CHAPTER -I INTRODUCTION A tube heat exchanger is a class of heat exchanger designs. It is the mostcommon type of heat exchanger in oil refineries and other large chemicalprocesses, and is suited for higher-pressure applications. As its name implies,this type of heat exchanger consists of a shell (a large pressure vessel) with abundle of tubes inside it. One fluid runs through the tubes, and another fluidflows over the tubes (through the shell) to transfer heat between the two fluids.The set of tubes is called a tube bundle, and may be composed by several typesof tubes: plain, longitudinally finned, etc.THEORY AND APPLICATION Two fluids, of different starting temperatures, flow through the heatexchanger. One flows through the tubes (the tube side) and the other flowsoutside the tubes but inside the shell (the shell side). Heat is transferred fromone fluid to the other through the tube walls, either from tube side to shell sideor vice versa. The fluids can be either liquids or gases on either the shell or thetube side. In order to transfer heat efficiently, a large heat transfer area shouldbe used, leading to the use of many tubes. In this way, waste heat can be put touse. This is an efficient way to conserve energy. Heat exchangers with only one phase (liquid or gas) on each side can becalled one-phase or single-phase heat exchangers. Two-phase heat exchangerscan be used to heat a liquid to boil it into a gas (vapor), sometimes calledboilers, or cool a vapor to condense it into a liquid (called condensers), with thephase change usually occurring on the shell side. Boilers in steam engine
locomotives are typically large, usually cylindrically-shaped shell-and-tube heatexchangers. In large power plants with steam-driven turbines, shell-and-tubesurface condensers are used to condense the exhaust steam exiting the turbineinto condensate water which is recycled back to be turned into steam in thesteam generator.
CHAPTER - II LITERATURE REVIEWTUBE HEAT EXCHANGER Tube heat exchangers consist of a series of tubes. One set of these tubescontains the fluid that must be either heated or cooled. The second fluid runsover the tubes that are being heated or cooled so that it can either provide theheat or absorb the heat required. A set of tubes is called the tube bundle and canbe made up of several types of tubes: plain, longitudinally finned, etc. Shell andTube heat exchangers are typically used for high pressure applications (withpressures greater than 30 bar and temperatures greater than 260°C. This isbecause the shell and tube heat exchangers are robust due to their shape.There are several thermal design features that are to be taken into account whendesigning the tubes in the shell and tube heat exchangers. These include: Tube diameter: Using a small tube diameter makes the heat exchanger both economical and compact. However, it is more likely for the heat exchanger to foul up faster and the small size makes mechanical cleaning of the fouling difficult. To prevail over the fouling and cleaning problems, larger tube diameters can be used. Thus to determine the tube diameter, the available space, cost and the fouling nature of the fluids must be considered. Tube thickness: The thickness of the wall of the tubes is usually determined to ensure: o There is enough room for corrosion o That flow-induced vibration has resistance o Axial strength
o Ability to easily stock spare parts cost Sometimes the wall thickness is determined by the maximum pressure differential across the wall.Tube length: heat exchangers are usually cheaper when they have asmaller shell diameter and a long tube length. Thus, typically there is anaim to make the heat exchanger as long as physically possible whilst notexceeding production capabilities. However, there are many limitationsfor this, including the space available at the site where it is going to beused and the need to ensure that there are tubes available in lengths thatare twice the required length (so that the tubes can be withdrawn andreplaced). Also, it has to be remembered that long, thin tubes are difficultto take out and replace.Tube pitch: when designing the tubes, it is practical to ensure that thetube pitch (i.e., the centre-centre distance of adjoining tubes) is not lessthan 1.25 times the tubes outside diameter. A larger tube pitch leads to alarger overall shell diameter which leads to a more expensive heatexchanger.Tube corrugation: this type of tubes, mainly used for the inner tubes,increases the turbulence of the fluids and the effect is very important inthe heat transfer giving a better performance.Tube Layout: refers to how tubes are positioned within the shell. Thereare four main types of tube layout, which are, triangular (30°), rotatedtriangular (60°), square (90°) and rotated square (45°). The triangularpatterns are employed to give greater heat transfer as they force the fluidto flow in a more turbulent fashion around the piping. Square patterns areemployed where high fouling is experienced and cleaning is moreregular.
Baffle Design: baffles are used in shell and tube heat exchangers to direct fluid across the tube bundle. They run perpendicularly to the shell and hold the bundle, preventing the tubes from sagging over a long length. They can also prevent the tubes from vibrating. The most common type of baffle is the segmental baffle. The semicircular segmental baffles are oriented at 180 degrees to the adjacent baffles forcing the fluid to flow upward and downwards between the tube bundle. Baffle spacing is of large thermodynamic concern when designing shell and tube heat exchangers. Baffles must be spaced with consideration for the conversion of pressure drop and heat transfer. For thermo economic optimization it is suggested that the baffles be spaced no closer than 20% of the shell’s inner diameter. Having baffles spaced too closely causes a greater pressure drop because of flow redirection. Consequently having the baffles spaced too far apart means that there may be cooler spots in the corners between baffles. It is also important to ensure the baffles are spaced close enough that the tubes do not sag. The other main type of baffle is the disc and donut baffle which consists of two concentric baffles, the outer wider baffle looks like a donut, whilst the inner baffle is shaped as a disk. This type of baffle forces the fluid to pass around each side of the disk then through the donut baffle generating a different type of fluid flow.PLATE HEAT EXCHANGER Another type of heat exchanger is the plate heat exchanger. One iscomposed of multiple, thin, slightly-separated plates that have very largesurface areas and fluid flow passages for heat transfer. This stacked-platearrangement can be more effective, in a given space, than the shell and tube heatexchanger. Advances in gasket and brazing technology have made the plate-type heat exchanger increasingly practical. In HVAC applications, large heat
exchangers of this type are called plate-and-frame; when used in open loops,these heat exchangers are normally of the gasketed type to allow periodicdisassembly, cleaning, and inspection. There are many types of permanently-bonded plate heat exchangers, such as dip-brazed and vacuum-brazed platevarieties, and they are often specified for closed-loop applications such asrefrigeration. Plate heat exchangers also differ in the types of plates that areused, and in the configurations of those plates. Some plates may be stampedwith "chevron" or other patterns, where others may have machined fins and/orgrooves.REGENERATIVE HEAT EXCHANGER A third type of heat exchanger is the regenerative heat exchanger. In this,the heat (heat medium) from a process is used to warm the fluids to be used inthe process, and the same type of fluid is used either side of the heat exchanger(these heat exchangers can be either plate-and-frame or shell-and-tubeconstruction). These exchangers are used only for gases and not for liquids. Themajor factor for this is the heat capacity of the heat transfer matrix. AlsoADIABATIC WHEEL HEAT EXCHANGER A fourth type of heat exchanger uses an intermediate fluid or solid storeto hold heat, which is then moved to the other side of the heat exchanger to bereleased. Two examples of this are adiabatic wheels, which consist of a largewheel with fine threads rotating through the hot and cold fluids, and fluid heatexchangers. This type is used when it is acceptable for a small amount ofmixing to occur between the two streams.
PLATE FIN HEAT EXCHANGER This type of heat exchanger uses "sandwiched" passages containing finsto increase the effectivity of the unit. The designs include cross flow andcounter flow coupled with various fin configurations such as straight fins, offsetfins and wavy fins. Plate and fin heat exchangers are usually made of aluminum alloys whichprovide higher heat transfer efficiency. The material enables the system tooperate at a lower temperature and reduce the weight of the equipment. Plateand fin heat exchangers are mostly used for low temperature services such asnatural gas, helium and oxygen liquefaction plants, air separation plants andtransport industries such as motor and aircraft engines.Advantages of plate and fin heat exchangers: High heat transfer efficiency especially in gas treatment Larger heat transfer area Approximately 5 times lighter in weight than that of shell and tube heat exchanger Able to withstand high pressureDisadvantages of plate and fin heat exchangers: Might cause clogging as the pathways are very narrow Difficult to clean the pathways
FLUID HEAT EXCHANGERS This is a heat exchanger with a gas passing upwards through a shower offluid (often water), and the fluid is then taken elsewhere before being cooled.This is commonly used for cooling gases whilst also removing certainimpurities, thus solving two problems at once. It is widely used in espressomachines as an energy-saving method of cooling super-heated water to be usedin the extraction of espresso.WASTE HEAT RECOVERY UNITS A Waste Heat Recovery Unit (WHRU) is a heat exchanger that recoversheat from a hot gas stream while transferring it to a working medium, typicallywater or oils. The hot gas stream can be the exhaust gas from a gas turbine or adiesel engine or a waste gas from industry or refinery.DYNAMIC SCRAPED SURFACE HEAT EXCHANGER Another type of heat exchanger is called "(dynamic) scraped surface heatexchanger". This is mainly used for heating or cooling with high-viscosityproducts, crystallization processes, evaporation and high-fouling applications.Long running times are achieved due to the continuous scraping of the surface,thus avoiding fouling and achieving a sustainable heat transfer rate during theprocess. The formula used for this will be Q=A*U*LMTD, whereby Q= heattransfer rate.
PHASE-CHANGE HEAT EXCHANGER In addition to heating up or cooling down fluids in just a single phase,heat exchangers can be used either to heat a liquid to evaporate (or boil) it orused as condensers to cool a vapor and condense it to a liquid. In chemicalplants and refineries, reboilers used to heat incoming feed for distillation towersare often heat exchangers. Distillation set-ups typically use condensers tocondense distillate vapors back into liquid. Power plants which have steam-driven turbines commonly use heatexchangers to boil water into steam. Heat exchangers or similar units forproducing steam from water are often called boilers or steam generators. In the nuclear power plants called pressurized water reactors, speciallarge heat exchangers which pass heat from the primary (reactor plant) systemto the secondary (steam plant) system, producing steam from water in theprocess, are called steam generators. All fossil-fueled and nuclear power plantsusing steam-driven turbines have surface condensers to convert the exhauststeam from the turbines into condensate (water) for re-use. To conserve energy and cooling capacity in chemical and other plants,regenerative heat exchangers can be used to transfer heat from one stream thatneeds to be cooled to another stream that needs to be heated, such as distillatecooling and reboiler feed pre-heating. This term can also refer to heat exchangers that contain a material withintheir structure that has a change of phase. This is usually a solid to liquid phasedue to the small volume difference between these states. This change of phaseeffectively acts as a buffer because it occurs at a constant temperature but stillallows for the heat exchanger to accept additional heat. One example where thishas been investigated is for use in high power aircraft electronics.
SPIRAL HEAT EXCHANGER A spiral heat exchanger (SHE), may refer to a helical (coiled) tubeconfiguration, more generally, the term refers to a pair of flat surfaces that arecoiled to form the two channels in a counter-flow arrangement. Each of the twochannels has one long curved path. A pair of fluid ports are connectedtangentially to the outer arms of the spiral, and axial ports are common, butoptional. The main advantage of the SHE is its highly efficient use of space. Thisattribute is often leveraged and partially reallocated to gain other improvementsin performance, according to well known tradeoffs in heat exchanger design. (Anotable tradeoff is capital cost vs operating cost.) A compact SHE may be usedto have a smaller footprint and thus lower all-around capital costs, or an over-sized SHE may be used to have less pressure drop, less pumping energy, higherthermal efficiency, and lower energy costs.HEAT TRANSFER Heat transfer can be defined as the transmission of energy from oneregion due to temperature difference.Modes of Heat Transfer Conduction Convection RadiationConduction
Heat conduction is a mechanism of heat transfer from a region of hightemperature to a region of low temperature within a medium (solid, liquid orgases) or between different medium in direct physical contact. In conduction,energy ex-change takes place by the kinematic motion or direct impact ofmolecules. Pure conduction is found only in solids.Convection Convection is a process of heat transfer that will occur between a solidsurface and a fluid medium when they are at different temperature. Convectionis possible only in the presence of fluid medium.Radiation The heat transfer from one body to another without any transmittingmedium is known as radiation It is an electromagnetic wave phenomenon.Fourier Law of Conduction Rate of heat conduction is proportional to the area measured normal tothe direction of heat flow and to the temperature gradient in that direction.
CHAPTER - III DESCRIPTION OF EQUIPMENTS3.1. COPPER TUBE: Copper tube is a part of this equipment copper tube is used in heatexchangers because of its many desirable properties, such as its conductivity ofelectricity and heat, its resistance to corrosion, its malleability and ductility, andits beauty, copper has long been used in a wide variety of applications. Theprincipal uses are electrical, because of copper’s extremely high conductivity,which is second only to that of silver. Because copper is very ductile, it can bedrawn into wires of any diameter from about 0.025 mm (about 0.001 in)upward. The tensile strength of drawn copper wire is about 4200 kg/sq cm(about 60,000 lb/sq in); it can be used in outdoor power lines and cables, as wellas in house wiring, lamp cords, and electrical machinery such as generators,motors, controllers, signaling devices, electromagnets, and communicationsequipment.3.2 GATE VALVE A Gate Valve is a valve that opens by lifting a round or rectangulargate/wedge out of the path of the fluid or air. The distinct feature of a gate valveis the sealing surfaces between the gate and seats are planar. The gate faces canform a wedge shape or they can be parallel. Gate valves are sometimes used forregulating flow, but many are not suited for that purpose, having been designedto be fully opened or closed. When fully open, the typical gate valve has noobstruction in the flow path, resulting in very low friction loss.
CHAPTER - IV DESIGN AND DRAWING4.1 COMPONENTS AND ITS SPECIFICATION The variable flow heat exchanger is consists of the following componentsto full fill the requirements of complete operation of the machine. 1. Copper tube 2. Gate valve 3.
CHAPTER - V WORKING PRINCIPLE This project is designed by following blocks, Condenser, Inlet port,Outlet port. The heat exchanger principle is used in different application inautomobile industry, thermal field, refrigeration. For example here we can takeautomobile engine radiator. The radiators are mainly used to reduce the heatenergy from the engine. The hot water from the engine block is connected to theinlet port of heat exchanger tube. When the hot water passes into the particularport and comes out with the low temperature in the outlet valve port. Alternatively the cold air or cold water is passed in the shell through theshell inlet port which is shown as in the below diagram. This process is used tocool the hot water from the engine gradually after this the cyclic process is takesplace to cool the engine block. The alternative cold water is always flowthrough the opposite direction of the hot water which is shown in the diagram.So this process is mainly used to transfer the heat energy from hot body to coldbody mainly the thermal conduction takes place in these particular elements. CHAPTER -6 MERITS & DEMERITS
CHAPTER VI MERITS & DEMERITSMERITS It is easy to operate Dissipate the heat Used for conduction and convection processDEMERITS Complicated to design. Developing these heat exchangers are not easy CHAPTER -7 APPLICATIONS
CHAPTER - VII APPLICATIONSIt is applicable in air conditioning, automobile field in steam engine etc..,
CHAPTER - VIII LIST OF MATERIALSFACTORS DETERMINING THE CHOICE OF MATERIALS The various factors which determine the choice of material are discussedbelow.1.PROPERTIES The material selected must posses the necessary properties for the proposed application. The various requirements to be satisfied Can be weight, surface finish, rigidity, ability to withstand environmental attack from chemicals, service life, reliability etc. The following four types of principle properties of materials decisively affect their selection a. Physical b. Mechanical c. From manufacturing point of view d. ChemicalThe various physical properties concerned are melting point, thermalConductivity, specific heat, coefficient of thermal expansion, specific gravity,electrical conductivity, magnetic purposes etc.The various Mechanical properties Concerned are strength in tensile,
Compressive shear, bending, torsion and buckling load, fatigue resistance,impact resistance, elastic limit, endurance limit, and modulus of elasticity,hardness, wear resistance and sliding properties. The various properties concerned from the manufacturing point of vieware, Cast ability Weld ability Surface properties Shrinkage Deep drawing etc.2. MANUFACTURING CASE Sometimes the demand for lowest possible manufacturing cost or surfacequalities obtainable by the application of suitable coating substances maydemand the use of special materials.3. QUALITY REQUIRED This generally affects the manufacturing process and ultimately thematerial. For example, it would never be desirable to go casting of a lessnumber of components which can be fabricated much more economically bywelding or hand forging the steel.4. AVAILABILITY OF MATERIAL Some materials may be scarce or in short supply, it then becomesobligatory for the designer to use some other material which though may not be
a perfect substitute for the material designed. The delivery of materials and thedelivery date of product should also be kept in mind.5. SPACE CONSIDERATIONSometimes high strength materials have to be selected because the forcesinvolved are high and space limitations are there.6. COST As in any other problem, in selection of material the cost of materialplays an important part and should not be ignored. Some times factors like scrap utilization, appearance, and non-maintenance of the designed part are involved in the selection of propermaterials.
CHAPTER - IX COST ESTIMATION1. LABOUR COST:Lathe, drilling, welding, grinding, power hacksaw, gas cutting cost2. OVERGHEAD CHARGES:The overhead charges are arrived by “manufacturing cost” Manufacturing Cost =Material Cost +Labour Cost = =Overhead Charges =20%of the manufacturing cost = 3. TOTAL COST: Total cost = Material Cost +Labour Cost +Overhead Charges = = Total cost for this project =
CHAPTER - X CONCLUSION The project carried out by us made an impressing task in the field ofautomobile department. It is very useful for vehicle to cool the steam enginequickly. This project will reduce the cost involved in the concern. Project has beendesigned to perform the entire requirement task at the shortest time available.