A115-volt electrical heater is used to warm 0.3 m3/s of air at 100 kpa and 15°c to 100 kpa and 30°c. how much current in amperes must be supplied to this heater? the gas constant of air is 0.287 kpa·m3/kg·k. the constant pressure specific heat of air at room temperature is cp = 1.005 kj/kg·°c.

The amount of current supplied to heater is 47.57 A

Solution:

As per the question:

Voltage of electric heater, V =  115 V

Volume rate of flow of air,

Initial temperature of air, T = = 273 + 15 = 288 K

Final temperature of air, T' = = 273 + 30 = 303 K

Initial Pressure = Final Pressure, P = 100 kPa

Specific heat of air,

Gas constant, R = 0.287

Now,

To compute the amount of current supplied to the heater, we assume the steady state operation and neglecting the effects of kinetic energy and potential energy:

Specific volume, 'v' of the air at the inlet is given by:

Mass flow rate of air can be given by:

Considering the system of the pipe containing air and using the energy balance on this system:

Therefore,

Thus

Also, we know that:

where

I = current in amperes

Now, comparing the two eqns, we get:

this is true

explanation:

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