Tinker's Flow Model for Shell & Tube Heat Exchanger Design

 TINKER’S FLOW MODEL FOR SHELL & TUBE HEAT EXCHANGER DESIGN

All the latest methods (Bell’s method) and many computer programs (HTRI, BJEC, Aspen EDR) for the process design of the heat exchangers without phase change are based on Tinker’s flow model.

If there is no phase change of shell side fluid then shell side heat transfer coefficient and the shell side pressure drop in all latest methods are calculated based on Tinker’s flow model. In conventional method for heat exchanger design like those developed by the Kern, it is assumed that entire shell side fluid is flowing across the tube bundle and between the baffles. But in really shell side fluid is flowing in various ways. In Tinker’s flow model the sell side flow is divided in total five different streams.

1.      Stream A

2.      Stream B

3.      Stream C

4.      Stream E

5.      Stream F

Fig 1: Tinker’s Flow Model

 

·        Stream A

Stream A is the tube-to-baffle leakage stream or it is the fraction of shell side fluid flowing through the clearance between tube hole in baffle and tube outside diameter. This stream does not bypass the heat transfer area (outside area of tubes) and hence, it does not create any adverse effect on the value of heat transfer coefficient. However, it makes the significant difference in pressure drop (loss). When stream A leaves this clearance, it forms free flowing jet. Hence, boundary layer separation occurs and considerable friction loss or pressure drop takes place. Effect of stream A must be considered in the calculation of pressure drop.

 

·        Stream B

Stream B is the actual cross flow stream or it is the fraction of shell side fluid which is flowing across the tube bundle and between the baffles. In Kern’s method and other old methods, it is assumed that entire shell side fluid is flowing like stream B.

 

·        Stream C

Stream C is bundle to shell bypass stream or it is the fraction of shell side fluid flowing through the clearance area between shell inside diameter and tube bundle. Stream C is the main bypass stream. (bypassing the heat transfer area). This clearance area provides low pressure drop path for the shell side fluid. Hence, % of shell side fluid bypassed through this clearance area is quite significant. It is maximum with pull through floating head heat exchanger and minimum with fixed tube sheet heat exchanger. Amount of stream C can be reduced considerably by using sealing strips which are attached on inside surface of shell. They provide the partial blockage or the additional resistance in the path of stream C.

 

·        Stream E

Stream E is the baffle to shell leakage stream. It is a part of shell side fluid flowing through the clearance between the edge of baffle and shell wall. Like stream C, this stream is also bypassing the heat transfer area and hence, reduces shell side heat transfer coefficient. But amount of stream E is lesser than amount of stream C. Normally, the clearance between baffle outside diameter and shell inside diameter is in the range of 1.6 to 4.8 mm while clearance between tube bundle and shell inside diameter is in the range of 10 to 100 mm.

 

 

·        Stream F

Stream F is the pass-partition bypass stream. In tube sheets where pass partition plates are attached (for forming tube side passes), in that portion tubes cannot be provided. In multipass heat exchangers, one can find more number of gaps in tube bundle. Stream F is the fraction of shell side fluid flowing through these gaps. If the gap is vertical it provides low pressure drop path for fluid flow. Just like stream C and stream E, this stream is also bypassing the heat transfer area and reduces shell side heat transfer coefficient. Amount of stream F and its adverse effects are significant in multipass heat exchanger. To reduce the amount of this stream sometimes dummy tubes are used.

 

NOTE: There is no stream designated as stream “D”.