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"The spontaneous combustion of coal stockpiles is a serious economic and safety problem. Unfortunately it is not easy to understand these phenomena. This is due to the mechanism of spontaneous combustion is affected by many internal and external factors including particle size. The low-temperatur oxidation reaction in the nature or stockpiles of coal piles is considered slow due to limited heat exchange between coal and direct surroundings. Thus, an adiabatic oxidation testing method used for determining the spontaneous combustion character propensity of a sub-bituminous coal. This work particulary focuses on studying the effect of particle size on the self-heating rate (R70) as well as the activation energy (Ea) and time to ignition (tad). The test showed that increase of the particle size decreased self-heating rate, increased ectivation energy and delayed time to ignition.One of certain way to process the preserving of food and beverage or to ease the packaging process is drying process. To acieve the efficiency and effectiveness, it needs to find out the characterisitic of water content. This is the reason of research about the flow rate of the evaporation. It depends on the humidity, surrounding temperature, and the velocity of air. The instrument device uses injection contained aquades. Air flows through the droplet with the variation of velocity and temperature. It shows the relationship of Reynolds (Re), Prandtl (Pr), Schmidt (Sc), Nusselt (Nu), and Sherwood (Sh) numbers. Heat and mass transfer occur in this process. Ranz-Marshall analogy used to calculate the equation. Data of the experiments show the tendency of being above the Ranz-Marshall analogy."

"Indonesia memiliki hasil alam yang sangat banyak, yang pada pengolahannya sering membutuhkan proses pengeringan dan diantaranya menggunakan pengering semprot (spray dryer). Kelebihan pengering jenis ini terutama adalah untuk material yang sensitif terhadap panas. Laju perpindahan panas dan perpindahan massa untuk suatu tetesan yang bergerak di dalam pengering semprot adalah sangat tinggi. Jadi karena laju penguapan sangat tinggi maka droplet terjaga pada temperatur rendah. Namun pengering jenis ini umumnya mempunyai kapasitas yang besar sehingga untuk kapasitas kecil masih banyak kendala. Sedangkan kapasitas yang kecil ini banyak dibutuhkan baik untuk industri farmasi maupun untuk industri sari buah-buahan dalam bentuk serbuk. Selain itu spray dryer dengan kapasitas kecil dibutuhkan terutama untuk industri mikro bahkan industri rumahan. Penelitian ini bermaksud melakukan eksperimen dan mengetahui karakteristik bahan dari pengujian dengan spray dryer (kapasitas kecil - 5 kg larutan tiap jam). Eksperimen dilakukan dengan parameter yang akan divariasikan pada alat ini meliputi laju aliran udara pengering, tekanan udara kompressor dan temperatur udara pengering. Hasil dari eksperimen dan simulasi CFD pada pengering semprot kapasitas kecil ini adalah diperoleh antara data eksperimen dengan simulasi didapat laju penguapan yang hampir sama. Dimana semakin tinggi suhu udara masuk ke ruang pengering maka laju penguapan semakin kecil. Untuk pengujian, bahan yang diuji adalah air dan air dengan kandungan gula 2 %.

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Indonesia has a natural outcome very much, which in its processing and drying process often requires them to use a spray dryer. The advantages of this type of dryer are mainly for heat-sensitive material. The rate of heat transfer and mass transfer for a droplet moving in a spray dryer is very high. So because the evaporation rate is very high then the droplet was maintained at law temperature. However, this type of dryer generally has a large capacity so that for small that for small capacity are still many obstacles. While the capacity of those small muchneeded goods for the pharmaceutical industry as well as for the fruit juice industry in the form of powder. Also spray dryer with a small capacity needs, especially for micro industries and even a cottage industry.

This study intends to conduct experiments and investigate the characteristics of the test material with a spray dryer (small capacity - 5 kg of solution per hour). Experiments carried out with the parameters to be varied in this include the drying air flow rate, air pressure and temperature of drying air compressor.

Result from experiment and CFD simulations on small capacity dryers are obtains between experimental data obtained by simulating the evaporation rate is almost the same. Where the higher the air temperature into the drying chamber, the smaller the evaporation rate. For testing, the tested materials are water and water with sugar content of 2%."