Chapter 1
Basics of Heat Transfer
130
A room is heated by the radiator, and the warm air is distributed by a fan. Heat is lost from the room.
The time it takes for the air temperature to rise to 20°C is to be determined.
Assumptions
1
Air is an ideal gas since it is at a high temperature and low pressure relative to its critical
point values of 141
°
C and 3.77 MPa.
2
The kinetic and potential energy changes are negligible,
.
3
Constant specific heats at room temperature can be used for air, C
ΔΔ
ke
pe
≅≅
0
p
= 1.007 and C
v
=
0.720 kJ/kg·K. This assumption results in negligible error in heating and airconditioning applications.
4
The local atmospheric pressure is 100 kPa.
Properties
The gas constant of air is
R
= 0.287 kPa.m
3
/kg.K (Table A1). Also, C
p
= 1.007 kJ/kg·K for air
at room temperature (Table A15).
Analysis
We take the air in the room as the system. This is a
closed system
since no mass crosses the
system boundary during the process. We observe
This is the end of the preview. Sign up
to
access the rest of the document.
This note was uploaded on 01/14/2012 for the course PHY 4803 taught by Professor Dr.danielarenas during the Fall '10 term at UNF.
 Fall '10
 Dr.DanielArenas
 Thermodynamics, Mass, Heat

Click to edit the document details