Enfriamiento De Manzanas Articulo De Transferencia De Calor

NUMERICAL STUDY OF APPLE COOLING IN TANDEM ARRANGEMENT ESTUDIO NÚMERICO DE ENFRIAMENTO DE MANZANAS DISPUESTAS EN TANDEM
MARCIO ARÊDES MARTINS
Associate ProfessorUniversidad Federal de Viçosa, MG, Brazil,aredes@ufv.br

LEANDRO SOARES DE OLIVEIRA
Associate Professor, Universidad Federal de Minas Gerais MG, Brazil,leandro@deeq.ufmg.br

JAIRO ALEXANDER OSORIO SARAZ
AssistantProfessor,Universidad Nacional de Colombia – Medellín, aosorio@unal.edu.co Received for review December 12 th, 2009, accepted September 16th, 2010, final version October 6 th, 2010 ABSTRACT: The conjugated cooling of apples in tandem arrangements on trays was studied in this work by numerical simulation using a CFD code. The governing equations were discretized and solved using the finite volume method onunstructured triangular meshes; and a coupling scheme for the fluid and solid heat transfer problems was proposed. The computational model was validated using two test cases in which local and average Nusselt numbers are reported in the literature. The local Nusselt number for each apple was obtained during one hour of air cooling as a function of the Reynolds number. Nusselt number and temperaturedistribution were found to vary in the apples due to the conjugate behavior of the problem. The conjugate approach showed itself to be a powerful tool for optimizing the convective heat transfer correlations reported in the literature. KEYWORDS: Cooling of fruits; conjugate problem; unstructured finite-volume; triangular mesh; numerical simulation. RESUMEN: El enfriamiento conjugado de manzanasdispuestas en tándem en bandejas fue estudiado en este trabajo usando una simulación numérica en CFD. Las ecuaciones gobernantes fueron discretizadas y resueltas usando el método de volúmenes finitos sobre mallas no estructuradas triangulares, y fue propuesto un esquema de acoplamiento de transferencia de calor entre la parte sólida y fluida. El modelo computacional fue validado usando el número de Nusseltlocal y Nusselt promedio que son reportados en la literatura. La variación del numero de Nusselt y de la distribución de temperatura en las manzanas, fueron encontrados debido al comportamiento conjugado del problema. La aproximación conjugada demostró ser una gran herramienta para optimizar correlaciones convectivas de transferencia de calor reportadas en la literatura. PALABRAS CLAVE:Enfriamiento de frutas, problemas conjugados, volumen finito no estructurado, malla triangular, simulación numérica.

1. INTRODUCTION Agricultural products should be cooled from ambient temperature conditions to their optimal storage temperature in order to minimize post-harvest deterioration [1]. Significant loss of fresh fruits is observed due to decay and shriveling as a result of improper storage andhandling conditions employed after harvest [2]. In practice, storage facility managers often establish and apply storage conditions based on experience thus allowing for some product losses due to the application of non-optimal conditions. Global heat and mass transfer rates through product layers are assumed and local transfer intensities are frequently

neglected. Thus, the complexinteractions between products in the same layer and between layers are not taken into account. Computational fluid dynamics and computer modeling have been used to study problems in the agricultural and food industries [1, 3, 4, 5 ]. Conjugate heat transfer and fluid flow in a channel containing heated elements has been studied for several decades, using both numerical and experimental methods [6, 7, 8, 9].Although such problems were mainly focused on the cooling of electronic components, some post-harvest processing techniques utilize the same problem configuration. The conjugate heat transfer problem for laminar flow over an array of three heated obstacles

Dyna, Year 78, Nro. 166, pp. 158-165. Medellin, April, 2011. ISSN 0012-7353

Dyna 166, 2011

159

was solved using a control volume...