A major concern for pump system engineers over the last fifty years has been caviation. Cavitation is defined as the formation of vapor bubbles in low pressure regions within a flow. Generally, this phenomenon occurs when the pressure value within the flow-path of the pump becomes lower than the vapor pressure; which is defined as the pressure exerted by a vapor in thermodynamic equilibrium conditions with its liquid at a specified temperature. Normally, this happens when the pressure at the suction of the pump is insufficient, in formulas NPSHa ≤ NPSHr, where the net positive suction head is the difference between the fluid pressure and the vapor pressure at the pump suction and the “a” and “r” stand respectively for the values available in the system and required by the system to avoid cavitation in the pump.The manifestation of cavitation causes the generation of gas bubbles in zones where the pressure gets below the vapor pressure corresponding to that fluid temperature. When the liquid moves towards the outlet of the pump, the pressure rises and the bubbles implode creating major shock waves and causing vibration and mechanical damage by eroding the metal surfaces. This also causes performance degradation, noise and vibration, which can lead to complete failure. Often a first sign of a problem is vibration, which also has an impact on pump components such as the shaft, bearings and seals.
Implementation feasibility of power plant design relies heavily on the economic benefits. More often than not, newer technology cannot be implemented due to high cost of electric generation which would not be acceptable in the market since energy is a price sensitive commodity. Sometimes while deciding on a design to choose, we are given a choice between a high initial equipment cost and efficiency versus a lower capital cost with lower efficiency. The designer must be able to choose which design would fit best with their needs and goals.
While running a power generation plant, there are three types of cost that need to be taken into consideration: capital cost, operational cost and financing cost. With point one and two to being of higher priority.
[:en]This post will examine the meshing requirements for an accurate analysis of flow characteristics in terms of turbomachinery applications, based on Marco Stelldinger et al study . Computational Fluid Dynamics (CFD) are widely used for the analysis and the design of turbomachinery blade rows. A well-established method is the application of semi-unstructured meshes, which uses a combination of structured meshes in the radial direction and unstructured meshes in the axial as well as the tangential direction. Stelldinger’s paper presents a library for turbomachinery meshing, which enables the generation of semi-unstructured meshes for turbomachinery blade passages, including cavities, fillets and varying clearance sizes. The focus lies on the generation of a mesh that represents the real geometry as accurately as possible, while the mesh quality is preserved.
The above was achieved by using two different approaches. The first approach divides the blade passage into four parts. Inside of these parts, a structured grid is generated by solving a system of elliptic partial differential equations. The second approach is based on the domain being split into fourteen blocks. It has benefits concerning computational time towards the first one, because of a faster generation procedure as well as a faster performance of the inverse mapping.
[:en] Combined Cycle Power Plants are among the most common type of power generation cycle. Demand of CCP application has risen across board due to the rising energy demand (and consumption) as well as growing environmental awareness. Combined cycle is a matured energy that has been proven to generate much lower CO2 (and other environmental footprints) compared to a traditional fossil fuel steam or gas turbine power generation cycle Consequently, this application is often looked as a “better” substitute compared to other a fossil fuel technologies. That being said, CCP is still a temporary alternative to substitute SPP since although CCP generally is more environmentally friendly, CCP process still requires the combustion of fossil fuel (though at a significantly lower degree compared to SPP) for initial heat/energy source.
The application takes two kinds of thermodynamic cycle in assembly to work together from the same heat source. Fluid Air and fuel enters a gas turbine cycle (Joule or Brayton) to generate electricity, waste heat/energy from working fluid will then be extracted then go through a Heat Recovery Steam Generator and towards steam turbine cycle (Rankine) to generate extra electricity. The main advantage of this cycle combination is the improvement of overall net efficiency (around 50-60% higher compared to each cycle alone), thus, lower fuel expenses. With that being said, net efficiency of a CCP is often inflated especially on systems which use a low-temperature waste heat.
[:en]With the advent of emerging technologies in the space of human-computer interaction (HCI), a prevalent challenge has been finding methods that can accurately represent these motions in real time. Applications using RGB-D cameras to track movements for consumer-based systems has already been employed by Microsoft in the space of tracking silhouette movements in video games as well as app navigation in the Microsoft Kinect system. However, tracking methods must evolve in order to successfully represent the complexity of human hand motion. The two main categories of 3D hand articulation tracking methods consist of appearance-based and model-based tracking. Appearance-based tracking methods are efficient in the limited space of comparing the present model to a number of already defined hand configurations. Model-based tracking methods allow the computational configuration to explore a continuous space in which the hand motions are optimized at a high dimensional space in near real time.
If the computer tracks the human wrist with six degrees of freedom and the other joints accordingly, the ensuing dimensional analysis occurs at a high dimensional space. A saddle joint (2 DOF) at the base of the each finger plus the additional hinge joints (1 DOF each) at the middle of the finger describes each finger with four degrees of freedom. In turn, the problem of tracking the articulation of a single hand is performed in a dimensional space of 27. This highly dimensional problem formulation requires an optimization technique specific to the problem that can provide a uniform coverage of the sampled space. Quasi-random sequences are known to exhibit a more uniform coverage of a high dimensional compared to random samples taken from a uniform distribution. The Sobol sequence, developed by Russian mathematician Ilya Sobol, describes a quasi-random low-discrepancy sequence that more evenly distributes a number of points in a higher dimensional space. Figure 1 represents the distribution discrepancy between a pseudorandom number generation and a quasi-random low-discrepancy Sobol sequence generation.
[:en]The use of computational fluid dynamics (CFD) in turbomachinery design is getting more and more popular given the increased computational resources. For the design process, however, there is no need for extensive CFD capabilities as the effort is put on minimizing engineering time while obtaining a design which is about 90% optimized. Here we are presenting two cases where CFD is used to derive significant information for pump design.
First, the influence of the blade shape on the parameters of the single blade hydrodynamic pump was studied by Knížat et al . The investigation of the pump properties was carried out experimentally with a support of CFD methods. The accuracy of applied steady-state calculations was satisfactory for the process of design of a single blade pump, because of the good agreement between measured and calculated power curves.
[:en]The heating, ventilation, and air-conditioning (HVAC) system is arguably the most complex system that is installed in a house and it is responsible for a substantial amount of the total house energy used. A right-sized HVAC system will provide the desired comfort and will run efficiently. Right-sizing of a HVAC system is the selection of equipment and the designing of the air distribution system to meet the accurate predicted heating and cooling loads of the house. Rightsizing the HVAC system begins with an accurate understanding of the heating and cooling loads on a space, however, a full HVAC design involves more than just the load estimate calculation as this is only the first step of the iterative HVAC design procedure. Heating and cooling loads are dependent on the building location, sighting, and the construction of the house, whereas the equipment selection and the air distribution design are dependent upon the loads and each other.
[:en]As with any turbomachinery, pump design requires a lot of effort on finding the right blade profile for the specified application. As there is no right or wrong in the process, engineers have to make some general assumptions as a starting point. Generally, we can say that the focus of this task is to minimize losses. It is obvious that the selected blade shape will affect several important hydrodynamic parameters of the pump and especially the position of optimal flow rate and the shape of the overall pump performance curves. In addition to axial and radial pump design in recent years, we also have seen the development of mixed-flow pumps. A mixed flow pump is a centrifugal pump with a mixed flow impeller (also called diagonal impeller), and their application range covers the transition gap between radial flow pumps and axial flow pumps.
Let’s consider a dimensionless coefficient called “specific speed” in order to be able to compare different pumps with various configurations and features. The “specific speed” is obtained as the theoretical rotational speed at which a geometrically-similar impeller would run if it were of such a size as to produce 1 m of head at a 1l/s flow rate. In formulas:
where ns is the specific speed, n the rotational speed, Q is the volume flow rate, H is total head and g is gravity acceleration.
[:en]In order to succeed as an engineer focused on rotor dynamics in rotating equipment, it is important to be fully aware of its foundation. The foundations of rotor dynamics consists of two parts, lateral analysis and torsional analysis. For part one of this blog, I will be focusing on lateral analysis and then exploring torsional analysis in part two next week.
Lateral analysis, also referred as critical speed analysis, is the study of when rotational speed meets or exceeds the shaft natural frequency. This is important since not knowing the critical speed can lead to instability, unbalance or even cause unknown forces to alter the functionality of rotating machinery. Since a rotating machinery consists of many components (rotor, bearing, motor, seals, etc), lateral analysis is made up of three categories: undamped critical speed analysis, steady state synchronous analysis (also known as damped unbalance response analysis) and stability analysis.
[:en]Supercritical carbon dioxide cycles have slowly become more popular in the engineering market for electricity generation from various sources. SCO2 is found to be an ideal working fluid for generating power cycles due to its high efficiency –more than supercritical or superheated steam, which results in lower cost of electricity.
Supercritical carbon dioxide is a fluid state where carbon dioxide is operated above its critical point which causes the compound to behave as both a gas and a liquid simultaneously with the unique ability to flow as a gas though at the same time dissolve materials like a liquid. SCO2 changes density over small difference in temperature or pressure, though stay in the same phase; allowing large amount of energy to be extracted at higher temperatures.