Avoiding Sedimentation and Air Entrainment in Pump Sump for Wet Pit Pumping Stations

In many places lifting systems represent central components of wastewater systems. Pumping stations with a circular wet-pit design are characterized by their relatively small footprint for a given sump volume as well as their relatively simple construction technique [1]. This kind of pumping stations is equipped with submersible pumps. These are located in this case directly in the wastewater collection pit. The waste water passes through the pump station untreated and loaded with all kind of solids. Thus, the role of the pump sump is to provide an optimal operating environment for the pumps in addition to the transportation of sewage solids. Understanding the effects of design criteria on pumping station performance is important to fulfil the wastewater transportation as maintenance-free and energy efficient as possible. The design of the pit may affect the overall performance of the station in terms of poor flow conditions inside the pit, non-uniform und disturbed inflow at the pump inlet, as well as air entrainment to the pump. The scope of this paper is to evaluate the impact of various design criteria and the operating conditions on the performance of pump stations concerning the air entrainment to the pump as well as the sedimentation inside the pit. This is done to provide documentation and recommendations of the design and operating of the station. The investigated criteria are: the inflow direction, and the operating submergence. In this context experiments were conducted on a physical model of duplex circular wet pit wastewater pumping station. Furthermore the same experiments were reproduced by numerical simulations. The physical model made of acrylic allowed to visualize the flow patterns inside the sump at various operating conditions. This model is equipped with five different inflow directions, two of them are tangential to the pit and the remaining three are radial in various positions relative to the pumps centerline. Particles were used to enable the investigation of the flow patterns inside the pit to determine the zones of high sedimentation risk. The air entrainment was evaluated on the model test rig by measuring the depth, the width and the length of the aerated region caused by the plunging water jet and by observing the air bubbles entering the pumps. The starting sump geometry called baseline geometry is simply a flat floor. The tests were done at all the possible combinations of inflow directions, submergence, working pump and operating flow. The ability of the numerical simulation to give a reliable prediction of air entrainment was assessed to be used in the future as a tool in scale series to define the scale effect as well as to analyze the flow conditions inside the sump and to understand the air entrainment phenomenon. These simulations were conducted using the geometries of the test setup after generating the mesh with tetrahedral elements. The VOF multiphase model was applied to simulate the interaction of the liquid water phase and the gaseous air phase. On the basis of the results constructive suggestions are derived for the design of the pit, as well as the operating conditions of the pumping station. At the end recommendations for the design and operating conditions are provided.

Electrical Capacitance Tomography Based Sorting Technique for Wasted Plastics

This study has launched a concept to measure real time two-dimensional temperature distribution non-invasively by a combination of electrical capacitance tomography (ECT) technique and a permittivity-temperature equation for plastic pellets. The concept has two steps which are the relative permittivity calculation from the measured capacitance among the many electrodes by ECT technique, and the temperature distribution calculation from the relative permittivity distribution by permittivity-temperature equation. ECT sensor with 12-electrode is designed to measure and visualize the cross sectional temperature distribution during polymethyl methacrylate (PMMA) pellets cooling process. The images of the normalized relative permittivity distribution are successfully reconstructed at every time step during the process. The images indicate that the normalized relative permittivity of PMMA pellets is decreased as the temperature is decreased.

A Cost-Effective Search of Collision Pairs in Lagrangian Particle Tracking Method

In the simulation of particle-laden flows, in which the inter-particle collisions have to be considered, using the Eulerian-Lagrangian approach, it is agreed that the search of collision pairs based on the deterministic particle tracking method together with the binary-collision, hard-sphere model is a time consuming job in the computational procedure particularly for the flow laden with a remarkably high number density of particles. A cost-effective algorithm for the particle tracking processes which include solving the equations of motion, searching the collision pairs, and updating the list of neighboring particles’ indices is developed. It is demonstrated in the turbulent, fully developed, particle-laden channel flows that the computational expenditure required for completing the particle tracking processes in a given Lagrangian time step can be optimally made with an approximately linear proportionally to the total number of particles (NPT) by setting the number of Lagrangian cells (Ncell) for computation in accordance with the criterion of NPT / Ncell = O(10°).

PIV Measurements in Diffuser of the Radial Pump

The performance characteristics of the radial pump commonly used as a multistage (8 or 10 stage) pump have been investigated experimentally. Due to the complex three-dimensional geometries, the hydraulic performance of multistage pumps is closely related to the internal flows in diffuser and return vanes. In order to investigate the flow characteristics in these regions by Particle Image Velocimetry (PIV) technique, a transparent pump is designed. A 532 nm continuous laser and a high-speed camera are used as a light source and an image acquisition device, respectively. The velocity field information in a diffuser of the radial pump is successfully obtained by two-dimensional PIV measurements at various operating conditions.

Linking Efficiency to Functional Performance by a Pump Test Standard for Wastewater Pumps

Upcoming Energy related Products (ErP) regulations on wastewater pumps by the European Commission will affect all pump manufacturers and operators of wastewater systems. Hence, the preparation of efficiency standards for wastewater pumps is intensively accompanied by input from the affected stakeholders and experts of different fields [1]. The previous approaches of ErP regulations, as in lot 11 (Electric motors, Ventilation fans, Circulators in buildings, Electric pumps), focus only on efficiency. However, when applying the philosophy of Ecodesign directly to wastewater pumps, the complex flow structure and the transport behaviour of this inhomogeneous multi-phase fluid must be taken into account. While efficiency is an important criterion, it is necessary to take the specifics of sewage transport into account when designing a new test standard, so as not to compromise on proven and “system-efficient” technologies. Therefore, the Berlin Institute of Technology is currently investigating wastewater compositions and limits for reliable pump operation in order to design a test standard for wastewater pumps comparable to the DIN EN ISO 9906 efficiency tests for clear water [2]. The test will assess the functional fulfilment level of the pump performance, differentiating between the wastewater classes.

Variation of Hydraulic Performance by Impeller Trimming of a Mixed-Flow Pump

One of the best examples of wasted energy is the selection of oversized pumps versus the rated conditions. Oversized pumps are forced to operate at reduced flows, far from their highest efficiency point. An unnecessarily large impeller will produce more flow than required, wasting energy. In the industrial field, trimming the impeller diameter is used more than changing the rotation speed to reduce the head of a pump. In this paper, the impeller trimming method of a mixed-flow pump is defined, and the variation in pump performance by reduction of the impeller diameter was predicted based on computational fluid dynamics. The impeller was trimmed to the same meridional ratio of the hub and shroud, and was compared in five cases. Numerical analysis was performed, including the inlet and outlet pipes in configurations of the mixed-flow pump to be tested. The commercial CFD code, ANSYS CFX-14.5, was used for the numerical analysis, and a three-dimensional Reynolds-averaged Navier-Stokes equations with a shear stress transport turbulence model were used to analyze incompressible turbulence flow. The performance parameters for evaluating the trimmed pump impellers were defined as the total efficiency and total head at the designed flow rate. The numerical and experimental results for the trimmed pump impellers were compared and discussed in this work.

A Meridian Profile Obtained by No Restriction in Optimum Process

In previous study of optimum meridian profile of impeller and guide-vane, almost all design parameters included in the specific speed and blade number are variable design parameters in optimum process. As the result, optimum specific speed and blade number were obtained. In the calculation, loss calculation consists of blade-to-blade diffusion loss and axial-symmetrical annular wall friction loss. The calculation result without annular friction loss head isn’t affected by normal diameter and rotational speed. In consideration of diffusion loss and annular friction loss, the result of calculation is affected by normal diameter and rotational speed. In this case study, normal diameter and rotational speed are also variable design parameters. The normal diameter is mid span impeller outlet diameter. So, normal velocity is peripheral velocity of mid span impeller outlet. The initial normal diameter is 100mm and the initial rotational speed is 1000min−1. And then, design parameters and all specification become variable. As there isn’t constant design parameter in this case study, there is no restriction in optimum process. As there is no restriction in optimum process, the best one optimum meridian profile can be obtained. In one case, the object function contains the efficiency and suction specific speed. In the other case, the object function contains the only efficiency. As the result, the optimum meridian profile of impeller and guide-vane can be obtained in each case.

Accuracy Verification of the Turbulent Flame LES Model by a Methane/Air Burner Flame

This paper focuses on the numerical simulation of Sandia National Laboratories “the piloted methane/air burner flame D.” Large Eddy Simulation and 2-scalar flamelet approach are applied for the turbulent and partially premixed combustion field, which is expressed by the LES filtered equations of scalar G for tracking the flame surfaces and mixture fraction of a fuel and an oxidizer. The flamelet data consists of temperature, specific volume and laminar flame speed are calculated by the detail chemical reaction with GRI-Mech 3.0. Two kinds of flamelet data are validated; one is “equilibrium flamelet data” calculated by 0-dimensional equilibrium solution based on equilibrium model; the other is “diffusion flamelet data” calculated by 1-dimensional counter flow solution based on laminar flamelet model. Consequently, the “diffusion flamelet data” gives better result in this type of combustion field.

Performance of Oil Separator According to the Depth of the Outlet Tube

Recent years have witnessed a growing concern over saving energy because of global warming issues and energy price hikes caused by increased oil prices. The need to improve energy efficiency to reduce energy consumption has been raised. Refrigeration systems are also expected to have their energy efficiency improved. A refrigeration system’s the compressor uses lubricating oil. Lubricating oil, along with refrigerant, circulates in a refrigeration system. During this process, the pressure drop increases, and the heat transfer coefficient decreases. Moreover, insufficient lubricant may incur a decrease in performance and damage to a compressor. Therefore, an oil separator is used to separate the lubricant and return it to the compressor. Since an oil separator causes an additional pressure drop, energy consumption should be decreased by increasing the oil separator’s separation efficiency and decreasing the pressure drop. The recent increase in development of large-scale buildings such as skyscrapers and large supermarkets has also increased the demand for large refrigeration machines. At the same time, refrigeration piping is becoming longer, and refrigerant must circulate up to the highest points. A high-pressure head and long piping configuration inevitably increase the quantity of lubricant left on the pipe wall, which in turn increases the loss of lubricants. The increased length and fall height for lubricants to circulate with refrigerant increase the related energy loss. In order to use a compressor in a high-head long-piping refrigeration system, the separation efficiency of the oil separator must be improved. Doing so will also reduce energy losses. Even with an improved separation efficiency, however, an increased pressure drop means additional energy losses. Thus, an oil separator with high separation efficiency and low pressure drop should be designed. So using the Numerical analysis, designed a new oil separator. A series of numerical simulation has been carried out to study peformance of a cyclone type oil separator, which is designed for the compressor of a refrigeration system. Working fluid is R22, which is a typical refrigerant, and mineral oil droplet is supplied. Depending on the outlet tube length, separation efficiency varies from 98.74 to 99.25%. Considering both of the separation efficiency, outlet tube length of the separator has been designed as 158 mm and oil separator length is 310mm.