive fracture network buried at 8–12 km depth: (1) crack‐seal microstructures with bands of mica inclusions and (2) collapse microstructures with jagged bands of residue embedded within euhedral crystals of quartz. The difference in texture reflects the closure of cracks: crack‐seal microstructures record the complete chemical sealing of the crack after each fracture event, whereas the collapse features record longer fluid‐filled periods followed by more rapid draining of fractures. Collapse features consist of pressure solution selvages trapped within veins and in the wall rock adjacent to euhedral growth terminations; the high concentrations of immobile elements in these selvages indicate that these fractures closed by collapse and penetration of quartz crystals into wall rock. Analysis of chemical composition on either side of four large euhedral growth veins and whole rock analysis of slates across the Kodiak Formation reveal local depletion of silica adjacent to veins but no evidence for long‐distance silica transport within the system. Both crack‐seal and collapse textures are observed in a regionally extensive vein system that displays a regular geometry, with thin, closely spaced (0.5–3 cm), near‐vertical crack‐seal veins that connect vertically and laterally with thicker euhedral growth veins arranged in widely spaced (∼500 mm) southeast dipping en echelon sets. The mesoscopic distribution and textural variability of the vein network suggests that the development of the vein system involved early nucleation and growth of vertical hydrofractures. As the fracture density increased, arrays of fractures locally provided zones of weakness and southeast dipping brittle‐ductile shear zones nucleated. These en echelon cracks remained open and provided small reservoirs of fluid. Textures show that en echelon fractures remain open but periodically grow by upward and downward propagation. Crack tips are then sealed with locally derived silica, and fluid drains back into en echelon fracture arrays. This local fluid movement is punctuated by less frequent events where the system links up over a greater distance, fractured reservoirs become interconnected, and the fluid within reservoirs is drained upward or laterally. Periodic inflation and deflation of en echelon arrays may reflect periodic slip on crosscutting faults and rupture of the seals that separate reservoirs.