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Indonesia has an opportunity in developing the coffee processing industry, because apart from having a large market, it is also supported by potential raw materials. Therefore, strategic efforts are needed, such as downstream in order to increase added value and increase production capacity (Kemenperin, 2019). To determine the quality of the coffee can be seen based on two tests namely physical quality testing, and taste. Moisture value of coffee beans the maximum is 12.5%. One form of control is an increase in coffee processing technology, namely roasting machines (Maulid et al, 2021). This research focuses on forced convection hot air flow by a blower whose speed is engineered using the help of a dimmer speed controller to obtain optimal heat and mass transfer results by experimentally varying airflow and heat transfer then obtaining optimal speed and temperature values. Temperature also affects the value of the forced convection coefficient. The largest convection coefficient is found in the variation of the highest temperature value test, namely 297.5 ᵒC with a value of 43.66 W/m2 ᵒC. The lowest convection coefficient value lies in the experimental variation with an air flow velocity value of 11.4 m/s at a temperature of 297.5 ᵒC with a convection coefficient value of 28.38 43.66 W/m2 ᵒC. The convection heat transfer value (Q) will increase when the flame temperature (T) and air flow velocity increase (v). The greatest electric power will increase when the air flow velocity increases with a low flame temperature value. Effect of airflow velocity (v) and flame temperature (T) simultaneously on the final roasting temperature of 87.5%. [ABSTRACT FROM AUTHOR]

Utilization of geothermal energy is still dominated by indirect use for electricity generation, beside geothermal energy can also be used for direct application. Direct use is mostly using a low enthalpy geothermal resources (<150°C), one of the applications of low enthalpy geothermal energy is for drying process. Drying is a post-harvest method that aims to improve the quality of agricultural products by removing some of the water to an agreed an d safe limit, while microorganisms unable to grow and multiply. Coffee is one of the important commodity which has an important role in economic sector in Indonesia. In this study, the Computational Fluid Dynamics (CFD) method is used to determine and predict the drying chamber's temperature and air flow distribution patterns. The simulation process is carried out by varying the thermosiphon heat temperature (50, 60, and 70 °C) and the air inlet velocity (0.2, 0.4, and 0.6 m/s). The simulation results show the uniformity of temperature in the drying chamber, with the highest drying air temperature is 57.72°C, where the air temperature is influenced by the thermal temperature of the thermosiphon and the large air flow velocity. Based on the simulation conditions, the highest amount of heat needed in the drying process is 118.79 kJ/kg at temperature condition of 50°C with velocity 0.6 m/s and the lowest is 117.41 kJ/kg. [ABSTRACT FROM AUTHOR]