SECTION 6: RADIANT TUBE AND TAILPIPE
SECTION 6: RADIANT TUBE AND TAILPIPE
The main purpose of the tailpipe and the radiant tube is to provide sufficient tube surface to transfer the heat from the flue gases to the tube wall where it radiates from the tube. Radiant tube is defined as the tubing between burners firing in a radiant branch, plus the radiant tubing immediately following the last down- stream burner. Tailpipe is defined as all tubing between the radiant tube and the pump.
Most of the radiant heat supplied by each burner is released from the radiant tube; the balance is released by the tailpipe. The placement of radiant tube to corre- spond to areas of major heat loss is the key to provid- ing uniform comfort levels. The use of adequate tailpipe is the key to high combustion efficiency and proper operation of the pump.
6.1 Radiant Tube Length
The considerations in the selection of the length of radiant tube include the following:
6.1.1 Minimum Radiant Tube Length
Provides for the highest level of intensity per length of radiant tube and good radiant heat uniformity between burners. More tailpipe length is required to maintain operating efficiency and pump capacity.
6.1.2 Maximum Radiant Tube Length
Provides the lowest level of intensity per length of radi- ant tube, and consequently the largest span between burners. The radiant intensity will be reduced slightly for the last
The length of radiant tube required varies according to the burner input. Consideration has been given to the use of a standard 10' (3 m) length of tube or lengths that can be cut from same without waste. See Page 12, Table 1.
When positioning radiant tube to give the required radiant distribution, it is important to consider:
•Clearances to combustible materials.
•Lighting equipment and other suspended objects.
6.2 Tailpipe
Tailpipe provides a low level of radiant intensity per length. The length of tailpipe for systems can be varied according to the flow units in the system and the designed radiant length. Longer lengths of tailpipe will attain higher operating efficiencies and therefore con- densation will occur.
Page 16, Figure 16 relates the effect on system ther- mal efficiency of variations in radiant and tailpipe lengths. The chart was created based on test data obtained in accordance with methodology developed by the National Bureau of Standards (NBSIR
NOTE: When accounting for the required tailpipe lengths during the design process, it is important to verify that the tailpipe for each branch is at least equal to the specified minimum.
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