Reservoir Enthalpy Research Articles

Measurements of T5 Shock Tunnel Freestream Temperature, Velocity, and Composition

We report on measurements of rotational and vibrational temperature, velocity, and concentrations of nitric oxide (NO) in freestream flows at the T5 reflected shock tunnel at California Instistute of Technology. Quantities were measured at 50 kHz by tunable diode laser absorption spectroscopy using five lasers simultaneously to sample 27 quantum state-specific transitions. To isolate core flow measurements from the shear flow surrounding it, optical flow-cutter arms were designed. Two sets of arms with differing optical path lengths were used to assess freestream spatial uniformity. This study consists of nine total experiments (“shots”) spanning four nominal conditions with reservoir enthalpy 8–21 MJ/kg and flow velocity 3.5–5.5 km/s. Freestream measurements generally imply thermal equilibrium of the rotational and vibrational temperatures except at lower-enthalpy conditions. We compare temperature measurements with predictions from five species air simulations and find reasonable agreement at lower-enthalpy conditions but underprediction of NO concentrations. At higher-enthalpy conditions, we observed transitory agreement in temperature but overprediction of NO concentrations. Measured and simulated velocity generally agree well across all conditions. Carbon monoxide, water, and potassium were also detected in the T5 flow, and their concentrations are reported where relevant.

Novel Direct Downhole Enthalpy Estimation at Geothermal Well in Cubadak, West Sumatra, Indonesia

Temperature, pressure and enthalpy data are very important and valuable, both during geothermal drilling and in well operation. Fibre optic distributed temperature sensors (DTS) that offer flexible and robust solutions for geothermal applications and temperature logging, an established method for well temperature measurement. All temperature measurement methods will be combined with reservoir enthalpy estimation using T-p-x state space correlation for H2O-NaCl geothermal brine. A geothermal brine enthalpy estimation model has been developed, based on T-p-x state space correlation using C programming language. This was able to provide estimations of pressure, mass fraction, density and enthalpy, solely based on measured temperature limited to below 300oC. The model can be applied to various geothermal fields with sodium chloride dominated waters. The study treated the mixture of geothermal brine and drilling fluid heated in the well for certain periods as a simulation of geothermal brine at the reservoir. The enthalpy monitoring graph proved useful for monitoring the enthalpy in the reservoir. The results from the model are used for early electrical power estimations of the Cubadak geothermal working area site, based on current geothermal gradient extrapolation of CBD-1 well.

Characterization of reflected shock tunnel air conditions using a simple method

A new method to characterize air test conditions in hypersonic impulse facilities is introduced. It is a hybrid experimental–computational rebuilding method that uses the Fay–Riddell correlation with corrections based on thermochemical nonequilibrium computational fluid dynamic results. Its benefits include simplicity and time-resolution, and using this method, a unique characterization can be made for each individual experimental run. Simplicity is achieved by avoiding the use of any optical techniques and overly expensive numerical computations while still maintaining accuracy. Without making any assumptions to relate the reservoir conditions to the nozzle exit conditions, the work done characterizing four test conditions in a reflected shock tunnel is presented. In this type of facility, shock compression is used to produce an appropriate reservoir, which is then expanded through a nozzle to produce hypersonic flow. Particular focus is given to the nozzle exit total enthalpy where a comparison is made with the reservoir enthalpy obtained using the measured shock speed and pressure in the shock tube. Good agreement is observed in all cases providing validation of the new approach. Additionally, static pressure measurements showed clearly that conditions III and IV have a thermochemical state which likely froze shortly after the nozzle throat. Also, the nozzle flow is shown to be almost isentropic. Due to the simplicity of the current method, it can be easily implemented in existing facilities to provide an additional independent estimate alongside existing results.

A novel total-flow geothermal power generator using Turgo turbine: Design and field tests

This paper presents a unique design of a total-flow geothermal power generator that uses Turgo turbine and two-phase supersonic nozzles. The high-speed flashing jets are formed by high-pressure subcooled liquid from the well through the nozzles and impinge turbine blades obliquely to drive the Turgo turbine. This new generator converts geothermal power directly from the geothermal fluid without implementing any phase separator or heat exchanger, which results in a simple and easy-to-maintain system. A prototype of the total-flow geothermal power generator was built and field-tested in Yilan, Taiwan. Results show that compared to traditional Organic Rankine Cycle generators and double flash geothermal power plants, the new design has a competitive geothermal efficiency operating at moderate reservoir enthalpies.

Freestream velocity-profile measurement in a large-scale, high-enthalpy reflected-shock tunnel.

We apply Krypton Tagging Velocimetry (KTV) to measure velocity profiles in the freestream of a large, national-scale high-enthalpy facility, the T5 Reflected-Shock Tunnel at Caltech. The KTV scheme utilizes two-photon excitation at 216.67 nm with a pulsed dye laser, followed by re-excitation at 769.45 nm with a continuous laser diode. Results from a nine-shot experimental campaign are presented where N_2 and air gas mixtures are doped with krypton, denoted as 99% N_2/1% Kr, and 75% N_2/20% O_2/5% Kr, respectively. Flow conditions were varied through much of the T5 parameter space (reservoir enthalpy h_Rapprox 5-16 MJ/kg). We compare our experimental freestream velocity-profile measurements to reacting, Navier–Stokes nozzle calculations with success, to within the uncertainty of the experiment. Then, we discuss some of the limitations of the present measurement technique, including quenching effects and flow luminosity; and, we present an uncertainty estimate in the freestream velocity computations that arise from the experimentally derived inputs to the code.Graphic

A Novel Total-Flow Geothermal Power Generator Using Turgo Turbine: Design and Field Tests

This paper presents a unique design of a total-flow geothermal power generator that uses Turgo turbine and two-phase supersonic nozzles. The high-speed flashing jets are formed by high-pressure subcooled liquid from the well through the nozzles and impinge turbine blades obliquely to drive the Turgo turbine. This new generator converts geothermal power directly from the geothermal fluid without implementing any phase separator or heat exchanger, which results in a simple and easy-to-maintain system. A prototype of the total-flow geothermal power generator was built and field-tested in Yilan, Taiwan. Results show that compared to traditional Organic Rankine Cycle generators and double flash geothermal power plants, the new design has a competitive geothermal efficiency operating at moderate reservoir enthalpies.

Two-phase flow measurement of geothermal fluid using orifice plate: Field testing and CFD validation

Measurement of the mass flow rate and enthalpy from two-phase geothermal wells is very important for monitoring individual well performance and for optimum reservoir management. Existing techniques are either expensive (separator and tracer dilution), low accuracy (tracer dilution) or require the geothermal well to be taken out of production (calorimeter and lip pressure methods). The two-phase orifice plate is the most widely examined alternative method and has been implemented in several geothermal fields worldwide. In this work, extensive geothermal field testing data is used to evaluate existing correlations using the concentric sharp-edge orifice plate. A new simplified correlation was then developed with high accuracy for the full range of geothermal reservoir enthalpies (600–2800 kJ/kg) and an analytical model was proposed to predict the pressure drop across the two-phase orifice.Computational fluid dynamics (CFD) simulation using ANSYS Fluent was used to investigate the pressure profiles, velocity and discharge coefficients of two-phase flow of geothermal fluids through the sharp-edge orifice plate. The model results showed good agreement between the CFD simulations, field test data and the newly proposed pressure drop model. CFD modelling also show that using an eccentric orifice plate results in lower pressure drop than the concentric orifice.

An analysis of thermodynamic properties in both traditional and enhanced geothermal systems to compare thermal efficiencies

This meta-study draws upon previous research on both Enhanced Geothermal Systems (EGS) and traditional geothermal systems (GS), using these findings to compare and investigate the thermal efficiency of each system. Efficiency calculations include reservoir enthalpy, maximum drilling well temperature, power output (per unit mass of liquid) and mass flow rate of these systems to determine whether EGS’s are viable as an alternative, more readily available renewable energy source. This meta-study suggests that EGS are more viable than naturally occurring GS in the context of future geothermal energy production as they perform with a similar average efficiency of 10-15% and, in addition, can be used in a wider range of geothermal environments.

Performance measures in geothermal power developements

Geothermal resource assessment requires several input parameters at a time when field information is normally very limited. The power plant efficiency is an important parameter as it affects investment cost and profit. However, there is significant debate in the geothermal industry on the appropriate performance measure to implement. In this paper we attempt to determine the best performance measures for financial decision making during the exploration stage of geothermal power developments. We compare and contrast current performance measures commonly used by the geothermal industry. This includes thermal efficiency, geothermal brine effectiveness, utilisation efficiency and enthalpy efficiency.We show that enthalpy efficiency, categorised by the geothermal reservoir enthalpy, is the best financial performance measure because it is similar to other measures on most criteria, but superior in terms of comparability across different geothermal sites, while satisfying homoscedasticity. Utilisation efficiency, on the other hand, was demonstrated to have the least reliability while requiring additional input parameters.We recommend using the modified enthalpy efficiency developed in this work for resource assessment of new geothermal fields, benchmarking with existing development and for comparison with conventional fossil-fuel thermal plants. This should also affect the choice of resource assessment methodology.

Effect of geological layers on hydrate dissociation in natural gas hydrate reservoirs

Naturally occurring reservoirs of methane gas hydrate have been found in arctic and marine environments around the world. They are an attractive source of energy as natural gas can be produced from these hydrate deposits by depressurization or thermal stimulation. Reservoir simulations are used to find the optimum production strategies for methane gas hydrate reservoirs. Most of these simulation are carried out for homogeneous hydrate reservoirs in absence of substantial well data. These gas hydrate reservoirs are inherently heterogeneous because of the geological settings of the hydrate bearing sediments. Majority of the heterogeneity comes from the depositional layering at different geological time scales. Examples are Mount Elbert, block 818 in Gulf of Mexico, Walker Ridge 313 Site. The effects of geological layering on gas production and hydrate dissociation fronts in the reservoir are still unknown. In the present work, a 3-dimensional, multiphase, multi-component, thermal simulator is used to study layered gas hydrate reservoir, underlain by an aquifer, with cross-flow between the layers. Gas production from the reservoir and gas hydrate dissociation fronts in the reservoir are found for different aquifer permeability, different layering and well completions. In layered confined reservoirs, recovery is found to be dependent on (a) the total volume of the hydrate present in the reservoir which governs the enthalpy requirement for dissociation, (b) depressurization potential of the reservoir which depends on the effective permeability and (c) the enthalpy available for dissociation which depends on the reservoir enthalpy and heat transfer from over and under-burden. The layering suggests the positions and progress of the dissociation fronts and affects the gas recovery depending on the aquifer permeability. This effect is seen because of the pressure variation in different layers and enthalpy available for hydrate dissociation. In unconfined reservoirs the effect of layering on dissociation front positions is found to be insignificant as the pressure variation in the layers is insignificant because of the unconfined aquifer. A weakly un-confined aquifer also renders the depressurization ineffective.

衝撃風洞の加熱増加現象における化学非平衡性の影響

Recently, shock-tunnel experiments have been conducted at high-pressure and high-enthalpy conditions such as a reservoir pressure of 50MPa and a reservoir enthalpy of 20MJ/kg in order to study laminar-to-turbulence transition on hypersonic vehicles. In those experiments, unexpected large wall heat flux to test models was measured, which was not observed at conventional pressure conditions. The cause of the heating augmentation remains an open issue. In this study, the influence of chemical nonequilibrium in the flowfield around test models on the heating augmentation was investigated by computational fluid dynamics (CFD) simulation, and it was found that the influence is small.

Free-stream density perturbations in a reflected-shock tunnel

Focused laser differential interferometry is used to quantify the free-stream density perturbations in the T5 reflected-shock tunnel. The investigation of reflected-shock tunnel disturbances is motivated by the study of hypervelocity boundary-layer instability and transition. Past work on hypersonic wind-tunnel noise is briefly reviewed. New results are reported for hypervelocity air flows at reservoir enthalpies between 5 and 18 MJ/kg at Mach ≈ 5.5. Statistical analysis finds no correlation of RMS density perturbations with tunnel run parameters (reservoir pressure, reservoir mass-specific enthalpy, free-stream unit Reynolds number, free-stream Mach number, and shot number). Spectrograms show that the free-stream disturbance level is constant throughout the test time. Power spectral density estimates of each of the experiments are found to collapse upon each other when the streamwise disturbance convection velocity is used to eliminate the time scale. Furthermore, the disturbance level depends strongly on wavelength. If the disturbance wavelength range of interest is between 700 μm and 10 mm, the tunnel noise is measured to be less than 0.5 % with the focused laser differential interferometer.

QrtzGeotherm: A revised algorithm for quartz solubility geothermometry to estimate geothermal reservoir temperature and vapor fraction with multivariate analytical uncertainty propagation

The quartz solubility geothermometry to calculate geothermal reservoir temperature and vapor fraction with multivariate analytical uncertainty propagation is programmed as two classes, SiO2TD and QrtzGeotherm in Visual Basic in Visual Studio 2010 (VB.NET). The class, SiO2TD calculates the total discharge concentration, SiO2TD and its uncertainty, SiO2TDErr from the analytical concentration of silica, SiO2msd and uncertainty, SiO2msdErr of separated water, sampled after N-separations of vapor and liquid. The class, QrtzGeotherm uses the following properties as input parameters: (i) HRes—reservoir enthalpy (kJ/kg), (ii) HResErr—uncertainty in the reservoir enthalpy (kJ/kg), (iii) SiO2TD—total discharge silica concentration (ppm), (iv) SiO2TDErr—uncertainty in the total discharge silica concentration (ppm) (v) GeoEq—number of quartz solubility regression equation, (vi) TempGuess—a guess value of the reservoir temperature (°C). The properties corresponding to the output parameters are (i) TempRes—reservoir temperature (K), (ii) TempResErr—uncertainty in the reservoir temperature (K), (iii) VaporRes—reservoir vapor fraction and (iv) VaporResErr—uncertainty in the reservoir vapor fraction. Similarly, it has a method, SiO2Eqn(EqNo, Temp) to provide the silica solubility as function of temperature corresponding to the regression equation.Four quartz solubility equations along the liquid–vapor saturation curve: (i) a quadratic equation of 1/T and pressure, (ii) a linear equation relating log SiO2to the inverse of absolute temperature (T), (iii) a polynomial of T including logarithmic terms and (iv) temperature as a polynomial of SiO2including logarithmic terms are programmed. A demonstration program, QGeotherm is written VB.NET. Similarly, the applicability of classes SiO2TD and QrtzGeotherm in MS-Excel is illustrated considering Los Azufres geothermal field as an example.

Qrtzgeotherm: An ActiveX component for the quartz solubility geothermometer

An ActiveX component, QrtzGeotherm, to calculate temperature and vapor fraction in a geothermal reservoir using quartz solubility geothermometry was written in Visual Basic 6.0. Four quartz solubility equations along the liquid–vapor saturation curve: (i) a quadratic equation of 1/ T and pressure, (ii) a linear equation relating log SiO 2 to the inverse of absolute temperature ( T), (iii) a polynomial of T including logarithmic terms and (iv) temperature as a polynomial of SiO 2 including logarithmic terms are programmed. The QrtzGeotherm has input parameters: (i) HRes—the reservoir enthalpy (kJ/kg), (ii) SiO2TD—silica concentration in total discharge (ppm), (iii) GeoEq—number of quartz solubility equation and (iv) TempGuess—a guess value of the reservoir temperature (°C). The reservoir enthalpy H res is assumed to be the same as the total discharge enthalpy H R. The output parameters are (i) TempRes—reservoir temperature (°C) and (ii) VapRes—reservoir vapor fraction. The first step is to calculate the total discharge concentration of silica SiO2TD from the concentration of silica SiO2Col of separated water, sampled after N-separations of vapor and water. To use QrtzGeotherm in MS-Excel, three functions SiO2TD, GeoResTemp and GeoResVap for an N-stage separation of geothermal reservoir fluid are written in Visual Basic for Application (VBA). Similarly, a demonstration program, QrtzGeothrm, is written in Visual Basic 6.0.

Experiments on Passive Hypervelocity Boundary-Layer Control Using an Ultrasonically Absorptive Surface

Recently performed linear stability analyses suggested that transition could be delayed in hypersonic boundary layers by using an ultrasonically absorptive surface to damp the second mode (Mack mode). Boundary-layer transition experiments were performed on a sharp 5.06-deg half-angle round cone at zero angle of attack in the T5 Hypervelocity Shock Tunnel to test this concept. The cone was constructed with a smooth surface around half the cone circumference (to serve as a control) and an acoustically absorptive porous surface on the other half. Test gases investigated included nitrogen and carbon dioxide at M∞ ≃ 5 with specific reservoir enthalpy ranging from 1.3 to 13.0 MJ/kg and reservoir pressure ranging from 9.0 to 50.0 MPa. Comparisons were performed to ensure that previous results obtained in similar experiments (on a regular smooth surface) were reproduced, and the results were extended to examine the effects of the porous surface. These experiments indicated that the porous surface was highly effective in delaying transition provided that the pore size was significantly smaller than the viscous length scale.

Test Time Increase by Delaying Driver Gas Contamination for Reflected Shock Tunnels

A gasdynamical detectorhas been applied to measure thearrival timeof driver gas in a low concentration in the testsectionofa high-enthalpyshock tunnel. Thedetection determines theusefultesttimewith uncontaminated test gas for a wide range of specie c reservoir enthalpies. Effects of over- or undertailored interface condition on severe contaminationhavebeeninvestigated.Itisexperimentallydemonstratedthatovertailoredinterfaceoperationmust beavoided toachievethetestdurationnecessary foraerodynamicmeasurements,especially forhigh-enthalpy e ow. Theinterfacecondition isoptimized forthelongesttesttimeattainable. Asan activemethod fordelaying drivergas contamination,adevicetotrapthedrivergasattheendoftheshocktubehasbeentriedforanovertailoredcondition. The method, however, causes the contamination to occur earlier. A modie ed device using a sleeve to capture driver gas upstream has been developed. Results with the longest sleeve tested show that strong contamination is dramatically delayed and that the uncontaminated test time is signie cantly increased. Nevertheless, improved test times are still shorter than the test time without the device at a slightly undertailored condition.

Flow Characterization in the ONERA F4 High-Enthalpy Wind Tunnel

Experimental results obtained in the ONERA F4 hot-shot wind tunnel have been analyzed to address two important problems for this type of wind tunnel, i.e., the determination of reservoir conditions and the thermochemical nature of the nozzle flow. Numerical tools (one-dimensional and two-dimensional inviscid or viscous, unsteady or space marching codes) are used to reproduce the results of the high-enthalpy experiments. To illustrate this approach, several runs are investigated with different arc-chamber material options, for which diode laser infrared absorption spectrometry (DLAS) has provided freestream velocity, translational temperature, and nitric oxide concentration measurements. The reservoir enthalpy can be determined using spherical and sharp-cone probe heat-transfer-rate measurements with adequate correlations. Recent direct measurements of freestream velocity with electron beam fluorescence time-of-flight technique are used to cross check DLAS and heat-transfer-rate probe results. Concerning the thermochemical nature of F4 nozzle flows, an unexpected conclusion is obtained, as the nozzle wall pressure and translational temperature are observed to be close to equilibrium values at high-enthalpy operating conditions

Establishment of steady separated flow over a compression-corner in a free-piston shock tunnel

The time required to establish steady separated compression–corner flow is examined under hypervelocity conditions in a free-piston shock tunnel. This time is reasonably well described using previous perfect gas analyses. The results suggest that, provided the nozzle reservoir enthalpy is 20 MJ kg\(^{-1}\) or less, there is sufficient time to establish steady separated flow before driver gas contamination becomes a significant problem in the present facility.

Phase step holographic interferometry applied to hypervelocity, non-equilibrium cylinder flow

For blunt bodies the reduced bow shock wave stand-off distance and the shock layer density rise in the stagnation region as compared to ideal gas flow are phenomena caused by dissociative effects. In this work experiments with aRBODY=45 mm radius cylinder and an aspect ratio ofL/RBODY ≈ 11 are described. The tests were carried out in the High Enthalpy Shock Tunnel in Gottingen (HEG), a free piston driven shock tunnel. Two different test conditions at reservoir enthalpies of around 21 MJ/kg and Mach numbers of around 9 in air and nitrogen were available.

High-enthalpy, hypersonic compression corner flow

The results of an experimental investigation of high-enthalpy, hypersonic flow over sharp leading-edge compression corners are presented and discussed. In particular, the possible effects of real gas behavior are examined. Measurements have been made of the heat transfer and pressure distributions for flat plate and compression corner flow. Some flow visualization data have also been obtained. Test flows were generated using a free-piston shock tunnel operating in the reflected mode. The reservoir enthalpy ranged from 3 to 19 MJ kg -1 , giving freestream speeds of 2.3-5.5 km s -1 . For these conditions, the flow remains laminar throughout. The flat plate data for both high- and low-enthalpy flows are in agreement with the reference enthalpy method for heat transfer and the weak interaction theory for pressure. Also, the measured flat plate boundary-layer thickness compares well with an expression strictly valid for perfect gas flows only. The high- and low-enthalpy compression corner flows have upstream influence and plateau pressure behavior similar to perfect gas flow. That is, real gas effects for the present flows appear to be negligible. This is consistent with the essentially chemically frozen viscous and inviscid flow upstream of the interaction.