Determination of interfacial heat transfer coefficient and its application in high pressure die casting process

In this paper, the research progress of the interfacial heat transfer in high pressure die casting (HPDC) is reviewed. Results including determination of the interfacial heat transfer coefficient (IHTC), influence of casting thickness, process parameters and casting alloys on the IHTC are summarized and discussed. A thermal boundary condition model was developed based on the two correlations: (a) IHTC and casting solid fraction and (b) IHTC peak value and initial die surface temperature. The boundary model was then applied during the determination of the temperature field in HPDC and excellent agreement was found

Predicting the Floc Characteristics and Settling Velocity of Flocs under Variable Dosage of Polyacrylamide

In this study, floc characteristics such as fractal dimension and settling velocity were investigated through a flocculantion process with a polyacrylamide (PAM) flocculant over a range of suspended particle concentrations, suspension type and flocculant dosage. The floc’s structure and morphology were characterized by optical microscopy and scanning electron microscopy (SEM) methods. Floc settling velocity was measured in a settling column in a laboratory. The results showed that, the surface fractal dimension ranged from 1.044 to 1.415, which quantitatively confirmed the round and layered structure of flocs observed in SEM analyses. The PAM flocculant was proved to be more effective in flocculantion process, increasing the settling velocity. Therefore, an appropriate PAM dosage is an excellent candidate as efficient flocculant. A possible flocculantion mechanism for PAM was further analyzed. For alkaline or neutral environments, adsorption and bridging effects are dominant while charge neutralization is favored in acidic conditions.In this study, floc characteristics such as fractal dimension and settling velocity were investigated through a flocculantion process with a polyacrylamide (PAM) flocculant over a range of suspended particle concentrations, suspension type and flocculant dosage. The floc’s structure and morphology were characterized by optical microscopy and scanning electron microscopy (SEM) methods. Floc settling velocity was measured in a settling column in a laboratory. The results showed that, the surface fractal dimension ranged from 1.044 to 1.415, which quantitatively confirmed the round and layered structure of flocs observed in SEM analyses. The PAM flocculant was proved to be more effective in flocculantion process, increasing the settling velocity. Therefore, an appropriate PAM dosage is an excellent candidate as efficient flocculant. A possible flocculantion mechanism for PAM was further analyzed. For alkaline or neutral environments, adsorption and bridging effects are dominant while charge neutralization is favored in acidic conditions

Study on the microstructural evolution of different component alloys consisting of B2-NiSc intermetallics

Ni-50%Sc and Ni-51%Sc alloy were prepared with a vacuum arc smelting and water cooled copper mold suction-casting machine. The results showed that the two component alloys consisted of the primary phase B2-NiSc and lamellar (Ni2Sc+NiSc)eutectic due to the loss of Sc duringmelting. Two groups of alloys underwent (970 ℃, 72 h) homogenization heat treatment, and spherical or plate shape Ni2Sc particles were dispersed on the B2-NiSc matrix. With the increase of Sc content from50% to 51%, the amount of the second phase in the alloy decreases, the microstructure becomes uniform, and the grain gradually changes from long bar to a spherical particle. According to the Jackson boundary theory, the Jackson factor α of B2-NiSc =0.5 < 2, so the interface is rough, which explains that the growth pattern of the B2-NiSc phase is anon-faceted growth. It is consistent with the dendritic growth pattern of the B2-NiSc phase, which is observed from the experiment. After a longheat treatment, the number of vacancies decreases and the microstructure became uniform. The loss rate of Sc in rapidly quenched solidification was higher than that after the heat treatment