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El-Mergib University Faculty of Engineering - Alkums Department of Chemical & Petroleum Engineering CHE 482, Transport Phenomena

The document is a homework assignment for a Transport Phenomena course. It contains: 1) A description of heat transfer and that temperature difference is the driving force for heat transfer. 2) A problem calculating the heat transfer and cost to heat a house from 10°C to 22°C using an electric heater. Assumptions are made about the air properties and calculations are shown to determine the mass of air, heat transferred, and cost. 3) A statement that thermal conductivity is a measure of the rate of heat transfer through a material based on its thickness, area, temperature difference, and material properties. 4) The document provides no other summary or context about the course.

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Esra Belhaj
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75 views9 pages

El-Mergib University Faculty of Engineering - Alkums Department of Chemical & Petroleum Engineering CHE 482, Transport Phenomena

The document is a homework assignment for a Transport Phenomena course. It contains: 1) A description of heat transfer and that temperature difference is the driving force for heat transfer. 2) A problem calculating the heat transfer and cost to heat a house from 10°C to 22°C using an electric heater. Assumptions are made about the air properties and calculations are shown to determine the mass of air, heat transferred, and cost. 3) A statement that thermal conductivity is a measure of the rate of heat transfer through a material based on its thickness, area, temperature difference, and material properties. 4) The document provides no other summary or context about the course.

Uploaded by

Esra Belhaj
Copyright
© © All Rights Reserved
We take content rights seriously. If you suspect this is your content, claim it here.
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Download as PDF, TXT or read online on Scribd
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Transport Phenomena CHE 482

El-Mergib University
Faculty of Engineering – Alkums
Department of Chemical & Petroleum
Engineering

CHE 482 ,Transport Phenomena

Name :
Esra Abdulmenem Ali Belhaj

ID:
3115128

Spring(2018-2019)

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Transport Phenomena CHE 482

problem one_II:
Correct the following statements giving any laws or examples you may see can
supportyour answer for each statement:
A- An energy transfer is heat transfer when its driving force is temperature
difference :
Heat transfer is energy in transit due to temperature difference . The temperature
difference is the driving force for heat transfer, just as the voltage difference is the
driving force for electric current flow and pressure difference is the driving force
for fluid flow. The rate of heat transfer in a certain direction depends on the
magnitude of the temperature gradient (the temperature difference per unit length
or the rate of change of temperature) in that direction. The larger the temperature
gradient, the higher the rate of heat transfer.

B- A house is heated from 10°C to 22°C by an electric heater, and some air
escapesthrough the cracks as the heated air in the house expands at constant
pressure. Theamount of heat transfer to the air and its cost are to be determined.
Assumptions
1- Air as an ideal gas with a constant specific heats at room temperature.
2- The volume occupied by the furniture and other belongings is negligible.
3- The pressure in the house remains constant at all times.
4- Heat loss from the house to the outdoors isnegligible during heating.
5- The air leaks out at 22°C.
Properties :The specific heat ofair at room temperature is Cp = 1.007 kJ/kg.°C.
Solution:

From ideal gas law :

PV = nRT

PV = (m/M)RT

Thus,the mass flow rate of air is :

-Assume the volume of air in the hous is :

A=400 m3

Then,the mass of the air :

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Transport Phenomena CHE 482

m=

( ) ( ) ( )
m=
( ) ( )

m =944.28 kg

The amout of the heat nedded to heating the air from 10 oC to 22 oC, at constant
pressure is:

Q = m Cp (T2 – T1)

Q =)499.28kg)*(1.007kJ/kg.K)*(22-10)K

Q =6033.3 kJ

1 KWh=0.075$

Cost =0,125$

C- The thermal conductivity of a material is the rate of heat transfre through a unit
thickness of the material per unit area and per unit temperature difference. The
thermal conductivity is a measure of how fast heat will be conducted in that
material. The mechanisms of heat transfer are Conductio ,Convection , and
Radiation . The parameters that effect the rate of heat conduction through a
windowless wall are the geometry and Surface area of wall, its Thickness, the
Material of the wall, and the Tempreture difference across the wall.

D-

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