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Drying is a process that is widely used in the food processing industry. There are several factors that influence during the drying process, one of which is the speed of air flow in the dryer unit. The air flow velocity inside drying unit can occur by forced airflow and natural airflow. Natural air flow is the flow of air created due to the difference in pressure caused by differences in temperature and air density, so there is no thrust by the blower. This study aims to estimate the natural airflow velocity in modeling system unit. This modeling system unit has a source of heat energy that can be used to adjust the room temperature level of the heat generator, and is equipped with a chimney that has an adjustable height and diameter. This research was conducted experimentally, through empirical mathematical model development using dimensional analysis. The variables measured include: heat generator room temperature (TS), system outside air temperature (TL), chimney diameter (d), chimney height (H), exhaust air flow velocity (V). The results of this study obtained mathematical model of airflow velocity. The mathematical model showed good agreement due to measurement results with average of errors was about 9%.

Crackers are a processed product that is much favored by the people of Indonesia. Crackers after frying have crunchy physical properties, however, if not stored properly the product is easy to change its physical properties, namely crackers become not crunchy or sluggish (mlempem). The change in crackers to "mlempem" can be understood because fried crackers have hygroscopic properties or easily absorb water. This study aims to examine changes in the quality of crackers during reconditioning, and the changes that occur are quantified in the form of a mathematical model. In this study, what is meant by reconditioning is an action to return the sluggish cracker to a crispy cracker. The quality of crackers is largely determined by the level of crispness. The physical properties of crackers that affect the level of crispness are water content, stress and strain. The research was conducted in a laboratory using ingredients in the form of crackers fried in sand (without oil) made from tapioca starch. The equipment used includes a stress and strain gauge (Universal Testing Machine), oven, analytical balance, sand fryer, tachometer, hygrometer, thermocouple, interface, data logger, and computer. The results of the study obtained a mathematical model of changes in the quality of crackers during reconditioning, which included reconditioning of moisture content, stress, and strain.

Quality evaluation, in particular chemical properties, of orange fruit commonly conducted by destructive method by extracting its juice. A near infrared spectrometer (NIRS) can be used to quantify orange chemical properties with non-destructive method. This research aimed to design a handheld NIRS using AS7263 sensor and Arduino programming to estimate the Siamesa orange quality in its acidity (pH), total soluble solids (TSS) and vitamin C. The AS7263 sensor has six NIR channels for different wavelengths, i.e. R (610 nm), S (680 nm), T (730 nm), U (760 nm), V (810 nm) and W (860 nm). For that, a performance test was carried out using 300 samples of orange. Result show that evaluation of orange quality in acidity and TSS has mean absolute percentage error (MAPE) < 10%, and the vitamin C shows > 10%. In addition, the estimation of orange chemical properties by backpropagation neural network (BPNN) yielded better results compared to simple regression and multiple regression methods.

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