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In modeling the characteristics of a cartridge valve with traditional methods, it is commonly required to determine the value of flow area and other coefficients such as discharge coefficient and jet angle, etc. However, these parameters often rely heavily on empirical or experimental data and often involve some uncertainties, especially with the variation of the spool displacement (valve opening). To avoid these uncertainties, this paper proposes a modeling method which calculates spool force and flow rate directly through the distribution of fluid field. Transient 3D flow field simulation with dynamic mesh technique is conducted using commercial code FLUENT, and Proper Orthogonal Decomposition (POD) method is introduced to simplify fluid field data. The results showed that the POD method can capture the main features of the fluid field while significantly reducing the amount of data. With reconstructed pressure field and velocity field, spool force and flow rate can be calculated directly without using traditional formulas which contain uncertain coefficients. Valve characteristics calculated with this method agree with Computational Fluid Dynamics (CFD) and experimental data well, which confirms the validity and effectiveness of this method. [ABSTRACT FROM AUTHOR]

The dominant phenomenon in laser welding processes is heat transfer by conduction, making it crucial to gain insights into energy distribution within the heat-affected region, including the melt pool. Thermal analysis enables the description of thermo-mechanical, metallurgical aspects, and also addresses studies related to fluid flow and energy transfer. As research in welding processes has advanced, these models have evolved. This is why it is now efficient to use computational modeling techniques as it allows us to analyze the behavior of laser welding during the process. This underlines the importance of this work which has carried out an exhaustive theoretical literature review with the objective of classifying and describing the numerical simulations of laser welding based on the physics involved. In that sense, the mathematical models and strategies used in laser welding are explored in a general way. Therefore, two types of laser welding by conduction and deep penetration are defined from this point and they are categorized according to the phenomena involved in Model Heat Conduction and Model Integral Multiphysics. This comprehensive review article serves as a valuable resource for higher education students by providing a structured and detailed exploration of laser welding and its mathematical modeling. By classifying and describing numerical simulations based on the physics involved, it offers a framework for students to understand the complexities of this field. Additionally, this innovative approach to organizing and presenting research contributes to educational innovation by facilitating a more efficient and effective learning experience, helping students acquire the knowledge and research skills necessary for advancements in the laser welding domain. [ABSTRACT FROM AUTHOR]

In this paper, a numerical model describing the heat transfer and air flow inside and outside the casing of the permanent magnet brushless direct current (PM BLDC) motor is presented. In the model, a conjugate heat transfer including the heat conduction with heat sources in windings, magnets, bearings, natural and forced convection and radiation phenomena within internal and external air domain were analysed. The complex geometrical model included windings, a magnet circuit, a rotor with neodymium magnets, a PCB electronic plate, plastic covers, internal air between solid parts as well as a portion of the external air. The validation process of the developed model was realised on the basis of the velocity and temperature fields. The experimental data were recorded by 7 constant temperature anemometers at 4 levels above the motor housing, Laser Doppler Anemometry sensors in two axes inside the rear portion of the motor and 25 thermocouples fixed inside and outside the motor. The experimental and numerical tests were performed for 4 motor loadings and 3 rotational speeds. The average temperature error for the internal point was of 9 K, while that of the external points was of 2 K. The velocity field was very well predicted close to the housing wall in terms of horizontal and vertical components. A slightly worse agreement was found for the vertical component, especially in the vicinity of the shaft. The results were consistent for all the considered motor loadings and rotational speeds. [ABSTRACT FROM AUTHOR]

The project reported in this paper used CFD as a tool to investigate the effect of multi-pass on the shell side heat transfer of a heat exchanger system. The heat exchanger system is equipped with six vertical thermosyphons transferring thermal energy from a heat source (air) to a heat sink (water). The CFD model has been experimentally validated. The two-phase change processes inside the thermosyphons were not modelled during the simulation. Instead, the thermosyphons were treated as solid rods with a constant thermal conductivity, which was calculated theoretically by applying the thermal resistance analogy with the aid of convection, boiling and condensation correlations found in the literature. The heat source consists of multiple air passes on the evaporator section of the thermosyphons and two water passes on the condenser section. Three different arrangements on the evaporator section were investigated with one, two or three shell passes and the thermal performance compared for the three configurations. The investigation was performed at various inlet conditions: a range of air inlet temperatures (100, 150, 200 and 250 °C) and mass flow rates (0.05, 0.08, 0.11 and 0.14 kg/s). The water inlet conditions were kept constant (a temperature of 15 °C and a mass flow rate of 0.08 kg/s). The overall rate of heat transfer was obtained by both CFD and a theoretical model, and the results lay within 15% of the experimental data. The numerical predictions demonstrated that the k − ε Realizable turbulence model is a reliable tool for predicting heat transfer and fluid flow in such heat exchangers. [ABSTRACT FROM AUTHOR]

High temperature heat pipes offer an efficient way of heat removal in nuclear reactors under both normal operation and postulated accidental scenarios. Heat pipes with sodium as a working fluid has been proposed to be used in Compact High Temperature Reactor (CHTR), 233 U-Thorium fuelled reactor being designed to operate at 1000 °C. High temperature heat pipes can also be used for decay heat removal from dump tanks of molten salt breeder reactor and heat removal from first wall of fusion reactors. High temperature heat pipes of special construction can also be used for heat removal from core without use of coolant. Thus, reliable and long term operation of heat pipes is essential for the safe working of the reactor. In this respect, computer codes have been developed for design and simulation of high temperature heat pipes. To assist in the design stages, codes have been developed, which incorporate performance limits based on correlations and having a user friendly GUI. For system level studies, simplified heat transfer model is developed using a FEM model. For a detailed study of the heat pipe, the vapour flow behavior and interface evaporation condensation phenomena using a full CFD analysis is essential. This has been done by using a commercial CFD code by incorporating user defined functions (UDFs) which address the saturated nature of the vapour phase and the vapour wick interface conditions. A three dimensional transient numerical model has been developed to predict the vapour core, wall temperatures, vapour pressure, and vapour velocity in the screen mesh wick of sodium heat pipe. The results have been compared using a sodium heat pipe developed in-house. This paper will give an outline of all the developed models and compared the predicted results against the experimental data. [ABSTRACT FROM AUTHOR]

Nanofluids have gained significant attention in recent years due their great potential for heat transfer enhancement . The heat transfer of nanofluids can be numerically studied using a single-phase or two-phase approaches. The first assumes that the fluid phase and nanoparticles are in thermal equilibrium and move with the same velocity, while the second requires more computational effort but provides the possibility of understanding the behavior of both fluid phase and solid particles in the heat transfer mechanism. This paper reviews various computational approaches to predict fluid flow and heat transfer characteristics of nanofluids. The characteristics of single-phase and two-phase (volume of fluid, mixture, Eulerian–Lagrangian and Eulerian–Eulerian) approaches have been analyzed and discussed systematically. Latest development and recent researches related to the computational nanofluids are also given. [ABSTRACT FROM AUTHOR]

The mathematical model has been developed to describe the hydrodynamics of supercritical fluid flow in the reactor, heat, and mass transfer during drying processes for aerogels production. The model is based on the provisions of continuum mechanics, and Ansys Fluent is used for its calculation. In this research, the medium inside the reactor is considered as homogeneous two-component compressible viscous fluid, which is described by Peng–Robinson equation of state. In this paper we consider the model of supercritical drying process. A considerable part of the mathematical model is description of the fluid flow inside the porous body (aerogel), where only diffusive transport of substance occurs. The model is used to scale-up the supercritical drying process; the reactor geometry and process parameters optimization in order to intensify the production process, achieve desired properties of aerogels. The geometry of 5 l reactor is proposed and studied using the developed model. [ABSTRACT FROM AUTHOR]

This article describes the studies’ results aimed at the gas turbine combined cycle (CCGT) with the pressurized heat recovery steam generator (PHRSG) modernization scheme for the existing steam-power unit. It is shown that this scheme meets the energy development program's formal requirements. It reduces the reconstruction costs due to the equipment parts preservation. The heat transfer study has shown the possibility of heat exchange process simulation with boiler designer software. It was shown that the optimal flue gas pressure in PHRSG is 4–5 bar. Raising the flue gas pressure up to this level gives the largest increase in heat transfer coefficient. The greatest decrease in metal consumption occurs in the same area. The inlet velocity range from 10 to 20 m/s is optimal in this scheme. Several modernization schemes for popular Russian T-100 and K-300 steam turbines and GTE-160 and GT-25PA gas turbines are presented. The promising equipment unification potential of these schemes is shown. Several challenging schemes based on the researched scheme are proposed. [ABSTRACT FROM AUTHOR]

Abstract: In this paper, the improved heat flux partitioning model based on first principal models of the underlying physics in determining the active nucleation site density, bubble size and bubble frequency is evaluated for subcooled flow boiling in vertical heated channels at low pressures. Salient features of this model include the fractal approach in determining the active nucleation site density, the force balance model in determining bubble diameters at sliding and lift-off as well as bubble frequency through the consideration of growth and waiting times and the additional heat flux at the heated wall due to surface quenching of sliding bubbles. Model predictions, covering a wide range of different mass and heat fluxes and inlet subcooling temperatures, are compared against local and axial measurements. In comparison to the measured data and selected combinations of empirical correlations such as described in Part 1, the current model predictions clearly demonstrate the effect of the subcooling effect on the activation of nucleation sites at the heated wall. The selected combinations of empirical correlations consistently under-estimate the wall superheat temperature while the current model yields predictions that agree very well with experimentally measured temperatures. Bubble sliding along the heat wall and its influence on heat partitioning and surface quenching heat flux has been ascertained to play an important role during the subcooled flow boiling process. [Copyright &y& Elsevier]

Fine powders in the size range of 20-200 μm are widely used in industries for fluid bed operations and are ideal for gas-solid reactions because of their large external surface areas and favorable heat transfer rates. The fine powders have very poor flow characteristics. Most of the earlier research work in heat transfer in bubbling fluidized beds is focused on coarse grained Geldart B and D particles. Acoustic energy of sufficient intensity and sound pressure level improved the quality of fluidization of fine powders. The objective of this investigation is experimental analysis and CFD simulations for heat transfer in a fluidized bed of fine powders at different acoustic conditions. The Eulerian approach has been identified as an efficient method for the numerical simulation of fluidized beds. The experimental and CFD results are in good agreement with each other. [ABSTRACT FROM AUTHOR]

The properties of plasma-sprayed coatings are controlled by the heat, momentum, and mass transfer between individual particles and the plasma jet. The particle behavior in conventional single-arc plasma spraying has been the subject of intensive numerical research, whereas multi-arc plasma spraying has not yet received the same attention. We propose herein a numerical model to serve as a scientific tool to investigate particle behavior in multi-arc plasma spraying. In the Lagrangian description of particles in the model, the mathematical formulations describing the heat, momentum, and mass transfer are of great importance for good predictive power, so such formulations proposed by different authors were compared critically, revealing that different mathematical formulations lead to significantly different results. The accuracy of the different formulations was evaluated based on theoretical considerations, and those found to be more accurate were implemented in the final model. Furthermore, a mathematical formulation is proposed to enable simplified calculation of partial particle melting and resolidification. [ABSTRACT FROM AUTHOR]

A comprehensive mathematical model has been developed to analyze transport phenomena in wetted wall absorption reactors. In this regard, a wetted wall reactor was modelled considering the entrance regions of momentum, heat and mass transfer, compressibility of the gas phase as a function of gas temperature, pressure, and composition, and also non-Newtonian behaviour of the liquid phase. In the developed model, a gas mixture of two components, A and B, was considered as the gas phase ( A as the diffusing component), while a binary liquid mixture of components C and D was taken as the liquid phase ( C as the reactant component). CFD methods were applied to solve nonlinear governing equations simultaneously and the simulation results were validated against experimental data reported in the literature and excellent agreement was found. Moreover, distributions of velocity, temperature, and species concentrations of both phases were obtained and the effects of various operating conditions and physicochemical properties on these distributions were carefully studied. Furthermore, the open-loop response of the reactor to some typical step and pulse inputs was examined. Moreover, the closed-loop response of the reactor was also examined; in this regard, a PI controller was designed to control the reactor's output properly. [ABSTRACT FROM AUTHOR]