Presentation on theme: "HEAT TRANSFER, HEAT EXCHANGERS, CONDENSORS AND REBOILERS, AIR COOLERS"— Presentation transcript:
1HEAT TRANSFER, HEAT EXCHANGERS, CONDENSORS AND REBOILERS, AIR COOLERS Reyad Awwad ShawabkehAssociate Professor of Chemical EngineeringKing Fahd University of Petroleum & MineralsDhahran, 31261Kingdom of Saudi Arabia
2Contents HEAT TRANSFER LAW APPLIED TO HEAT EXCHANGERS 2 Heat Transfer by Conduction 3The Heat Conduction Equation 9Heat Transfer by Convection 12Forced Convection 12Natural Convection 14Heat Transfer by Radiation 15Overall heat transfer coefficient 18Problems 22DESIGN STANDARDS FOR TUBULAR HEAT EXCHANGERS 23Size numbering and naming 23Sizing and dimension 27Tube-side design 32Shell-side design 33Baffle type and spacing 33General design consideration 35THERMAL AND HYDRAULIC HEAT EXCHANGER DESIGN 37Design of Single phase heat exchanger 37Kern’s Method 45Bell’s method 49Pressure drop inside the shell and tube heat exchanger 57Design of Condensers 65Design of Reboiler and Vaporizers 72Design of Air Coolers9 85MECHANICAL DESIGN FOR HEAT EXCHANGERS10 88Design Loadings 88Tube-Sheet Design as Per TEMA Standards 90Design of Cylindrical shell, end closures and forced head 91References 95
8ExampleCalculate the heat flux within a copper rod that heated in one of its ends to a temperature of 100 oC while the other end is kept at 25 oC. The rode length is 10 m and diameter is 1 cm.
9ExampleAn industrial freezer is designed to operate with an internal air temperature of -20 oC when external air temperature is 25 oC. The walls of the freezer are composite construction, comprising of an inner layer of plastic with thickness of 3 mm and has a thermal conductivity of 1 W/m.K. The outer layer of the freezer is stainless steel with 1 mm thickness and has a thermal conductivity of 16 W/m.K. An insulation layer is placed between the inner and outer layer with a thermal conductivity of 15 W/m.K. what will be the thickness of this insulation material that allows a heat transfer of 15 W/m2 to pass through the three layers, assuming the area normal to heat flow is 1 m2?
10The Heat Conduction Equation Rate of heat conduction into control volumeRate of heat generation inside control volumeRate of heat conduction out of control volumeRate of energy storage inside control volume=++
17Heat Transfer by Radiation q = ε σ (Th4 - Tc4) AcTh = hot body absolute temperature (K)Tc = cold surroundings absolute temperature (K)Ac = area of the object (m2)σ = (W/m2K4)The Stefan-Boltzmann Constant
18Emissivity coefficient for several selected material Surface MaterialEmissivity Coefficient - ε -Aluminum Commercial sheet0.09Aluminum Foil0.04Aluminum Commercial SheetBrass Dull Plate0.22Brass Rolled Plate Natural Surface0.06Cadmium0.02Carbon, not oxidized0.81Carbon filament0.77Concrete, rough0.94Granite0.45Iron polishedPorcelain glazed0.93Quartz glassWaterZink Tarnished0.25
19Overall heat transfer coefficient For a wallFor cylindrical geometry
20Typical value for overall heat transfer coefficient Shell and TubeHeat ExchangersHot FluidCold FluidU [W/m2C]WaterOrganic solvents Organic Solvents Light oilsHeavy oilsReduced crudeFlashed crudeRegenerated DEAFoul DEAGases (p = atm)5 - 35Gases (p = 200 bar)CoolersOrganic solventsBrineGases
21Heat ExchangersHot FluidCold FluidU [W/m2C]HeatersSteamWaterOrganic solventsLight oilsHeavy oilsGasesHeat Transfer (hot) OilFlue gasesHydrocarbon vaporsCondensersAqueous vaporsOrganic vaporsRefinery hydrocarbonsVapors with some non condensableVacuum condensersVaporizersAqueous solutionsLight organicsHeavy organicsHeat Transfer (hot) oil
22DESIGN STANDARDS FOR TUBULAR HEAT EXCHANGERS Size of heat exchanger is represented by the shell inside diameter or bundle diameter and the tube lengthType and naming of the heat exchanger is designed by three letters single pass shellThe first one describes the stationary head typeThe second one refers to the shell typeThe third letter shows the rear head typeTYPE AES refers to Split-ring floating head exchanger with removable channel and cover.
30Arrangement of tubes inside the heat exchanger Tube-side designArrangement of tubes inside the heat exchanger
31Shell-side design types of shell passes one-pass shell for E-type, split flow of G-type,divided flow of J-type,two-pass shell with longitudinal baffle of F-typedouble split flow of H-type.types of shell passes
32Shell-side designShell thickness for different diameters and material of constructions
50Shell and Tube design procedure Kern’s MethodThis method was based on experimental work on commercial exchangers with standard tolerances and will give a reasonably satisfactory prediction of the heat-transfer coefficient for standard designs.Bell’s methodThis method is designed to predict the local heat transfer coefficient and pressure drop by incorporating the effect of leak and by-passing inside the shell and also can be used to investigate the effect of constructional tolerance and the use of seal strip
64Design of Reboiler and Vaporizers Suitable to carry viscous and heavy fluids.Pumping cost is highForced-circulation reboilerThe most economical type where there is no need for pumping of the fluidIt is not suitable for viscous fluid or high vacuum operationNeed to have a hydrostatic head of the fluidThermosyphon reboilerIt has the lower heat transfer coefficient than the other types for not having liquid circulationUsed for fouling materials and vacuum operation with a rate of vaporization up to 80% of the feedKettle reboiler
65Boiling heat transfer and pool boiling Nucleate pool boilingCritical heat fluxFilm boiling
73Mechanical Design for HE A typical sequence of mechanical design procedures is summarized by the flowing stepsIdentify applied loadings.Determine applicable codes and standards.Select materials of construction (except for tube material, which is selected during the thermal design stage).Compute pressure part thickness and reinforcements.Select appropriate welding details.Establish that no thermohydraulic conditions are violated.Design nonpressure parts.Design supports.Select appropriate inspection procedure