Transient Pulse Technique Research Articles

The non-planar surface of carbonate rock sample affecting the behaviour of thermal response and the measurement of thermophysical parameters by Pulse Transient Technique

The main target of the paper is to present the problems in measuring the thermal properties of natural stones and evaluating the influence of cavities at the interface of non-planar surfaces of samples. Air voids present between the surfaces of the sample set induce anomalous heat transfer behaviour in the rocks by increasing the thermal contact resistance. The Slab model derived for the Pulse Transient Technique supports data evaluation by introducing two additional parameters in the experiment i.e. the heat capacity of the heat source (C) and the heat transfer coefficient between the heat source and specimen (α) that is related with the specimen planarity, surface roughness and the air gaps at the interfaces. The experiment was performed under two different states of thermal contact at the sample - heat source interfaces to show the influence of the decreased thermal contact resistance by filling the air voids with a thermally conductive paste made of bentonite powder mixed with water. Temperature response during measurement of thermal properties of the samples has clearly shown the effect of poor thermal contact at the untreated interfaces compared to the case when thermal contact at the interface has been improved by application of thermally conductive bentonite paste. Moreover, measurements using the bentonite paste as the heat contact agent exhibited reduced scattering in data calculated using the Slab model.

Thermophysical Parameters of Carbonate Rock estimated by Slab Model Developed for Pulse Transient Technique

Abstract The slab model has been used for parameter estimation from the measurement performed by the Pulse Transient Technique. The estimation of thermophysical parameters was done on carbonate rock sample. In addition to basic thermal parameter for example thermal diffusivity, thermal conductivity and specific heat capacity, the slab model takes into account the heat capacity of the heat source, as well as the heat transfer coefficient between the heat source and the sample. The thermophysical parameters were estimated for the case when thermal conductive paste as a heat contact agent was not used for the measurements. The paste contains silicone oil that penetrates into the porous stone material and thus causes irreversible changes of properties during the measurement so we decided not to use it. The experiment was done with dry contacts at the interfaces that causes the disturbances in the measurement that have been introduced and resolved using the slab model. Uncertainty analysis of the estimation of the parameters by the slab model was done for real measurements conducted on the carbonate rock. In this paper we analyzed the quality of the temperature response fit in dependency on the originally free fitted parameters of the heat transfer coefficient and the heat capacity of the heat source that was replaced by constant values in two steps. The heat capacity of the heat source was calculated from the material properties, e.g., the nickel and Kapton. The fit results obtained by the slab model were compared with the data obtained by the ideal and cuboid model. The analysis of the sensitivity coefficients and calculated uncertainties of estimated parameters with the slab model help to improve the accuracy of parameter estimation.

Uniform, Scalable, High-Temperature Microwave Shock for Nanoparticle Synthesis through Defect Engineering

Summary Here we demonstrate a thermal shock synthesis method triggered by microwave irradiation for the rapid synthesis of nanoparticles on reduced graphene oxide (RGO) substrate. With properly controlled reduction, RGO has high electrical conductivity while maintaining functional groups, leading to an extremely efficient microwave absorption of ∼70%. The high utilization of microwaves results in the ability to raise the temperature to 1,600 K in just 100 ms, which is followed by rapid quenching to room temperature. The defects on the RGO are crucial for achieving this record-high microwave-induced temperature as these defects play a fundamental role in absorbing the radiation as well as the self-quenching mechanism. By loading precursors onto RGO, we can utilize rapid temperature change to synthesize nanoparticles. The nanoparticles are ∼10 nm with uniform distribution. This facile, rapid, and universal synthesis technique has the potential to be employed in large-scale production of nanomaterials and suggests a new direction for nanosynthesis.

Water, CO2 and Argon Permeabilities of Intact and Fractured Shale Cores Under Stress

As shale is the caprock over many reservoirs targeted for CO2 storage, shale permeability to CO2 has become an important concern. Measurements of this permeability need to be performed under in-situ conditions, with realistic temperatures, confining pressures and fluid pressures, and the effects of variables such as pressure, temperature, and shale moisture content need to be thoroughly addressed. Furthermore, the exposure of wet shale to dry CO2 can lead to, for example, dehydration and two-phase flow, that in turn affect permeability. This paper reports shale permeability measurements performed on two shale core plugs from Svalbard, under in-situ pressure and temperature conditions relevant for CO2 storage, using argon, CO2, and water as the permeate, and using both transient pulse and constant flow techniques. Permeability was found to be dependent mainly on effective confining pressure and on shale moisture content. The following was observed: (1) permeability decreased with increasing effective confining pressure; (2) permeability to water was lower than permeability to Ar or CO2; (3) shale moisture content had a strong inhibiting effect on the flow of Ar and CO2; (4) when a high CO2-flow was applied to a shale sample containing a hydrous pore fluid, a breakthrough effect occurred; and (5) in the presence of pore water, compaction creep can occur, causing a permanent decrease in permeability.

Effect of Moisture Content on Thermal Properties of Porous Building Materials

The thermal conductivity and specific heat capacity of characteristic types of porous building materials are determined in the whole range of moisture content from dry to fully water-saturated state. A transient pulse technique is used in the experiments, in order to avoid the influence of moisture transport on measured data. The investigated specimens include cement composites, ceramics, plasters, and thermal insulation boards. The effect of moisture-induced changes in thermal conductivity and specific heat capacity on the energy performance of selected building envelopes containing the studied materials is then analyzed using computational modeling of coupled heat and moisture transport. The results show an increased moisture content as a substantial negative factor affecting both thermal properties of materials and energy balance of envelopes, which underlines the necessity to use moisture-dependent thermal parameters of building materials in energy-related calculations.

Permeability evolution of sandstone under short-term and long-term triaxial compression

Permeability of sandstone under increasing deviatoric stress both in short-term and creep compression condition are measured with pulse transient technique. Based on the experimental results of short-term triaxial compression coupled with gas permeation, the influence of confining stress on the strength and failure mode of sandstone specimen are analyzed. The results show that the variation patterns of permeability under different confining stresses are similar, and the pressure differential has little influence on the mechanical behavior of sandstone. The crack volumetric strain is also calculated, and a linear relationship between the crack volumetric strain and permeability of sandstone specimen can be concluded. According to the creep test results with various loading procedures and different permeation fluids, the permeability evolution of sandstone is characterized as having four stages according with the typical deformation stages in a monotonic loading creep test. The failure strength of sandstone specimen under cyclic loading creep is lower and the system of cracks is more complicated than that under multi-stage loading creep with the same confining stress and permeation pressure.

Effect of Cap Rock Thickness and Permeability on Geological Storage of CO2: Laboratory Test and Numerical Simulation

Geological storage of CO2 is considered widely as an efficient method of mitigation of greenhouse gas emission. CO2 storage mechanism includes structural trapping, residual gas trapping, solubility trapping and mineral trapping. The shale cap rock acts as a seal for the storage when CO2 accumulates at the top of the reservoir. The injected CO2 may migrate through the cap rock under buoyancy force or pressure build-up which depends on the seal capacity of the cap rock. As a result, the effectiveness of containment of injected CO2 in the reservoir is largely dependent on the migration rate of CO2 through the cap rock. This paper investigates the effects of CO2 leakage through cap rock by a combination of experimental studies and numerical simulation. Firstly, experimental measurements on shale core samples collected from Australian cap rocks were conducted to determine properties, such as capillary pressure, pore size distribution and permeability. Based on the measured cap rock properties, the effect of thickness and permeability of cap rocks on CO2 leakage was studied using a commercial compositional simulator. Experimental results show that the permeabilities of the shale samples measured by transient pulse technique range from 60 to 300 nD; a non-Darcy calibration factor which equals the ratio of the measured permeability divided by 1000, is identified for samples with permeability lower than 1000 nD. Numerical simulation results show that the largest leakage of CO2 through the seal (cap cock) is about 7.0% with seal thickness of 3m and vertical permeability of 90 nD; both shale thickness and permeability affect the CO2 leakage significantly; with a given seal permeability, the leakage rate has a power relationship with shale thickness.

An Ultrasound System for Tumor Detection in Soft Tissues Using Low Transient Pulse

Different techniques are used for breast tumor detection that include microwave imaging, X-ray imaging, and magnetic resonance imaging. They provide accurate assessment of tumor size and location but suffer from some inherent drawbacks. Ultrasound is a detection technique that has been demonstrated as the one without harmful side effects on patients. This paper presents a method to detect the size and location of echogenic tumor in soft tissues using ultrasound. Quantitative ultrasound is utilized to allow an ultrasound signal to be sent from a transmitter to multiple receivers. This received signal is analyzed for echogenic and echolucent tumors to differentiate between them, along with a non-tumor sample. It is also studied for the delay and signal distortion, in order to determine the tumor location. The results are implemented by using field-programmable-gate-array (FPGA) and digital-signal-processor (DSP) technologies. The low transient pulse (LTP) technique is successfully utilized to generate the required short-duration ultrasonic signals in the proposed system. This codesign demonstrates a good application of the FPGA/DSP platform for LTP generation and processing received signals.

Experimental Study of the Laws Between the Effective Confining Pressure and Mudstone Permeability

The stress dependent permeability of a mudstone sample was measured using a transient pulse technique in a specially designed apparatus in which the confining pressure, pore pressure, and temperature were independently controlled. Experiments were conducted with the confining pressure first gradually increased from 10 to 30 MPa and then subsequently reduced back to 10 MPa. And the pore pressure was kept constant of 5 MPa during the whole process. During the loading process of effective confining pressure, the permeability of the mudstone had a nonlinear reduction with increasing stress and showed a high stress sensitivity (varying three orders of magnitude). The phenomenon can be explained that microcrack closure is the dominant mechanism controlling the evolution of mudstone permeability with the effective confining pressure during the loading process. The experimental results indicate that there is good fit of a model with exponential relationship of permeability and effective confining pressure to the data points. When unloading the effective confining pressure, the permeability of mudstone had very tiny increase and showed weak recovery capability. This is the result of the irreversibility of crack closure.

Uncertainty analysis for the determination of permeability and specific storage from the pulse-transient technique

and k ofsamples in the laboratory e.g., [1–8]. Most methods are based onfluid flow during stabilized conditions in a closed flow system(e.g., oscillating pore pressure, linear pressurization, and constant-rate flow injection methods) [3–8]. One major disadvantage ofthese approaches is the long duration of experiments required forhydraulically tight specimens; the initial transient stage necessi-tates experiments of weeks duration in some cases. Because of itsrelative expediency, the pulse-decay technique for determining β

Measurement of the drift mobilities and the mobility-lifetime products of charge carriers in a CdZnTe crystal by using a transient pulse technique

In this work we present results on the measurement of the drift mobility and the mobility-lifetime product of charge carriers in a 16-pixellated CdZnTe detector. For the determination of an interaction position based on the pulse rise-time method in a CZT detector, it is necessary to characterize the transport properties governed by drift mobility and lifetime for electrons and holes. In order to extract the transport properties of an electron and a hole, we bombarded 5.5-MeV alpha particles from a 241Am source and 81-keV gamma rays emitted from a 133Ba source on the negatively biased contact of the CZT detector. A time-of-flight (TOF) method was used to measure the electron drift mobility at room temperature whose value turned out to be 906.4 cm2/V⋅s. With the Hecht's equation, the electron mobility-lifetime product was also determined from the bias-dependent alpha response and was equal to (9.88 ± 2.33) × 10−3 cm2/V. On the other hand, the hole mobility-lifetime product was evaluated by a model based on the average charge collection efficiency which accounts for the absorption probability with a given photon energy. By using a single parameter fitting of the model, we obtained the hole mobility-lifetime product of (8.28 ± 0.17) × 10−4 cm2/V.

Thermophysical Properties of Electrically Conductive SiC–(Nb,Ti–C)ss-Based Cermets

Multifunctional cermets are being developed for a range of novel applications. The present paper deals with thermophysical properties of electrically conductive SiC-based cermets. The cermets were prepared by in situ reaction using a two-step sintering process. The thermophysical properties, namely, thermal conductivity, thermal diffusivity, and heat capacity, were measured using the pulse transient technique. The microstructure and chemical composition of the samples were characterized by SEM (scanning electron microscopy), TEM (transmission electron microscopy), STEM (scanning transmission electron microscopy), and EDX (energy dispersive X-ray analysis) techniques. The observed thermophysical data were correlated with the observed microstructures and chemical nature of the SiC-based cermets.

Laboratory Characterization of Permeability and Its Anisotropy of Chelungpu Fault Rocks

In Taiwan an international project to drill into the Chelungpu fault (TCDP) was initiated after the M w7.6 Chi-Chi earthquake in 1999. At Takeng, two vertical holes (A and B) to depths of about 2 km have been drilled through the northern portion of the Chelungpu fault system. In this study, we conducted systematic hydromechanical tests on TCDP drillcores collected from Hole-A at various depths above and below the major slip zone of the Chelungpu fault. We focus on the measurements of permeability as function of pressure and the brittle failure behavior. Evolution of permeability as a function of pressure and porosity was measured using either steady-state flow or a pulse transient technique. When subjected to an effective pressure reaching 100 MPa, permeability values of shaly siltstone samples range from 10−16 to 10−19 m2. In comparison, permeability values of porous sandstones are at least an order of magnitude higher, ranging from 10−14 to 10−18 m2. To characterize permeability anisotropy associated with the bedding structure of the rocks of the Chelungpu fault, cylindrical samples were taken from the TCDP drillcores along three orthogonal directions, denoted X, Y and Z respectively. Direction Z is parallel to the TCDP core axis, and the other two directions are perpendicular to the core axis, with X (N105°E) perpendicular and Y (N15°E) parallel to the strike of the bedding. In shaly siltstones, permeability values of samples cored along the strike of bedding (direction Y) can be up to 1 order of magnitude higher than those cored perpendicular to the strike of bedding (direction X). These observations indicate that permeability anisotropy is controlled by the spatial distribution of bedding in Chelungpu fault host rocks. Permeability evolution of fault rocks plays an important role in dynamic weakening processes, which are particularly pertinent to large earthquakes such as the Chi-Chi earthquake. Our experimental data on permeability and its anisotropy of TCDP core samples provide necessary constraints on fault models and proposed weakening mechanisms.

Transient analysis of reactions between NO and H2 with Pt-Al2O3 thin film catalyst

Transient pulse techniques using time-of-flight mass spectrometry were used to investigate the reduction of NO by H 2 over Pt/Al 2 O 3 thin film. A typical result measured at 400 °C shows different behaviors of N 2 , NH 3 and N 2 O. Changing the temperature with corresponding numerical simulations, we elucidated that N 2 O was produced via a consecutive process of NO reduction with NH 3 molecules. A specially designed apparatus employing (1) pulse valves for injection of reactant molecules onto catalysts and (2) a time-of-flight mass spectrometer was used to investigate processes of NO + H 2 reaction using Pt-Al 2 O 3 thin film on Si substrate. First, the planar layer of the catalyst was located in a vacuum chamber and the reactants were supplied onto the surface by pulse valves. This process is considered to involve few consecutive reactions. There, the transient production of N 2 and NH 3 was observed simultaneously. Second, the reactants were supplied into the micro reactor filled with square pieces of planar catalysts spaced with SiC balls. Here, N 2 O was observed as well as NH 3 and N 2 . The experiments and the numerical simulation of the NO and H 2 reaction rates clearly elucidated some aspects of NO reduction passes, i.e., while N 2 and NH 3 were directly produced from N and H adatoms dissociated from NO and H 2 admolecules, N 2 O was produced via consecutive process of NO reduction with NH 3 molecules which were produced in transient reactions.

Measurement of Reinforcement Corrosion Rate Using Transient Galvanostatic Pulse Method

Corrosion rate evaluation of concrete structure steel reinforcement was performed through investigation of a galvanostatic pulse transient response technique. A number of short sections of concrete embedded steel bar were used to conduct measurement of galvanostatic pulse transient measurements. There was a 30 to 180 second variation in applied galvanostatic pulse duration. A typical 1 kHz sampling rate was used to investigate the resulting transient potential response. To obtain separate equivalent electronic components, comprising a capacitance and resistance series, with reinforcing steel corrosion condition dependent values, there was analysis of the electrochemical potential transient response. Separate resistive components summation allowed evaluation of corrosion rate, which was then compared with a conventional linear polarization resistance (LPR) measurement corrosion rate on the same specimens. That the galvanostatic pulse transient technique enables resolution of the separate polarization resistance components, which provides a more conservative ongoing corrosion rate evaluation and offers significant advantages over either the galvanostatic or potentiostatic LPR method, is shown by obtained results.

Experimental study on gas permeability of mudstones

The paper presents the results of gas permeability measurements of mudstones from MHM (Meuse/Haute-Marne) site by the help of measurement facilities in GIG laboratory. The transient pulse technique was used, which can measure very low permeabilities (up to 10 −22 m 2). Cylindrical 40 mm diameter and about 40 mm length samples come from different distances with respect to the wall of the main access shaft of the MHM URL. The relationship between the permeability and the state of stress is studied and the problem of gas transfer in the saturated sample is analyzed. The relationship between the rupture of sample and the permeability will be also discussed. Experimental (and numerical) results show that the Callovo-Oxfordian stratum of MHM has very low gas permeabilities (∼2 × 10 −21 m 2). The disturbance linked to the excavation of shafts is not significant. Results show that the interstice gradient of gas pressure can induce pore water displacement. Furthermore, it was found that the permeability does not change very much even if a rupture occurs in tests with a confining pressure (11 MPa) equivalent to the lithological pressure at the depth of about 467 m.

Assessment of Corrosion Rate of Reinforcing Steel in Concrete Using Galvanostatic Pulse Transient Technique

This paper discusses a method of measuring transient potential response of a corrosion interface to a small galvanostatic pulse perturbation for a rapid assessment of the corrosion rate of reinforcing steel in concrete structures. Measurements were taken on 100 mm sections of steel bars which were subjected to a wide range of corrosion conditions, from passive steel to actively corroding steel. The duration of the applied galvanostatic pulse was varied between 5s and 180s, and the lateral distance of the point of measurement on the steel bar varied from zero to 400 mm. The result of the electrochemical transient response was investigated using a typical sampling rate of 1 kHz. Analysis of the transient potential response to the applied galvanostatic pulse has enabled the separation of equivalent electronic components so that the components of a series of capacitances and resistances, whose values are dependent on the corrosion condition of the reinforcing steel, could be isolated. The corrosion rate was calculated from a summation of the separate resistive components, which were associated with the corrosion interface, and was compared with the corrosion rate obtained from linear polarization resistance (LPR) method. The results show that the galvanostatic pulse transient technique enables the components of the polarization resistance to be evaluated separately so as to give more reliable corrosion rate values than those obtained from the LPR method. Additionally, this paper shows how the galvanostatic pulse transient response technique can be implemented. An appropriate measurement time for passive and actively corroding reinforcing steel is suggested for the galvanostatic pulse transient response measurements in the field site.

Electrochemical transient techniques for the evaluation of reinforcement corrosion in concrete

A galvano static pulse technique has recently been developed which enables the transient electrochemical potential response of a corrosion interface to an applied current to be studied. The technique has shown some promise in determining the corrosion rate of steel in concrete in both the laboratory and in the field. However, this technique is less well known in the civil engineering community than other techniques and there are a number of pitfalls to be avoided in carrying out field measurements. This paper reports on the results of a series of galvanostatic pulse transient response measurements carried out to determine the optimummeasurement parameters for assessing corroding reinforcing steel in concrete. Measurements were conducted on bars, which were undergoing a range of corrosion rates, from passive steel to actively corroding steel. The duration of the applied galvanostatic pulse was varied from 5 s to 300 s and the sampling rate used to capture the transient response was also varied from 50 Hz to 10 kHz. The electrochemical potential transient response was analysed to obtain equivalent electronic components that comprise a series of capacitor and resistor pairs, whose values are dependent on the corrosion condition of the reinforcing steel. The corrosion rate was calculated from a summation of those separate resistive components, which could be identified as being associated with the corrosion interface. The selection of measurement parameters to give the most accurate assessment of corrosion rate of steel in concrete was discussed. Guidance is given on the use of the galvanostatic pulse transient technique to assess the corrosion rate of steel in concrete and for the interpretation of the data obtained.

Thermophysical Analysis of Gioia Marble in Dry and Water-Saturated States by the Pulse Transient Method

Measurements of the thermophysical properties of Gioia marble in the temperature range from −20 to 60 ◦ C are presented. Thermophysical properties, namely, thermal diffusivity, thermal conductivity, and specific heat, were measured by the pulse transient technique. The data were compared for dry and water-saturated states. Despite the very low porosity of marble of about 0.6 vol%, an increase of the transport property parameters (thermal diffusivity and thermal conductivity) up to 20% after water saturation was found. To verify the differences in the transport parameters, the ultrasonic pulse velocity method was employed. A detailed analysis of thermophysical property data during the freeze/thaw process for dry and water-saturated marble was carried out in the temperature range from − 8t o 1 ◦ C, where an anomaly in the water freezing process was observed. In order to study artificial aging of Gioia marble, up to 60 freeze/thaw cycles were performed. No significant changes in the thermophysical properties of Gioia marble were observed during the artificial aging process.

DNA hybridization detection on electrical microarrays using coulostatic pulse technique

We demonstrated a novel application of transient coulostatic pulse technique for the detection of label free DNA hybridization on nm-sized gold interdigitated ultramicroelectrode arrays (Au-IDA) made in silicon technology. The array consists of eight different positions with an Au-IDA pair at each position arranged on the Si-based Biochip. Immobilization of capture probes onto the Au-IDA was accomplished by self-assembling of thiol-modified oligonucleotides. Target hybridization was indicated by a change in the magnitude of the time dependant potential relaxation curve in presence of electroactive Fe(CN)(6)(3-) in the phosphate buffer solution. While complementary DNA hybridization showed 50% increase in the relaxation potential, the non-complementary DNA showed a negligible change. A constant behaviour was noted for all positions. The dsDNA specific intercalating molecule, methylene blue, was found to be enhancing the discrimination effect. The changes in the relaxation potential curves were further corroborated following the ELISA like experiments using ExtraAvidine alkaline phosphatase labelling and redox recycling of para-aminophenol phosphate at IDAs. The coulostatic pulse technique was shown to be useful for identifying DNA sequences from brain tumour gene CK20, human herpes simplex virus, cytomegalovirus, Epstein-Barr virus and M13 phage. Compared to the hybridization of short chain ONTs (27 mers), the hybridization of long chain M13 phage DNA showed three times higher increase in the relaxation curves. The method is fast enough to monitor hybridization interactions in milli or microsecond time scales and is well suitable for miniaturization and integration compared to the common impedance techniques for developing capacitative DNA sensors.