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newbphysic
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Consider an electric motor with a shaft power output of
20 kW and an efficiency of 88 percent. Determine the rate at
which the motor dissipates heat to the room it is in when the
motor operates at full load. In winter, this room is normally
heated by a 2-kW resistance heater. Determine if it is necessary
to turn the heater on when the motor runs at full load.
My question is how can i find heat dissipate ?
1. Homework Statement
power output = 20 kW
efficiency = 0.88
operates at full load
power input = 20/0.88 = 22.72 kW
Method 1 (only inefficiency causes heat) : (1-0.88)* (22.72) = 2.72 kW
Method 2 (inefficiency causes heat & energy from shaft movement cause increase in air kinetic energy which in the end become thermal energy) = power input = 22.72 kW
Method 3 (from solution manual which i don't understand) = (1-0.88) * power output = 0.12 * 20 = 2.4 kW
Which one should i use and why ?
20 kW and an efficiency of 88 percent. Determine the rate at
which the motor dissipates heat to the room it is in when the
motor operates at full load. In winter, this room is normally
heated by a 2-kW resistance heater. Determine if it is necessary
to turn the heater on when the motor runs at full load.
My question is how can i find heat dissipate ?
1. Homework Statement
power output = 20 kW
efficiency = 0.88
operates at full load
power input = 20/0.88 = 22.72 kW
The Attempt at a Solution
Method 1 (only inefficiency causes heat) : (1-0.88)* (22.72) = 2.72 kW
Method 2 (inefficiency causes heat & energy from shaft movement cause increase in air kinetic energy which in the end become thermal energy) = power input = 22.72 kW
Method 3 (from solution manual which i don't understand) = (1-0.88) * power output = 0.12 * 20 = 2.4 kW
Which one should i use and why ?