Tema shell and tube heat exchanger pdf
File Name: tema shell and tube heat exchanger .zip
- Shell and tube heat exchanger
- Effectively Design Shell-and-Tube Heat Exchangers (PDF)
- Effectively Design Shell-and-Tube Heat Exchangers (PDF)
The shell and tube heat exchanger STHE is the workhorse in the steam world, and it is used in many process steam applications.
There are various types of heat exchangers used in process piping. Shell and tube heat exchanger is the most widely used heat exchanger and are among the most effective means of heat exchange. Shell and tube heat exchanger is a device where two working fluids exchange heats by thermal contact using tubes housed within a cylindrical shell. The fluid temperature inside the shell and tube are different and this temperature difference is the driving force for temperature exchange.
Shell and tube heat exchanger
TEMA designations for shell- and -tube heat exchangers. A disadvantage of this design isthat since the bundle is fixed to theshell and cannot be removed, the outsidesof the tubes cannot be cleanedmechanically. Thus, its application islimited to clean services on the shellside. However, if a satisfactory chemicalcleaning program can be employed,fixed-tubesheet constructionmay be selected for fouling serviceson the shellside. In the event of a large differentialtemperature between the tubes and the shell, the tubesheets will be unableto absorb the differential stress,thereby making it necessary to incorporatean expansion joint.
This takesaway the advantage of low cost to asignificant extent. As the name implies, thetubes of a U-tube heat exchanger Figure 3 are bent in the shape of aU. There is only one tubesheet in a U-tube heat exchanger. However, thelower cost for the single tubesheet isoffset by the additional costs incurredfor the bending of the tubes and thesomewhat larger shell diameter dueto the minimum U-bend radius , makingthe cost of a U-tube heat exchangercomparable to that of a fixedtubesheetexchanger.
The advantage of a U-tube heatexchanger is that because one end isfree, the bundle can exp and or contractin response to stress differentials. In addition, the outsides of thetubes can be cleaned, as the tube bundlecan be removed. The disadvantage of the U-tubeconstruction is that the insides of thetubes cannot be cleaned effectively,since the U-bends would require flexible-enddrill shafts for cleaning.
Thus, U-tube heat exchangers shouldnot be used for services with a dirtyfluid inside tubes. Floating head. The floating-headheat exchanger is the most versatiletype of STHE, and also the costliest.
Fixed-tubesheet heat exchanger. U-tube heat exchanger. Thispermits free expansion of the tubebundle, as well as cleaning of boththe insides and outsides of the tubes.
Thus, floating-head SHTEs can beused for services where both theshellside and the tubeside fluids aredirty — making this the st and ard constructiontype used in dirty services,such as in petroleum refineries. There are various types of floating-headconstruction. The floating-head cover is securedagainst the floating tubesheet by boltingit to an ingenious split backingring.
This floating-head closure is locatedbeyond the end of the shell and contained by a shell cover of a largerdiameter. To dismantle the heat exchanger,the shell cover is removedfirst, then the split backing ring, and then the floating-head cover, afterwhich the tube bundle can be removedfrom the stationary end.
In the TEMA T construction Figure5 , the entire tube bundle, includingthe floating-head assembly, canbe removed from the stationary end,since the shell diameter is larger thanthe floating-head flange.
The floatingheadcover is bolted directly to thefloating tubesheet so that a split backingring is not required. The advantage of this constructionis that the tube bundle may be removedfrom the shell without removingeither the shell or the floatingheadcover, thus reducing maintenancetime.
This design is particularlysuited to kettle reboilers having adirty heating medium where U-tubescannot be employed. Due to the enlargedshell, this construction has thehighest cost of all exchanger types. Classificationbased on serviceBasically, a service may be singlephase such as the cooling or heatingof a liquid or gas or two-phase suchas condensing or vaporizing.
Sincethere are two sides to an STHE, thiscan lead to several combinations ofservices. The following nomenclature isusually used: Heat exchanger: both sides singlephase and process streams that is,not a utility. Cooler: one stream a process fluid and the other cooling water or air. Heat er: one stream a process fluid and the other a hot utility, such assteam or hot oil. Condenser: one stream a condensingvapor and the other cooling wateror air.
Chiller: one stream a processfluid being condensed at sub-atmospherictemperatures and the other aboiling refrigerant or process stream. Reboiler: one stream a bottomsstream from a distillation column and the other a hot utility steam or hotoil or a process stream. This article will focus specificallyon single-phase applications. Design dataBefore discussing actual thermaldesign, let us look at the data thatmust be furnished by the process licensorbefore design can begin This is required for gases,especially if the gas density is notfurnished; it is not really necessaryfor liquids, as their properties do notvary with pressure.
This is a very importantparameter for heat exchanger design. Generally, for liquids, a value of0. A higher pressure drop is usually warrantedfor viscous liquids, especiallyin the tubeside.
For gases, the allowedvalue is generally 0. If this is not furnished, thedesigner should adopt values specifiedin the TEMA st and ards or basedon past experience.
These include viscosity,thermal conductivity, density, and specific heat, preferably at both inlet and outlet temperatures. Viscositydata must be supplied at inlet and outlet temperatures, especially forliquids, since the variation with temperaturemay be considerable and isirregular neither linear nor log-log. The duty specifiedshould be consistent for both theshellside and the tubeside.
If notfurnished, the designer can choosethis based upon the characteristics ofthe various types of construction describedearlier. In fact, the designer isnormally in a better position than theprocess engineer to do this. It is desirable tomatch nozzle sizes with line sizes toavoid exp and ers or reducers.
However,sizing criteria for nozzles are usuallymore stringent than for lines, especiallyfor the shellside inlet. Consequently,nozzle sizes must sometimesbe one size or even more in exceptionalcircumstances larger than thecorresponding line sizes, especiallyfor small lines. Tube sizeis designated as O. Some plant owners have apreferred O. Many plant owners prefer to st and ardizeall three dimensions, againbased upon inventory considerations.
Thisis based upon tube-bundle removal requirements and is limited by crane capacities. Such limitations apply only toexchangers with removable tube bundles,namely U-tube and floating-head. Thus, floating-headheat exchangers are often limited to ashell I. Ifthe tubes and shell are made of identicalmaterials, all components shouldbe of this material. Thus, only theshell and tube materials of constructionneed to be specified.
However, ifthe shell and tubes are of differentmetallurgy, the materials of all principalcomponents should be specifiedto avoid any ambiguity. The principalcomponents are shell and shellcover , tubes, channel and channelcover , tubesheets, and baffles.
Tube sheets may be lined or clad. Theseinclude cycling, upset conditions, alternativeoperating scenarios, and whether operation is continuous orintermittent. Heat -transfercoefficient and pressure drop bothvary with tubeside velocity, the lattermore strongly so. A good design willmake the best use of the allowablepressure drop, as this will yield thehighest heat-transfer coefficient. If all the tubeside fluid were toflow through all the tubes one tubepass , it would lead to a certain velocity.
Usually, this velocity is unacceptablylow and therefore has to be increased. By incorporating pass partitionplates with appropriate gasketing in the channels, the tubeside fluidis made to flow several times througha fraction of the total number of tubes. Thus, in a heat exchanger with tubes and two passes, the fluid flowsthrough tubes at a time, and thevelocity will be twice what it wouldbe if there were only one pass.
Thenumber of tube passes is usually one,two, four, six, eight, and so on. Viscosity influences the heat-transfercoefficient in two opposing ways— as a parameter of the Reynoldsnumber, and as a parameter of Pr and tlnumber. Thus, from Eq. Similarly,the heat-transfer coefficient isdirectly proportional to thermal conductivityto the 0. These two facts lead to some interestinggeneralities about heat transfer. A high thermal conductivity promotesa high heat-transfer coefficient.
Hydrogen is an unusual gas, becauseit has an exceptionally highthermal conductivity greater thanthat of hydrocarbon liquids. Thus,its heat-transfer coefficient is towardthe upper limit of the rangefor hydrocarbon liquids.
The range of heat-transfer coefficientsfor hydrocarbon liquids isTie Rods and SpacersFloating Tube sheet Shell Cover Heat -transfer coefficientThe tubeside heat-transfer coefficientis a function of the Reynoldsnumber, the Pr and tl number, and the tube diameter. These can be brokendown into the following fundamentalparameters: physicalproperties namely viscosity, thermalconductivity, and specific heat ;tube diameter; and , very importantly,mass velocity.
The variation in liquid viscosity isquite considerable; so, this physicalproperty has the most dramatic effecton heat-transfer coefficient. The large variation in the heat-transfercoefficients of hydrocarbon gases isattributable to the large variation inoperating pressure.
As operating pressurerises, gas density increases. Pressuredrop is directly proportional tothe square of mass velocity and inverselyproportional to density. Therefore,for the same pressure drop, ahigher mass velocity can be maintainedwhen the density is higher.
Thislarger mass velocity translates into ahigher heat-transfer coefficient. Pressure dropMass velocity strongly influencesthe heat-transfer coefficient. For turbulentflow, the tubeside heat-transfercoefficient varies to the 0. Thus, with increasingmass velocity, pressure drop increasesmore rapidly than does theheat-transfer coefficient.
Consequently,there will be an optimum mass velocityabove which it will be wastefulto increase mass velocity further. Furthermore, very high velocitieslead to erosion. However, the pressuredrop limitation usually becomescontrolling long before erosive velocitiesare attained. The minimum recommendedliquid velocity insidetubes is 1.
Pressure drop is proportional tothe square of velocity and the totallength of travel. Thus, when the numberof tube passes is increased for agiven number of tubes and a giventubeside flow rate, the pressure droprises to the cube of this increase. Inactual practice, the rise is somewhatless because of lower friction factorsat higher Reynolds numbers, so theexponent should be approximately2.
Tube side pressure drop rises steeplywith an increase in the number of tubepasses. Consequently, it often happensTable 1. Heat exchanger service for Example 1.
Effectively Design Shell-and-Tube Heat Exchangers (PDF)
Shell and Tube Heat Exchangers are one of the most popular types of exchanger due to the flexibility the designer has to allow for a wide range of pressures and temperatures. There are two main categories of Shell and Tube exchanger :. Regardless of the type of industry the exchanger is to be used in there are a number of common features see Condensers. A shell and tube exchanger consists of a number of tubes mounted inside a cylindrical shell. Two fluids can exchange heat, one fluid flows over the outside of the tubes while the second fluid flows through the tubes. Front Header—this is where the fluid enters the tubeside of the exchanger. It is sometimes referred to as the Stationary Header.
Effectively Design Shell-and-Tube Heat Exchangers (PDF)
A shell and tube heat exchanger is a class of heat exchanger designs. As its name implies, this type of heat exchanger consists of a shell a large pressure vessel with a bundle of tubes inside it. One fluid runs through the tubes, and another fluid flows 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 of several types of tubes: plain, longitudinally finned, etc. Two fluids, of different starting temperatures, flow through the heat exchanger.
TEMA designations for shell- and -tube heat exchangers. A disadvantage of this design isthat since the bundle is fixed to theshell and cannot be removed, the outsidesof the tubes cannot be cleanedmechanically.