Air passes over an electrical heater at a steady rate of 2500cm^3 per second.

[Student-]

Homework Statement

Air passes over an electrical heater at a steady rate of 2500cm^3 per second. The inlet temperature of the air is 20^oC ( 20 degrees celsius ) and the steady outlet temperature is 40^0C ( 40 degrees celsius)
a) What heat is absorbed by air passing over the heater in 2 hours
b) Obtain an estimate for the power rating of the heater
Density of air ( 1.2 kgcm-3)
Specific heat capacity of air : 1000 J-1Kg-1K-1

Homework Equations

So I think that I should use the equation Q=mcΔθ

The Attempt at a Solution

Here's what I did :
2500cm^3=2500g=2.5kg
Since 2.5kg is heated every second then 2hrs of heating would heat 2.5x7200 = 18,000kg of air.
ΔθOutlet-Inlet temperature = 40-20 = 20 degree celsius change in temperature,
Specific Heat capacity of air : 1000 Jkg-1K-1
Q=mxcxΔθ
= 18000x1000x20
=3.6x10^8
Which is wrong because the answer at the back of the book had 4.32x10^5. I've tried, but I really need some help :) Thanks

 

[tiny-tim]

Welcome to PF!

Hi Student-! Welcome to PF!

(try using the X² button just above the Reply box )

Quickly dividing 4.32 by 3.6, my eye is drawn to …

Density of air ( 1.2 kgcm-3)

 

[technician]

I think you have mis- calculated the mass of air.
The density of air is 1.2kg/m^3 not 1.2kg/cm^3

 

[Student-]

I think you have mis- calculated the mass of air.
The density of air is 1.2kg/m^3 not 1.2kg/cm^3

Thanks a lot :D I got out the question and I saw my error- :)

 

[Student-]

Hi Student-! Welcome to PF!

(try using the X² button just above the Reply box )

Quickly dividing 4.32 by 3.6, my eye is drawn to …

Thanks I got it out eventually :D :)