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

• Student-
In summary, the conversation discusses the heat absorbed by air passing over an electrical heater at a steady rate and the power rating of the heater. The solution involves using the equation Q=mcΔθ and calculating the mass of air heated in 2 hours, taking into account the density and specific heat capacity of air. The incorrect calculation of the mass of air was identified as the source of error in obtaining the correct answer.
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 celcius ) and the steady outlet temperature is 40^0C ( 40 degrees celcius)
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 celcius 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

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 …
Student- said:
Density of air ( 1.2 kgcm-3)

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

technician said:
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- :)

tiny-tim said:
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 :)

## 1. What is the purpose of an electrical heater?

An electrical heater is used to convert electrical energy into heat energy, which can then be used to warm up the surrounding air or fluid.

## 2. How does the rate of air flow affect the heating process?

The rate of air flow determines how quickly the surrounding air will be heated. In this case, the steady rate of 2500cm^3 per second means that a consistent amount of air is being heated every second.

## 3. What is the role of air in the heating process?

Air is a necessary component in the heating process as it is the medium through which heat is transferred. In this scenario, the air is passing over the electrical heater, allowing the heat energy to transfer from the heater to the air.

## 4. How does the size of the heater affect the rate of air flow?

The size of the heater does not directly affect the rate of air flow, but it can indirectly impact it. A larger heater may require more energy to heat up the air, resulting in a slower rate of air flow. On the other hand, a smaller heater may heat up the air more quickly, resulting in a faster rate of air flow.

## 5. What are some factors that can affect the efficiency of the heating process?

The efficiency of the heating process can be influenced by various factors such as the quality of the heater, the temperature of the surrounding air, and any obstructions or barriers that may impede the flow of air over the heater. Additionally, the design and placement of the heater can also impact its efficiency.

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