Choose Coil Diameter

Volume 1, Chapter 9 explains the criteria for choosing a diameter and wall thickness of pipe. This procedure can be applied to choosing a coil diameter in an indirect fired heater. Erosional flow criteria will almost always govern in choosing the diameter. Sometimes it is necessary to check for pressure drop in the coil. Typically, pressure drop will not be important since the whole purpose of the line heater is to allow a large pressure drop that must be taken. The allowable erosional velocity is ffiven bv  

The fluid density must be for the combined stream of oil and gas and should be calculated at the average gas temperature. 

The required pipe internal diameter can be calculated based on the volumetric flow rate and a maximum velocity. The maximum velocity may be the erosional velocity or a limiting value based on noise or inability to use corrosion inhibitors. In gas lines it is recommended that the maximum 

Z = gas compressibility factor R = gas/liquid ratio, ft /bbl T = operating temperature, °R P = pressure, psia Qi = liquid flow rate, bbl/day V = maximum allowable velocity, ft/sec 

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In order to choose the coil length and diameter, a temperature must first be chosen upstream of the choke the higher Tj, the longer the coil L and the shorter the coil L2. In Chapter 2 we showed that the greater the LMTD between the gas and the bath temperature, the greater the heat transfer per unit area, that is, the greater the LMTD, the smaller the coil surface area needed for the same heat transfer. The bath temperature is constant, and the gas will be coldest downstream of the choke. Therefore, the shortest total coil length (L[ -I- L2) will occur when L is as small as possible (that is, Tj is as low as possible). 

Can we make any use of all this Yes, of course, a lot Look, for example, at the following problem. Take a real polymer coil. All we really need to know about it is just its size, R = bN /. Now try to squeeze it into a capillary of diameter D, as Figure 13.11 demonstrates. You may just look at Chapter 8, to see that even the simple question about a real polymer coil with excluded volmne is very complicated. Moreover, if the coil is placed in a capillary, it is hard even to think how to start. However, imagine that it is de Germes himself who is tackhng it, using the idea of self-similarity. He is free to choose the monomer rniits in any way he likes. Suppose g is such that the size of the unit is equal to the size of the capillary, that is, = D, and therefore g = The technical term for such monomer units... 

Differing from 8a and 8b, norbornene-appended HBC 8c (Fig. 10), designed for ROMP, affords nanocoUs as well as nanotubes (Fig. 12) [35]. By choosing appropriate conditions, either nanocoils or nanotubes are selectively formed. For example, by EtzO vapor diffusion into a CH2CI2 solution of 8c (0.65 mM) at 15 °C, the nanocoils form exclusively. At the same time, when the vapor diffusion is conducted at 25 °C at a lower concentration of 8c (0. 22 mM), the nanotubes can be obtained as the sole product. As observed by TEM and SEM, the nanocoil consists of a 20-nm-wide bilayer tape with 30 nm in diameter and 60 nm in pitch (Fig. 13a), while the nanotube possesses a diameter of 20 nm and a wall thickness of 3 nm (Fig. 13b). Interestingly, when the suspension of the nano coils is allowed to stand for 5 days at... 

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