CIP: Principles of Fluid Flow Dynamics

Introduction

The understanding of the basic fluid flow dynamics is important for an efficient cleaning during CIP of any food processing equipment like tanks and pipelines.  Fouling deposits will form during processing and also the storage, therefore the effective removal of all these deposits(soil), thereby leaving the surface free of chemical residues and micro-organisms, is essential for ensuring food safety and product quality.

Cleaning - In - Place (CIP) is all about contacting the cleaning solution and sanitizers with soiled food processing surfaces, and involves the pumping of the detergent across the surface.  Therefore it is important to understand the principles of fluid statics and fluid dynamics.  Fluid statics deals with fluids at rest,  while fluid dynamics deals with fluids in motion or which we refer to (Mechanical Action).

Background information

Pressure - is defined as force per unit area. The SI unit of pressure is the pascal (Pa), which is a very small unit, So for convenience, the bar is often used, where 1 bar = 1,000,000 Pa. One bar is approximately equal to 1 atmosphere. Also used are kilopascals (kPa) and megapascals (MPa), whereas the Imperial units are pounds per square inch (psi)

Temperature - is a very important property, because it will affect viscosity and alter reaction rates, which is important for chemical detergents.  Temperature can simple be defined as the degree of hotness, it determines the direction of heat transfer: energy is transferred from high to a low temperature, and the rate of heat transfer (J/sec or W) is proportional to the temperature difference.  Temperature control is important, and hotter is not always better. In this context , accurate temperature measurement and periodic calibration of thermometers are important.  Energy is required in cleaning operations to bring detergents to the required temperature.  

Volumetric Flowrate - is defined as unit volume per time. the SI unit of volumetric flowrate is cubic meter per sec (m3/sec) and this will play a major role in the cleaning process.  Not enough volumetric flowrate for a particular pipe line or vessel would mean insufficient cleaning.

   

Laminar and Turbulent Flow - When a fluid flows through a pipe, the flow is one of two possible types: Laminar (streamline) flow or turbulent flow.  For cleaning operations and efficient heat transfer, turbulent flow is usually required.  The type of flow can be distinguished by a dimensionless group known as the Reynolds number (Re): this represents the ratio of the internal forces to the viscous forces acting upon the liquid.  When inertial forces predominate, the flow is turbulent, and when viscous forces predominate, the flow is streamline (laminar).  If the Reynolds number is less than 2000, the flow is laminar; if it is greater than 4100, the flow is turbulent. 

Streamline or Laminar flow  & Turbulent flow 

Fluid flow velocity - is defined as the distance traveled per time, (m/sec, feet/sec) this can be calculated using this equation:

where: v = velocity, m/sec

            Q = volumetric flowrate, m3/hr

            d = inside pipe diameter

            pi = 3.1416 (dimensionless)

            3600 sec = 1 hour

Pipe work: FLow velocity versus flowrate

Pipe CIP: Sub-laminar layer

The fluid velocity varies across the pipe diameter, high in the middle of the pipe, lower at the pipe wall due to friction, this is called the velocity profile.  The fluid velocity at the surface of the pipe is always "zero" this liquid layer is called the sub-laminar layer or the non-slip condition.

As the fluid velocity increases, the sub-laminar becomes thinner and soil on the pipe surface can be subjected to Mechanical Action, while the minimum required fluid velocity is 1.50m/sec for cleaning, inorder to satisfy the minimum required flow velocity at the sub-laminar layer of at least>0.30m/sec an ideal flow velocity of 1.80m/sec is highly recommended to compensate for flow velocity variations during the cleaning cycle.

With this phenomenon, It is therefore wise to increase the fluid flow velocity to at least 1.80m/sec to ensure effective cleaning every time anytime, of course this should be going along with the four other cleaning paramaters, (time, chemical, temperature and coverage)

Many of the cleaning problems encountered in the factory are fluid dynamic issues, however, since the quickest parameter to change are temperature and detergent concentration.  Without the required flow it will always follow in time that microbiological problems will occur.  Potential biofilm formation may happen in the production lines and will certainly lead to product quality issues and a risk to food safety standards.