17-04-2012, 04:57 PM
Human-Powered Refrigerator
[attachment=20255]
Introduction
We sought to build a human-powered thermoelectric refrigerator. A thermoelectric refrigerator, unlike normal in-home compressor-based refrigerators, tends to be more portable, quiet, and ozone friendly. Instead of using refrigerant, a thermoelectric refrigerator uses thermocouple wires; thermocouple wires consist of two wires made of semiconductors joined at two separate junctions. According to the Peltier Effect, an electric current applied to two wires joined at two junctions of different materials, exemplified by the set-up of our thermocouple wires, will result in one junction becoming hot and the other cool. A Peltier Junction (commonly called a peltier), extends the idea of the Peltier Effect and the principle of the thermocouple wires to a more effective end. A peltier is a semiconductor thermoelectric device supplied a direct current. A peltier has semiconductor wires weaved between two ceramic plates such that they are electrically in series and thermally in parallel, allowing, similar to the thermocouple wires, one side to become hot and the other cold. A thermoelectric refrigerator uses a the cool side of a peltier to cool a specified space, while typically using a heat sink to divert the heat created on the other side. Because a peltier tends to be very small in size, a thermoelectric refrigerator can be more portable than the standard compressor-based refrigerator, yet also because of its small size it can only cool a relatively small space.
Apparatus
We obtained two Koozies to construct our small human-powered thermoelectric refrigerator. A soda can was placed in one of the Koozies, out of which a hole was cut to allow contact with the aluminum plate that would help transfer heat away from the soda can. The aluminum plate was cut to fit around the can and kept flat on top so that the peltier might rest on it. Between the can and the aluminum plate exists a layer of thermal
compound to further aid in the transfer of heat. On top of the aluminum plate is another layer of thermal compound and then the peltier. The top side, quite obviously, is the one
intended to become warm on top of a layer of thermal paste an aluminum heat sink rests on the peltier. The heat sink is an aluminum plate that has ridges so as to further aid in the transfer of heat by allowing greater surface area to disperse the heat into the air.
Experimental Setup and Results
We performed many different kinds of experiments to determine the effectiveness of our design and of our peltier. Initially, we connected the peltier to a power supply to determine the effectiveness of it. We found that with about two Amperes and about five Volts, we were able to obtain temperatures on the hot side of one hundred and twelve degrees Fahrenheit. On the cold side, we were able to obtain a temperature down to forty-one degrees Fahrenheit.
Conclusion
Through experimentation we have found that a peltier is capable of cooling a soda, but, as illustrated by the test performed over sixteen minutes, it would take a considerably long time to do so. This continues to illustrate that a peltier is less efficient as a cooling device than a standard compressor-based refrigerator. The level of inefficiency associated with our thermoelectric device is firstly associated with the minimal amount of current and voltage that can be applied via human power. Secondly, the thickness and size of the aluminum plate that was placed on the soda and on which the peltier rests takes a considerable amount of time to cool. A smaller plate would have allowed for much faster cooling, but because the larger plate presented greater ease in construction, it was chosen. Though our refrigerator is not entirely efficient, the size of our refrigerator further illustrates the advantage of using thermoelectric cooling. Further study of designs to help divert the heat away from the space that is one wishes to cool and designs to make the decrease the size and thickness of the aluminum plate in contact with the refrigerated space will most likely prove a greater efficiency on the part of a thermoelectric device.
[attachment=20255]
Introduction
We sought to build a human-powered thermoelectric refrigerator. A thermoelectric refrigerator, unlike normal in-home compressor-based refrigerators, tends to be more portable, quiet, and ozone friendly. Instead of using refrigerant, a thermoelectric refrigerator uses thermocouple wires; thermocouple wires consist of two wires made of semiconductors joined at two separate junctions. According to the Peltier Effect, an electric current applied to two wires joined at two junctions of different materials, exemplified by the set-up of our thermocouple wires, will result in one junction becoming hot and the other cool. A Peltier Junction (commonly called a peltier), extends the idea of the Peltier Effect and the principle of the thermocouple wires to a more effective end. A peltier is a semiconductor thermoelectric device supplied a direct current. A peltier has semiconductor wires weaved between two ceramic plates such that they are electrically in series and thermally in parallel, allowing, similar to the thermocouple wires, one side to become hot and the other cold. A thermoelectric refrigerator uses a the cool side of a peltier to cool a specified space, while typically using a heat sink to divert the heat created on the other side. Because a peltier tends to be very small in size, a thermoelectric refrigerator can be more portable than the standard compressor-based refrigerator, yet also because of its small size it can only cool a relatively small space.
Apparatus
We obtained two Koozies to construct our small human-powered thermoelectric refrigerator. A soda can was placed in one of the Koozies, out of which a hole was cut to allow contact with the aluminum plate that would help transfer heat away from the soda can. The aluminum plate was cut to fit around the can and kept flat on top so that the peltier might rest on it. Between the can and the aluminum plate exists a layer of thermal
compound to further aid in the transfer of heat. On top of the aluminum plate is another layer of thermal compound and then the peltier. The top side, quite obviously, is the one
intended to become warm on top of a layer of thermal paste an aluminum heat sink rests on the peltier. The heat sink is an aluminum plate that has ridges so as to further aid in the transfer of heat by allowing greater surface area to disperse the heat into the air.
Experimental Setup and Results
We performed many different kinds of experiments to determine the effectiveness of our design and of our peltier. Initially, we connected the peltier to a power supply to determine the effectiveness of it. We found that with about two Amperes and about five Volts, we were able to obtain temperatures on the hot side of one hundred and twelve degrees Fahrenheit. On the cold side, we were able to obtain a temperature down to forty-one degrees Fahrenheit.
Conclusion
Through experimentation we have found that a peltier is capable of cooling a soda, but, as illustrated by the test performed over sixteen minutes, it would take a considerably long time to do so. This continues to illustrate that a peltier is less efficient as a cooling device than a standard compressor-based refrigerator. The level of inefficiency associated with our thermoelectric device is firstly associated with the minimal amount of current and voltage that can be applied via human power. Secondly, the thickness and size of the aluminum plate that was placed on the soda and on which the peltier rests takes a considerable amount of time to cool. A smaller plate would have allowed for much faster cooling, but because the larger plate presented greater ease in construction, it was chosen. Though our refrigerator is not entirely efficient, the size of our refrigerator further illustrates the advantage of using thermoelectric cooling. Further study of designs to help divert the heat away from the space that is one wishes to cool and designs to make the decrease the size and thickness of the aluminum plate in contact with the refrigerated space will most likely prove a greater efficiency on the part of a thermoelectric device.