Investigation of diesel generator shaft and bearing failures

A shaft failure in a 634 kW diesel generator after 4000 hours of operation required investigation, especially when similar sets began to show signs of excessive bearing housing wear. The failure was found to be due to torsional fatigue caused by operation at an unforeseen resonant condition. The damage to the bearing housing of this type of set was also attributed to this behaviour. Replacement of the bearings and housings and redesign of the flexible coupling has been undertaken to prevent further failures. Modifications to design procedures are now being adopted to ensure similar problems do not occur in other existing or new machines

Effects of aircraft integration on compact nacelle aerodynamics

To reduce specific fuel consumption, it is expected that the next generation of aero-engines will operate with higher bypass-ratios, and therefore fan diameters, than current in-service architectures. These new propulsion systems will increase the nacelle size and incur in an additional overall weight and drag contribution to the aircraft. In addition, they will be installed more closely-coupled with the airframe, which may lead to an increase in adverse installation effects. As such, it is required to develop compact nacelles which will not counteract the benefits obtained from the new engine cycles. A comprehensive investigation of the effects of nacelle design on the overall aircraft aerodynamic performance is required for a better understanding on the effects of aero-engine integration. This paper presents a method for the multi-objective optimisation of drooped and scarfed non-axisymmetric nacelle aero-engines. It uses intuitive Class Shape Tranformations (iCSTs) for the aero-engine geometry definition, multi-point aerodynamic simulation, a near-field nacelle drag extraction method and the NSGA-II genetic algorithm. The process has been employed for the aerodynamic optimisation of a compact nacelle aero-engine as well as a conventional nacelle configuration. Subsequently, the designed architectures were installed on a conventional commercial transport aircraft and evaluated at different installation positions. A novel thrust-drag bookkeeping method has been used to evaluate different engine, nacelle and aircraft performance metrics. The main flow mechanisms that impact the installation effects on compact aero-engines configurations are identified. For the expected close-coupled installation position of future high bypass-ratio engines, the net vehicle force is increased by 0.44% with respect to a conventional architecture. The proposed method complements a set of enabling technologies that aim at the analysis, optimisation and evaluation of future civil aero-engines

CFD modelling of a two-phase closed thermosyphon charged with R134a and R404a

This paper examines the application of CFD modelling to simulate the two-phase heat transfer mechanisms in a wickless heat pipe, also called a thermosyphon. Two refrigerants, R134a and R404a, were selected as the working fluids of the investigated thermosyphon. A CFD model was built to simulate the details of the two-phase flow and heat transfer phenomena during the start-up and steady-state operation of the thermosyphon. The CFD simulation results were compared with experimental measurements, with good agreement obtained between predicted temperature profiles and experimental temperature data, thus confirming that the CFD model was successful in reproducing the heat and mass transfer processes in the R134a and R404a charged thermosyphon, including the pool boiling in the evaporator section and the liquid film in the condenser section

Experimental and numerical investigation of an air-to-water heat pipe-based heat exchanger

An experimental and analytical investigation was conducted on an air-to-water heat exchanger equipped with six wickless heat pipes (thermosyphons) charged with water as the working fluid. The flow pattern consisted of a double pass on the evaporator and condenser sections. The six thermosyphons were all made from carbon steel, measured 2m in length and were installed in a staggered arrangement. The objectives of the reported experimental investigation were to analyse the effect of multiple air passes at different air inlet temperatures (100 to 250°C) and air mass flow rates (0.05 to 0.14kg/s) on the thermal performance of the heat exchanger unit including the heat pipes. The results were compared with a CFD model that assumed the heat pipes were solid rods with a constant conductivity. The conductivity of the pipes was extracted from modifications of correlations available in the literature based around the theory of Thermal Resistance. The results proved to be very accurate within 10% of the experimental values

Aerodynamics of aero-engine installation

This paper describes current progress in the development of methods to assess aero-engine airframe installation effects. The aerodynamic characteristics of isolated intakes, a typical transonic transport aircraft as well as a combination of a through-flow nacelle and aircraft configuration have been evaluated. The validation task for an isolated engine nacelle is carried out with concern for the accuracy in the assessment of intake performance descriptors such as mass flow capture ratio and drag rise Mach number. The necessary mesh and modelling requirements to simulate the nacelle aerodynamics are determined. Furthermore, the validation of the numerical model for the aircraft is performed as an extension of work that has been carried out under previous drag prediction research programmes. The validation of the aircraft model has been extended to include the geometry with through flow nacelles. Finally, the assessment of the mutual impact of the through flow nacelle and aircraft aerodynamics was performed. The drag and lift coefficient breakdown has been presented in order to identify the component sources of the drag associated with the engine installation. The paper concludes with an assessment of installation drag for through-flow nacelles and the determination of aerodynamic interference between the nacelle and the aircraft

Sizing of a reversible magnetic heat pump for the automotive industry

[EN] This paper focuses on the design of an innovative air-conditioning system, namely a magnetocaloric air-conditioner for an electric minibus. An integrated design of the complete system is necessary, as the hot and cold side of the regenerator will work under dynamic conditions which depend on the instantaneous thermal load in the cabin. In order to assist the design of the system, a dynamic model has been developed for the cabin, the hydraulic loops and heat exchangers, and the magnetocaloric unit. This paper presents (i) a description of the dynamic models, (ii) an analysis of the operating conditions of the magnetocaloric unit and (iii) a discussion on the design of the magnetocaloric air-conditioner. The results show that the electric minibus requests 1.60 kW of cooling power over a span of 37 K in cooling mode, and 3.39 kW of heating power over a span of 40 K.This work has been supported by the European Commission under the 7th European Community framework program as part of the ICE project "MagnetoCaloric Refrigeration for Efficient Electric Air-Conditioning", Grant Agreement no. 265434. B. Torregrosa-Jaime acknowledges the Spanish Science and Innovation Ministry (Ministerio de Ciencia e Innovacion) for receiving the Research Fellowship FPU ref. AP2010-2160.Torregrosa Jaime, B.; Corberán Salvador, JM.; Vasile, C.; Muller, C.; Risser, M.; Payá Herrero, J. (2014). Sizing of a reversible magnetic heat pump for the automotive industry. International Journal of Refrigeration. 37:156-164. https://doi.org/10.1016/j.ijrefrig.2013.06.018S1561643

Lubricated revolute joints in rigid multibody systems

The main purpose of this work is to present a general methodology for modeling lubricated revolute joints in constrained rigid multibody systems. In the dynamic analysis of journal-bearings, the hydrodynamic forces, which include both squeeze and wedge effects, generated by the lubricant fluid, oppose the journal motion. The hydrodynamic forces are obtained by integrating the pressure distribution evaluated with the aid of Reynolds’ equation, written for the dynamic regime. The hydrodynamic forces built up by the lubricant fluid are evaluated from the system state variables and included into the equations of motion of the multibody system. Numerical examples are presented in order to demonstrate the use of the methodologies and procedures described in this work.Fundação para a Ciência e a Tecnologia (FCT

An Investigation into the use of Water as a Working Fluid in Wraparound Loop Heat Pipe Heat Exchanger for Applications in Energy Efficient HVAC Systems Energy

Wraparound heat pipes have been used for many years and have found a niche application in outside air handling units in hot and humid climates. They are used in conjunction with primary, chilled water cooling coils to enhance the efficiency of moisture removal and ensure that the process consumes minimal energy. The type of heat pipe employed is a gravity assisted thermosyphon which is formed into a loop and ‘wrapped’ around the main cooling coil. The traditional working fluid for HVAC heat pipes has been a refrigerant and a replacement fluid is desirable as a short and long-term option. From an environmental standpoint, water is an ideal candidate and many of its thermal transport properties suggest that it should be viable. There are manufacturing issues associated with using water which are not the concern of this paper; the paper’s intention is to prove the viability of water and compare its performance with that of traditional refrigerants. At the conditions used for the experimentation, the results suggest that the use of water in a loop heat pipe can enhance the effectiveness of the arrangement by up to 18% when compared with a conventional refrigerant filled pipe. The type of thermosyphon, or gravity-assisted heat pipe, that is under consideration has a performance which can be quantified using an effectiveness model. This model has been used in the investigation to compare the performance of identical pipes filled with different working fluids. The effectiveness of the heat pipe is determined by many variables and a good proportion of these are related simply to tube orientation, size and flow path. The application of wraparound heat pipes that is under consideration relies upon specific sizes and orientations of tubes and the conclusions of the report give pointers towards further research which needs to be undertaken, or is currently underway, in order to determine the extents of applicability of water as a working fluid

Analysis of increasing torque with recurrent slip in interference-fits

Previous research associated with interference-fitted assemblies has shown that as recurring slip occurs (i.e. load to total slip, unloading and reload to total slip) there is an observed increase in the holding torque after each loading cycle. The aim of this work was to identify the reasons for this ‘torque strengthening’ phenomenon. The work also has industrial relevance in the optimum design of interference-fitted rolls used for the hot rolling of steel sections. Previous work has shown that the major contributors to the overall holding torque were the interface pressure, material properties and the coefficient of friction between component materials. In this work, neutron diffraction tests and crack compliance tests showed no correlation between the interface pressure and increased holding torque. Meanwhile, experimental holding torque tests on sample interference-fits showed that for each recurring holding torque failure (slip) in a test cycle, the holding torque increased. Subsequent wear investigations showed that the wear of the surfaces increased throughout the testing and once a specific type of wear had occurred through a ‘ploughing’ mechanism, significant damage could be done to the more expensive shaft component. These observations suggest that an effective increase in the coefficient of friction between shaft and hub is responsible for the increase in holding torque, while the same level of interface pressure is maintained throughout slipping. The research provides a basis for the optimisation of interference-fit design in order that the working lives of expensive shafts, which are prone to damage through ploughing, and brittle hubs, which are prone to sudden fracture, are maximised when experiencing recurrent slipping