How to Determine the Rate of Heat Supply by an Electric Car Motor?

What is the rate of heat supply by a 90-hp electric car motor with 91 percent efficiency?

A 90-hp electric car is powered by an electric motor with an average efficiency of 91 percent. What is the rate of heat supply by the motor to the engine compartment at full load?

Answer

The rate of heat supply is 8.901 horse-power.

From Thermodynamics, energy efficiency of the electric car (η), no unit, is the ratio of translational mechanical power (E_out), measured in horse power, to electric power (E_in), measured in horse-power. The rate of heat supply (E_l), measured in horse-power, by the motor to the engine compartment at full load is the difference between electric energy and translational mechanical energy.

Mathematically, if η = 0.91 and E_out = 90 hp, then the rate of heat supply can be calculated as:

E_l = (1/η - 1) * E_out

Substituting the values, we get:

E_l = (1/0.91 - 1) * 90 hp

E_l = 8.901 hp

Therefore, the rate of heat supply by the motor is 8.901 horse-power.