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Heat Transfer and Combustion Assignment

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Added on  2020-05-28

Heat Transfer and Combustion Assignment

   Added on 2020-05-28

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HEAT TRANSFER ANDCOMBUSTION[Document subtitle][COMPANY NAME][Company address]
Heat Transfer and Combustion Assignment_1
HEAT TRANSFER AND COMBUSTIONIntroduction to Heat Exchanger and Determining Heat Transfer CoefficientExample The return condensate from a steam trapping assembly is to be used to warm boiler make upwater, utilizing a double tube counter-flow heat exchanger[CITATION raj16 \l 16393 ]. Thecondensate has an average temperature of 800C and is available at a rate of 10kg/s. The boilermakes up water has an average temperature of 250C and has a mass flow rate of 15 kg/s. Theinner tube of heat exchanger has a diameter of 40mm, the outer shell is 60 mm in diameter.Assumptions:The thermal resistance of the inner tube is negligible as the tube is highly thermallyconductive and its thickness is negligible.Both the oil flows are fully developed.The properties of the water are constant. Hot water 10 kg/s Cold water 15 kg/sGiven: Using fluid properties table(table A-9)for water, properties are obtained.1Cold waterTaverage =25oC = 997 kg/m3Pr = 6.14K =0.607 W/m-K=0.891*10-3 kg/m-sCp=4180 J/kg-KHot waterTaverage = 80oC = 971.8 kg/m3Pr = 2.22K =0.670 W/m-K=0.355*10-3 kg/m-sCp=4197 J/kg-K
Heat Transfer and Combustion Assignment_2
For Cold water, prandtl number can be calculated by- Pr=cpkPr=4180∗0.891∗10−3.607=6.1357For Hot water, prandtl number can be calculated by- Pr=cpkPr=4197∗0.355∗10−3.670=6.2238So, we can see that the Prandtl numbers for Hot and Cold Water are approximately same as givenin table A-9.In Heat Exchanger, Heat transfer is mainly due to Convection. So overall Heat transfercoefficient “U” will be -1U=1hi+1hoWhere:hi =heat transfer coefficient for inner tubeho =heat transfer coefficient for outer annulus.Calculation for hi:Diameter of tube=40 mm=0.040mSo hydraulic diameter of circular tube=0.040mMass flow rate (mo)=15 kg/sSo Mean velocity (Vm) is,2
Heat Transfer and Combustion Assignment_3
Vm=moAc=mo(14D2)Vm=15997∗14∗¿0.042=11.97m/sWhere: =DensityAc=Cross Sectional AreaReynold’s number[ CITATION Cor17 \l 16393 ] (Re)-Reynold’s number is used to determine the type of flow of fluid.It is the ratio of Inertia forces to Viscous Forces.ℜ=InertiaForceViscousForce=VmDH❑=DHVm❑ℜ=0.04∗11.978.937∗10−7=5,35,750.25For,Re< 2300–Laminar Flow2300<Re<4000 –Transition to turbulentRe>4000 –Turbulent flowHence Flow inside the tube is Turbulent.Prandtl Number (Pr)-The thermal Boundary layer is best described by the dimensionless parameter Prandtlnumber (Pr)[CITATION Mal09 \l 16393 ].3
Heat Transfer and Combustion Assignment_4

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