Assignment 1 Thermodyanmics

7/28/2019 Assignment 1 Thermodyanmics

1/23

ASSIGNMENT 1 THERMODYANMICS

COURSE : CHEMICAL ENGINEERING

NAME : SHILENGE T.P

STUDENT NO : 212046710

PATNER : LEKHULENI N.P

DUE DATE : 20/03/13

SUBMITTING TO : PROFFESOR KOLESNIKOV


2/23

APPARATUS USED TO PERFORM THESE EXPERIMENT


3/23

TITLE PAGE

EXPERIMENT PROOVING THE FIRST LAW OFTHERMODYNAMICS

1.ABSTRACT

2. INTRODUCTION

3.THEORY BASED ON THE CHAPTER4.OBJECTIVE OF THE EXPERIMENT

5. APPARATUS AND PROCEDURE

6. SAFETY PRECAUTIONS

7.ACKNOWLEDGEMENTS

8.CONCLUSION

9. RECOMMENDATIONS

10. REFERENCES

11. NOMENTLATURE


4/23

ABSTRACT

A hairdryer , digital anenometer, thermocouple, and multimeter can beused to demonstrate the first law of thermodynamics. A hairdryer which

is cheaper makes an excellent example of an open thermodynamic

system, and can be used as an effective piece of lab equipment.

Heat , work and mass all cross boundary. From the first law of

thermodynamics , the energy into the system has to equal the energy

out for the steady state. From the conservation of mass, which states

that mass can neither be created nor destroyed meaning the mass going

in to the system should equal to the mass going out of the system

The experiment requires one to consider all of the energy terms

associated with the hairdryer.

The energy going in includes the electric , work the total enthalpy of theincoming air, kinetic energy of the incoming air. Energy out includes the

total enthalpy of the outgoing air , and any heat transfer from the case to

the ambient. Potential energy differences between the inlet and the

outlet are also considered. By accounting for all of the energy terms one

should begin to recognise what is most significant and what could be

neglected

The first law of thermodynamic can be prooven in a form of any energy

in nature.


5/23

INTRODUCTION

A common hairdryer makes an example of an open thermodynamic

system. The figure below shows the energy terms that are involved in a

first law analysis. For a steady state condition the total energy in must

equal the total energy out. Attempt to measure all of these energy terms

and then compare the energy in with the energy out to show that the

hairdryer obeys the first law of thermodynamics. A hairdryer uses three

different forms of energies to work, electrical energy, heat energy andmechanical energy, electricity is used to generate forms of energy in the

hairdryer.


6/23


7/23

THEORETICAL BACKGROUND

The first law of thermodynamics also known as the conservation of

energy principle which stated that energy can neither be created nor

destroyed but it can only be converted from one form to the other


8/23

If we are interested in how heat transfer is converted into doing work,

then the conservation of energy principle is important. The first law of

thermodynamics applies the conservation of energy principle to systems

where heat transfer and doing work are the methods of transferring

energy into and out of the system. The first law of thermodynamics

states that the change in internal energy of a system equals the net heat

transferinto the system minus the net work done bythe system. In

equation form, the first law of thermodynamics is

U=QW.

Here U is the change in internal energyU of the system. Q is the

net heat transferred into the systemthat is, Q is the sum of all heat

transfer into and out of the system. W is thenet work done by the

systemthat is, W is the sum of all work done on or by the system. We

use the following sign conventions: if Q is positive, then there is a net

heat transfer into the system; if W is positive, then there is net work done

by the system. So positive Q adds energy to the system and positive W

takes energy from the system. Thus U=QW Note also that if more

heat transfer into the system occurs than work done, the difference is

stored as internal energy. Heat engines are a good example of this

heat transfer into them takes place so that they can do work. We will

now examine Q , W and U further.


9/23

The first law of thermodynamics is actually the law of conservation of

energy stated in a form most useful in thermodynamics. The first law

gives the relationship between heat transfer, work done, and the change

in internal energy of a system.

Heat Q and WorkW

Heat transfer (Q) and doing work (W) are the two everyday means of

bringing energy into or taking energy out of a system. The processes are

quite different. Heat transfer, a less organized process, is driven by

temperature differences. Work, a quite organized process, involves a

macroscopic force exerted through a distance. Nevertheless, heat and

Figure 2: The first law of thermodynamics is the

conservation-of-energy principle stated for a system where

heat and work are the methods of transferring energy for a

system in thermal equilibrium. Q represents the net heat

transfer

it is the sum of all heat transfers into and out of the

system. Q is positive for net heat transferinto the system. W

is the total work done on and by the system. W is positive

when more work is done bythe system than on it. The

change in the internal energy of the system, U, is related to

heat and work by the first law of thermodynamics, U=QW


10/23

work can produce identical results.For example, both can cause a

temperature increase. Heat transfer into a system, such as when the

Sun warms the air in a bicycle tire, can increase its temperature, and so

can work done on the system, as when the bicyclist pumps air into the

tire. Once the temperature increase has occurred, it is impossible to tell

whether it was caused by heat transfer or by doing work. This

uncertainty is an important point. Heat transfer and work are both energy

in transitneither is stored as such in a system. However, both can

change the internal energy( U)of a system. Internal energy is a form of

energy completely different from either heat or work.

Internal Energy U

We can think about the internal energy of a system in two different but

consistent ways. The first is the atomic and molecular view, which

examines the system on the atomic and molecular scale. The internal

energy(U)of a system is the sum of the kinetic and potential energies of

its atoms and molecules. Recall that kinetic plus potential energy is

called mechanical energy. Thus internal energy is the sum of atomic and

molecular mechanical energy. Because it is impossible to keep track of

all individual atoms and molecules, we must deal with averages and

distributions. A second way to view the internal energy of a system is in

terms of its macroscopic characteristics, which are very similar to atomicand molecular average values.

Macroscopically, we define the change in internal energy U to be that

given by the first law of thermodynamics:

U=QW.


11/23

Many detailed experiments have verified that U=QW, where U is

the change in total kinetic and potential energy of all atoms andmolecules in a system. It has also been determined experimentally that

the internal energy U of a system depends only on the state of the

system and not how it reached that state. More specifically, U is found to

be a function of a few macroscopic quantities (pressure, volume, and

temperature, for example), independent of past history such as whether

there has been heat transfer or work done. This independence means

that if we know the state of a system, we can calculate changes in its

internal energy U from a few macroscopic variables.


12/23

OBJECTIVES OF THE EXPERIMENT

1.To proove the first law of thermodynamics, to give students a basic

understand of the fundamental laws of thermodynamics and the ability to

use them in solving a range of simple engineering problems

2. To illustrate the relationship of the different energies found when the

hairdryer is operating

3.To transform energy in one form to another.


13/23

APPARATUS AND PROCEDURE

Hair dryer with 2 speed and 3 heat settings (max power 2000 W)

Stand for mounting hair dryer

Custom made holder for five thermocouples with thermocouples

Digital anenometer (measures air velocity, 0-30 m/s)

Two digital multimeters for measuring voltage and current

Any device for reading the thermocouples

Infrared thermometers temperature range -50 C to 300C

Dial calipers to measure the area

SAFETY PRECAUTIONS

During the experiment, the hairdryer should be well insulated to

avoid shocks caused by electric current

PROCEDURE

Setup a hairdryer and mount it on the holder to hold and balancethe hairdryer from moving

Measure the ambient temperature and the barometric pressure

using the thermocouples and barometer

Turn on the hairdryer and allow it to reach a steady condition

Record the voltage and current to the hairdryer

Measure and record the temperature


14/23

in each of the 17 regions of the hairdryer using the thermocouples

holding feature

Measure and record the differential speed the hairdryer driven by

the turbine inside the hairdryer

Measure and record the temperature of the nozzle

Turn off the hairdryer and measure and record all the necessary

physical dimensions

Inside diameter is to be measured using the dial caliper

Measure the velocity of the moving turbine inside the hairdryer,

using anenometer


15/23

TEST PROCEDURE

Before the experiment is perfomed the required data should be

measured, which includes:

Ambient temperature

Inside diameter of the outlet

Any measurements needed to determine the inlet area

Electrical work in: Voltage and current

Mass flow rate and enthalpy out: The outlet is divided into 17

equal area regions (figure5). Within each of these regions the

outlet temperature

The reason for dividing the outlet into regions is because the

temperatures and velocities have large variations across the outlet

due to the

locations of the internal components. This method gives much better

results than using

an average value across the cross-sections

Heat out: Surface temperature of the nozzle and length and

diameter of the heated area.

figure5


16/23

CALCULATIONS REGARDING THE EXPERIMENT

The basic first law of thermodynamics for the hairdryer can be written as

(

)

equation 1

Electric Work In:

W=

.equation 2

The above equation is used since the hairdryer has power(2000W)

and the mass flow rate can be calculated in order to get the work in

joules per kilogram.

The area of the nozzle is given by:

A=

..equation 3

The diameter of the nozzle of the hairdryer is to be measured using

the dial caliper making it easier to calculate the area using equation

3.

Heat Transfer:

Q = hA(TsT)equation 4

h is the convection coefficient. This number is given as 5 w/m2- 0C. The

area can be calculated using equation 3.The surface temperature is

measured using an digital thermometer. The temperature varies across


17/23

the surface, a judgment can be made about what to use as an average

temperature. No effort is made to break the nozzle surface into regions

of different temperatures, mainly because the heat loss through the

nozzle is quite low and the extra effort would not be worth the extra time

it would take.

Specific enthalpy in:

.equation 5

Cp is the specific heat of the incoming air, given to the students as 1.004

KJ/kg-0C. The temperature T is the absolute temperature of the

incoming air (room temperature) in K.

Specific Enthalpy Out:

is calculated using equation 5, but the temperature used is thetemperature for each data region in the outlet.

Air Density:

= .equation 6

In this equation Pb is the barometric pressure in inches of mercury and T

is the temperature of the air in the data region measured in 0C. Theother constants are conversion factors so the units of density are kg/m3.

The constants are correction factors for inconsistent units.

Mass Flow Rate Out:

equation 7


18/23

In this equation is the density of the exiting air as determined byequation 6, V is the velocity measured using the digital anemometer,

and A is the area of the region of interest. The exit is divided into 17

equal regions, so A becomes the total exit area divided by 17.

Velocity In:

The velocity in is to measured between zero and 30 because the inlet

area is much larger than the exit, so the velocity will be very low. From

this information the inlet velocity can be calculated from equation 8.

equation 8

Where is the density of the room air , is the inlet velocity, and Ainis the total inlet area. The velocity is assumed to be constant across the

inlet area. The students are required to take any necessary

measurements to determine the total inlet area.

Potential Energy:

The vertical distance between the centre of the inlet and the centre of

the outlet is measured. This elevation change is used to calculate the

potential energy change.

Miscellaneous Information:

Many of the equations above contain correction factors for unit

conversion. As mentioned, these factors are not provided for more

advanced classes. However, some of the measurements still contain


19/23

inconsistent units, such as the measurements for the heated area of the

nozzle, the nozzle diameter, and the measurements for the inlet area.

The students must recognize inconsistent units throughout the

calculations and make conversions as needed.


20/23

CONCLUSION

The above experiment shows the demonstration of the first law of

thermodynamics at a very low cost for equipment. Most of the

instrumentation is available in any typical lab. The hairdryer cost is

negligible, and the two custom holding fixtures are very simple to

make. The hairdryer uses three different forms of energy tom work,

heat energy and mechanical energy, electricity is used to generate

forms of energy in the hairdryer.

Energy can be converted in different forms but it cannot be createdor destroyed , proven by the first law of thermodynamics.

RECOMMENDATIONS

Bigger equipments such as turbines are recommended to do the

above experiment, and will give better results since the inside

diameter and the temperatures can be measured accurately because

it is wide open on the nozzle.


21/23

ACKNOWLEDGEMENTS

We would like to thank professor Kolesnikov for providing us with the

start up equipments and futher thanks to my patner NkhensaniLekhuleni who worked with me on this assignment.

REFERENCES

R. Edwards, A Simple Hair Dryer Experiment to Demonstrate the

First Law of Thermodynamics,

Proceedings of the American Society for Engineering EducationAnnual Conference & Exposition, 2005.

[6] M.J. Prince, R. M. Felder, Inductive Teaching and Learning

Methods: Definitions, Comparisons, and

Research Bases, Journal of Engineering Education, 2006.

L.C. McDermott, Oerstead Medal Lecture 2001: Physics

Education Research The Key to Student


22/23

Learning, American Journal of Physics 69, 1127-1137, 2001.

D.E. Kanter, H.D. Smith, A. McKenna, C. Rieger, R.A.

Linsenmeier, Inquiry-based Laboratory

Instruction Throws Out the Cookbookand Improves Learning,

Proceedings of the American Society for

Engineering Education Annual Conference & Exposition, 2003.

L.C. McDermott, et.al., Physics by Inquiry, John Wiley & Sons,

1996.


23/23

NOMENCLATURE

= mass flow rate of the incoming air(

mass flow rate of the outgoing air(

specific enthalpy of the incoming air

specific enthalpy of the outgoing air

g= acceleration due to gravity(

D=diameter of the nozzle(m)

= density of the air((

A= Area of the nozzle ()

Assignment 1 Thermodyanmics

Documents