9th Edition

ISBN: 9781259822674

Author: Yunus A. Cengel Dr., Michael A. Boles

Publisher: McGraw-Hill Education

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Chapter 4.5, Problem 39P

A 40-L electrical radiator containing heating oil is placed in a 50-m³ room. Both the room and the oil in the radiator are initially at 10°C. The radiator with a rating of 2.4 kW is now turned on. At the same time, heat is lost from the room at an average rate of 0.35 kJ/s. After some time, the average temperature is measured to be 20°C for the air in the room, and 50°C for the oil in the radiator. Taking the density and the specific heat of the oil to be 950 kg/m³ and 2.2 kJ/kg·°C, respectively, determine how long the heater is kept on. Assume the room is well sealed so that there are no air leaks.

FIGURE P4–39

Chapter 4.5, Problem 39P, A 40-L electrical radiator containing heating oil is placed in a 50-m3 room. Both the room and the

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Chapter 4.5, Problem 38P

Chapter 4.5, Problem 40P

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3 A 40-L electrical radiator containing heating oil is placed in a 50-m³ room. Both the room and the oil in the radiator are initially at 10°C. The radiator with a rating of 2.4 kW is now turned on. At the same time, heat is lost from the room at an average rate of 0.35 kJ/s. After some time, the average temperature is measured to be 20°C for the air in the room, and 50°C for the oil in the radiator. Taking the density and the specific heat of the oil to be 950 kg/m3 and 2.2 kJ/kg-°C, respectively, determine how long the heater is kept on. Assume the room is well sealed so that there are no air leaks. The gas constant of air is R = 0.287 kPa-m³/kg-K (Table A-1). Also, c = 0.718 kJ/kg-K for air at room temperature (Table A-2). Oil properties are given to be p = 950 kg/m³ and Cp = 2.2 kJ/kg.°C. 3 10°C Room Radiator The heater is kept on for Q min. 4

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