bluuebunny/crossref_metadata_2025 huggingface dataset:
Effects of Liquid Properties on Pressure Drop of Two-Phase Gas-Liquid Flows Through a Microchannel
Authors: Kawahara Akimaro , Sadatomi Michio , Okayama Kazuya , Kawaji Masahiro
Published: March 2009

Adiabatic experiments were conducted to measure pressure drop for single-phase liquid and gas-liquid two-phase flows through a circular microchannel with an internal diameter of 100 μm. In order to study the effects of liquid properties on the pressure drop, aqueous solutions of ethanol with different mass concentrations (4.8, 9.5, 49 and 100 wt%) in distilled water and distilled water were used as the working liquid, while nitrogen gas was used for the gas phase. The surface tension of the working liquid ranged from 0.023 N/m (100 wt% ethanol) to 0.072 N/m (water), and viscosity from 0.9 mPa·s (water) to 3.4 mPa·s (49 wt% ethanol aqueous solution). For the single-phase flow experiments, the friction factor data were obtained for each working liquid used, over a Reynolds number range of 2 < Re < 800. For the two-phase flow experiments, pressure drop data were collected over 0.2 < jG < 7 m/s for the superficial gas velocity and 0.1 < jL < 1 m/s for the superficial liquid velocity. For single-phase flows, friction factor data were shown to be in reasonable agreement with conventional theory. Furthermore, early transition from laminar to turbulent flow was not observed over the present experimental flow conditions. For two-phase flows, Lockhart & Martinelli’s correlation was found to be capable of predicting the present pressure drop data irrespective of the working liquid tested, if an appropriate constant needed in the correlation is adopted.
Pressure Drop of Taylor Flow in Capillaries: Impact of Slug Length
Authors: Kreutzer Michiel T. , Wei Wei , Kapteijn Freek , Moulijn Jacob A. , Heiszwolf Johan J.
Published: March 2009

In a single capillary, the frictional two-phase pressure drop in Taylor flow has been measured using various liquids, and a correlation to predict the friction factor has been developed. A carefully designed inlet section for the capillary allowed the independent variation of gas bubble and liquid slug length. Gas and liquid superficial velocities were varied in the range 0.04–0.3 m/s. If the slug length was lower than 10 times the capillary diameter, the frictional pressure drop in the liquid slug increased drastically from the single phase limit (f = 16/Re). The slug length dependence is caused by a larger contribution to the pressure drop of the end effects near the bubble caps. Increased pressure drop at the ends of the slug is caused by two separate effects: (1) near the bubbles the circulation inside the liquid slug induces extra friction, and (2) the difference in curvature of the gas-liquid interface at the front and at the rear of the bubble gives rise to extra pressure drop. The use of different liquids allowed the independent variation of the Reynolds number Re and the Capillary number Ca, and an expression for the frictional pressure drop as a function of Re, Ca and the slug length was developed. The results of this work allow the determination of slug length from pressure drop measurements in closed equipment where the slug length cannot otherwise be measured easily. The applicability of the pressure drop model to estimate mass transfer is demonstrated by combined pressure drop and gasliquid measurements in a monolith, which is essentially an array of capillary channels.
Mass Flowrate Distribution and Phase Separation of R-22 in Multi-Microchannel Tubes Under Adiabatic Condition
Authors: Cho Honggi , Cho Keumnam , Kim Young-Saeng
Published: March 2009

The present study investigated mass flowrate distribution and phase separation of R-22 in multimicrochannel tubes under adiabatic condition. The test section consisted of inlet and outlet headers with the inner diameter of 19.4 mm and 15 parallel multi-microchannel tubes. Each microchannel tube had 8 rectangular ports with hydraulic diameter of 1.32 mm. The key experimental parameters were the orientation of the header (horizontal and vertical), flow direction of refrigerant into the inlet header (in-line, parallel and cross flow) and inlet quality (0.1, 0.2 and 0.3). The effect of inlet quality on the mass flowrate distribution and phase separation in the microchannel tubes was negligible. The effect of the orientation of the header on the flow mass flowrate distribution and phase separation was the largest among the test parameters. Horizontal header showed better mass flowrate distribution and phase separation characteristics than vertical header. Both parallel and cross flow conditions showed better mass flowrate distribution and phase separation than in-line flow condition.
Flow Boiling and Pressure Drop in Parallel Flow Microchannels
Authors: Steinke Mark E. , Kandlikar Satish G.
Published: March 2009

The use of microchannels for advanced heat transfer applications has quickly become commonplace. They are found in automotive applications, fuel cells, and even electronics cooling. However, there are fundamental issues still unresolved with heat transfer and fluid mechanics and the application of microchannels. Researchers have reported microchannel data using very different hydraulic diameters, sometimes as much as 2 orders of magnitude. An experimental investigation of the heat transfer, pressure drop, and flow boiling in microchannels is performed. A new channel size classification has been developed based upon the manufacturing techniques as well as the underlying fluid mechanics and heat transfer theory. Six parallel channels with a hydraulic diameter of 207 micrometers is manufactured and tested. Flow boiling patterns have been observed in the channels. Observations suggest that the conventional flow boiling patterns also occur in microchannels. This suggests that there is no difference in the theory used for conventional channels. Therefore, a microchannel can be model in the conventional manor. Heat fluxes of up to 930 kW/m2 have been maintained in the microchannel. The local heat transfer coefficient and quality has been measured. The largest heat transfer coefficient achieved is 192 kW/m2K. In addition, the highest quality achieved is 1.0. Dry-out was also observed during experimentation.
Hysteresis Phenomena at the Onset of Subcooled Nucleate Flow Boiling in Microchannels
Authors: Piasecka Magdalena , Poniewski Mieczyslaw E.
Published: March 2009

In this paper, attempts were made to experimentally investigate the boiling incipience in a narrow rectangular vertical channel of 1 mm depth with an external 40 mm wide wall heated uniformly and others assumed quasiadiabatic. The “boiling front” location was determined from the temperature distribution of the heated wall obtained from liquid crystal thermography. Boiling incipience occurs when considerable rise in wall temperature above the saturation temperature takes place. Thus, boiling incipience is accompanied by “nucleation hysteresis”. The impact of various factors on the boiling incipience in microchannels, such as: pressure, the inlet liquid subcooling and flow velocity were investigated.
Restriction of Critical Heat Flux by Critical Flow Condition in Capillary Tube
Authors: Umekawa Hisashi , Ozawa Mamoru , Sanami Takeshi
Published: March 2009

Critical heat flux (CHF) is a very important design factor of boiling channel, then, so many investigations have been conducted so far. In the case of small diameter channel, the main interest is related with the heat removal of high heat flux component. Therefore, CHF of that system should be predicted by DNB condition. On the other hand, CHF under low heat flux condition in small channel can be considered as the relation with two kinds of restrictions. In this investigation, the confirmation of the relationship of two restrictions in CHF was principal purpose. The CHF of this system was basically decided by the dryout condition, but it deviated from the dryout under certain conditions. In those conditions, the critical flow condition achieved in lower heat flux compared with that of the dryout. Owing to this restriction of the flow rate by critical flow condition, pseudo CHF condition occurs. Experimental results have expressed these relationships between CHF and critical flow condition well.
Preliminary Consideration to Avoid Eruptive Flow Boiling in Microchannels
Authors: Jeong Dong Woon , Koh Kwang Uoong , Lee Sang Yong
Published: March 2009

With boiling flows in very smooth heated channels, in general, the bulk liquid is superheated before the bubble formation takes place at the wall surface. Thus the eruptive boiling occurs once the superheat requirement for nucleation is satisfied, and this can be a source of flow instability. In the present work, a preliminary consideration has been given to predict the limiting heat flux for stable boiling in microchannels. The minimum heat-flux value to avoid this eruptive boiling is inversely proportional to the square of the channel diameter, and becomes enormously large as the channel diameter decreases. The stable heat-flux limit also depends on the cavity size in the channel wall. A map showing stable nucleation criteria was given and discussions were made on the simplifying assumptions made for the analysis.
Two-Phase Flow Instability of Boiling in a Double Microchannel System at High Heating Powers
Authors: Li H. Y. , Lee P. C. , Tseng F. G. , Pan Chin
Published: March 2009

The present work investigates experimentally the two-phase flow instability of convective boiling heat transfer in a system of two parallel microchannels at a given low mass flux and several different heating surface temperatures. The test section employed in this work is fabricated by silicon bulk micro machining and anodic bounding processes. Both channels are triangular with the channel-width of the topside of 100 i`m and hydraulic diameter of 51.7 i`m. The topside width of the central island between two channels is 20 i`m. The forced flow of de-ionized water is provided by a syringe pump. The two-phase flow visualization under boiling conditions is made possible by a high-speed digital video camera. The temperatures of inlet and outlet reservoirs, the inlet pressure as well as the pressure drop during the experiments are recorded and analyzed with flow visualization. The results of the study demonstrate clearly that two-phase flow instabilities with significant oscillations in two-phase flow properties can be developed in the system of double microchannels at high heating surface temperatures due to channel-to-channel interactions. Flow visualization confirms the presence of flow reversal during large amplitude oscillations. Such two-phase flow instabilities involving flow reversal should be of great concern for the design of a micro evaporator.
Characteristics of Water Flow in a Vertical Micro Tube
Authors: Wang Xiaoping , Watanabe Makoto , Shoji Masahiro
Published: March 2009

Fluid flow and heat transfer in micro-channel has received attention in developing electronic element cooling systems and in designing thermal elements of micro machines and refrigerators. In the present experiment, pressurized water in the chamber flushed out of a vertical capillary tube of 0.5mm in inner diameter and 1150mm in length. The outer surface of the tube was insulated. The chamber excess pressure was changed from 0.1 MPa to 0.6 MPa and also the inlet water temperature was widely varied. At low excess pressures, the flow is liquid single-phase flow but at high excess pressures, phase change (flushing) takes place inside and/or near the exit end of the tube and the flow becomes two-phase flow of oscillatory or intermittent. Mass flow rate as well as tube wall temperature (distribution and fluctuation) were measured, and the aspect of flushing at the tube exit end was observed using high-speed video movie. It is found that the flow regime can be classified into three (single-phase, two-phase and transient flow regimes) depending on the chamber excess pressure.
Heat Transfer and Pressure Drop for Flow Boiling of Water in Narrow Vertical Rectangular Channels
Authors: Shuai Jianyun , Kulenovic Rudi , Groll Manfred
Published: March 2009

Flow boiling in small-sized channels attracted extensive investigations in the past two decades due to special requirements for transfer of high heat fluxes from narrow spaces in various industrial applications. Experiments on various aspects of flow boiling in narrow channels were carried out and theoretical attempts were undertaken. But these investigations showed large differences, e.g. up till now the knowledge on the development of flow patterns in small non-circular flow passages is very limited. This paper deals with investigations on flow boiling of water in two rectangular channels with dimensions (width×depth) 2.0×4.0 mm2 and 0.5×2.0 mm2 (corresponding hydraulic diameters are 2.67 mm and 0.8 mm). The pressure at the test section exit is atmospheric. For steady-state experimental conditions the effects of heat flux, mass flux and inlet subcooling on the boiling heat transfer coefficient and the pressure drop are investigated. Flow patterns and the transition of flow patterns along the channel axis are visualized and documented with a video-camera. Bubbly flow, slug flow and annular flow are distinguished in both channels. Preliminary flow pattern maps are generated.
Boiling Flow Pressure Drop Modeling in a Minichannel
Authors: Brutin D. , Tadrist L.
Published: March 2009

The present paper deals with two-phase flow pressure drop modeling. This is based on solving the mass, momentum and energy balance equations in steady state conditions. In the two-phase zone, the liquid-vapor is assumed to be a homogeneous fluid. The calculated pressure drop variation is found to be similar to the experimental one when the two–phase flow is steady. In the unsteady state conditions characterized by high amplitude of the pressure fluctuations, the computed pressure drop is found to be different from the experimental mean pressure drop. This difference is all the higher as the pressure fluctuation is high.
Testing of a Microchannel Partial Condenser and Phase Separator in Reduced Gravity
Authors: TeGrotenhuis Ward E. , Stenkamp Victoria S.
Published: March 2009

Heat exchange has been successfully integrated with microchannel phase separation concepts to produce devices capable of simultaneous partial condensation and phase separation in reduced gravity. An air-cooled microchannel condenser has been tested on NASA’s KC-135 reduced gravity aircraft. The condenser was fed a mixture of air and water vapor at 70–95°C, which was cooled to below 40°C thereby generating water condensate. The condensate was successfully collected and removed as a separate stream over a range of operating conditions, thereby achieving simultaneous condensation and phase separation. Ambient air was used to cool in cross-flow with inches of water pressure drop. The microchannel device is presented along with an explanation of the principles of operation. Phase separation effectiveness and heat exchanger performance are reported for reduced gravity testing. Heat fluxes, effectiveness, and overall heat transfer coefficients are reported.
Complete Convective Condensation Inside Small Diameter Horizontal Tubes
Authors: Mederic Be´atrice , Miscevic Marc , Platel Vincent , Lavieille Pascal , Joly Jean-Louis
Published: March 2009

An experimental study of complete convective condensation inside narrow channels is presented in this paper. Two-phase flows patterns and their transition (annular, annular-wavy, slug and bubbly flow) are visualized for the two tube diameters under study. A significant difference is observed for the two sizes of tube. Experimental results of the bubble radius decrease are then determined and compared to a model of bubble collapse in a subcooled and infinite liquid.
Test Facilities for a Continuous Transition From Mini- to Microchannels
Authors: Herwig H. , Hausner O.
Published: March 2009

Two different experimental set-ups are suggested which both have the advantageous features that channels of continuously varying size between mini- and microchannels are realized, that these channels are formed between macroparts without any need for microfabrication and last but not least that the channel walls are freely accessible and can be manipulated with high precision by macro surface manipulation techniques. In the limit of vanishing channel height (h → 0) the flow approaches plane channel flow. For small but finite values of h deviations from this limiting flow case are discussed in detail. For one of the experimental set-ups construction details are shown; for the other one (which is still in the conception phase) heat transfer measurements within the microchannels are discussed.
Direct Write Patterning of Microchannels
Authors: Fries Carolyn , Fries David , Broadbent Heather , Steimle George , Kaltenbacher Eric , Sasserath Jay
Published: March 2009

Microchannel-based master molds or final devices are typically produced using a series of resist deposition, exposure, development and etching steps. These steps can then be repeated to create multi-layer fluidic structures. Traditional fabrication of these devices requires the use of a physical mask for the photolithographic exposure process. In the research and development environment, where designs are constantly undergoing changes, or in rapid-time-to-device applications, this can be a costly and time-consuming practice. We have employed a novel, micron-scale resolution maskless photoimaging/patterning tool that permits the creation of small, arbitrary features. This microdevice printer is useful for constructing fluidic channels, devices, structures and packages utilizing any photoimageable or photoreactive material that can be applied towards fabrication of integrated microfluidic-based systems. The fabrication technology can provide features down to 20 microns simultaneously over a 2×2 cm2 field of view. Additionally, manual stitching techniques can yield unlimited field-of-view for large area fluidic patterns with high-resolution elements. The instrument relies on the use of microoptics and spatial light modulation to create the required 2D aerial image for photoimprinting. The instrument creates mask-free designs on planar and curved surfaces and has been applied to a variety of materials, including metals, ceramics, organic polymers and semiconductors. We have demonstrated the utility of the instrument for creating mechanical, optical, fluidic and electronic components and combinations that would form the basis of integrated microfluidic systems, microanalytical systems and micrototal analysis systems (uTAS). We have also created fluidic channels having structures integrated within the channel geometry. The technology has widespread applications in the MEMS, bioMEMS, microcooling technologies and sensor markets. A further extension of the technology is the application of the direct printer to rapid prototyping of microchannels and minichannels for fuel cells, microrefrigerators, heat exchangers, and biomedical devices.
Dispensing Picoliter Droplets Using DEP Micro-Actuation
Authors: Ahmed R. , Hsu D. , Bailey C. , Jones T. B.
Published: March 2009

Non-uniform, AC electric fields created by coplanar electrodes patterned on a substrate are used to move and manipulate aqueous liquid masses, and to dispense very small droplets. This liquid dielectrophoretic microactuation scheme has potential applications for microfluidic systems in the laboratory on a chip. Simple, co-planar electrode strips are used to divide microliter-sized, sessile water droplets into large numbers of droplets down to ∼40 picoliters. The dispensing system uses the electrodes to draw a long finger or rivulet of liquid from the parent microliter droplet. When the voltage is removed, the rivulet breaks up into numbers of droplets as a result of the familiar capillary instability. We propose and provide data that supports a very simple power law dependence of the finger length upon time: Z(t)∝t, which governs the time required to fill a structure. A capillary instability, very similar to the case of the cylindrical jet, leads to droplet formation when voltage is removed. The hydrodynamic instability features a critical wavelength, below which instability is not possible, and a most unstable wavelength, which controls the volume and spacing of the droplets formed.
Fluid Transport and Phase Transition Experiments in Closed Multiwall Carbon Nanotubes
Authors: Yazicioglu Almila G. , Megaridis Constantine M. , Gogotsi Yury
Published: March 2009

Multiwall carbon nanotubes show potential for use in various micro- and nanofluidic devices, since they resemble cylindrical channels used in the macroscopic world. However, in situ experimental studies of fluid behavior in nanotubes or nanochannels have been rare. In this work, transmission electron microscopy experiments are performed on closed-end multiwall carbon nanotubes filled with an aqueous multiphase fluid. The nanotubes form an experimental apparatus that is a few orders of magnitude smaller than the smallest channels used in other fluidic experiments. These nanotubes are synthesized hydrothermally, using Ni as a catalyst, and they contain segregated aqueous liquid and gas inclusions with clearly defined interfaces. Using electron irradiation, the multiphase fluid inside individual nanotubes is excited thermally, by expanding and contracting the electron beam. The excellent wettability of the graphitic inner tube walls by the aqueous fluid and the mobility of this liquid in the nanotubes are observed in real time with nanometer-scale resolution. Interface dynamic phenomena are visualized, as driven by thermocapillary forces as well as by evaporation and condensation. The hydrothermal nanotubes examined herein offer a promising platform for studying the behavior of multicomponent, multiphase fluids in nanosize channels at high-pressure conditions. The phenomena documented in this study demonstrate the potential of implementing such tubes in future nanofluidic devices.
Fluid Flow Through Microscale Fractal-Like Branching Channel Networks
Authors: Alharbi Ali Y. , Pence Deborah V. , Cullion Rebecca N.
Published: March 2009

Flow through fractal-like branching flow networks is investigated using a three-dimensional computational fluid dynamics approach. Results are used to assess the validity of, and provide insight for improving, assumptions imposed in a one-dimensional model previously developed. Assumptions in the one-dimensional model include (1) reinitiating boundary layers following each bifurcation, (2) negligible minor losses at the bifurcations, and (3) constant thermophysical fluid properties. It is concluded that the temperature dependence of fluid properties, boundary layer development, and minor losses following a bifurcation are not negligible in analyses of branching flow networks.
A Comparison of Micro-PIV Experiments in a Mini-Channel to Numerical and Analytical Solutions
Authors: Newport D. , Curtin D. , Davies M.
Published: March 2009

In this paper, measurements are presented of the velocity profile in a mini-channel at different locations. The channel is rectangular in cross-section, approximately 1.2mm wide, 1.4mm deep and 29mm long. A micro-PIV system was used to obtain the velocity profiles at the inlet, mid-length and exit of the channel. The raw image maps were processed using three different commercial PIV software packages, and compared to an exact analytical solution. The mini-channel system was also simulated using a commercial CFD code as a further check on the dataset, and the experimental rig itself. It was found that the different processing procedures had little influence on the micro-PIV data, and good agreement was found with theory, numerical prediction and experiment. This establishes confidence in micro-PIV as a measurement tool in micro-systems.
Flow Pattern Measurement by PIV in the Microchannels of a Heat Exchanger and Associated Problems Due to Fouling
Authors: Heinzel V. , Jianu A. , Sauter H.
Published: March 2009

This paper presents preliminary experimental results of measuring velocity fields of a transparent liquid flow in a closed circuit, through a 100 μm, 200 μm and 500 μm depth flat cell with and without included 200 μm × 200 μm heat exchanger microchannel elements. A microscopic particle image velocimetry system has been developed which consists of a 5 ns pulsed Nd:YAG laser, an epi-fluorescent microscope and a cooled interline transfer CCD camera to record high-resolution 0.7 μm diameter fluorescent particle image fields. The development of the optical micro-flow measuring instrument for the present application took into consideration the fact that the test object is aimed to be exposed to pressures up to 0.6 MPa leading to flow velocities up to 15 m/s, as well as temperatures up to 100°C. Particle fouling phenomenon proved to be the main difficulty in performing velocity field measurements in microchannels and techniques to avoid or limit it are proposed.
Examples of Microchannel Mass Transfer Processes in Biological Systems
Authors: Kandlikar Satish G. , Steinke Mark E.
Published: March 2009

Heat and mass transfer processes become highly efficient as the channel hydraulic diameter is reduced in size. Biological systems, such as human body, rely on the extremely efficient transport processes occurring at microscale in the functioning of its vital organs. In this paper, the transfer processes in lungs and kidneys will be reviewed. Although the flow in the microchannels present in these organs is laminar, it yields very high mass transfer coefficients due to the coupling of small channel diameters. Furthermore, the molecular transport mechanisms occurring across the membranes at nanoscales through diffusion controlled processes also become extremely important. Understanding these transport processes will enable us to develop more efficient artificial organs and processes that closely mimic the performance of the natural systems. These ideas can be extended to other microscale system designs in different technologies, such as IC cooling and MEMS micro fuel cells.
A Platform for Cross-Disciplinary Microchannel Research
Authors: Spearing Scott , Son Sang Young , Allen Jeffrey , Monaco Lisa A.
Published: March 2009

A team from the structural biology group located at the Marshall Space Flight Center in Huntsville Alabama is developing a platform suitable for cross-disciplinary microchannel research. The original objective of this engineering development effort was to deliver a multi-user flight-certified facility for iterative investigations of protein crystal growth; that is, Iterative Biological Crystallization. However, the unique capabilities of this facility are not limited to the low-gravity structural biology research community. Microchannel-based research in a number of other areas may be greatly accelerated through use of this facility. In particular, the potential for gas-liquid flow investigations and cellular biological research utilizing the exceptional pressure control and simplified coupling to macroscale diagnostics inherent with the facility will be discussed. Also noted will be the opportunities for research-specific modifications to the microchannel configuration, control and diagnostics.
Rational Allocation of Heat-Electricity Cost Allocation in Cogeneration
Authors: Li Chunxi , Ye Xuemin
Published: March 2009

A reasonable cost allocation in cogeneration is very important for plant and heating consumer. According to the different roles of anergy and exergy in the heat supply process of cogeneration, the reduced exergy model for cogeneration cost allocation is formulated by introducing the concept of the reduced exergy and available anergy. This model considers not only the energy differences in quantity and quality, but also the roles of the available anergy and exergy. Furthermore, the contribution of the available anergy is expressed as a user factor, which can reflect different utilization for different practical conditions. The results for several practical units verify that the reduced exergy model is more rational, convenient and practical than existing models in theory and practice.
Study and Design of Heat Recovery Steam Generators
Authors: Vedanth S.
Published: March 2009

In the modern scenario of energy systems, we see that the efficiency of the modern day power plants attain a maximum possible limit of 40%–50% in most cases. This is a result of the wastage’s that are prevalent in the systems in the form of heat loss, friction losses due to flow in pipes and flow in other units. The modern day power plants employ the Heat Recovery Steam Generators ( HRSG) which help in converting the waste heat coming out of the turbine into useful work, thus increasing the overall efficiency of the plant. The application of Gas turbine generator (GT) based co-Generation power plants as a part of the industrial plants is on the rise. These plants are required to meet the industrial plants power and steam demand with variations associated with it. This paper deals with the study of a versatile industrial HRSG with specifications in order to support the design. The study and design is based on the design and production unit “Babcock Borsig power systems”, Chennai, India. The paper focuses on the Heat recovery Steam Generator design inclusive of selecting the parameters like pressure of steam, velocity of fluids at different stages with respect to the conditions, material selection etc. The design of HRSG involves primary inputs such as the Engineering Flow diagrams, Arrangement of Equipment’s at proper elevation and Engineering data (Specifications). The considerations of line sizing with respect to pressure drop, Net positive Suction Head, Pipe line erosion, Water Hammer and noise are taken into account. A well-specified and designed HRSG can substantially help the Industrial Co-Generation plant to meet the demand variation and imbalances without sacrificing the reliability of operation. The study is an important contribution to the exponentially rising population and hence the energy demands in the world.
Squirter™ DTI’s Make SCR/HRSG Bolting Easy
Authors: Wallace Wayne , Carrato Peter J.
Published: March 2009

Field installation and inspection of structural bolts in SCR’s and HRSG’s consume thousands of man-hours. Bolts are installed by various qualities of labor: ironworkers, boilermakers, pipefitters, millwrights, laborers, or non-union workers, especially in offshore locations. Project schedules require rapid assembly of steelwork so that the mechanical systems can be located and made operational in the least possible time. Tightening specifications for bolts used in these applications change frequently, and field personnel often have difficulty keeping abreast of the changes. Direct Tension Indicating (DTI) washers have made bolt tightening in these applications more or less foolproof for twenty or more years, but their installation and inspection has been labor-intensive. With the development of the DTI ‘Squirter Washer’, bolts can be tightened and inspected in about one-half the time previously devoted to this operation. Duke/Fluor Daniel, Bechtel, Babcock & Wilcox, The Industrial Company, and other contractors are now using Squirter DTI’s and sharing the savings with their client power project owners.
Statistical Determination of Natural Gas Superheat Requirements
Authors: Wilkes Colin
Published: March 2009

The ASME Fuel Specification B133.7M [1] states that a typical margin of 25 to 30° C (45 to 54° F) of superheat is used for natural gas fuel but offers no basis for the estimate. The purpose of this paper is to propose a method for the safe determination of superheat that is less conservative, yet will meet the six sigma requirement of less than 4 defects (condensate formation) in one million opportunities. A drop in the total temperature of natural gas will be experienced as the gas expands in pressure reducing stations and across control valves. If the temperature falls below the hydrocarbon or moisture dew point, condensation will take place and liquids will collect or will be entrained with the gas. The temperature drop is inversely proportional to the pressure drop and is often termed ‘Joule-Thomson cooling’ or ‘J-T cooling’. The rate of cooling is described by the Joule-Thomson coefficient that can be determined by experiment or calculated from the gas composition. Superheating the gas prior to expansion can prevent condensation. The degree of superheat required for hydrocarbons, however, is often greater than the expected temperature loss across the valve as the hydrocarbon dew point may increase as the pressure falls. This paper describes a method for determining the quantity of superheat required for a specific gas composition and develops a general equation in terms of gas supply pressure that will satisfy the needs for the majority of natural gases. The general equation is based on the statistical analysis of superheat requirements for over 230 natural and liquefied natural gas compositions. A similar equation is also presented that describes the superheat requirements to avoid moisture condensation. The two equations can be used to specify the heating requirements upstream of pressure reducing stations or control valves.
Distributed Plant Data for Improved Predictive Maintenance
Authors: Kalanik John B. , Walejeski Walter
Published: March 2009

The power industry generates more data than any other. The trick is collecting all of this data, down to the sub-second, storing it and making it accessible — in real time — to those who need it, when they need it for advanced decision making. This includes everyone from those on the power plant floor and executive offices to the buyers and sellers of power. Clearly integration is critical. Increasingly, utilities and large corporate power users are learning how to harness that data to capture true value. This is especially important when deregulation and rising utility costs are putting power generating companies under a microscope, forcing them to be accountable to their boards, stockholders and the public. Power generators are increasingly relying on data historians to gather information in real-time for performing trend reporting, predictive maintenance functions and optimizing overall operational efficiency.
Wall Thinning Analyses for Secondary Side Piping of Korean NPPS Using CHECWORKS Code
Authors: Hwang K. M. , Jin T. E. , Lee S. H. , Jeon S. C.
Published: March 2009

Since the mid-1990s, nuclear power plants in Korea have experienced wall thinning, leaks, and ruptures of secondary side piping caused by flow-accelerated corrosion (FAC). The pipe failures have increased as operating time progresses. In order to prevent FAC-induced pipe failures and to develop an effective FAC management strategy, KEPRI and KOPEC, along with KHNP’s support, have conducted a study for developing a systematic FAC management technology for all domestic nuclear power plants. As part of the study, FAC analyses were performed using CHECWORKS code. The analysis results were used to select components for inspection on each nuclear power plant. The site application feasibility of the analysis results was proven by comparisons of predicted and measured wear rates. This paper focuses on the introduction of the FAC analysis results for secondary side piping associated with three types of domestic nuclear power plants and the comparisons of predicted and measured wear rates. This paper also represents the comparisons of analysis results according to reactor types, power rates, and systems to facilitate the development of FAC management technology.
Accurate Measurement of Water in Feedwater Heaters
Authors: Carsella Boyce
Published: March 2009

The accurate measurement of liquid levels in power plant operations is key to efficient operation. Although water is a liquid that can be easily measured by numerous measurement technologies, detection in applications like feedwater heaters, for example, takes on a range of complexity that stresses even the most robust devices. Feedwater heaters operate in various ranges depending upon the stage of the process. High-pressure heaters typically operate at 1030 psig @550°F (71 bar @288°C). Further, liquid level transmitters should operate ideally from ambient start-up to operating conditions at full capacity; a wide variation. Torque tube and differential pressure transmitters have been the technologies of choice for many years, each technology having a set of strengths, weaknesses and idiosyncrasies. Performance of both technologies are dependent on the Specific Gravity (SG) of the medium of they are measuring; both suffer inaccuracies when the SG of water varies over temperature. A new level measurement technology, Guided Wave Radar (GWR), has emerged that eliminates the issues that have plagued torque tube and DP transmitters. Guided Wave Radar (GWR) has shown to accurately measure the level of water throughout the changing conditions seen in the life cycles of vessels like feedwater heaters. GWR is a technology based on the speed of light, or more precisely, electromagnetic energy. Inaccuracies due to Specific Gravity (SG) variations are not an issue. In fact, Guided Wave Radar has shown to accurately measure media with wide variations in dielectric.
Repowering and Retrofitting
Authors: Pickard Andreas
Published: March 2009

At the start of this new century, environmental regulations and free-market economics are becoming the key drivers for the electricity generating industry. Advances in Gas Turbine (GT) technology, allied with integration and refinement of Heat Recovery Steam Generators (HRSG) and Steam Turbine (ST) plant, have made Combined Cycle installations the most efficient of the new power station types. This potential can also be realized, to equal effect, by adding GT’s and HRSG’s to existing conventional steam power plants in a so-called ‘repowering’ process. This paper presents the economical and environmental considerations of retrofitting the steam turbine within repowering schemes. Changing the thermal cycle parameters of the plant, for example by deletion of the feed heating steambleeds or by modified live and reheat steam conditions to suit the combined cycle process, can result in off-design operation of the existing steam turbine. Retrofitting the steam turbine to match the combined cycle unit can significantly increase the overall cycle efficiency compared to repowering without the ST upgrade. The paper illustrates that repowering, including ST retrofitting, when considered as a whole at the project planning stage, has the potential for greater gain by allowing proper plant optimization. Much of the repowering in the past has been carried out without due regard to the benefits of re-matching the steam turbine. Retrospective ST upgrade of such cases can still give benefit to the plant owner, especially when it is realized that most repowering to date has retained an unmodified steam turbine (that first went into operation some decades before). The old equipment will have suffered deterioration due to aging and the steam path will be to an archaic design of poor efficiency. Retrofitting older generation plant with modern leading-edge steam-path technology has the potential for realizing those substantial advances made over the last 20 to 30 years. Some examples, given in the paper, of successfully retrofitted steam turbines applied in repowered plants will show, by specific solution, the optimization of the economics and benefit to the environment of the converted plant as a whole.
Numerical Investigation on Premixed Combustion Using a Fiber Mat Burner With a Boiler
Authors: Golder T. , Kawaguchi O.
Published: March 2009

This paper presents a numerical study of combustion and multi mode heat transfer in inert porous media. In this case a sintered fiber mat is used. From this work it is understood that the premixed flame is stabilized on the downstream surface of the fiber mat burner. The influence of the flame location, the radiative properties of the porous material, the solid thermal conductivity, and stoichiometry on the flame speed and flame stability are determined using a one-dimensional conduction, convection, radiation, and combustion model. The fiber mat is allowed to emit, absorb, and scatter radiant energy. Non-local thermal equilibrium between the solid and gas was taken into account. Here, separate energy equations for the two phases are introduced, i.e. gas energy equation for the entire system and solid energy equation for the fiber mat. The results indicate that stable combustion can be maintained near the downstream surface of the fiber mat which is mostly controlled by solid-phase radiation.
Experience With the Non-Contacting Blade Vibration Measurement Method Using Two Sensors in a Low Pressure Model Steam Turbine
Authors: Hu Zechun , Eyb Gerhard , Regnery David
Published: March 2009

This paper presents an application of a non-contacting blade tip timing measurement system using two-sensor method (so-called BSSM) at a low-pressure model steam turbine to investigate dynamic blade stress in extended operation conditions (so-called windage). An analysis method to identify the vibration frequencies and to determine the response amplitudes for the first few excited vibration mode shapes is described in detail. Objective of this paper is to discuss the performance and inherent limitations of the non-contacting measurement system. For that the BSSM results were compared with the blade vibration data obtained from strain gauges. Some experiences and suggestions are also made to improve the reliability and accuracy of this measurement system.
Advanced Steam Turbine Bypass Valve Design for Flexible Power Plants
Authors: Logar Andreas , Depolt Thomas , Gobrecht Edwin
Published: March 2009

The authors company has had extensive experience providing steam turbines including auxiliary systems as a turn key contractor for more than 40 years. Bypass systems are an integrated part of modern Combined Cycle Power Plants (CCPP) [1]. Bypass systems contribute a major part for operational flexibility. They allow the shortest start-up times by minimising mismatches between boiler/HRSG and turbine. Bypass systems also lead to predictable and repeatable start-up times, as well as reducing solid particle erosion of component, to a great extent. The functional requirements for bypass valves are: • Control mode for an accurate control of the IP and LP bypass steam flow during the unit start-up and shut-down, as well as during normal operating transients. • Fast closing mode for bypass-trip (supported by spring force) when required for condenser protection. • Combined mode for fast reaction on pressure increase to a define set point and further action in control mode. In the past, a combined stop and control valve design, each with a separate stem, was common. The challenging objective for the bypass valve design was to integrate the control function and the trip function with a single stem design. The authors company has developed this advanced steam turbine bypass valve that incorporates hydraulic actuator with a single stem design. The valve bodies have noise reduction fittings and are equipped with large extensions on the outlet side to reduce vibration throughout the bypass system. The bypass valve body has an integrated steam strainer which protects both valve parts and the condenser from external debris. The bypass design is prepared for Power Plants with elevated temperatures which allow for the highest plant efficiencies [2]. Surface coating protect moving components against oxidation and reduce friction by means of a surface coating. Steam at high temperature passes through the bypass to the condenser. An incorporated water attemporating flow control system reduces the steam temperatures before entering the condenser. Condensate water is injected through an orifice in the bypass system. The orifice is located down stream in the pipe between the bypass valve and condenser. Electro-hydraulic supply units deliver the control fluid to the bypass valves. An optimized bypass system has to provide: • Long service life with low maintenance costs; • High stroke speed; • Pressure control by unit set point; • High actuation forces; • Accurate positioning; • Very short trip time into closed position. By means of bypass station, one can get highest flexibility of power plants use of the new valve one will get highest control performance and shortest reaction time.
Reaction Characteristics of Wastepaper Gasification With CO2 Catalyzed by Molten Carbonate Salts
Authors: Iwaki Hiroyuki , Jin Gong , Furuhata Tomohiko , Arai Norio
Published: March 2009

In this paper, wastepaper gasification with steam and carbon dioxide was tested in the presence of molten carbonate salt catalysts. Reactions with steam or carbon dioxide were first compared. Hydrogen was mainly produced by gasification with steam, but no carbon monoxide was generated. For the case where carbon dioxide was used as a reactant instead of steam, generation of carbon monoxide greatly increased via the Boudouard reaction. Different ratios of mixtures of lithium, sodium and potassium carbonates were examined. Lithium was found to play a critical role in the various catalyst combinations. The reaction rate with respect to carbon conversion was approximately first order for low carbon conversions. The rate constants were investigated at different temperatures (923–1023K) and the activation energies were determined. In addition, the flexibility of this technique was examined with three different types of wastepaper. These results suggest the applicability of this process for the effective use of wastepaper and recovery of carbon dioxide.
Parametric Study to Optimize Air/Fuel Mixing for Lean, Premix Combustion Systems
Authors: Yimer Ibrahim , Campbell Ian
Published: March 2009

New designs of gas turbine combustors for power generation applications have to meet ever-tightening emission standards (mainly NOx, CO and UHC) while operating at high combustor pressures. This requires a detailed understanding of the physical processes involved. The air-fuel mixture preparation is a critical step in most advanced gas turbine combustion strategies to achieve lower emissions. It has long been established that the level of unmixedness between the fuel and air is strongly tied with NOx levels. The present paper applies the statistical technique of Design Of Experiments (DOE) to a generic mixer set-up that includes an axial swirler, with fuel injected at discrete locations and transverse to the flow. The objective is to identify influential design and operating parameters that will provide rapid and enhanced mixing. The parameters tested include Swirl strength as measured by the Swirl number, Swirl type (Constant angle vs. Free vortex), number and momentum of fuel injection sites and gas temperature. Planar Laser Induced Fluorescence of acetone (PLIF) was used to quantify mixing at various planar locations in the mixing section. Commercial CFD software is used to model the flow field and predict the spatial mixing at selected conditions. Comparisons are made with experimental measurements with the aim to validate the CFD code and also on comparing the model results with the measurements.
Tribomechanical Properties of Self Lubricated Oxide Ceramic Hard Coatings
Authors: Kireitseu Maksim , Yerakhavets Sergey , Istomin M.
Published: March 2009

A lot of researches indicate a great importance of thermal sprayed coatings for wear resistance. However some valuable properties such as self-lubrication ability of thermal sprayed coatings become hesitated some times. This paper revealed tribomechanic properties of hard oxide aluminum ceramic coating and bronze-based thermal flame sprayed coatings in view of self lubrication that take place under insufficient lubrication due to vaporization, localized load etc. In this work, hard oxide ceramic coating and bronze based coatings were investigated. Some of them were impregnated by polyethylene or oil sealant. The test revealed an effect of lubricant temperature on tribological properties of the coatings and its self sealing properties. The tests revealed an effect of porosity, hardness, adhesion and structure on wear rate and coefficient of friction of the coatings. The obtained results demonstrate an optimal load range for the coatings.