Fintube testing removes guesswork from equipment improvement
Steel welded fintubes are used to reduce the size and cost of heat exchangers and in power boilers such as heat recovery steam generators (HRSG), and are a fundamental element of their design. Competing companies look for advantages by offering different tube sizes and fin pitches, with solid or serrated fin surfaces.
Fintube, a fintube manufacturing firm in Tulsa, Okla., has designed and built a test facility that incorporates a large-scale, forced-draft, high-temperature wind tunnel with a test coil that has a flow area four feet by four feet that can accommodate test coils of approximately 100 tubes. The unit is capable of measuring the heat transfer coefficient and pressure loss of various fintube designs.
The facility?s five major components are: a fan and air flow measurement section, which measures up to 20,000 standard cubic feet per minute; a duct burner and gas metering section, which measures up to 15 mmBtu an hour; a test coil section; a water flow control and measurement section, which measures 130 gallons per minute; and a control room.
All instrument signals are fed to the control room computer where test variables are manipulated and data is recorded.
Debugging and calibrating the test facility took more than six months. Qualification runs were completed in May 1994, including duplicating previously published data. To date, more than 25 coil arrangements have been tested. Experimental uncertainties are 2 percent for Reynolds Number, 3.6 percent for Colburn j-factor and 3.6 percent for friction factor.
OAdvances in performance testing must be the future basis for large HRSG cost reductions,O said Don R. Reid of Fintube.
Fin side coefficient has several components, including assembly tolerance, incomplete specifications and experimental inaccuracies, extrapolation of data and service coefficient.
Tests at the facility have allowed Fintube to improve several coefficient components. Assembly tolerance is steady at 12 percent, but incomplete specifications and experimental inaccuracies fell from 12 percent to 3 percent, extrapolation of data fell from 10 percent to 2 percent, and service coefficient rose from 66 percent to 83 percent.
OActual data, rather than forecasts, can be used in selecting new, better performing fintubes,O Reid said. OThis tool will greatly help long-term equipment cost reduction.O