Pressure transient analysis for asymmetrically fractured wells in dual-permeability organic compound reservoir of hydrogen and carbon

In this paper, a comprehensive semi-analytical model was presented to investigate pressure transient behavior for asymmetrically fractured wells in organic compound reservoir of hydrogen and carbon with dual-permeability behavior. Stehfest inversion algorithm can be used to transform it back into time domain to obtain pressure solution. The presented solution was validated well with numerical solutions. Flow characteristics for asymmetrically fractured wells in dual-permeability organic compound reservoir of hydrogen and carbon were divided into five regime. The effects of some important parameters on dimensionless pressure and its derivative curves were analyzed in details, including inter-porosity flow coefficient from matrix to natural fractures λ, storage coefficient ω, fracture asymmetry factor θ and permeability ratio κ. The presented model can be used to predict production performance and do well test analysis in the development of dual-permeability organic compound reservoir of hydrogen and carbon.     

Single phase transformerless wide range ac boost voltage regulator based on z-source network

This paper proposes a new type of voltage regulator based on single-phase z-source converter that compensates wide range voltage variations. This is not only capable of compensating variations at a much higher bandwidth but also boost the voltage level even twice that of input supply. The proposed system employs a pulse width modulation (PWM) z-source ac–ac converter along with a simple closed loop control. The input rms voltage can be sensed and divided by the desired value to find the instantaneous value of gain, which mathematically calculates the possible duty ratio of PWM switching signal based on the open loop characteristics of the converter. High speed IGBTs are used as bi-directional switch of the ac–ac converter and the circuit ultimately can easily and steadily maintain regulated voltage supply to the end user. The whole system operating principle and analysis are provided. Simulation results show the improvement of voltage disturbances both in voltage rise and fall conditions.     

Adaptive noise cancellation based on EMD in water-supply pipeline leak detection

In water-supply pipeline leak detection and location, both the leak signals and blurred noises are closely related to the pipeline states and surroundings and most of the conventional noise-cancellation methods have to depend on the empirical parameters of either signals or noises. EMD (Empirical Mode Decomposition) is an adaptive signal decomposition method and is exclusive of base functions. A signal is decomposed into several IMFs (Intrinsic Mode Functions) in EMD, then the noise in a signal can be cancelled through removing uncorrelated IMFs. The existing EMD noise cancellation methods need to know the characteristics of either the wanted signal or the noise for rebuilding the noise-removed signal. However the characteristics of leak signals and noises are not fixed in various pipeline conditions, so the existing EMD noise cancellation methods can’t be directly applied in water-supply pipeline leak detection. This paper proposes an adaptive noise cancellation method based on EMD, in which the IMFs that don’t or less contain the components related to the leak can be removed through the cross-correlation between the IMFs and another signal collected at the either side of a suspect leak. In simulation analysis, the adaptive noise cancellation method can increase the SNRs (Signal to Noise Ratios) of leak signals as high as 16 dB. In processing practical pipeline vibro-acoustic signals, with the proposed method the peak of adaptive time delay estimate of leak signals, which determines the location of a leakage, becomes more distinguished, and thus the error of leakage location is improved.     

Co-adsorption behaviors of asphaltenes and different flow improvers and their impacts on the interfacial viscoelasticity

Commonly used flow improvers in oilfields, such as ethylene–vinyl acetate copolymer (EVA), poly(octadecyl acrylate) (POA), and polymethylsilsesquioxane (PMSQ) are proven to be effective to enhance the flowability of crude oil. However, the addition of these flow improvers may change the stability of the emulsion and make the crude oil treatment process challenging. In this research, the impacts of different flow improvers on the interfacial properties of the emulsions containing asphaltenes are systematically investigated. The co-adsorption behaviors of the flow improvers and asphaltenes are analyzed through dynamic interfacial tension (DIFT). The rheological properties of the interfacial layer after the adsorption are explored via dilational viscoelasticity. Significant difference is observed in the structural properties of the interface adsorbed by different flow improvers, which is attributed to different interactions between the flow improvers and asphaltenes. To investigate these interactions, conductivity, asphaltenes precipitation, dynamic light scattering (DLS), and contact angle experiments are conducted systematically. Results show that EVA and POA can alter the interfacial properties by changing the asphaltene dispersion state. The interaction between EVA and asphaltenes is stronger than that between POA and asphaltenes due to the difference in molecular structures. Unlike EVA and POA, the change of interfacial property with the addition of PMSQ is attributed to the partial adsorption of asphaltenes on PMSQ.     

Metal doped black phosphorus/molybdenum disulfide (BP/MoS2–Y (Y: Ni,Co)) heterojunctions for the photocatalytic hydrogen evolution and electrochemical nitrite sensing applications

Recently, 2D semiconductor-based heterojunctions emerge as a focal point of intensive research owing to their unique properties, including efficient charge separation and large interface areas. Herein, Ni or Co-doped black phosphorus/molybdenum disulfide (BP/MoS₂–Y (Y: Ni, Co)) heterojunctions fabricate for photocatalytic H₂ evolution and electrochemical nitrite sensor. Compared to the BP/MoS₂, the BP/MoS₂–Ni and BP/MoS₂–Co exhibit enhanced H₂ performance, as 6.4139 mmol h⁻¹ g⁻¹ and 7.4282 mmol h⁻¹ g⁻¹, respectively, in the presence of Eosin-Y (λ ≥ 420 nm). Furthermore, BP/MoS₂–Co applies as an electrocatalyst on a GCE for the electrochemical detection of nitrite. To optimize the nitrite sensing performance of BP/MoS₂–Co, the effect of the pH, amount of material, scan rates, and other conditions study in detail. The BP/MoS₂–Co displays a linear response within the range of 100–2000 μM with a detection limit of 4.1 μM for DPV. This work can offer an opportunity for hydrogen systems as well as electrochemical sensor applications.     

Optical efficiency analysis of cylindrical cavity receiver with bottom surface convex

The bottom surface of conventional cavity receiver cannot be fully covered by coiled metal tube during fabrication, which would induce a dead space of solar energy absorption. The dead space of solar energy absorption can severely decrease the optical efficiency of cavity receiver. Two new types of cavity receiver with bottom surface convex are put forward with the objective to solve the problem of dead space of solar energy absorption and improve the optical efficiency of cavity receiver. The optical efficiency and heat flux distribution of the two new types of cavity receiver are analyzed by Monte Carlo ray tracing method. Besides, the optical efficiency comparisons between conventional cavity receiver and the two new types of cavity receiver are conducted at different characteristic parameter conditions.     

Analysis of laminar heat transfer in micro-Poiseuille flow

The present study examines laminar forced convective heat transfer of a Newtonian fluid in a microchannel between two parallel plates analytically. The viscous dissipation effect, the velocity slip and the temperature jump at the wall are included in the analysis. Both hydrodynamically and thermally fully developed flow case is examined. Either the hot wall or the cold wall case is considered for the two different thermal boundary conditions, namely the constant heat flux (CHF) and the constant wall temperature (CWT). The interactive effects of the Brinkman number and the Knudsen number on the Nusselt numbers are analytically determined. Different definitions of the Brinkman number based on the definition of the dimensionless temperature are discussed. It is disclosed that for the cases studied here, singularities for the Brinkman number-dependence of the Nusselt number are observed and they are discussed in view of the energy balance.     

Dimethyl ether (DME) as an alternative fuel

With ever growing concerns on environmental pollution, energy security, and future oil supplies, the global community is seeking non-petroleum based alternative fuels, along with more advanced energy technologies (e.g., fuel cells) to increase the efficiency of energy use. The most promising alternative fuel will be the fuel that has the greatest impact on society. The major impact areas include well-to-wheel greenhouse gas emissions, non-petroleum feed stocks, well-to-wheel efficiencies, fuel versatility, infrastructure, availability, economics, and safety. Compared to some of the other leading alternative fuel candidates (i.e., methane, methanol, ethanol, and Fischer–Tropsch fuels), dimethyl ether appears to have the largest potential impact on society, and should be considered as the fuel of choice for eliminating the dependency on petroleum.DME can be used as a clean high-efficiency compression ignition fuel with reduced NO_x, SO_x, and particulate matter, it can be efficiently reformed to hydrogen at low temperatures, and does not have large issues with toxicity, production, infrastructure, and transportation as do various other fuels. The literature relevant to DME use is reviewed and summarized to demonstrate the viability of DME as an alternative fuel.