A review of literature for the structural assessment of mitred bends

This paper presents a state-of-the-art review of literature available for the structural assessment of all types of mitred pipe bends. Compared with smooth bends, the volume of literature available for mitres is less extensive and its scope is not as wide. Historically, this reflects a reduced application level, as well as a less demanding range of applications, such as non-high temperature use. There is also the issue that an analysis of a mitred bend is complicated by discontinuity stresses, as well as those due to cross-section ovalisation. This fact delayed the development of non-linear analysis of mitred bends. Nevertheless, there is now a substantial body of work on mitred bends. This review tabulates and characterises all publications to date in chronological order. The details of experimental specimens are highlighted, with a view to these perhaps providing useful verification data for any future finite element analysis for example. Issues of particular interest to pipework designers are discussed, including the effects of combinations of loading, out-of-circularity, tangent pipe length and flanges. Failure characteristics and loads are discussed where relevant. Topics for further research are also noted. For example, comprehensive design curves do not exist for the elastic and plastic behaviour of all mitre types, over a practical range of geometry and loading parameters. Similarly, there is still scope for further work on the effect of combined loading, end effects and out-of-circularity. Limit, collapse and burst loads are not yet available across the entire spectrum of bends and loading parameters either. Creep and optimisation represent virgin territory as far as mitred bends are concerned and given that unforeseen vibration is a common source of high-cycle fatigue failure in pipework, there must also be scope for vibration-induced fatigue studies

Modelling of hot air chamber designs of a continuous flow grain dryer

The pressure loss, flow distribution and temperature distribution of a number of designs of the hot air chamber in a continuous flow grain dryer, were investigated using CFD. The flow in the dryer was considered as steady state, compressible and turbulent. It is essential that the grain is uniformly dried as uneven drying can result in damage to the end-product during storage. The original commercial design was modified with new guide vanes at the inlets to reduce the pressure loss and to ensure a uniform flow to the line burner in the hot air chamber. The new guide vane design resulted in a 10% reduction in pressure loss and a γ-value of 0.804. Various design changes of the hot air chamber were analysed in terms of pressure loss and temperature distribution with the aim of a temperature variation of ±5 K at the outlet ducts. An obstruction design was analysed, which improved mixing and gave a temperature distribution within the limits. However, the pressure loss was six times larger than the original design with new guide vanes. Finally, The static mixer design resulted in a 23% reduction in the pressure loss, but had a mean absolute deviation of 22.9 K. Keywords: CFD, Fluid flow, Temperature distribution, Uniformity index, Continuous flow dryer, Grid convergence inde

Design of power-plant installations pressure-loss characteristics of duct components

A correlation of what are believed to be the most reliable data available on duct components of aircraft power-plant installations is presented. The information is given in a convenient form and is offered as an aid in designing duct systems and, subject to certain qualifications, as a guide in estimating their performance. The design and performance data include those for straight ducts; simple bends of square, circular, and elliptical cross sections; compound bends; diverging and converging bends; vaned bends; diffusers; branch ducts; internal inlets; and an angular placement of heat exchangers. Examples are included to illustrate methods of applying these data in analyzing duct systems. (author

The design and performance of a 1.9m x 1.3m indraft wind tunnel

This Thesis has endorsed employing a novel indraft configuration for a severely spatially and financially constrained wind tunnel aimed at undergraduate and postgraduate aeronautical and automotive instruction. The novel horseshoe indraft configuration employed may be considered to either bend a traditional open circuit or remove corners 3 and 4 from a traditional closed circuit. By connecting the inlet and exit to atmosphere the new configuration prevents pressure loading of the surrounding building; eliminates the problem of exhausting a jet within a laboratory; and eliminates costs associated with a heat exchanger. The modest budget (£350,000) is commensurate with the financial means of a University or small enterprise. Aerodynamic performance data suggests future designers should not shy away from an indraft tunnel by default: Velocity uniformity in the working area of jet has been shown to vary by less than 0.3% of the mean in the presence of ambient gusts up to 11.5% of the test velocity. Lift and drag coefficients derived from a 27% scale Davis automotive model (5.9% frontal area blockage) repeated to 6 units (0.6%) and 2 units (0.2%) respectively in the presence of ambient gusts up to 13% of the test velocity. Axial turbulence intensity was measured to be in the region of 0.15% (negligible ambient gusts) and 0.35% (ambient gusts up to 16% of the test velocity). This data compares favourably to that for the significantly larger NASA Ames 80ft x 120ft open circuit wind tunnel. Maximum test section velocity has been shown to be in excess of the desired 40m/s. The test section boundary layer closely follows the profile for a 1/7th power law turbulent boundary layer, which suggests the contraction is free from separation. This Thesis contributes to the body of knowledge by publishing performance data for a new type of wind tunnel configuration. It also augments existing design guidelines and rules of thumb by providing a complete reference point (including design flowcharts) for the design of comparable low speed wind tunnels. The Thesis offers the following specific conclusions and implications: Screens: Whilst the inlet filer mesh is effective at damping ambient gusts it suffers the worst correlation to the governing equations (significant under prediction of loss), likely due to wire-wake coalescence. This highlights the importance of performing pipe rig tests for screens with open areas significantly less than 57%. Safety screen loss was under-predicted (assumed drag coefficient, CD of 1.0 due to treatment as isolated wires). Whilst measurements suggest a CD of ~1.25 designers are advised to conduct pipe rig tests. Contraction: To allow pressure gradients to decay prior to the working section, it is advised that the parallel duct at end of the contraction be 1 hydraulic diameter rather than the 1 hydraulic radius proposed by the major texts. Working section: To allow for model wake recovery (and hence reduce the effect of non-uniformity on the downstream diffuser), a working section length-to-diameter ratio of 2.5 is suggested rather than 2 proposed by the established texts. Additionally, the static ports of tunnel pitot-static should be at least 0.55 hydraulic diameters upstream of the model leading edge to position them away from the static pressure signature of the model. Diffusers: Whilst the safety screen would ideally have to be removed to prove the hypothesis - it is suggested that turbulent mixing aft of the safety screen (located at the end of the working section) appears to offer a ~10% Cpr improvement to the first diffuser. Corner cascades: Whilst the established texts focus on corner loss coefficient (KL) this Thesis has shown that KL should not be the sole metric used to select the space-to-chord ratio (s/c) of corner cascades. Uniformity far downstream of a test cascade has been shown to improve with more closely spaced vanes (s/c of 0.190 rather than 0.237) despite KL being similar. Improvements to inlet boundary layer quality have also been shown to reduce KL. Fan: The fan static pressure rise was measured to be less than predicted due to smaller than expected leakage losses. A leakage loss of 2.5% is therefore proposed rather than the 10% suggested by the major texts

An experimental study of improvement of a micro hydro turbine performance

The thesis includes a literature survey of small hydraulic turbines, incorporating a historical review. The possible role of "micro hydros" in generating power in various parts of the world, and particularly in Iran, is discussed. The theory of turbo machinery, particularly with regard to axial flow turbines, is presented next. This is followed by some details on the design of guide vanes, runner blades and draft tube of axial flow turbines, these components being usually regarded as areas which have major impact on the performance of hydraulic turbines. The next chapter gives the details of the test circuit that was constructed. This could provide water volume flow rates of up to 0.15 m3/s at heads of up 25m. The two dynamometers that were used could adsorb pores to up to 25 kw and 50 kw respectively. An existing micro-turbine, the Agnew turbine, was selected for examination and possible improvement. The first possible improvement was the introduction of guide vanes upstream of the turbine runner (this inclusion necessitated a second support for the main shaft). It was found that this gave significant improvements - efficiency raised by over 20% in some cases. The domain of high efficiency working was considerably extended. It was observed that instability (with fall in power output) could occur after a period of running. This seemed to be associated with an accumulation of air bubbles at the highest point in the casing of the machine. Introduction of a vent from this point was found to relieve this problem and ensure stable operation

MIXED-FLOW PUMP OPTIMISATION AND FLOW CHARACTERISTICS BASED ON THE ‘DUAL CARBON’ GOALS

Urban water supply and drainage, the shipbuilding industry, the petrochemical industry and other professional fields rely heavily on mixed-flow pumps. Enhancing the efficiency of mixed-flow pumps is crucial for achieving the ‘dual carbon’ goals and promote energy saving and emission reduction. In this study, the guide vane and impeller of the mixed-flow pump were optimised, focusing on its low head and effectiveness in power plants. The performance of the original and optimised pumps was then evaluated under various flow rate conditions, and their hydraulic performance was compared. Results showed that the efficiency of the optimised mixed-flow pump was improved, resulting in effective enhancement of energy loss in the pump passage. The optimised guide vane facilitated smoother water flow into the outlet pipeline, achieving energy savings, emission reduction and contributing to the realisation of the ‘dual carbon’ goals

A novel flow-guide device for uniform exhaust in a central air exhaust ventilation system

Exhaust ventilation system with one central fan and multiple terminals has been widely used for the heat and contaminant removal in building environment. Conventional design without pressure balancing leads to uneven distribution of exhaust airflow rate among the multiple outlets. Existed balancing methods usually uses dampers (constant-air-volume valve or regulating valve), tapered duct, or varied inlet area. However, these methods result in higher fan energy consumption, or complicated construction and on-site commissioning. In this paper, a flow-guide device was developed for adjusting the pressure distribution of duct branches. This new device is integrated with the interflow Tee-junction and does not need any commissioning or regulating. The resistance performance of the device responding to the structural parameter was derived using the CFD simulation and experiment. The negative direct resistance featured by the device was found to effectively benefit exhaust at the outlets farther away from the central fan. The ductwork hydraulic model based on the Bernoulli's law of airflow and the fitted resistance correlations were further proposed to fulfill the parametric design. Finally, full-scale test was carried out for a central exhaust system installed with the flow-guide devices referring to a factory workshop with heat and contaminant sources. Compared to the system without the devices, the total rate of the system increased by 25%. Discrepancy of exhaust rate decreased by 78% and uneven degree decreased by 82%, which well meets the engineering balancing requirement. Meanwhile, total resistance of the system reduced 23.8% owing to the negative loss the devices bring

Calibration of the Langley 16-foot transonic tunnel with test section air removal

The Langley 16-foot transonic tunnel with test section air removal (plenum suction) was calibrated to a Mach number of 1.3. The results of the calibration, including the effects of slot shape modifications, test section wall divergence, and water vapor condensation, are presented. A complete description of the wind tunnel and its auxiliary equipment is included