THE
interest in high pressure research and development is growing at an accelerated rate. I t is rapidly becoming a n important tool in the ever-expanding scientific field. New processes, applications, equipment, and techniques are appearing from many sources. University, government, commercial, and industrial laboratories are all contributing to the fund of high pressure knowledge. Design and fabrication of the needed equipment have kept pace with the laboratories. For small scale research programs, most of the needed equipment is available commercially “from stock,” and it is also safe, when used under, the conditions for which it was designed. The papers presented at the High Pressure Symposium, Division of Industrial and Engineering Chemistry, were
I
representative of the interest and progress in “extreme conditions research.” The general categories were design of high pressure equipment, chemical reactions at high pressure, safety at high pressure, and the fundamental subjects of high pressure physics, transport properties, and thermodynamics. The outstanding characteristic of high pressure symposia is the freedom of open discussion that prevails, and the willingness of participants to present papers related to their investigations. John F. Miller Dow Chemical Co. Midland, Mich.
LEON N. VERNON1 and C. M. SLIEPCEVICH University of Oklahoma, Norman, Okla.
Heat Transfer in a High Pressure Reactor A practical design eliminates need for internal cooling or heating coils or external jacketing H E A T TRANSFER and fluid flow were studied in a high pressure reactor, designed for a working pressure of 4000 pounds per square inch at 900’ F. Its unusual feature is the continuous ‘/s-inch radius groove (half-circle in cross section), machined around the liner made of Type 347 stainless steel. The liner was machined to 0.002 inch greater than the maximum bore of the body, to obtain a shrink fit. At each end of the helical groove, ‘/*-inch pipe taps were placed, so that a heat transfer fluid could be passed through the helix. The temperature gradients required to obtain heat transfer are reduced appreciably in the reactor wall, and stresses arising from temperature gradients are decreased. This design permits operating the outer layer of the reactor body at a lower temperature. Each end of the reactor is sealed by a button-type closure using an 18-8 Flexitallic gasket (Flexitallic Gasket Go., Camden, N. J.). Temperature measurements along the reactor are made by five thermocouples, placed approximately 6 inches apart, and each embedded in a stainless tube ‘/I6 inch in outside diameter.
Pressure Drop in Reactor Helix
The amount of pressure drop through the reactor helix is important, as heat transfer fluids have to be recirculated a t high temperatures. Relatively little work has been done on pressure drop Present address, Continental Oil Co., Ponca City, Okla. 1
through coiled pipe, with no existing correlation for pressure drop in turbulent flow. Friction losses in curved pipe are larger than in straight pipe, because of a secondary flow. The high velocity particles near the flow axis are forced to the outside of the coil by a larger centrifugal force than the slower particles near the wall. The outside particles are then directed back to the inside of the coil along the wall. Increased friction loss is due to the energy supplied to promote this secondary motion. Detra ( 2 ) found that a curved pipe having an elliptical cross section with its major axis parallel to the plane of the curve will have a greater secondary flow velocity than a curved pipe of circular cross section, and, therefore, a greater friction lass. If the major axis is perpendicular to the plane of the curve, the flow loss is less than in a curved pipe of circular cross section. Drew (3) and Prandtl (5) have empirical correlations for calculating the friction factor for laminar flow through coiled pipe. Both methods depend on the Dean number, R e d D j j c . Drew’s correlation consists of a plot of fc/f us. RedD/D,. Drew specifies that if the Fanning friction factor is less than 0.009, the flow is turbulent and the chart should not be used. Prandtl’s equation, fc = f (0.37) (Red/DID,)033, is good for the range 20 < R e d D T o < 1000. These two methods will give two values of the friction factor: A plot of log fc/f us. log R e d / D T , should be a straight line according to Prandtl’s equation, but Drew’s plot on logarithmic paper is not a straight line. Thus, any attempt to calculate a
pressure drop through the coil of the reactor would be largely guesswork; the problem is further complicated by the noncircular cross-sectional area of the coil. For taking pressure drop data, tap water was pumped upward through the helix until the temperature and pressure drop were constant. The flow rate and pressure drop across the helix were recorded. The data are plotted in Figure 1 as f us. Reynolds number, where
The length of the helical coil, L, is equal to the number of helical turns multiplied by T times D,,the outside diameter of the liner minus twice the distance from the inside wall to the centroid of the semicircle. As the pipe is noncircular, the equivalent diameter, De, which is 4 times the cross-sectional area of flow divided by the wetted perimeter, is used. Thus: 0.125 0.137 foot
L
=
72 X
T
X 0.137 = 31.0 feet
?r X 0.1252 4x 2 D, = ?r X 0.25
+ 0.25
1 x -12 =
0.01275 foot Reliability of the data is shown by excellent agreement of three methods for measuring pressure drop (Figure 1). VOL. 49, NO. 12
DECEMBER 1957
1945
