Measurement of torque in steam turbine-generator shafts followingsevere disturbances on the electrical supply system-analysis andimplementation

Phenomena that affects the performance of transducers that measure torque at positions along a turbine-generator shaft are reviewed, and the design of a transducer for precise measurement of torque at positions on a steam turbine-generator shaft that results from severe disturbances of the electrical supply system is discussed. Torque at shaft couplings following severe supply system events predicted using continuum models of turbine-generator shafts are analyzed and compared with that obtained over a section of the shaft by shaft twist and overall stiffness of the section. Algorithms for processing torque deduced from twist over a section to estimate true torque at specific shaft locations are discussed. Studies are performed for severe L-L-L short circuits with clearance. The design of a transient shaft torque transducer which uses disks with slits which are secured to the rotating shaft is described     

Effects of two-phase flow in a model for nitramine deflagration

Methods of asymptotic analysis are employed to extend an earlier model for the deflagration of nitramines to account for the presence of bubbles and droplets in a two-phase layer at the propellant surface during combustion. Two zones are identified in the two-phase region: one, at higher liquid volume fractions, maintains evaporative equilibrium, whereas the other, at lower liquid volume fractions, exhibits nonequilibrium vaporization. By introducing the most reasonable estimates for two-phase behavior of nitramines, the steady burning rates are found to be close to those obtained for models with a sharp liquid-gas interface. Good agreement with measured burning rates and pressure and temperature sensitivities are achieved through reasonable approximations concerning overall chemical-kinetic parameters.     

Effect of high negative incidence on the performance of a centrifugal compressor stage with conventional vaned diffusers

Three vaned diffusers, designed to have high negative incidence (-8°) at the design operating point, are studied experimentally. The overall performance (efficiency and pressure ratio) are measured at three rotational speeds, and flow angles before and after the diffuser are measured at the design rotational speed and with three mass flow rates. The results are compared to corresponding results of the original vaneless diffuser design. Attention is paid to the performance at lower mass flows than the design mass flow. The results show that it is possible to improve the performance at mass flows lower than the design mass flow with a vaned diffuser designed with high negative incidence. However, with the vaned diffusers, the compressor still stalls at higher mass flow rates than with the vaneless one. The flow angle distributions after the diffuser are more uniform with the vaned diffusers.     

Mixed Convection Heat Transfer Analysis in an Enclosure with Two Hot Cylinders: A Lattice Boltzmann Approach

The aim of this work is to study laminar mixed convection heat transfer characteristics within an obstructed enclosure by using the Lattice Boltzmann method. Flow is driven by a top cold lid while other walls are stationary and adiabatic. Hot cylinders are located at different places inside the cavity to explore the best arrangement. Comparison of streamlines, isotherms, average Nusselt number are presented to evaluate the influence of Richardson number and location of cylinders on flow field and heat transfer. Results indicate that heat transfer decreases with a rise of Richardson number for all considered arrays of cylinders. Among them, horizontally‐located cylinders at the top of the cavity have the greatest heat transfer at all Richardson numbers. Horizontally located cylinders at the bottom of the cavity have the lowest heat transfer at Richardson numbers of 0.1 and 1 while the lowest heat transfer rate belongs to cross diagonal located cylinders at a Richardson number of 10.     

Near wake flow analysis of a vertical axis wind turbine by stereoscopic particle image velocimetry

The development of the near wake of a vertical axis wind turbine is investigated by stereoscopic particle image velocimetry. The experiments are conducted in an open-jet wind tunnel on an H-shaped rotor, operated at a tip speed ratio of 4.5 and at an average chord-based Reynolds number of 1.7 × 10⁵. Phase-locked measurements are acquired at the turbine mid span in order to study the horizontal wake dynamics at the symmetry plane. Results show the evolution of the vorticity shed by the blade, how it organizes in large scale vortical structures at the edges of the wake and the resulting asymmetric induction field in the wake. The evolution of the blade tip vortices and the 3D wake geometry are detailed by a second set of measurements acquired at several vertical planes aligned with the free stream. The dynamics of the system of tip vortices, their vertical motion and interactions are discussed and related to the geometry and the recovery of the wind turbine wake. The experimental data are made publicly available for research purposes.     

Numerical study of unsteady flows with cavitation in a high-speed micro centrifugal pump

The unsteady flows caused by the interaction between the impeller and the volute in a high-speed micro centrifugal pump are numerically studied. The internal flows of both with and without cavitations are analyzed using the CFX. The characteristics of unsteady pressure on the blade surfaces and the symmetric plane of the volute are presented and compared. The results show that the amplitudes of pressure fluctuations of critical cavitation on the blade pressure surface (PS) are bigger as compared with those at the non-cavitation condition, but on the suction surface (SS), the situation is on the contrary. When cavitation occurs, reduction of load in the impeller is a result. In the present study, such reduction of load is observed mainly on the first half of the blades. Pressure fluctuations at five monitoring points, denoted by WK1 to WK5 in the volute, are also analyzed. No matter at the critical cavitation or at the non-cavitation conditions, the monitored pressure fluctuations are at the same frequencies, which equal to the blade passing frequency (BPF) and its multiples. However, the amplitudes of the fluctuations at critical cavitation condition are considerably stronger, as compared with those for without cavitation.     

Comparison of losses and heating in generator rotors followingsevere supply system disturbances

Losses and heating in rotors of large synchronous generators are examined following sustained stator-terminal and HV busbar line-to-line short-circuits at full load and no load, three-phase (L-L-L) short-circuits on a weak line connected to the HV generator transformer busbar with clearance at fault current zeros where the generator either remains in synchronism or falls from synchronism, and worst-case malsynchronization. Comparisons are made with negative sequence losses in solid generator rotors following these disturbances. The analysis uses a phase-variable model of a synchronous generator with detailed and reduced damper representations to compute stator and rotor current following a severe electrical disturbance at either the machine terminals or the HV unit transformer busbar. Simulations at full load and no load for a variety of assumptions and approximations, with connection of a field discharge resistor on tripping the main generator breaker, are performed     

The fluctuation of solar radiation in Thailand

Fluctuations in the daily solar radiation are examined in an unbroken 5-yr sequence of measurements at Bangkok, and are also estimated from daily sunshine measurements at Bangkok and 3 other stations in Thailand. Seasonal effects are shown by separate studies for eight $\text{1}\text{1}\text{2}$ month periods of the year defined by standard solar declination values.During the dry season in winter and spring the frequency distribution of daily totals of global solar radiation at Bangkok has a peak near 20 MJ m^?2 d^?1 and is skewed towards low values. During the wet season in summer and autumn the distribution is more dispersed. Elsewhere the distributions are similar to those at Bangkok.The time series of daily totals of global solar radiation at Bangkok is analysed as a second order random process. The observed annual frequencies of runs of consecutive days with low radiation at Bangkok are given. There are 32.0 isolated days, 9.4 pairs of days, and 3.4 runs of 3 days per year with radiation less than 12.57 MJ m^?2 d^?1. These results are adequately described by the second order theory. The runs are most likely to occur in summer and autumn. Elsewhere in Thailand the annual frequencies of the runs and their seasonal distributions are almost the same as at Bangkok, except that in the south the runs are more likely to occur later in the year.     

Soot formation in high pressure laminar diffusion flames

The details of the chemical and physical mechanisms of the soot formation process in combustion remain uncertain due to the highly complex nature of hydrocarbon flames, and only a few principles are firmly established mostly for atmospheric conditions. In spite of the fact that most combustion devices used for transportation operate at very high pressures (e.g., aircraft gas turbines up to 40 atm, diesel engines exceeding 100 atm), our understanding of soot formation at these pressures is not at a desirable level, and there is a fundamental lack of experimental data and complementary predictive models. The focus of this review is to assess the experimental results available from laminar co-flow diffusion flames burning at elevated pressures. First, a brief review of soot formation mechanisms in diffusion flames is presented. This is followed by an assessment of soot diagnostics techniques, both intrusive and non-intrusive, most commonly used in soot experiments including the laser induced incandescence. Then the experimental results of soot measurements done at elevated pressures in diffusion flames are reviewed and critically assessed. Soot studies in shock tubes and in premixed flames are not covered. Smoke point fuel mass flow rate is revisited, and shortcomings in recent measurements are pointed. The basic requirements for tractable and comparable measurements as a function of pressure are summarized. Most recent studies at high pressures with aliphatic gaseous fuels show that the soot yield displays a unified behaviour with reduced pressure. The maximum soot yield seems to reach a plateau asymptotically as the pressure exceeds the critical pressure of the fuel. Lack of experimental data on the sensitivity of soot morphology to pressure is emphasized. A short summary of efforts in the literature on the numerical simulation of soot formation in diffusion flames at high pressures is the last section of the paper.     

Heat Transfer and Hydrodynamic Investigations of a Baffled Slurry Bubble Column

Heat transfer and hydrodynamic investigations have been conducted in a 0.108 m internal diameter bubble column at ambient conditions. The column is equipped with seven 19mm diameter tubes arranged in an equilateral triangular pitch of 36.5 mm. A Monsanto synthetic heat transfer fluid, Therminol-66 having a viscosity of 39.8 cP at 303 K, is used as a liquid medium. Magnetite powders, average diameters 27.7 and 36.6 μm, in five concentrations up to 50 weight percent in the slurry, are used. As a gas phase, industrial grade nitrogen of purity 99.6 percent is employed.Gas holdup in different operating modes and regimes have been measured for the two- and three-phase systems over a superficial gas velocity range up to 0.20 m/s in the semi-batch mode. Heat transfer coefficients are measured at different tube locations in the bundle at different radial and vertical locations over a range of operating conditions. All these data are compared with the existing literature correlations and models. New correlations are proposed.     

On numerical modelling of low-pressure subcooled boiling flows

Although models of subcooled flow boiling at high pressure have been studied extensively, there are few equivalent studies for numerical modelling at low pressure. Recent experimental and numerical studies on subcooled boiling flow at low pressure have indicated that empirical models developed, and verified, for high-pressure situations are not valid at low pressures. A study has been conducted to extend a two-fluid model, previously used for predicting subcooled boiling flow at high pressures into being applicable for low-pressure conditions. This study demonstrates that the following closure relationships or parameters are important for an accurate prediction of void fraction distributions at low pressures: (i) partition of the wall heat flux; (ii) bubble size distribution and interfacial area concentration; and (iii) bubble departure diameter and its relationship with bubble frequency. Different existing correlations for all these are tested and some new correlations are proposed. Predictions of the proposed model agree closely with a number of published experimental data.     

Performance characteristics of solar ponds operating at different latitudes

The results of a comparative study of the performance of solar ponds operating at different latitudes are presented in this paper. A mathematical tool was developed to study the behaviour of solar ponds operating under different physical and operational conditions. The hourly meteorological data of Kew and Singapore were used. The pond operating at higher latitudes, i.e. Kew, where seasonal variations are significant, must be deeper than a pond operating near the equator. The deeper pond can also act as an interseasonal storage device. A pond operating at a location in Singapore attains a fairly high temperature but the temperature requirements are also high for the desired applications such as space cooling in conjunction with a refrigeration cycle. Although a pond at Kew attains a lower temperature compared with a pond at Singapore, it can supply considerable amounts of thermal energy to support a space heating load. Both the ponds require auxiliary heating, the magnitude being dependent upon the nature of the load.     

Pipeline vs. truck transport of beef cattle manure

Anaerobic digestion (AD) of manure can be conducted at a wide range of capacities. As capacity increases, economies of scale in capital equipment are realized but transportation costs increase as manure must be carried longer distances to the plant site. In this study, we evaluate the cost of pipelining manure from beef cattle feedlots and digestate from an AD plant as an alternative to truck transport. Pipeline transportation cost for manure is minimized at a slurry concentration of about 12%; low concentrations require a larger pipeline, and high concentrations require higher pumping costs. Pipelining costs are highly scale dependent, while trucking costs are virtually independent of scale for a given carrier size. A stand-alone manure pipeline competes with trucking at 90,000 head of beef cattle. Digestate volume is about 2.4 times the volume of manure and a stand-alone digestate pipeline is more economic than trucking at 21,000 head, and a two-way pipeline at 29,000 head. Incremental net fixed costs for trans-shipment from truck to pipeline are low for manure and zero for digestate because equipment installed at the pipeline inlet eliminates the need for identical equipment within the digester plant. A manure pipeline must run for a minimum distance to recover the incremental fixed cost of trans-shipment; at 300,000 animals, the minimum economic pipeline distance is 9 km. Pipeline transport of beef cattle manure has the potential to reduce overall transportation cost to a large centralized digester in areas such as Dodge City, Kansas or Lethbridge, Alberta where very large numbers of beef cattle are in feedlots. A 50 km pipeline carrying manure from 300,000 beef cattle has an overall transport cost of 40% of ongoing truck transport.     

NUMERICAL SIMULATION OF TRANSIENT NATURAL CONVECTION FROM AN ISOTHERMAL CAVITY OPEN ON A SIDE

Numerical simulations are presented for buoyancy-induced flow and heat transfer in a square isothermal cavity open on a side. The vorticity-stream function formulation with improvised boundary conditions at the window of the cavity is employed. It is shown that flows at moderate to high Rayleigh numbers are periodic or unsteady. The interaction of the buoyant elements generated at the three sides and their entrainment characteristics are complex. The basic physical mechanisms underlying these complex flows are discussed in detail. Nusselt number data are provided for steady and unsteady flows.     

Dynamic Characteristics of a Free-Flow-Channel Heat Exchanger

The performance of sewage heat exchangers plays an important role in the sewage source heat pump systems when the sewage does not enter the heat pump unit directly, especially when untreated sewage is used as heat or cold source. In this article, a free-flow channel heat exchanger is proposed to be used in an untreated sewage source heat pump system. First the article designs the sizes of heat exchanger according to the real system requirements, and then it models and analyzes dynamic characteristics on the simulink platform. The transfer functions that are suitable for the heat exchanger are deduced. The analysis shows that the wall temperature is 9.1°C when the untreated sewage and water temperatures at the inlet are 15 and 7°C, respectively. The result is obtained when considering the temperature at the outlet is affected by the temperature at the inlet. The variable quantity of water temperature at the outlet is affected greatly by the variable quantity of water temperature at the inlet and the variable quantity of sewage temperature at the outlet by the variable quantity of sewage temperature at the inlet. Besides, the measured values of water temperatures at the inlet and outlet are also observed from the real system where the free-flow channel heat exchanger is adopted. The variable quantities of water temperature at the outlet are calculated according to the measured values, and are compared with the model results deduced by the transfer functions. The comparative result shows that the differences between the measured and model results of water temperature variable quantities at the outlet range from ?1 to 1°C, thus getting the water temperatures at the outlet according to the model results. The differences of the water temperature at the outlet between the measured values and the deduced results are from ?0.5 to 0.5°C. It illustrates the temperature at the outlet can be estimated by modeling the temperature variable quantity at the outlet.     

Exact solution of constriction resistance and temperature field within a homogeneous cylindrical body heated by an isothermal circular contact spot

An exact method, without simplifying assumptions, for calculating thermal constriction resistance and stationary temperature field due to applying a circular isothermal contact spot axially at the upper surface of a homogeneous cylindrical body is presented. The boundary conditions are adiabatic at the convex surface and the rest of the upper surface, and isothermal at the lower surface. The solution is expressed by Fourier-Bessel-series; coefficients are determined by the Gram-Schmidt-process, since Dirichlet and Neumann conditions appear at two parts of the same surface. The calculated constriction resistance is compared with results of a customary approximation.     

Pump-induced fluctuating pressure in a reactor coolant pipe

An analytical model is proposed to describe the propagation of pressure pulsations originated at the pump outlet through the inlet pipe of a pressurised water reactor (PWR). Pressure pulsations data from a pre-critical vibration monitoring programme (PVMP) for a C-E reactor are presented and compared with those calculated by the analytical model. The propagation of pump-induced pressure pulsation is important because of the potential for vibration and resultant damage of reactor internals.

The theory of pump-induced pressure pulsation distributions in the coolant annulus in a PWR has been developed by Penzes¹ and by Bowers and Horvoy² on the assumption that the pressure pulsations are due to excitations at the inlet nozzles. The pressures in the annulus are calculated based on prescribing the pressure at the inlet nozzles and on the concept of time dependent body force in the governing differential equations. The analytical model presented in the present paper and the theory given by Penzes¹ and Bowers and Horvoy² describe the propagation of pump-induced pressure pulsations in the critical regions (from the pump outlet through the inlet pipe and the coolant annulus in a PWR) for deterministic loads on PWR internals.

In the present analytical model the pressure pulsations are assumed to travel in plane waves so that the governing equation is one-dimensional in nature. The boundary condition at the pump outlet end of the inlet pipe is a time-dependent harmonic function; amplitudes for pump related frequencies are established based on an existing theory for hydraulic noise in centrifugal pumps.³ At the inlet nozzle end of the inlet pipe, due to the complexity of its acoustic characteristic, three types of boundary condition are considered—open, closed and piston-spring supported. Therefore, the analytical model essentially consists of a one-dimensional wave equation with time-dependent non-homogeneous boundary conditions. Closed-form solutions for the problem are derived using a linear transformation technique which reduces the problem to one involving a non-homogeneous differential equation with homogeneous boundary conditions.

Numerical examples are given for a typical reactor. Pressure power spectral density data are presented for data taken at inlet nozzles during a C-E PVMP. Distinct peaks at various pump related frequencies such as rotor speed, twice rotor speed, blade passing frequency and twice blade passing frequency, are observed. RMS pressures predicted by the analytical model at pump related frequencies are compared with those from PVMPs. The spatial distributions of the pressure field along the length of the inlet pipe for the three typical boundary conditions are given. Finally, the effect of the pipe geometry on the pressure field and the acoustic frequencies is analysed.     

Power quality assessment of grid-connected wind farms considering regulations in turkey

This paper presents measurement system and detailed analysis of power quality at the substation of two different wind farm sites which are of low and high power rate. Measurement system has been designed using a data acquisition board (DAQ), Labview software, Matlab programming and a portable PC. The system has been installed at medium voltage level at substation of both wind farms. The real measurement results at substations are compared to current regulations in Turkey.     

Switching from oil to coal firing for steam raising A case study at a large industrial site

The prospects for a switch from oil to coal at large industrial sites are assessed, using a detailed examination of the problems at one particular site. These large sites, where combined heat and power generation is common, represent a sizeable fraction of coal's potential industrial market. The problems of coal transport, stocking and handling are discussed, as well as ash disposal, local environmental effects and boiler choice. The economics, as determined by the strict investment criteria currently applied by many companies, of a switch to coal are examined in the light of possible fuel price movements. The implications of boiler plant age and piecemeal replacement for the possible rate at which coal might penetrate the industrial energy market are discussed.