Application note

Flow control in temperature imaging

The German company LaVision develops and manufactures modular laser imaging systems for the visualization of reactive and non-reactive flow processes. One of the optical techniques used is Laser Induced Fluorescence (LIF). Bronkhorst provided a solution to create an accurate mixture of nitrogen and a tracer substance, consisting of an evaporator module (VDM) and a liquid feed module. Precise control of the gas flow, liquid flow and temperature in this process are important. 

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What is temperature imaging?

Temperature imaging is a technique which is used in many different industries such as automotive, aerospace and power generation for the development of efficient and cleaner combustion processes. A very common approach to visualize flow- and temperature profiles is Laser Induced Fluorescence (LIF) thermometry using a tracer substance such as Anisole (C7H8O).

Flow control for temperature imaging in thermal flows
Temperature imaging in heated jet flow

Application requirements

One of the most important aspects of the temperature analysis is a precise and repeatable mixture of the tracer liquid and gas. The challenge is to create different but consistent mixtures for varying test conditions. Precise control of gas flow, liquid flow and temperature are key to this process.

Important topics

Process solution

In this setup of 2-colour Laser Induced Fluorescence (LIF) thermometry, Anisole is used as ‘colourant’ to make the internal thermal flow visible for the camera. The Anisole has to be available in vapour phase where the accuracy of the liquid Anisole flow control is crucial. 

Liquid feed system

As the accuracy of the liquid Anisole flow is crucial, Bronkhorst developed a dedicated liquid feed module. This liquid feed module includes a reservoir and a pressure controlled liquid pump with return to the reservoir. The electronic pressure controller enables a constant pressure at the inlet of the evaporator module (VDM) even though the speed of the pump is changing. 

Flow scheme Evaporating module for temperature imaging
Flow scheme

VDM – Evaporator module

To create an accurate vapour mixture of Anisole and Nitrogen, an evaporator module is used. Small amounts of liquid Anisole (up to 25 g/h) are atomised in the Nitrogen gas flow in the Controlled Evaporation and Mixing (CEM) module, and then heated to ensure total evaporation and avoid cooling down to below condensation temperatures. At the vapour outlet, optional dilution gas is added to further reduce the concentration of Anisole in the vapour flow.
All components are assembled in a Vapour Delivery Module (VDM) which also contains the power supply, communication interfaces and a display for readout and control.

To adjust the system to the customers processes, the relevant PID parameters of the flow controllers can be adjusted via a digital (RS232 or bus) interface using Bronkhorst FlowSuite and FlowPlot software. 

Bronkhorst supported LaVision and the end user with commissioning on site.

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Prototype of vapour system
Prototype of an Evaporator Module (VDM) with a Liquid Feed Module

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