Effects of Tank Configuration on Flow Pattern of a Recirculating Aquacultural Tank

Transcription

1 J. Fish. Soc. Taiwan, 26(3): Effects of Tank Configuration on Flow Pattern of a Recirculating Aquacultural Tank Kuo-Feng Tseng 弋 Chyng-Hwa Liou and Jea-Gwan Lai (Receivd, June 23, 1999; Accepted, September 9, 1999) ABSTRACT The ideal flow pattern in a recirculating aquaculture systern is a completely mixed flow with no dead zone. The type of tank and layout of the inlet and outlet influence the efficiency of water exchange. The residence time distribution (RTO) approach was used to investigate the flow in circular and square tanks. Ratios of water depth (d) to diameter or to side width (0) (d/o; 1:1, 1:2 and 1:3) and influent port locations (surface (8), middle (M) or bottorn (B) of tank) were studied at two influent flow velocities. The RTO data showed that no dead zone existed in all of the tested square tanks but dead zone existed in circular tanks. Water in all tested tanks was alrnost completely rnixed. Key words: Recirculating system, Tank configuration, Water mixing, Flow pattern INTRODUCTION In a recirculating aquaculture system, the recirculating water flows into culture tank continuously and supplies the oxygen demand of cultured organism. The used water flows out from the tank at the same time with high concentration of ammonia-n, residual feed and feces excreted by cultured organism. A plug flow tank would have gradients of water quality build-up and result in non-uniform organisms distribution (Westers and Pratt, 1977; Ross et 訓, 1995). The growth rates and survival rates of organisms which are depending on the water quality would be different at different position of the tank (Meade et al., 1985; Krise and Meade, 1986; Ross θ t al., 1995) Culture tank is considered operating in optimum condition when the influent water is distributed homogeneously in tank. In other words, there are no dead zone in the tank and no bypass of recirculating water through the tank (Timmons et al., 1998). Usually, culture tank does not have such ideal condition. It is known that the type of tank and the layout of inlet and outlet influence the flow in the tank (Klapsis and Burley, 1984; Ross et al., 1995). Some dead zones and bypass are present in tank (Leon, 1986; Totlandθ t al., 1987). The flow type in a culture tank is described by the approach of residence time distribution (RTD) of water element in tank. The RTD of water element in a tank could be determined by tracer method (Burley and Klapsis, 1985; Watten and Beck, 1987; Watten and Johnson, 1990) In this study, the negative-response of tracer study was used to determine the RTD of circular and square tanks. The results were used to determine the volume fraction of dead zone and the extent of mixing in culture tanks. The choice of tank type and configuration were discussed MATERIALS AND METHODS 1. Experimental Apparatus The experimental apparatus (Fig.1) includes water reservoir (R), model culture Department of Aquaculture, National Taiwan Ocean University, Keelung 202, Taiwan. *Corresponding author

2 162 Kuo-Feng Tseng, Chyng-Hwa Liou and Jea-Gwan Lai Culture tank R Fig. 1. The experimental apparatus system (Inf: influent ports: S, M, B; Eff: effluent; TO: tracer detector; V1, V2: valves; M. P.: meter pump). tank (T), tracer detector (TO, a spectrophotometer (8himadzu UV-1201, 8himadzu co., Japan)) and computer recorder. Wa ter was stored in R and maintained at a constant temperature. A meter pump (Cole Parmer Instrument Co. Master 干 lex 7553) introduced water from R into T. Tanks with two different types but with the same water volume were used in this study. They were circular tanks (CT, with water depth x diameter of 24 cm x 24 cm, 15 cm x 31 cm and 11.5 cm x 35 cm) and square tanks with round corner (8T, with water depth x side width of 22.3 cm x 22.3 cm, 14 cm x 28 cm and 10.5 cm x 32 cm). The influent ports were located at water surface (8), middle (M) or bottom (B) of tank. Table 1 shows the ratios of water depth/diameter (d/o) for CT, water depth/ side length (d/o) for 8T and the positions of influent ports. The opening of influent port is 1 cm in diameter. The influent water flows into tank horizontally and tangentially with tank wal l. There is a trap (diameter 2.6 cm) at the center of tank bottom. Water flows out of tank from the effluent port in the trap. The water level of tank was maintained with a flexible tube connected to the effluent port. 11. Tracer Selection 80dium chloride (Burely and Klapsis, 1985; Watten and Beck, 1987) and dyes have been used as tracer. In this study, a blue color surfactant with main component of sodium dodecyl-benzene-sulphor.late was used as the tracer. The absorption spectrum of the solution of tracer was determined by scanning with the spectrophotometer. The results indicated that the peak of absorption spectrum was at 629 nm. The absorbance of tracer was not decay over 24 hrs under light. This showed that the tracer did not degrade automatically or by light and was suitable to used as a tracer. Table 1. The configuration (water depth/side width (or diameter) ratio, d/o) of culture tanks and locations of influent ports (surface, 8; middle, M, bottom, B) Type of tank circular tank (CT) square tank (ST) d/o 1/2 1/3 1/1 1/2 1/3 Water volume (1)( 土 SE) Influent port 10.9 士 0.1 S, M, B 11.3 :1: 0.1 S, M, B 11.1:1: 0.1 S, B 11.1 士 0.1 S, M, B 士 0.1 S, M, B 11.1 土 0.1 S, B

3 Effects of Tank Configuration on Flow Pattern of a Recirculating Aquacultural Tank Experimental Methods Tracer study was used to determine the residence time distribution (RTO) of water element in tank. There are three methods for the input of tracer in RTO determination. They are pulse input, positivestep input, and negative-step input methods (Fogler, 1986). The negative-step method was used in this study. Because it is more convenient to operate than pulse method and requires less amount of tracer than positive-step method. Initially, water with a fixed concentration (C o ) of tracer was recirculated in the experimental system with the designated flow rate. The effluent from tank was pumped into a spectrophotometer by a meter pump. The flow-cell was used for spectrophotometer in determining the concentration of dye. The plug flow passing through cell was quickly and the absorbance of solution was detected continuously, but the instantaneous data was recorded every 10 sec. The absorbance at wavelength of 629 nm was measured and recorded by a personal computer. Then the two-way switch-valve (V1, Fig. 1) was turned right to let the influent of fresh water without tracer from reser 凶 voir flowed in with the same flow rate. The other valve (V2, Fig. 1) was open to let the effluent discharged without recirculating. The concentration of tracer in tank was diluted. The tracer concentration (C t ) of the effluent was recorded every 10 sec. The test was conducted till the Ct value was reduced to zero. For each tank condition, the experiment was performed three times. The experiments were performed for various configurations of tanks (Table 1) and influent flow rates of 0.44 I/min and 0.90 I/min (with corresponding influent flow velocities of 5.6 and 11.4 m/min). The mean residence time (T c) of tracer element (the same with water element) within tank, the variance about the mean (σ2) and the dispersion number (the degree ofaxial dispersion or mixing, 0 /ul) could be calculated by the following equations (Watten and Johnson, 1990). Dispersion number was calculated by try and error method. Jn(Cmin-Ct)dt T c =..::...-'! 川 (1 ) f:!. C max 9 2J 圳 Cmin-Ct)d J_ \') σ~ "'U-'-IIIIII -lf-'- -(T c ) 已 (2) - ~max σ2 /T c 2=2(O/uL)-2(O/uL)2[1-exp-uL!D] (3) Where Cmin = Tracer concentration in influent following step down; o = Oispersion coefficient; O/uL = Tank dispersion number, dimensionless; L = Characteristic length; f:!. Cmax = Maximum change (negative) in tracer concentration, and u = Fluid velocity. The theoretical hydraulic retention time (T) of water element in tank is equal to the tank volume (V) divided by the flow rate of influent (Q). If the mean residence time determined by tracer study (T c) is smaller than T, then there is some dead zone existed in culture tank (Levenspiel, 1985, 1999). The extent of these regions expressed as a fraction of the tank's total liquid volume (f d ) is equal to one minus the quotient of Tc/T. Sometime, there are noise existed in experiment to cause the mean res idence time greater than theoretical hydraulic retention time. For example, the longer the tube connected the effluent port and spectrophotometer the more time delay would be and had a greater calculated mean residence time. The degree of axial dispersion, or mixing within a tank is characterized by the dimensionless group O/uL. The tank dispersion number (O/uL), ranges in value from zero for ideal plug flow to infinity (V) for completely mixed flow tank. IV. Dimensional analysis The flow system in aquacultural tank is rectilinear and its equation could be expressed as following (Raghuna 酬, 1967): f (d, 0, u, f:!. p, T, 戶, μ, 'Y, κ, σ, Pv)=O (4)

4 164 Kuo-Feng Tseng, Chyng-Hwa Liou and Jea-Gwan Lai Where d and D are the linear dimensions defining the boundary geometry water depth, and side length or diameter; u,!l p, T, (velocity, pressure gradient and shear respectively) are the variables describing the flow; and p, μ, "'1, κ, σ, pv (density, viscosity, specific weight, elasticity, surface tension and vapor pressure respectively) are the fluid properties. In equation (4) there are 11 variables and involve 3 fundamental dimensions M-L -T. From the π-theorem, the variables can be grouped into (11-3) or 8 dimensionless parameters. Taking d, u, p as the 3 repeat 司 ing variables and one at a time from the remaining variables and get dimensionless parameters as described by Raghunath (1967). The equation (4) is finally transformed to the form: 拉 (d/d, pu 2 /!l p, pu 2 / T, dup/μ, pu 2 /d"'l, pu 2 /κ, d pu 2 /σ, pu 2 /pv) = 0 (5) For a model to predict the true performance of the prototype, the two flows should be mechanically similar. Mechanical similarity implies: (i) Geometric (d/d) similarity, (ii) Kinematic similarity and (iii) Dynamic similarity. Among these three conditions, geometric similarity was done in practice in other size tank and got some good similar result in our other experiment. But the kinematic and dynamic similarity were not precise to appl y in aquacultural tank design, though the same hydraulic retention time seemed to be an correct parameter for scaling-up of tank. The :< O 2 effect of influent flow velocity may be considered to be expressed by Reynold number (du p / μ). Thus we suggest that geometric (d/d) similarity and kinematic and dynamic similarity parameter Reynold number (du p / μ) to be the control parameters for aquacultural tank design. RESUL TS AND DISCUSSIONS 1. Flow Pattern in Circular Tanks Fi g. 2. shows the tyþical response of a circular tank. The data were used to calculate T o 'σ2 and D/uL by using equations (1), (2) and (3), where Cmin was zero and!l C max was Co. Table 2 shows the practical hydraulic retention time (the mean residence time calculated, To), the dead zone fraction (fd) and the dispersion number for circular tanks with low influent flow rate. It indicates that influent port B always has smallest dead zone fraction. The value of D/uL indicates the extent of mixing in culture tank. Influent at S had better extent of mixing than at M or B when d/d was 1/1 and 1/3. But the tanks with d/d of 1/2 showed opposite results. However,. the dispersion numbers for circular tanks with influent flow velocity of 5.6 m/min were all we ll mixed. The extent of mixing increases with decreasing d/d ratio at the same influent port. Among the eight tests for circular tanks with infl uent flow velocity 5.6 m/mi 的, the tank with d/d of 1/3 had the least dead volume and the best mixing. At high influent flow velocity (11.4 m/ Duration time/theoretical retention tim 巴 (t/t) Fig. 2. The tracer concentration (expressed by absorbance of tracer, Abs.) of the effluent in a circular tank with d/o of 1/1, influent port B and at 5.6 m/min influent flow velocity.

5 Effects of Tank Configuration on Flow Pattern of a Recirculating Aquacultural Tank 165 Table 2. The theoretical hydraulic retention time (T), practical hydraulic retention time (Tc), volume fraction of dead zone (fd) and dispersion number (0/ ul) of circular tank with various water depth/ diameter (d/o) ratios, locations of influent port (8, M, B) and at 5.6 m/min influent flow velocity d/o Influent port T(min) T c (rnin) ( 士 SE) T)T( 士 SE) fd O/uL S 士 士 M 23.3 土 士 B 25.1 土 士 0.01 O /2 S :!: 士 M 23.2 土 :!: B 24.2 士 :!: /3 S 土 :!: B 25.9 土 :!: 0.01 O Table 3. The theoretical hydraulic retention time (T), practical hydraulic retention time (Tc)' volume fraction of dead zone (f d ) and dispersion number (0/ ul) of circular tank with various d/o ratios, influent ports (8, M, B) and at 11.4 m/min influent flow velocity d/o Influent port T(min) T c (min) ( 士 SE) T)T (:!:SE) f d O/uL S 士 土 M 10.9:!: 士 C 自 B 士 土 /2 S 土 士 M (i 可 11.4 士 土 C 自 B 11.8 士 士 DO 1/3 S 12.5 B 于 min), the dead zone fraction (f d ) was shown in Table 3. It indicated that tanks with influent port B was the smallest regardless the d/o values. Oispersion numbers (0/ ul) of tanks were very large and showed that all tanks have high degree of water mixing. 11. Flow Type in Square Tank A typical tracer concentration variation in the effluent of a square tank is shown in Fig. 3. The fd values were zero, that is, no dead zone within tank, for all tanks with low influent flow velocity (Table 4). AII the square tanks have high degree of water mixing. There were no dead zone existed (fd = 0) in all square tanks at high influent 12.0:!: :!: 士 :!: DO flow (Table 5). The dispersion numbers were also high, which indicated a high degree of mixing The Effect of Influent Flow Velocity n Water Mixing and Dead Zone Fraction of Tank When the influent flow velocity increased from 5.6 m/min to 11.4 m/min, the dispersion number of circular tank increased except the tank with d/o of 1/1 and influent port 8. Almost all circular tanks had a completely mixed flow type. The dead zone fraction increased with increase of the influent flow velocity, except tanks with d/o of 1/2 and influent port of 8 and M. When the influent flow

6 166 Kuo-Feng Tseng, Chyng-Hwa Liou and Jea-Gwan Lai 還 O I Test time/theoretica1 Retention Time (tlt) Fig. 3. The concentration of tracer (expressed by absorbance of tracer, Abs.) in the effluent of a square tank with d/o of 1/1 and influent port B at 5.6 m/min flow velocity Table 4. The theoretical hydraulic retention time (T), practical hydraulic retention time (Tc)' volume fraction of dead zone (f d ) and dispersion number (0/ ul) of square tank with various (d/o) ratio, influent ports (S, M, B) at 5.6 m/min influent flow velocity d/o Influent port T(min) T c (min) ( 士 SE) Tc/T ( 土 SE) f d O/uL S 士 土 0.01 O M 26.5 士 土 0.01 O B 26.9 士 土 0.01 O /2 S :!: :!: 0.01 O M 25.4:!: 士 0.01 O B 25.0 士 士 0.00 O /3 S 土 士 0.02 O t 自 26.7 土 0.1 t 1.07 士 0.01 O a Table 5. The theoretical hydraulic retention time (T), practical hydraulic retention time (Tcl, volume fraction of dead zone (f d ) and dispersion number (0/ LmJL/ )of squa e tanks wlth various d/d ratio, influent port(s, M, B)at 114 min influent flow velocity d/o Influent port T (min) T c (min) ( 士 SE) T)T( 士 SE) fd O/uL S 士 :!: 0.01 O M 13.0 士 :!: 0.01 O B 13.0:!: :!: 0.01 O /2 S :!: :!: 0.01 O 00 M 12.8 士 士 0.00 O B 12.7 士 :!: 0.00 O /3 S :!: 士 0.00 O B 12.6 土 士 0.00 O

7 Effects of Tank Configuration on Flow Pattern of a Recirculating Aquacultural Tank 167 velocity at the influent port doubles, the Reynold number doubles, too. But in the points other than the influent port, the Reynold number or flow velocity may not double. The degree of water mixing in square tanks at high influent flow velocity (11.4 m/ min) were better than those tanks with low velocity (5.6 m/min). This may be due to that in a square tank the flow and secondary flow velocity (or Reynold number) increases with the increasing velocity at influent port. IV. The Effects of d/d, Location of Influent Ports and Influent Flow Velocity on Flow Type of Tank (可怕)口 The dead zone fraction of the circular tanks with high influent flow velocity (CH) decreased when the tank d/d ratio changed from 1/1 to 1/2 and 1/3 (Fig. 4) AU...,,) -A 叫N抖H M吋咱U白晶 因 AV nυau 1S 1M B c The tanks with high influent flow rate (H) generally have a greater value of D/uL, that is, the higher degree of mixing. At higher flow rate (CH, SH), most of the circular tanks (CH) had a higher degree of water mixing than square tanks (SH). When tanks operated with low flow rates, the circular tanks had a. slightly higher degree of water mixing than the square tanks. After the beginning of experiment, we can observe the secondary flow as indicated by tracer stream. In the latter, most of the tracer was diluted out of tank and only some tracer remained in the dead zone. Fig. 6 showed the dead zone located at the center of tank. Base on visual observation, we found that the flow type in circular tank could be divided into three parts (1) rapid discharge zone: a vortex flow located at center of tank; (2) dead zone (Iow mixing): surrounding the M抽2mv 站wmnu 2B nu n 一 --CL --f!r- CH Fig. 4. The dead zone fraction (fd) of circular (C) tanks at high (H) and low (L) influent flow rates, with various con figurati ons of d/o values (1:1/1; 2:1/2; 3:1/3) and layout of influent ports (S, M and B) 3S 3B 35 53O ê 25 出 20 ø 15 <!) 會 10 口 5 O 1S 1M lb 2S 2M 2B Configuration 3S 3B 一 -CL --CH 一口 -SL --o- SH Fig. 5. The dispersion nurnber (O/uL) of circular (C) and square (S) tanks at high (H) and low (L) influent flow rates, with various configurations of d/o values (1: 1/1; 2:1/2; 3:1/3) and layout of influent ports (S, M and B)

8 168 Kuo-Feng Tseng, Chyng-Hwa Liou and Jea-Gwan Lai Fig. 6. The dead zone (in center) of a circular tank with d/d of 1:1, influent port at bottom and influent flow velocity of 11.4 m/min. center of tank, like a hollow pipe perpendicular to the bottom of tank; and (3) complete mixing zone: located outside of the dead zone. As it was seen in tracer experimentation, the influent water from influent port B flowed into tank counter clock 月 wise along tank wall and at the same time flowed upward to water surface (the secondary flow). The stream then focussed to the centerline of tank and rapidly moved downward as a counterclockwise vortex rapidly to discharge through the effluent port. The dead zone area found in circular tank was different from that reported by Larmoyeux et al. (1973) This may be caused by the different design of effluent port. Watten and Johnson (1990) reported that the cross-flow tank and plug flow tank had dead zone fractions of 0.14 and 0.09 and dispersion numbers and 0.33, respectively. This indicated that the crossflow tank had a flow type of complete mixing and the plug flow tank had axial mlxlng. Burley and Klapsis (1985) studied the flow type of a square tank (1 m wide) with various water depths (10, 15 and 25 cm) and influent flow rates (8, 10, 12, 14 I/min) and showed that all the tanks, except tanks with 10 cm water depth (d/d = 1/10), had dead zone. The dead zone fraction increased with the increasing water depth (also the d/d value) at the same flow rate and water volume in the tank. In this study, the square tanks had no dead zone and good water mixing. This may be caused by the continuously dispersion of flow with surrounding water when the main stream of influent water flow along side wall and take turning at corner of tank. During experiment, there is no significant high concentration zone of tracer found V. Flow model As suggested by Levenspiel (1999), dispersion model deals primarily with small deviations from plug flow. The results of this experiment may be like a continuously stirred tank reactor and thus similar to an ideal mixing model. For an ideal completely mixed flow, the concentration of tracer in effluent of tank at time t decreased from C o to C t and they could be expressed

9 Effects of Tank Configuration on Flow Pattern of a Recirculating Aquacultural Tank 169 as In (C t - C o ) = HRT (t), HRT the hydraulic retention time. The experiment value of HRT was calculated in this study and their value had compared with the theoretical value. Although the deviation extent of flow from completely mixed flow pattern can be hinted by the variation of RTD curve, but they are not critical. We can not compare the extent of flow mixing between square tank and circular tank from the variation of RTD. Thus we need a more critical parameter. In general, the flow velocity in an aquaculture tank should not be so quickly as in a chemical reactor or a hydraulic construction. The high 國 speed mixer would not be used in aquacultural tank to mix water. The water mixing was done by the influent impulse and the suction force of effluent. A poor design of tank would have dead zone and significant water quality gradient (plug flow). In contrast, in a vigorously turbulent flow, fish can not get its position and direction and would be harmed. Thus the flow pattern suitable for aquacultural tank would be plug flow with highly dispersion. The water is mixed well but the flow velocity is not too high. In practice, in operation of another experimental aquaculture tank we found homogeneous water quality existed in tank with dispersion number greater than 0.2, though it was not a critical boundary. Thus we suggested that the suggestion of a dispersion number 0.2 by Levenspiel (19 72) could be accepted as good water mixing in aquacultural tank. Really, the optimal flow pattem for various cultured organisms and the model to analyze the flow pattern need more studies. CONCLUSIONS From the results of this study, we get the following conclusions: 1. AII the tested tanks have high degree of water mixing and almost have a completely mixed flow type. The tanks with high influent flow velocity have higher degree of water mixing than those tanks with low flow velocity. 2. According to the criteria of minimum dead zone fraction and maximum water mixing, square tanks with high flow velocity were the best choice and square tanks with low flow velocity were the secondary choice among the tested tanks. ACKNOWLEDGEMENTS The authors would like to thank Council of Agriculture, Taiwan, Republic of China for part of the grant supporting. Authors also thank to Dr. Chian, Chi-Min of Hydraulic Research Center in Tainan for his help on calculation of dispersion number. REFERENCES Burley, R. and A. Klapsis (1985). Flow distribution studies in fish rearing tanks. Part 2 > Analysis of hydraulic perforrnance of 1-m square tanks. Aqυacult. Eng., 8: Fogler, H. S. (1986). Elements of chernical reaction engineering. Prentice-Hall, Inc., Englewood Cliffs, New Jersey, 639pp. Klapsis, A. and R. Burley (1984). Flow distribution studies in fish rearing tanks. Part 1-Design constraints. Aqυacult. Eng., 3: Krise, W. F. and J. W. Meade (19 86). Review of the intensive culture of walleye fry. Prog. Fish 司 CuJt., 48: Larmoyeux, J. D., R. G. Piper and H. H. Chenoweth (1973). Evaluation of circular tanks for salmonid production. Prog. Fish-Cult., 35: Leon, K. A. (19 86). Effect of exercise on feed consumption, growth, food conversion, and stamina of brook trout. Prog. Fish-CuJt., 48: Levenspiel, O. (1972) 回 Chemica l Reaction Engineering. John Wiley and Sons Inc., New York. Levenspiel, O. (1985). Cornment on mean re 刮目 dence time in flow systems. Chem. Eng. Sci., 40: Levenspiel, O. (1999). Chemical Reaction Engineering. Third edition, John Wiley and Sons Inc., New York, pp Meade, J. W. (1985). Allowable amrnonia for fish culture. Prog. Fish-Cult., 47: Raghunath H. M. (1967). Dimensional analysis and hydraulic model testing. Asia Publishing House, Bombay, India Ross, R. M., B. J. Watten, W. F. Krise, M. N. DiLauro and R. W. Soderberg (1995)φInfluence of tank design and hydraulic loading on the behavior, growth, and metabolism of rainbow trout. Aquacult. Eng., 14: Timmons, M. B 且, S. T. Summerfelt and B. J. Vinci (1998). Review of circular tank technology and management. Aquacult. Eng., 18: 5 干 69

10 170 Kuo-Feng Tseng, Chyng-Hwa Liou and Jea-Gwan Lai Totland, G. K., H. Kryvi, K. A. Jodestol, E. N. Christiansen, A. Tangeras and E. Slinde (1987) Growth and composition of the swimming muscle of adult Atlantic salmon (Salmo sa/ar L.) during long-term sustained swimming Aquaculture, 66: Watten, B. J. and L.T. Beck (1987). Comparative hydraulics of a rectangular cross 寸 low rearing unit. Aquacult. Eng., 6: Watten, B. J. and R. P. Johnson (1990). Comparative hydraulics and rearing trial performance of a production scale cross-flow unit. Aquacult. Eng., 9: Weste 悶, H. and K. Pratt (1977). Rational design of hatcheries for intensive salmonid culture, based on metabolic characteristics. Prog. Fish-Cult., 39: 循環水養殖槽之組態對槽中水流型態之影響 會團鋒 *.室 1] 擎華.賴王王光 循環水養殖槽中之水流型態很重要, 理想之水流型態為無 ; 帶流區之完全混合式 7)\ 流 合高濃度 ; 容氧之進流水由進水口流入槽中, 以供應養殖生物氧氣, 並將槽 7)\ 交換及排出槽外, 以排除槽內廢物, 此種水交換之效率, 受養殖槽型態及其進 出水口配置之影響 本研究, 利用追蹤劑法, 淇 1] 定槽中水分子停留時間分佈 (residence time distribution RTD) 情形, 以探知槽中之水流型態 試驗之養殖槽有圓形及方形圓弧角兩種型態, 同時測試三種水深與槽直徑 ( 或水深與槽邊長 ) 比例 (d/d = 1:1 1:2 及 1: 3) 配置 三種進水口位置 (7)\ 面 (8) 中間木深 (M) 或槽底部 (8)) 設計及兩種操作進流水量時, 槽內之水流型態 由試驗所得 RTD 數據, 計算槽內 7)\ 流混合程度及槽內是否有水流交換不佳之滯流區 (dead zone) 存在 研究結果顯示, 所試驗各種配置之方形水槽, 在兩種水流操作條件下, 當無 ; 帶流直存在, 槽中水 ; 而混合良好 ; 但圓形槽貝 Ij 有滯流區存在, 惟槽中其他區域之 7)\ 流則仍混合良好 關鍵詞. 循環水養殖系統, 養殖槽組態, 水流混合, 水流型態 國立台灣海洋大學水產養殖學系