This paper describes the fabrication of integral screen printed platinum resistance elements. A detailed description is given of the techniques of element manufacture and…
Abstract
This paper describes the fabrication of integral screen printed platinum resistance elements. A detailed description is given of the techniques of element manufacture and performance. The paper is finally illustrated by an example of sensor integration into a temperature critical subsystem. This example serves to demonstrate the potential manufacturing economies achieved by this approach.
T. Gilles, Q. Reynolds and J. Steinberg
The increasing complexity of hybrid circuits has led to a need for a reliable multilayer system. As well as reliability, the manufacturer will, of course, also attach considerable…
Abstract
The increasing complexity of hybrid circuits has led to a need for a reliable multilayer system. As well as reliability, the manufacturer will, of course, also attach considerable importance to material and production costs. Until now, thick film multilayer applications have been limited by the inability of existing technology to reduce their susceptibility to galvanic effects occurring between individual conductive layers during fabrication. Now, however, this company has developed a multilayer dielectric which prevents metal migration. The system is supported by conductor and resistor systems.
Q. Reynolds, H.G. MacMahon and J. Freitag
The powder and rheology properties of a gold and a silver thick film ink are associated with its fine line performance. Printing 100 micron lines is shown to be straightforward…
Abstract
The powder and rheology properties of a gold and a silver thick film ink are associated with its fine line performance. Printing 100 micron lines is shown to be straightforward and 75 microns is speculated as being feasible.
The purpose of this paper is to study the dimensionless characteristics of a molten salt pump and propose an approach to carry out the modeling experiment by using water instead…
Abstract
Purpose
The purpose of this paper is to study the dimensionless characteristics of a molten salt pump and propose an approach to carry out the modeling experiment by using water instead of molten salts.
Design/methodology/approach
External characteristics of the pump were estimated by using the steady flow model and compared with the experimental results. By taking water as the working fluid, the pathlines in the volute of the model pump were validated by the results obtained of high-speed photography. According to the derived dimensionless characteristics of the molten salt pump, the modeling experimental schemes were proposed. Adopting the validated numerical simulation model, the performance of the molten salt pump was studied in detail.
Findings
The modeling experimental schemes designed according to the dimensionless characteristics are theoretically feasible. However, to carry out the experiment successfully, factors such as rotational speed, geometric size, flow rate and head should be taken into account. The flow in the pumps is similar under the similar operating condition and the external characteristics of the similar pump can be converted to each other. Compared with transporting water, the decline of the head and efficiency is within 5 per cent when the viscosity is lower than 0.01453 Pa · s. The pump is not suitable for running under the critical Reynolds number of 1.0 × 107.
Originality/value
The current work revealed the relationships among the dimensionless performances of a molten salt pump and proposed a critical Reynolds number ReQcr for the pump running.
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Amir Rezazad Bari, Mohammad Zabetian Targhi and Mohammad Mahdi Heyhat
This study aims to examine the effect of a combination of hybrid pin-fin patterns on a heat sink's performance using numerical techniques. Also, flow characteristics have been…
Abstract
Purpose
This study aims to examine the effect of a combination of hybrid pin-fin patterns on a heat sink's performance using numerical techniques. Also, flow characteristics have been studied, such as secondary flow formation and flow-wall interaction.
Design/methodology/approach
In this study, the effect of hybrid arrangements of elliptical and hexagonal pin-fins with different distribution percentages on flow characteristics and performance evaluation criteria in laminar flow was investigated. Ansys-Fluent software solves the governing equations using the finite volume method. Also, the accuracy of obtained results was compared with the experimental results of other similar papers.
Findings
The results of this study highlighted that hybrid arrangements show higher overall performance than single pin-fin patterns. Among the hybrid arrangements, case 3 has the highest values of performance evaluation criteria, that is, 1.84 in Re = 900. The results revealed that, with the instantaneous change in the pattern from elliptic to hexagonal, the secondary flow increases in the cross-sectional area of the channels, and the maximum velocity in the cross-section of the channel increases. The important advantages of case 3 are its highest overall performance and a lower chip surface temperature of up to about 2% than other hybrid patterns.
Originality/value
Prior research has shown that in the single pin-fin pattern, the cooling power at the end of the heat sink decreases with increasing fluid temperature. Also, a review of previous studies showed that existing papers had not investigated hybrid pin-fin patterns by considering the effect of changing distribution percentages on overall performance, which is the aim of this paper.
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Ahmed M. Galal, Muhammad Zeemam, Muhammad Imran, Muhammad Abdul Basit, Madeeha Tahir, Saima Akram and Jihad Younis
Nanofluids are used in technology, engineering processes and thermal exchanges. In thermal transfer processing, these are used for the smooth transportation of heat and mass…
Abstract
Purpose
Nanofluids are used in technology, engineering processes and thermal exchanges. In thermal transfer processing, these are used for the smooth transportation of heat and mass through various mechanisms. In the current investigation, we have examined multiple effects like activation energy thermal radiation, magnetic field, external heat source and especially slippery effects on a bioconvective Casson nanofluid flow through a stretching cylinder.
Design/methodology/approach
Several studies used non-Newtonian fluid models to study blood flow in the cardiovascular system. In our research, Lewis numbers for bioconvection and the influence of important parameters, such as Brownian diffusion and thermophoresis effects, are also considered. This system is developed as a partial differential equation for the mathematical treatment. Well-defined similarity transformations convert partial differential equation systems into ordinary differential equations. The resultant system is then numerically solved using the bvp4c built-in function of MATLAB.
Findings
After utilizing the numerical approach to the system of ordinary differential equations (ODEs), the results are generated in the form of graphs and tables. These generated results show a suitable accuracy rate compared to the previous results. The consequence of various parameters under the assumed boundary conditions on the temperature, motile microorganisms, concentration and velocity profiles are discussed in detail. The velocity profile decreases as the Magnetic and Reynolds number increases. The temperature profile exhibits increasing behavior for the Brownian motion and thermal radiation count augmentation. The concentration profile decreased on greater inputs of the Schmidt number and magnetic effect. The density of motile microorganisms decreases for the increased value of the bio-convective Lewis number.
Originality/value
The numerical analysis of the flow problem is addressed using graphical results and tabular data; our reported results are refined and novel based on available literature. This method is useful for addressing such fluidic flow efficiently.
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The purpose of this paper is to numerically study inflow turbulence effects on the transitional flow in a high pressure linear transonic turbine at the design incidence.
Abstract
Purpose
The purpose of this paper is to numerically study inflow turbulence effects on the transitional flow in a high pressure linear transonic turbine at the design incidence.
Design/methodology/approach
The three‐dimensional (3‐D) compressible turbulent flow in a turbine inlet guide vane is simulated using a finite volume based fluid solver coupled with dynamic large eddy simulation (LES) computations to investigate the effects of varying inflow turbulence length scale and the turbulence intensity on the aero‐thermal flow characteristics and the laminar‐turbulent transition phenomena. The computational analyses are extended to very high exit Reynolds number flow conditions to further study the effect of high exit Reynolds numbers on the transitional behavior of the present flow around the inlet guide vane cascades of the turbine. The calculations are performed with varying degree of inflow turbulence intensity values ranging from 0.8 to 6 percent and the inflow turbulence length scales ranging from one to five percent of pitch for different exit isentropic Mach and Reynolds numbers.
Findings
The numerical predictions in comparison with the experimental data demonstrate that the level of inflow turbulence closure provided by the present LES computations offers a reliable framework to predict complex turbulent flow and transition phenomena in high free‐stream turbulence environments of high pressure linear turbines.
Originality/value
This is the first instance in which both artificially modified random flow generation method in association with the dynamic procedure of LES application is employed to represent the realistic inflow turbulence conditions in the high pressure turbine and to resolve the transitional flow in a dynamic approach.
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Bengt Ake Sunden, Zan Wu and Dan Huang
The purpose of this paper is to numerically investigate the heat transfer performance of aviation kerosene flowing in smooth and enhanced tubes with asymmetric fins at…
Abstract
Purpose
The purpose of this paper is to numerically investigate the heat transfer performance of aviation kerosene flowing in smooth and enhanced tubes with asymmetric fins at supercritical pressures and to reveal the effects of several key parameters, such as mass flow rate, heat flux, pressure and inlet temperature on the heat transfer.
Design/methodology/approach
A CFD approach is taken and the strong variations of the thermo-physical properties as the critical point is passed are taken into account. The RNG k-ε model is applied for simulating turbulent flow conditions.
Findings
The numerical results reveal that the heat transfer coefficient increases with increasing mass flow rate and inlet temperature. The effect of heat flux on heat transfer is more complicated, while the effect of pressure on heat transfer is insignificant. The considered asymmetric fins have a small effect on the fluid temperature, but the wall temperature is reduced significantly by the asymmetric fins compared to that of the corresponding smooth tube. As a result, the asymmetric finned tube leads to a significant heat transfer enhancement (an increase in the heat transfer coefficient about 23-41 percent). The enhancement might be caused by the re-development of velocity and temperature boundary layers in the enhanced tubes. With the asymmetric fins, the pressure loss in the enhanced tubes is slightly larger than that in the smooth tube. A thermal performance factor is applied for combined evaluation of heat transfer enhancement and pressure loss.
Research limitations/implications
The asymmetric fins also caused an increased pressure loss. A thermal performance factor ? was used for combined evaluation of heat transfer enhancement and pressure loss. Results show that the two enhanced tubes perform better than the smooth tube. The enhanced tube 2 gave better overall heat transfer performance than the enhanced tube 1. It is suggested that the geometric parameters of the asymmetric fins should be optimized to further improve the thermal performance and also various structures need to be investigated.
Practical implications
The asymmetric fins increased the pressure loss. The evaluation of heat transfer enhancement and pressure loss Results showed that the two enhanced tubes perform better than the smooth tube. It is suggested that the geometric parameters of the asymmetric fins should be optimized to further improve the thermal performance and also various structures need to be investigated to make the results more engineering useful.
Originality/value
The paper presents unique solutions for thermal performance of a fluid at near critical state in smooth and enhanced tubes. The findings are of relevance for design and thermal optimization particularly in aerospace applications.
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Ranjan Kumar Mohanty and Sachin Sharma
This paper aims to develop a new high accuracy numerical method based on off-step non-polynomial spline in tension approximations for the solution of Burgers-Fisher and coupled…
Abstract
Purpose
This paper aims to develop a new high accuracy numerical method based on off-step non-polynomial spline in tension approximations for the solution of Burgers-Fisher and coupled nonlinear Burgers’ equations on a graded mesh. The spline method reported here is third order accurate in space and second order accurate in time. The proposed spline method involves only two off-step points and a central point on a graded mesh. The method is two-level implicit in nature and directly derived from the continuity condition of the first order space derivative of the non-polynomial tension spline function. The linear stability analysis of the proposed method has been examined and it is shown that the proposed two-level method is unconditionally stable for a linear model problem. The method is directly applicable to problems in polar systems. To demonstrate the strength and utility of the proposed method, the authors have solved the generalized Burgers-Huxley equation, generalized Burgers-Fisher equation, coupled Burgers-equations and parabolic equation in polar coordinates. The authors show that the proposed method enables us to obtain the high accurate solution for high Reynolds number.
Design/methodology/approach
In this method, the authors use only two-level in time-direction, and at each time-level, the authors use three grid points for the unknown function u(x,t) and two off-step points for the known variable x in spatial direction. The methodology followed in this paper is the construction of a non-polynomial spline function and using its continuity properties to obtain consistency condition, which is third order accurate on a graded mesh and fourth order accurate on a uniform mesh. From this consistency condition, the authors derive the proposed numerical method. The proposed method, when applied to a linear equation is shown to be unconditionally stable. To assess the validity and accuracy, the method is applied to solve several benchmark problems, and numerical results are provided to demonstrate the usefulness of the proposed method.
Findings
The paper provides a third order numerical scheme on a graded mesh and fourth order spline method on a uniform mesh obtained directly from the consistency condition. In earlier methods, consistency conditions were only second order accurate. This brings an edge over other past methods. Also, the method is directly applicable to physical problems involving singular coefficients. So no modification in the method is required at singular points. This saves CPU time and computational costs.
Research limitations/implications
There are no limitations. Obtaining a high accuracy spline method directly from the consistency condition is a new work. Also being an implicit method, this method is unconditionally stable.
Practical implications
Physical problems with singular and non-singular coefficients are directly solved by this method.
Originality/value
The paper develops a new method based on non-polynomial spline approximations of order two in time and three (four) in space, which is original and has lot of value because many benchmark problems of physical significance are solved in this method.
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A. Raji and M. Hasnaoui
The interaction between mixed convection and thermal radiation in ventilated cavities with gray surfaces has been studied numerically using the Navier‐Stokes equations with the…
Abstract
The interaction between mixed convection and thermal radiation in ventilated cavities with gray surfaces has been studied numerically using the Navier‐Stokes equations with the Boussinesq approximation. The effect of thermal radiation on streamlines and isotherms is shown for different values of the governing parameters namely, the Rayleigh number (103 ≤ Ra ≤ 106), the Reynolds number (50 ≤ Re ≤ 5000) and the surfaces emissivity (0 ≤ ε≤ 1). The geometrical parameters are the aspect ratio of the cavity A = L’/H’ = 2 and the relative height of the openings B = h’/H’ = 1/4. Results of the study show that thermal radiation alters significantly the temperature distribution, the flow fields and the heat transfer across the active walls of the cavities.