ESG-6 Isothermal Pressure Drop Tests on 2-inch Serrated and Solid Finned Tubes
This report summarizes the results from two studies:
Isothermal pressure drop data obtained on the HTRI wind tunnel are presented for 2-in. OD base tubes with 1- and 3/4-in. high fins laid out in 30 degree staggered and 90 degree inline arrangements on 4-1/2-inc pitch. Flow velocities ranged from about 5 to 40 ft/sec based on the minimum free flow area. The main area of investigation included comparison between solid and serrated fins, effects of serration width and effects of 30 degree versus 90 degree layouts. Results of the predictive method from the ESCOA Catalog (1969) are also shown.
This experimental test project consisted of two parts. In Part 1, the effects on pressure drop performance were compared for similar serrated tubes manufactured by different techniques. One set of tubes had a slight distortion of fin cross section while the other had a regular cross section (see Fig. 2c). There was a negligible difference in performance for inline tube arrangement if the pressure drop was based on the flow velocity through the minimum cross-sectional area of the bundle.
In Part 2, the effect of tube layout pitch for inline arrangements of 2-in. OD tubes with 4-in. diameter fins was investigated. A strong effect due to the tube pitch was found, inversely proportional to the 2.6 power of the pitch ratio. This differs from what has been found for staggered tube layouts. It is suggested that when using inline arrangements, careful attention be paid to optimizing the pitch with respect to both pressure from and heat transfer.