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  1. 1. 1 Submitted by MUDAVATH BABURAM 13001-M-036 Under the Guidance of Mr. ANAND (Lecturer) FOR THE PARTIAL FULFILLMENT OF THE DIPLOMA IN MECHANICAL ENGINEERING 2013-2016
  2. 2. 2 It is with the sense of great satisfaction and pride that we are sitting down to pen our project report. On this day, we stand indebted to Mr. Anand Sir, Lecturer at Government Polytechnic, Masab Tank, Hyderabad for his valuable advices, guidance and suggestions through our project work which played a vital role in carrying out this project successfully. We are also thankful for his cooperation and help for successful completion of this project. We are profoundly thankful to Mr. Venkateshwarlu, Head of Mechanical department, for his dynamic invaluable technical guidance and constant encouragement, without which we couldn’t have completed our project successfully. In this context we would like to thank all our staff members in Department of Mechanical engineering, Masab Tank, for there constant encouragement in carrying out our project work. We would like to thank our friends whose constant doubts and suggestions inspired us throughout the course of the project.
  3. 3. 3 GOVERNMENT POLYTECHNIC, MASAB TANK Affiliated to SBTET, ASIFNAGAR, HYDERABAD-500028. CERTIFICATE This is to certify that the project entitled, “DESIGN OF MINI COMPRESSOR LESS PELTIER REFRIGERATOR” is being submitted by MUDAVATH BABURAM (13001-M-036) In partial fulfilment for the degree of DIPLOMA IN MECHANICAL ENGINEERING, Government Polytechnic, Masab tank, Hyderabad-500028, Affiliated to SBTET, is record of bonafide work carried by him under our supervision. Mr. Anand A. VENKATESHWARLU (LECTURER) (HOD, MECHANICAL) INTERNAL GUIDE K. RAMULU EXTERNAL GUIDE (PRINCIPAL)
  4. 4. 4 DECLARATION We hereby declare the results embodied in this dissertation titled “ DESIGN OF MINI COMPRESSOR LESS PELTIER REFRIGERATOR” is carried out during the year 2015-2016 in the practical fulfilment of the award DIPLOMA from “GOVERNMENT POLYTECHNIC, MASAB TANK, HYDERABAD”. We have not submitted the same to any other university or organization for the award of any other degree.
  5. 5. 5 Abstract we designed and constructed a COMPRESSOR LESS PELTIER REFRIGERATOR with an interior cooling volume of 3.45 cubic meters (1.5m x 1.0m x 2.3m). The Peltier refrigerator was equipped with on/off control which was found to be adequate to meet the required precision of +/- 15 degrees Celsius put forth in the project requirements. One liter of water was placed inside the cooler to test the performance of the device. We tested the maximum performance of the device by cooling a sample down to -5 degrees Celsius. Temperature control was also tested by cooling one liter of water from room temperature down to -5 degrees Celsius. On/off control was found to give adequate performance and we met or exceeded all of our project requirements set forth in the fall semester of 2016.
  6. 6. 6 TITLE PAGE NO. CHAPTER:1 INTRODUCTION 6 CHAPTER:2 THEORY OF PELTIER UNIT  Peltier History  Peltier Structure  Peltier theory  Why use TE coolers  Disadvantages  Which industries use TE cooling and their applications?  Basic Principles  Semiconductor P and N Type Doping  Thermoelectric materials  Condensation  TE performance 8 CHAPTER:3 MATERIALS USED 26 CHAPTER:4 CONSTRUCTION AND DESIGN 32 CHAPTER:5 WORKING OF FRIDGE 35 CHAPTER:6 COST ANALYSIS 37 CHAPTER:7 CONCLUSION 39
  7. 7. 7 Conventional cooling systems such as those used in refrigerators utilize a compressor and a working fluid to transfer heat. Thermal energy is absorbed and released as the working Fluid undergoes expansion and compression and changes phase from liquid to vapor and back, respectively. Semiconductor thermoelectric coolers (also known as Peltier coolers) offer Several advantages over conventional systems. They are entirely solid-state devices, with no moving parts; this makes them rugged, reliable, and quiet. They use no ozone- depleting chlorofluorocarbons, potentially offering a more environmentally responsible alternative to conventional refrigeration. They can be extremely compact, much more so than compressor-based systems. Precise temperature control (< ± 0.1 °C) can be achieved with Peltier coolers. However, their efficiency is low compared to conventional refrigerators. Thus, they are used in niche applications where their unique advantages outweigh their low efficiency. Although some large-scale applications have been considered (on submarines and surface vessels), Peltier coolers are generally used in applications where small size is needed and the cooling demands are not too great, such as for cooling electronic components.
  8. 8. 8 The objectives of this study is design and develop a working thermoelectric refrigerator interior cooling volume of 5L that utilizes the Peltier effect to refrigerate and maintain a selected temperature from 5 °C to 25 °C. The design requirements are to cool this volume to temperature within a time period of 6 hrs. and provide retention of at least next half an hour. The design requirement, options available and the final design of thermoelectric refrigerator for application are presented
  9. 9. 9 Peltier History Early 19th century scientists, Thomas Seebeck and Jean Peltier, first discovered the phenomena that are the basis for found that if you placed a temperature gradient across the junctions of two Dissimilar conductors, electrical current would flow. Peltier, on the other hand, learned that passing current through two dissimilar electrical conductors, caused heat to be either emitted or absorbed at the junction of the materials. It was only after mid-20th Century advancements in semiconductor technology, however, that practical applications for thermoelectric devices became feasible. With modern techniques, We can now produce thermos electric efficient solid state heat-pumping for both cooling and heating; many of these units can also be used to generate DC power at reduced efficiency. New and often elegant uses for thermo-electrics continue to be developed each day.
  10. 10. 10 Peltier structure A typical thermoelectric module consists of an array of Bismuth Telluride semiconductor pellets that have been carrier–either positive or negative–carries the majority of current. The pairs of P/N pellets are configured so that they are connected electrically in series, but thermally in parallel. Metalized ceramic substrates provide the platform for the pellets and the small conductive tabs that connect them. Peltier Theory When DC voltage is applied to the module, the positive and negative charge carriers in the pellet array absorb heat energy from one substrate surface and release it to the substrate at the opposite side. The surface where heat energy is absorbed becomes cold; the opposite surface where heat energy is released becomes hot. Reversing the polarity will result in Reversed hot and cold sides
  11. 11. 11 Why is TE Coolers Used for Cooling?  No moving parts make them very reliable; approximately 105 hrs of operation at 100 degrees Celsius, longer for lower temps (Goldsmid,1986).  Ideal when precise temperature control is required.  Ability to lower temperature below ambient.  Heat transport controlled by current input.  Able to operate in any orientation.  Compact size make them useful for applications where size or weight is a constraint.  Ability to alternate between heating and cooling.  Excellent cooling alternative to vapor compression coolers for systems that are sensitive to mechanical vibration. DISADVANTAGES  Able to dissipate limited amount of heat flux.  Less efficient then VCR system  Relegated to low heat flux applications.  More total heat to remove than without a TEC.
  12. 12. 12  Electronic  Medical  Aerospace  Telecommunications Cooling:  Electronic enclosures  Laser diodes  Laboratory instruments  Temperature baths  Refrigerators  Telecommunications equipment  Temperature control in missiles and space systems  Heat transport ranges vary from a few mill watts to several thousand watts, however, since the efficiency of TE devices are low, smaller heat transfer applications are more practical.
  13. 13. 13 When a p type semiconductor (doped with holes) is used instead, the holes move in a direction opposite the current flow. The heat is also transported in a direction opposite the current flow and in the direction of the holes. Essentially, the charge carriers dictate the direction of heat flow.
  14. 14. 14 Method of Heat Transport There are several methods which can be employed to facilitate the transfer of heat from the surface of the thermoelectric to the surrounding.  Electrons can travel freely in the copper conductors but not so freely in the semiconductor.  As the electrons leave the copper and enter the hot- side of the p-type, they must fill a "hole" in order to move through the p-type. When the electrons fill a hole, they drop down to a lower energy level and release heat in the process.  Then, as the electrons move from the p-type into the copper conductor on the cold side, the electrons are bumped back to a higher energy level and absorb heat in the process.  Next, the electrons move freely through the copper until they reach the cold side of the n-type semiconductor. When the electrons move into the n- type, they must bump up an energy level in order to move through the semiconductor. Heat is absorbed when this occurs.  Finally, when the electrons leave the hot-side of the n- type, they can move freely in the copper. They drop down to a lower energy level and release heat in the process.
  15. 15. 15  To increase heat transport, several p type or n type thermoelectric(TE) components can be hooked up in parallel.  However, the device requires low voltage and therefore, a large current which is too great to be commercially practical.  The TE components can be put in series but the heat transport abilities are diminished because the interconnecting’s between the semiconductors creates thermal shorting.
  16. 16. 16  The most efficient configuration is where a p and n TE component is put electrically in series but thermally in parallel . The device to the right is called a couple.  One side is attached to a heat source and the other a heat sink that convects the heat away.  The side facing the heat source is considered the cold side and the side facing the heat sink the hot side.  Between the heat generating device and the conductor must be an electrical insulator to prevent an electrical short circuit between the module and the heat source.
  17. 17. 17  The electrical insulator must also have a high thermal conductivity so that the temperature gradient between the source and the conductor is small.  Ceramics like alumina are generally used for this purpose.  The most common devices use 254 alternating p and n type TE devices.  The devices can operate at 12-16 V at 4-5 amps. These values are much more practical for real life operations. An entire assembly
  18. 18. 18 Semiconductor Doping: N Type N doped semiconductors have an abundant number of extra electrons to use as charge carriers. Normally, a group IV material (like Si) with 4 covalent bonds (4 valence electrons) is bonded with 4 other Si. To produce an N type semiconductor, Si material is doped with a Group V metal (P or As) having 5 valence electrons, so that an additional electron on the Group V metal is free to move and are the charge carriers
  19. 19. 19 Semiconductor Doping: P Type For P type semiconductors, the dopants are Group III (In, B) which have 3 valence electrons, these materials need an extra electron for bonding which creates “holes”. P doped semiconductors are positive charge carriers. There’s an appearance that a hole is moving when there is a current applied because an electron moves to fill a hole, creating a new hole where the electron was originally. Holes and electrons move in opposite directions.
  20. 20. 20 THERMOELECTRIC MATERIALS Semiconductors are the optimum choice of material to sandwich between two metal conductors (copper) because of the ability to control the semiconductors’ charge carriers, as well as, increase the heat pumping ability. The most commonly used semiconductor for electronics cooling applications is Bi2Te3 because of its relatively high figure of merit. However, the performance of this material is still relatively low and alternate materials are being investigated with possibly better performance. Alternative materials include:  Alternating thin film layers of Sb2Te3 and Bi2Te3.  Lead telluride and its alloys  SiGe  Materials based on nanotechnology
  21. 21. 21 A plot of various p-type semiconductor figures of merit times temperature vs. temperature are shown. Within the temperature ranges concerned in electronics cooling (0-200C) Bi2Te3 performs the best. Similar results are shown for n-type semiconductors
  22. 22. 22 Bi2Te3 Properties: Below is a plot of the figure of merit (Z), Seebeck coefficient, electrical resistivity, and thermal conductivity, as a function of temperature for Bi2Te3. Carrier concentration will alter the values below. Bi2Te3 figure of merit as a function of tellurium concentration.
  23. 23. 23 Condensation A common problem with TE cooling is that condensation may occur causing corrosion and eroding the TE’s inherent reliability. Condensation occurs when the dew point is reached. The dew point is the temperature to which air must be cooled at constant pressure for the water vapor to start to condense Condensation occurs because the air loses the ability to carry the water vapor that condenses. As the air’s temperature decreases its water vapor carrying capacity decreases. Since TE coolers can cool to low and even below ambient temperatures, condensation is a problem. The most common sealant employed is silicon rubber. Research has been performed to determine the most effective sealing agent used to protect the chip from water. Four sealants were used to seal a TE cooling device and the weight gain due to water entering the device measured. The best sealants should have the lowest weight gain. The epoxy has virtually no weight Gain
  24. 24. 24 According to the previous results, it seems that the epoxy is the best sealant. These results are verified by the published permeability data showing the epoxy having the lowest permeability (vapor transmission rate) of all the sealants.
  25. 25. 25 Thermoelectric Performance  TE performance depends on the following factors:  The temperature of the cold and hot sides.  Thermal and electrical conductivities of the device’s materials.  Contact resistance between the TE device and heat source/heat sink.  Thermal resistance of the heat sink. Coefficient of Performance A typical AC unit has a COP of approximately 3. TE coolers usually have COP’s below 1; 0.4 to 0.7 is a typical range. Below are COP values plotted versus the ratio of input current to the module’s Imax specification. Each line corresponds with a constant DT/DTmax (the ratio of the required temperature difference to the module's max temperature difference specification).
  27. 27. 27 CHAPTER: 3 MATERIALS USED EVAPORATOR:- • A mini sized Evaporator is made of Aluminum as it retains cooling effect for long period. • The size of Evaporator is 15*12*23 = 4140 cc Aluminium box recieves chilling effect from one side of the peltier and transfer to the the storage.
  28. 28. 28 Pump:- A pump is a device that moves fluids. Pumps are selected for processes not only to raise and transfer fluids, but also to meet some other criteria. This other criteria may be constant flow rate or constant pressure. In this project pumping system is provide to water inorder to circulate around the hotside of the peltier. It is done because the rate of heat dissipation is higher with water rather than fan. This increases the efficiency of the system. The water pump employed is mini sized, it is capable of running at 12v and 5Amp
  29. 29. 29 SUMP: A sump is a cubiodal shape water container in which pump is employed for circulation of coolant.the size of the sump employed in this project is 20*130*200 mm. Sump serves as a base part of peltier cooler, on which evaporator is mounted. The peltier that is attached to the bottom side of the evaportor is fixed with heatsink over it which is submerged in the water of the sump.
  30. 30. 30 12V –BATTERY:- Peltier device is powered by 12v battery. an electric battery is a device consisting of two or more electrochemical cells that convert stored chemical energy into electrical energy. each cell has a positive terminal, or cathode, and a negative terminal, or anode. the terminal marked positive is at a higher electrical potential energy than is the terminal marked negative. the terminal marked negative is the source of electrons that when connected to an external circuit will flow and deliver energy to an external device. ` `
  31. 31. 31 HEATSINK:- HEATSINK is a passive heat exchanger that transfers the heat generated by an electronic or a mechanical device into a coolant fluid in motion. Then-transferred heat leaves the device with the fluid in motion, therefore allowing the regulation of the device temperature at physically feasible levels.. The heat sink used in this fridge is of the dimension 7.5cm X 8cm X 4.5 cm (L x B x H).
  32. 32. 32 Insulation Material:- As we know the ice vendors take advantage of thermocol for its economic value and good insulation property as it does not allow the inner temperature of cooling medium to go down. Hence it is also an economic source of insulation. So the external structure of the whole refrigerator is made of thermocol. PLASCTIC TUBE:- Plastic tube conveys the water from the sump to the peltier device which is employed at the upper side of the evaporator box. One end of the tube is connecting to the water pump and another is connected to a section attached to the peltier.
  33. 33. 33 Chapter4:- Construction and Design Dimensions of the Fridge 1. Outer dimensions  Length 160mm  Breadth 110mm  Height 240mm 2. Inner dimensions  Length 150mm  Breadth 100mm  Height 230mm 3. Volume of the Fridge 3450000mm3 4. DIMENSIONS OF PELTIER 40mm x 40mmx 2mm
  34. 34. 34 STEPS IN THE CONSTRUCTION OF THE FRIDGE  Firstly a box of Thermocol is made of given dimensions and then the aluminum box is made and fixed into it.  The aluminum box is mounted with a Peltier device at the top and bottom with the help of thermal paste.  At the top of the aluminum box a small rectangular box is made in which hot side of the Peltier is faced.  Base of the evaporator is attached with cold side of the Peltier and hot side is attached to a heat sink which is submerged in sump water.  The sump is placed beneath evaporator has a pump and heat sink submerged in it.  One end of the tube is connected to the Water Pump and another end is connected to the small rectangular box mounted on the top side of the evaporator.  A small rectangular has a channel to the sump in which the water flows to the sump.  A battery is placed beside the evaporator with proper insulation.  The terminals of the Peltier devices, and Pump should be connected properly.
  35. 35. 35 Circuit diagram of fridge Circuit diagram showing the Peltier and Pump connections with a Power Source. The circuit of the fridge is made quite simple and convenient so that in case of any fault, it can be easily dissembled and can be repaired without any major changes to the design. The two Peltier units are used in series with each other connected to the 12 volt DC supply. A pump is also connected in series as same that of Peltier.
  36. 36. 36 Chapter 5 WORKING OF THE PROJECT Fridge:-  The fridge is provided power supply form a 12 volt DC 7.5 amps battery. To start the fridge, the switch on the fridge is turned on. When the switch is turned on the Peltier devices and Pump start functioning. The water from the sump is pumped to the upper smaller rectangle and directs to the hotter side of the Peltier (P1). The hot side of the second Peltier is cooled by the sump. Cold sides of the both Peltier transfers the chilling effect to the evaporator.  The Peltier thermoelectric Device will be so arranged in a box with proper insulation system and heat sink so that efficient cooling takes place at all the time. To turn off the fried, switch can be turned off.
  37. 37. 37 Calculation of COP of FRIDGE 1. Input power = product of current and voltage = ------ ----- W 2. Initial temperature of the evaporator = --------K 3. Final temperature of the evaporator = --------- k 4. Total amount of heat removed = Total cooling effect produced 5. Total amount of heat removed = Mw* cp * change in temperature = --------------------- = ------------- 6. Coefficient of performance = refrigeration effect / input work= -------------------
  38. 38. 38 Chapter6: COST ANALYSIS The cost analysis for this project is done as follows. All the components along with the miscellaneous cost are included in the total cost of this fridge. S.No Name of the Material / Equipment Cost Rs. 1. Peltier devices -2 660/- 2 Aluminum box 200/- 3 Thermocol box 200/- 4 Pump 300/- 5 Battery 12v 650/- 6 Heat sink – 2 400/- 7 Thermal paste 80/- 8 Plastic tube 50/- 9 Sump 60/- 10 Insulating material 150/- Total cost Rs.2750/- The cost Analysis shows that the Overall Cost of the Project strikes Rs. 2750/-
  39. 39. 39 CHAPTER 7 CONCLUSION During construction of the device several minor changes were made to the design. Each of these changes we feel was justified as they made for easier construction while maintaining the performance of the device with respect to the project goals. The device passed its final inspection and was deemed to have a professional appearance by the design project coordinator The device was discovered to have ample precision and total heat transfer capabilities while meeting its accuracy requirement. REFERENCES 1. Wikipedia https://en.wikipedia.org/wiki/Main_Page 2. Google.com 3. Astrain D and Vian J G (2005), “Computational Model for Refrigerators Based on Peltier Effect Application”, Applied Thermal Engineering, 4. Christian J L and Jadar R Barbosa Jr (2011), “Thermodynamic Comparison of Peltier, Stirling, and Vapor Compression Portable Coolers”, Applied Energy, Vol. 5. Roy J Dossat (2002), Principles of Refrigeration, Vol. 2