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"Experimental investigation on two-phase flow boiling heat transfer of R-410A and R-134A in horizontal small tubes is reported. The pressure drop and local heat transfer coefficients were obtained over heat flux range of 5 to 40 kW/m2, mass flux range of 70 to 600kg/ m2s, saturation temperature range of 2 to 12°C, and quality up to 1.0 in test section with inner tube diameters of 3.0 and 0.5mm, and lengths of 2000 and 330mm, respectively. The section was heateduniformly by applying a direct electric current to the tubes. The effects of mass flux, heat flux, and inner tube diameter on pressure drop and heat transfer coefficients are presented. Theexperimental results are compared against several existing correlations. A new boiling heat transfer coefficient correlation based on the superposition model for refrigerants in small tubesis also presented."

"Experimental investigation on two-phase flow boiling heat transfer of R-410A and R-134A in horizontal small tubes is reported. The pressure drop and local heat transfer coefficients were obtained over heat flux range of 5 to 40 kW/m2 , mass flux range of 70 to 600kg/ m2 s, saturation temperature range of 2 to 12°C, and quality up to 1.0 in test section with inner tube diameters of 3.0 and 0.5mm, and lengths of 2000 and 330mm, respectively. The section was heated uniformly by applying a direct electric current to the tubes. The effects of mass flux, heat flux, and inner tube diameter on pressure drop and heat transfer coefficients are presented. The experimental results are compared against several existing correlations. A new boiling heat transfer coefficient correlation based on the superposition model for refrigerants in small tubes is also presented."

"Heat exchanger merupakan bagian vital dalam sebuah perangkat elektronik yang dapat menjaga suhu optimum dari alat tersebut. Penelitian tentang microchannel heat exchanger telah sangat berkembang untuk aplikasi kearah pendingin elektronik pada satu dekade terakhir ini. Microchannel heat exchanger memiliki beberapa keunggulan yakni memiliki dimensi yang lebih kecil dan memiliki koefisien perpindahan kalor yang lebih baik daripada alat penukar kalor lainnya. Dalam pengujian ini, peneliti akan mencoba membuktikan performa dari koefisien perpindahan kalor dari microchannel heat exchanger tersebut beserta efek negatifnya. Peneliti akan mencoba menguji pengaruh pressure drop pada saluran microchannel heat exchanger. Kemudian dalam pengujian ini juga digunakan fluida kerja air,nano fluida Al2O3 1%, dan nano fluida SnO2 1% dengan fluida dasar air. Dari hasil pengujian ini didapatkan bahwa perpindahan kalor akan lebih baik jika menggunakan nano fluida sebagai fluida kerja pendingin.

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Heat exchanger is a vital part in an electronic devices that can maintain the optimum operation temperature of that devices. Research on microchannel heat exchanger application has been highly developed on electronics cooling towards the last decade. Microchannel heat exchanger has several advantages which have smaller dimensions and heat transfer coefficient better than the other heat exchanger. The experiment also want to measure the pressure drop in microchannel. It used water, nanofluids Al2O3 1%,and nanofluids SnO2 1% as working fluids in cold side microchannel heat exchanger. Result from this research indicate that heat transfer would be better if we use nanofluids as cooling working fluids."

"Kinerja perpindahan kalor pada alat penukar kalor dapat ditingkatkan dengan mengurangi ukuran diameter hidrolik atau dengan menggunakan fluida kerja yang memiliki konduktivitas termal lebih baik dibandingkan dengan fluida kerja konvensional. Salah satu contoh penggunaan diameter hidrolik yang kecil adalah microchannel heat exchanger (MCHE). Pada penelitian ini, perancangan alat dan pengujian kinerja perpindahan kalor pada MCHE berkonfigurasi counter-flow dengan menggunakan fluida kerja air dan nano fluida Al2O3-air dengan konsentrasi 1%, 3%, dan 5% sebagai fluida pendingin telah dilakukan. Dalam pengujian, temperatur masuk fluida pada sisi panas dan sisi dingin MCHE diatur tetap pada temperatur 50°C dan 25°C, sedangkan debit aliran pada saluran masuk divariasikan dari 100 ml/menit hingga 300 ml/menit. Hasil pengujian menunjukkan bahwa peningkatan konsentrasi partikel nano pada fluida dasar dapat meningkatkan kinerja perpindahan kalor fluida dasar tersebut. Pada konsentrasi partikel nano tertinggi yang digunakan dalam pengujian, nano fluida Al2O3-air konsentrasi 5% dapat menyerap panas sebesar 9% lebih baik dibandingkan air biasa dan dapat meningkatkan koefisien perpindahan kalor keseluruhan MCHE sebesar 13% lebih besar dibandingkan dengan air.

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The heat transfer performance in heat exchanger can be enhanced by decreasing its hydraulic diameter or using working fluid that has better thermal conductivity than the conventional one. One of the examples of small hydraulic diameter application is microchannel heat exchanger (MCHE). Designing the MCHE and doing experimental investigation of the heat transfer performance on counter-flow MCHE by using water and Al2O3-water nanofluid with nanoparticle concentration 1%, 3%, and 5% as coolant fluid has been done in this experiment. Inlet fluid temperatures in hot and cold side are set at 50°C and 25°C, meanwhile the inlet flow rate is set from 100 to 300 ml/minute.

The experimental results show that the increase of nanoparticle concentration in the base fluid can enhance its heat transfer performance. In highest concentration of nanoparticle used in this experiment, Al2O3-water 5% nanofluid can absorb heat 9% better than conventional water do and can enhance the overall heat transfer coefficient of MCHE 13% higher than water."

"ABSTRAKSebuah kajian eksperimental telah dilakukan untuk mengetahui karakteristikrespon dinamik yang berupa getaran pada struktur alat penukar kalor shell and tubetipe AES. Penelitian dilakukan dengan menggunakan aktuator getaran sebagai sumbereksitasi dengan frekuensi maksimum adalah 7.33 Hz pada alat penukar kalor tanpabeban aliran. Eksitasi dilakukan dengan arah horizontal pada tiga titik yaitu, noselmasuk, nosel keluar, dan bagian tengah. Pengukuran dilakukan secara horizontal,vertikal, dan aksial pada titik yang sama ditambah dua titik lain pada support struktur.Ada dua hasil pengukuran getaran yaitu pengukuran overall dan pengukuran diskretyaitu dengan frekuensi spektrum dari masing-masing tiitk yang akan diklasifikasikanberdasarkan vibration severity chart dan table identifikasi karakteristik spektrumfrekuensi. Hasil pengukuran secara overall menunjukkan secara umum pengukuranyang dilakukan secara horizontal akan menampilkan respon yang lebih besardibandingkan dengan pengukuran vertikal dan aksial. Pada pengukuran frekuensispektrum terjadi perbedaan sekitar 1 Hz pada frekuensi eksitasi dari aktuator getarandengan yang terukur. Pengukuran spektrum frekuensi secara vertikal dan aksialmenunjukkan adanya looseness pada struktur alat penukar kalor.

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ABSTRACTAn experimental study has been developed to understand dynamic responsecharacteristic which is vibration in a shell and tube heat exchanger AES type.Experiment was done by using a vibration aktuator as the excitation source withmaximum frequency about 7.33 Hz in no flow condition. The direction of the excitationis only horizontal on three different excitation points, inlet nozzle, outlet nozzle andmiddle part of the heat exchanger. Measurements were done on the same points of theexcitation and two other points, on the support of the heat exchanger, horizontally,vertically, and in the axial direction. There are two results of the measurements, theyare the overall vibration and the frequency spectrum on each point that will be classifiedbased on vibration severity chart and identification table of frequency spectrumcharacteristic. Generally the overall vibration measurement horizontally indicate thebigger response than the vertical or axial measurements. The results of frequencyspectrum measurements can indicate there is a difference between excitation frequencyand response frequency about 1 Hz. Frequency spectrum measurements done verticallyor in axial measurement can indicate there is a looseness in the structure."