Using the right thermal flow meter for your applications is important if you want accurate flow rate readings. Read on to learn how to find suitable thermal flow meters for your flow system.
To select the right type of flow meter, you need to do your homework to find the specifications needed in your application. By doing proper research when looking for the right flow meter, you will save time and extra expenses. Whether you want to upgrade your plant, expand your project, or improve the process, you will ensure success by selecting the right flow meter. Thermal mass flow meters, also known as submersible or thermally dispersed mass flow meters, are a series of devices used to measure the total mass flow of liquid (mainly gas) flowing through a closed pipeline.
You need to ask yourself several key questions when you want to specify which kind of thermal flow meter is required in your application. This guide will explain these questions to help you narrow your search down to a suitable thermal mass flow meter. Once you have the correct answers to these questions, you will make the right decision when buying a thermal mass flow meter. Read on for more insights and details.
What is the Required Installed Accuracy?
When looking for the perfect flow meter to install in your application, it is not enough to check only the general accuracy statement. You also need to factor in the installed accuracy regarding basic accuracy capability, flow profile disturbances, and calibration requirements. This also includes the ability of the flow meter to compensate for the gas or installation temperatures.
The plant operator also needs to know whether the required actual gas calibration. An actual gas calibration will give the best accurate results in any case. The calibration needs to be done at pressure conditions and process temperature. An actual gas calibration offers the best solution to aim for the best possible repeatability and accuracy in your application.
However, it may not be practical, economical, or achievable in some applications in some applications to do an actual gas calibration. In this case, an equivalency calibration will be the only solution. Such situations may be included for various safety precautions and or complex gas mixtures.
Which Type of Gas Needs to be Measured?
Before you decide which type of thermal mass flow meter you want to buy, you need to know which kind of gas will be measured in the industrial process. Different types of gas substances can be measured using the thermal mass flow meter. You can use it to measure inert gas, air, or hydrocarbon-based gas. The plant operator should also know if it’s a mixture of gases or a single gas substance. In a mixture of gases, the proportions of each gas should be known. Is the gas to be measured clean or dirty? If you are going to use the thermal flow meter to measure the flow rate of dirty gas, you should know its quantity and quality. You should also know whether the gas is corrosive or not if it contains moisture or not.
All manufacturers can process clean, dry or liquid gases. Constant power technology is the best if you will deal with a moist gas in your application. When measuring the flow of gases, the working principle of thermal flow meters entails gas flow heat transfer. A sudden change in the heat transfer that causes a spike or fluctuations in readings may be due to condensate or moisture that comes into contact with the heated sensor. This creates an unstable or inaccurate flow measurement. The type of thermal mass flow meters that utilize the constant ∆T (CT) method react to moisture droplets. On the other hand, thermal flow meters that use the constant power (CP) method are not affected by moisture droplets since they have a slightly heated sensor’s temperature above the gas’s dew point.
What is the Fow Range Requirement?
The wide turndown capability is among the compelling features of the thermal flow meter. Most manufacturers will have a turndown ratio of 100:1. What differentiates the technology and the supplier are the flow range capabilities. Due to the sensor power limitations, CP-type devices have a higher range than CT-type technology meters. However, special techniques are used by other manufacturers to push their measuring ranges up to 1000 fps [300 mps]. That is why knowing your flow meter range is crucial.
What is the Response Time Requirement?
Faster response times are not always ideal in all measuring instruments. Too fast response time may cause excessive valve responses if the thermal flow meter is part of a PID control loop. This will lead to premature valve failure or unstable flow control. On the other hand, too slow a response time is not good since the control valve action might lag behind too much leading to less control. Moreover, erratic, unstable readings will be produced when water droplets hit the sensors due to an entrained moisture in the air/gas flow stream in a fast-responding flow meter.
What Pipe Size and Type will be Used in the Flow Meter Installation?
The plant operator should also know the type of pipe to be used to install the thermal flow meter and the required size of the pipe. Does the installation require a rectangular duct or around pipe? The diameter of the round pipe needs to be known. If it is a rectangular duct, the dimension needs to be also known. The dimension of the socket needs to be known if you are going to use an insertion-style meter. In this case, the plant operator also needs to establish if the flow meter will be installed through a ball valve. The three main reasons why these considerations are important to include:
- Instead of using insertion-type flow meters, inline or spool-piece designs are used in smaller diameter pipes.
- A single-point or multi-point averaging option is advisable if you are going to use an insertion-type flow meter.
- It is also important to know the pipe size to achieve the proper insertion depth. Into the pipe by ensuring the probe length is correct.
What is the Length of Straight Run Available?
A repeatable flow profile is required by a thermal mass flowmeter to meet their particular application demands. Naturally, this will occur with 5 days to 10 days of downstream straight run and 15 days to 20 days of the straight upstream run. There is no room for debate because these are laws of dynamics in physics. Failure to attain enough straight run may force you to inquire from the manufacturer about the degradation of accuracy expected. Besides, reliable manufacturers provide some type of technology that gives flow conditioning. This technology produces inadequate straight run with accurate and repeatable measurement in installations.
Those are all the essential considerations that need to be made to purchase a thermal flow meter that meets your needs. Suppose you are not sure of all the mentioned considerations. In that case, it is advisable to seek advice from thermal flow meter experts. You can consult the manufacturer who will explain to you various application demands. Proper thermal mass flow selection will ensure that you maximize the productivity and profitability of your flow system.