Dimensionless Conduction Heat Rate Models for Cyclic Heating/Cooling of Spheres, Cylinders, Plane Walls, and TPMS Solids

Importance of gravity and friction on the targeted energy transfer of vibro-impact nonlinear energy sink

The Fetkovich decline curve analysis method was extended for application to vapor-dominated geothermal reservoirs to estimate the permeability-thickness product (kh) from a well's transient production response. The analytic dimensionless terms for pressure, steam flowrate, decline rate, and decline time were derived for saturated steam using the real gas pseudopressure and customary geothermal production units of pounds-mass per hour. The derived terms were numerically validated using "Geysers-like" reservoir properties at permeabilities of 1, 10, and 100 mD and at a range of initial matrix liquid saturations from 0 to 100%. The rate-time responses collapsed onto a single set of curves using the derived dimensionless terms, validating the derived dimensionless equations. This collapse was accomplished by including the effective compressibility of a boiling liquid or by an alternative formulation considering an apparent time. This technique was applied to actual field production data at The Geysers, California, the world's largest developed geothermal, vapor-dominated reservoir. The production data for over 100 wells in the southeast Geysers were analyzed and the permeability-thickness products determined by application of the derived analytic dimensionless terms and the Fetkovich production decline type curve. Introduction Reservoir engineering studies of The Geysers are hampered by a lack of formation evaluation techniques typically used to characterize hydrocarbon reservoirs. An improved method is needed for an understanding of the reservoir permeability distribution and to develop a better conceptual reservoir description and numerical model. The goal of this study is to extend the Fetkovich production decline method to vapor-dominated geothermal reservoirs using customary geothermal production mass units with particular emphasis on the transient production response for the determination of the kh. Analytic expressions for dimensionless pressure, dimensionless production rate, dimensionless decline time, and dimensionless decline rate are derived for saturated steam in a porous media. A "Geysers-like" numerical model is used to validate the analytic terms. The derived dimensionless expressions are applied to a set of wells located in the southeast Geysers to demonstrate the practical utility of this approach for estimating permeability-thickness from the transient production response and the identification and quantification of interference effects. Literature Review Production decline curve analysis has been used at The Geysers since 1969 when Ramey demonstrated through the use of material balance calculations, the p/z method modified for geothermal reservoirs, and production decline curve analysis, that The Geysers shallow steam reservoir was undergoing depletion. Empirical rate-time semi-log analysis using Arps method is the standard method used to forecast remaining steam reserves for individual wells and leases at The Geysers. Fetkovich noted that the concepts of dimensionless pressure and dimensionless time, used in pressure transient analysis, could be used to analyze the transient production response of a well. A dimensionless production rate was defined as the reciprocal of dimensionless pressure. Two additional terms were defined; the dimensionless decline time and the dimensionless decline rate. These two terms were combined to completely describe the transient production response and the depletion or pseudo-steady state period of a well producing at a constant pressure. P. 139^

Chaos and voltage collapse are qualitative behaviors in power systems that exist due to lack of reactive power in critical loading. These phenomena are deeply explored using both detailed and approximate models in this paper. The ANFIS-based CC-SVC with an additional PID-loop was proposed to control these problems and to improve transient response of the detailed model. The main function of the PID-loop was to increase the minimum voltage and to decrease the settling time at transient response. The ANFIS-based method was chosen because its computational complexity was more efficient than Mamdani fuzzy logic controller. Therefore the convergence of training processes was more rapidly achieved by the ANFIS-based method. The load voltage was held to the setting value by adjusting the SVC susceptance properly. From the experimental results, the PID-loop was an effective controller which achieved good simulation result for the reactive load, the minimum voltage increased and the settling time decreased at the values of j0.12pu, 0.9435pu and 7.01s, respectively.

Potential of a vibro-impact nonlinear energy sink for energy harvesting

Triply periodic minimal surface (TPMS) structures are widely used in scaffold design for biomaterials due to their excellent porous architecture and mechanical properties. This study utilized selective laser melting (SLM) to fabricate TPMS scaffold models with porosities of 50%, 60%, 70%, and 80%, based on Gyroid and Primitive unit cells. Compression tests were conducted to investigate the changes in mechanical properties of TPMS scaffolds before and after heat treatment. The mechanisms underlying these changes were elucidated through fracture morphology analysis, microstructural observation, and finite element simulation. Results indicate that Gyroid porous scaffolds exhibit superior compressive performance compared to Primitive scaffolds, with yield strength inversely related to porosity—lower porosity corresponds to higher yield strength. During compression, Primitive scaffolds exhibited a layer-by-layer stacking failure mode, whereas Gyroid scaffolds displayed a 45° shear failure mode. The Gyroid porous scaffolds showed uniform and continuous stress distribution, and heat treatment effectively relieved residual stresses, enhancing yield strength and toughness. In contrast, Primitive porous scaffolds demonstrated stress concentration regions that reach yield limits under compression, leading to fracture. Heat treatment did not alleviate these stress concentrations but instead reduced the material’s yield limit, accelerating scaffold failure.

Corrected adsorption rate model of activated carbon–ethanol pair by means of CFD simulation

The effects of a heat barrier, located in the ceiling wall of an enclosure, on conjugate conduction/natural convection are investigated numerically. The vertical walls of the enclosure are differentially heated and the horizontal walls are adiabatic. Heatline technique is used to visualize heat transport. The variations of average Nusselt number, dimensionless heat transfer rate through the ceiling wall, and dimensionless overall heat transfer rate are studied. Calculations are performed for different Rayleigh numbers (103 ≤ Ra ≤ 106), thermal conductivity ratios (1 ≤ K ≤ 100), dimensionless locations of the heat barrier (0 < X h < 1),and two dimensionless ceiling wall thicknesses (D = 0.05 and D = 0.20). For high thermal conductivity ratio (K = 100), the heat barrier considerably reduces the dimensionless overall heat transfer rate. The effect of the heat barrier on dimensionless heat transfer rate through the enclosure increases as the Rayleigh number decreases. For low Rayleigh number (i.e., Ra = 103), a location exists in the ceiling wall for which the dimensionless overall heat transfer rate is minimum.

Dynamics of two vibro-impact nonlinear energy sinks in parallel under periodic and transient excitations

Applicability of linear driving force (LDF) mass transfer model for heavy metal biosorption in packed bed column

The so-called (first-order) linear driving force (LDF) model for gas adsorption kinetics is frequently and successfully used for analysis and design of adsorptive processes because it is simple, analytical, and physically consistent. Yet, for certain operating conditions, such as cyclic adsorption and desorption, significant differences between the LDF model and the rigorous Fickian diffusion (FD) model can be found. In principle, increasing the order of the approximate LDF model can yield predictions closer to the FD model. As in the classical first-order LDF model, generalized LDF must be consistent with the physics of the FD model. This paper provides a minimal set of properties that generalized LDF models should meet in order to be physically consistent. This is done by showing that the FD model describes positive real dynamics, which are closely related to the thermodynamics of the adsorption−diffusion process. In this form, a generalized LDF model should inherit this property in order to guarantee that the main thermodynamic characteristics of the adsorption−diffusion dynamics will be retained to some extent.

Heat transfer scaling analysis of the single-phase natural circulation flow system

Improving the charging performance of latent heat thermal energy storage systems using triply periodic minimal surface (TPMS) structures

In recent times, interest in the fabrication of porous NiTi structures have grown significantly. Porous structures have remarkable potential to be used in the areas of tissue engineering, impact absorption, and fluid permeability. However, fabrication of NiTi structures poses challenges such as poor machinability, high work hardening, and inherent springback effects, which render them difficult to tackle through conventional manufacturing routes. Additive manufacturing (AM) can alleviate the aforementioned issues associated with NiTi shape memory alloys (SMAs). In addition, this technology can be employed for producing metallic scaffolds and porous structures of complex architectural details. Recently, a class of minimal surface topologies, known as triply periodic minimal surface (TPMS) structures has emerged as an attractive configuration for building architected constructs. Very little work can be found in the literature addressing the fabrication of NiTi TPMS structures and investigating their behaviors. The complex geometries of these structures may influence the dynamics of the melt pool in beam-based AM processes as well as the solidification rate within different regions of a product, thereby affecting the microstructures of fabricated parts. An inhomogeneity in microstructures of fabricated parts was observed, which motivated a detailed examination of these structures. The novelty of the present work lies in studying the influence of geometries of NiTi TPMS lattices along with laser process parameters.

This paper addresses one-dimensional transient conduction in simple geometries. It is well known that the transient thermal responses of various objects, or of an infinite medium surrounding such objects, collapse to the same behavior as a semi-infinite solid at small dimensionless time. At large dimensionless time, the temperature reaches a steady state (for a constant surface temperature boundary condition) or increases linearly with time (for a constant heat flux boundary condition). The objectives of this paper are to bring together existing small and large time solutions for transient conduction in simple geometries, put them into forms that will promote their usage, and quantify the errors associated with the approximations. Approximate solutions in the form of simple algebraic expressions are derived (or compiled from existing solutions) for use at both small and large times. In particular, approximate solutions, which are accurate for Fo&amp;lt;0.2 and which bridge the gap between the large Fo (single-term) approximation and the semi-infinite solid solution (valid only at very small Fo), are presented. Solutions are provided for the surface temperature when there is a constant surface heat flux boundary condition, or for the surface heat flux when there is a constant surface temperature boundary condition. These results are provided in terms of a dimensionless heat transfer rate. In addition, the dimensionless energy input is given for the constant surface temperature cases. The approximate expressions may be used with good accuracy over the entire Fourier number range to rapidly estimate important features of the transient thermal response. With the use of the approximations, it is now a trivial matter to calculate the dimensionless heat transfer rate and dimensionless energy input, using simple closed-form expressions.

In this work an approximate model is developed that is valid for diffusion-reaction processes and that is free of the drawbaks of earlier models. The approximate, linear driving-force (LDF) formula, which is also analogous to Gluackauf's formula, has been derived. The accuracy of the developed model is very high. Moreover, the method applied for derivation of the approximate model can be useful not only for diffusion and reaction process in porous catalysts, but also for any process that takes into account internal diffusion, adsorption, and the like.