Aei405

DEPARMENTOF TECHNICALEDUCATION ANDHRAPRADESH Name Designation Branch Institute Year/Semester Subject Sub. Code Topic Duration Sub- Topic Teaching Aids

: N. Sanjeeva Rao : Lecturer : Applied Electronics & instrumentation Engg. : Govt. polytechnic for women,srikakulam : IV Semester : Process instrumentation –II : AEI-405, : Flow : 50minutes : Thermal flow meter : PPT, Animations, photograph AEI-405.41

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Objectives On completion of this topic you would able to know :  Thermal flow meter.  Operation  Advantages and Disadvantages  Applications

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Recap In the last class you have learnt about  Thermal flow meter  Classification

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Thermal flow meter - Construction  It has no restrictive orifice or moving parts  It is also useful for flow measurement of corrosive liquids  It consists of a heater and two temperature sensors T1 and T2 such as resistance thermometers or thermocouples

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Thermal flow meter - Operation  The temperature sensors are located symmetrically with respect to the heater .  One at upstream side and other at down stream side at short distance from the heater as shown in the figure A.  Under no flow conditions the temperatures T1 and T2 of the sensors will be same .  The differential signal measured on a detector will be zero. AEI-405.41

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Thermal flow meter - Operation  When the fluid of whose flow rate to be measured flow through the pipe then ,the temperature T1 will fall and temperature T2 will rise until steady state is reached.  The heat transferred to the liquid is proportional to the mass flow rate of the fluid

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Thermal flow meter

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Other type thermal flow meter

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 The heat transferred to the liquid by the heater is given by Q = W CP(T2 – T1)--------------------(1)  Q = heat transferred  W = mass flow rate of the fluid  CP = specific heat of the fluid  T1 = temperature of the fluid before heat is transferred  T2 = temperature of the fluid after heat has been supplied AEI-405.41

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W = Q / Cp(T2 – T1) ---------- (2)  In the equation (2) the mass flow rate ‘W’ can be obtained by measuring the (T2 – T1) heat transfer to the fluid ‘Q’ and specific heat of the fluid ‘Cp’

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 Under constant power input to the heater for given fluid the temperature difference is inversely proportional to the mass flow rate  The dynamic response of this type of flow meter is depend on the flow conditions and is generally poor

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Advantages  It has no restrictive orifice  It has no moving parts

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Disadvantages  Low dynamic response

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Applications  Flow rate of corrosive liquids can be measured

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Summary We have discussed about :  Thermal flow meter  Operation  Advantages and Disadvantages  Applications

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Quiz 1. Which of flowing thermal flow meter are suitable for the measurement of large flow rates a) Heat transfer flow meter b) Thermal flow meter with external elements and heater c) Heated tube-type mass flow meter d) By pass-type thermal mass flow meter AEI-405.41

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Frequently asked questions 1.

Explain the principle of operation of Thermal flow meter.

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THANK YOU

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