A preheating exchanger is developed for improving acidic water degassing. Reasonable optimization of dual-inlet swirl heating tubes is analyzed by computations of the flow and heat transfer. The comparisons of the swirl number and circumferential average Nusselt number between isobaric injection and isokinetic injection are performed. Inlet area ratios ranging from 0. 1 to 0. 9 exhibit an important influence on the flow phenomena and the heating performance. A lower value of inlet area ratio leads to the tendency for the fluid passing through inlet 2 to move upstream of inlet 2 and results in more vortex pairs between inlets 1 and 2. An inlet area ratio value of 0. 5 exhibits the largest global average Nusselt number, normalized Nusselt number, and thermal performance factor. The optimized inlet area ratio is suitable for improving the degassing efficiency.

In the present study, the flame response and the effect of equivalence ratio and inlet temperature on the flame response are numerically investigated using Weller flamelet combustion and LES turbulent models. The results show that with increasing excitation amplitude at a constant frequency, theheat release ratio increases; the increment is smaller at higher frequencies. Due to the combustor geometry, two recirculating zones are formed. Any change in the amplitude and frequency can affect these recirculation zones, especially the central recirculation zone. At the low frequencies (below 50Hz), increasing the excitation amplitude affects flame transfer functioninconsiderably, because of no influence of the recirculation zoneson the heat release. At higher frequencies, an increase in the amplitude has a more influence on value of flame transfer function. It is shown that by increasing the amplitude, up to frequency of 140 Hz, the phase of flame transfer function slightly reduced, while this is intensified with increasing the equivalence ratio or flame inlet temperature. Furthermore, by increasing the equivalence ratio or inlet temperature of the flame, heat release ratio and the flame transfer function are reduced.

One of the important parts of the urban and agriculture water conveyance systems are channel junctions. In this research, the effects of different factors such as inlet discharge ratio, bed elevation of lateral channels and height of weirs at the end of outlet channels on characteristics of the subcritical flow in 90 degrees four-branch open channel junctions with two inlets and two outlets were investigated experimentally. The results showed that as the inlet discharge ratio, bed elevation of lateral channels and height of weirs at the end of outlet channels increased, the outlet discharge in the main channel also increased. Increasing the inlet discharge ratio and decreasing the height of weirs at the end of outlet channels caused more fluctuation in the water surface profile at the junction, but variation of the bed elevation of lateral channels had no effect on fluctuations of the water surface profile. Furthermore, conjunction of the two inlet flows caused changing the velocity profiles in the inlet channels.

Morning glory spillway is one of the spillways that used to passing of flood from high to low level. This spillway is used in the reservoir dams that are placed in narrow valleys and in many locations with high slope in reservoir walls. In the Morning glory spillways, the vortex flow can reduce discharge, discharge coefficient and the performance of spillway. The zigzag spillway, as another type, is introduced as a proper option for compensating the problem of passing maximum possible flow rate, usually encountered by spillways. In the present study, the experimental results of a physical model were used to develop a hydraulic design with squire and circle inlet and analysis method for Labyrinth Morning Glory Spillway. The analysis of experimental data in circle and square inlet showed, that increase in length of spillway and zigzag, causes decrease in the discharge coefficient. Finally the result of effect spillway inlet on flow rate demonstrate that discharge coefficient in square inlet is more than circle, whereas without vortex breaker.

Introduction The formation of vortices at the intake and the air entertainment into the intake duct is an important hydraulic phenomenon that usually occurs in the dam intakes and causes such problems as energy loss and reduction of intake discharge coefficient. Among different types of intakes exposed to the vortex phenomenon are hydropower intakes used to supply water to turbines and generate electricity. These intakes are mainly horizontal. To prevent the formation of strong surface vortices, their strength must be physically controlled. A practical solution for this is to use anti-vortex structures. These structures mainly eliminate the vortex by reducing the flow velocity near the intake, lengthening the flow path between the free water surface and the mouth of the intake, as well as energy dissipation. Some studies on the structural methods of vortex dissipation have been done by Amiri et all (2011), Tahershamsi et all (2012), Monshizadeh et all (2018), Taghvaei et all (2012). In this study, the effect of horizontal perforated plates on the dissipation of the strong vortices, the intake discharge coefficient and inlet loss coefficient of the intake is studied, so far no special studies have been done in this area. MethodologyIn the present study, a physical model was used to investigate the performance of horizontal perforated plates. This model was designed to produce the strongest type of vortex with air core and different strengths. The main components of the experimental setup are: reservoir, intake duct, pump and electromotor speed controller device. The dimensions of reservoir is 1.3 m in wide, 3.5 m long and 2 m high. The mouth of intake extends 20 cm into the reservoir and is positioned so that the side walls and the bottom of the reservoir do not affect the flow conditions. The length of the intake pipe is 4.5 m and its diameter is 16 cm. At a distance of 2 m upstream of the intake in the reservoir, some blades are installed vertically that by changing their angle relative to the intake axis, the angle of inflow to the intake can be changed. This makes it possible to strengthen the upstream vorticity to reach stronger vortices. For modeling the perforated anti-vortex plates, some plastic mesh with different openings and different thicknesses were used. For each plate, the corresponding mesh was placed in a metal coil and this coil is screwed to the reservoir wall so that the perforated plate be placed on the mouth of the intake. By creating 36 types of strong vortices, the performance of 10 types of perforated plates with different dimensions, thicknesses and openings was tested.Results and DiscussionCalibration tests showed that in the range of 1.5D to 2D (D is the diameter of the intake pipe) for submergence depth, flow discharges of 15 to 30 lit/s and blade angles of 0 to 20 degrees, the stable strong vortices are formed. A total of 36 strong vortices (three relative submergence depths, four flow discharges and three blade angles) were formed with different strengths in the model. In order to consider the appropriate confidence limit in this study, the performance of each of the anti-vortex plates in the model was considered so that it is able to dissipate vortex type-six or decrease to type-two vortices. Therefore, the conditions in which the strength of a type-six vortex was reduced by the relevant anti-vortex plate to a type-three (or higher) vortex are known as critical conditions. It should be noted that the type of vortex is determined based on its appearance. Finally with 360 tests it was concluded that the effect of opening of the plates to eliminate the vortex strength is more than the dimensions and the thickness of the plates. In addition, the effect of using perforated horizontal plates on discharge coefficient and inlet loss coefficient of the intake was investigated. It was concluded that the use of perforated anti-vortex plate with openings of 70%, 58% and 50% reduces the intake discharge coefficient by 5.9%, 10.5%, and 13.4%, respectively. It is also caused 12.9%, 24.7% and 33.5% for inlet loss coefficient of the intake, respectively.ConclusionThe effect of submergence depth on the vortex strength is greater than the flow discharge and it is also greater than the geometric asymmetry. Dimensions of the plate have little effect on the vortex dissipation. The thickness of the plates has little effect on the vortex strength. The opening rate of the plates has a great effect on the vortex and a plate with 50% opening, was able to dissipate all strong vortices. The vortex strength has a direct relationship with the inflow angle and the flow discharge and is inversely proportional to the submergence depth. As the flow discharge increases, the discharge coefficient decreases and the inlet loss coefficient increases.

IntroductionPiano key weir is a form of nonlinear weir designed to improve the discharge capacity of spillway structures. Due to the increase in effective length, they can be used in dam spillways or water regulation structures. It is modified form of labyrinth weir which easy to place on the existing spillway or newly constructed dam with less base area. There is no standard method available for PK weir design, and the amount of published information is insufficient for the design of PK weir. A large number of geometric and hydraulic parameters affect the discharge capacity of PK weir, and their effect on the hydraulic performance of the weir can be investigated with a numerical model or laboratory data. Simulation of flow over PKW using FLOW-3D software and the effect of the turbulence model on the accuracy of the numerical model is one of the goals of this study. Also, in this research, the effect of the ratio of the inlet key width to the outlet key width (Wi/Wo) and the effect of the energy head on the discharge capacity are investigated.MethodologyLaboratory data from Anderson (2011) were used to validate the numerical model. The total length and height of the weir are 4.848 and 0.197 m respectively, the floor slope in inlet and outlet key are 1:1.8, and number of keys is 4. The inlet and outlet key width are 0.116 and 0.925 m respectively, and the Wi/Wo ratio is 1.25. Selection of boundary conditions for the numerical model is one of the most basic stages of simulation. In order to define the boundary conditions, in the inflow point (Xmin) volume flow rate, in the sides of the weir (Ymin, Ymax) and bed (Zmin) wall condition, on the upper border (Zmax) symmetry condition and in the outflow section of the weir, outflow condition was used.Results and discussionThe numerical model results were compared with the laboratory data. The results showed that if the second order scheme and RNG k-ε turbulence model are used in the numerical model, the simulation accuracy of the flow over PKW increases. Also, the results show that increasing the He/P decreases the discharge coefficient. So that the discharge coefficient for He/P=0.92 decreases by about 50% compared to He/P=0.24. With the increase of the water depth on the weir, the interference of the flow takes place at the breaking point of the weir cycles, and as a result, the discharge coefficient decreases. Another factor affecting the flow coefficient of the piano key is the ratio of the inlet key width to the outlet key width. By increasing the Wi/Wo, the flow coefficient has increased, and then it becomes maximum at Wi/Wo=1.5.ConclusionsIn this research, the simulation of the flow over piano key and labyrinth weir was done using a numerical model. The results showed that for a fixed depth, the piano key weir passes more discharge than the labyrinth weir, and the ratio of flow through the piano key weir to the labyrinth weir is about 1.08. In other words, at a constant depth, the piano key weir passes 8% more flow. In this research, the effect of head energy on the discharge coefficient of the piano key weir was also investigated. The results show that increasing the He/P decreases the discharge coefficient. The results showed that if the Wi/Wo equal to 1.5, the highest discharge coefficient occurs for the piano key weir.

Study of separation zone is so important in right-angled three-branch or four-branch open channel junctions. Some effective parameters in this case are inlet discharge ratio and flow depth which in this research the effect of inlet discharge ratio and weir height ratios (flow depth) on flow pattern and dimensions of separation zone has been simulated numerically. Investigation of numerical results showed that k-ω model well validated with experimental results and had good agreement, so that simulation error was less than 20%. Dimensions of separation zone in main and side channels were directly proportional with the inlet discharge ratio. Also as increases of height ratio of outlet weirs, flow depth increases and separation zone dimensions decreased. According to the analysis of numerical results, dimensions of separation zone in vertical direction, of the channel bed to water surface increased, so that for discharge ratio 0.6 and height ratio of outlet weirs 0.377, length of separation zone at the channel bed, 0.1 m up the bed and water surface was about 60 cm, 75 cm and 85 cm, respectively. So of the water surface towards the channel bed, length of separation zone decreased about %29.

Study of separation zone is so important in right-angled three-branch or four-branch open channel junctions. Some effective parameters in this case are inlet discharge ratio and flow depth which in this research the effect of inlet discharge ratio and weir height ratios (flow depth) on flow pattern and dimensions of separation zone has been simulated numerically. Investigation of numerical results showed that k-ω model well validated with experimental results and had good agreement, so that simulation error was less than 20%. Dimensions of separation zone in main and side channels were directly proportional with the inlet discharge ratio. Also as increases of height ratio of outlet weirs, flow depth increases and separation zone dimensions decreased. According to the analysis of numerical results, dimensions of separation zone in vertical direction, of the channel bed to water surface increased, so that for discharge ratio 0.6 and height ratio of outlet weirs 0.377, length of separation zone at the channel bed, 0.1 m up the bed and water surface was about 60 cm, 75 cm and 85 cm, respectively. So of the water surface towards the channel bed, length of separation zone decreased about %29.