A Heat Exchanger Device Biology Essay

Part 2

Condenser is a heat money changer device in which the heat generated will be removed from the system by distilling air. It is besides known as two-phase flow heat money changer. Basically in heat money changers, the two fluids are separated by solid walls, so they are non straight in contact with one another. There are two manners of energy transportation in heat money changer, which is convection and conductivity. Convection occurs in the boundary bed of fluid on each side of the solid wall, while the conductivity occurs in the wall itself.

Kakac et Al. ( 2002 ) by and large classified capacitor into two chief types:Condenser in which the condensate watercourse and coolant are separated by a solid surface.Condenser in which the condensation vapour and coolant are brought into direct contact.Direct contact type of capacitors usually made up of a steam bubble signifiers in a pool of liquid, the liquid is sprayed into the steam. In other words, the liquid flows downwards as a movie for boxing stuffs against the upward flow of steam. Capacitors in which the condensate watercourses are separated into three chief types:Shell-and-tubeHome plateAir-cooledIn the shell-and-tube heat money changer, condensation may happen inside or outside the tubings. The orientation of the device can be vertically or horizontally. They are classified harmonizing to whether they are spirals or shell-and-tube capacitor.

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Evaporator and condenser spirals are used when the 2nd fluid is air because of low coefficient of heat transportation in the air. Condensation occurs indoors tubings in the air-cooled type with blowing or sucking air in the tubings for chilling. Fives with big surface countries are normally provided in the air to countervail the lower heat exchange coefficient of air-side.For the intent of effectual heat transportation sweetening, the choice of a shell-and-tube heat money changer as a heat transportation device is the best manner.

2.2 Shell-and-tube heat money changer

Shell-and-tube heat money changers are normally used in infrigidation, power production, air conditioning, and chemical processing. It besides used in atomic power workss as capacitors, steam power generators in pressurized H2O reactor, every bit good as provender H2O warmer. Shell-and-tube heat money changers are likely the most various and common type of heat money changers in usage.

Kakac et Al. ( 2002 ) indicated that shell-and-tube heat money changer have larger heat transportation surface country to volume ratios than dual pipe heat money changers, and easy to bring forth in a assortment of sizes and flow constellations. It can run at high force per unit areas on the environment and can be easy cleaned.

2.2.1 Basic constituents of shell-and-tube heat money changer

A shell-and-tube heat money changer is an extension of a dual pipe constellation. It consists of a closed tubing within a cylindrical shell. It operates with a flow of fluid through the tubing, while the other fluid flows within the infinite between the tubings and shell. The basic constituents of the shell-and-tube heat money changer are tubings, shell, front-end caput, rear-end caput, baffles, and tube sheets.

As shown in Figure 2.1, the baffles are placed along a package of tubings to coerce the fluid between the tubings and shell to flux across the tubing.Figure 2.1: A shell-and-tube heat money changer consists of a bundle tubing surrounded by a shell.

( hypertext transfer protocol: //beta.cheresources.com/ ) Degree centigrade: UsersShahrinDesktopUntitled.jpgThere are many fluctuations of the shell-and-tube heat money changer design, which is one-tube base on balls, two-tube base on balls, four-tube base on balls, one-shell base on balls, and two-shell base on balls heat money changer. Fraas et Al. ( 1998 ) indicated several Numberss of basic constituents of shell-and-tube heat money changer:Tubes – the tubings are the basic constituent of the shell-and-tube heat money changer. It provides heat transportation between a fluid fluxing in the tubing and the other fluid fluxing out of the tubings.

It largely made of Cu or steel. For specific applications, nickel, Ti, or aluminium may besides be used. Most of the surface of the tubing is extended or enhanced. Extended or enhanced surface tubings are used when one fluid has a much lower heat transportation coefficient of the other fluid. Double enhanced tubings, the betterment both inside and outside, so as to cut down the size and cost of the heat money changer. Extended surfaces ( fives and tubings ) to supply two to four times the country of heat transportation at the exterior of the bare tubing is appropriate. With the ratio, it helps to countervail the lower heat transportation coefficient outside.

Tube sheets – the tubings are held in topographic point by inserted into the hole in the tube sheet. Tube sheet is normally a individual unit of ammunition metal home base that was based on drilled and grooved to take the tubings, the gaskets, the spacer rods, and the bolt circle in which they are tied to the shell. The infinite between the tubing sheets is unfastened to the ambiance so that any leaks can be rapidly detected. To let any liquid leaking into the ambiance individually without blending, the ternary tubing sheets are used in instances of utmost jeopardy or high value of the fluid. In add-on, the tube sheet should defy caustic onslaught by both fluids in a heat money changer.

Other than that, the tubing sheet besides should be electrochemically compatible with all the tubing and tube-side stuff. Tube sheets are normally made from low C steel with a thin bed of corrosion-resisting articulation metallurgically bound on one side.Shell and shell-side noses – the shell is normally has a round cross subdivision and by and large made by turn overing a metal home base of the suited dimensions. Shell is the container for the shell-side fluid, while the noses are the ports of recess and mercantile establishment. The rotundity of the shell is of import in bettering the maximal diameter of the baffles that can be inserted and hence the consequence of shell-to-baffle escape. For the big money changers, the shell normally made out of low C steel, although other combination can be and are used when corrosion or high temperature strength demands must be fulfilled.Tube-side channels and noses – tube-side of the channels and noses are used to command the tube-side fluid flow into and out of the tubings of the heat money changer.

These channels and noses are usually made out of metal stuff which is compatible with the combination of the tubings and tube sheets from the tube-side fluid are by and large more caustic.Channel covers – the channel covers are round home bases that bolt to the channel rims and can be removed for review without upseting the tube-side piping every bit good. For smaller heat money changers, bonnets with flanged noses or threaded connexions to the tube-side piping are frequently used alternatively of channels and channels screens.

Pass splitter – in one channel or bonnet, a base on balls splitter is needed for an money changer holding two tube-side base on ballss, and they are required both in channels and money changer have a bonnets for more than two base on ballss.Baffles – baffles provides two maps, foremost, to back up the tubings in proper place during assembly and operation of the tubings and prevent quiver caused by whirl induced flow, and secondly, they guide the flow of the shell-side dorsum and Forth in the tubing, therefore increasing the velocity and the coefficient of heat transportation.

2.2.2 Type of shell-and-tube heat money changer

Hagen et Al. ( 1999 ) indicated that if the fluid in the tubings flows from one terminal of the heat money changer to the other terminal merely one time, it is called one-tube base on balls heat money changer, as shown in Figure 2.2.Figure 2.

2: A one-tube base on balls heat money changer. ( hypertext transfer protocol: //en.wikipedia.org/ ) Degree centigrade: UsersShahrinDesktopasa.

jpgIf the fluid in the tubings flows from one terminal to the other terminal and returns to the inlet terminal, it is called a two-tube base on balls heat money changer, as shown in Figure 2.3.Figure 2.3: A two-tube base on balls heat money changer.

( hypertext transfer protocol: //en.wikipedia.org/ ) Degree centigrade: UsersShahrinDesktop2 tube.jpgA four-tube base on balls constellation is besides common. For the shell-side flow constellation, if the fluid between the tubings and the shell flows from one terminal to the other merely one time, it is called one-shell base on balls heat money changer.

If the fluid makes two base on ballss through the shell side, it is called two-shell base on balls heat money changer. The tubings fundamentally straight in form, but shell-and-tube heat money changer besides have form of U, called U-tubes.U-tubes largely used in atomic power workss to boiling H2O recycled from a surface capacitor into steam to drive a turbine to bring forth power as shown in Figure 2.

4.Figure 2.4: A U-tube heat money changer. ( hypertext transfer protocol: //en.wikipedia.

org/ )Shell-and-tube heat money changers are available in a assorted sizes to suit specific applications. A typical industrial size of shell-and-tube heat money changer is shown in Figure 2.5 and for illumination shell-and-tube heat money changer is shown in Figure 2.6.Figure 2.5: Shell-and-tube heat money changers are normally used in an industrial application. ( hypertext transfer protocol: //www.

secshellandtube.com/ )Figure 2.6: Miniature shell-and-tube heat money changers are used in low-flow-rate and research applications. ( hypertext transfer protocol: //stms.kr/ ) Degree centigrade: UsersShahrinDesktopminiature.

jpgTubular Exchanger Manufacturers Association ( TEMA ) published criterions for the design, industry, proving, installing, operation, and care of shell-and-tube heat money changers. They are identified by an alphabetic character, as shown in Figure 2.7 ( TEMA, 1998 ) .

Figure 2.7: Standard shell type and front terminal rear terminal caput types. ( http: //pump-heat-exchanger.blogspot.com/ ) C: UsersShahrinDesktopjournal fyppicsHeat Exchanger Type.JPG

Advantages of shell-and-tube heat money changer

Wang et Al. ( 2009 ) indicated the grounds for the shell-and-tube heat money changer had been widely used are ; for case, it provides a comparatively big ratio of heat transportation country to volume and weight. Most of the parts of shell-and-tube heat money changer are easy replaced if damaged occur and besides easy to cleaned, such as baffles.

Baffles are used in shell-and-tube heat money changer to excite flow across the tubings, therefore increasing heat transportation public presentation. In add-on, shell-and-tube heat money changers are robustness to high-pressure when operates. The surface of shell-and-tube heat money changer is easy to build in a assortment of sizes and mechanical rough.

2.3 Nanofluid

Nanofluid is a conventional coolant incorporating nanometer-sized atoms suspension. The nanofluids have a high thermal conduction than conventional coolants.

The public presentation of nanofluids depends on assorted parametric quantities such as temperature, atom size, and volume fraction. The conventional coolants has been widely used in industrial procedures affecting the electronic french friess, heat money changers, automotives, fabrication, refrigerant and air conditioning, aircraft, and optical maser applications. Due to the low public presentation of conventional coolants such as H2O, ethene ethanediol, and oil, a assortment of methods and surveies have been undertaken to better the thermic conduction of fluids by suspending nanoparticles in these conventional coolants.Nanofluids are suited for technology applications and have shown some advantages compared with conventional coolant, such as better stableness, higher thermic conduction, and no excess force per unit area bead.

Since thermic conduction is the most of import parametric quantities for enhanced heat transportation, legion research have been conducted on the thermic conduction of nanofluids. All experimental consequences have indicated the sweetening of thermic conduction with the add-on of nanoparticles.

2.3.1 Production of nanofluids

Yu et Al. ( 2008 ) stated nanofluids have been produced by two techniques, which are a two-step procedure and a one-step procedure. The two-step procedure starts with nanoparticles produced whether the physical or chemical synthesis techniques, and dispersed them into a base fluid.

The one-step procedure straight disperses the nanoparticles into a base fluid.

2.3.1.1 Two-step procedure

An advantage of this measure is the technique used in the commercialisation of nanofluids. By the two-step method, production of nanofluids can be made if the agglomeration job can be overcome utilizing such nanopowders produced economically in majority. Producing nanofluids utilizing the two-step method is rather ambitious because single atoms tend to rapidly agglomerate before accomplishing scattering.

This agglomeration is happening due to attractive new wave der Waals forces between nanoparticles, and the agglomerations of atoms tend to rapidly settle out of liquids. A cardinal measure to success in accomplishing great public presentation of heat transportation is to bring forth and suspend about monodispersed or non-agglomerated nanoparticles in liquids. The agglomeration job becomes worse at high volume concentrations. Some surface-treated nanoparticles show first-class scattering in base fluid and good thermal belongingss. To bring forth well-dispersed nanofluids in big volumes, the challenge is to develop advanced ways to better the two-step procedure.

2.3.

1.2 One-step procedure

Yu et Al. ( 2008 ) states that a one-step procedure more preferable than two-step procedure to forestall oxidization of the atoms to the high conduction of nanofluids incorporating metal such as Cu. Nanoparticles are formed and dispersed in the fluid in a individual procedure with this method. One-step method that involves direct vaporization was used to bring forth Cu nanoparticles fixed figure of non-uniformly spread and stable depends on ethylene ethanediol.

By utilizing this method, the nanophase pulverizations, condensed from the vapor stage fluxing straight to the low vapour force per unit area ethene ethanediol in the vacuity chamber. Although a one-step procedure have produced nanofluids in little measures of nanofluids for experimental intents, they are improbable to be the pillar of the production of nanofluids. There are two jobs with this method.

First, to bring forth nanofluids with these one-step procedures is expensive. Second, a procedure affecting vacuity significantly slows the production of nanoparticles and the nanofluids, thereby impacting production leves.Polyvinylpyrrolidone was added as a defender and as a stabilizer that prevents the agglomeration. With this one-step chemical method, Cu nanofluids was produced, shows that about the same addition in thermic conduction of nanofluids produced by the one-step physical method. This method has the possible to bring forth big sums of nanofluids and faster than one-step physical procedure.

2.3.2 Thermal belongingss of nanofluids

Namburu et Al.

( 2008 ) indicated that the heat transportation coefficient non merely depends on the thermic conduction, but it besides depends on other fluid belongingss such as the particular heat, denseness, and viscousness of nanofluids. In add-on, it besides depends on the geometry and the raggedness of the solid surface. The thermophysical belongingss are listed in table 2.1.Table 2.1: Thermophysical belongingss of nanofluids of 293 K.

( Namburu et al, 2008 )

Properties

Volume concentration ( % )

Viscosity ( mPa s )

Density ( kg/m3 )

Specific heat

( J/kg K )

Thermal conduction ( W/m.K )

Mixture of ethene glycol/water ( basal fluid )05.381086.273084.000.349Mixture of Cu oxide/ethylene ethanediol H2O618.

751399.692393.990.424Mixture of Si dioxide/ ethene ethanediol H2O( 20 nm diameter )67.581154.292814.090.381Mixture of Si dioxide/ ethene ethanediol H2O( 50 nm diameter )67.

161154.292814.090.381Mixture of Si dioxide/ ethene ethanediol H2O ( 100 nm diameter )66.531154.292814.090.381Mixture of alumina/ethylene ethanediol H2O69.

671259.292645.350.425Namburu et Al.

( 2008 ) indicated that CuO, Al2O3, and SiO2 nanofluids for the same concentration and at a peculiar Reynolds figure, CuO nanofluids have higher heat transportation public presentation followed by Al2O3 and SiO2. For the viscousness of nanofluids, it will increase as the nanoparticle diameter lessenings. For 6 % CuO nanofluids, it increases Nusselt figure by 1.35 times and heat transportation coefficient by 1.75 times over the base fluid at fixed Reynolds figure of 20000. Heat transfer coefficient of nanofluids additions when increasing the volume concentration of nanofluids and Reynolds figure.

2.

3.3 Experimental surveies on nanofluids

Das et Al. ( 2009 ) obtained that the thermic conduction ratio is higher for smaller size of nanoparticles as shown in Figure 2.8.Figure 2.8: Consequence of nanoparticle size on thermic conduction ratio of nanofluid for changing temperature at two different atom volumetric concentrations of ZnO nanofluid in 60:40 ethylene glycol/water. ( Das et al, 2009 )Temperature KC: UsersShahrinDesktopgraf.jpgThis behaviour intuitively right as the transportation of thermic energy depends on surface country and little atom volumetric concentration at supplying more surface country to reassign thermic energy.

Therefore, the effectivity of thermic conduction is higher for smaller atoms. To acquire a sense of order size additions, the thermic conduction ratio is 3 % higher in 305 K for 29 nm atom over that of 77 nm atom at 2 % of volumetric concentration. For the 4 % , volumetric concentration the thermic conduction ratio is 3.3 % higher for atom of 29 nanometers that of 77 nm atoms.

Nguyen et Al. ( 2007 ) was investigated the consequence of nanoparticles size on thermic conduction. Several experiments were done for the Al2O3/water nanofluid with 47 nm mean diameter. The comparative was done merely for a certain atom volume concentration of 6.

8 % . As shown in Figures 2.9 and 2.10, a comparative on consequence obtained for the waterblock coefficient of heat transportation and the convective Nusselt Numberss.

Figure 2.9: Consequence of atom size on hw-block for 6.8 % atom volume concentration. ( Nguyen et al, 2007 ) Degree centigrade: UsersShahrinDesktopjournal fyppicsgraff.jpgFigure 2.

10: Consequence of atom size on Nu for 6.8 % atom volume concentration. ( Nguyen et al, 2007 ) Degree centigrade: UsersShahrinDesktopjournal fyppicsfigure 7.jpgThe consequence has revealed that for the same nanofluids household ( the same type of components ) , a nanofluid with smaller atom size does supply a better heat transportation.

So, for the scope of mass flow rate considered in this survey and harmonizing to the inclination of the curve shown in Figure 2.9, one can clearly see that the value of heat transportation waterblock obtained with 36 nm atom size are systematically higher than 47 nm atoms. As consequence, one can merely explicate that for a given volume concentration and with finer atoms, their entire contact country are higher and the figure of atoms, will supply a better heat transportation. From the consequences of Nusselt figure as shown in Figure 2.

10, for a given Reynolds figure, the value of Nu obtained for 36 nm atom nanofluids is clearly higher than the one corresponding to nanofluid with 47 nm atoms.Namburu et Al. ( 2008 ) obtained from his experiment about the consequence of nanoparticles diameter on the Nusselt figure for SiO2 nanofluids of 6 % volume concentration and revealed that the fluid incorporating 20 nm atoms diameter have higher Nusselt Numberss. It is followed by 50 nanometers and 100 nm atoms diameter for a given same Reynolds figure.

These consequences achieved because of the viscousness values of 20 nm nanofluid are higher, followed by 50 nanometers and 100nm. With lower diameter of atoms for the same volume concentration, it provides big surface country of interaction with the fluid. Therefore, the higher the viscousness, the higher the Prandtl figure for same concentration of SiO2 nanofluids.Figure 2.11 shows the consequence of nanoparticle diameter on the Nusselt figure for a 6 % volume concentration of SiO2 nanofluids.Figure 2.11: Consequence of nanoparticles diameter on the Nusselt figure for a 6 % volume concentration of SiO2 nanofluids.

( Namburu et al, 2008 ) Degree centigrade: UsersShahrinDesktopSiO2.jpg

2.3.4 Advantages of nanofluids

Kondaraju et Al. ( 2009 ) reveals that the advantages of nanofluids are:No excess force per unit area beadMinimal cloggingIncreasing heat transportationReducing the pumping powerHigh-speed flow can be reducedLack of eroding of shrieking constituentsLubrication and chilling for the engine operation can be improvedReduce the size of the heat money changer

2.

4 Drumhead

In this portion, we may reason that shell-and-tube heat money changer have many advantages compared to other heat money changer, which is provides big ratio of heat transportation country to volume and weight, can be easy cleaned, and hardiness to hard-hitting operations. For the public presentation of nanofluids, it is fundamentally depends on several parametric quantities such as temperature, atom size and volume fraction. Nanofluids are produced by two techniques, which is one-step procedure and two-step procedure. From the experimental consequences research workers, one can reason that for CuO, Al2O3, and SiO2 nanofluids at a same concentration, CuO nanofluid give higher heat transportation public presentation compared to those two. In add-on, the effectivity of thermic conduction is higher for finer atoms use.

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