Pressure drop coils

The simple thermostatic expansion va/verelies on the pressure under the diaphragm being approximately the same as that at the coil outlet, and small coil pressure drops can be accommodated by adjustments to the spring setting. 

Mittal et al. (1999) modeled the coil-soaker as a PFR coupled with CSTRs in series. The furnace pressure drop was estimated using the Beggs and Brill (1973) correlation. Coil pressure drop, coil-soaker temperature profiles, and residue conversion were predicted within a narrow range of accuracy. The model was developed for one feed and for a single cracking reaction, i.e., vacuum residue to gas and naphtha. 

The shape of the coohng and warming curves in coiled-tube heat exchangers is affected by the pressure drop in both the tube and shell-sides of the heat exchanger. This is particularly important for two-phase flows of multicomponent systems. For example, an increase in pressure drop on the shellside causes boiling to occur at a higher temperature, while an increase in pressure drop on the tubeside will cause condensation to occur at a lower temperature. The net result is both a decrease in the effective temperature difference between the two streams and a requirement for additional heat transfer area to compensate for these losses. 

Performance Data for Direct-Heat Tray Dryers A standard two-truck diyer is illustrated in Fig. 12-48. Adjustable baffles or a perforated distribution plate is normally employed to develop 0.3 to 1.3 cm of water-pressure drop at the wall through which air enters the truck enclosure. This will enhance the uniformity of air distribution, from top to bottom, among the trays. In three (or more) truck ovens, air-reheat coils may be placed between trucks if the evaporative load is high. Means for reversing air-flow direction may also be provided in multiple-truck units. 

The water pressure drop through the coil is as low as economically possible. 

Figure 5-1 shows a typical LTX process. The inlet gas stream is choked at the well to 2,000 to 3,000 psi or until the temperature declines to approximately 120°F, which is well above the hydrate formation temperature. The inlet stream next enters a coil in the bottom of the low temperature separator. The stream is then cooled to just above the hydrate formation temperature with the outlet gas coming off the low temperature separator. This assures the lowest possible temperature for the inlet stream when it enters the vessel after the choke. This choke is mounted in the vessel itself. When the pressure drop is taken, the temperature will... 

To calculate the heat duty it must be remembered that the pressure drop through the choke is instantaneous. That is, no heat is absorbed or lost, but there is a temperature change. This is an adiabatic expansion of the gas w ith no change in enthalpy. Flow through the coils is a constant pressure process, except for the small amount of pressure drop due to friction. Thus, the change in enthalpy of the gas is equal to the heat absorbed. 

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 ... 

In the design of tailor-made plant it is necessary to calculate the above as they occur within the plant and add the pressure drop of all other items such as air filters at their dirty conditions, coils, etc. In the case of proprietary units it is normal for the manufacturers to quote an external pressure against which they will deliver the specified air quantity. 

Where an evaporator coil is divided into a number of parallel passes, a distribution device with a small pressure loss is used to ensure equal flowthrough each pass. Pressure drops of 1-2 bar are common. There will nowbe a much larger finite difference between the pressure under the diaphragm and that at the coil inlet. To correct for this, the body of the valve is modified to accommodate a middle chamber and an equalizing connection which is taken to the coil outlet, close to the phial position. Most thermostatic expansion valves will have provision for an external equalizer connection (see Figure 8.8). 

The cross-flow fan generates only very slight pressure and its use is limited to appliances where the air pressure drop is low and predetermined. Its particular shape is very suitable for many kinds of air-handling devices such as fan coil units and fan convectors. 

APC = Pressure drop across a coil trol valve, psi... 

P0 = Np = Power number, dimensionless, Equation 5-19 Ppew = Plate coil width, one plate, ft Ap = Pressure drop, psi AP0 = Pressure drop for open pipe, psi AP, = Static mixer pressure drop in turbulent flow, psi Q = Flow rate or pumping capacity from impeller, cu l t/sec, or Ls/1... 

Pressure Drop and Heat Transfer in Coils", The Chem. Engr. 218, CE 113 (1968)... 

The heat transfer coefficient at the inside wall and pressure drop through the coil can be estimated using the correlations for flow through pipes see Section 12.8 and Volume 1, Chapters 3 and 9. Correlations for forced convection in coiled pipes are also given in the Engineering Sciences Data Unit Design Guide, ESDU 78031 (2001). 

Then, 11 m3 (70 barrels) of 15 /, HC1 were pumped downhole through a coil tubing. The bottomhole pressure history is in this case precisely derived from surface data, since the latter are collected in the open annular space between the coil tubing and the casing. No computation of friction pressure drops all along the injection string is needed, which removes a major source of errors in the derivation of bottomhole data. The bottomhole pressure is just equal to the sum of the surface... 

A number of equations have been proposed for use in the calculation of pressure drop in coils of constant curvature [Srinivasan et al (1968)]. The latter are known as helices. For laminar flow, Kubair and Kuloor (1965) gave an equation for the Reynolds number range 170 to the critical value. In terms of the Fanning friction factor, their equation can be written as... 

Kubair, V. and Kuloor, N.R., Non-isothermal pressure drop data for liquid flow in heated coils. Indian Journal of Technology, 3, pp. 5-7 (1965). 

The pressure drop through the coil depends on the flow rate F ... 

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