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Laminar flow of fluids is one of the most common forms of motion in oilfield practice. In such a flow regime of fluid, the determination of velocity-flow rate performance which takes into account the rheological properties of the fluid is of great importance for the development of hydraulic criteria. On the other hand, from the moment of the beginning of fluid motion in the pipe, a certain time is required to ensure the steady flow of fluid, i.e. independence of its parameters on time. The issues of diagnosing steady-state characteristics in laminar flow of both Newtonian and non-Newtonian fluids are of particular relevance. In this paper, the velocity distribution along the cross-section of a pipe in laminar flow of Newtonian and non-Newtonian fluids is studied while taking into consideration rheological factors, and the change of flow rate is investigated. Determination of the time of transition to the steady-state flow regime and parameters affecting the variation of this time are shown.

This paper presents several series of multi-stage permeability tests in laboratory with both steady-state and pulse decay methods on core samples of the low permeable Callovo-Oxfordian claystone from Meuse/Haute-Marne (France). The focus is to explain why water permeability values obtained in laboratory with the steady-state method are lower than those obtained with the pulse decay method and those obtained in situ in the Underground Research Laboratory designed for a feasibility of a deep geological repository of radioactive waste. The focus is also to assess the influence of the percolating water chemistry and the duration of resaturation and steady flow stages on the permeability values, and the impact of these permeability measurements on the mechanical properties (elastic coefficients, peak strength). The water permeability values measured with the pulse decay method are homogeneous and around 10−20 m2. Those obtained with the steady flow method are significantly lower (up to one order of magnitude) when using the synthetic water of ANDRA. This difference can be explained by an additional hydration of the clay minerals during steady-state flow which induces a swelling and then a decrease of the interparticle porosity. These physicochemical mechanisms slow down the water flow during the steady flow tests. When using a chemically balanced water and reducing the test duration, the difference is only about half an order of magnitude. Sample resaturation and steady-state flow induce a significant damage of the material which is mainly due to the opening of the bedding planes of swelling clay minerals. HighlightsLaboratory permeability tests with steady state and pulse decay methods were performed on core samples of Callovo-Oxfordian claystone from Meuse/Haute-Marne (France)Permeability values measured with the steady flow method are significantly lower than those obtained from the pulse decay method when using the synthetic water of ANDRAThis difference could be explained by an additional hydration of the clay minerals during steady state flow, which induces swelling and slows down the water flowA more accurate assessment of the permeability with the steady state method was obtained using a chemically balanced water and experiment with shorter run timeInitial resaturation and steady state flow induce a significant damage of the material which is mainly due to the opening of the bedding planes of swelling clay minerals

The rheological properties and limited flow velocities of solvent-free nanofluids are crucial for their technologically significant applications. In particular, the flow in a solvent-free nanofluid system is steady only when the flow velocity is lower than a critical value. In this paper, we establish a rigid-flexible dynamic model to investigate the existence of the upper bound on the steady flow velocities for three solvent-free nanofluid systems. Then, the effects of the structural parameters on the upper bound on the steady flow velocities are examined with the proposed structure-preserving method. It is found that each of these solvent-free nanofluid systems has an upper bound on the steady flow velocity, which exhibits distinct dependence on their structural parameters, such as the graft density of branch chains and the size of the cores. In addition, among the three types of solvent-free nanofluids, the magnetic solvent-free nanofluid poses the largest upper bound on the steady flow velocity, demonstrating that it is a better choice when a large flow velocity is required in real applications.

The Periyar River, a vital component of Kerala's ecosystem in India, serves as a lifeline supporting agriculture, hydropower generation, and ecological equilibrium. This study adopts a multifaceted approach to address critical challenges in the Periyar basin, with a primary focus on flood mitigation due to the region's susceptibility to devastating floods. Covering a length of 67.85 km, the study intricately segments the Periyar River into distinct reaches for a comprehensive steady flow analysis, considering factors such as seasonal monsoon fluctuations, diverse catchment topography, and human-induced alterations. Utilizing advanced modeling techniques, particularly HEC-RAS software, the study effectively predicts and simulates shifts in hydraulic behavior. The results, including velocity plots and cross-sectional maps, offer accurate insights into critical parameters, enabling the identification of areas with high velocity occurrence. This information proves instrumental in making informed decisions for the construction of river restoration structures, crucial for mitigating the impact of floods. The study's findings contribute valuable tools for future forecasting and sustainable management of the Periyar River, addressing the complex interplay of natural and anthropogenic factors.

This work extends the steady flow Lenoir cycle within finite-time thermodynamics (FTT) by incorporating heat transfer irreversibilities through the ε−NTU formalism and a non-isentropic expansion modeled via the expander isentropic efficiency ηE. The total conductance UT (sum for the two heat exchangers) is partitioned between hot and cold units using uL=UL/UT, with UT=UH+UL. For each triplet (τ=TH/TL, UL, UT), we closed the cycle by determining T1, the working fluid temperature at the cooler outlet and heater inlet, T2, the heater outlet and expander inlet, and T3, the expander outlet and cooler inlet. Using these states, we compute the heat rates Q˙12, Q˙31 and the net power P. In addition to the thermal efficiency η, the following extended objective functions are evaluated: the efficient power EF, the ecological efficiency ϕ, and the second law efficiency ηII. Parametric sweeps on uL for τ ϵ 3.25,3.75 and UT ϵ 2.5,5.0,7.5,10 kW show unimodal curves for P(uL) and maxima. A robust result places the optima of P, η, EF, ϕ, and ηII in a distribution band at uL~0.6. This guideline offers clear design guidance for allocating exchange area in heat recovery and microgeneration, maximizing power, high η, and exergetic utilization with contained entropic penalty.

Exergy efficiency is a measure of thermodynamic perfection. A device that operates reversibly has an exergy efficiency of 100 percent and is said to be thermodynamically perfect. A reversible process involves zero entropy generation and thus zero exergy destruction since Xdestroyed = T0Sgen. Exergy efficiency is generally defined as the ratio of exergy output to exergy input ηex = Xoutput/Xinput = 1 − (Xdestroyed + Xloss)/Xinput or the ratio of exergy recovered to exergy expended ηex = Xrecovered/Xexpended = 1 − Xdestroyed/Xexpended. In this paper, exergy efficiency relations are obtained first for a general steady-flow system using both approaches. Then, explicit general relations are obtained for common steady-flow devices, such as turbines, compressors, pumps, nozzles, diffusers, valves and heat exchangers, as well as heat engines, refrigerators, and heat pumps. For power and refrigeration cycles, five different forms of exergy efficiency relations are developed, and their equivalence is demonstrated. With the unified approach presented here and the insights provided, the controversy and confusion associated with different exergy efficiency definitions are largely alleviated.

In the present work, a review for the methodologies that have been proposed to calculate the main soil hydraulic properties, hydraulic conductivity (K) and sorptivity (S), at negative pressure heads near to saturation of the soil using a tension infiltrometer is presented. These hydraulic properties can be calculated either from the analysis of steady flow or from early time observations. In particular, the main steady state methods described here are those of Ankeny et al., Reynolds and Elrick, and White and Sully, which are all based on Wooding’s equation. As for the transient flow, the approaches of Haverkamp et al. (complete, two-, three-, four-, five-terms expansions), Zhang and two different linearization methods are examined for the estimation of S and K. Generally, in steady state methods studied, a sequence of pressure heads is applied on the same disc (Ankeny et al., Reynolds and Elrick) or a unique pressure head is applied on a single disc radius (White and Sully), while in transient methods, a unique pressure head is applied on a single disc radius (Zhang and Haverkamp et al.). The conditions of their application and the way of calculating the soil parameters included into each method are critically commented. This gives to the researchers the opportunity to choose the appropriate method and a way to analyze the experimental data.

An intelligent modelling method driven by flow field images for predicting steady and unsteady flow filed around aerofoils has been developed. Signed Distance Field (SDF) images achieve dimensionality enhancement of aerofoil geometric information, and ‘synthesised images’ achieve dimensionality enhancement of the angle of attack of the aerofoil and Mach number. An intelligent aerodynamic model for steady flow field of aerofoils is constructed based on the U-Net neural network architecture, and further incorporating a long short-term memory (LSTM) module to construct a U-Net-LSTM neural network architecture to extract the temporal features. Typical NACA aerofoils results show that, the prediction error for steady flow is less than 1.98%, while the prediction error for unsteady flow is less than 2.56%. Additionally, the model demonstrates good generalization capability, with a generalization error for steady flow less than 2.45% and a generalization error for unsteady flow less than 3.34%. This research provides a new method for intelligent aerodynamic modelling based on physical representations. Compared to existing methods, this method avoids the need for extracting aerofoil geometry information and eliminates the necessity of predicting the flow field point by point, making it more concise and efficient. Highlights 1. An aerodynamic model was constructed using U-Net to rapidly predict the steady flow field around airfoils. 2. A Long Short-Term Memory (LSTM) module was incorporated to capture temporal information, enabling the rapid prediction of the unsteady flow field around airfoils. To address the problem of ‘dimension loss’ in the modelling datasets, effective data dimensionality enhancement was achieved using SDF images and ‘synthesized images’.

This paper presents the design optimization of a heat exchanger for a free-piston Stirling engine (FPSE) through an improved quasi-steady flow (iQSF) model and a central composite design. To optimize the tubular hot heat exchanger (HHX) design, a design set of central composite designs for the design factors of the HHX was constructed and the brake power and efficiency were predicted through the iQSF model. The iQSF model is improved because it adds various heat and power losses based on the QSF model and applies a heat transfer model that simulates the oscillating flow condition of an actual Stirling engine. Based on experimental results from the RE-1000, an FPSE developed by Sunpower, the iQSF model significantly improves the prediction error of the indicated power from 66.9 to 24.9% compared to the existing QSF model. For design optimization of the HHX, the inner diameter and the number of tubes with the highest brake power and efficiency were determined using a regression model, and the tube length was determined using the iQSF model. Finally, the brake output and efficiency of FPSE with the optimized HHX were predicted to be 7.4 kW and 36.4%, respectively, through the iQSF analysis results.

Floods can cause widespread devastation, resulting in loss of life and damages to personal property and critical public health infrastructure. River flooding is the most common type of flooding in many parts of the world. It occurs when a water body exceeds its capacity to hold water and usually happens due to prolonged heavy rainfall. The one-dimensional (1-D) hydrodynamic model is used to evaluate the geomorphic effectiveness of floods on the Ambica river basin, South Gujarat region. The study region was subjected to frequent flooding. Major flood event occurred in the year 1981, 1984, 1994, 1997, 2001, 2003, 2004, 2006, 2013 and 2014. In the present study, the geometry of the Ambica river, floodplain of Unai, and past flood data have been used to develop a 1-D hydrodynamic model using HEC-RAS (6.0.0)software. After collecting the required data, the 1-D hydrodynamic model has been developed to simulate the floods of the years 1984 and 1994. The segment of the Ambica river reach with approximately 9 km length between Padam Dungari to Sidhai village is selected for analysis. The study area consists of 23 cross-sections. The model is used to evaluate steady flow analysis, flood conveyance performance, and uniform flow analysis. The outcome obtained from the model is in the form of water depth and water surface elevation. Based on the above results, it shows that the low-lying areas of Navsari city are susceptible to flooding when the discharge in the river exceeds 6500 m 3 /s. This study can be utilised for disaster management, flood management, early warning system by authorities in addition to infrastructure growth decisions.