Heat Transfer in Solar Dryers
Figure 4. Two examples of mixed-mode dryers.Copyright 2022 Roberto Dimaliwat, University of Houston RET
Understanding the concepts of conduction, convection and radiation help engineers design and build systems that employ the process of heat transfer. In this activity, students use a hair dryer, hot plate and a heat lamp to show the three types of heat transfer and how these processes can be used in agricultural engineering applications. They compare the time it takes for each process and, as they learn about these processes, students delve deeper into why there are time differences for each.
Since ancient times, people have been preserving food using solar energy by the process of heat transfer using solar dryers. Designs of different solar dryers have improved from the simple hanging of food to some involving some sort of automation. All three types of heat transfer, conduction, convection, and radiation are observed in solar dryers and these processes are used to engineer efficiency within solar dryer designs.
Solar drying is considered to be a simultaneous application of heat and the removal of moisture from foods which is an important process for the future of food security and sustainability. Solar drying is a method used in the food industry and in agricultural engineering as a sustainable food processing technology that minimizes waste while complying with extremely rigorous food safety challenges.
Solar dryers are used to improve the quality of the product and to reduce the drying time compared to drying products by direct sunlight. There are many types and applications of solar dryers to dry different types of agricultural products such as cereals, fruits, vegetables, meat, fish, and aromatic plants. These applications have been, and continue to be, improved by many engineers to increase the drying efficiency and improve the final quality of the dried products.
Heat transfer is a specific concept in engineering. It deals with the impact of conduction, convection, and/or radiation in specific applications. Thermal engineers can help product engineers and designers optimize the thermal energy efficiency of their device or system.
After this activity, students should be able to:
- Define conduction, convection and radiation.
- Describe at the molecular level how heat is transferred by conduction, convection and radiation.
- Explain the time differences on each process as they transfer heat from a source to an object or a substance.
- Show how conduction, convection and radiation is applied in a solar dryer and give examples for each process.