I n d . E n g . C h e m . Res. 1988,27, 1543-1545
half nipple. The prethreaded nipple is press fit into the seal housing and secured by a 1/4-in. fillet weld. The opposite side of the seal housing is then spot faced to a depth of 0.50 in. This spot face allows accurate alignment of the backup plate and the high-pressure seal. The backup plate, which is 0.75-in. thick and approximately 2.00-in. diameter, must fit snuggly in the spot face. The clearance between these parts must not exceed 0.001 in. The backup plate is secured by six 1/4-in.class 8 machine screws, on a 1.25-in. bolt circle. Proper alignment of the probe passage in the backup plate and seal cavity is provided by drilling the assembled parts on a lathe. An undersized l/&. pilot hole is drilled and then reamed to size. The backup plate is then removed, and the seal cavity machined. The seal cavity requirements can be found in the Bal-Seal Design Manual. Performance of the seal is excellent without chrome plating on the seal cavity or probe provided good surface finishes ( ~ 1 pin. 4 rms) are maintained. Of great importance is the mounting of the high-pressure head to, and the construction of, the probe guide. The probe guide is a linear motion device consisting of a three-piece, 45" dovetail way which guides the clamping block. The clamping block holds the bottom end of the probe and is powered by a lead screw. All parts other than the screw were machined from T3-2024 aluminum. The lead screw is of mild steel with a pitch of 24 threads/in. This pitch assured that the screw/block combination would be self-locking under load. To provide smooth movement of the clamping block in the way, a tensioning strip, made of 0.188- X 0.625-in. aluminum bar stock, was mounted in a grove on the base of the way. Tension was adjusted by five equally spaced screws positioned along the back of the probe guide (see Figures 3 and 4). Proper alignment of the head to the probe guide is obtained by using a dial indicator. The head is then bolted in place and reference pinned. This allows future assembly without tedious alignment. The two front pieces of the way are each secured by five machine screws. The front pieces are positioned by use of gage blocks and a dial indicator. When aligned properly the way must allow the clamping block to move parallel to the probe passage in the high-pressure head. To fasten the probe to the clampling block, a 0.125-in. wide slot is milled in the clamping block and the probe is held in place with four screws. The depth and position of this slot are important if the probe is to be concentric with the seal. Careful attention to fitting and assembly is important so that the probe enters the seal squarely and that the two are concentric. Accurate alignment is provided by machining the slot after the block has been
1543
mounted and pinned and the ways assembled. The lowest section of the assembly is the drive mechanism. A gear reducer, made by Precision Instrument Corp. (Model DJ-lo), is positioned on a two-piece angle such that its output shaft powers the lead screw. The angle is mounted on a circular hub with an external snap ring. This allows the angle and the gear reducer to rotate 360°, and alignment of the motor shaft [18] to the reducer input shaft is greatly simplified. A flexible coupling is also used on the input shaft for further protection against shaft failure due to misalignment.
Conclusion The pump and probe assembly presented here allow the construction of a versatile apparatus for the determination of phase equilibria at high pressure. The apparatus described allows quick and accurate sampling as proven by testing on the C02 + n-decane binary mixture (Kneisl, 1988). This represents a very strigent test of the apparatus since the gas phase is very lean in n-decane and the isotherm studied contained a critical point. The addition of density, surface tension, and viscosity measurements, as outlined by Simon and Schmidt (1983), illustrates the unique capabilities attainable by this sampling technique. Acknowledgment The authors thank the Union Carbide Corporation for several fruitful discussions. Funding for this research was provided by the U S . Department of Energy under Grant DE-FG05-82ER75056 and The Energy Research Center of the State of West Virginia under Grant ST86-CP7-2. Acknowledgment is made to the donors of the Petroleum Research Fund, administered by the American Chemical Society, for partial support.
Literature Cited Bal-Seal Design Manual; Bal-Seal Engineering Company: Santa Ana, CA. Capps, E. F.; Eubank, P. T.;Gielen, H.L.; Hall,K. R.; Mansoorian, H.Rev. Sei. Instrum. 1975,46(10), 1350-1351. Kneisl, P. Ph.D. Dissertation, West Virginia University, Morgantown, WV, 1988 (in progress). Simon, R.; Schmidt, R. L. Fluid Phase Equilib. 1983, 10, 133.
Philip Kneisl, John W. Zondlo,* Wallace B. Whiting Department of Chemical Engineering West Virginia University Morgantown, West Virginia 26506 Received for review April 29, 1987 Revised manuscript received March 23, 1988 Accepted April 22, 1988
Entrainment of Ambient Air into a Cylindrical Duct by a Turbulent Jet from a Single Nozzle Measurements were made of the rate of air entrainment induced by a turbulent jet stream from a single nozzle in a semiconfined flow system. A simple correlation was then developed between the rates of air entrainment and jet flow. The correlation agreed with measurements to within f3.1% . This study will prove useful for the design of furnaces, dust collectors, and fluid mixing equipment in the chemical industry. As a jet issues from a nozzle into a stationary medium, it entrains fluid from the surroundings. Albertson et al. (1950) assumed that the sole force producing the deceleration of the jet and the acceleration of the surrounding 0888-5885/88/2627-1543$01.50/0
fluid is the tangential shear within the mixing region. This led to the conclusion that the momentum flux must be constant for all normal sections of a given flow pattern. From this conclusion, an explicit form of the axial velocity 0 1988 American Chemical Society
1544
Ind. Eng. Chem. Res., Vol. 27, No. 8, 1988 Valve
Hot wire ammo meter
T a
i Hat wire
Blower
I
Nozzel
2
- 1
H
c
Figure 1. Schematic diagram of experimental apparatus. one-seventh- power law
Table I. Size of Cylindrical Duct diam. m length. m diam, m
length, m
1.185 1.735
2.000 2.400
0.105
0.155
0.190 0.265
distribution was derived, which in turn was used to calculate the rate of entrainment. Since then the topic of mixing and entrainment in jet streams has been treated by a number of authors (Hinze, 1959; Ricou and Spalding, 1961; Schlichting, 1968; Rajaratham, 1976; Habib and Whitelaw, 1979; Islam and Tucker, 1980; Wall et al., 1982; Joseph et al., 1983; Schneider, 1985; Choi et al., 1986). It appears, however, that the air entrainment in the case of a semiconfined coaxial jet (as depicted in Figure 1)has not been studied to date. The jet issuing from a nozzle entrains air from its surroundings into the duct. The present system has direct relevance to the design of furnaces, dust collectors, and equipment for fluid feeding and mixing in the chemical industry. The objective of the present study is to develop an empirical correlation between the rate of air entrainment and the rate of jet flow.
Experimental Apparatus and Procedures The schematic diagram of the experimental apparatus is shown in Figure 1. The inside diameter of the nozzle was 27.6 mm. Ducts of four different radii and lengths as listed in Table I were used. The axis of the jet coincided with the axis of the cylindrical duct. The nozzle tip was set on the cross section of the duct inlet. The jet air stream, whose volumetric flow rate is Q2 (m3/s) (at atmospheric pressure), was issued from the nozzle into the duct. This induced the entrainment of ambient air, Q1, into the duct. The resulting air flow rate, Q1 + Qz, was determined by measuring the velocity profile along the cross section in the downstream of the duct. Results Representative distributions of measured velocities near the duct exit are shown in Figure 2, which indicates that the measured velocity profiles can be well represented by the one-seventh power law. Measured rates of air entrainment were plotted in Figure 3 against the rates of jet flow for ducts of different sizes. The ratio Q1/Q2 was evaluated for each duct tested and was plotted against Da/Dn in Figure 4,where D, and D, refer t o the diameters of the cylindrical duct and nozzle, respectively. The data lie on a straight line represented by the relationship
81
Da -1 Dn
- = 1.1-
Qz
Equation 1 agreed with measurements to within f3.170. Linear relationships between Q1/Qz and Da/Dn can be found in Albertson et al. (1950),Ricou and Spalding (1961), and Perry (1984). The coefficients of D,/Dn in these works are different from ours since the fluid mechanical config-
0
0
0.2
0.8
0.6 r [-I
0.L
1.0
Figure 2. Velocity profile. 0.4 I
1
I
1
0.3
0.2
c
01
1
0
0.02
0
0.0 1
[m3/sl
Q2
Figure 3. Effect of duct size on the rate of entrainment. 10
8m
L
6-
N
0, o
L-
2
0
0
2
L
6
8
1
0
D a / D n [-I
Figure 4. Empirical correlation of the rate of entrainment.
urations of their systems are different from the present one. Supplemental experiments provided the following information on the rate of entrainment: The rate of entrainment will not be influenced appreciably if the distance between the nozzle tip and the cross section of the duct inlet is kept within 0.70,, if the axis of the jet and the duct does not differ by more than 0.17 rad, and if the duct length is greater than 4.50,.
Conclusions A study was made on the entrainment of ambient air into a cylindrical duct by a turbulent jet from a single
I n d . Eng. Chem. Res. 1988,27, 1545-1547
nozzle. The inside diameter of the nozzle used was 27.6 mm. Ducts of four different radii and lengths (Table I) were used. The nozzle tip was set on the cross section of the duct inlet. The velocity profile within the duct was measured. A simple empirical correlation was obtained between the rates of air entrainment and jet flow. The correlation agreed with measurements to within f3.170.
Nomenclature
D, = diameter of cylindrical duct, m D, = diameter of nozzle, m H = length of cylindrical duct, m Q1,Q2= rates of air entrainment and jet flow,respectively, m3/s 2 = axial coordinate, m
Literature Cited Albertson, M. L.; Dai, Y. B.; Jensen, R. A.; Rouse, H. Trans. ASCE 1950. 115. 639. Choi, D. W.;’Gessner, F. B.; Oates, G. C. J. Fluid Eng. 1986,108,39.
1545
Habib, M. A.; Whitelaw, J. H. J. Fluid Eng. 1979, 101, 521. Hinze, J. 0. Turbulence, 2nd ed.; McGraw-Hill: New York, 1959; Chapter 6. Islam, S. M. N.; Tucker, H. J. J. Fluid Eng. 1980, 102, 85. Joseph, D. D.; Nguyen, K.; Matta, J. E. J. Fluid Mech. 1983, 128, 443. Perry, R. H.Chemical Engineers’ Handbook, 6th ed.; McGraw-Hill: Singapore, 1984; Chapter 5. Rajaratnam, N. Turbulent Jets; Elsevier Science: Amsterdam, 1976. Ricou, E. P.; Spalding, D. B. J. Fluid Mech. 1961, 11, 21. Schneider, W. J . Fluid Mech. 1985, 154, 91. Schlichting, H. Boundary Layer Theory, 6th ed.; McGraw-Hill: New York, 1968; Chapter 24. Wall, T. F.; Subramanian, V.; Howley, P. Trans. ICE 1982,60,231.
Tetsuo Akiyama,* Taketoshi Marui Department of Chemical Engineering Shizuoka University Ha mama t s u 432, J a p a n Received f o r review March 30, 1988 Accepted April 18, 1988
Steaming of Activated Carbon Beds When activated carbon is used in a thermal swing adsorption process, it may be regenerated by a hot inert gas or by steam. Preliminary experiments with steam (and without removal of an adsorbate) showed intermediate axial temperatures to be higher than inlet or exit temperatures. It was concluded that the heat of adsorption of water is the primary source of energy for the regeneration step of thermal swing adsorption involving steaming. Activated carbon is employed extensively as an adsorbent in both liquid- and gas-phase separations. Its affinity for nonpolar over polar adsorbates makes activated carbon particularly suitable for water purification and for the removal of organics from high-humidity gas streams. It is commonly employed in the area of solvent recovery. Steam regeneration is the most widely used in-situ method of activated carbon bed regeneration. Because of partial condensation and adsorption, steam can provide significantly more energy than hot inert gas. While regeneration is the energy-intensive phase of an adsorption cycle, it is rarely the time-limiting step. This may explain, at least in part, the lack of discussion of steam regeneration in the open literature. Published experimental data are extremely limited, and modeling has not been addressed at all. Wankat and Partin (1980) and Partin (1977) collected some steam regeneration data as part of a study of a new solvent recovery process. Steaming was not considered a critical step, however, and therefore not discussed extensively. Scamehorn (1979) limited discussion of his steam regeneration data because of difficulties encountered in controlling the operating conditions. He did present plots of total desorbed material versus time and concluded that both the heating and purging functions of the steam were important. The present paper reports the results of an experimental investigation of heat transfer within an adsorbate-free bed of activated carbon. Temperature profiles within the bed were recorded as the bed was purged with low-pressure steam. This work, undertaken as part of a larger study of carbon bed adsorption and regeneration (Schork, 1986), is intended as a preliminary step in the investigation of steam regeneration.
Experimental Equipment The experimental equipment and procedures used in this study have been described elsewhere (Schork, 1986;
Schork and Fair, 1988). Broadly, the equipment included a gas feed system, a 7.44-cm i.d. by 30.5-cm-long column, and extensive temperature monitoring and recording equipment. The activated carbon used was 8 X 10 US mesh Witco JXC, a petroleum-based cylindrical extrudate material. The column was wrapped with electrical heating tape and insulated with about 5 cm of Fiberglas. Pressure gauges and thermocouples were installed above and below the column. Four thermocouples were located in the carbon bed, two at 10 cm from the top and two at 20 cm from the top. These entered the column through Cajon Ultra-torr fittings which allowed insertion to any desired radial position. Four surface thermocouples were attached to the exterior of the column, evenly spaced along the length. The thermocouples were connectea to an Omega 2700A digital thermometer through a relay system controlled by a TRS Color Computer 2. All 10 temperatures were read within a 5-s period and stored in computer memory every 15 s.
Discussion of Results The steam required for these experiments, about 3 lb/h, was drawn from a large building header. This presented considerable control problems which caused several runs to be abandoned. The remaining runs are summarized in Table I. The notation “preheated indicates that the bed was heated externally to approximately the inlet steam temperature before steaming was begun. The notation “residual water” indicates that there was already some water on the carbon at the start of the run. Complete data sets for all runs are available in tabular form (Schork, 1986). Data presented here represent temperatures measured at the center axis of the bed. Temperatures recorded during run S10 are plotted in Figure 1. Data presented in Figure 2 represent the heating of the same experimental system with a nitrogen purge. Several features of the data differentiate steaming from
0888-5885/88/2627-1545$01.50/0 0 1988 American Chemical Society
