90-degree Elbow Research Articles

CFD Analysis of Two-Phase Flow Characteristics in a 90 Degree Elbow

Computational fluid dynamics (CFD) analysis was performed for a two-phase air-water flow through a horizontal to vertical 900 elbow with a 12.7 mm pipe diameter. Three different air velocities of 15.24, 30.48, and 45.72 m/sec along with three different water velocities of 0.1, 1.0, and 10.0 m/sec were used in this study. To analyze the flow behavior in the elbow, pressure and velocity profiles at six different upstream and downstream locations of the elbow were compared. Computational fluid dynamics (CFD) analysis was performed for 9 different cases using FLUENT commercial code. A mixture model was used to account for different gas and liquid velocities to solve continuity, momentum and energy equations. CFD analysis results showed a decrease in pressure as fluid leaves the elbow in addition to a larger pressure drop at higher air velocities. No significant change in pressure was observed when water velocity was increased from 0.1 to 1.0 m/sec compared to water velocity change from 1.0 to 10.0 m/sec. The normalized pressure drop was larger at lower air velocities compared to higher water velocities. CFD analysis results were compared with available experimental data showing a reasonably good agreement.

Analysis of turbulent flow through a square-sectioned duct with installed 90-degree elbow

This paper presents the results of a theoretical and experimental investigation of the flow of air through a square-sectioned duct with installed bend. A special test stand was built which allowed testing two different bends with dimensionless mean radius values 2.01 and 1.5. To measure the volumetric flow rate, a measuring orifice plate was installed for control purposes. Additionally, numerical integration of the continuity equation, equations of motion, and equations of selected turbulence models was carried out using FLUENT. As a result of the numerical calculations, time-averaged velocity fields, pressures, and components of the turbulent stress tensor in a developing hydrodynamic flow through a square-sectioned duct with installed bend were determined. The numerical results obtained were subjected to detailed verification by comparison with experimental results obtained on the constructed test stand and those available in the literature.

Measures Of Upper And Lower Body Emg Activity In Stable And Unstable Surfaces

Adam Leja, Jordan Glenn, Ludmila Cosio-Lima, and Bhargav Desai University of West Florida, Pensacola, FL 32514 Research has been conducted to confirm the idea that the rectus abdominus is affected by training on an unstable surface (Cosio-Lima, et al., 2003), but research involving upper and lower body is scarce. Therefore, the purpose of this study is to investigate the effects of a training program on the BOSU Ball on muscles of the upper and lower body. METHODS: Sixteen collegiate students (8 males and 8 females age21.9 ± 3.1 years) from the University of West Florida with no background experience using a BOSU Ball participated in the study. Subjects performed 3 sets of 5 pushups on and off a BOSU Ball achieving90 degree elbow flexion and 3 sets of 5 squats achieving 90 degree knee flexion. There was no rest period in between each exercise and sets were alternated until all repetitions were fully completed. Statistical significance was set at (P< 0.05). Data was analyzed using repeated measures ANOVA (SPSS 17). RESULTS: Rectus abdominus activation increased significantly (P= 0.013) when the BOSU ball was introduced for the purpose of the push-up exercise. Additionally, there was a significant increase (P= 0.040) in mean triceps brachii activation the unstable surface (317.8 mV ±SD) of the BOSU ball vs. mean triceps activity on the stable surface floor (272.6 mV ± SD) during the push-up exercise.Moreover there was a significant increase (P = 0.047) seen in rectus abdominus activity during the squat exercise on the BOSU ball vs. the floor. No significant difference was found (P > 0.05) in the pectoralis major activity during the push-up exercise. CONCLUSIONS: The present study demonstrates the implementation of a BOSU ball will elicit a significant increase in rectus abdominus and triceps brachii activation during a push-up as well as an increase in rectus abdominus activation during a squat exercise. The prescription of unstable surface training may be beneficial when attempting to increase muscle proprioception.

Numerical and experimental investigation of the 3D free surface flow in a model Pelton turbine

This investigation focuses on the numerical and experimental analysis of the 3D free surface flow in a Pelton turbine. In particular, two typical flow conditions occurring in a full scale Pelton turbine – a configuration with a straight inlet as well as a configuration with a 90 degree elbow upstream of the nozzle – are considered. Thereby, the effect of secondary flow due to the 90 degree bending of the upstream pipe on the characteristics of the jet is explored. The hybrid flow field consists of pure liquid flow within the conduit and free surface two component flow of the liquid jet emerging out of the nozzle into air. The numerical results are validated against experimental investigations performed in the laboratory of the Institute of Fluid Mechanics (FLM). For the numerical simulation of the flow the in-house unstructured fully parallelized finite volume solver solver3D is utilized. An advanced interface capturing model based on the classic Volume of Fluid method is applied. In order to ensure sharp interface resolution an additional convection term is added to the transport equation of the volume fraction. A collocated variable arrangement is used and the set of non-linear equations, containing fluid conservation equations and model equations for turbulence and volume fraction, are solved in a segregated manner. For pressure-velocity coupling the SIMPLE and PISO algorithms are implemented. Detailed analysis of the observed flow patterns in the jet and of the jet geometry are presented.

Horizontal bubbly flow with elbow restrictions: Interfacial area transport modeling

The present study develops an interfacial area transport equation applicable to an air–water horizontal bubbly flow, along which two types of horizontal elbows are installed as flow restrictions. Two sets of experiments are performed in a round glass tube of 50.3 mm inner diameter. Along the test section, a 90-degree elbow is installed at L/ D = 206.6 from the two-phase mixture inlet and then a 45-degree elbow is installed at L/ D = 353.5. In total, 15 different flow conditions in the bubbly flow regime for each of the two flow restriction experiments are studied. Detailed local two-phase flow parameters are acquired by a double-sensor conductivity probe at four different axial locations in the 90-degree experiment and three different axial locations in the 45-degree experiment. The effect of the elbows is found to be evident in the distribution of local parameters as well as in the development of interfacial structures. It is clear that the elbows make an effect on the bubble interactions resulting in significant changes to both the void fraction and interfacial area concentration. In the present analysis, the interfacial area transport equation is developed in one-dimensional form via area averaging. In the averaging process, characteristic non-uniform distributions of the flow parameters in horizontal two-phase flow are treated mathematically through a distribution parameter. The mechanistic models for the major bubble interaction phenomena developed in vertical flow analysis are employed in the present study. Furthermore, the change in pressure due to the minor loss of an elbow is taken into consideration by using a newly developed correlation analogous to Lockhart and Martinelli's. In total, 105 area-averaged data points are employed to benchmark the present model. The present model predicts the data relatively well with an average percent difference of approximately ±20%.

The hydrodynamic effects of single-phase flow on flow accelerated corrosion in a 90-degree elbow

The hydrodynamic effects of single-phase flow on flow accelerated corrosion (FAC) in a single 90-degree elbow were investigated at a Reynolds number of 40,000. Experiments were performed to determine the surface wear patterns using elbows fabricated from hydrocal. The time evolution of the local surface wear was quantified using a laser scanning coordinate measurement system. Numerical simulations for the flow field were performed, and the wear patterns were correlated to the flow structures within the elbow. The wear patterns indicated the development of surface wear in the form of scallops over most of the elbow surface. Elevated levels of wear were found along the inlet of the elbow intrados. Along the elbow extrados, increased levels of wear, starting from 37° downstream of the elbow inlet and up to the elbow exit, were found at prolonged test times. The magnitude of the maximum wear on the surface along the elbow inner radius was found to be approximately 37% higher than the corresponding value at the surface along the outer radius.

Quantification of the yield strength-to-elastic modulus ratio effect on TES plastic loads from finite element limit analyses of elbows

This paper quantifies the effect of the yield strength-to-elastic modulus ratio on twice-elastic-slope plastic loads for 90-degree elbows under in-plane and out-of-plane bending. Based on extensive and systematic finite element limit analyses using elastic-perfectly plastic materials, simple regression equations between the yield strength-to-elastic modulus ratio and twice-elastic-slope plastic loads for elbows under in-plane closing, in-plane opening and out-of-plane bending are proposed, and validated against published experimental data. Applicability of the proposed equations to circumferential cracked elbows under in-plane bending is also investigated.

Geometric effects of 90-degree Elbow in the development of interfacial structures in horizontal bubbly flow

Present study investigates the geometric effects of flow obstruction on the distribution of local two-phase flow parameters and their transport characteristics in horizontal bubbly flow. The round glass tubes of 50.3 mm in inner diameter are employed as test sections, along which a 90-degree Elbow is located at L/ D = 206.6 from the two-phase mixture inlet. In total, 15 different flow conditions are examined within the air–water bubbly flow regime. The detailed local two-phase flow parameters are acquired by the double-sensor conductivity probe at four different axial locations. The effect of elbow is found to be evident in both the distribution of local parameters and their development. The elbow clearly promotes bubble interactions resulting in significant changes in interfacial area concentration. It is also found that the elbow-effect propagates to be more significant further downstream ( L/ D = 250) than immediate downstream ( L/ D = 225) of the elbow. Furthermore, it is shown that the elbow induces significant oscillations in the flow in both vertical and horizontal directions of the tube cross-section. Characteristic geometric effects due to the existence of elbow are also shown clearly in the transport of one-dimensional interfacial area concentration and void fraction along the flow.

VIBRATION ALTERS PATTERN OF MUSCLE ACTIVITY DURING FATIGUING RESISTANCE EXERCISE

The purpose of the present research was to determine the effects of vibration on motor unit recruitment patterns during muscular fatigue. Eight males (age = 21.4±1.6 yr., height = 69.44 2.62 cm. body mass = 78.06±10.68 kg, body composition = 12.48±2.00%) volunteered to participate. Data collection was divided into three sessions, each separated by a minimum of five days. During the first session, a ten repetition maximum (10RM) was determined for biceps curls (10RM = 16.44±2.47 kg). The second and third sessions consisted of the resistance exercise protocol (10 sets of a 10RM) designed to evoke muscular fatigue. During one of these sessions (V), a vibration (44 Hz) was superimposed by using a custom-designed dumbbell, whereas the other session (NV) was conducted using a traditional dumbbell. Prior to the first set and after each subsequent set, subjects performed a maximal isometric contraction of the biceps brachii at a one hundred and seventy degree elbow angle. During this isometric maximal contraction electromyography (EMG) was utilized to determine maximum EMG, average EMG and the median frequency. At all but one data point, the maximum EMG of session NV were elevated above their baseline readings (pre = 100%, t1 = 116.0±51.4, t2 = 138.6±44.0, t3 = 135.4±48.0, t4 = 110.8±30.9, t5 = 110.5±37.3, t6 = 112.0±45.0, t7 = 116.2±41.7, t8 = 120.5±35.4, t9 = 121.9±39.5, t10 = 110.4±34.3, t11 = 61.9±32.1, p ≤ 0.05). Conversely, maximum EMG of session V was below its baseline at almost every data point (pre = 100%, t1 = 105.9±31.1, t2 = 103.4±40.5, t3 = 101.0±29.5, t4 = 97.7±31.4, t5 = 90.0±28.4, t6 = 98.6±35.8, t7 = 89.9±40.6, t8 = 97.1±34.3, t9 = 93.7±29.7, t10 = 99.9±36.2, t11 = 58.9±20.4). Although the trend for median frequency was not quite as distinct, session V was higher than NV in most instances. It is clear that vibration alters patterns of muscle recruitment with resistance exercise, however, the mechanisms for these observed pattern changes is unclear.

A CFD Based Correlation for Erosion Factor for Long-Radius Elbows and Bends

A model for predicting sand erosion in 90 degree elbows and bends has been developed based on computational fluid dynamics (CFD), particle tracking and erosion data. After the flow field was obtained from the flow (CFD) model, particles were introduced into the flow and particle trajectories were computed using a Lagrangian approach. A model was also implemented that accounts for the interaction between the particles and the target material. Based on predicted particle impingement velocities, erosion rates and penetration rates were predicted using the empirical equations for erosion ratio. The predicted penetration rates are compared with available experimental data for several different elbows. The agreement between the predicted penetration rates and the experimental data is good. In addition, based on many predictions and erosion rate results, a new CFD based correlation is developed that can be used for an approximate engineering calculation to account for effects of elbow radius on erosion in long-radius elbows. This equation is for computing the ratio of the wall thickness loss (or the penetration rate) in a long-radius elbow to the penetration rate of a standard (short-radius) elbow. The results from the correlation agree well with the trend of available data in the literature.

Reynolds Number Effect on Turbulence downstream from Elbow Pipe.

Measurements of turbulence intensities downstream from a 90 degree elbow of circular cross section in the case of 1.1, 2 and 4 radius ratios were obtained using a laser-Doppler velocimeter at Reynolds numbers of 5×104-1×106 in order to clarify the Reynolds number effect on turbulence downstream from the elbow. The cross-sectionally averaged turbulence intensity decreased slightly with increasing Reynolds number. The effect of Reynolds number on it near the elbow was smaller than that for fully developed turbulent flow and decreased with decreasing radius ratio. The power spectrum of the turbulence intensity downstream near the elbow with any radius ratio had a distinct peak at the reduced frequency of about 0.5. No marked effect was observed of the Reynolds number on it.

Force and EMG power spectrum during eccentric and concentric actions.

This study was designed to examine the force and activation levels of elbow flexor muscles during preactivated eccentric, concentric and isometric actions. Force, average EMG (aEMG), and the EMG power spectrum were investigated at different constant movement velocities (1 rad x s(-1), 2 rad x s(-1), 3 rad x s(-1), and 4 rad x s(-1)) at different joint angles. Average force at a 110 degree elbow angle was lower and aEMG was higher in concentric actions as compared with eccentric and isometric actions. At a 55 degree elbow angle, there was no difference in aEMG, or it was slightly higher in eccentric actions. MF was higher in the concentric as compared with eccentric actions at the three fastest velocities at the 110 degree elbow angle, whereas no difference was observed at the 55 degree elbow angle. In concentric action, MF was higher in 4 rad x s(-1) in comparison with 1 rads x s(-1) at 110 degree elbow angle. These results suggest that it is difficult to maintain the maximal eccentric force throughout the whole range of motion. Maximal EMG activity and frequencies of the EMG power spectrum can be at the same level or lower in eccentric actions as compared with concentric actions, depending on the joint angle and preactivation mode. The results of the EMG power spectrum do not support the concept that in maximal eccentric actions fast units are selectively activated.

Suitability of air sampling locations downstream of bends and static mixing elements.

The revised standard for sampling effluent air from stacks and ducts of the nuclear industry places limits on the non-uniformity of velocity and contaminant profiles at the sampling location; namely, the coefficients of variation must not exceed 20% over an area that encompasses at least the center 2/3 of the cross sectional area. Tests were conducted to characterize the degree of mixing at downstream locations as affected by several types of flow disturbances, including 90 degree elbows and commercial static mixing devices. Flow straighteners were incorporated into the ducting upstream of the mixer to be tested to simulate the dampening of flow turbulence that might occur because of upstream HEPA filters. The coefficients of variation of velocity and tracer gas concentration measured in a straight tube at a distance of 3 diameters downstream from a 90 degree elbow were 17% and 69%, respectively. The mixing is impacted by the upstream flow turbulence. Without a flow straightener, the tracer gas concentration coefficient of variation was reduced to 33% at the 3-diameter location. The use of static mixing elements can greatly enhance the mixing process. A ring placed just downstream of a 90 degree elbow, which blocks the outer 56% of the cross sectional area, results in a coefficient of variation of 19% for tracer gas concentration at the 3-diameter location. Pressure loss across the elbow with the ring is about nine times that of the basic elbow. One of the commercially available static mixers provides coefficients of variation that are less than 10% for both velocity and tracer gas concentration at 4 diameters downstream from the mixer with a pressure loss that is only about 3.5 times as large as that of a 90 degree elbow.

Effect of Pumping on Air Characteristics of Conventional Concrete

The stability of the air content of concrete during pumping has been the subject of a number of recent investigations. Because increasing volumes of concrete are placed with the aid of pumps and the durability of such concrete to freezing and thawing (ASTM C666) as well as the scaling resistance (ASTM C672) preoccupy engineers, a study concerning the stability of the air-void system of a concrete with 45 to 50 MPa compressive strength was carried out. The slump of the three tested concretes ranged between 85 and 115 mm. Three pumping setups were studied. In the first, the concrete was pumped horizontally; in the second the concrete was pumped upward and then downward. In the third, the vertical setup was used but a reduced section was placed at the end of the pump line, and the concrete was allowed to free fall a short distance. For each pump setup, the concrete was sampled before being placed in the pump and after leaving the pump. The results clearly show that when the concrete is pumped horizontally, the spacing factor (L) and the specific surface of the air-void system are barely altered. On the other hand, after pumping the concrete vertically without a reduced end section, it was impossible to obtain an L less than 230 μm, the maximum spacing factor allowed by Canadian standards (CSA A23.1) to ensure good frost durability. Furthermore, the specific surface of the air bubbles fell to 20 mm−1, which is inferior to the 25-mm−1 value recommended in Canadian standards. By placing a reduced section at the end of the vertical pump line, it was possible to enhance the air-void system but that procedure still fell short of ensuring a system that satisfies the air-void system recommended by Canadian standards to ensure proper frost durability. Although the pumped concrete mixtures did not always satisfy the requirements of CSA A23.1 regarding air-void systems, they satisfied the requirements of ASTM C666 (Procedure A) for resistance to freeze-thaw cycles. Freeze-thaw resistance in the presence of deicing salts was evaluated according to ASTM C672. After 50 frost cycles, all but one concrete exhibited mass losses that were lower than the maximum permissible limit of 0.50 kg/m2 required by BNQ 2621-900, the standard currently enforced in the province of Quebec. Placing a reduced section at the end of the pump line creates a light counterpressure in the descending section of the pump line, which allows the conservation of an acceptable air-void system. Considering the appreciable improvement in the preservation of air-void characteristics when a reduced section was placed at the end of the pump line, it was decided to proceed with further experimental work using four 90-degree elbows placed at the end of the vertically hanging pump line.

Grip Strength as a Function of Forearm Rotation and Elbow Posture

An investigation was performed to assess the effect of forearm rotation (pronation and supination) and elbow orientation upon maximum grip strength of 10 male and 10 female subjects. Seven positions of forearm rotation which ranged from 90 degrees pronation to 90 degrees supination in both the 90 degree elbow flexion (arm adducted, forearm horizontal) and 0 degree flexion (shoulder flexed, whole-arm extended forward and horizontal) postures were examined. Thus a total combination of 14 postures were documented. Results indicate that maximum grip strength decreased significantly with forearm pronation, relative to the “neutral” forearm posture (p = 0.086). Other rotation postures did not yield significantly different grip strength from the neutral, but there was a clear decreasing trend in grip strength with forearm rotation away from neutral, particularly in pronation. The 0 degree elbow flexion showed the highest average grip strength values compared to 90 degree elbow flexion postures. Also, in the 90 degree elbow flexion posture, grip strength tended to increase with some supination from neutral rotation. It is recommended that for repetitive grasping activities, the arm and forearm postures should be considered in evaluating maximum grip strength. A regression model is presented to estimate maximum grip strength as a function of forearm rotation and elbow posture.

The delivery of therapeutic aerosols through endotracheal tubes.

We used an in vitro model system to examine the sites of deposition of aqueous therapeutic aerosols administered through 3-mm, 6-mm, and 9-mm endotracheal tubes (commonly used in infants, children, and adults) at clinically relevant inspiratory flow rates. Aerosol was delivered to the endotracheal tube via a "T" piece and a 90 degree elbow. Aerosol exiting the endotracheal tube passed through an appropriately sized Plexiglas model of the trachea and mainstem bronchi, and then into an 80-liter bag. Aerosol deposited in the "T" and elbow, endotracheal tube, large airway model, and collection bag was quantitated separately using 0.1% uranine as a tracer. Study of a conventional aerosol typical of those in common clinical use (aerodynamic mass median diameter = 3.95 microns) showed that most of the aerosol delivered into each endotracheal tube was deposited before leaving the mainstem bronchi. Substitution of an alternative nebulizer that produced a much smaller aerosol particle size (aerodynamic mass median diameter = 0.54 micron) dramatically decreased aerosol deposition in the "T" and elbow, endotracheal tube, and large airway model, and increased the quantity of aerosol penetrating beyond the mainstem bronchi up to ninefold. The mass median particle diameter of the conventional aerosol was reduced during endotracheal tube and large airway passage by poorly defined aerodynamic mechanisms that selectively removed larger particles. The smaller submicron aerosol was not similarly affected. Thus, conventional therapeutic aerosols appear to penetrate poorly through endotracheal tubes. Use of smaller particle size aerosols in treatment of intubated patients may be an effective way to circumvent this problem.

Effect of elbow position on grip and key pinch strength

Twenty-nine college women participated in a study to investigate the effect of elbow position on grip and key pinch strength evaluations. Standardized instructions and positioning were followed with the exception of the two elbow positions. The elbow was flexed to 90 degrees in one test condition and it was fully extended in the other. The results showed a significantly stronger grip strength measurement in the 90 degree elbow flexed position than in the fully extended position. For evaluation of key pinch strength, both hands were stronger in the elbow flexed position, but only the right hand was significantly stronger. This study supports the use of the elbow flexed position in standardized grip and key pinch evaluations.

1724 PENETRATION OF THERAPEUTIC AEROSOLS (TA) THROUGH ENDOTRACHEAL TUBES (ETT)

Because of observations of occasional toxicity from TA in intubated patients, we examined the site of deposition of TA delivered into 3.0, 6.0, and 9.0mm endotracheal tubes (ETT) using a constant flow in vitro model and 0.1% fluorescein as a tracer. A typical nebulizer (N) was used (aerodynamic massmedian diameter of 4.1) and a range of clinically relevant Inspiratory flow rates were studied. The N was connected to the ETT through a “T” piece and a 90 degree elbow. ETT ws bent 90° with a radius of curvature of 5.25 cm. TA exiting the ETT was collected in 80 L polyethylene bags. Because preliminary experiments showed that much of the TA which originally deposited the ETT, ran to the end of the ETT and dripped into the collection bag, appropriately sized plexiglass models of the trachea, and mainstem bronchi (MB), were constructed and placed on the end of each ETT to collect this drippage. Results, expressed as percent of inspired trace in each location, follow: Penetration of aerosol beyond the mainstem bronchi is decreased with increasing flow rate and decreasing ETT diameter. The study ws repeated with an alternative nebulizer delivering TA with an aerodynamic mass median diameter of .54. Aerosol penetration beyond the MB increased dramatically (to a range of 78-98%). Thus, a significant percentage of the TA delivered into the ETI during inspiration by usual nebulizers is deposited as a liquid bolus poured into the airway. This problem is nearly eliminated when a smaller particle size aerosol is used.

Acoustical Transmission Losses in Pneumatic Systems in Cotton Gins

ABSTRACT THE pneumatic conveyance of seed cotton through sheet-metal pipes in cotton ginning systems con-tributes strongly to the noise levels of the system. Numerous acoustical treatments were applied separately to a straight pipe and a 90-degree elbow inside an acoustical chamber. Sound-power levels were measured and transmission losses were calculated as seed cotton was conveyed through the system. A rubber-lined elbow covered with a 10.2-cm layer of fiber glass and a layer of lead produced the highest transmission loss. However, all of the acoustical treatments significantly lowered the sound-power level of the standard elbow. Selection of the optimum solution for a particular application depends primarily on the degree of noise reduction required and the cost of the acoustical treatment.

Axial dispersion in turbulent flow through standard 90 degree elbows

AbstractAxial dispersion was studied experimentally for turbulent flow through a 1 1/4‐in. piping system containing 90 deg. elbows. The Reynolds number range was 15,400 to 96,555. The imperfect pulse tracer technique was used with the axial dispersion numbers being obtained from the difference in variances of concentration‐time curves observed at two points in the system.Elbows interconnected by short lengths of pipe with each succeeding one reversed so as to cause a change in the direction of flow, increased axial dispersion by 35 to 61% over that expected for straight pipe, while the same elbows turned so as to form a helix decreased the dispersion substantially; however, the amount of axial dispersion was still 8 to 22% greater than that observed for straight pipe.The equivalent lengths of the elbows depend upon both their arrangement and the Reynolds number. Closely placed, helically arranged elbows required equivalent lengths of from 2.9 to 5.1 diam., while a reversed arrangement required 6.9 to 11.6 diam. Elbows separated by a developing length and randomly arranged yielded an equivalent length range of 3.6 to 10.6 diam. The geometical l/d ratio of the elbows used was 2.05.