What is the theoretical time necessary to...

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Question 1 of 205eccef9dbacbc34ba4d45e41

What is the theoretical time necessary to reduce the temperature of 40,000 pounds of onions (placed in a refrigerated container) from 75°F to a set point temperature of 46°F? (The specific heat of onions is 0.90 BTU/LB/°F. The trailer heat gain is 6,500 BTU/hr, with a properly operating refrigeration cooling capacity of 45,500 BTU/hr.)

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🔍 Key Concepts

• Sensible heat formula for cooling a product: Q = weight × specific heat × temperature change • How to adjust net refrigeration capacity when there is a constant trailer heat gain • Converting BTU/hr cooling load into time (hours and minutes) once total BTUs to be removed are known

💭 Think About

• First, how many total BTUs must be removed from the onions alone to go from 75°F down to 46°F, using weight and specific heat? • Once you know the total BTUs, what is the effective cooling capacity when you consider both the unit’s rated capacity and the constant heat gain into the trailer? • After finding the time in hours from BTUs ÷ (BTU/hr), how do you accurately convert any decimal fraction of an hour into minutes to compare with the choices?

✅ Before You Answer

• Be sure to use the temperature difference (ΔT) between 75°F and 46°F, not the absolute temperatures • Subtract the trailer heat gain from the unit’s rated capacity to get the net BTU/hr available for cooling the onions • Double-check unit consistency: pounds, BTU/LB/°F, and BTU/hr so that your final division yields hours, then convert to hours and minutes carefully

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