A device and method for accurately calculating floc strength under laminar flow conditions

Abstract

A device for accurately calculating floc strength under laminar flow conditions, comprising an inner cylinder and an outer cylinder arranged coaxially; a gap b is provided between the inner cylinder and the outer cylinder; the outer cylinder is connected to a horizontal base in the form of a flange through the outer cylinder base; a screw is installed in the center of the inner cylinder, one end of the screw is installed on the outer cylinder base through a bearing, and the other end of the screw is connected to a motor transmission, and the motor is installed on the horizontal base through a motor fixing bracket; the motor is connected to a motor controller through a cable. The method for calculating floc strength is mainly based on the principle that under laminar flow conditions, when the viscous shear force F of the fluid is equivalent to the viscous force B of the floc, the floc will be destroyed, and the shear force on the floc is calculated by Newton's law of internal friction to obtain the floc strength. The invention has a simple testing method and a relatively accurate calculation result, and can be used to quantitatively test the floc strength.

Description

Technical Field

[0001] The invention belongs to the technical field of environmental protection, and specifically relates to a device and a method for accurately calculating the strength of flocs. Background Art

[0002] Coagulation is a common process in water treatment, mainly used to remove colloids and some turbid particles in water. At present, the evaluation indicators for coagulation effect include effluent water quality and floc morphology evaluation indicators. Among them, the evaluation indicators of flocs are mainly concentrated on the evaluation of parameters such as particle size and fractal dimension, while there are few reports on the strength detection of flocs.

[0003] The floc strength test reported so far mainly relies on breaking the flocs under mechanical stirring conditions, and then analyzing the particle size of the flocs before and after breaking. The floc breaking factor and recovery factor are obtained based on the particle size ratio before and after breaking. This method is an indirect calculation based on the change of floc particle size, and does not directly characterize the floc strength at the microscopic level. Other literature reports that the capillary force is used to stretch and deform a single floc to destroy it, and the floc strength value is obtained by testing the capillary force. However, this method has a complex device and is only applicable to testing the strength of flocs with a particle size smaller than the capillary.

[0004] At present, Chinese patent application number 2014103365765 reports a method for testing and calculating floc cohesion by using the relationship between the cohesion between floc particles and the fractal dimension, which is also an indirect testing method.

[0005] Therefore, how to provide a more accurate direct test and evaluation method for floc strength has become a technical problem that needs to be solved urgently. Summary of the invention

[0006] The invention provides a device and method for accurately calculating the floc strength under laminar flow conditions, which utilizes the viscous shear force of the fluid to shear and destroy the floc, thereby obtaining the accurate value of the floc strength.

[0007] To achieve the above purpose, the technical solution adopted by the present invention is as follows:

[0008] A device for accurately calculating floc strength under laminar flow conditions comprises an inner cylinder and an outer cylinder arranged coaxially; a gap b is provided between the inner cylinder and the outer cylinder; the outer cylinder is connected to a horizontal base in the form of a flange via the outer cylinder base; a screw is installed in the center of the inner cylinder, one end of the screw is installed on the outer cylinder base via a bearing, and the other end of the screw is connected to a motor in transmission, and the motor is installed on the horizontal base via a motor fixing bracket; the motor is connected to a motor controller via a cable.

[0009] The inner cylinder is a solid structure.

[0010] A leveling knob and a level bubble are installed on the horizontal base.

[0011] The gap b between the inner cylinder and the outer cylinder is 5 mm; the diameter of the inner cylinder is 30-40 mm, and the diameter of the outer cylinder is 40-50 mm; the rotation speed of the inner cylinder is 35-80 r / min.

[0012] A method for accurately calculating floc strength under laminar flow conditions is specifically carried out in the following steps:

[0013] Step 1: When calculating the floc strength, define the viscous force inside the floc as B; when the inner cylinder rotates and the outer cylinder remains stationary, the fluid in the gap between the inner and outer cylinders rotates with the inner cylinder; the fluid rotates under laminar flow conditions and generates shear force. When the fluid shear force F on the flocs in the gap between the inner and outer cylinders is less than the viscous force B inside the flocs, the flocs move synchronously with the fluid in the gap and will not break;

[0014] When the critical value F ≥ B is reached, the flocs will break;

[0015] According to Newton's law of internal friction under laminar flow conditions Calculate the shear stress of the fluid in the gap, where is the kinematic viscosity of water, du is the centerline velocity, denoted as v; dy is the thickness of the gap between the inner and outer cylinders, denoted as b;

[0016] Step 2: The shear force F exerted on the flocs by the water flow is proportional to the projected area A of the flocs; the shear force is , where μ is the dynamic viscosity of water;

[0017] Step 3: When the outer cylinder is stationary and the inner cylinder is driven by the motor to rotate, its speed n can be known; according to the formula The linear velocity v at the center can be obtained, where D is the diameter of the central area;

[0018] Step 4: The projected area A of the floc particles can be calculated by image analysis software;

[0019] Step 5: Just keep adjusting the rotation speed of the inner drum to increase the shear force on the floc surface until the floc breaks. Record the inner drum rotation speed n at this time to calculate the shear force F of the floc. Since B=F, the precise value of the floc viscosity, i.e., the floc strength, can be obtained.

[0020] The present invention can directly and accurately calculate the floc strength. Meanwhile, the testing device is simple and portable, and does not require the coordination of large, complex, and precise instruments. During the testing process, the floc bonding strength can be calculated by simply adjusting the rotation speed of the inner drum. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the drawings required for describing the embodiments are briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative work.

[0022] Figure 1 It is a structural schematic diagram of the present invention;

[0023] Figure 2 for Figure 1 A schematic diagram of the main view;

[0024] Among them, 1-inner cylinder; 2-outer cylinder; 3-outer cylinder base; 4-bearing; 5-screw; 6-motor; 7-cable; 8-motor controller; 9-horizontal base; 10-leveling knob; 11-level bubble; 12-motor fixing bracket. DETAILED DESCRIPTION

[0025] The present invention is described in detail below in conjunction with specific embodiments. The following embodiments will help those skilled in the art to further understand the present invention, but are not intended to limit the present invention in any form. It should be noted that, for those of ordinary skill in the art, without departing from the concept of the present invention, several variations and improvements can also be made, which all belong to the protection scope of the present invention.

[0026] like Figure 1 As shown, a device for accurately calculating floc strength under laminar flow conditions comprises an inner cylinder 1 and an outer cylinder 2 arranged coaxially, with a gap b between the inner cylinder 1 and the outer cylinder 2; the outer cylinder 2 is connected to a horizontal base 9 in the form of a flange through an outer cylinder base 3; a screw 5 is installed in the center of the inner cylinder 1, and the screw 5 is installed on the outer cylinder base 3 through a bearing 4, and the other end of the screw 5 is connected to a motor 6 in a transmission manner, and the motor 6 is installed on the horizontal base 9 through a motor fixing bracket 12 (the motor 6 is connected to the fixing bracket 12 through bolts, and the base of the fixing bracket 12 is installed on the horizontal base 9). The motor 6 is connected to a motor controller 8 through a cable 7.

[0027] The motor 6 is connected by a motor fixing bracket 12, a screw rod 5 and a bearing 4 in a simply supported structure, so that the upper and lower ends of the screw rod 5 are fixed at the same time to ensure concentricity and prevent eccentric vibration caused by excessive rotation speed of the inner cylinder.

[0028] The inner cylinder 1 is a solid structure. The inner cylinder adopts a solid structure mainly to allow the screw 5 to completely penetrate to form a simply supported structure. Considering the convenience of processing, a solid cylinder is used here instead of a hollow cylinder.

[0029] The horizontal base 9 is provided with a leveling knob 10 and a level bubble 11. The concentricity of the inner and outer cylinders is ensured to ensure laminar flow conditions.

[0030] The entire process of calculating flocs needs to be controlled under laminar flow conditions. The theoretical value of Reynolds number under laminar flow is 0~2300. To ensure the stability of laminar flow conditions and the accuracy of floc strength calculation, the Reynolds number should be controlled below 1500 to ensure the laminar flow conditions of the fluid. To avoid capillary phenomena and ensure the integrity of flocs, the gap b between the inner cylinder 1 and the outer cylinder 2, that is, the flow layer spacing b, should be 5mm, the inner cylinder diameter should be 30-40mm, the outer cylinder diameter should be 40-50mm, and the inner cylinder speed should be 35-80r / min.

[0031] A method for accurately calculating floc strength under laminar flow conditions is specifically carried out in the following steps:

[0032] When the floc analysis test is started, the motor 6 is turned on, and the inner cylinder 1 is rotated driven by the screw 5. The initial speed of the inner cylinder is preferably 30-40r / min, that is, the floc sample in the test area is rotated to a suspended state.

[0033] Furthermore, the speed of the inner drum is gradually increased, and the running time under each speed condition is preferably between 2-3 minutes. The destruction of the floc particles is observed at each speed. When the flocs are obviously destroyed at a certain speed, the speed of the inner drum n1 is recorded. The speed of the inner drum is preferably stabilized at 35-80r / min.

[0034] Furthermore, it is known that the inner diameter of the outer cylinder is The outer diameter of the inner cylinder is , the flow layer spacing ; The center line speed of the floc strength test area is , where D is the diameter of the central area D = inner cylinder diameter + flow layer spacing = .

[0035] Furthermore, according to Newton's internal friction theorem under laminar flow conditions Calculate the shear stress. Substitute the centerline velocity v of the floc strength test area into , where μ is the kinematic viscosity of water at a pressure of 101.325 kPa and a temperature of 20°C. The floc area A can be obtained by image analysis software, such as ImageProPlus, Batteau image analysis software, Digimizer and other image analysis software.

[0036] Furthermore, when the fluid shear force F≤ on the floccules reaches a balance with the viscosity force B inside the particles, the particles will reach critical damage, and when F≥B, the floccules will break. Therefore, it is only necessary to continuously adjust the rotation speed of the inner cylinder to increase the traction force on the particle surface until the particles break. At this time, the viscosity force B of the particles can be calculated, and the strength of the floccules can be quantitatively described and analyzed.

[0037] The whole process of calculating flocs needs to be controlled under laminar flow conditions. The theoretical value of Reynolds number under laminar flow is 0~2300. In order to ensure the stability of laminar flow control and the accuracy of floc strength calculation, this example controls the Reynolds number within 1500 and uses the liquid layer Reynolds number conduct check, Where R is the hydraulic radius of the liquid layer.

[0038] Verification method (refer to Reynolds test):

[0039] (1) Fill the gap between the inner and outer cylinders with deionized water, adjust the motor to 35-80r / min, such as 65r / min, and the inner cylinder starts to rotate at 65r / min.

[0040] (2) Pipette 2 ml of red liquid into a 2 ml glass pipette, insert the glass pipette into the deionized water in the gap between the inner and outer tubes, slowly release the liquid in the pipette into the deionized water, and observe the streamlines formed by the colored liquid. If obvious red lines are formed, it indicates that the fluid is in a laminar flow state.

[0041] Furthermore, when the inner cylinder rotates, the fluid in the liquid layer rotates horizontally, and the cross section through which the fluid passes is rectangular, then the hydraulic radius of the liquid layer is ,in is the wetted perimeter, and H is the height of the inner and outer cylinders.

[0042] The above calculation formula mainly provides a calculation method for the Reynolds number Re for the inner and outer cylinders, so as to calculate at which rotation speed the flow layer can maintain a laminar state under different sizes of inner and outer cylinders.

[0043] When the raw water turbidity is 500NTU, the stirring conditions are: 250rpm fast stirring for 30s, 80rpm medium stirring for 5min, 60rpm slow stirring for 15min, and 5mg / L, 10mg / L, 15mg / L, 20mg / L, 25mg / L, 30mg / L, 35mg / L, 40mg / L flocculants are added respectively to form flocs of different sizes. The flocs formed are placed in the device of the present invention respectively, and the floc strengths measured are: 2.22nN, 3.86nN, 6.48nN, 13.39nN, 19.01nN, 21.6nN, 17.10nN, 13.51nN. This data is close to the floc strength data reported in patent CN104075950.

[0044] The present invention can be used to calculate the floc strength formed under different coagulation conditions and different coagulation modes, can effectively and accurately evaluate the density of the floc, and can also calculate and predict the dynamic change of the floc.

[0045] The content of the present invention described above is not limited to the embodiments listed, and those skilled in the art can read the specification of the present invention and make any equivalent changes to the technical solution of the present invention, which are covered by the claims of the present invention.

Claims

1. A method for accurately calculating floc strength under laminar flow conditions, characterized in that: A device for accurately calculating floc strength under laminar flow conditions is used, comprising an inner cylinder (1) and an outer cylinder (2) arranged coaxially; a gap b is provided between the inner cylinder (1) and the outer cylinder (2); the outer cylinder (2) is connected to a horizontal base (9) in the form of a flange via an outer cylinder base (3); a screw (5) is installed in the center of the inner cylinder (1); one end of the screw (5) is installed on the outer cylinder base (3) via a bearing (4); the other end of the screw (5) is connected to a motor (6) in a transmission manner; the motor (6) is installed on the horizontal base (9) via a motor fixing bracket (12); the motor (6) is connected to a motor controller (8) via a cable (7); the specific steps are as follows: Step 1: When calculating the floc strength, define the viscous force inside the floc as B; when the inner cylinder rotates and the outer cylinder remains stationary, the fluid in the gap between the inner and outer cylinders rotates with the inner cylinder; the fluid rotates under laminar flow conditions and generates shear force. When the fluid shear force F on the flocs in the gap between the inner and outer cylinders is less than the viscous force B inside the flocs, the flocs move synchronously with the fluid in the gap and will not break; When the critical value F ≥ B is reached, the flocs will break; According to Newton's law of internal friction under laminar flow conditions Calculate the shear stress of the fluid in the gap, where μ is the dynamic viscosity of water, du is the centerline velocity, denoted as v; dy is the thickness of the gap between the inner and outer cylinders, denoted as b; Step 2: The shear force F exerted on the flocs by the water flow is proportional to the projected area A of the flocs; the shear force is , where μ is the dynamic viscosity of water; Step 3: When the outer cylinder is stationary and the inner cylinder is driven by the motor to rotate, its speed n can be known; according to the formula The linear velocity v at the center can be obtained, where D is the diameter of the central area; Step 4: The projected area A of the floc particles can be calculated by image analysis software; Step 5: Just keep adjusting the rotation speed of the inner drum to increase the shear force on the floc surface until the floc breaks. Record the inner drum rotation speed n at this time to calculate the shear force F of the floc. Since B=F, the precise value of the floc viscosity, i.e., the floc strength, can be obtained.

2. The method for accurately calculating floc strength under laminar flow conditions according to claim 1, characterized in that: The inner cylinder (1) is a solid structure.

3. The method for accurately calculating floc strength under laminar flow conditions according to claim 1, characterized in that: The horizontal base (9) is provided with a leveling knob (10) and a level bubble (11).

4. The method for accurately calculating floc strength under laminar flow conditions according to claim 1, characterized in that: The gap b between the inner cylinder (1) and the outer cylinder (2) is 5 mm; the diameter of the inner cylinder (1) is 30-40 mm, and the diameter of the outer cylinder (2) is 40-50 mm; the rotation speed of the inner cylinder (1) is 35-80 r / min.

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