FE 478 PLANT DESIGN FOR FOOD ENGINEERS

SECTION ONE

FLUID FLOW

Dr. Ali Coşkun DALGIÇ

TRANSPORTATION OF FLUIDS

Fluids are substances that flow without disintegration when pressure is applied. This definition of a fluid includes gases, liquids, and certain solids. A number of foods are fluids. In addition, gases such as compressed air and steam are also used in food processing and they exhibit resistance to flow just like liquids. In this chapter, the subject of fluid flow will be discussed from two standpoints: the resistance to flow and its implications in the design of a fluid handling system, and evaluation of rheological properties of fluid foods.

The basic equations characterizing flow and forces acting on flowing fluids are derived using the laws of conservation of mass, conservation of momentum, and the conservation of energy.

FLUID FLOW REGIMES

The Reynolds number is a dimensionless quantity that can be used as an index of laminar or turbulent flow. The Reynolds number, represented by Re, is a function of the tube diameter, L, the average velocity Vm , ρ, the density of the fluid , and μ, the viscosity .

LAMINAR AND TURBULENT FLOWS

For values of the Reynolds number below 2100, flow is laminar and the pressure drop per unit length of pipe can be determined for a Newtonian fluid and for power law fluids. For Reynolds numbers above 2100, flow is turbulent and pressure drops are obtained using an empirically derived friction factor chart.

Momentum Balance

Fluids are substances that flow without disintegration when pressure is applied. This definition of a fluid includes gases, liquids, and certain solids. A number of foods are fluids. In addition, gases such as compressed air and steam are also used in food processing and they exhibit resistance to flow just like liquids. In this chapter, the subject of fluid flow will be discussed from two standpoints: the resistance to flow and its implications in the design of a fluid handling system, and evaluation of rheological properties of fluid foods.

The basic equations characterizing flow and forces acting on flowing fluids are derived using the laws of conservation of mass, conservation of momentum, and the conservation of energy.

Momentum is the product of mass and velocity and has units of kg · m/s. When mass is expressed as a mass rate of flow, the product with velocity s the rate of flow of momentum and will have units of kg · m/s2, the same units as force. The momentum balance may be expressed as:

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