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The purpose of this study is to examine the physical processes experienced by a particle-laden gas due to various types of collisions, different heat transfer modalities and jet axis switching. Here, attention is focused on a particle-laden gas subjected to jet axis switching while experiencing fluid flow and heat transfer.

The methodology used to model and solve these complex problems is numerical simulation treated here as a two-phase turbulent flow in which the gas and the particles keep their separate identities. For the turbulent flow model, validation was achieved by comparisons with appropriate experimental data. The considered interactions between the fluid and the particles include one-way fluid–particle interactions, two-way fluid–particle interactions and particle–particle interactions.

For the fluid flow portion of the work, emphasis was placed on the particle collection efficiency and on independent variables that affect this quantity and the trajectories of the fluid and of the particles as they traverse the space between the jet orifice and the impingement plate. The extent of the effect depended on four factors: particle size, particle density, number of particles and the velocity of the fluid flow. The major effect on the heat transferred to the impingement plate occurred when direct heat transfer between the impinging particles and the plate was taken into account.

This paper deals with issues never before dealt with in the published literature: the effect of jet axis switching on the fluid mechanics of gas-particle flows without heat transfer and the effect of jet axis switching and the presence of particles on jet impingement heat transfer. The overall focus of the work is on the impact of jet axis switching on particle-laden fluid flow and heat transfer.

To investigate the influence of conical and annular nozzle geometric configurations on the flow structure and heat transfer characteristics near the stagnation point of a flat plate with limited heated area.

The conical and annular conical nozzles were designed such that the exit area of both nozzles is the same and the mass flow rate passing through the nozzles is kept constant for both nozzles. The governing equations of flow and heat transfer are modeled numerically using a control volume approach. The grid independent solutions are secured and the predictions of flow and heat transfer characteristics are compared with the simple pipe flow with the same area and mass flow rate. The Reynolds stress turbulence model is employed to account for the turbulence. A flat plate with a limited heated area is accommodated to resemble the laser heating situations and air is used as assisting gas.

It is found that nozzle exiting velocity profiles differ considerably with changing the nozzle cone angle. Increasing nozzle cone angle enhances the radial flow and extends the stagnation zone away from the plate surface. The impinging jet with a fully developed velocity profile results in enhanced radial acceleration of the flow. Moreover, the flow structure changes considerably for annular conical and conical nozzles. The nozzle exiting velocity profile results in improved heat transfer coefficient at the flat plate surface. However, the achievement of fully developed pipe flow like velocity profile emanating from a nozzle is almost impossible for practical laser applications. Therefore, use of annular conical nozzles facilitates the high cooling rates from the surface during laser heating process

The results are limited with theoretical predictions due to the difficulties arising in experimental studies.

The results can be used in laser machining applications to improve the end product quality. It also enables selection of the appropriate nozzle geometry for a particular machining application.

This paper provides information on the flow and heat transfer characteristics associated with the nozzle geometric configurations and offers practical help for the researchers and scientists working in the laser machining area.

The first gas turbine patent was granted in England to John Barber in 1791, and since then there have been numerous gas turbine inventions. These have been adequately described elsewhere, 1, 2 and I shall concern myself only with the developments which have led directly to recent British achievements.

The depletion of fossil fuel and emissions of harmful gases forced the pioneers in search of alternate energy source. The purpose of this study is to present an effective use of hydrogen fuel for turbojet engines based on its exergetic performance.

This study was performed to measure the assessment of exergetic data of turbojet engines. Initially, the test was carried out on the Jet A-1 fuel. Then, a series of similar tests were carried out on turbojet engines with hydrogen fuel to measure their performance results. Finally, the exergetic values of both were compared with each other.

The introduction of hydrogen fuel reduced the exergy efficiency, and a 10 per cent reduction was observed in exergy efficiency. Simultaneously, the waste exergy rate increased by 9 per cent. However, because of the high specific fuel exergy, hydrogen fuel was better than Jet A-1 fuel. Note that parameters such as environmental effect factor and ecological effect witnessed an increase in their index owing to the addition of hydrogen.

Introduction of alternative blends is necessary for achieving lower emission of gases such as CO, NOx and CO₂ from gas turbine engines without compromising on performance. The Jet A fuels were replaced by blends to obtain better emission characteristics.

The use of hydrogen in turbojet engines showed an adverse effect on exergetic performance. However, it was very impressive to see a 200 per cent reduction in emissions. From the comparison of exergy efficiency results of inlet, combustion and nozzle, it is evident that the combustion chamber has the largest values of exergy ratio, waste exergy ratio, cost flow, ecological factor, environmental factor and fuel ratio owing to irreversibility in the combustion process.

Based on a lecture prepared as part of the celebration of Cranfield University's 50th anniversary. After briefly reviewing the early years, including Cranfield University's entry into this technology, discusses the nature of this industry, Some of the technology drivers, including environmental concerns, are examined to provide a background against which the development and the future of the industry can be considered. This is followed by a brief survey of some of the possible new civil aero gas turbine applications over the next 50 years, both the very likely and some curiosities. Finally, the changes that are likely to occur within the industry as a result of wider economic and political trends are considered, as well as the implications for those working within the industry. The development of the civil aero gas turbine has contributed, in large measure, to today's, US$ 300 billion civil aviation industry and is rightly seen as one of mankind's major engineering achievements. A single paper cannot do justice to this industry.

IT is well known that war gives a great impetus to development in many fields, not least of which is that of aircraft propulsion. Such was the case in World War II, when great strides were made, but it is interesting to note that the pace has hardly slackened in the years following its conclusion. This is perhaps because of the ‘cold’ war which took its place, or perhaps because the introduction of jet propulsion has stimulated thought and action in realms beyond the dreams of the piston engine era. Whatever the cause, the results are apparent and this is a suitable moment to look back and measure the progress of the past seven or eight years.

A new product design required the addition of a second layer of electronics to control a base module. This product was designed with significant overhangs of heavy leads and components which presented a significant challenge to many different solder assembly processes. Only the heated gas jet process was able to solder the product successfully without damaging the printed wiring boards.

To answer the challenge, a new machine was developed, combining dispensing of solder paste with hot gas jet reflow technology. This provided a combination of capabilities resulting in a flexible process which was significantly superior to alternative technologies.

Other soldering processes such as laser, focused xenon lamp, robotic soldering iron, and focused IR soldering technologies were evaluated. Each of these technologies causes some damage or defect to the assembly due to the heat sinking aspect of the circuit assembled. These alternative processes would create damage or defects to the assemblies by burning the laminate, delaminating the pads on the printed wiring board, or not soldering the pads.

Proof of concept tests before machine designs were initiated demonstrated the potential and capabilities of this technology for automated assembly soldering. Testing indicated that the heated gas jet processing would provide a means of soldering the assemblies at a controllable rate without damaging the circuit boards.

While evaluating the machine ion its design phase, a designed experiment was initiated to help understand the relationships between head temperature settings versus gas flow rates, the measurable output was time to reflow.

The process meets all expectations in terms of solder fillet appearance, volume, and overall visual quality while maintaining process cycle time requirements.

In laser drilling applications, hole wall remains almost the melting temperature of the substrate material and the thermodynamic pressure developed at high temperature molten surface vicinity influences the heat transfer rates and the skin friction at the surface of the hole wall. This effect becomes complicated for the holes drilled in coated substrates. In this case, melting temperatures of the coating and base materials are different, which in turn modifies the flow field in the hole due to jet impingement. Consequently, investigation of the heat transfer rates from the hole wall surfaces and the skin friction at the hole surface becomes essential. The paper aims to discuss these issues.

Numerical solution for jet impingement onto a hole with high wall temperature is introduced. Heat transfer rates and skin friction from the hole wall is predicted. The numerical model is validated with the experimental data reported in the open literature.

The Nusselt number attains high values across the coating thickness and it drops sharply at the interface between the coating and the base material in the hole. Since fluid temperature in the vicinity of the substrate surface is higher than that of the wall temperature, heat transfer occurs from the fluid to the substrate material while modifying the Nusselt number along the hole wall. This results in discontinuity in the Nusselt variation across the coating-base material interface. The Raighly line effect enhances the flow acceleration toward the hole exit while increasing the rate of fluid strain. Consequently, skin friction increases toward the hole exit. The influence of average jet velocity on the Nusselt number and the skin friction is significant.

The findings are very useful to analyze the flow field in the hole at different wall temperature. In the simulations hole diameter is fixed in line with the practical applications. However, it may be changed to examine the influence of hole diameter on the flow field and heat transfer. However, this extension be more toward academic study than the practical significance.

The complete modeling of turbulent flow jet flow impinging onto a hole is introduced and boundary conditions are well defined for the numerical solutions. The method of handing the physical problem will be useful for those working in the area of heat transfer and fluid flow. In addition, the importance of heat transfer rates and skin friction at the hole wall is established, which will benefit the practical engineers and the academicians working in the specific area of laser machining.

The findings are useful for those working to improve the laser technology in the machining area.

The work presented is original and never being published anywhere else. The findings are reported in detail such that academicians and engineers are expected to benefit from this original contribution.

A description about the use of the chromatic methodology for monitoring an arc plasma jet utilised for heating micro particles for forming plasma sprayed coatings is given. It is shown that the behaviour of both the plasma and heated micro particles are distinguishable from their different coordinates on an H‐S polar map. Calibration with a standard ribbon lamp would appear feasible for tracking the temperature of the plasma heated micro particles.

The purpose of this paper is to examine entropy generation rate in the flow field due jet emanating from an annular nozzle and impinging on to a flat plate. Since the flow field changes with the geometric configuration of the annular nozzle, the influence of nozzle outer cone angle on the entropy generation rate is considered.

The steady flow field pertinent to jet impingement on to a flat plate is modeled with appropriate boundary conditions. A control volume approach is introduced to discretize the governing equations of flow and to simulate the physical situation numerically. Entropy generation rate due to heat transfer and fluid friction is formulated. The resulting entropy equations are solved numerically.

Thermodynamic irreversibility, which is quantified through entropy generation rate, gives insight into the thermodynamics losses in the flow system. Entropy generation rate is highly affected by the nozzle outer cone angle. In this case, increasing nozzle outer cone angle enhances the entropy generation rate, particularly due to fluid friction.

The predictions may be extended to include the nozzle area ratio and mass flow rate variation.

The paper is a very useful source of physical information for improving nozzle design, particularly that which is used in a laser thick material cutting operation. It disseminates information for those working on both laser machining applications and entropy generation in flow systems.

This paper discusses the physical issues related to the entropy generation rate and offers practical help to an individual starting out on an academic career.