Shell and Tube Heat Exchanger with Condensing Steam

3 Shell and Tube Heat Exchanger with Condensing Steam 

The following assumptions are being made in this case  

It is assumed that the heat capacity of the wall (M c ) carmot be ignored with respect to the heat capacity of the liquid Mff). If it is ignored later on, this will then be a special case of this more general case. The energy balance for a section of the wall at every point z can be written as  

Af heat transfer area per unit length at the fluid side, m 

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A shell-and-tube heat exchanger has condensing steam at 00°C in the shell side with one shell pass. Two tube passes are used with air in the tubes entering at 10°C. The total surface area of the exchanger is 30 m2 and the overall heat-trartSftr coefficient may be taken as 150 W/m2 °C. If the effectiveness of the exchanger is 85 percent, what is the total heat-transfer rate ... 

A shell-and-tube heat exchanger with one shell pass and two tube passes is used to heat 5.0 kg/s of water from 30°C to 80°C. The water flows in the tubes. Condensing steam at 1 atm is used in the shell side. Calculate the area of the heat exchanger, if the overall heat-transfer coefficient is 900 W/m2 - °C. Suppose this same exchanger is used with entering water at 30°C, U = 900, but with a water flow rate of 1.3 kg/s. What would be the exit water temperature under these conditions ... 

A shell-and-tube heat exchanger with one shell pass and four tube passes is designed to heat 4000 kg/h of engine oil from 40°C to 80°C with the oil in the tube side. On the shell side is condensing steam at 1-atm pressure, and the overall heat-transfer coefficient is 1200 W/m2 °C. Calculate the mass flow of condensed steam if the flow of oil is reduced in half while the inlet temperature and U value are kept the same. 

After the parameters for estimating equipment sizes and the utility parameters are adjusted, and a new steam utility is defined, the simulation units (blocks, modules, or subroutines) are mapped into Aspen IPE. In this case, there is only one distillation unit, Dl, to be mapped. The default mapping results in (1) a tray tower, (2) a shell-and-tube heat exchanger with a fixed tube sheet for the condenser, (3) a horizontal drum for the reflux accumulator, (4) a centrifugal reflux pump, and (5) a kettle reboiler with U tubes. 

Most boiler plants with electrical power generating facilities employ surface condensers. These are shell-and-tube heat exchangers in either one-, two-, or four-pass configurations. Surface condensers typically receive cooling water on the tube-side and steam on the shell-side of the heat exchanger. The LP turbine steam generally is received at the top of the condenser and proceeds through the condenser in a downward flow, while the FW turbine exhaust steam enters at the side. 

A shell-and-tube heat exchanger is designed for condensing steam at 200°C in the shell with one shell pass 50 kg/s of water are heated from 60 to 90°C. The overall heat-transfer coefficient is 4500 W/m2 °C. A controller is installed on the steam inlet to vary the temperature by controlling the pressure, and the effect on the outlet water temperature is desired. Calculate the effectiveness and outlet water temperature for steam inlet temperatures of 180, 160, 140, and I20°C. Use the analytical expressions to derive a relation for the outlet water temperature as a function of steam inlet temperature. 

Two dissimilar metals in contact in an aqueous environment does not necessarily give rise to galvanic corrosion. Turner [1990] cites an example of a shell and tube heat exchanger (steam condenser), containing aluminium brass tubes expanded into carbon steel tube plates. It could be anticipated that with the relatively large area of the noble aluminium brass, severe galvanic corrosion would occur on the smaller area of exposed steel resulting in a short service life. In fact the condenser had been in service for 26 years when the examination took place ... 

Gough and Rogers [1987] report (and discussed by Bott [1990]) the use of wire matrix tubulators inside the tubes of a shell and tube heat exchanger used for heating tar oil. The tar oil passed through the tubes with steam at the appropriate pressure condensing in the shell. The data obtained from the operation of the heat exchanger showed a rapid reduction in overall heat transfer coefficient over a period of 4 months (see Table 15.3). 

Guideline 8 The manipulated variables should affect the controlled variables directly, rather than indirectly. Compliance with this guideline usually results in a control loop with favorable static and dynamic characteristics. For example, consider the problem of controlling the exit temperature of a process stream that is heated by steam in a shell and tube heat exchanger. It is preferable to throttle the steam flow to the heat exchanger rather than the condensate flow from the shell, because the steam flow rate has a more direct effect on the steam pressure and on the rate of heat transfer. 

For shdl and tube heat exchange Numerous related topics including evaporation Section 4.1, distillation. Section 4.2, crystallization Section 4.6, freeze concentration Section 4.3, melt crystallization. Section 4.4, PFTR reactors Sections 6.5-6.12. Approach temperature 5 to 8°C use 0.4 THTU/pass design so that the total pressure drop on the liquid side is about 70 kPa. Allow 4 velocity heads pressure drop for each pass in a multipass system. Put inside the tubes the more corrosive, higher pressure, dirtier, hotter and more viscous fluids. Recommended liquid velocities 1 to 1.5 m/s with maximum velocity increasing as more exotic alloys used. Use triangular pitch for all fixed tube sheet and for steam condensing on the shell side. Try U = 0.5 kW/m °C for water/liquid U = 0.3 kW/m °C for hydrocarbon/hydrocarbon U = 0.03 kW/m °C for gas/ liquid and 0.03 kW/m °C for gas/gas. 

Horizontal shell-side and vertical tube-side are the most commonly used types of condenser. A horizontal exchanger with condensation in the tubes is rarely used as a process condenser, but is the usual arrangement for heaters and vaporisers using condensing steam as the heating medium. 

M8 Repeat Prob. I0-47, assuming that condensing steam at I38°C is used instead of the hot oil and that the exchangers are of the shell-and-tube type with the water making two passes on the tube side. The overall heat-transfer coefficient may be taken as 1700 W/m2 °C for this application. 

Because of priority requirements the hot fluid flow rate for the exchanger in Probs. 10-19 and 10-20 must be reduced by 40 percent. The same water flow must be heated from 35 to 85°C. To accomplish this, a shell-and-tube steam preheater is added, with steam condensing at I50°C and an overall heat-transfer coefficient of 2000 W/m- °C. What surface area and steam flow are required for the preheater ... 

A shell and tube exchanger (one shell pass, two tube passes) condenses steam (0.14 bar). The 130 brass tubes (inner and outer diameters of 0.0134 and 0.0159 m) have a length of 2 m. Coolant (water) enters the tubes at 20°C with an average velocity of 11.25 m/sec. Condensation heat transfer coefficient is 13,500 W/m °K. What are the water outlet temperature, the condensation steam rate and the overall heat transfer coefficient ... 

The superheated steam goes to the steam turbine generator, produces electricity, and is condensed producing boiler feed water. The steam condenser is usually a shell and tube type heat exchanger supplied with cooling water. Alternatively, air-cooled steam condensers can be used. 

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