Neşet AKAR, Kadir KOCATEPE, H. Mehmet ŞAHİN, Ramazan KAYIKCI

Ötektik Al-Si alaşımında soğutucu yüzey pürüzlülüğünün arayüzey ısı transfer katsayısına etkisi

Ara yüzey ısı transfer katsayısının metalden kalıba olan ısı transfer oranı üzerinde önemli rolü vardır. Dökümlerin makro ve mikro yapıları esas olarak ısı transfer oranına bağlıdır. Bu çalışmanın amacı su soğutmalı çelik soğutucu (H13) üzerinde tek yönlü dikey olarak katılaşan ötektik Al-Si alaşımında soğutucu yüzey pürüzlülüğünün ara yüzey ısı transfer katsayısına etkisini incelemektir. Ara-yüzey ısı transfer katsayısı soğutucu yüzey pürüzlülüğüne bağlı olarak, Sonlu Farklar Metoduna dayalı FORTRAN programı ile belirlenmiştir. Sonuç olarak; ısı transfer katsayısı soğutucu yüzey pürüzlülüğü azaldıkça artmıştır, maksimum ısı transfer katsayısı değerleri; 0.15 $mu$ m soğutucu yüzey pürüzlülüğünde 3320 W/$m^2$K, 0.22 $mu$ m soğutucu yüzey pürüzlülüğünde 3302 W/$m^2$K ve 2.47 $mu$ m soğutucu yüzey pürüzlülüğünde 2954 W/$m^2$K olarak elde edilmiştir, ara yüzey ısı transfer katsayıları zamanın güçlü bir fonksiyonu olarak belirlenmiştir, nümerik çözümün hassaslığı Fourier sayısı azaldıkça artmıştır, optimum çözüm hesaplama zamanı göz önünde tutularak Fo=0.0625 ve $Delta$x=0.25 mm ile elde edilmiştir.

The effect of surface roughness of chill on the interfacial heat transfer coefficient in eutectic Al-Si casting

The interfacial heat transfer coefficient plays an important role in the rate of heat transfer from the metal to the mould. The macro and microstructures of castings are mainly related on the heat transfer rate. The objective of the present work was to investigate the effect of surface roughness of chill on the interfacial heat transfer coefficient (IHTC) for vertically upward unidirectional solidification of a eutectic Al-Si casting on water cooled steel chills during solidification. The interfacial heat transfer coefficient measured as a function of different surface roughness of the chill was determined by using finite difference method solving FORTRAN language. The obtained results; the heat transfer coefficients increases as chill surface roughness decreases, the maximum heat transfer coefficient values were obtained; 3320 W/$m^2$K with 0.15 µm, 3302 W/$m^2$K with 0.22 $mu$ m and 2954 W/$m^2$K with 2.47 $mu$ m chill surface roughness, the interfacial heat transfer coefficients have been expressed as a power function of time, the sensitivity of numerical solution increased as Fourier number decreases, the optimum solution were achieved with Fo=0.0625 and $Delta$x=0.25 mm by considering the calculation time.

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