Human Powered Refrigerator

plantcalicobeansΠολεοδομικά Έργα

29 Νοε 2013 (πριν από 3 χρόνια και 9 μήνες)

89 εμφανίσεις






Human Powered Refrigerator



Final Report



Submitted to


The Faculty of Operation Catapult LX
X
X
II


Rose
-
Hulman Institute of Technology


Terre Haute, Indiana







Group
22



Kiefer Hicks

Marble Falls High School

Marble Falls
, Texas


Hannah Radecki

C
larion Area High School

Clarion
, Pennsylvania


July 28, 2007


22
-
1


Introduction

The refrigerator is one of the developed world's greatest
luxuries
.
One application is

keep
ing

food fresh for
weeks

and medicines viable for months.
Additionally
, it can cool o
r heat
buildings to comfortable
temperatures
. The refrigerator essentially works against t
he second law
of thermodynamics;

it uses
energy

to locally decrease entropy, although total entropy is
increased.
Efficient

refrigerators
,

however, require
electric
ity
, which is in short supply in many
parts of the world. A highly
efficient

human powered refrigerator or a human driven
electricity

delivery
system

co
uld solve this problem.
If this
shortage

of electricity
were to be

solved
,

it
would mean access to the

benefits of refrigeration for those in the underdeveloped world. This
improvement in quality of life
was our motivation for working on this pro
ject
. There are
two
ways to solve the problem. The first is to build a
completely

mechanical system, in which

a
compressor would be driven directly from the rotational
energy

of a bicycle. This solution
,

however, would preclude the use of more efficient
refrigerants
;

Freon

or
ammonia

only work
within a relatively narrow range of compression. These
two gases
req
uire an exact
pressurization and depressurization to
complete

the
ir

phase shift
s

and deliver maximum cooling.
Therefore
,

using a
variable speed
compressor

w
ould
mandate the use of
a less
efficient

refrigerant
,

such as air. Another option is to build a hu
man powered electric generator and run
an electric refrigerator with it. This option is more
versatile

and more efficient
: a refrigerator i
s
not the only appliance that

can

be

power
ed and the refrigerator

is not limited to
a

phase

change
refrigerator
. Th
is was our motivation for
choosing

an electrical system over a mechanical
system.

Objectives

In general terms, we wanted to create a refrigeration system that could run
solely

off of
human power. To make sure that the average human could actually supply
enough power, it was
importan
t to consider ideas with regard

to their maximum
efficiency
. Our group also desired to
gain a greater understanding of the refrigeration cycle that is used in home refrigerators. A third
goal
we had

was to accurately measure ho
w much power a human can produce so that other
appliances could be powered, instead of simply a refrigerator. All of these again fall under the
umbrella goal of creating an
electricity

generating system to run a refrigerator that could,
theoretically, be e
mployed in a country where refrigeration is not readily available but still
needed.

Procedure

As with any experiment
,

we
began ours

with research.
We

found three methods for
cooling air: continuous absorption, thermoelectric cooling, and the vapor
-
compress
ion cycle.
22
-
2


Continuous absorption involves the use of ammonia gas
, which we could not
obtain
,

so that
option was quickly dispatched
.
An advisor
informed us that previous Operation Catapult
researchers had tried to use thermoelectric cooling but with little
success because of its great
inefficiency. The obvious choice

then
, and the one we were most familiar with, was the vapor
-
compression cycle
,

which is based on

of the principle of the refrigeration cycle. In vapor
-
compression refrigeration a gas, often Freo
n, enters a compressor. As this gas is compressed it
heats up. The heated gas travels to a condenser which cools down the gas until it
condenses
.
From there, the liquid moves into an expansion valve, which quickly decreases the pressure on
the
refrigerant
,

causing some of it to vaporize and
cool
the air around it. This liquid
-
gas mixture
then flows into an evaporator where the rest of the liquid is vaporized and the surrounding air is
again cooled. The
refrigerant

continues around this loop indefinitely.

Or
iginally, we planned on building a vapor
-
compressio
n cycle in the same style as is
found in
a home refrigerator. Unfortunately, that idea would involve a large amount of piping

for

our refrigerant
to

flow through as well as the time needed to track down th
e various valves and
containers. We mutually decided that our two and a half weeks woul
d be better spent on building
an

electrical arrangement and

testing

it
.
Mike Fulk
, our consultant,

offered us

of a pre
-
made mini
refrigerator which eliminated the need f
or us to build a refrigeration cycle and compressor and
also allowed us more time to concentrate on the electrical aspect.


After deciding upon the method of refrigeration we
wanted

to use
,

the mode of power
supply became p
riority. To run
an alternator rot
ational energy had to be used. H
aving a person
ride a bicycle was the solution we chose
.
Using

some type of electrical storage was also
important because it would be impractical for the
operator

of a refrigerator to
have to pedal
constantly. To fill these
purposes we used a 12 volt battery and an alternator.


We had some difficulty acquiring a suitable bicycle
.

Because we were working under a
budget and were unsure of how much money we might need to spend on an alternator, our best
idea was to look for a bi
cycle
frame, gear set, and chain at the junkyard. Luckily, we were able to
salvage all of these items
in relatively good condition
. One problem arose when we began to
construct the bicycle frame. This operation entailed welding steel to s
teel
,

which neithe
r of us
had any

familiarity with.
Another problem
was that the bicycle parts were rusted together to the
point of inseparability. These problems became
moot

when we were offered an exercise bike in
working condition. When we found it
,

we abandoned our pr
evious work of constructing our own
exercise

bike.


Once we hooked up the bike to the alternator, we noted the resistance offered by the
(non
-
functional) alternator was negligible, so we sought a system to increase the gear ratio. We
first attempted to co
nstruct a gear set using gears from the two junkyard
bicycles. W
hen we
found ourselves unable to remove
the gears
, we sought to use a wheel and belt system

of which
we built one wh
eel and the stand for another.
While we were attempting to obtain a belt
,

we

hooked up the replacement
alternator and found that instead of too little resistance, the system
was impossible to pedal

because

of too much resistance
.
The

alternator was powering up a
maximum magnetic field
, and

if we added resistance to the field
line
, we could
make the
22
-
3


alterna
tor require less torque to turn. We added the only resistor that was available

(12.5 Ω)
, and
it happened to suit our needs.

The a
lternator now accepted
,

in a tolerable
manner, human
powered input

and produced DC output at reas
onable power levels.


The alternator is connected to a battery. The battery charges the field line which allows
the alternator to produce electricity.
This electricity
re
charges the battery.
The energy required

fro
m the battery
,

however, introduces a lo
wer limit on the spin speed of the alternator
. If the
rotational speed

fall
s

below this bound

the alternator fai
ls to charge the battery

and drains it. The
battery, regardless of charge from the alternator
,

po
wers an inverter which
, in turn
,

powers an
app
liance
. I
f that appliance draws more power then can be supplied by the human cyclist, then
the appliance will draw off all the en
ergy confined in

the battery and ultimately fail.


22
-
4


Results


Relying upon the information

sticker on our refrigerator
,

we foun
d the reported 290
kWh/year that the refrigerator uses to be equivalent to 33 watts
. The conversion between watts
and kWh/year was somewhat awkward because the watt is a unit of power (one joule per second)

and a watt hour is a unit of energy (
3600 joules
)
. Using these two
relations, we found

a
watt hour
per year
to be 0.
0
00
114
wat
ts. 290
,
0
00

watt hours per year
would then approximately equal

33.
1
watts.



To test our system we performed two distinct types of tests. In one type
,

we tested the
ability

of
a human (or
a cumulative
group of humans) to power it, and in the other we tested the
actual
capacities

of the system itself. We performe
d two tests using

human cyclists. The first
test
(Figure 1)
was most like a sprint: we instructed the cyclist to ride
as fast as possible, and then to
continue riding as fast as possible until they failed to charge the battery. In the second test

(Figure 2)
, we instructed the cyclist t
o ride for as

long as
possible while still
keeping the input
voltage high enough to char
ge the battery.

In a third test

(Figure 3)

the cyclists were instructed
to ride as fast as possible for 6 seconds.

Eq
u
. 1

22
-
5



To test the system itself we recorded the battery voltage
;

then

we had a human rider
s
print for exactly one minute. Afterwards, we attach
ed a 40 watt light bulb, the load equivalent
o
f

a refrigerator
, for one minute. F
inally
,

we
recorded the battery voltage
again
to measure the
ene
rgy gain or loss in the system. The voltages measured before and after the test were exactly
equal
. This prove
s that a sprinting cyclist can power a refrigerator for one minute.


Note that that the maximum length of time we were able to keep the battery at a positive
charge rate was four minutes and a cyclist could add notable charge to the battery for only one
mi
nute.

Fig. 1
Sprint:
testers were
asked to ride
as fast as
possible for
one minute

22
-
6


Lessons Learned

We have realized a greater respect for the power of electricity. By physically having to
generate the electricity to light a simple bulb
, and then only for a minute or two, perhaps we will
be more thoughtful about turning off lights a
fter leaving a room.
We have learned that there is
more energy in a good size tank of gasoline then most of us will ever expend a
s anything but
heat in a year.
100 watts is a good estimate for the maximum power output of a human over one
minute. Our machi
ne

struggles to produce 40 watts, which falls in its

expected
efficiency
. The
lion’s

share of
wastefulness

is the alternator, which has about 50%
efficiency
. The remaining
5%
efficiency

loss
is due to mechanical
inefficiencies

such as faulty gear and cha
in friction,
whee
l friction, and battery loss
.

Between waiting for parts to arrive and the frustration of having
seemingly good ideas become ineffectual, we learned the value of planning for roadblocks.

Conclusions

From our results, we
believe that we can

safely claim

that the average
teenager
would not
be able to power our refrigerator alone for much longer then two minutes.

A human can produce
a significantly measurable amount of power but not enough to power a commercial mini
refrigerator

indefinitely
.

The loss of energy in both our alternator and also our refrigerator
eliminates the possibility

of generating anywhere near the ideal .2 horsepower
. For any
application of our machine to be useful the power draw of the appliance plugged in would have
to be

far less than 30 watts. This eliminates many of the amenities that are common in the United
States but still does not rule out
uses that could be helpful in the developing world such as
telephones or radio.

References

<http://www.chemistry.wustl.edu/~cour
ses/genchem/Tutorials/Fridge/refrigeration.htm >

<http://www.lpappliances.com/G
-
Absorp.html>

<http://www.marlow.com/AboutMarlow/pdf/MRL1002G.pdf>