What is the purpose of this article? This article explores the speed, viscosity and density conditions under which the Type-SR sensors (SRV and SRD sensors) operate safely
What products are involved?
SRV - Inline Viscosity Meter, SRD - Inline Density and Viscosity meter, and installation accessoriesTABLE OF CONTENTS
- The effect of high viscosities or speeds on an inline viscometer and density meter
- Scenario 1: Viscometer and density meter installations for highly viscous fluids
- Scenario 2: Viscometer and density meter installations for high fluid speeds
- Noise-induced speed limits for viscometers and density meters
The effect of high viscosities or speeds on an inline viscometer and density meter
Whenever a body is exposed to the flow of a fluid it experiences a drag force, whose magnitude depends on the fluid’s behavior. The way fluid flow can be generally described is by using a dimensionless quantity known as the Reynolds Number (Re). This number helps us determine the flow regime (laminar or turbulent, a transitional regime is excluded in this analysis) given fluid characteristics. The flow regime is critical in determining which fluid characteristics will dominate the overall drag experienced by the body. In this way, the flow regime (Re value) allows us to determine the operational limits of the Rheonics SRV and SRD sensor probe’s sensing element before the force experienced exceeds its mechanical limits.
In this analysis, the operational limitations of Type-SR sensors (SRV and SRD sensors) will be evaluated against two scenarios. The first consists of highly viscous fluids flowing at low speeds (resulting in a low Re value or laminar flow) and the second comprises fluids of low viscosity flowing at high speeds (resulting in a high Re value or turbulent flow).
The analysis of Type-SR sensors has been conducted under regular perpendicular installations. This means that the SRV and SRD sensor probe’s sensing elements are installed perpendicular to the flow of fluid and that the SRD is properly oriented (see Figure 1). This setup allows us to extend the results to both inline and tank wall installations since the fluid flow in these cases is generally the same.
| Note: It is difficult to translate the rotational speed (RPM) of a mixing vessel to a linear speed (m/s) since the velocity gradient of the fluid varies across the tank's radius and depends on other factors such as the impeller type, vessel shape, and many more. For this reason, Rheonics recommends empirically measuring the actual tank wall speed with appropriate instrumentation in order to make use of the information presented in this article. |
Note: The fluids explored in this article are considered to be solid-free, meaning that they do not contain any suspended particles or debris that could collide with the sensing element. In this way, the data presented is only valid for fluids without solid particles. If your fluid contains suspended particles or debris that you suspect could harm the sensing element, please contact Rheonics Support for evaluation. |
Scenario 1: Viscometer and density meter installations for highly viscous fluids
Highly viscous fluids tend to flow laminarly at low speeds. Here the drag forces are caused mainly by the skin friction drag of the fluid with the sensing element. The sensing element is rated to withstand a maximum torque of 2 Nm before the possibility of deformation.
The plot below shows the dynamic viscosities (in Pa.s) under which the respective Type-SR sensor operates safely.
Note: The maximum viscosity that a sensor probe is able to measure depends on the sensor configuration that is ordered. |
Scenario 2: Viscometer and density meter installations for high fluid speeds
When fluids flow at high speeds, the drag forces caused against a body are mainly due to the pressure of the moving fluid. High speeds can be achieved by low-viscosity fluids and create a drag force that is determined by the fluid density and speed.
The plot below shows the velocities (in m/s) under which the respective Type-SR sensor operates safely.
Figure 3: Plot showing fluid density on the X-axis and maximum allowed velocity on the Y-axis for the SRV and SRD.
Noise-induced speed limits for viscometers and density meters
When dealing with high-speed applications an additional limitation exists. The Type-SR sensors begin to experience noise pickup at high speeds:
12 m/s for the SRV
10 m/s for the SRD
While the noise present at these speeds can be filtered out, an increase in speeds above these values will correspond to an increase in noise, therefore using the Type-SR sensor probes beyond these speeds is not recommended. Below are two tables showing these limits for various pipe sizes and alternative units.
Table 1: Flow conditions necessary to exceed the noise limit conditions for the SRV for various pipe sizes.
| Pipe | STD ID | Max velocity | Max. volumetric flow | Max. mass flow* | BPD | |||||
| Nom. | DN | In. | mm | ft/s | m/s | gal/min | L/min | lb/h | kg/h | bbl/d |
| 2" | 50 | 2.01 | 52.48 | 39.4 | 12 | 441.4 | 1 557.4 | 206 012 | 93 446 | 14 106 |
| 2-1/2" | 65 | 2.47 | 62.69 | 587.1 | 2 222.4 | 293 968 | 133 343 | 20 129 | ||
| 3" | 80 | 3.07 | 77.93 | 907.2 | 3 434.2 | 454 269 | 206 055 | 31 105 | ||
| 3-1/2" | 90 | 3.55 | 90.12 | 1 213.3 | 4 592.7 | 607 500 | 275 560 | 41 597 | ||
| 4" | 100 | 4.03 | 100.26 | 1 562.1 | 5 913.4 | 782 169 | 354 801 | 53 559 | ||
| 5" | 125 | 5.05 | 128.19 | 2 454.8 | 9 292.5 | 1 229 171 | 557 548 | 84 165 | ||
*Mass flow was calculated with a density of 62.4 lb/ft3 and 1000 kg/m3
Table 2: Flow conditions necessary to exceed the noise limit conditions for the SRD for various pipe sizes.
| Pipe | STD ID | Max velocity | Max. volumetric flow | Max. mass flow* | BPD | |||||
| Nom. | DN | In. | mm | ft/s | m/s | gal/min | L/min | lb/h | kg/h | bbl/d |
| 2" | 50 | 2.01 | 52.48 | 32.8 | 10 | 342.9 | 1 297.9 | 171 676 | 77 872 | 11 755 |
| 2-1/2" | 65 | 2.47 | 62.69 | 489.2 | 1 852 | 244 974 | 111 119 | 16 774 | ||
| 3" | 80 | 3.07 | 77.93 | 756 | 2 861.9 | 378 558 | 171 712 | 25 921 | ||
| 3-1/2" | 90 | 3.55 | 90.12 | 1 011 | 3 827.2 | 506 250 | 229 633 | 34 664 | ||
| 4" | 100 | 4.03 | 100.26 | 1 301.8 | 4 972.8 | 651 830 | 295 668 | 44 633 | ||
| 5" | 125 | 5.05 | 128.19 | 2 045.7 | 7 743.7 | 1 024 309 | 464 632 | 70 137 | ||
*Mass flow was calculated with a density of 62.4 lb/ft3 and 1000 kg/m3