FlowFlow is fluid in motion. Gases, like liquids, flow from one point to another depending on pressure and temperature. When fluids flow, they mix easily because of the continual movement between molecules. The rate that a fluid flows is a measure of how much fluid is flowing or moving through a pipe or channel within a given period of time. The term flow is often used interchangeably with flow rate in industry.Fluid movement may be either laminar or turbulent depending on the path taken.

When the path is smooth and without obstruction, the flow is called, laminar flow, also called streamlined flow since the molecules line out to a smooth flowing pattern. Piping bends, corrosion, valves or any other obstruction to the flow inside a line causes turbulence or turbulent flow. If a stream of water passes over rock formations, the water looks like it is boiling and may even cause bubbles to form as air is entrained into the water from the turbulence. If an airplane goes through a section of turbulent air flowing by the plane, then the plane moves violently in response to the turbulence. At first this may seem undesirable, but in most cases, the opposite is true. A turbulent flow is consistent and therefore manageable.Reynolds NumberThe Reynolds number can be used to identify whether a flow is laminar or turbulent. The Reynolds number is a mathematical computation known as the fluid velocity profile that describes flowing fluids numerically.Types of Flow Measurement:1. Direct and Indirect Flow MeasurementTotal flow is a direct form of flow measurement as determined by totalizers. Flow indicators such as flappers and paddlewheels seem to be direct but indicate the result of an impinging fluid force, categorizing them as indirect flow measurement devices. Flow rate is measured indirectly. Indirect flow measurement measures one variable in the process to infer another. Although there are devices known as direct-read flow meters (such as rotameters, weirs, etc.), these are still indirect methods when examined closely.

2. Positive Displacement Flow MeasurementPositive displacement flow measurement is used within industry where the measurements of absolute volumes are required.

3. Percentage Flow RatePercentage flow rate is a common way to indicate a flowing process. A 100 percent flow rate is equated to an actual quantity such as gallons per minute (gpm).

4. Volumetric Flow UnitsVolumetric flow units are instantaneous flow rate measurements for how much volume passes through a certain location in a pipe or channel per unit of time.

5. Mass Flow UnitsMass flow rate is a measure of how much actual mass passes a certain location per unit of time.

Nakalimutan ko yung title na under itoWEIRSWeir is defined as a barrier over which the water flows in an open channel. The edge or surface over which the water flows is called the crest. The overflowing sheet of water is the nappe.If the nappe discharges into the air, the weir has free discharge. If the discharge is partly under water, the weir is submerged or drowned.Types of Weirs.A weir with a sharp upstream corner or edge such that the water springs clear of the crest is a sharp-crested weir. All other weirs are classed as weirs not sharp crested. Sharp-crested weirs are classified according to the shape of the weir opening, such as rectangular weirs, triangular or V-notch weirs, and trapezoidal weirs. Weirs not sharp crested are classified according to the shape of their cross section, such as broad-crested weirs, triangular weirs, and trapezoidal weirs.The channel leading up to a weir is the channel of approach. The mean velocity in this channel is the velocity of approach. The depth of water producing the discharge is the head.Sharp-crested weirs are useful only as a means of measuring flowing water. In contrast, weirs not sharp crested are commonly incorporated into hydraulic structures as control or regulation devices, with measurement of flow as their secondary function.

FLOW OVER WEIRS.1) Rectangular Weir

The Francis formula for the discharge of a sharp-crested rectangular weir having a length b greater than 3h is:q = 3.33 (b - 0.2 h) h3/2 Where:q = flow rate (ft3/s)h = head on the weir (ft)b = width of the weir (ft)

2) Triangular Weir

The discharge of triangular weirs with notch angles of 30, 60, and 90 is given by the formulas as:Discharge of Triangular WeirsNotch (vertex) angle Discharge formula

90Q0.685h2.45

60Q1.45h2.47

30Q2.49h2.48

h is as defined above in the Francis formula.

3) Trapezoidal (Cipolletti) Weir The Cipolletti weir, extensively used for irrigation work, is trapezoidal in shape. The sides slope outward from the crest at an inclination of 1:4, (horizontal/vertical). The discharge isQ=3.367bh3/2where b, h, and Q are as defined earlier. The advantage of this type of weir is that no correction needs to be made for contractions.Reference: http://www.engineeringcivil.com/weirs.html http://web.deu.edu.tr/atiksu/ana52/ani4022-2.html http://ocw.usu.edu/Biological_and_Irrigation_Engineering/Irrigation___Conveyance_Control_Systems/6300__Weirs_for_Flow_Measurement_Lecture_Notes.pdf http://www.usbr.gov/pmts/hydraulics_lab/pubs/wmm/chap07_03.html