Papers by Keyword: Superheating

Abstract: The cooling curve and its derivatives display patterns that can be used to predict the characteristics of a cast iron. The effects of melting, superheating and holding in an acid lined coreless induction furnace were explored, as they affect the role of preconditioning and / or inoculation to restore solidification with low eutectic undercooling. Increased chill (iron carbides amount) in the experimental irons correlates well with certain thermal analysis parameters, such as the degree of eutectic undercooling. Preconditioning of the molten base iron before tapping led to improved solidification parameters in both untreated and inoculated irons as measured by the most significant thermal analysis cooling curve events. A double treatment incorporating preconditioning with inoculation improved the thermal analysis parameters, and consequently, the quality of the cast iron. If standard Ca-FeSi alloys do not have sufficient inoculation potential, the addition of the inoculant enhancing alloy (S, O and oxy-sulphides forming elements) will greatly enhance inoculation, well illustrated by changes to the thermal analysis parameters. A newly defined Inoculation Specific Factor [inoculation effect / inoculant consumption which led to that beneficial effect ratio] of different alloys is illustrated by thermal analysis, with good correlation with microstructural characteristics.

Abstract: This paper proposes a simplified theoretical model of Pulsating Heat Pipe (PHP) employed in a vapour compression refrigeration system. The model developed is mainly based on well known physical equations and partially based on empirical correlation. The present theoretical investigation of PHP is focused to explore its suitability as a heat exchanger in the condenser of vapour compression refrigeration system. A parametric analysis is carried out to design the vapour compression refrigeration system with PHP as the condenser. The performance of the system is evaluated for different PHP diameters, working fluids, evaporator and condenser temperatures and evaporator and condenser lengths. The effect of super heating and sub cooling the refrigerant are also studied. The results showed an increase in performance of the system at higher evaporator and lower condenser temperatures. The best results are obtained with R-12 as the working fluid. Also there is an increase in the COP of the system due to decrease in pressure drop in the condenser.

Abstract: Organic Rankine Cycle (ORC) has attracted much attention in recent years, since it has potential of reducing fossil fuel consumption and many favorable characteristics to exploit low-grade energy sources. This work carries out an exergetical performance assessment of ORC with superheating comparatively for various organic fluids. Special attention is paid to the effect of evaporating temperature on the exergy destructions (anergies) at various system components and the exergy efficiency of system. Results show that for a given source both the anergies at the components and exergy efficiency may have a peak value or monotonically increase with evaporating temperature.

Abstract: In order to find the relationship between tensile sample laminations and inner quality of Q345 slabs, casting trials in conditions of with and without EMS and different superheating have been carried out. It is found that slab inner quality can be improved a lot with EMS, center equiaxial grain ratio increases greatly. Lowering superheating leads to downgrading of center deviation, however, center equiaxial grain ratio increases not too much compared with EMS. Tensile samples produced by above-mentioned measures do not break in the center area.

Abstract: The modification of liquid metal by electric pulse (EP, EPM) is a novel method for grain refinement. In this study, based on the reported structural heredity of EP-modified liquid aluminium, the structure tests of EP-modified liquid aluminium with different technique parameters were conducted by using high temperature X-ray diffractometer. The results show that the quantitative structure changes of EP-modified liquid aluminium have a close relationship with the modifying time and modifying temperature. The decrease of modifying time could result in an obvious weaker principal peak in structure factor curve compared with the optimal EP technique parameters, but a slight increase of coordination number (Ns), correlation radius (rc) and average atom number per cluster (Nat) is still observed under this condition. These facts indicate that the EP-modified liquid aluminum could gain an increasing order degree, and thus have an advantage during the formation of a stable nucleus, eventually leading to a grain-refining solidification structure. On the other hand, the structure factor curve of EP-modified liquid aluminum at the high modifying temperature of 850°C tends to be overlapped with that of the unmodified during the principal peak range. In this case, the competition result between the EP strengthening effect and the destruction of superheating would determine the final structure of EP-modified liquid aluminum.

Abstract: The cohesive energy is the energy to divide the crystal into isolated atoms, and the direct result of cohesive energy is to create new surface. The increased surface energy should equal the cohesive energy of the crystal, which results from the surface area difference between the total atoms and the crystal. This is the basic concept of Surface-Area-Difference (SAD) model. The SAD model has been extended to account for the melting temperature of metallic nanocrystals with non-free surface (embedded in a matrix) in the present work. It is shown if the melting temperature of the matrix must be much higher than that of the bulk value of the nanocrystals, and the nanocrystals has coherent or semi-coherent interface with the matrix, the nanocrystals may be superheated. The present results are supported by the available experimental values.

Abstract: The effect of manganese on grain refinement of a commercial AZ31 alloy has been investigated using an Al-60%Mn master alloy splatter as an alloying additive at 730 °C in aluminium titanite crucibles. It is shown that grain refinement by manganese is readily achievable in AZ31. Electron microprobe analyses reveal that prior to the addition of extra manganese the majority of the intermetallic particles found in AZ31 are of the Al8Mn5 type. However, after the addition of extra manganese in the range from 0.1% to 0.8%, the predominant group of intermetallic particles changes to the metastable AlMn type. This leads to a hypothesis that the metastable AlMn intermetallic particles are more effective than Al8Mn5 as nucleation sites for magnesium grains. The hypothesis is supported by the observation that a long period of holding at 730 °C leads to an increase in grain size, due probably to the transformation of the metastable AlMn to the stable Al8Mn5. The hypothesis has also been used to understand the mechanism of grain refinement by superheating.