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Simulasi Pemerkiraan Parameter Sifat Fisikawi Bahan Makanan dengan Metode Penjejak Parameter B. Rahardjo
agriTECH Vol 14, No 2 (1994)
Publisher : Faculty of Agricultural Technology, Universitas Gadjah Mada, Yogyakarta, Indonesia

Simulation of the parameter tracking method was used to estimate the physical parameters of food material. The input-output relationships of the materials were based on known mathematical models. Three mathematical models of the food properties were studied: the Kelvin model of linear viscoetastic material, the power law of non Newtonain liquid, and the impact model of a non linear viscoelastic spherical object. The results indicated that the parameter tracking method can determine the parameters of the models correctly. However the speed of the estimation depends on the models. The estimation of the parameters of the linear model converged Faster than that of non linear models.

Model Perubahan Kadar Air Emping Selama dalam Kemasan Plastik Polipropelin B. Rahardjo; P. Setyowato; T. Wibowo
agriTECH Vol 17, No 3 (1997)
Publisher : Faculty of Agricultural Technology, Universitas Gadjah Mada, Yogyakarta, Indonesia

The objective of this study was to develop a mathematical model for predicting the moisture content of food chips during packaged by permeable plastic film. The mathematical model developed was based on water vapor migration trough permeable film, equilibrium moisture content and mass balances. Samples for the experiment were fried chips made from roasted, pounded flat and dried Gnetum gnemon seeds (emping) found around the city of Yogyakarta. The fried emping chips were packaged using polypropelin plastics. The packages of the fried chips were than stored in glass bottles. The relative humidities of the storage atmosphere inside the bottles were adjusted using salts such that their ranges were between 10% to 90%. The moisture content of the fried emping chips were observed for about twenty (20) days until they reach their equilibrium moisture contents. The results indicate that the model can be used quite well to predict the moisture content of fried chips during packaged in plastic film. However, for dried chip packages stored on atmospheric relative humidity higher than 70% the rate of the moisture content change tends to increase. The range of food moisture content stored under higher atmospheric relative humidity was wider than that stored on atmosphere with lower relative humidity. This wider range of moisture content change makes the model can not predict adequately the equilibrium moisture content by using a single moisture-humidity linear relationship. Estimation of the chip moisture content during storage using two linear relationships was better than that using a single linear relationship.

Pengukuran Volume Benda Padat Berbagai Bentuk dengan Berdasarkan Volume Desakan Pada Bahan Curah B. Rahardjo; B. Suratmo; R. Kushendrati
agriTECH Vol 17, No 4 (1997)
Publisher : Faculty of Agricultural Technology, Universitas Gadjah Mada, Yogyakarta, Indonesia

Some of the standard methods to measure the solid volume are based on fluid displacement. However, most of agricultural products are absorbable to water and certain fluids. Therefore the use of fluids to determine the volume of agricultural products can cause error. Where as bulk materials on certain condition behave and flow such as fluids but are not absorbable to products. Accordingly the objectives of the research were to evaluate the accuracy of volume measurement of solid particles with several shapes using bulk materials and to determine the measurement error and its relation to the pertinent parameters. The volume determined using bulk materials were compared with that measured using standard methods. The errors of the measurements were related to the pertinent parameters such as granular size and solid particle size. Samples used were spheres, cylinders, cubes, prisms and any shapes of solid particles made from wood, glass, bronzes or stone with any shapes. The bulk material was sand found on rivers around the city of Yogyakarta. The results indicate that the particle volume can be determined using bulk materials. However, volume measured using bulk materials was higher than that determined using standard methods. The volume errors increases as the granular size increases and as the solid particle size decreases. The error can be related to the granular particle size ratio quite well. The corrected volume with the estimed error was closely similar to the volume determined using standard methods. Bulk materials consisting of small size, smooth surface and sphere like shape granules are likely ideal medium for solid volume measurements.

Penentuan Koefisien Perpindahan Panas Permukaan Bola Berdasarkan Pendekatan Analitik Perpindahan Panas Tak Tunak B. Rahardjo; Suhargo Suhargo; H. Tambunan
agriTECH Vol 17, No 4 (1997)
Publisher : Faculty of Agricultural Technology, Universitas Gadjah Mada, Yogyakarta, Indonesia

The standard method to determine the coefficient of surface heat transfer on spheres is based on the lumped capacitance method using spherical particles with Biot number less than 0,1. However, most agricultural products with spherical shapes have Blot number greater than 0,1. Several analytical approaches are available to determine the temperature distribution within the spheres with higher Biot number. Accordingly, the objectives of this research were to determine the coefficient of surface heat transfer based on analytical approaches and to compare the values to that determined by the standard method. Samples were spheres made from wood for analytical approach and made from copper for lumped capacitance method. The results indicate that the values of the coefficient of surface heat transfer determined by both methods were significantly similar. The conductivity, and the coefficient of surface heat transfer of spherical wood simultaneously can be determined using the analytical approaches for transient heat transfer on spheres.

Koefisien Perpindahan Panas Permukaan Bola dengan Aliran Udara Paksa dalam Pipa B. Rahardjo; B. Suratmo; Sukarjo Sukarjo
agriTECH Vol 18, No 2 (1998)
Publisher : Faculty of Agricultural Technology, Universitas Gadjah Mada, Yogyakarta, Indonesia

Handling and processing of agricultural products mostly consist of heat transfer. Commonly the heat process of agricultural products is conducted in closed systems with air forced circulation. The process of heat transfer is significantly controlled by the values of the coefficient of surface heat transfer. Therefore the objectives of the research were to determine the pertinent parameters affecting the coefficient of heat transfer of sphere in forced air circulation and then to develop the mathematical relationship of those parameters. The mathematical relationship was determined using dimensional analysis composing dimensionless numbers such as Nusselt, Reynolds and size ratio. The coefficient of surface heat transfer were determined by heat capacitance method and analytical approaches using samples of spheres made from copper and wood respectively. The results indicate that the relation of the dimensionless groups were significant. The coefficient of surface heat transfer appropriately can be expressed using the pertinent parameters.

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