Heat Exchangers

Heat exchangers are widely used in shipbuilding, metallurgy, food, machinery, petrochemicals, living area heating, air conditioning, pharmaceuticals, leather, dairy, beverage, wine, waste water, refrigeration and other industries in the heat, concentration, poverty fungus, condensation, evaporation and other processes. The most common examples of heat exchangers in our daily life is automotive radiators, condensers, evaporators, heating radiator and oil cooler.

 Technical Features of Shell-and-Tube Heat Exchanger:

Shell-and-Tube heat exchanger is classified as different structure : stationary tube sheet type、U-pipe type、packing box type and floating head type

 ①Stationary Tube Sheet Heat Exchanger

The common heat exchanger is that both ends are fastened on the fixed tube sheet placed on the ends of shell. It’s named stationary tube sheet heat exchanger because that tube sheet and shell are fixed together. Compared with the latter products, It has simple structure, light weight, more tube sheets available in the same condition of shell side number, however, the shell side can’t be examined ,repaired and cleaned, so it’s easy to pass the clean fluid without scale formation. It produces different thermal expansion as the temperature difference between tube bundle and shell body become too large. It’s easy to make connector between tube and tube sheet fall off and it appears fluid leakage. To avoid future trouble, the expansion joint should be installed on the outer shell while the temperature range between shell body and the wall of heat-transfer pipe is more than 50℃, see Fig.1 . But heat-transfer pipe can just reduce the thermal stress caused by temperature difference, instead of removing completely, also, this method can not take into account the pipes’ relative motion among the multi-sides heat exchangers.

② U-tube Heat Exchanger

 The pipe bundles of U-type pipe heat exchange is consisted of U-type elbow pipe. The ends of pipe are fixed on the same pipe sheet. Its bend end is not fixed it. In this way, each pipe can telescope freely and is not influenced by other pipes and shell body. The whole pipe bundles can be withdrawn while the heat exchanger need to be cleaned. However, it is more difficult to clean the fouling of the wall of pipe because the elbow pipe need certain bend radius, so that it need different curvature mould elbow pipe while making and it reduces the effective usage ratio of tube sheet. Besides, the damaged pipe is difficult to exchange. The center space of U-tube bundles has adverse effect for heat exchanger. The heat exchanger’s application is limited greatly because of these disadvantages.

③Packing Box Heat Exchanger

 One end tube sheet of heat exchanger is fixed and the other end tube sheet can be slid in the packing box. Please see Fig.3 & Fig.4, that is structure chart.  Actually, it is the floating head type heat exchanger which floating head is on the outer of shell body, also named outer floating head type heat exchanger. Because the place of packing seal is easy to leak, it is not suitable for the heat exchanger which is easy to volatilize, fire, explode and has poison and high pressure liquid. Complex manufacture and inconvenient installation decide that this kind of structure is not adopted frequently.

④Packing Box Heat Exchanger

 Please see Fig.5, that is floating head type heat exchanger. Only one end of channel is connected with shell by flange, called stationary end. The other end of tube sheet is not connected with shell but slid relative to shell, called floating head end. Therefore, thermal explosion of pipe bundle is not restrained by shell in this kind of heat exchanger. Thermal effect doesn’t appear because of differential expansion between shell and tube bundles.

Advantages: The tube bundle can be withdrawn in order to clean pipe and shell pass conveniently. Temperature difference among the medium can’t be limited. It can work under high temperature and high pressure. Generally, temperature and pressure are separately no more than 450℃ and 6.4MPa. It can be used in the situation that the dirt is very heavy and the tube side is easy to be corrosive.

Disadvantages: The flange connecting area between floating head cover and tube sheet is quite large, so that the diameter of shell increase, and the annual channel with small resistance between tube bundle and shell is formed. Part of fluid will pass here and don’t take part in the heat exchange process. The disadvantage includes complex structure; high metal consumption, high cost.

Above advantages and disadvantages indicate that the floating head type heat exchanger can suit the condition of large temperature difference between pipe and shell , high causticity of shell side medium and scale formation easily . It can be applied widely although it has complex structure, high metal consumption and high cost.