Your vessel has received a refrigeration container of 16 long tons of cabbage, loaded at 1700 hours on Friday, with a beginning temperature of 80°F. At what time on Saturday will the box theoretically reach its set point temperature of 50°F, assuming the system is operating correctly? (The specific heat of cabbage is 0.94 BTU/LB/°F. The container has a heat gain of 6,000 BTU/hr, and the refrigeration system's capacity is 40,000 BTU/hr.)
• Specific heat and how to calculate total BTUs to cool a cargo from one temperature to another • How to convert long tons to pounds correctly • Net refrigeration effect: refrigeration capacity minus heat gain gives effective BTU removal per hour
• First, find how many pounds of cabbage you have and how many degrees it must be cooled. What formula links mass, specific heat, temperature change, and BTUs? • Once you know the total BTUs that must be removed from the cabbage, how do you adjust the system capacity to account for the constant heat gain into the container? • After finding the net BTUs removed per hour, how do you turn that into a time, and then add that time to the starting time of 1700 Friday to get to a clock time on Saturday?
• Double-check your long tons to pounds conversion (1 long ton = 2,240 lb). • Be sure you are using only the cabbage mass with specific heat, not including the container, when calculating BTUs to be removed. • Confirm you subtract heat gain from system capacity before calculating the cooling time.
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