67A-4 |
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L. G. RÍOS-CASAS1, A. López-Malo2, R. Chavela-Guerra, and A. Alarcón-García. (1) Departamento de Ingeniería Química y Alimentos, Universidad de las Américas, Puebla, Sta. Catarina Mártir, Cholula, Puebla, 72820, Mexico, (2) Ingenieria Quimica y Alimentos, Universidad de las Americas-Puebla, Cholula, Puebla, 72820, Mexico Refrigeration and freezing of perishable food products is an important application area of Thermodynamics. Thus, they can be presented as motivating examples in basic engineering courses for undergraduate students. Excel and Visual Basic were used to develop a computer program that performs mass, energy and entropy (S) balances for both systems: the refrigerant and the food product. R-134a was chosen to be the working fluid in a vapor-compression refrigeration cycle and the food product can be selected from a data base that includes several fresh fruits and vegetables. The variables implicated in the analysis for the cycle are: power and efficiency for the compressor, condenser and evaporator heat duty and pressure drop in the valve. The process path for the refrigerant is visualized on a T-S diagram. For simplicity, the temperature is assumed to be uniform within the fruit or vegetable and its thermal properties like heat capacity and latent heat are calculated on the basis of its water content. One of the parameters involved in the study is the time required to achieve the desired temperature; otherwise, the food final temperature is obtained. Besides, the food freezing curve is displayed showing the freezing point and the temperature variation with time, as well as the T-H and T-S diagrams. In addition to the classroom instruction, the program was provided to the students as a resource to solve problems. They found this way of learning highly innovating and exciting, as revealed in the course evaluations that exceeded our expectations. The user-friendly interface demonstrated to be an excellent tool to teach Thermodynamics; it encouraged the students to work and enhanced their analysis and learning skills.
Session 67A, Education: General
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