Chapter 1: INTRODUCTION

Transcription

1 Chapter 1: INTRODUCTION 1.1 Project background This assignment is focus on designing and building a Stirling engine water proof model. This project focus on using Carnot cycle thus help student have a better understanding on how the Carnot cycle work. 1.2 Problem statement To determine whether the student are able to create a working Stirling engine. On the final testing day, student is required to show their product to the lecture to determine the success of the project. 1.3 Research objectives The research objectives of this project problem are for us as a student to: 1. Complete a hands-on experience by working in group to design, build and test a Stirling engine. 2. Demonstrate the student understanding of the assumptions they choose design model for Stirling engine with regard of heat-exchange process that allows near-ideal efficiency in conversion of heat into mechanical movement by following the Carnot cycle principle. Page 1

2 1.4 Project scope The scope of the project are to study about design, build and test a water proof model based on objective to test the capability of our Stirling engine model to work. The project also meant to deliver us the understanding of the concept of external combustion engine and how the simple temperature phenomena can lead into power generation potential. These studies are also for new graduates especially to have hands-on experience by working in group and demonstrate our understanding of the assumptions of our chosen design model for Stirling engine wit according to Carnot cycle principle. Page 2

3 Chapter 2: THEORY 2.1 Introduction A Stirling engine is a heat engine operating by cyclic compression and expansion of air or other gas, the working fluid, at different temperature levels such that there is a net conversion of heat energy to mechanical work. In easy word, Stirling engine is some kind of closed cycle heat engine. This means that the Stirling engine works by converting heat into mechanical output, and the fluid that does the mechanical work, called the working fluid, is normally enclosed within the engine and is not mixed with any other material. Basically, there are two major types of Stirling engines that are distinguished by the way they move the air between the hot and cold sides of the cylinder. One of it is the two piston alpha type design is that has pistons in independent cylinders, and gas is driven between the hot and cold spaces. The other type of Stirling engine is a displacement type Stirling engines, known as beta and gamma types, use an insulated mechanical displacer to push the working gas between the hot and cold sides of the cylinder. The displacer is large enough to insulate the hot and cold sides of the cylinder thermally and to displace a large quantity of gas. It must have enough of a gap between the displacer and the cylinder wall to allow gas to flow around the displacer easily. But in our project, we constructed the beta type Stirling engine. 2.2 Beta Stirling Engine The basic information of a beta Stirling is it has a single power piston arranged within the same cylinder on the same shaft as a displacer piston. Its displacer piston is a loose fit and does not extract any power from the expanding gas but only serves to shuttle the working gas from the hot heat exchanger to the cold heat exchanger. When the working gas is pushed to the hot end of the cylinder it expands and pushes the power piston. When it is pushed to the cold end of the cylinder it contracts and the momentum of the machine, usually enhanced by a flywheel, pushes the power piston the other way to compress the gas. Unlike the alpha type, the beta type avoids the technical problems of hot moving seals. So, we can say that the beta Stirling engine is much more practical than the alpha type. Page 3

4 2.3 Basic component A fixed mass of gas Known as the working fluid which is normally sealed inside the engine. Ideally the gas should have low heat capacity so it expands a lot in volume when heated. In this project, we used air as the fixed mass or the working fluid Heat source The source can be almost anything, since it does not come into direct contact with the working fluid or the internal parts of the engine, so we are using the candle as the heat source. It is really helpful and suitable for our mini Stirling engine model. Plus, it is also cheap and easy to find A heater to transfer the heat from the heat source to the working fluid The heater needs to be effective at transferring heat to the working fluid but at the same time it should not introduce too much pumping loss (friction) to the working fluid. The heater also needs to withstand the high temperature of the heat source without deforming A regenerator The regenerator is a device that sits between the cold and hot places of the Stirling engine so that the working fluid moves through it in both directions. The regenerator acts as a temporary storage of heat, and its purpose is to help retain the heat within the engine instead of letting the heat dissipate in the colder parts, thereby improving the engine s thermal efficiency. Ideally, the regenerator should take up as little volume as possible, introduce almost no pumping friction, has very high heat storage capacity, and has high thermal conductivity perpendicular (but not parallel) to the fluid flow. A cooler (ice) is to cool the working fluid in the cold end of the engine, show in the figure that an error. Page 4

5 2.3.5 Displacer piston When there is temperature dissimilarity between upper displacer space and lower displacer space, the engine pressure is transformed by the movement of the displacer. The pressure increases when the displacer is located in the upper part of the cylinder and as we know, most of the air is on the hot lower side. The pressure decreases when the displacer is moved to the lower part of the cylinder. The displacer only moves the air back and forth from the hot side to the cold side. It does not run the crankshaft and the engine. In other words, the connecting rod to the displacer could be a string in this engine and it would still work. 2.4 Basic process Heating Let's start from top dead centre of the hot piston. The hot piston moves to the upper part of the cylinder and the cold piston moves to the lower part of the cylinder during the first 90 degrees of revolution. The working air is moved from the cold space to the hot space. And the pressure in the engine is increased Expansion During the next 90 degrees of revolution, the two pistons both move the lower part accepting the air pressure. The engine gets its power during this portion of its cycle Cooling The crankshaft revolves by power stored in the flywheel for the next 90 degrees. The hot piston moves to the lower part and the cold piston moves to the upper part. The air is moved from the hot space to the cold space. And the pressure in the engine is decreased Contraction The two pistons are moved to upper part by the contraction of the air during the next 90 degrees. The engine also gets power during this portion of its cycle. The two piston type Stirling engine then repeats this cycle. Page 5

6 Chapter 3: METHODOLOGY 3.1 Materials Aluminium can Plastic cardboard Plastic bottle Balloon Bolt and nut Ice-cream stick Plasticine Wire Disc 3.2 Apparatus Scissor and knife Duct tape Super glue Candle Page 6

7 3.3 Procedure The Stirling engine created for this project is environmental friendly. Thus most of the material use in this project is made out of recycle material Body The body of the Stirling engine is made out of aluminium can. The top portion of the can is cut off so that the piston can easily insert in the aluminium can. To cover up the hole in the top portion we use a cut out of plastic cardboard. We calculate the size so that it will fit exactly at the top of the aluminium can. Figure Piston 1 The piston is made by cutting out the plastic cardboard and places it inside the Stirling engine. The cut out is offset about 1mm smaller than the aluminium can to reduce the friction between the wall of the aluminium can and the piston. It is also to create a pressure difference between the cold compartment and the hot compartment. The different pressure causes the first piston to move upwards. Figure 2 Page 7

8 3.3.3 Piston 2 First, the top part of a bottle is cut out. Then a balloon is cut into size and a bolt is pierce in the balloon which is secure with a nut and some super glue. This will act as our second piston. When the air is push by the first piston, it will cause the balloon to expand thus pushing the shaft of the piston. Figure Weight A weight has been placed at one end of the Stirling engine to provide the Stirling engine with inertia so that it can continue moving. For this component we use a disc which the middle hole has been cover by a piece of cardboard. It is critical to ensure the disc is placed in the center so that the center of gravity is correct. Figure 4 Page 8

9 3.3.5 Ice holder To create a colder compartment at the top of the aluminium can we create an ice holder. It is made by cutting a bottle where the top part and the bottom part is removed. The smaller hole is make exactly the same size with the outer side of the aluminium can. Plasticine is used to seal the hole between the cone shape bottle and the aluminium can. Figure Drive shaft A piece of wire is bend with the correct size and specification so that the piston can move better and freely. The wire is connect with the connecting shaft from both piston and fixed in place by using ice-cream stick. Figure 6 Page 9

10 3.3.7 Assembly Two holes are punch at the cover of the aluminium can. The first hole is made exactly at the center of plastic cardboard. This hole is make exactly the same size with the piston shaft to reduce the pressure loss from the hole to the surrounding. The next hole is make lager in size at the side part of the cover. This hole is cover by the second piston. The hole allows the air to move freely from the can into the piston. Piston 1 is placed inside the aluminium can. A wire is use to connect the piston to the drive shaft. A second piece of wire is also use to connect piston 2 to the shaft. The entire air opening is seal off to ensure we have a closed system. Figure 7 Page 10

11 Chapter 4: RESULTS 4.1 Result The result for this Stirling engine was failed. The piston failed to expand. This is because, the mass of the piston was too heavy, and the size is big, got friction and not flexible volume. Besides that, it is because of not enough heat source and cooling system. Page 11

12 Chapter 5: DISCUSSIONS. 5.1 Problem encounter during the making process of Stirling engine In this project our group have fail to make a working Stirling engine. This is cause by several problem encounters during the process of making the Stirling which will be discuss later Volume First of all the volume inside the body of the Stirling engine is too huge. Increase in volume means more heat energy is needed to supply enough energy to the system. This causes not enough pressure difference between the top part of the Stirling engine and the lower part of the Stirling engine. To overcome this problem student must first decrease the body size of the Stirling engine. By doing so they decrease the volume in the Stirling engine. Then student must make Piston 1 fit almost the whole inside of the body. The piston will fill up most of the space inside the body of the Stirling engine thus reduce the volume inside the engine even more. Small volume mean less energy require to move the piston Huge Payload First of all to ensure the Stirling can work perfectly student needs a load to supply inertia to the engine. The resources in the internet suggest the usage of disc since the disc is round and will give equal amount of inertia to all direction. This will help make our Stirling engine more stable and not shake. However when using this method students are unable to discover to centre of the disc thus making the distribution of inertia unbalance. The drive shaft which is not straight cause friction between the ice-cream stick and the drive shaft need a lot of energy to overcome. Friction from the piston and the wall of the body also need a certain amount of energy to overcome. Due to this three reason, the total weight that needs to be overcome increase in a huge amount however the energy produce is just too small to push the weight of the whole system. Page 12

13 To ensure the success of our project student must first try and reduce the total weight of the system. Student must first ensure that the piston is loosely fit inside the body of the engine. Next the drive shaft must make out of new unbend wire so that they can have a smooth and straight wire for our drive shaft. Lastly student must ensure to determine the true centre of the disc so that the inertia acting on the system will be in equilibrium Leakage of Pressure Student need sufficient amount of pressure so that the Stirling engine can work properly. However the pressure produce during the heating process has escape through the opening in the body of the engine. The hole at where the connecting shaft comes out is one of the examples where the air pressure can escape. Although the hole is small, it brings great effect towards whether the experiment is a success or a failure. Other than that the seal on the cover of the body and the main body might also have a leakage. The balloon might also been puncture and the air pressure leaked from there. This entire situation will contribute a huge amount of pressure lost and thus reduce the energy within the system. Student must ensure all of the opening is completely seal off and the opening at the connecting shaft is make as small as possible to reduce the pressure loss. Student can use soap water test to see if there is any hole which we did not cover completely Unsuitable material The material use for making the Stirling engine is unsuitable. First of all is the body of the Stirling engine. Aluminium is a good conductor of heat. That mean the heat from the bottom of the can is easily transferred to the top of the can this causes no temperature difference in the body of the Stirling engine. As we all know the principle which allows the engine to work is having a temperature difference. If there is no temperature difference, then the Stirling engine will not work. Page 13

14 5.1.5 Temperature Difference Although an ice compartment is build for our engine, student cannot put a lot of ice in it since it might block the movement of the connecting shaft. The ice might be too few to cool down the top part of the Stirling engine thus create too few temperature difference. The heat transfer from the bottom might melt the ice to fast before any changes can be observed. When heating of the body, there is loss of heat energy to the surrounding. The condition at UMP Pekan is windy. It blows the fire from the candle thus reduce the heat transfer to the aluminium can. We should make wind breaker to divert the wind and reduce the heat loss to the surrounding Regenerator Students are unable to build a suitable regenerator for the Striling engine. This cause the temperature from the hot end might seep into the cold compartment. Thus reduce the efficiency of our product. To ensure the product can work perfectly. Student must first find a way to separate the hot compartment and the cold compartment since temperature difference will give the pressure to move the engine Safety Precaution It is very important that student follow certain safety precaution when conducting this experiment. First of all student should be very careful when burning candle to supply heat to the sterling engine. Student should use suitable stand to hold both the candle and the Stirling engine in place. Next we are there is high pressure in the body of the Stirling engine. The high pressure in the Stirling engine might cause the engine to explode and cause injury to those standing nearby. Thus it is recommended that everyone should stand 15m away from the Stirling engine so ensure the safety of bystander. Page 14

15 5.2 Application in daily life Application of sterling engine in our society First of all it is a basic knowledge that Stirling engine is a very efficient system since the principle behind moving it is through the temperature difference at two different compartment which cause pressure difference and thus supply energy to the system. The heat energy can be obtained from any source from the sun, from combustion, geothermal and even the waste heat from conventional engine. This engine is far more efficient and environment friendly if compare with gasoline engine. There is no need to intake gaseous in every cycle thus there is no air pollution. It also does not require to burn fossil fuel which is one of the major pollution in the world. Although Stirling engine has many good point there is not much development in this technology until recent year. Nowadays Stirling plays a major role in supply electricity in space exploration shuttle since there is limited air for combustion in space. Stirling engine can also work the other way around. When work is place into the system from motor we can see that this engine can become an efficient heat pump or refrigerator. When work is supply into the system one end we start to absorb heat and the other end will start expelled heat. If you design the machine correctly, the cold end will get extremely cold. In fact, Stirling coolers have been made that will cool below 10 degrees Kelvin. Micro Stirling coolers have been produced in large numbers for cooling infrared chips down to 80 degrees Kelvin for use in night vision devices Modern Stirling Engine Development Today, there are many companies developing Stirling devices for niche markets, such as cogeneration units and power generation using alternative fuels. Stirling engines have come a long way from the large and heavy engines of the 19th century, thanks to advancements in materials, manufacturing processes, and theory and analysis methods. This page contains a handful of links to some of these companies. Click on the images to learn more about these organizations and the engines they produce. All images and information related to these devices are property of and are assumed to be copyrighted by their respective owners. Page 15

16 STM Corporation SOLO Kleinmotoren GmbH Stirling Energy Systems, Inc. Kockums Sweden. Sunpower, Inc. Infinia Corporation Page 16

17 Tamin Enterprises NASA Glenn Research Center 5.3 Calculation for Better Understanding Propagation of heat in the air. The equation describing the propagation of heat in a substance can be deduced from three simple and almost obvious experimental observations. We will make the hypothesis that the thermal conductivity and the specific heat of materials are constant. It is not the case, but it is not very important for us: what interests us is to understand the physical mechanisms. The first observation is that in any point of a substance, the heat flows from hot to cold. The quantity of heat flowing per second (i.e. its current) is proportional to two things: the thermal conductivity of the substance and the slope with which the temperature decreases at the observed point. δ Q = - k.s.(δ T(x,t)/δ x).δ t (1a) i.e. that the quantity of heat δ Q (joule) flowing for a short time δ t (en sec) through an area S (in square metres), is proportional to the temperature drop δ T (Kelvin degrees) found at the location x, at time t for a short distance δ x (en m) taken in the direction of flow. The ratio δ T(x,t)/δ x is not other than the partial derivative of T with respect to the variable x, i.e. its slope. The proportionality factor K is the thermal conductivity of the substance (i.e. its ability to conduct heat) and the minus sign indicates that the flow is in line with the temperature drop. Page 17

18 If one considers a small volume of tube or wire, section S and thickness Δ x, the net quantity of heat which penetrates is equal to the one which enters at the point x, less the one which leaves at (x + Δ x). One can write by taking account of the signs: δ Q = k.s.{δ T(x+ Δ x,t)/δ x - δ T(x,t)/δ x}.δ t -----(1b) The second experimental observation is that the temperature of a volume containing a substance increases when a quantity of heat penetrates there. This increase in temperature is, of course, proportional to the quantity of heat received and inversely proportional to the volume, to the density of the substance which is there, and to its specific heat. δ Q = ρ.c.δ T.S.Δ x -----(2) i.e. that the quantity of heat δ Q (joule) which penetrated in small volume S.Δ x (m 3 ), caused an temperature increase δ T (K). The coefficients of proportionality ρ (the Greek letter rho) and c are respectively the density of the substance (kg/m 3 ) and its specific heat (J/kg/K). The latter expresses the quantity of heat which it is necessary to raise of one degree the temperature of one kg of the substance. For the gases which are compressible, this quantity is different according to whether the operation is done with constant volume or constant pressure. Below, we used the values corresponding to constant volume. The third experimental observation is that no energy is created from nothing. The result is a principle of continuity: the heat which penetrates in an element of volume (according to the first observation) must necessarily correspond to that which makes increase its temperature (according to the second observation). In other words, in the absence of a source of heat in the volume, two afore-said heat quantities must be equal otherwise there would be creation of spontaneous heat, which is not possible. By equalizing the terms δ Q of the equations (1b) and (2) above: ρ.c.δ T.S.Δ x = k.s.{δ T(x+Δ x,t)/δ x - δ T(x,t)/δ x}.δ t -----(3a) By rearranging this equation by dividing it by δ t, by (ρ.c), by S and by Δ x: δ T/δ t = (k/(ρ.c)).{δ T(x+Δ x,t)/δ x - δ T(x,t)/δ x}/δ x -----(3b) Page 18

19 This equation says that the temperature variation δ T (degrees) during the short period of time δ t (seconds) i.e. the speed with which the temperature varies is proportional to the variation of the slope of the temperature (δ T/δ x) on the distance Δ x. The coefficient of proportionality is k/ρ.c. If Δ x approach zéro, the expression{δ T(x+Δ x,t) /δ x - δ T(x,t)/δ x}/δ x becomes the second partial derivative of T compared to x which is written δ 2 T/δ x 2. Finally, the equation (3b) becomes: δ T/δ t = (k/(ρ.c)).(δ ²T/δ x²) (3c) which is the partial differential equation of heat. Table 1 With this equation, it is possible to calculate the temperature profile, according to time, in a tube filled with gas and finished at both ends with a hot source and a cold source. Its resolution is not obvious. We use the famous harmonic series of Fourier. Above, you can see the result with a hot source at 800 degrees K on the left of the tube (x = 0). Initially all the gas is 300 degrees K. Page 19

20 The equation (3c) indicates that the speed δt/δ t with which the temperature varies in a point, is proportional to the constant k/(ρ.c) of the gas used. And it is there that hydrogen and helium show a superiority compared to the air or nitrogen. In what follows, k is expressed in watt/meter/degree K, ρ in kg/m 3 and c in joule/kg/degree K. For air : k/(ρ.c) = 0,025 / (1,29 x 718) = 0, m²/sec). For helium : k/(ρ.c) = 0,14 / (0,164 x 3116) = 0,00027 m²/sec (10 times more than air). For hydrogèn : k/(ρ.c) = 0,18 / (0,083 x 10183) = 0,00021 m²/sec (8 times more than air). For nitogen : k/(ρ.c) = 0,026 / (1,15 x 743) = 0,00003 m²/sec (almost like air). Comparison with a metal: For copper: k/(ρ.c) = 401/(8900 x 386) = 0,00012 m²/sec (4,4 times more than air). For steel: k/(ρ.c) = 80,2/(7840 x 450) = 0, m²/sec (a little less than the air). More quickly the heat diffuses in the gas, more easily we will be able to make run the engine with a high speed and with a great power. When we solve numerically the equation (3c) (see the graph), we are surprised to note that the speed of diffusion falls quickly less than 3 mm/sec! This is more than 100,000 times slower than the speed of sound or pressure. This is really not fast. That shows that, in a Stirling engine, the totality of gas to be heated or cooled must be in very intimate contact with the exchangers. When we design a Stirling engine, to get a good efficiency it is necessary to take account this point. If the engine does not run too quickly and if the exchangers are effective, it is not necessary to use hydrogen or helium. In this case, the only way to increase the power of an engine without changing its configuration or its initial velocity, is to increase the internal pressure of gas. A warning statement is essential here for those which would like to test this technique on a model. The use of air at high pressure into a Stirling engine can cause an explosion of vapours of the lubricating oil by diesel effect and the destruction of the engine. Such an explosion had caused the death of seasoned experimenters, for example in Philips Company. Choose low pressure when you use air, or an inert gas such as nitrogen or helium if you want to use high pressures. Page 20

21 Finally, we must still remember that the speed of propagation of heat in the gas is not the only factor for the efficiency and speed of a Stirling engine. There is also the transfer of heat between the exchangers and the gas. The speed of this transfer is roughly proportional to the difference in temperature and to the surface of the heat exchanger. The theory is highly complex, but in practice we see that the heat exchange is inversely proportional to the density of gas. We can still see that hydrogen and helium have a clear advantage over air or nitrogen Basic principles of thermodynamics. To understand the operating principle of the Stirling engine, it is not necessary to know many things. It is considered that the gas used (air, hydrogen, helium, nitrogen...) is a perfect gas, i.e. that it obeys the following law: for a mass of gas given and at constant temperature, the product of the pressure of gas by its volume remains constant. It is Mariotte's law, we can write it like that: PV = constant where P represents the pressure of gas and V its volume. If the temperature of gas is introduced, this law becomes: PV = nrt Where P represents the pressure of gas, V its volume, n the number of gram molecule (or the quantity of gas)), R the universal gas constant (R = 8, J / K mol) et T the température of the gas (expressed in Kelvin: T = t + 273, if t is the temperature expressed in Celsius degrees). According to the good old principle: "nothing is lost, nothing is created, and everything is transformed" we can approach the energy exchanges during a cycle of Stirling: any loss of calorific energy during a cycle is equal to the recovered mechanical energy during this same cycle. Page 21

22 Figure 8 On the diagram above, we see that we provide in calorific energy: Qexp + Qheat However, we recover: Qcool + Qcomp. About the mechanical energy, we recover Wexp but we provide Wcomp. The overall balance becomes, by stipulating that the heat energy lost was fully transformed into mechanical energy: Qexp + Qheat - Qcool - Qcomp = Wexp - Wcomp This leads us to speak about mechanical efficiency: it is the ratio of recovered mechanical energy (the engine goal, in fact) to the heat energy that we must provide: Efficiency = ( Wexp - Wcomp ) / (Qexp + Qheat ) NB: as we can see it in the page the regenerator, it is not necessary to provide Qheat if a regenerator is installed. Indeed, at this time there, we recover Qcool. If we refer to the page the principles, we are able to show that the efficiency may be expressed according to the temperatures (expressed in Kelvin) of the heat source and of the cold source, according to the following formula: Efficiency = 1 - T m / T M Page 22

23 5.3.3 Kinematics in a few equations. Figure 9 We assume, first, that the movement of moving parts of the engine are the consequence of the uniform rotation (ω = constant) of a motor shaft from 0 to 360 at each cycle. On the diagram opposite, you can see the representation of a slider-crank mechanism. By supposing λ small, when the covered angle is φ, the value of d is: d = r (1-cosφ) + 0,5λ r sin 2 φ Where λ = r/l When we know the section of the piston S, it is easy to determine the volume of gas V above the piston at each moment, for a given φ. V = d S Page 23

24 Figure 10 When we have several pistons (alpha engine) or a piston and a displacer (beta and gamma engines), it is advisable to take into account the phase shift dφ between the two. The above equation becomes, for the second element: d 2 = r 2 [1-cos(φ-dφ)] + 0,5λ 2 r 2 sin 2 (φ-dφ) where λ 2 = r 2 /L 2 In the same way that above, we obtain the value of instantaneous volume: V 2 = d 2 S How calculate the engine Join together your knowledge in kinematics and thermodynamics: If you combine your knowledge in thermodynamics and those in kinematics, you can calculate your engine. By setting the maximum and minimum temperatures, the pressure in the engine can be calculated for each value of rotation of the main shaft. Page 24

25 Figure 11 There are several volumes to consider: - a volume of expansion (variable). - a volume of cooling (constant). - a volume of regeneration of heat (constant). - a volume of reheating (constant). - a volume of compression (variable). This is true whatever the type of engine, even if the diagram opposite seems show, rightly, an alpha engine. According to the engines, the expression of volumes of compression and expansion are not the same. These volumes depend on the input variable, which is the angle of rotation φ. In the table below, for three types of engine, we have collected the expressions of the volumes of expansion and of the volumes of compression: Table 2 Page 25

26 Then, for each volume, it is necessary to apply the following relationship that adds the various gas masses (n is the number of gram molecules in the engine) n = Σ PV i / RT i In this expression, i takes the following values: - i = e for the volume of expansion, T i = T M - i = cool for the volume of cooling, T i = T m - i = reg for the volume of the regenerator, T i = 1/2 ( T m + T M ) - i = heat for the volume of reheating, T i = T M - i = c for the volume of compression,, T i = T m It should be noted that we consider that the pressure is uniform throughout the engine at any moment. Page 26

27 Chapter 6: SUMMARY, CONCLUSIONS & RECOMMENDATIONS 6.1 SUMMARY The purpose of this project is to design, build and test a Stirling engine model with an objective, to demonstrate the Stirling engine process which include compression and expansion process. The goal of this project is to demonstrate understanding of the assumptions and limitations of our design model for model performance according to the Carnot cycle principle. Based on some discussion among the team members, we have come out with the best design model. All the material that was used was suggested by all team members as we are all looking for the high quality and suitable materials. During the test day, we prepared our model and test weather our Stirling engine can run or not. But, unfortunately, our Stirling engine cannot run. 6.2 CONCLUSION As the conclusion, in order to produce a Stirling engine which is functional, we need to apply the theory of thermodynamics to the process. But there still got some problem that we can t solve due to the limitation of materials and sources that we got. As results, we failed to operate our group Stirling engine. We strongly believe that we manage to produce a functional Stirling engine if we got extra time to solve that problem. Page 27

28 6.3 RECOMMENDATIONS (i) Use large heat source that can give a higher temperature while cooling the other side. But this will only work up until a critical temperature because of the materials we have used. (ii) Ensure that there is as small as possible heat-leaking, which can be assured by using the right materials. (iii)use a much more practical material to design this Stirling engine so that it can work more efficient. Page 28

29 REFERENCES FLUID MECHANICS, Fundamentals and Applications By Yunus A. Cengel and John M. Cimbala Retrieve from Retrieve from Page 29