The use of nozzles has been widely exploited to help ease fluids that are restricted within containers. The benefits of these vary from place to place and in different fields. Of importance is the field of sciences especially in biology, physics, and chemistry and so on. Fluids that are talked about here include gases and some liquids. When restricted in a container, there would be need to use the properties of the fluid to control it or direct it to your liking so that you can use it for a desired activity for certain results. A micro nozzle is one that is very small and is used to propel fluids at higher speeds than the normal nozzles. It is found in various gadgets and instruments that we use in our daily life. For instance, insecticide cans, devices for cleaning test tubes in the lab, and so many other devices that are generally used to propel gases using the fluid channels in the labs. According to Plumlee, Steciak and Moll (2010, pg. 1), micro nozzles can also be used to provide thrust in experiments where gases are to be introduced into certain stages of an experiment under a certain amount of pressure so as to achieve a desired result. In some cases, big nozzles in equipment like fire extinguishers, the main nozzle is designed to have micro nozzles so as to produce enough pressure that can hence be used to put out fire. This is shown by equipment developed by Hydramist (2010) which find application across a wide range of areas within which fires are highly likely to occur and cause damage to property. Micro nozzles are generally produced by use of different methods and as such, for different uses.
Therefore, they are recognised to be of very big importance in the different industries within which they are required to be used. The micro nozzles find applications in a number of areas as mentioned before and this ranges from domestic use like in insecticide propellants and in the big manufacturing industries and chemical labs where experiments take place. There are different ways in which micro nozzles can be produced. One of them is by the use of micro-electromechanical systems (MEMS). In MEMS, structures of very small sizes are put together in silicon basically integrating mechanical, optical and fluidic components with electronics. Other methods that can be used in the production of micro nozzles include the use of machining. Opoz et al (2006) describe machining as the technology that is important in producing very small components whose sizes range from millimetres to sub-millimetres. The machining technique includes micro electrical discharge machining and micro electrochemical machining.
Aims and Objectives
This thesis seeks to look into the areas in which the use of micro nozzles is applied. The production of micro nozzles is also going to be part of the thesis and of major concern is the production of micro nozzles through the use of Micro-electromechanical systems otherwise referred to as MEMS. Another method through which micro nozzles are produced is through the use of micro Electrical Discharge Machining, micro EDM. The third and last method of producing micro nozzles is by the use of micro Electro-Chemical Machining. A background of the methods used to produce micro nozzles will also be considered. This will cover the basic steps followed when these nozzles are being produced using the mentioned techniques.
Literature Review
The advancement of science has seen machines requiring more and more sophisticated designs in new processes. This has led to the invention of different technologies as a solution to the demands for better working equipment that are efficient and result oriented. Nozzles have been used from the last century from early nineteen eighties in various industrial processes and for domestic use. In as much as the original use was restricted within industrial and laboratory set-ups, the introduction of such products as insecticides for domestic and large-scale use in places like farms made its introduction to these areas imminent. Therefore, it was used in such equipment as spray cans that needed only to administer a certain controlled quantity or dosage of insecticide or whichever chemical at a specific time.
This gave rise to the use of micro nozzles in different areas. The first application of micro nozzles is in spray cans. This is the most immediate application which we are exposed to. It is used in cans that are pressurised and release jets from nozzles that are measured in terms of micro-millimetres. The next application is in the engine of a vehicle or basically a machine for fuel injection. This is particularly found in diesel fuel injection where nozzles of the best quality measuring less than 145 micrometres need to be drilled for this particular use. It is bound to change the future of fuel combustion in engines as the efficiency of the engine will be improved while keeping the environmental pollution rates within safer levels as compared to the current fuel injections. According to Li et al (2006), the main drawback in this application of micro nozzles is that the tools involved in drilling the nozzles are very expensive hence presenting a higher overhead for the companies that would like to develop engines with nozzles of this size and quality. The third application of micro nozzles is in the satellite adjustment applications. In recent times, the use of satellites has required smaller and lighter satellites that can still be efficient and manageable by scientists. This has thus required even smaller micro nozzles located in the rocket propellers that are use to propel the satellites into space.
Plumlee, Steciak and Moll (2004) suggest that the use of these smaller satellites propelled by rockets with the micro nozzles could drastically reduce costs of launching satellites and increase the number of satellites as there is a chance to launch more rockets within a smaller time-frame. The only demerit to this is that the cost of the recommended propellants used as fuel is quite exorbitant. Considering the high temperatures needed to combust this fuel, silicon has been used through the microelectromechanical systems (MEMS) to produce nozzles that can withstand such high temperatures. The fourth application of micro nozzles is in inkjet printers. These printers can produce ink in micro quantities through the nozzles that are so small in size. One nozzle can actually be the size of between fifty and sixty microns. Tyson (2008) says that they are so small they could be smaller than the size of human hair which measures around 70 microns. A Microelectromechanical system is a system that brings together electrical and mechanical parts like actuators and sensors. Vittorio (2001) gives some examples of device applications like inkjet-printer cartridges, accelerometers, small engines and locks that are developed using this technology. It has a capability to detect, control and trigger mechanical processes in very small scales to produce a much larger effect.
This technology as such enables a set of devices that perform easy tasks to be fabricated and in the end be able to work in harmony to perform larger and much complex tasks. MEMS are actually grouped into two types. There are the sensors and the actuators. Each plays a role to make a process a success. For instance, sensors detect information that has been fed into the system while the actuators translate the information into action. In the article MEMS introduction (2002), smart roads have MEMS planted in them so that they could transmit information about incidences on the road such as accidents and other occurrences to devices like global positioning systems. This would be communicated to drivers who will in turn take detours to avoid the trouble spots or ignore the affected route totally. On such devices, when the MEMSs sensors detect any action, signals are sent to the actuators which produce a designated action by pumping, injecting or filtering a desired fluid at a regulated pressure to a point that is required through micro nozzles in the device.
A second method that can be used for producing micro nozzles is through the use of a technique called micro electrical discharge machining (micro EDM). In this technique, spark charges are used mainly to reduce the size of a conductive material. This, applied to a surface, can produce the effect of drilling holes that are as small as millimetres to very minute micro millimetres. Apart from micro EDM, there are some other techniques for drilling holes. These are techniques like Electrochemical Discharge Machining (ECDM). In ECDM, the rate at which material is displaced is comparatively higher and can be as high as 1.5 mmminute. This has drawbacks that are detrimental in the long run as in reducing roughness to a record minimal level of up to 0.08 micro metres, it causes etching of the insides of the micro holes drilled through the material. Yan, Huang and Wang (2002) suggest that this technique should be used in materials that are less abrasive when exposed to the environment. The next technique is the Wire Electric Discharge Grinding (WEDG). It is not a major technique in the production of micro nozzles. Uhlmann, Piltz and Oberschmidt (2008) reckon that it is a technique mainly applied when producing micro-rotational parts used in the various sectors of the industry.
Micro electrochemical machining (micro ECM) is another technique that can be used in the drilling of these nozzles. This technique bases its practicability on chemical reactions that are based on dissolution processes. It therefore encompasses very intricate processes that result in gas production from such reactions. Materials that are removed from the nozzles created are then transported out of the nozzles. It can be noted here that hydro-dynamical forces result during the production of the micro nozzles and the whole process is aided by an oscillating tool electrode. Bohlke and Forster (2005) further state that the oscillating tool, in stark contrast to the ones used in EDM (EDM actually has two electrodes submerged in electrolyte), has a relatively low rate of wearing down and can actually remain without damage on the surface.
The next method of production of micro nozzles is the micro Ultrasonic Machining. In this technique, the technologies of both WEDG and EDM are utilised in the production of micro nozzles. It is a very efficient technique that comes up with nozzles as small as 15 micrometres. It has also made the production of many other high-aspect-ratio microstructures a success. This is attributed to the diligence obtained when the technologies of WEDG and EDM are combined according to Sun, Masuzawa and Fujino (1996).
The second last technique is called laser beam machining (LBM). A beam of high intensity laser is propagated over a path with unwanted material, say a location where you need to drill a micro nozzle Watanabe (2002). It then removes, with a lot of accuracy, the part that has been marked for removal. Laser beam machining (2006), proposes this as a more accurate way of drilling nozzles. Micromachining can be done using this technology on materials such as graphite, silicon, diamond and graphite with a very high level of precision. This has been noted as a very expensive technique with very high overhead. The final method of production of micro nozzles is the micro punching of the holes. Here, nozzles of up to 100micrometre could be produced. Later on, upon reducing of the standard conditions for drilling, nozzles of up to 25moicrometres could be drilled. A diamond wheel was originally used though it has since been replaced by tools that are mainly made from tungsten carbide fabricated during the grinding process. Joo, Rhim and Oh (2005) record this as a huge development from the one before that could only manage 100micrometres.
All the above mentioned techniques fall under the Micro-Electro-Mechanical Systems (MEMS). This is due to the fact that in all of them, a basic sensor and an actuator are located in the machine to do the sensing of information that is sent containing instructions on what to do. The actuators then carry out the instructions fed to it by drilling the nozzles to the required standards. The main difference come in at the point where different techniques are used to reach one desired goal the drilling of micro nozzles. Whichever way it is done, it is of high importance to note that all the techniques have merits and demerits. A shared demerit is the cost of overhead. A technique such as Electro Chemical Machining (ECM) is seen to be very complex and involving very intricate chemical reactions. WEDG can be said to be limited when it comes to drilling particularly nozzles though it can be successfully used in other surface clearing or removal techniques to a good satisfaction level. On the other hand, Electrochemical Discharge Machining is harmful to the material as it leads to the etching of the wall within the nozzles that were drilled. Therefore the lifespan of such nozzles cannot be guaranteed in-case it is to be used to jet fluids that corrode the material it was made from. Opoz (2006) notes that Laser Beam Machining (LBM) is used to achieve nozzles of up to a diameter of 4 micrometres. On the flipside, it causes deterioration and very small cracks on the surface which has been machined.
All the demerits noted, it is also good to realise that each technique is suitable for particular materials and for drilling holes of certain sizes. This is due to the fact that each technique has a limit of nozzle diameter size that it can drill. Of importance is the fact that each method is applied in the making of different appliances. For instance, laser beaming is good for drilling materials with very hard surfaces which require a lot more care than the average surface. Diamond and graphite are examples of materials with very tough surfaces that would require a technique that will likely not destroy it in the process.
The MEM system techniques described above have a relatively long history. In the late fifties, Jack Kilby came up with the first integrated circuit (I.C.) using germanium (Ge). This would change completely the scenery in most scientific processes. Engineering as a whole took a good turn as the production of micro mechanical parts became easier aided by the I.C.s. A while later on in the same period, Robert Noyce developed a planar double diffused silicon (Si) I.C. the element proved to be famous for the job a it was relatively cheaper and commonly obtainable in the form of sand (SiO2). The fabrication of I.C.s relies on sensors that provide information to the actuators from the locality.
This information from the locality is relayed to the actuators for an action to be carried out as instructed. In the early eighties, micromachining came up as a method of fabricating very small mechanical parts that were in micro or even nano sizes. The small parts were developed by etching sections of the silicon substrate that were not needed to come up with the desired shape or micromechanical device. Vittorio (2001) describes one of the techniques, the sacrificial layer technique, as a process through which a layer of material is deposited in between two sheets of mechanical substance for total separation from each other. When the layer is removed, the layers of the material etch to free themselves. This in essence gave birth to surface micromachining around the year 1985. To date, there has been recorded several advancement of the MEM system. A lot is still in advance stages to come up with more efficient techniques that can be used to perform even less micromechanical activities. The Laser Beam Machining, which currently provides one of the finest machining, is set to improve with advances in technology.
Supersonic micro nozzles designs is basically employed in the aeronautics and astronautics field where there is need for micro propulsion through thrust provided by a micro-thruster with a linear aero-spike nozzle. Here, the main propellant that is employed is decomposed hydrogen peroxide. Supersonic micro nozzles are consequently used as key components of any micro propulsion that is dependent on chemicals which convert the pressure energy of the gases that are in combustion to produce thrust. The flow in these nozzles is usually affected by a viscous effect that slows down drastically the performance of the thruster. Zilic, Hitt and Alexeenco mention this as the main cause of layers that pile onto each other on the expander wall. Subsequent layer that pile together increase in size to lower the general performance.
Discussion and conclusions
The MEMS technology prides itself in application in various areas. Of particular notice is in the field of fluidics. Of special concern is the restriction of fluids in containers so that it can be released in regulated amounts, usually in jets, to a specific area where one is interested in applying the fluid. This technique is therefore found to be a basic principle in the field of science. An expansive usage in the manufacturing of more efficient diesel combusting engines is aided by the use of MEMs technologies to come up with engines that are friendlier to the environment. This is seen as a huge step towards saving the environment from depletion that threatens it everyday. Therefore, this is an industry friendly technology. The costs of producing MEMS technology is quite exorbitant but of note is that the main basis for its existence depends on future inventions that would make it cheaper so that efficiency can be increased and improved to favourable levels.
Application of the technology is found in various sciences. Physics, chemistry and biology might be beneficiaries but engineering takes the lions share as most of the mechanicals parts are mainly studied at an advanced level in the engineering field. In engineering, the small details of the processes are studied to come up with the actual inventions that dominate the MEMS techniques. The other section that is of notice is in the launching of satellites where satellites as small as one kilogram have been launched into the space using propellants that utilise micro-nozzles in their propellers. This has also been touted as a cheaper option as more and more satellites are launched with the fuel used in the process being minimised due to the nature of the satellites.
Recommendations that can be made are to observe the stages upon which the engineering field ha reached in the designing of better micro nozzles. More and more materials should be tested to find out if they too can be used in developing the critical micromechanical parts that usually suffer surface damage during their use. This would go a long way in ensuring that the micro mechanical parts last longer hence cut costs associated with frequent replacement due to wear and tear. As a means of increasing efficiency, the technology should be employed in more equipment so that if necessary, efficiency can be deployed everywhere possible. For instance, some farm machines would maybe require such parts to make them more efficient. These are machines like the manual mechanical sprayer that uses macro nozzles to spray disinfectant on crops. Maybe if the technology is deployed, a more efficient and fast spraying machine could be developed. It would reduce costs for farmers who incur other costs in crop production.
To increase efficiency, Lehnert, Laine and Gijs (2003) suggest a new way in which surface interaction (giga seal formation) can be improved. Here, the silicon dioxide (SiO2) micro nozzles are covered with a micro-coating of polydymethylsiloxane (PDMS). This is then exposed to plasma of oxygen. There are recorded measurements with living cells that indicated better seal resistances.
Therefore, they are recognised to be of very big importance in the different industries within which they are required to be used. The micro nozzles find applications in a number of areas as mentioned before and this ranges from domestic use like in insecticide propellants and in the big manufacturing industries and chemical labs where experiments take place. There are different ways in which micro nozzles can be produced. One of them is by the use of micro-electromechanical systems (MEMS). In MEMS, structures of very small sizes are put together in silicon basically integrating mechanical, optical and fluidic components with electronics. Other methods that can be used in the production of micro nozzles include the use of machining. Opoz et al (2006) describe machining as the technology that is important in producing very small components whose sizes range from millimetres to sub-millimetres. The machining technique includes micro electrical discharge machining and micro electrochemical machining.
Aims and Objectives
This thesis seeks to look into the areas in which the use of micro nozzles is applied. The production of micro nozzles is also going to be part of the thesis and of major concern is the production of micro nozzles through the use of Micro-electromechanical systems otherwise referred to as MEMS. Another method through which micro nozzles are produced is through the use of micro Electrical Discharge Machining, micro EDM. The third and last method of producing micro nozzles is by the use of micro Electro-Chemical Machining. A background of the methods used to produce micro nozzles will also be considered. This will cover the basic steps followed when these nozzles are being produced using the mentioned techniques.
Literature Review
The advancement of science has seen machines requiring more and more sophisticated designs in new processes. This has led to the invention of different technologies as a solution to the demands for better working equipment that are efficient and result oriented. Nozzles have been used from the last century from early nineteen eighties in various industrial processes and for domestic use. In as much as the original use was restricted within industrial and laboratory set-ups, the introduction of such products as insecticides for domestic and large-scale use in places like farms made its introduction to these areas imminent. Therefore, it was used in such equipment as spray cans that needed only to administer a certain controlled quantity or dosage of insecticide or whichever chemical at a specific time.
This gave rise to the use of micro nozzles in different areas. The first application of micro nozzles is in spray cans. This is the most immediate application which we are exposed to. It is used in cans that are pressurised and release jets from nozzles that are measured in terms of micro-millimetres. The next application is in the engine of a vehicle or basically a machine for fuel injection. This is particularly found in diesel fuel injection where nozzles of the best quality measuring less than 145 micrometres need to be drilled for this particular use. It is bound to change the future of fuel combustion in engines as the efficiency of the engine will be improved while keeping the environmental pollution rates within safer levels as compared to the current fuel injections. According to Li et al (2006), the main drawback in this application of micro nozzles is that the tools involved in drilling the nozzles are very expensive hence presenting a higher overhead for the companies that would like to develop engines with nozzles of this size and quality. The third application of micro nozzles is in the satellite adjustment applications. In recent times, the use of satellites has required smaller and lighter satellites that can still be efficient and manageable by scientists. This has thus required even smaller micro nozzles located in the rocket propellers that are use to propel the satellites into space.
Plumlee, Steciak and Moll (2004) suggest that the use of these smaller satellites propelled by rockets with the micro nozzles could drastically reduce costs of launching satellites and increase the number of satellites as there is a chance to launch more rockets within a smaller time-frame. The only demerit to this is that the cost of the recommended propellants used as fuel is quite exorbitant. Considering the high temperatures needed to combust this fuel, silicon has been used through the microelectromechanical systems (MEMS) to produce nozzles that can withstand such high temperatures. The fourth application of micro nozzles is in inkjet printers. These printers can produce ink in micro quantities through the nozzles that are so small in size. One nozzle can actually be the size of between fifty and sixty microns. Tyson (2008) says that they are so small they could be smaller than the size of human hair which measures around 70 microns. A Microelectromechanical system is a system that brings together electrical and mechanical parts like actuators and sensors. Vittorio (2001) gives some examples of device applications like inkjet-printer cartridges, accelerometers, small engines and locks that are developed using this technology. It has a capability to detect, control and trigger mechanical processes in very small scales to produce a much larger effect.
This technology as such enables a set of devices that perform easy tasks to be fabricated and in the end be able to work in harmony to perform larger and much complex tasks. MEMS are actually grouped into two types. There are the sensors and the actuators. Each plays a role to make a process a success. For instance, sensors detect information that has been fed into the system while the actuators translate the information into action. In the article MEMS introduction (2002), smart roads have MEMS planted in them so that they could transmit information about incidences on the road such as accidents and other occurrences to devices like global positioning systems. This would be communicated to drivers who will in turn take detours to avoid the trouble spots or ignore the affected route totally. On such devices, when the MEMSs sensors detect any action, signals are sent to the actuators which produce a designated action by pumping, injecting or filtering a desired fluid at a regulated pressure to a point that is required through micro nozzles in the device.
A second method that can be used for producing micro nozzles is through the use of a technique called micro electrical discharge machining (micro EDM). In this technique, spark charges are used mainly to reduce the size of a conductive material. This, applied to a surface, can produce the effect of drilling holes that are as small as millimetres to very minute micro millimetres. Apart from micro EDM, there are some other techniques for drilling holes. These are techniques like Electrochemical Discharge Machining (ECDM). In ECDM, the rate at which material is displaced is comparatively higher and can be as high as 1.5 mmminute. This has drawbacks that are detrimental in the long run as in reducing roughness to a record minimal level of up to 0.08 micro metres, it causes etching of the insides of the micro holes drilled through the material. Yan, Huang and Wang (2002) suggest that this technique should be used in materials that are less abrasive when exposed to the environment. The next technique is the Wire Electric Discharge Grinding (WEDG). It is not a major technique in the production of micro nozzles. Uhlmann, Piltz and Oberschmidt (2008) reckon that it is a technique mainly applied when producing micro-rotational parts used in the various sectors of the industry.
Micro electrochemical machining (micro ECM) is another technique that can be used in the drilling of these nozzles. This technique bases its practicability on chemical reactions that are based on dissolution processes. It therefore encompasses very intricate processes that result in gas production from such reactions. Materials that are removed from the nozzles created are then transported out of the nozzles. It can be noted here that hydro-dynamical forces result during the production of the micro nozzles and the whole process is aided by an oscillating tool electrode. Bohlke and Forster (2005) further state that the oscillating tool, in stark contrast to the ones used in EDM (EDM actually has two electrodes submerged in electrolyte), has a relatively low rate of wearing down and can actually remain without damage on the surface.
The next method of production of micro nozzles is the micro Ultrasonic Machining. In this technique, the technologies of both WEDG and EDM are utilised in the production of micro nozzles. It is a very efficient technique that comes up with nozzles as small as 15 micrometres. It has also made the production of many other high-aspect-ratio microstructures a success. This is attributed to the diligence obtained when the technologies of WEDG and EDM are combined according to Sun, Masuzawa and Fujino (1996).
The second last technique is called laser beam machining (LBM). A beam of high intensity laser is propagated over a path with unwanted material, say a location where you need to drill a micro nozzle Watanabe (2002). It then removes, with a lot of accuracy, the part that has been marked for removal. Laser beam machining (2006), proposes this as a more accurate way of drilling nozzles. Micromachining can be done using this technology on materials such as graphite, silicon, diamond and graphite with a very high level of precision. This has been noted as a very expensive technique with very high overhead. The final method of production of micro nozzles is the micro punching of the holes. Here, nozzles of up to 100micrometre could be produced. Later on, upon reducing of the standard conditions for drilling, nozzles of up to 25moicrometres could be drilled. A diamond wheel was originally used though it has since been replaced by tools that are mainly made from tungsten carbide fabricated during the grinding process. Joo, Rhim and Oh (2005) record this as a huge development from the one before that could only manage 100micrometres.
All the above mentioned techniques fall under the Micro-Electro-Mechanical Systems (MEMS). This is due to the fact that in all of them, a basic sensor and an actuator are located in the machine to do the sensing of information that is sent containing instructions on what to do. The actuators then carry out the instructions fed to it by drilling the nozzles to the required standards. The main difference come in at the point where different techniques are used to reach one desired goal the drilling of micro nozzles. Whichever way it is done, it is of high importance to note that all the techniques have merits and demerits. A shared demerit is the cost of overhead. A technique such as Electro Chemical Machining (ECM) is seen to be very complex and involving very intricate chemical reactions. WEDG can be said to be limited when it comes to drilling particularly nozzles though it can be successfully used in other surface clearing or removal techniques to a good satisfaction level. On the other hand, Electrochemical Discharge Machining is harmful to the material as it leads to the etching of the wall within the nozzles that were drilled. Therefore the lifespan of such nozzles cannot be guaranteed in-case it is to be used to jet fluids that corrode the material it was made from. Opoz (2006) notes that Laser Beam Machining (LBM) is used to achieve nozzles of up to a diameter of 4 micrometres. On the flipside, it causes deterioration and very small cracks on the surface which has been machined.
All the demerits noted, it is also good to realise that each technique is suitable for particular materials and for drilling holes of certain sizes. This is due to the fact that each technique has a limit of nozzle diameter size that it can drill. Of importance is the fact that each method is applied in the making of different appliances. For instance, laser beaming is good for drilling materials with very hard surfaces which require a lot more care than the average surface. Diamond and graphite are examples of materials with very tough surfaces that would require a technique that will likely not destroy it in the process.
The MEM system techniques described above have a relatively long history. In the late fifties, Jack Kilby came up with the first integrated circuit (I.C.) using germanium (Ge). This would change completely the scenery in most scientific processes. Engineering as a whole took a good turn as the production of micro mechanical parts became easier aided by the I.C.s. A while later on in the same period, Robert Noyce developed a planar double diffused silicon (Si) I.C. the element proved to be famous for the job a it was relatively cheaper and commonly obtainable in the form of sand (SiO2). The fabrication of I.C.s relies on sensors that provide information to the actuators from the locality.
This information from the locality is relayed to the actuators for an action to be carried out as instructed. In the early eighties, micromachining came up as a method of fabricating very small mechanical parts that were in micro or even nano sizes. The small parts were developed by etching sections of the silicon substrate that were not needed to come up with the desired shape or micromechanical device. Vittorio (2001) describes one of the techniques, the sacrificial layer technique, as a process through which a layer of material is deposited in between two sheets of mechanical substance for total separation from each other. When the layer is removed, the layers of the material etch to free themselves. This in essence gave birth to surface micromachining around the year 1985. To date, there has been recorded several advancement of the MEM system. A lot is still in advance stages to come up with more efficient techniques that can be used to perform even less micromechanical activities. The Laser Beam Machining, which currently provides one of the finest machining, is set to improve with advances in technology.
Supersonic micro nozzles designs is basically employed in the aeronautics and astronautics field where there is need for micro propulsion through thrust provided by a micro-thruster with a linear aero-spike nozzle. Here, the main propellant that is employed is decomposed hydrogen peroxide. Supersonic micro nozzles are consequently used as key components of any micro propulsion that is dependent on chemicals which convert the pressure energy of the gases that are in combustion to produce thrust. The flow in these nozzles is usually affected by a viscous effect that slows down drastically the performance of the thruster. Zilic, Hitt and Alexeenco mention this as the main cause of layers that pile onto each other on the expander wall. Subsequent layer that pile together increase in size to lower the general performance.
Discussion and conclusions
The MEMS technology prides itself in application in various areas. Of particular notice is in the field of fluidics. Of special concern is the restriction of fluids in containers so that it can be released in regulated amounts, usually in jets, to a specific area where one is interested in applying the fluid. This technique is therefore found to be a basic principle in the field of science. An expansive usage in the manufacturing of more efficient diesel combusting engines is aided by the use of MEMs technologies to come up with engines that are friendlier to the environment. This is seen as a huge step towards saving the environment from depletion that threatens it everyday. Therefore, this is an industry friendly technology. The costs of producing MEMS technology is quite exorbitant but of note is that the main basis for its existence depends on future inventions that would make it cheaper so that efficiency can be increased and improved to favourable levels.
Application of the technology is found in various sciences. Physics, chemistry and biology might be beneficiaries but engineering takes the lions share as most of the mechanicals parts are mainly studied at an advanced level in the engineering field. In engineering, the small details of the processes are studied to come up with the actual inventions that dominate the MEMS techniques. The other section that is of notice is in the launching of satellites where satellites as small as one kilogram have been launched into the space using propellants that utilise micro-nozzles in their propellers. This has also been touted as a cheaper option as more and more satellites are launched with the fuel used in the process being minimised due to the nature of the satellites.
Recommendations that can be made are to observe the stages upon which the engineering field ha reached in the designing of better micro nozzles. More and more materials should be tested to find out if they too can be used in developing the critical micromechanical parts that usually suffer surface damage during their use. This would go a long way in ensuring that the micro mechanical parts last longer hence cut costs associated with frequent replacement due to wear and tear. As a means of increasing efficiency, the technology should be employed in more equipment so that if necessary, efficiency can be deployed everywhere possible. For instance, some farm machines would maybe require such parts to make them more efficient. These are machines like the manual mechanical sprayer that uses macro nozzles to spray disinfectant on crops. Maybe if the technology is deployed, a more efficient and fast spraying machine could be developed. It would reduce costs for farmers who incur other costs in crop production.
To increase efficiency, Lehnert, Laine and Gijs (2003) suggest a new way in which surface interaction (giga seal formation) can be improved. Here, the silicon dioxide (SiO2) micro nozzles are covered with a micro-coating of polydymethylsiloxane (PDMS). This is then exposed to plasma of oxygen. There are recorded measurements with living cells that indicated better seal resistances.
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