Al–Si cast alloys under isothermal and thermomechanical fatigue conditions

This work presents a survey of the isothermal and anisothermal fatigue behavior of aluminum casting alloys obtained from different processes. Experimental results have shown that porosity, especially large and irregular pores, provides the main factor in decreasing fatigue properties of the tested alloys. In materials with similar porosity levels, other microstructural factors became relevant such as, matrix morphology and the amount of alloying elements. Fractographic analyses showed that fatigue cracks preferentially start to propagate in microcracks or interdendritic shrinkage usually located next to the surface. In most cases, propagation takes place in the eutectic phase, although in the thixoformed material, a transition from transgranular to intergranular mode was observed in the crack propagation mode.     

Optimal determination of warranty region for 2D policy: A customers' perspective

Warranty is treated by the manufacturer as a marketing strategy that creates better customer satisfaction, which finally helps to get hold of a bigger market share. The cost incurred towards this service is termed as warranty cost, which is a function of warranty policy and region, product quality and reliability, and the customers' usage pattern. Under the 2D warranty policy, there exists numerous iso-cost regions for any specified value of warranty cost. In this article, we propose a methodology to determine the optimal region when customers' utility is measured by the length of warranty coverage time. It is believed that the results will help the manufacturer to provide improved customer service.     

Effect of bulk flow pulsations on film cooling with compound angle holes

Experiments are conducted to investigate the effects of bulk flow pulsations on film cooling with compound angle holes. A row of five film cooling holes is considered with orientation angles of 0°, 30°, 60°, and 90° at a fixed inclination angle of 35°. Static pressure pulsations are produced by an array of six rotating shutter blades, which extend across the span of the exit of the wind tunnel test section. The pulsation frequency is fixed at 36 Hz, but changes in the time-averaged blowing ratios of 0.5, 1.0 and 2.0 produce three different coolant Strouhal numbers, 3.6, 1.8 and 0.9, respectively. Detailed film cooled boundary layer temperature distributions are measured by a cold wire and the adiabatic film cooling effectiveness by thermochromic liquid crystal (TLC). The boundary layer temperature surveys show that pulsations induce large disruptions to the boundary layer temperature distribution and the film coverage. As the orientation angle increases, the injectant concentration spreads further into the spanwise direction because of pulsations than the steady case. With pulsations the adiabatic film cooling effectiveness value decreases regardless of the orientation angle. The amount of reduction, however, depends on the orientation angle in such a way that the larger the orientation angle is, the smaller the reduction is.     

A probabilistic method for calculating the usefulness of a store with finite energy capacity for smoothing electricity generation from wind and solar power

This paper describes a novel method of modelling an energy store used to match the power output from a wind turbine and a solar PV array to a varying electrical load. The model estimates the fraction of time that an energy store spends full or empty. It can also estimate the power curtailed when the store is full and the unsatisfied demand when the store is empty. The new modelling method has been validated against time–stepping methods and shows generally good agreement over a wide range of store power ratings, store efficiencies, wind turbine capacities and solar PV capacities.Example results are presented for a system with 1 MW of wind power capacity, 2 MW of photovoltaic capacity, an energy store of 75% efficiency and a range of loads from 0 to 3 MW average.     

Redox flow cells for energy conversion

Energy storage technologies provide an alternative solution to the problem of balancing power generation and power consumption. Redox flow cells are designed to convert and store electrical energy into chemical energy and release it in a controlled fashion when required. Many redox couples and cell designs have being evaluated. In this paper, redox flow systems are compared in the light of characteristics such as open circuit potential, power density, energy efficiency and charge-discharge behaviour. The key advantages and disadvantages of redox flow cells are considered while areas for further research are highlighted.     

A study on the thermal contact conductance in fin–tube heat exchangers with 7 mm tube

The thermal contact resistance has been frequently neglected in the process of design of heat exchangers because of the difficulty of measurement and the lack of accurate data. However, the thermal contact resistance is one of principal parameters in heat transfer mechanism of fin–tube heat exchangers. The objective of the present study is to investigate new factors such as fin types and manufacturing types of the tube affecting the thermal contact conductance and to find a correlation between the thermal contact conductance and the effective factors in fin–tube heat exchangers with 7 mm tube. The thermal contact conductances in the 22 heat exchangers with 7 mm tube have been investigated through the experimental–numerical method. A numerical scheme has been employed to calculate the thermal contact conductance and the portion of thermal resistances using the experimental data. As a result, the thermal contact conductance has been evaluated quantitatively, and a new correlation including the influence of new factors such as fin types and manufacturing types of the tube has been developed in the fin–tube heat exchanger with 7 mm tube. Also, the portion of each thermal resistance has been evaluated in each case.     

Development of a small DMFC bipolar plate stack for portable applications

The direct methanol fuel cell (DMFC) is regarded as a promising candidate in portable electronic power applications. Bipolar plate stacks were systematically studied by controlling the operating conditions, and by adjusting the stack structure design parameters, to develop more commercial DMFCs. The findings indicate that the peak power of the stack is influenced more strongly by the flow rate of air than by that of the methanol solution. Notably, the stack performance remains constant even as the channel depth is decreased from 1.0 to 0.6 mm, without loss of the performance in each cell. Furthermore, the specific power density of the stack was increased greatly from ∼60 to ∼100 W l⁻¹ for stacks of 10 and 18 cells, respectively. The current status of the work indicates that the power output of an 18-cell short stack reaches 33 W in air at 70 °C. The outer dimensions of this 18-cell short stack are only 80 mm × 80 mm × 51 mm, which are suitable for practical applications in 10–20 W DMFC portable systems.