Thermo-energy audit

Services for thermo-energy audit

Flow measurement

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Flow measurement

• Elaboration of a thermo-energy audit or balance involves analysis of characteristic data for different energy flows. One of this characteristic data is flow. For measuring the flow there can be used different methods and devices that are presented bellow.

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Flow measurement

• Obtained data after measurements can be used for energy efficiency analysis for different industrial contours. Values of flow can also be used for elaboration of energy balances. After elaborating thermo-energy audits and/or balances, using measured data, there ca be proposed different measures for increasing energy efficiency.

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Flow measurement

• Devices that are used for flow measurements are characterized by the precision class. Depending on the precision class of the device there can be performed measurements with higher or lower precision. This fact can influence the results of a thermo-energy audit or balance, and finally the energy efficiency.

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Flow measurement

• It is important to mention that flow measurement can be performed with devices installed permanently on different technological equipment or with devices that are only installed for one measurement. Another important thing is that obtained data can be stocked, ideally in electronic format, and then can be used for different analysis for increasing energy efficiency.

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Flow measurement

• Diaphragm. Diaphragm consists of a metallic plate with an orifice in interior of known size. It is installed on the interior of the pipe. Before diaphragm static pressure has a slight increase, due to turbulences that appear in the pipe.

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Flow measurement

• Diaphragm. After entering the diaphragm, due to turbulences and friction, a part of fluid energy is transformed into sound and heat. Thus, there is a pressure drop. The minimum pressure (and maximum velocity) is obtained just after exiting the diaphragm, at the point named contracted vein.

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Flow measurement

• Diaphragm. After this point velocity starts to drop, and due to this fact pressure increases. Pressure do not increase up to initial value, pressure difference represents local pressure losses in diaphragm.

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Flow measurement

• Diaphragm.Pressure profile

Local pressure loss

Diaphragm Contracted vein

Max. pressure difference

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Flow measurement

• Diaphragm. Advantages and limitations.• Introduces local pressure losses• Generated pressure difference• Low price• There are no moving parts• Easy installation and maintenance• Needs a linear part of network• Corrode in time

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Flow measurement

• Turbine flow meter.

• Turbine flow meter is used for liquids and gasses. It contains a light rotor with radial blades for measuring rotation velocity (proportional with fluid speed, thus with flow.

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Flow measurement

• Turbine flow meter.

• Rotor can be placed axial or perpendicular to pipe. Depending on the fluid rotor is fabricated from: aluminum, stainless steel, monel, titan, plastic etc.

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Flow measurement

• Turbine flow meter.

sensor

rotor

Axial to the pipe Perpendicular to the pipe

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Flow measurement

• Turbine flow meter.

• Sensor is used for measuring the rotation velocity of the blades. The most used sensors are based on electromagnetic induction: reluctive and inductive

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Flow measurement

• Turbine flow meter. Advantages and limitations.

• Good precision

• The measured value is influenced by fuild viscosity

• Magnetic field can be perturbed from exterior

• Sensible to mechanic shocks, dirt

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Flow measurement

• Turbine flow meter. Advantages and limitations.

• It is difficult to maintain the direction of the turbine

• The meter is not responding instant to flow variations, due to inertia of moving parts (it is not recommended for rapid variable flows)

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Flow measurement

• Rotameter. Rotameter is used for measuring flows of liquids and gasses. The operation principle is based on moving of a float in the interior of a truncated vertical tube through which flows the fluid.

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Flow measurement

• Rotameter. The fluid enters into the device at the base of apparatus. Fluid pressure rises the float at the height where all forces are equal and equilibrate. Float position depends on the flow and on the circular section around it.

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Flow measurement

• Rotameter.

Fluid

p1

p2

G

Fa

Fp2

Fp1

Forces that act on the float:- Float weight - Archimedes force- Pressure force from down to upwards- Pressure force from up to downwards- Friction force between float and fluid: where: p, f – density of float/fluid [kg/m3]; p1, p2 – fluid pressure before/after float [Pa]; Ap – float section [m2]

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Flow measurement

• Rotameter. Advantages and limitations.

• Simple and cheap

• Easy installation and maintenance

• Needs no power supply

• Low and relative constant pressure losses

• Linear scale

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Flow measurement

• Rotameter. Advantages and limitations.

• Large measurement domain

• Can be used for very low flows

• Can be increased precision through increasing the length of float displacement

• Can be used for liquids, gasses and steam

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Flow measurement

• Ultrasonic flow meter with transit time.• Ultrasonic flow meter with transit time uses

two sensors on both parts of the pipe with an angle to the fluid flowing. Every sensor has an emitter and a receiver. The two sensors transmit a sound signal one to another.

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Flow measurement

• Ultrasonic flow meter with transit time.• For a zero flow, the transit time of the two

signals is the same.• If there is flow in the pipe, due to adding the

speed of sound and fluid, the signal transmitted downstream is accelerated, and the signal transmitted upstream is decelerated.

• Using fluid speed there can calculated flow.

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Flow measurement

• Ultrasonic flow meter with transit time.

Emitter/receiver

Emitter/receiver

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Flow measurement

• Ultrasonic flow meter with transit time. Advantages and limitations.

• It is used only clean fluids, in one phase

• There can be measured low flows, bidirectional flows

• Robust device

• Easy installation

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Flow measurement

• Ultrasonic flow meter with transit time. Advantages and limitations.

• Can be installed without interrupting technological process

• Easy maintenance• Do not introduce local pressure losses• Sensible to modification of flowing regime• It is used for fluids with temperatures under

200 °C