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Heat Exchanger

Transcript: By Eng. Talal Alnouman Thermal Engineering & Desalination Technology Heat Exchangers Shell-and-Tube Heat Exchanger Design. 1 Heat Exchanger Definition: Heat Exchanger is symbolized by (HX) symbol. Heat Exchanger is facilities the change of heat transfer (Q). Heat Exchanger consists of two types of a stream (s1,s2), and each stream has a temperature (T1,T2) with follwoing under condition: - the T1 of s1 NOT equal to T2 of s2 (T1<>T2). - There is NO mixing between the streams. In General, Heat Exchanger are processing equipment in which heat is contuously or semi-continuously transferrd from a hot to a cold fluid dirctly or indirectly through a heat transfer surface that separates the two fluids. Heat exchangers consist primarily of boundles of pipes, tubes or plate coils. 1 2 Types of Heat exchangers. Heat Exchangers are classified according to: - Flow arrangement. - type of construction. 2 1. The Simplest Heat Exchanger Type Simplest heat exchanger is a concentric tube (or double-pipe) construction has a hot or cold fluids move in the same or oppssite directions. Parallel flow counter flow 3 3 2. Compact Heat Exchanger Type The compact heat exchanger has a large heat transfer area and described by Beat (Bβββ) which its callrea density. The area density (βB) equal the surface area of the heat exchanger divided by the volume Beta for a typical compact heat exchanger > 700 m2/m3 Beta for a radiador ~= 1000 m2/m3 Beta for Gas sturbine ~= 6000 m2/m3 Beta for Human Lunge ~=20,000 m2/m3 4 A Rule of thumb. A rule of thumb is meaing a practical and approximate way of doing or measuring something. A good rule of thumb is that the handfull of rice fills up on or two palms. The origin of the phrase ' rule of thumb' is come from the belife that English law allowed a man to beat his wife by a stick no bigger than his thumb to discipline her . 4 5 A Rule of Thumb in Heat exchanger. A fins on the Gas side is use to increase the surface area 5 6 Terme of Compact heat exchanger the compact heat exchanger devices have dense arrays of finned tubes or plates and are typically used when at least one of the fluids is a gas, and is hence characterized by a small convection coefficient. The tube may be flat or circular, and also the fines may be plate or circular. Parallel-plate heat exchanger may be finned or corrugated and may be used in single-pass or multipass modes of operation. 6 7 cross flow heat exchanger the definition of cross-flow heat exchangers are two fluid streams has a different direction and they are perpendicular to each other by 90 degree. Type of cross flow heat exchanger. - UnMixed cross flow heat exchanger - Mixed cross flow heat exchange. 7 90 Fluid Stream 1 Fluid Stream 2 Can't move trans phase direction 8 Mixed & UnMixed cross flow heat exchanger. cross flow is perpendicular to each other and the tubular heat exchanger either finned or unfinned. the two tubular heat exchanger is treating fluid motion over the tubes as Mixed or UnMixed. the UnMixed fluid happens when the fins inhibit motion in the vertical direction ( y-axis) and main flow pass through x-direction. Resulting, the fluid temperature varies with x and y directions. the Mixed fluid happens when the bundle tube heat exchanger is UnFinned and the fluid motion passes through the main flow direction. So, the temperature variations are primarily in the main flow direction. To sum up, the mixing condition can significantly influence heat exchanger performance. 8 9 The most Important Heat Exchanger is: Shell & Tube Heat Exchanger. (it's widely used in the industrial field) Heat Exchanger (One-Shell pass & One Tube pass). 9 10 Heat Exchanger Shell & Tube with a Baffles. baffles have a mainly two function: 1. To Support & fixed the heat exchanger tubes and prevent the tube slagging or slacken. 2. Change the heat exchanger counterflow to cross-flow heat exchanger type. 10 11 11 One Shell pass & multi Tubes pass Heat Exchanger. the configuration of shell & tube heat exchanger pass One Shell pass & Two Tube pass One Shell pass & Four Tubes pass Two Shell pass & Four Tubes pass 12 12 Shell & Tube Heat Exchanger Assemble & Main Parts 13 13 Plate & Frame heatexchanger Type ىخهيييخم خقخ. The plate heat exchanger consists of a thin, rectangular, metal sheet into which a corrugated has been formed by precision-pressing. One side of each plate has a full peripheral gasket. The comprises a number of such plates, mounted in a frame. and clamped toghether, face to face, by a bolting system. The space between adjacent plates forms a flow channel and system is arranged so that the hot and cold fluid flow through alternate flow channels, parallel to the long side. 14 14 Regenerative Heat Exchanger. The idea of regeneration to increase the thermal efficiency of a thermodynamic cycle. A regenerative heat exchanger is a type of heat exchanger where heat from the hot fluid is intermittently stored in a thermal storage medium before it is transferred to the cold fluid. To 15

HEAT EXCHANGER

Transcript: corrugated plates are held in contact and the two fluids flow separately along adjacent channels in the corrugation Definition finned Tubes: Types: Heat exchangers are widely used in industry both for cooling and heating large scale industrial processes. STHE counter flow Applications one flow goes along a bunch of tubes and the other within an outer shell, parallel to the tubes, or in cross-flow parallel flow An air cooled heat exchanger is simply a pressure vessel which cools a circulating fluid within finned tubes by forcing ambient air over the exterior of the tubes. A common example of an air cooler is a car’s radiator. ACHE PHE Frame plate Mild steel, Epoxy painted Nozzles Carbon steel Metal lined: Stainless steel, Titanium Rubber lined: Nitrile, EPDM Plates Stainless steel: Alloy 304, Alloy 316 Titanium Alloy C-276 Alloy 254 SMO Thank you for your attention!!! Shell-and-tube heat exchanger (STHE) Plate heat exchanger (PHE) Open-flow heat exchanger (OFHE) Air cooler heat exchanger (ACHE) A heat exchanger is a piece of equipment built for efficient heat transfer from one medium to another. The media may be separated by a solid wall to prevent mixing or they may be in direct contact. They are widely used in space heating, refrigeration, air conditioning, power plants, chemical plants, petrochemical plants, petroleum refineries, natural gas processing, and sewage treatment. Separation of air gases Hydrocarbon processing Natural gas liquefaction Industrial gas liquefaction (oxygen, nitrogen, argon, helium, etc.). Waste water treatment Refrigeration Wine and beer making Petroleum refining cross flow Shell-and-tube heat exchanger HEAT EXCHANGER Justyna Jendro, III IChiP 2013/2014 elliptical finned Flow configuration smooth Construction

Heat Exchanger

Transcript: tube corroded and normal tube, courtesy (Corinth, 2014) Strong and stable design Composed of 4 main parts Encased tubing system creep-fatigue showing a craking mechanisms, courtesy (Holdsworth, 2015) Physical Thanks for listening There are 3 heat transfer operations that describe the movement of heat throughout a heat exchanger. 1.The convective heat transfer from the fluid to the material of the pipe walls. (q1) 2.Conduction heat transfer from a pipe wall with high temperature to an adjacent pipe wall at a lower temperature.(q2) 3.Convection from pipe walls to the coolant fluid or the stream.(q3) Heavy and space consuming Less thermally efficient Flow rates can cause damage Overview thermal effect in the tubes, image courtesy of Victaulic Company Narrow operational range Subject to fouling Material choice can be a make or break factor Pros Introduction Uses Knowledge Furthermore, Materials have to be resistant to leakages that can affect heat exchanger such as water and acids copy and paste as needed to add notes to your brainstorm standard tensile test, illustration courtesy Dr. Dmitri Kopeliovich Compact Heat Exchangers - Design ELEMENTS The most common STHEs are the single pass types as shown below. Thermal conductivity, is required for a heat exchanger as heat is transferred, thus it is vital to find the prime material. This graph shows the best materials that can resist salt water (sea water) All materials displayed are in the excellent category, and vary in price Many ceramics and metals such as silicon and copper are reasonably priced Steady state Unsteady state Classification Compact Heat Exchangers - Pros and Cons Causes of Failure Group menbers Manfredi Vargas, Brayan, J Miah, Naseem Nelson, Ashley, S Smith, Rhys, L Fane, Florida however the optimum material is copper as it is an average price and has a very high thermal conductivity Chemical plants Fertilizer Oil and gas refineries Nuclear power plants Refrigeration system Food and diary industries Marine First type of heat exchanger included a simple concentric-pipe exchangers and nowadays complex surface exchangers with huge place to be heated. Cons •Conduction is the heat transfer that occurs in a stationary medium, when there is a temperature gradient present. •The value of q dot is the heat transfer rate (J/s) therefore shows the amount of heat transferred through a particular material over time. •The value of k is thermal conductivity (W/m*K) it is a property which is considered in the material selection of heat exchangers. High durability and strength Versatile Low cost High thermal efficiency and effective heat transfer Lots of variations Removable plates Heat Transfer In Heat Exchangers Cons Conduction and Fourier's Law Tensile Graph shows materials excellent in resisting fresh water, and the price range of these metals. From those highlighted, optimum materials are displayed such as copper, titanium and other metal alloys and also several ceramics The graph produced show cost of materials and their thermal conductivity First CHE designed in 1878 German invention Originally used in wine manufacture Other variables also considered is corrosion prevention from acids, for example from sulfuric acid Many ceramics are an excellent choice for resistance to corrosion from sulfuric acid and are considerably cheaper than expensive metals Use in Industry Corrosion This is a Plate Heat Exchanger (PHE), the most common type of CHE. Creep and Fatigue Mechanical Shell and Tube Heat Exchanger - Design Compact Heat Exchangers CHEs Evolution Using tungsten alloys and nickel is better as they have high yield strength than silver. There are a range of metal alloys to choose from Shell and Tube Heat Exchanger - Pros and Cons More commonly used Conventional name for many different variations Convection is the heat transfer that occurs between a surface and a moving fluid when they are at different temperatures. Shell and Tube Heat Exchangers STHEs Smart Selection Certain characteristics taken into account: Price Yield strength (elastic limit) Thermal Conductivity BRAINSTORM What is it? It is an apparatus to transfer heat between two or more fluids or from a solid object to a fluid. Maintenance Small and compact design Overlapping corrugated plates Alternating plates for primary and secondary fluids Counter-flow system Two Types of Heat Exchanger Heat Exchanger Excessive Loading Corrosion Fouling Failing of Individual Components Loss in Steam Pressure The material with highest thermal conductivity is silver Conduction Convection Radiation Tank suction heater built for U.S Navy (1942) courtesy Graham corporation. Titanium tube stacks(2015) desined by Bowman courtesy of Spatex. Heat Transfer in Heat Exchangers Convection and Newton's law of cooling Two very different types Different applications Different advantages and disadvantages Both extremely useful in all sorts of industries Pros Types Theory Heat transfer Three ways to transmit heat Flow Type There is a

Heat Exchanger

Transcript: Polynomial fits of the same data indicate a fouling factor limit for each pressure. MathCAD Sheets for Sizing By Stephen McNary, Logan Beal, and Eric Fuller Objectives HX unit Step 2 Sizing Results Tank and Water Inlet Experimental Methods Shipment of heat exchanger to Belhalf, Yemen. Results 1. Gain experience with heat exchangers. 2. Calculate the fouling factor, and determine if fouling factor is dependent on flow rate. 3. Using fouling factor, select a heat exchanger to heat 175GPM water from 25°C to 80°C using 300psi steam. Equations and Theory Calculation Process Slide Sources: Results End Results Step 1 Linear Fits of the data at each pressure indicates that the fouling factor is dependent on flow rate. Fouling Dependance on Flow Results continued Slide 2: Heat exchanger pic from http://en.wikipedia.org/wiki/Heat_exchanger Slide 3: Picture found on 475 UO Lab website under the HX experiment manual. Slide 4: Picture found on 475 UO Lab website under the HX experiment manual. Slide 5: equations from Fundamentals of Heat and Mass Transfer book by Bergman Slide 12: small heat exchanger picture- http://www.bracton.com/equipment/draught-beer-equipment/cool-tube-heat-exchanger-compact. Big heat exchanger picture- http://www.heavyliftspecialist.com/tag/apci-heat-exchanger/ Slide 13: Specification sheet found on http://uolab.groups.et.byu.net/files/shelltube/hints/SSCF%20Design%20Data.pdf. Inputs= Water Flow Rate Steam Pressure Inlet Temperature Outlet Temperature Outlet= Fouling factor Available Heat Exchangers Apparatus Recommended Model References Flow Diagram UO Lab HX: Tube side fluid=water Shell side fluid=steam Shell and Tube Heat Exchanger Inputs= Fouling Factor Number of Tubes Diameter Length Outlet= Outlet Temperature At low pressures and/or flow rates, we are not 95% confident that the fouling factor is independent of flow rate. At high pressures (>40 psi) and/or flow rates (>50 GPM), the fouling factor does seem to be independent of flow rate. where b=circumference Process: Heat 175 gpm of water from 25°C to 80°C using 300 psig steam. Fouling Factor A "worst case" fouling factor of 3.6x10^-5 K*s^3/kg was used to find T-out Set steam pressure (10-50 psig) Set flow rate (20-50 gpm) Wait for inlet and outlet temperatures to get to steady state Record data Repeat for several flow rates Repeat above for several pressures At 40 psi, a slope of 0 is within the 95% confidence interval. The slope of the linear fit for the 25psi data is 0.00000036. At the extreme low end of the confidence interval, that becomes 0.0000007. Any Questions?

Heat exchanger

Transcript: HEAT TRANSFER GROUP 2 Photography credit : ABB engineering and consulting Problem statement Problem statement In a factory , heat exchanger is used to preheat the mixure of alcohol ( Ethanol and Methanol) in order to be used for the distilation process. From the distilation process fusel oil is produced , it is then used as the hotstream in the heat exchanger. In a 2 shell and tube the hot stream the mass flow rate of 3-Methyl-1Butanol (cp=2.586kJ/kg°C) is fed into the tube side of 1kg/s at 100°C. The mixture of alcohol flows (cp=3.237kJ/kg°C) through the shell of 2kg/s (mole fraction of methanol is 0.45 and ethanol is 0.55) at room temperature (30°C). Determine the exit temperature of the cold and hot stream. Given : U=159.8 w/m^2*K A= 3.5m^2 1 TEMA type : BFM Material : SS304 Shell pass: 2 Tube pass: 4 Shell ID/OD: 175 mm / 180.54mm Tube OD : 19.05mm Length : 2.5m Pitch :25.4mm Number if baffle : 30 Type of baffle : single segmental Heat exchanger specification Heat exchanger specification 2 Design Aspen Exchanger design 3 Console Geometry The optimum ratio of baffle spacing to shell size diameter is normally between 0.3 to 0.6 4 Process data & Geometry Fouling resistance is less than 0.001 which means that the prefered tube size for light tube side fouling service is 0.75 inch O.D. 5 Exchanger Geometry Baffle cuts between 20% and 35% be employed. Horizontal baffle cut is recommended for single phase fluid on the shell side for minimizes accumulation of the deposit at the buttom of the shell and also prevent stratification. 6 Tube layout 7 Analyzing the Graph Analyzing the Graph T exit of fusel oil 67.62°C T exit of alcohols 46.56°C For liquid-liquid HEX : temperature difference 11-24°C obtained : 21.06°C } ΔT 8 Warnings Warnings 9 HTRI PROGRAM HTRI PROGRAM 10 3D Picture 3D Picture 11 HEAT EXCHANGER Veeranuch Sirisook 5810755370 Suphasin Perunavin 5810751775 Chanyanuch lertjaruwong 5810751544 Chanyanuch Chanunan 5710753038 Suphawit keakultanes 5810750843 Jiroj Sariddipanthawat 5810750082 Hand Calculation T h,out =? Tc,out =? Cold stream (inlet) : Ethanol+Methanol mC = 1.5 kg/s Tc,in = 30°C P= 2 bar Hot stream (inlet) : 3-Methyl-1-Butanol mh=1 kg/s Th,in= 100°C P= 2 bar Mole fraction of substances : Ethanol : 0.55 Methanol: 0.45 Fusel oil (3-Methyl-1Butanol) : 1 12 parameters The NTU method is used to determine the outlet temperature of both streams . NOTE : we know all the inlet parameters (Area , U , Ltube and Dtube) Given parameters: Tube OD : 19.05mm Length : 2.5m Surface area (A) = 3.5 m2 U = 519.8 W/m2.C 13 Calculations Method 1. Obtain HEX data (known : surface area , U ,Length , Diameters etc.) 2.Properties of fluids : to obtain specific heat capacities 3. Find maximum heat transfer possible : Qmax=CminΔTmax 4.Determine Heat transfer effectiveness "ε" ε (C,NTU) - can use graph or formula - C= Cmin/Cmax - NTU equation 5. Calculate Q actual = εQmaxห 6. Obtain the outlet temperatures 14 Assumption 1.Steady state 2. neglect ΔKE and ΔPE of the fluids 3. Fluid properties are constant 4.Heat loss to surrounding is neligible as the heat exchanger is new and well insulated. 15 Property table Ethanol Methanol FROM : Mole fraction of the mixture : Methanol = 0.45 ; Ethanol = 0.55 Cp,mixture=(mole fraction methanol)( Cp,methanol) + (mole fraction ethanol)(Cp,ethanol) = (0.45)(3.499 kg/J.K) + (0.55)(3.086 kg/J.K) = 3.271 kg/J.K 16 Property table Now we have : Cp,mixture : 3.271 kg/J.K Cp,fusel oil : 2.586 kg/J.K 17 Finding minimum heat capacity (Cmin) Given : ṁc =1.5 kg/s ṁh = 1 kg/s from the equation --> [C,rate = mass flowrate * liquid specific heat] Cc =mc Cp,cold=1.5x3.271= 4.9078 kg/J.K Ch=ṁh Cp,hot =1x2.586 = 2.586 kg/J.K The one with the least value is Cmin and higher one is Cmax Calculations Cmax Cmin 18 Find ∆Tmax : From the equation ---> ∆Tmax= Th,in-Tc,in ∆Tmax= Th,in-Tc,in= 100 – 30 = 70 °C Plugging ∆Tmax and Cmin in to this equation ----> Qmax=CminΔTmax Qmax=CminΔTmax=(2.586kg/J.K )( 70C)=181 kW Find Heat transfer effectiveness "ε" C = Cmin/Cmax = 2.586/4.9078 = 0.526 NTU = 3.5x519.8/(2.586x〖10〗^3 ) = 0.704 From graph ε=0.45 19 Find actual Q : Q ̇= εQmax⁡〖=0.45x181=81.45 kW〗 This Q is used to obtain the outlet temperatures For cold side Q ̇=Cc*∆Tc 81.45kW =(4.9078 kg/J.K )(Tc,out-30) Tc,out=46.596° C For hot side Q ̇=Ch *∆Th 81.45 =(2.586 kg/J.K )(〖100-T〗h,out ) Th,out=68.5 °C 20 EXTRA : CORRECTION FACTORS ***chose the graph that is suitable for the type of HEX you're using*** P=(t2-t1)/(T1-t1)= (68.5-100)/(30-100)= 0.45 R =(T1-T2)/(t2-t1)= (30-48.6)/(30-1068.5-100)=0.60 From graph correction factor is 0.99 which is good as log mean temperature correction factor should be greater than 0.75 to avoid temperature approach problems. 21 Result summary Result summary Comparision between Aspen EDR and hand calculation 22 TEMA SHEET 23 Comparison chart Comparison chart 24

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