换热器外文翻译 2.docx

1、换热器外文翻译 2Heat ExchangersKey Terms Bafflesevenly spaced partitions in a shell and tube heat exchanger that support the tubes, prevent vibration, control fluid velocity and direction, increase turbulent flow, and reduce hot spots.Channel heada device mounted on the inlet side of a shell-and-tube heat

2、exchanger that is used to channel tube-side flow in a multipass heat exchanger.Condensera shell-and-tube heat exchanger used to cool and condense hot vapors.Conductionthe means of heat transfer through a solid, nonporous material resulting from molecular vibration. Conduction can also occur between

3、closely packed molecules.Convectionthe means of heat transfer in fluids resulting from currents.Counterflowrefers to the movement of two flow streams in opposite directions; also called countercurrent flow.Crossflowrefers to the movement of two flow streams perpendicular to each other.Differential p

4、ressurethe difference between inlet and outlet pressures; represented as P, or delta p.Differential temperaturethe difference between inlet and outlet temperature; represented as T, or delta t.Fixed heada term applied to a shell-and-tube heat exchanger that has the tube sheet firmly attached to the

5、shell.Floating heada term applied to a tube sheet on a heat exchanger that is not firmly attached to the shell on the return head and is designed to expand (float) inside the shell as temperature rises.Foulingbuildup on the internal surfaces of devices such as cooling towers and heat exchangers, res

6、ulting in reduced heat transfer and plugging.Kettle reboilera shell-and-tube heat exchanger with a vapor disengaging cavity, used to supply heat for separation of lighter and heavier components in a distillation system and to maintain heat balance.Laminar flowstreamline flow that is more or less unb

7、roken; layers of liquid flowing in a parallel path.Multipass heat exchangera type of shell-and-tube heat exchanger that channels the tubeside flow across the tube bundle (heating source) more than once.Parallel flowrefers to the movement of two flow streams in the same direction; for example, tube-s

8、ide flow and shell-side flow in a heat exchanger; also called concurrent.Radiant heat transferconveyance of heat by electromagnetic waves from a source to receivers.Reboilera heat exchanger used to add heat to a liquid that was once boiling until the liquid boils again.Sensible heatheat that can be

9、measured or sensed by a change in temperature.Shell-and-tube heat exchangera heat exchanger that has a cylindrical shell surrounding a tube bundle.Shell siderefers to flow around the outside of the tubes of a shell-and-tube heat exchanger. See also Tube side.Thermosyphon reboilera type of heat excha

10、nger that generates natural circulation as a static liquid is heated to its boiling point.Tube sheeta flat plate to which the ends of the tubes in a heat exchanger are fixed by rolling, welding, or both.Tube siderefers to flow through the tubes of a shell-and-tube heat exchanger; see Shell side.Turb

11、ulent flowrandom movement or mixing in swirls and eddies of a fluid.Types of Heat Exchangers换热器的类型Heat transfer is an important function of many industrial processes. Heat exchangers are widely used to transfer heat from one process to another. A heat exchanger allows a hot fluid to transfer heat en

12、ergy to a cooler fluid through conduction and convection. A heat exchanger provides heating or cooling to a process. A wide array of heat exchangers has been designed and manufactured for use in the chemical processing industry.In pipe coil exchangers, pipe coils are submerged in water or sprayed wi

13、th water to transfer heat. This type of operation has a low heat transfer coefficient and requires a lot of space. It is best suited for condensing vapors with low heat loads.The double-pipe heat exchanger incorporates a tube-within-a-tube design. It can be found with plain or externally finned tube

14、s. Double-pipe heat exchangers are typically used in series-flow operations in high-pressure applications up to 500 psig shell side and 5,000 psig tube side.A shell-and-tube heat exchanger has a cylindrical shell that surrounds a tube bundle. Fluid flow through the exchanger is referred to as tubesi

15、de flow or shell-side flow. A series of baffles support the tubes, direct fluid flow, increase velocity, decrease tube vibration, protect tubing, and create pressure drops.Shell-and-tube heat exchangers can be classified as fixed head, single pass; fixed head, multipass; floating head, multipass; or

16、 U-tube.On a fixed head heat exchanger (Figure 7.1), tube sheets are attached to the shell. Fixed head heat exchangers are designed to handle temperature differentials up to 200F (93.33C). Thermal expansion prevents a fixed head heat exchanger from exceeding this differential temperature. It is best

17、 suited for condenser or heater operations.Floating head heat exchangers are designed for high temperature differentia is above 200F (93.33C).During operation, one tube sheet is fixed and the other “floats” inside the shell.The floating end is not attached to the shell and is free to expand.Figure 7

18、.1 Fixed Head Heat ExchangerReboilers are heat exchangers that are used to add heat to a liquid that was once boiling until the liquid boils again. Types commonly used in industry are kettle reboilers and thermosyphon reboilers.Plate-and-frame heat exchangers are composed of thin, alternating metal

19、plates that are designed for hot and cold service. Each plate has an outer gasket that seals each compartment. Plate-and-frame heat exchangers have a cold and hot fluid inlet and outlet. Cold and hot fluid headers are formed inside the plate pack, allowing access from every other plate on the hot an

20、d cold sides. This device is best suited for viscous or corrosive fluid slurries. It provides excellent high heat transfer. Plate-and-frame heat exchangers are compact and easy to clean. Operating limits of 350 to 500F (176.66C to 260C) are designed to protect the internal gasket. Because of the des

21、ign specification, plate-and-frame heat exchangers are not suited for boiling and condensing. Most industrial processes use this design in liquid-liquid service.Air-cooled heat exchangers do not require the use of a shell in operation. Process tubes are connected to an inlet and a return header box.

22、 The tubes can be finned or plain. A fan is used to push or pull outside air over the exposed tubes. Air-cooled heat exchangers are primarily used in condensing operations where a high level of heat transfer is required.Spiral heat exchangers are characterized by a compact concentric design that gen

23、erates high fluid turbulence in the process medium. As do other exchangers, the spiral heat exchanger has cold-medium inlet and outlet and a hot-medium inlet and outlet. Internal surface area provides the conductive transfer element. Spiral heat exchangers have two internal chambers.The Tubular Exch

24、anger Manufacturers Association (TEMA) classifies heat exchangers by a variety of design specifications including American Society of Mechanical Engineers (ASME) construction code, tolerances, and mechanical design: Class B, Designed for general-purpose operation (economy and compact design) Class C

25、. Designed for moderate service and general-purpose operation (economy and compact design) Class R. Designed for severe conditions (safety and durability)Heat Transfer and Fluid FlowThe methods of heat transfer are conduction, convection, and radiant heat transfer (Figure 7.2). In the petrochemical,

26、 refinery, and laboratory environments, these methods need to be understood well. A combination of conduction and convection heat transfer processes can be found in all heat exchangers. The best conditions for heat transfer are large temperature differences between the products being heated and cool

27、ed (the higher the temperature difference, the greater the heat transfer), high heating or coolant flow rates, and a large cross-sectional area of the exchanger.ConductionHeat energy is transferred through solid objects such as tubes, heads, baffles, plates, fins, and shell, by conduction. This proc

28、ess occurs when the molecules that make up the solid matrix begin to absorb heat energy from a hotter source. Since the molecules are in a fixed matrix and cannot move, they begin to vibrate and, in so doing, transfer the energy from the hot side to the cooler side.ConvectionConvection occurs in flu

29、ids when warmer molecules move toward cooler molecules. The movement of the molecules sets up currents in the fluid that redistribute heat energy. This process will continue until the energy is distributed equally. In a heat exchanger, this process occurs in the moving fluid media as they pass by ea

30、ch other in the exchanger. Baffle arrangements and flow direction will determine how this convective process will occur in the various sections of the exchanger.Radiant Heat TransferThe best example of radiant heat is the suns warming of the earth. The suns heat is conveyed by electromagnetic waves.

31、 Radiant heat transfer is a line-of-sight process, so the position of the source and that of the receiver are important. Radiant heat transfer is not used in a heat exchanger.Laminar and Turbulent FlowTwo major classifications of fluid flow are laminar and turbulent (Figure 7.3). Laminaror streamlin

32、eflow moves through a system in thin cylindrical layers of liquid flowing in parallel fashion. This type of flow will have little if any turbulence (swirling or eddying) in it. Laminar flow usually exists atlow flow rates. As flow rates increase, the laminar flow pattern changes into a turbulent flow pattern. Turbulent flow is the random movement or mixing of fluids. Once the turbulent flow is initiated, molecular activity speeds up until the fluid is uniformly turbulent.Turbulent flow allows molecules of fluid to mix and absorb heat more readily