Finned tube bundle

HumidiRcation Chambers The air-cooled heat exchanger is provided with humidification chambers in which the air is cooled to a close approach to the wet-bulb temperature before entering the finned-tube bundle of the heat exchanger. 

In air-cooled heat exchangers, the air flows upward umixed across the finned tubes/bundle, and the tube-side process fluid can flow back and forth and downward as established by the pass arrangements. At 4 or more passes, the flow is considered counter-current, and the F factor = 1 0 216 q-pg other fewer-passes correction factors are given in Figures 10-187A, 10-187B, 10-187C. 

In a forced-draft air cooler, cool air is blown through the underside of the fin tube bundle. In an induced-draft air cooler, cool air is drawn through the underside of the fin tubes. Either way, road dust, dead moths, catalyst fines, and greasy dirt accumulate along the lower row of tubes. As the tubes foul, they offer more resistance to the airflow. However, note that... 

One factor that does not reduce airflow is crushed fins at the top of the tube bundle. Walking across a fin tube bundle will crush these fins. It looks bad, but does not appear to affect cooling efficiency. 

A different type of cross-flow exchanger is shown in Fig. 10-5. In this case the gas flows across finned-tube bundles and thus is unmixed since it is confined in separate channels between the fins as it passes through the exchanger. This exchanger is typical of the types used in air-conditioning applications. 

The heat transfer in a finned tube bundle is calculated using similar equations. For this we suggest [3.23] in the literature. 

The outside film coefficient based on the inside surface area for the finned tube bundles described is 180 Btu/hr. sq. ft. °F at a face velocity of 675 ft./min. An outside fouling factor of 0.001 is generally used. The inside fouling factor depends on the service. 

The solution to the problem of limited coker capacity was solved by jet blasting the fin tube bundle. 

Further inspection revealed that the underside of the condenser tube bundle was encrusted with a thick layer of coke fines and dirt. I showed the foreman how to use strips of paper under the fin tube bundle to locate areas where the bundle was fouled enough to restrict air flow through the bundle. 

I also demonstrated that temperature measurements across the top of the fin tube bundle would indicate hot areas where the bundle was fouled. These areas corresponded to the fouled areas indicated by the paper strips. 

To inform the foreman further about the problem, I explained how fouling of the fin tube bundle decreased the heat transfer in the condenser, limiting condensing capacity. I explained how this would increase the vol-... 

Air cooler units are entirely different from the previously mentioned arrangements in that the cooling agent used is circulating air instead of a liquid As seen in Exhibit 6-9, an air cooler unit consists of fin-tube bundles with a header box attached to each end, supported horizontally by a steel frame or struaure. For the single-pass arrangement, the inlet nozzles are mounted on the top of the header box the outlet nozzles are at the opposite end and mounted on the bottom of the header box. For die double-pass arrangement, the outlet nozzles are located at the same end as the inlet nozzles. For additional surface area, more passes can be added or additional units can be... 

A finned tube bundle acts as an air filter. Air is drawn up through the lower two rows of fins where much of the dust, dirt, bugs, and moths are filtered out, and thus restricts air flow. Water-washing is the most effective method of removing these deposits. However, many of my clients will not water-wash hot air cooler bundles while running for fear of pulling out the tubes from the tube sheets due to thermal contraction of the tubes. 

The problem can be corrected by realigning the fan assembly. Alternately, vane tip clearance mesh can be attached to the interior of the shroud, which will eliminate excessive blade-to-shroud clearance and thus push more cooling air through the finned tube bundle. 

You may have seen bundles constructed with serrated, or very small, fins covering the exterior of the tubes. These are called low-fin-tube bundles. These fins increase the outside surface area of the tubes by a factor of 2.5. However, this does not mean that the heat-transfer efficiency of the exchanger will increase by 250 percent. Two factors curtail this improvement ... 

The air cooler bundle was then replaced with an ordinary finned tube bundle. The use of wire inserts in fouling service, where extra pressure drop is totally unacceptable, represents poor engineering design practice. This is especially so when the controlling resistance to heat transfer is going to be on the air side of the precondenser cooler. 

Fin tube bundle Serrated, or extended-surface, exchanger tubes. 

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