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Gas and Process Sample Transport Systems for Analyzer Applications

Finite Element Analysis (FEA)
To predict the performance of special applications, O'Brien uses Finite Element Analysis, a computer modeling of heat distribution within the tubing bundle. It accurately predicts temperature performance of your bundle under the conditions of your specific application. Using FEA techniques O'Brien has successfully designed and supplied bundles with cut-to-length self regulating heaters that can withstand up to 1100ÿF blow down temperatures.

Static Conditions vs. Flowing Conditions
O'Brien standard calculations assume that the process fluid enters the bundle at or above the desired maintenance temperature. All formulas are based on static conditions. This is truly the worst case for fluids in small diameter pipes that do not require heat up. A static fluid provides no heat, thus relying on the tracer to replace all the energy lost through conduction, convection and radiation. A static fluid also has lower thermal conductivity, which restricts the flow of heat energy and sets up a temperature gradient across the tube. Properly sizing the tracer and using heat transfer aids such as aluminum mylar in the tubing bundle guarantees that no portion of the fluid will drop below the required maintenance temperature.

The following examples show various conditions in which O'Brien has used FEA to accurately predict performance.

FEA - Predicted Temperature Distribution

		Cross section of TPE2-B4-B5, two 1/2" 0.049 seamless stainless steel process tubes and a 5 watt XTV tracer
		FEA showing the predicted temperature distribution in a cross section of TRACEPAK on a 0®F day and 80®F day.
0®F ambient	80®F ambient

Using FEA to Predict Performance Under Extreme Conditions
(High temperature blowdown up to 1100ÿF.)

		The configuration of this bundle shows a buffered or isolated tracer. This configuration allows O'Brien TRACEPAK to use self regulating tracers to provide freeze protection for lines that are intermittently blown down with up to 1100ÿF steam.
		At -20®F we see that the process tube is maintained at about 60®F.
		During 750®F blowdown on a 100®F day, the tracer is at 400®F, 20®F below the maximum allowable.

Using FEA to Predict Changes not Possible by Other Methods

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A six tube bundle consisting of a combination of Teflon and HDPE tubes with an electric tracer. Two aluminum plates are used to maintain position of the tubes and increase heat transfer.

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Without mylar foil.

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With mylar foil. With mylar foil the heater was about 20®F cooler and process tubes were 10®F warmer.

Additionally, an environmental chamber testing facility at O'Brien's headquarters allows testing of products to verify their performance in many environmental conditions.

Integrated Solutions Improving Process Accuracy

©2003 O'Brien Corporation