Judul: Kajian Pengering Rotari Tipe Co-Current untuk Pengeringan Sawut Ubijalar
Abstrak: Rotary drying is a very complicated process that implies not only thermal drying but also movement of wet material within the dryer. The objective of this research were to evaluate performance of rotary dryer, to identify amount of energy consumption which are used during the drying process, to develop model of rotary drying and to identify drying cost per kg of sweet potato grates. Drying characterisctics of product need to be established because of important information for the design, prediction, and modelling. The model of rotary drying was constructed based on energy and mass balance. The differential equations were solved by simultaneous-numerically. This model applied to predict temperature dryer chamber, temperature product, moisture content and RH. The result showed that the performance of rotary dryer depends on feed rate sweet potato grates into drying chamber. High feed rate could decrease temperature in drying chamber. The residence time of all experiments were 18 minutes. Hold-up of all experiments in this study were relatively low that ranges 9-36 kg. The specific energy consumption in all of the experiments was between 5.51-14.26 MJ/kg H2O. The high feed rate (3 kg/1 min) had the lowest specific energy consumption. Conversely, the lowest feed rate (3 kg/4 min) had the highest specific energy consumption for all experiments. The high total efficiency could be found from high feed rate, the feed rate (3 kg/1 min) is highest total efficiency for all experiments. The model can be used to obtain temperature profiles of air and the product in dryer chamber. Using the model, change of air temperature and product during drying were successfully predicted. Coefficient of determination (COD) between measured and calculated ranges 0.819-0.992, respectively. However, the model could not predict moisture content and RH accurately. The drying cost of grates is Rp 1 494 per kg wet grates. It is relatively expensive for drying.
Keyword: Co-current rotary dyer, Specific energy consumption, Feed rate, Sweet potato

Judul: Performance of Rotary Bed Dryer for Paddy in Several Configured Rotations
Abstrak: Mesin pengeringan tipe rotari tumpukan merupakan jenis pengeringan tipe mekanis untuk biji-bijian yang menggunakan prinsip putaran saat mengaduk bahan. Jenis biji-bijian yang digunakan pada penelitian ini adalah gabah. Penelitian ini bertujuan utuk mengetahui pengaruh perlakuan jeda dan lama waktu pengadukan dengan suhu tetap 45°C dalam meningkatkan keseragaman kadar air gabah menggunakan pengering tipe rotari tumpukan. Metode pengujian beda kadar air pada titik A dan B adalah pengukuran kadar air dengan prinsip gravimetri (oven) dan pengukuran keseragaman dengan prinsip t-test dengan P(t>T) dan faktor kesalahan α=0,05 pada dua sisi (two-tail). Hasil pengujian mesin pengering tipe rotari tumpukan menunjukkan bahwa seluruh perlakuan memberikan kadar air yang tidak berbeda (beda 0 %bb.) antar lapisan dalam dan luar pada akhir pengeringan. Konsumsi energi spesifik yang dibutuhkan sebesar 2684,7-4144,8 kJ/kg uap air sehingga menunjukkan bahwa konsumsi energi spesifik pengering tipe rotari tumpukan pada pengeringan gabah lebih kecil dibandingkan KES pengeringan biji-bijian konvensional (4260 kJ/kg uap air). Energi pengadukan hanya 2 % sedangkan energi pemanasan sebesar 89 % dari konsumsi energi total pengeringan dan biaya kebutuhan listrik. Hasil pengujian yang telah dilakukan menunjukkan adanya pengaruh besar proses pengadukan bahan yang dikeringkan untuk memperkecil nilai beda kadar air di lapisan luar dan lapisan dalam. Proses pengadukan tidak berpengaruh besar terhadap konsumsi energi spesifik dan biaya kebutuhan listrik., Rotary bed dryer is mechanical dryer for grains with rotary system for mixing grains. The grains that used in this study is paddy. The aim of this study is determine the impact of interval and duration of rotations with a fixed temperature in 45°C to increase the uniformity of the paddy with rotary bed dryer. Different moisture content test method for A and B point with gravimetric method (oven) and define uniformity using is used t-test statistic method in P(t>T) and failure factor (α) is 0,05 with two-tails test. The result of this rotary bed dryer show that all treatment was uniform (difference 0 %bb.) between inner and outer layer at the end of the drying process. The specific energy consumption required is 2684,7-4144,8 kJ/kg, it shows that the specific energy consumption of rotary bed dryer to reduce moisture content is smaller than the specific energy consumption of conventional grain drying (4260 kJ/kg). The mechanical energy was 2 % and the heated energy was 89 % of the total energy consumption and the cost of electricity. The results of the tests showed that the stirring process has to influence to decrease the different moisture content in outer later and inner layer. The stirring process does not effect the total energy consumption and the cost of electricity.
Keyword: drying, paddy, rotary bed dryer, uniformity

Judul: Approximation of the Median of Poisson Distribution Using the Relation of Poisson-Gamma Distribution
Abstrak: A major drawback of median is that median cannot usually be defined in closed form, even in the cases where their distribution functions are known. This study gives an approximation of the closed form for the median of the Poisson distribution by using the relation of Poisson-Gamma distribution. The approximation uses elementary techniques based on the monotonicity of certain sequences involving tail probabilities of the Poisson distribution and the Central Limit Theorem. Furthermore, a closed form expression for the mean absolute deviation 􀜧|􀜰􀰒 􀵆 􀜯􀝁􀝀􁈺􀜰􀰒􁈻| is also studied. The median is relevant because of the fact that it minimizes the mean absolute deviation of a Poisson random variable (􀜰􀰒􁈻 by considering median as central tendency.
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