how to configure a shell and tube heat exchanger with Lab VIew to get data

[HXdaq]

HiI

In our undergraduate chemical engineering labboratory we want to configure our shell and tube heat exchanger  with a DAq and Lab VIEW to get information about the temperaure (of the cold fluid stream being heated), the pressure (of the steam on the shell side of the heat exchanger) and the flowrate (of the water being heated).

Can anyone suggest thermocouples, pressure transducers and flowmeters to fit between the heat exchanger and the DAq?

P.S. the heat exchanger is already fitted with thermometers, a pressure gauge and a rotameter but we don't know how to connect these hardware to the DAq

[nathand]

Not enough information to help you. What are the flow rates and temperature ranges? What fluids are flowing in the heat exchanger? Do you need to worry about material compatibility between the sensors and the fluid? How precise a measurement do you need? Can you easily insert devices into the line? Do the existing measurement devices already provide some sort of electrical signal and you just need to connect them to a DAQ card, or you need to replace (or add to) the existing sensors? (Every rotameter I've seen is purely mechanical.)

A good source for all sorts of fluid flow sensors is http://www.omega.com.

[HXdaq]

Hi Nathand!!!!

Thank you for the information on the flowmeter!!!

Here are some additional details:

-the flowrate range is between 0 gpm and 6gpm and this measurement can be off by 1/5th of a gallon

-the temperature range should be between 0-225 degrees Fahrenheit and this measurement should be as precise as possible with maybe a 1 degree flexibility range

-the fluid flowing through the heat exchanger is water; liquid water flows through the tubes and hot vapor steam flows through the shell side

-thus, all sensors should be water resistant

-there is a mechanic here that can reconfigure the system to insert sensors..For the temperature measure we have thermocouples that can be aeasily inserted but for flow an additional flowmeter that can give signals to a DAQ may have to be installed and since the pressure gauge hooked up to the system does not give off a signal an addition pressure transducer may have to be installed that can send signals to a DAQ card

[HXdaq]

P.S.

the pressure range is between 0 -15 psig

[nathand · Accepted solution]

It sounds like you have enough information to pick out appropriate sensors, you just need to do the research. I would start looking through the Omega catalog, or give them a call - they're usually helpful. I can't take the time to spec out parts for you - that would be a lot of time spent on someone else's project. Most pressure sensors put out either a 4-20mA or 0-5V signal, either of which you can read through an analog input on a DAQ; measuring a 4-20mA signal requires a resistor to convert to voltage. Most of the NI DAQ boards can read a thermocouple on an analog input, but make sure that your hardware does support reading thermocouples. For accurate readings, use a device that has built-in cold junction compensation - for example, the SCB-68 connector block - and for the most accurate readings, get a board specifically designed for temperature measurement.

For the flow measurement, a standard, simple solution is an orifice plate. You put a differential pressure transducer across it, look up the appropriate equations, and use them to calculate the flow rate given the density of the fluid (which you'll be able to calculate from the pressure and temperature, since steam tables are widely available). There are other differential pressure devices available as well - at a previous job we used a V-Cone from McCrometer. If you call them they'll spec one for you - but get an approximate cost first to make sure it's within your budget.

[HXdaq]

I have a water flow sensor installed that has a positive, negative and a ground wire.  I am going to connect it to my DAQ do you know what settings to use in labVIEW to get the volumetric flowrate?

[nathand]

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@HXdaq wrote:

I have a water flow sensor installed that has a positive, negative and a ground wire.  I am going to connect it to my DAQ do you know what settings to use in labVIEW to get the volumetric flowrate?

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No, I don't. How could I know from the limited information you've provided? Different sensors require different scaling, you'll have to read the sensor manual. You can either configure the scaling in Measurement and Automation Explorer, or you can write the scaling code yourself in LabVIEW. Neither approach is difficult if it's a simple linear relationship between the electrical signal and the flowrate.

[HXdaq]

thanks

[nathand]

If you do get stuck, and you provide more specific information (sensor model, a link to the manual, your DAQ equipment type, the type of electrical signal, and how to convert the signal to flowrate according to the manufacturer) then I will be happy to try to provide a more helpful answer.

[HXdaq]

Okay 🙂