1、CHAPTER 10,College of Nuclear Science and Technology,1,Heat-transfer process analysis and heat calculation of heat exchanger,CHAPTER 10,College of Nuclear Science and Technology,2,10-1 Introduction,The application of the principles of heat transfer to the design of equipment to accomplish a certain
2、engineering objective is extremely important.,Product development for economic gain: Performance Weight Size Cost Service/maintenance,CHAPTER 10,College of Nuclear Science and Technology,3,10-2 Analysis and calculation of heat transfer process,Diabatic process: heat flow from one side of fluid to th
3、e other side of fluid through the wall,Heat-transfer equation:,K- the overall heat-transfer coefficient,K is different for different heat-transfer process.,CHAPTER 10,College of Nuclear Science and Technology,4,Heat transfer through the flat wall,CHAPTER 10,College of Nuclear Science and Technology,
4、5,Heat transfer through cylindrical wall,Internal convection,Heat conduction of cylindrical wall,CHAPTER 10,College of Nuclear Science and Technology,6,External convection:,CHAPTER 10,College of Nuclear Science and Technology,7,CHAPTER 10,College of Nuclear Science and Technology,8,Heat transfer thr
5、ough fin,-overall fin surface officiency,CHAPTER 10,College of Nuclear Science and Technology,9,-rib change coefficient,CHAPTER 10,College of Nuclear Science and Technology,10,Heat transfer coefficient of flat wall:,Heat transfer coefficient of fin:,In engineering heat transfer calculation,in order
6、to characterize the superiority of strengthening surface relative to smooth surface,usually make surface area with no fin(or germ tube area before rolling ribbed) as the area of calculating the overall heat transfer coefficient and heat transfer rate.,CHAPTER 10,College of Nuclear Science and Techno
7、logy,11,Circular tube and rib, increase surface area(namely reduce surface heat resistance), but also increase conduction resistance.,Enhance heat transfer,Fin is made with metal. Its thermal conductivity is very big, and heat exchange area increased by fin is higher multiples.,Critical radius of in
8、sulation,CHAPTER 10,College of Nuclear Science and Technology,12,Circular tube outer laying thermal insulation layer can reduce surface convection heat resistance and increase conduction thermal resistance.,Thermal conductivity of heat insulating material is small. Increasing heat exchange area by l
9、aying insulation layer is due to simply expanding diameter. The increase is limited.,Weaken heat exchange,CHAPTER 10,College of Nuclear Science and Technology,13,Critical radius of insulation,Adding thermal Insulation layer can reduce heat loss,?,?,?,CHAPTER 10,College of Nuclear Science and Technol
10、ogy,14,Tnen,total thermal resistance through cylindrical wall:,Circular tube:internal diameter,external diameter,Thermal conductivity , after adding thermal insulation layer,external diameter ,thermal conductivity .,CHAPTER 10,College of Nuclear Science and Technology,15,CHAPTER 10,College of Nuclea
11、r Science and Technology,16,Bi of pipeline outer surface,When Bi 2, increase thickness of the thermal insulation layer can further reduce heat loss.,When Bi 2, increase thickness of the thermal insulation layer can strengthen heat transfer.,CHAPTER 10,College of Nuclear Science and Technology,17,10-
12、3 Heat exchanger,definition,classification,One kind of equipment used to make heat transfer from hot fluid to cold fluid in order to meet the specified technological requirements,Operation process,Surface compact degree,CHAPTER 10,College of Nuclear Science and Technology,18,Main types of recuperato
13、rs,1.double-pipe heat exchanger,CHAPTER 10,College of Nuclear Science and Technology,19,2.Shell and tube heat exchanger,CHAPTER 10,College of Nuclear Science and Technology,20,CHAPTER 10,College of Nuclear Science and Technology,21,3.Cross flow heat exchanger,(c)fin type,CHAPTER 10,College of Nuclea
14、r Science and Technology,22,4.Plate heat exchanger,CHAPTER 10,College of Nuclear Science and Technology,23,5.Spiral plate heat exchanger,CHAPTER 10,College of Nuclear Science and Technology,24,10-4 Mean temperature difference analysis,Heat-transfer equation:,Countercurrent,Fair current,CHAPTER 10,Co
15、llege of Nuclear Science and Technology,25,CHAPTER 10,College of Nuclear Science and Technology,26,Temperature difference:,Infinitesimal heat exchange amount:,Heat release of hot fluid:,Heat absorption capacity of cold fluid:,CHAPTER 10,College of Nuclear Science and Technology,27,CHAPTER 10,College
16、 of Nuclear Science and Technology,28,CHAPTER 10,College of Nuclear Science and Technology,29,Countercurrent:,CHAPTER 10,College of Nuclear Science and Technology,30,If then arithmetic mean tem- perature difference:,Arithmetic mean difference is equivalent to that the fluid temperature changes in a
17、linear relationship along the heat exchange surface. Arithmetic mean temperature difference is always greater than logarithmic mean temperature difference.,CHAPTER 10,College of Nuclear Science and Technology,31,Notes: 1. is decided by dimensionless constant P and R,2. P shows the ratio of the actua
18、l temperature rise and the available maximum temperature rise of fluid 2,so P1.R shows the heat capacity ratio of two fluid.,3. For shell and tube heat exchanger, need to notice flow path number.,CHAPTER 10,College of Nuclear Science and Technology,32,comparison,(1)Countercurrent and fair current ar
19、e two extreme case. In the same import and export temperature,mean temperature difference of countercurrent is maximum, while that of fair current is minimum.,(2)Fair current:,CHAPTER 10,College of Nuclear Science and Technology,33,10-5 Thermal design of heat exchanger,Design calculation:design a ne
20、w heat exchanger, confirm the heat exchange area.,Performance calculation:for heat exchanger with the existing or selected heat exchange area,in off-design conditions, performance calculate whether it is fit for the new task.,Heat-transfer equation:,Thermal balance equation:,CHAPTER 10,College of Nu
21、clear Science and Technology,34,method,Mean temperature difference method (applying heat transfer and heat balance equation for thermal calculation directly),Effectiveness-NTU method,CHAPTER 10,College of Nuclear Science and Technology,35,Effectiveness-NTU method,Effectiveness of heat exchanger : th
22、e ratio of actual heat transfer and maximum possible heat transfer.,CHAPTER 10,College of Nuclear Science and Technology,36,assuming:,then:,CHAPTER 10,College of Nuclear Science and Technology,37,CHAPTER 10,College of Nuclear Science and Technology,38,CHAPTER 10,College of Nuclear Science and Techno
23、logy,39,Countercurrent heat exchange:,Fair current,countercurrent,CHAPTER 10,College of Nuclear Science and Technology,40,CHAPTER 10,College of Nuclear Science and Technology,41,CHAPTER 10,College of Nuclear Science and Technology,42,10-6 Fouling factor,Fouling resistance:,Fouling can produce additi
24、onal thermal resistance, which reduces heat transfer coefficient and decline heat exchange performance.,CHAPTER 10,College of Nuclear Science and Technology,43,10-7 Heat transfer enhancement,Definition,Increasing the heat transfer quantity in the heat transfer process.,Enhancing heat transfer techno
25、logy,Passive technology: no additional power,Active technology: need additional power,CHAPTER 10,College of Nuclear Science and Technology,44,method,Increase heat transfer area,Increase heat transfer temperature difference,Increase heat transfer coefficient,Increase convection heat transfer coeffici
26、ent,For no phase transition convection heat transfer, measures of strengthening heat exchange are reducing the boundary layer thickness,increasing fluid disturbance,prompting fluid each part in mixed and increasing velocity gradient on solid wall.,CHAPTER 10,College of Nuclear Science and Technology
27、,45,Wilson graphical method,The total surface heat transfer coefficient of shell and tube heat exchanger:,CHAPTER 10,College of Nuclear Science and Technology,46,CHAPTER 10,College of Nuclear Science and Technology,47,10-8 Heat-exchanger design considerations,Heat exchanger design is a comprehensive
28、 subject. It must consider the initial investment, operation cost, safety and reliability factors, in order to achieve the best comprehensive technical and economic index as the goal.,Flow resistance calculation, material strength calculation, the necessary technical economic analysis and comparison.,Velocity proper,Consider fouling resistance,CHAPTER 10,College of Nuclear Science and Technology,48,Thank you!,
