Allen Hazen (August 28, 1869 – July 26, 1930) was an American civil engineer and expert in hydraulics, flood control, water purification, and sewage treatment. His career lasted from 1888 to 1930 and he is perhaps best known for his contributions to hydraulics with the Hazen-Williams equation. Hazen published some seminal work on sedimentation and filtration.

Hazen is best known for developing the Hazen-Williams equation, which describes the flow of water in pipelines, in 1902 with Gardner S. Williams. This equation expresses the pressure loss due to friction on the pipe surfaces for fluids. It uses a constant known as the Hazen-Williams coefficient.

He established some of the basic parameters for the design of Hazen's slow sand filters. One of his greatest contributions to filtration technology was his development of two terms to describe the size distribution of filter media.

Effective size and coefficient of uniformity.

These two parameters are used today to determine the size of filter materials in water treatment plants.

“Hazen Theory” formulated by Allen Hazen constitutes a fundamental principle in settling tank or clarifier design in the field of water treatment.

This theory provides a mathematical relationship that helps understand the sedimentation behavior of particles suspended in water.

This theory is related to the settling speed of particles in a fluid medium.

The theory describes the relationship between the sedimentation rate of particles, their size, shape, and the properties of the fluid in which they are suspended.

Hazen Theory introduces the concept that the settling rate of a particle in a liquid is proportional to the square of its diameter and the density difference between the particle and the liquid. Hazen Theory is also known as “Hazen Speed”. It is expressed by the following equation.

**Vh=k⋅d2⋅(ρp−ρf)/μ**

Vh: is the settling-settlement speed of the particle.

k: is a constant.

d is the diameter of the particle.

ρp: is the density of the particle.

ρf: is the density of the liquid.

μ: is the dynamic viscosity of the liquid.

This equation helps them estimate the sedimentation efficiency of the treatment plant to be built. It is a very important tool for the design of settling tanks and clarifiers in water treatment plants. It allows parameters such as tank size, flow rates and particle properties to be evaluated to ensure the removal of suspended solids from water.

"Hazen Velocity" refers to a measurement used in engineering and fluid dynamics. Calculates the flow rate in the hydraulic system. Hazen Speed is named after the famous engineer Allen Hazen, known for his work in sanitary engineering and fluid mechanics.

"Hazen Rate" is commonly used to measure water clarity. The Hazen Scale is generally a simple method for assessing clarity or turbidity. Water clarity is measured in turbidity units (NTU).

NTU is important in terms of showing the water quality as well as the quality of water for drinking and industrial use.

The lower the Hazen velocity value, the clearer the water.

The formula for “Hazen Speed” or “Hazen Theory” in lamella sedimentation tanks is as follows.

Vh=Q/TA Q=6(m3/h)/ 11.93 (m2/) =0.503 m/h

For CT55 Model Lamella; Q:6 m3/h, A60: 11.93

Vh: Particle settling velocity (m/h)

Q: Flow rate (m3/h)

TA: Lamella Total Active Area (Different for each model - given as A55 and A60 on Lamella.net.)

L: Lamella length, C: Plastic pipe friction coefficient, A: 1 mesh cell area of CT55 model lamella (conversion from area to circular section), Q: Upper surface load was chosen as 6 m3/m2/h (accordingly, 1 mesh cell section is 0.0648 m2 The water flow rate passing through is 0.0252 m3/h.) - Vs: m/h. Water passage rate Vs=Q/A,= (0.0252/0.0648 =0.389 m/h

**Hydraulic head loss for Tubesettler;**

Lamella length is short compared to pipes and channels (1-2 meters), and the water velocity passing through the lamella honeycomb cells is much less than the water velocity passing through the pipe and channel.

For this reason, there is not much hydraulic head loss in the lamella eyes. It is around 1-5 mm and is at a negligible level.

Hazen-Williams Calculation - Excel

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