ME 304_Design Project-Cool Fruit1

ME 304_Design Project-Cool Fruit1 - The Design and Analysis...

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The Design and Analysis of a Fruit Refrigeration System Clemson University ME 304-001 April 21, 2009 David Floyd Mike Julian Josh Martin

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Problem Statement Design a forced-air cooling system for a company whose refrigeration capacity is 200 tons. The cooling system must be designed for fruits whose diameters do not exceed 7 cm. The fruits are to be cooled from an initial temperature of 28 ºC to an average temperature of 8 ºC. The air temperature is to remain between -2 ºC and 10 ºC at all times, while the velocity of the air approaching the fruit must remain under 2m/s. The cooling section can be as wide as 3.5 m and as high as 2 m. Obtain reasonable values for the fruit properties (specific heat, density, etc.) and assuming a reasonable value of the packing of the box (i.e., fraction of air volume in a box), recommend reasonable values for the quantities related to the thermal aspects of the forced air cooling, including: a) How long the fruits need to remain in the cooling section b) The length of the cooling section c) The air velocity approaching the cooling section d) The product cooling capacity of the system, in kg (fruit)/hr e) The volume flow rate of air f) The type of heat exchanger for the evaporator and the surface area of the air inside Assumptions: 1. Neglect heat generation from the fermentation and rotting of fruit. 2. Neglect heat transfer loss from radiation to the environment. 3. Neglect heat transfer loss from conduction to the wires holding the fruit in place due to the wire diameter being very small in comparison to the size of the orange. 4. Laminar flow is assumed over all of the oranges from the front slate to the last slate in each crate. 5. Boundary Layer is not greater than 1 cm [Ref. 6] Constants of the incoming air and the slates: The initial velocity of air, V i , was chosen to be 2 m/s to maximize the cooling capacity. A higher velocity will reduce the cooling time of the fruit. The height of the slate containing the fruit is 2 m. The width of the slate containing the fruit is 3.5 m. 2
The dimensionless ratio of inner and outer radii, r*, is taken as 1. The incoming air temperature, T ambient , is chosen to be 271 K. This incoming air temperature is as low as allowed, which will maximize cooling. Properties of an Orange: Oranges were chosen for the analysis because of their dimensional consistency. The diameter, D, was assumed to be 7 cm for all fruit. The initial temperature of each fruit, T fi , was given to be 301 K. The final average fruit temperature throughout the refrigeration system does not exceed 8.4 ºC. The 0.4 was chosen to accommodate higher temperatures for additional rows; however, it is considered appropriate to avoid rounding up to 9 ºC.

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ME 304_Design Project-Cool Fruit1 - The Design and Analysis...

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