Gravity changes in the Tauhara sector of the Wairakei–Tauhara geothermal field,New Zealand

Five microgravity surveys, done between 1972 and 2006, show that in the northern part of the Tauhara geothermal field there were large gravity decreases prior to 1985 associated with the expansion of steam zones resulting from pressure drawdown caused by fluid extraction at Wairakei. Since 1985 there have been gravity increases of up to 240 μgal in the northern part of Tauhara, corresponding to a mass increase of about 20 Mt. The gravity increases are centred near the unused deep well TH4, and are inferred to result mainly from resaturation of a deep steam zone due to a downflow of water in the well. We suggest that the water entered the well from a confined groundwater aquifer at a known casing break at 393 m depth and exited in the region of slotted casing at about 900–1000 m depth causing displacement of single-phase liquid upwards into the overlying steam zone. The average downflow rate is estimated to be about 110 t/h (30 kg/s); however, no downhole measurements in the well have been possible due to casing breaks. Simple modelling of the gravity data suggests the region of resaturation had the form of a cone of impression 150–250 m high and extending laterally for 1–2 km. Since 1985, gravity changes in the central and southern parts of the Tauhara field have been less than 50 μgal, indicating little net mass loss (<2 Mt), and hence little effect in this area from the continuing production at Wairakei. The subsidence centred near Crown Road has been attributed to compaction of a thin, elliptical lens of porous, thermally-altered volcanic deposits at shallow depth as a result of a water level decline in the near-surface, steam-heated groundwater aquifer. Gravity data (1994 onwards) at a point near the centre of the subsidence bowl show that, despite ground subsidence of about 0.55 m, there have been no significant gravity changes. One explanation for the absence of gravity changes is that the water lost from the near-surface aquifer has drained downwards increasing the saturation in part of a deeper, partly saturated layer.     

Saturated flow boiling heat transfer and pressure drop in silicon microchannel arrays

Flow boiling in arrays of parallel microchannels is investigated using a silicon test piece with imbedded discrete heat sources and integrated local temperature sensors. The microchannels considered range in width from 102 μm to 997 μm, with the channel depth being nominally 400 μm in each case. Each test piece has a footprint of 1.27 cm by 1.27 cm with parallel microchannels diced into one surface. Twenty five microsensors integrated into the microchannel heat sinks allow for accurate local temperature measurements over the entire test piece. The experiments are conducted with deionized water which enters the channels in a purely liquid state. Results are presented in terms of temperatures and pressure drop as a function of imposed heat flux. The experimental results allow a critical assessment of the applicability of existing models and correlations in predicting the heat transfer rates and pressure drops in microchannel arrays, and lead to the development of models for predicting the two-phase pressure drop and saturated boiling heat transfer coefficient.     

Thermo-hydraulic predictions for multi-pass evaporators by orthogonal collocation using a new flow pattern map

A recently published paper by this author [S. Thyageswaran, Analysis of multi-pass evaporators using orthogonal collocation, Int. J. Refrigeration doi:10.1016/j.ijrefrig.2007.06.011 (in press)], shows that orthogonal collocation is an effective alternative to traditional integration for the thermal analysis of multi-pass evaporators. The steady rate of heat exchanged (Q) and overall pressure drop (Δp), for an R-22 based chiller having one shell and eight tube passes, were predicted using the Kattan–Thome–Favrat and the Müller-Steinhagen and Heck models for the boiling R-22. While Q was over-predicted by 0.95%, Δp was over-predicted by 20.3%. In the present work, results have been obtained using state-of-the-art, unified heat transfer and pressure drop sub-models based upon an improved flow pattern map by Wojtan et al. [L. Wojtan, T. Ursenbacher, J.R. Thome, Investigation of flow boiling in horizontal tubes, part 1: a new diabatic two-phase flow pattern map, Int. J. Heat Mass Transfer 48 (2005) 2955–2969; L. Wojtan, T. Ursenbacher, J.R. Thome, Investigation of flow boiling in horizontal tubes, part 2: development of a new heat transfer model for stratified-wavy, dryout and mist flow regimes, Int. J. Heat Mass Transfer 48 (2005) 2970–2985], and Moreno Quibén and Thome [J.M. Quibén, J.R. Thome, Flow pattern based two-phase frictional pressure drop model for horizontal tubes, part 1: diabatic and adiabatic experimental study, Int. J. Heat Fluid Flow 28 (5) (2007) 1049–1059; J.M. Quibén, J.R. Thome, Flow pattern based two-phase frictional pressure drop model for horizontal tubes, part 2: new phenomenological model, Int. J. Heat and Fluid Flow 28 (5) (2007) 1060–1072]. The new predictions for Q and Δp are 141.76 kW and 13.3 kPa, respectively, compared to their rated values of 140.67 kW and 13.789 kPa.     

Simplified models for the performance evaluation of desiccant wheel dehumidification

In the present communication, simple models have been presented to evaluate the performance of rotary desiccant wheels based on different kind of solid desiccants e.g. silica gel and LiCl. The first part of the paper presents ‘Model 54’ which is developed for silica gel desiccant rotor. The model has been derived from the interpolation of experimental data obtained from the industry and the correlations have been developed for predicting outlet temperature and absolute humidity. The ‘Model 54’ consists of 54 coefficients corresponding to each correlation for outlet absolute humidity and temperature and it is found that the model predicts very well the performance of silica gel desiccant rotor (Type-I). In the second part of the paper, a psychrometric model has been presented to obtain relatively simple correlations for outlet temperature and absolute humidity. The developed psychometric model is based on the correlations between the relative humidity and enthalpy of supply and regeneration air streams. The model is used to predict the performance of three type of desiccant rotors manufactured by using different kind of solid desiccants (Type I, II and III). The model is tested corresponding to a wide range of measurement data. The developed psychometric model is simple in nature and able to predict very well the performance of different kind of desiccant rotors. Copyright © 2002 John Wiley & Sons, Ltd.     

Heat transfer in micro-channels: Comparison of experiments with theory and numerical results

This paper considers experimental and theoretical investigations on single-phase heat transfer in micro-channels. It is the second part of general exploration “Flow and heat transfer in micro-channels”. The first part discussed several aspects of flow in micro-channels, as pressure drop, transition from laminar to turbulent flow, etc. [G. Hetsroni, A. Mosyak, E. Pogrebnyak, L.P. Yarin, Fluid flow in micro-channels, Int. J. Heat Mass Transfer 48 (2005) 1982–1998]. In this paper, the problem of heat transfer is considered in the frame of a continuum model, corresponding to small Knudsen number. The data of heat transfer in circular, triangular, rectangular, and trapezoidal micro-channels with hydraulic diameters ranging from 60 μm to 2000 μm are analyzed. The effects of geometry, axial heat flux due to thermal conduction through the working fluid and channel walls, as well as the energy dissipation are discussed. We focus on comparing experimental data, obtained by number of investigators, to conventional theory on heat transfer. The analysis was performed on possible sources of unexpected effects reported in some experimental investigations.     

Biologically derived diesel fuel and NO formation: Part 2: Model development and extended validation

Part 1 of this two part series presented a chemical kinetic model for the simulation of high pressure shock tube pyrolysis and oxidation data of two representative biodiesel surrogate components and the application of this model for predicting prompt NO at practical diesel combustion conditions. The present work discusses in greater detail the model’s development, structure, and rate parameters as well as expands the model’s validation range to include complementary 10 atm jet stirred reactor (JSR) oxidation experiments conducted at lower temperatures (550–1200 K) and longer reaction times of 0.7 s. In addition, shock tube ignition delay measurements of 1-heptene and 1,6-heptadiene, analogs of the hydrocarbon side chains of the methyl esters, have also been performed and are presented to further constrain the model.     

Investigation of the calcareous deposits formation controlled by interfacial pH and its effect on the hydrogen entry into AISI 4135 steel in seawater

The influence of interfacial pH between AISI 4135 steel and seawater under different polarization potentials on the formation of calcareous deposits has been studied. An interfacial pH of 9.61 at ?0.9 V vs. SCE using state of the art iridium oxide microelectrode was found to be the critical pH for the precipitation of magnesium hydroxide. Calcareous deposits with a double-layer structure comprising an inner-brucite layer and an outer-aragonite layer were found to form at potentials between ?1.0 V and ?1.2 V vs. SCE. Furthermore, the facilitation of hydrogen permeation into steel induced by the formation of calcareous deposits was verified using the Devanathan-Stachurski electrochemical test. The mechanism of calcareous deposits facilitates hydrogen permeation into steel is related to its inhibition on hydrogen recombination and escape processes.     

Thermal analysis of slurry ice production system using direct contact heat transfer of carbon dioxide and water mixture

This research studies the heat transfer characteristic during ice formation of a direct contact heat transfer between carbon dioxide and water mixture. This research is divided into two parts. For the first part, the low temperature carbon dioxide, between − 15 and − 60 °C, is injected into water initially at 28 °C and exchanges heat directly. The flow rate of carbon dioxide is varied between 0.003 and 0.017 kg/s while the volume of water is between 1 and 3 L. From the experiment, it is found that the effectiveness of the direct contact heat transfer between the carbon dioxide and the water is closed to 100%. Moreover, the lumped model is found to be used for predicting the temperature of water and the mass of ice formation quite well.     

Lithium,a preliminary survey of its mineral occurrence in flint clay and related rock types in the United States

Maximum concentrations of lithium found in samples of flint clay and associated rocks of Pennsylvanian age in different States, in parts per million (ppm), are: Missouri, 5100; Pennsylvania-Maryland, 2100; Kentucky, 890; Ohio, 660; Alabama, 750; and Illinois, 160. Lithium-bearing kaolin deposits are distributed in the Coastal Plain province from New Jersey to Texas, and one occurs in Idaho; maximum lithium concentrations in samples from these deposits range from 64 to 180 ppm. The maximum concentration found in the Arkansas bauxite region is 460 ppm and that in flint clay in Colorado is 370 ppm. Samples from areas other than Pennsylvania, Maryland, Kentucky and Missouri are relatively few in number, represent mostly commercially valuable clays, and represent only a part of the refractory clay deposits in the United States. Data are not available on the clays associated with these deposits that may be unusable because they contain too much lithium as well as other deleterious elements. In both Pennsylvania and Missouri, lithium contents vary regionally between districts and locally between deposits.In samples containing more than 2000 ppm lithium, the lithium occurs in a dioctahedral chlorite mineral very similar to cookeite, which previously has not been recognized in sedimentary clays. The associated clays consist chiefly of well-crystallized kaolinite. The dioctahedral chlorite, however, seems to be most abundant where diaspore and boehmite occur along with the kaolinite. Barium, chromium, copper, phosphorus and strontium are present in some samples in amounts of several hundred pans per million or more, and may contribute to the failure of some clays to perform satisfactorily in firing tests.Lithium-rich clays could serve as a significant lithium resource in the very distant future. Clays that contain as much as 1% lithium may be common enough in Missouri or in Pennsylvania to be produced as a by-product to help support benefication costs for refractory clays. Sufficient amounts of lithium-rich clay may be found in deposits that have been explored, found unsatisfactory for normal refractory uses, and not developed. The lithium-rich clay in some deposits presently being worked may be worth stockpiling for eventual use.     

Predicting turbulence and heat transfer in 3-D curved ducts by near-wall second moment closures

This paper presents discussions on predicting turbulence and heat transfer in two types of square sectioned U-bend duct flows with mild and strong curvature by recent second moment closures. Batten et al.'s [AIAA J. 37 (1999) 785] modified version of Craft and Launder's [Int. J. Heat Fluid Flow 17 (1996) 245] two-component-limit (TCL) turbulence model and Shima's [Int. J. Heat Fluid Flow 19 (1998) 549] wall-reflection free model are presently focused on. They are low-Reynolds-number models totally free from geometrical parameters. The former model is realizable and called the TCL model. For turbulent heat flux, a higher order version of the generalized gradient diffusion hypothesis by Suga and Abe [Int. J. Heat Fluid Flow 21 (2000) 37] is applied along with the TCL model. The results suggest that although both second moment closures are generally good enough for predicting flow and heat transfer in the case of mild curvature, only the realizable TCL model is reliable in the strong curvature case.     

Methane catalytic decomposition over ordered mesoporous carbons: A promising route for hydrogen production

Methane decomposition offers an interesting route for the CO₂-free hydrogen production. The use of carbon catalysts, in addition to lowering the reaction temperature, presents a number of advantages, such as low cost, possibility of operating under autocatalytic conditions and feasibility of using the produced carbons in non-energy applications. In this work, a novel class of carbonaceous materials, having an ordered mesoporous structure (CMK-3 and CMK-5), has been checked as catalysts for methane decomposition, the results obtained being compared to those corresponding to a carbon black sample (CB-bp) and two activated carbons, presenting micro- (AC-mic) and mesoporosity (AC-mes), respectively. Ordered mesoporous carbons, and especially CMK-5, possess a remarkable activity and stability for the hydrogen production through that reaction. Under both temperature programmed and isothermal experiments, CMK-5 has shown to be a superior catalyst for methane decomposition than the AC-mic and CB-bp materials. Likewise, the catalytic activity of CMK-5 is superior to that of AC-mes in spite of the presence of mesoporosity and a high surface area in the latter. The remarkable stability of the CMK-5 catalyst is demonstrated by the high amount of carbon deposits that can be formed on this sample. This result has been assigned to the growth of the carbon deposits from methane decomposition towards the outer part of the catalyst particles, avoiding the blockage of the uniform mesopores present in CMK-5. Thus, up to 25 g of carbon deposits have been formed per gram of CMK-5, while the latter still retains a significant catalytic activity.     

Joint development of seabed hydrocarbon resources: an overview of precedents in the North Sea

When I first wrote about joint development of international common petroleum deposits some 12 years ago,¹I allowed that the subject was then somewhat academic. At that time, the number of known shared deposits on the international level was insignificant. In the intervening years, however, this situation has changed dramatically.Major commercial hydrocarbon discoveries which straddle international offshore boundaries have now been made on the North Sea continental shelf. Specifically the vast Statfjord oilfield as well as the smaller Murchison oilfield and the Frigg gasfield are all commercially exploitable deposits which overlap in part the Norway-United Kingdom (U.K.) offshore boundary. A heightened economic impetus to develop these deposits has resulted in an acceleration and crystallization of both State practice and exploration/development activity in the area concerned. These deposits, brought to production jointly by the relevant States and their licensees, have proved thus far to be a “watershed” for precedent and State practice in the area of joint development of common hydrocarbon reserves. It is, therefore, the intention of this paper to consider these developments, factually and as precedents, as evidence of the body of international law which has evolved on the subject of joint development.     

Effect of gradient wetting surface on liquid flow in rectangular microchannels driven by capillary force and gravity: An analytical study

A model is presented for predicting liquid flow velocity in a rectangular microchannel driven by capillary force, gravity and an extra driving force due to the surface wettability gradient. The nth power function, , for the cosine of contact angle (CA) with typical n order of 0.5, 1 and 2 is applied to analyze how the inner surface wettability gradient of the microchannel affects the flow velocity. Flow simulations revealed that the velocity of liquid flow decreases with the length of microchannel and the wettability gradient (e.g. from 80° to 2°) on channel surface will accelerate the motion of liquid when the flow-front approaches to the end of the microchannel although the gradient surface may decrease the initial motion of liquid due to the great CA at channel entrance in comparison to the uniform CA channel (with respect to the lowest CA of 2°). The linear function (n = 1) of wetting gradient profile may achieve relatively more stable and higher flow velocity than the other n power functions. The analysis of driving force along the moving path matches well with the flow velocity predicted by the model.     

Detailed study of sulfide scaling at la courneuue nord, a geothermal exploitation of the Paris Basin, France

The fluid of the Dogger aquifer is always used through a closed loop formed by the production well, the heating plant and the injection well. After two or three years of exploitation of the geothermal doublets in the northern part of the Paris basin, scaling and plugging problems have appeared in some cases. The results of the detailed study carried out at La Courneuve Nord, a typical site of this area, are presented.The drawdrown of production rate, scaling in the heat exchanger and the increase of injection pressure required a rapid decision for workover operations on the wells. These cleaning operations and joint research studies allowed us to identify the cause of the plugging as well as to locate these deposits and to estimate their importance. Iron sulfide was found from the base of the production well casing all the way to the injection well casing. The thickness of this scale induces hydraulic pressure loss along the casings. Moreover, part of this sulfide is carried away by the fluid and fills up the bottom of the open hole injection well. After the cleaning operations, the hydraulic properties of the reservoir seem to be recovered.Chemical and mineralogical analyses of theses deposits identified the presence of a large variety of iron sulfide (mackinawite, pyrite, pyrrhotite) and a typical corrosion product (Fe₂(OH)₃Cl). Biochemical and bacteriological studies show a very high content of micro-organisms. At the end of the workover operations, several geophysical logs gave information on the corrosion of the casing as well as the residual scale. A balance of the iron content is calculated, between the volume of deposits and the iron removed by the corrosion of the casing.A chemical model, TPDEGAZ, is used to calculate the evolution of the saturation indexes of the fluid with respect to iron sulfide phases. The effects of parameters such as pressure, temperature, degassing and addition of iron by corrosion are simulated. The results of the observation and modeling approaches are compared.     

A sealed optical cell for the study of lithium-electrode|electrolyte interfaces

A sealed, symmetrical, lithium optical cell, which enables optical images of lithium surface deposits and in situ Raman spectra to be obtained simply and conveniently during charge–discharge cycling of lithium metal electrodes, has been designed and tested. A conventional aprotic liquid, 1 M lithium hexafluorophosphate in propylene carbonate, and an experimental ionic liquid, 20 mol% lithium bis(trifluoromethanesulfonyl)amide in 1-ethyl 3-methyl imidazolium bis(trifluoromethanesulfonyl)amide, are investigated as electrolyte solutions. Images obtained from the cell with the former electrolyte solution demonstrate the problems associated with cycling lithium metal electrodes. Images obtained with the latter electrolyte solution provide clear evidence that continued investigation of ionic liquids for use with lithium metal electrodes is warranted. Operation of the cell with the conventional electrolyte yields Raman spectra of good quality. The spectra display vibrational modes which arise from the electrolyte, as well as several additional modes which are associated with the deposits formed during cycling.     

Using the results of creep crack incubation tests on CrMoV steel for predicting long time creep rupture properties

The results of a series of creep crack incubation (CCI) tests have been used to examine the effectiveness of the LICON methodology for predicting long duration uniaxial rupture strength of a CrMoV steel at 550° C. The study has revealed that effective long time predictions can be made, but only with the availability of additional information including: an awareness of the short and long time rupture mechanisms and the associated multi-axial rupture criteria obeyed by the material, the results of uniaxial and multi-axial creep tests, and a knowledge of the steady state creep stress conditions existing in the testpieces (structures) forming part of the evaluation.     

Dynamic simulation of fouling in a circulating fluidized biomass-fired boiler

A dynamic model is presented for a biomass-fired circulating fluidized bed boiler. The model is based on energy and mass balances for the components in the boiler and on a combustion model for the fluidized bed. The main purpose of the model is to simulate how deposits affect the boiler efficiency and performance. The model is verified against the municipal circulating fluidized bed boiler in Västerås, Sweden, which produces 157 MW. The distribution of deposits on the surfaces in the boiler is well known from inspections. These observations are used as inputs to the model to simulate their effects on boiler performance.     

Heat Transfer in a Scraped-Wall,Continuous Unit

The effect of the use of scrapers on the film heat transfer coefficient was investigated. Experimental runs were conducted in liquid-full, continuous-flow heat exchangers of commercial size, with a 6-in. ID and 6-ft length. Three test fluids were used: two petroleum lube fractions and corn syrup. Flow rates were varied from 0.8 to 5.8 gpm and the scraper speed from 0.5 to 25 rpm. The data collected were utilized in developing a design correlation in the laminar regime (Rer < 150). The correlation obtained for heating and cooling was Nu = 57 Re_f ^0.059 Re_r ^0.113 Pr^0.063 Visr^?0.018, for 0.0016 < Ref < 9.23 and 0.0164 < Re_r < 68.65.

A possible flow pattern in the heater was suggested to explain the relative ineffectiveness of scraping for improving the film coefficient for heating very viscous fluids in liquid-full heat exchangers.

Comparison of the experimentally obtained film coefficient with those predicted by the penetration theory model indicate that this model is unsuitable for predicting the coefficients for viscous fluids in laminar flow.     

Characterization of clay scales forming in Philippine geothermal wells

Smectite scales occur in 24 out of 36 blocked wells located in Tongonan, Palinpinon and Bacon-Manito. These comprise 2–85% of the well scales and form at depths of 36–2620 m. where measured and fluid inclusion temperatures are 41–320°C. Most, however, occur below the production casing shoe where temperatures are 230°C, often at depths coinciding with aquifers. The clay scales are compositionally and structurally different from the bentonite used in drilling, which is essentially a sodium-rich montmorillonite. The clay deposits are expanding, generally disordered, and combine the characteristics of a montmorillonite, saponite and vermiculite in terms of reaction to cationic exchange treatments, structure and composition. Six types of clay scales were identified, but the predominant one, comprising 60–100% of the clay deposits in a well, is Mg- and Fe-rich and referred to as a vermiculitic species. The crystallinity, degree of disorder, textures, optical characteristics, structure and relative amounts of structural Al, Mg and Fe vary with time, temperature and fluid composition, but not with depth and measured pressure. Despite its variance from bentonite characteristics one of the dominant suggested mechanisms for clay scale formation uses the drilling mud in the well as a substrate, from which the Mg and Fe-rich clay evolves. Another important possible mechanism for formation of the clay scale is the precipitation of the clays from hydrothermal fluids, wherein Mg and Al appear to be the limiting elements. Other, less important, mechanisms of formation are: alteration of chloritized cuttings in the well to the vermiculitic species and the probable introduction of smectite from the formation.     

Carbonaceous deposits in direct utilization hydrocarbon SOFC anode

Carbonaceous deposits formed in Cu-based SOFC anode compartment by exposing porous YSZ anodes to n-butane at elevated temperatures were studied using a combination of V–I curves, impedance spectroscopy, SEM, and TPO measurements. While short-term exposure of a porous YSZ matrix to n-butane at 973 K resulted in the deposition of electronically conducting carbonaceous film and therefore to enhance the fuel cell performance, the power density decays quickly in n-butane at temperature 1073 K or higher for long-term operation. SEM results indicate that the carbonaceous deposits arising from gas phase reaction have different morphology, and a dense layer composed of poly-aromatic rings has been formed on the porous anode surface. The dense layer could block the penetration of fuels to the anode and ions transfer to the three-phase boundaries where electrochemical reactions occur, resulting in the drop of the power density. TPO measurements revealed that the amount of carbonaceous deposits increased and the type of deposits changed with exposure time to n-butane. The stability of deposits increased with extending the exposure time according to the increased oxidation temperature. Steam can remove the carbonaceous deposits from the porous YSZ anode, but the reaction temperature was severely elevated compared to that of oxygen. The carbonaceous deposits can also be removed at 973 K by steam but the deposition of carbon will be controlled by the speed of removal and formation from the gas phase reaction.