Initial Research
Initial Group Work
Once our group had been given the Stirling engine task it was our intention to gain a better understanding of the Stirling engine cycle. The first decision was to visit the library and withdraw some books covering the topics of hot air engines. One book which seemed the best for background information about the workings and manufacturing of a Stirling engine was “Stirling and Hot Air Engines” by Roy Darlington and Keith Strong.
Upon further research into Stirling engines it was initially our decision to try and develop a working low temperature difference Stirling engine over the next 13 weeks. To strengthen our understanding of the Stirling engine we decided to build a basic Stirling engine out of regular household objects. The reason for spending time on this task was to ensure that each team member understood the functionality of the Stirling engine and all of the components. The full lists of items needed to create the engine are as follows;
3x Coke cans
3x CD’s
1x Balloon
6x 5A Electrical terminal blocks
Fine steel wool
Steel wire
Fishing line
Plastic drink cap
The figure shows our attempt at the basic Stirling engine.
Unfortunately our design did not function fully. Our reason for the Stirling engine to fail was that the balloon, which acted as a diagraph was too tight. This then did not expand as the air was heated in the displacer cylinder so the crank shaft did not turn without aid. Although our design did not function fully are group learnt many valuable lessons while working on this project. Firstly that even a basic Stirling engine can still cause some manufacturing issues. Clearly a refined low temperature difference Stirling engine would be more difficult to produce and would have much lower tolerance components. However this task did allow each team member to grasp the basic cycle of a hot air engine.
Atleration of Design Task
After meeting with Professor John Counsell our design task had swayed from designing a working Stirling engine to assigning a working Stirling engine to a productive application. From the discussion with Prof Counsell it was clear that Stirling engines have an almost perfect cycle thermodynamically but to find an application in the real world is a much less perfect situation.
The basic requirement for an operational Stirling engine is a temperature difference. There are two types of Stirling engines which are operational in the mechanical engineering department and we would be looking at using one of these to find an application. The engines available are either a low temperature difference Stirling engine or a Gama Stirling engine which requires a high grade heat source for operation. This gave us two different scenarios; either a low grade heat source or high grade heat source.
However it must be made clear that although the basic requirement for operation is a temperature difference it is a very subtle cycle. The control of a Stirling engine depends on the temperature difference, so they can only operate under a constant temperature conditions. This limits the applications of the Stirling engine because it must be applied in a practical situation with a constant temperature.
Taking these factors into consideration we came up with some applications of the Stirling engines available to us in the department. These ideas are discussed below.
· Creation of a model house to capture waste heat energy and produce DC power
· Circulation hot air around rooms through a fan mounted on a Stirling engine
· Pumping a coolant fluid through a pipe system to cool down equipment
A development from the final idea was a Stirling engine located on top of a computer server could be utilized to pump water to cool the servers down. This idea correctly fitted the required criteria for a Stirling engine.
Stirling Engine Server Cooling System
The cycle of heat energy emitted form computer servers fitted the required criteria ideally for use with a Stirling engine. Firstly it is a low grade heat source which is currently going to waste. It is a well known fact that the internet contributes an equal amount to global emissions as the airline industry, and that 50% of this energy is required maintain a constant temperature for the servers to operate. If the Stirling engine could be efficiently utilized the need for air conditioning in server rooms would be no longer needed reducing the emissions by half the current level.
The design would be to use a low temperature difference Stirling engine to pump water around the server rack keeping the servers cool. If the temperature was to increase about the optimum server temperature the Stirling engine would also increase which would result in an increase in flow rate of the coolant around the pipe system, lowering the server temperatures. Also if the servers we not at the desired temperature, but were operating at a lower temperature the Stirling Engines would not begin the cycle so in a way they only operate when they are required, and automatically increase work rate as the temperature rises resulting in a constant temperature cycle.
Although this application seems like an ideal way of utilizing the Stirling engine to reuse wasted energy the practicalities of it become apparent when basic calculations are carried out evaluating the system. Firstly as the temperature difference is low the power output from the Stirling engine would be equally low. So we would need an extremely low friction pipe system with a low mass flow rate to give the engine any chance of pumping a fluid to cool a server. Although this could be possible the next piece of work was crippling to our design application. By researching the dimensions of computer servers the average height was found to be 2m, which would mean that the head of our pipe system would roughly be 2m also. By calculating the power required for a pump to move water around a system with a 1cm diameter we calculated that the required power would be 5.13W. Although this is a rough calculation, not including the length of the pipe system or any frictional losses the power is far higher than would be possible from any low temperature difference Stirling engine could possible produce.
This then left us asking the question whether or not it would be possible for us to utilize either of the Stirling engines available for a productive application. After further consideration of options and discussions with Prof Counsell it was decided that on the timescale it was not possible. However through this discussion the idea of optimizing a previously build Stirling engine was brought up which formed the basis for our new design project.
Once our group had been given the Stirling engine task it was our intention to gain a better understanding of the Stirling engine cycle. The first decision was to visit the library and withdraw some books covering the topics of hot air engines. One book which seemed the best for background information about the workings and manufacturing of a Stirling engine was “Stirling and Hot Air Engines” by Roy Darlington and Keith Strong.
Upon further research into Stirling engines it was initially our decision to try and develop a working low temperature difference Stirling engine over the next 13 weeks. To strengthen our understanding of the Stirling engine we decided to build a basic Stirling engine out of regular household objects. The reason for spending time on this task was to ensure that each team member understood the functionality of the Stirling engine and all of the components. The full lists of items needed to create the engine are as follows;
3x Coke cans
3x CD’s
1x Balloon
6x 5A Electrical terminal blocks
Fine steel wool
Steel wire
Fishing line
Plastic drink cap
The figure shows our attempt at the basic Stirling engine.
Unfortunately our design did not function fully. Our reason for the Stirling engine to fail was that the balloon, which acted as a diagraph was too tight. This then did not expand as the air was heated in the displacer cylinder so the crank shaft did not turn without aid. Although our design did not function fully are group learnt many valuable lessons while working on this project. Firstly that even a basic Stirling engine can still cause some manufacturing issues. Clearly a refined low temperature difference Stirling engine would be more difficult to produce and would have much lower tolerance components. However this task did allow each team member to grasp the basic cycle of a hot air engine.
Atleration of Design Task
After meeting with Professor John Counsell our design task had swayed from designing a working Stirling engine to assigning a working Stirling engine to a productive application. From the discussion with Prof Counsell it was clear that Stirling engines have an almost perfect cycle thermodynamically but to find an application in the real world is a much less perfect situation.
The basic requirement for an operational Stirling engine is a temperature difference. There are two types of Stirling engines which are operational in the mechanical engineering department and we would be looking at using one of these to find an application. The engines available are either a low temperature difference Stirling engine or a Gama Stirling engine which requires a high grade heat source for operation. This gave us two different scenarios; either a low grade heat source or high grade heat source.
However it must be made clear that although the basic requirement for operation is a temperature difference it is a very subtle cycle. The control of a Stirling engine depends on the temperature difference, so they can only operate under a constant temperature conditions. This limits the applications of the Stirling engine because it must be applied in a practical situation with a constant temperature.
Taking these factors into consideration we came up with some applications of the Stirling engines available to us in the department. These ideas are discussed below.
· Creation of a model house to capture waste heat energy and produce DC power
· Circulation hot air around rooms through a fan mounted on a Stirling engine
· Pumping a coolant fluid through a pipe system to cool down equipment
A development from the final idea was a Stirling engine located on top of a computer server could be utilized to pump water to cool the servers down. This idea correctly fitted the required criteria for a Stirling engine.
Stirling Engine Server Cooling System
The cycle of heat energy emitted form computer servers fitted the required criteria ideally for use with a Stirling engine. Firstly it is a low grade heat source which is currently going to waste. It is a well known fact that the internet contributes an equal amount to global emissions as the airline industry, and that 50% of this energy is required maintain a constant temperature for the servers to operate. If the Stirling engine could be efficiently utilized the need for air conditioning in server rooms would be no longer needed reducing the emissions by half the current level.
The design would be to use a low temperature difference Stirling engine to pump water around the server rack keeping the servers cool. If the temperature was to increase about the optimum server temperature the Stirling engine would also increase which would result in an increase in flow rate of the coolant around the pipe system, lowering the server temperatures. Also if the servers we not at the desired temperature, but were operating at a lower temperature the Stirling Engines would not begin the cycle so in a way they only operate when they are required, and automatically increase work rate as the temperature rises resulting in a constant temperature cycle.
Although this application seems like an ideal way of utilizing the Stirling engine to reuse wasted energy the practicalities of it become apparent when basic calculations are carried out evaluating the system. Firstly as the temperature difference is low the power output from the Stirling engine would be equally low. So we would need an extremely low friction pipe system with a low mass flow rate to give the engine any chance of pumping a fluid to cool a server. Although this could be possible the next piece of work was crippling to our design application. By researching the dimensions of computer servers the average height was found to be 2m, which would mean that the head of our pipe system would roughly be 2m also. By calculating the power required for a pump to move water around a system with a 1cm diameter we calculated that the required power would be 5.13W. Although this is a rough calculation, not including the length of the pipe system or any frictional losses the power is far higher than would be possible from any low temperature difference Stirling engine could possible produce.
This then left us asking the question whether or not it would be possible for us to utilize either of the Stirling engines available for a productive application. After further consideration of options and discussions with Prof Counsell it was decided that on the timescale it was not possible. However through this discussion the idea of optimizing a previously build Stirling engine was brought up which formed the basis for our new design project.
