Dairy Pipe Sizing & Reynolds Number

Pipe Duty, Product Quality and Cleaning

Specify product flow and cleaning flow separately. The same fixed pipe diameter may need to carry a viscous, shear-sensitive product during production and a much less viscous cleaning solution at a different flow rate. Select the pipe and pump duties together.

What Reynolds Number Tells You

For a Newtonian liquid in a circular pipe, Re = density × mean velocity × internal diameter / dynamic viscosity. It compares inertial and viscous effects. The familiar ranges below are useful for preliminary assessment; they do not certify product quality or cleanability.

Reynolds number	Screening interpretation
Below about 2,300	Usually laminar flow in a straight circular pipe.
About 2,300–4,000	Transition depends on disturbances and the installation.
Above about 4,000	Usually turbulent in a straight circular pipe; local conditions still matter.

For non-Newtonian products, an apparent viscosity is only a screening input. Use an appropriate rheological model or suitable operating trials for the final design.

CIP: Validate the Circuit, Not Just a Velocity

Mechanical action at the wall matters, but a turbulent Reynolds number alone does not prove soil or biofilm removal. Local expansions, contractions, valves and other geometry change the wall conditions. Research on stainless-steel equipment demonstrates that local shear and its variation affect removal, and that increasing bulk flow does not improve every geometry equally.

The calculator shows CIP flows at 1.5 m/s and 2.0 m/s as comparison cases. Establish the actual required duty from the approved cleaning process and equipment. There is no universal 3 Pa wall-shear threshold, or fixed multiple of production flow, that guarantees removal of every dairy soil or biofilm.

For the same pipe, flow is proportional to mean velocity. For example, a 50 mm internal-diameter pipe needs about 14,137 L/h to reach 2.0 m/s. If product velocity is 1.0 m/s, reaching 2.0 m/s requires twice the product flow; if production already runs at 2.0 m/s, it does not. Include the actual pressure losses and required return conditions.

Pumps, Bypasses and Cleaning Paths

Check whether each pump can accommodate the cleaning duty and whether the circuit reaches all required product-contact surfaces. A bypass may be appropriate where a product pump would restrict the cleaning flow, but it does not automatically clean the pump's own internal passages. Establish the intended valve sequence and validated cleaning route for the complete arrangement.

Pipe Sizing and Reynolds Calculator

Enter the actual internal diameters, flow and fluid properties. The results screen the stated cases; final selection also requires the complete hydraulic duty, product assessment and cleaning validation.

Calculation basis: cross-sectional area = πd²/4; mean velocity = volume flow / area; Re = ρvd/μ. Convert flow, diameter and viscosity to consistent units. The displayed product ranges and CIP cases are screening settings, not validated process limits. Use the site's approved operating requirements when interpreting the results.

Product Quality and Fluid Properties

Temperature, composition and processing history affect dairy-product viscosity. Pumping, air entrainment, agitation and local fittings can also affect product quality. Select the duty from the actual product and its required quality, rather than treating a single pipe-velocity limit as proof that the milk fat globule membrane is protected or damaged.

Measure viscosity at relevant temperature and shear conditions. For shear-thinning products, a single viscosity value cannot represent every part of the circuit. Verify the final design against suitable rheological data or operating trials.

Practical Design and Operating Checks

• Confirm the tube's internal diameter, material, condition, fittings and valve arrangement.
• Check production and CIP flows against the actual pump curve and full pressure losses.
• Verify flow, temperature, concentration and time at the relevant locations during cleaning.
• Investigate air pockets, poor drainage, inaccessible surfaces and recurring local failures.
• Use cleaning-verification and product-quality results to confirm performance after changes.

Frequently Asked Questions

Does turbulent flow prove that CIP is effective?

No. Reynolds number describes the flow regime. Cleaning also depends on local geometry, mechanical action, chemistry, concentration, temperature, time, soil and drainage. Validate the actual circuit and monitor its approved operating conditions.

What velocity should be used for CIP?

Establish the required velocity and flow from the circuit, equipment and validated cleaning process. The calculator displays 1.5 m/s and 2.0 m/s screening cases so the corresponding pump duties can be compared. They are not universal acceptance limits.

Must every positive-displacement pump have a CIP bypass?

No universal arrangement applies. Assess whether the pump and its drive can pass the required cleaning flow and whether all product-contact passages are cleaned. Where a bypass is used, the pump itself still needs a validated cleaning route. Follow the approved equipment and circuit design.

How should shear-sensitive dairy products be handled?

Assess the product, temperature, air entrainment, pump, fittings and operating history together. Mean pipe velocity alone does not establish fat-globule damage or product quality. Confirm the selected duty with suitable product trials and quality measurements.

Which diameter should be entered?

Use the actual internal diameter of the installed or proposed tube. Nominal sizes and outside diameters are not interchangeable with internal diameter. Include fittings, valves and equipment when checking the complete pressure-drop and pump duty.