Half Pipe Coil Jackets

Figure 4: Half Pipe Coil Jacket

Half pipe coils provide high velocity and turbulence. The velocity can be closely controlled to achieve a good film coefficient. The good heat transfer rates, combined with the structural rigidity of the design, make half-pipe coils a good choice for a wide range of applications. A good design velocity for liquid utilities is 2.5 to 5 ft/s.

The maximumspacing between coils should be limited to 3/4". Half-pipe coils are ideally suited for high temperature applications where the utility fluid is a liquid.

There are no limitations of the number of inlet and outlet nozzles, so the jacket can be divided in multipass zones for maximum flexibility. The rigidity of the half-pipe coil design can also minimize the thickness of the inner vessel wall which can be especially attractive when utilizing alloys.

Half-pipe coil jackets are not covered in Section VIII, Division I of the ASME code. Generally, they are limited to 600 psig design pressure and a design temperature up to 720 °F. A carbon steel half-pipe jacket can be applied to a stainless steel vessel up to 300 °F. Over 300 °F, the jacket should be stainless steel as well.

Heat Transfer Coefficients: Half-Pipe Coil Jackets

Half-pipe coil jackets are generally manufactured with either 180° or 120° central angles (D_ci):

Figure 5: Depiction of Center Angles

Figure 6: Half-Pipe Coil to Tank Details

For a 180° central angle:

Equivalent Heat Transfer Diameter, De = Π / (4 D_ci)

Cross Section Area of Flow, Ax = Π / (8 (D_ci²))

For a 120° central angle:

Equivalent Heat Transfer Diameter, De = 0.708 D_ci

Cross Section Area of Flow, Ax = 0.154 (D_ci²)

Using the same nomenclature as previous, the heat transfer coefficients are calculated as follows:

hj De/ k= 0.027(NRe)0.8 (NPr)0.33 (µ/µW)0.14 (1+3.5 (Dc/De) ) (For NRe>10,000)

Eq. (7)

hj De/ k = 1.86 [ (NRe) (NPr) (Dc/De) ] 0.33 (µ/µW)0.14 (For NRe<2,100)

Eq. (8)

Do not confuse D_ci with D_c. D_c is defined as D_ji + ((D_jo-D_ji)/2).

Hydraulic Radius: Half-Pipe Coil Jackets

Figure 7: Hydraulic Radius Dimensions

Referring to Figure7:

Eq. (9)