Heat transfer augmentation characteristics of various inserts in a heat exchanger tube

The characteristics of heat transfer and pressure drop were experimentally studied for a heat exchanger (recuperator) with several kinds of inserts. T he augmentation of heat transfer was investigated for proposed inserts and compared with the typical inserts that have been already used in recuperato r tubes. Two test tubes with the same insert were used for the measurements of the f riction and the heat transfer coefficients respectively. The length of the tubes was 64 times that of the tubes' inner diameter. Air was used as a. wo rking fluid in the tube and the experiments were executed in the turbulent how region (Reynolds number: 2 x 10(4)similar to 8 x 10(4)) and the entranc e region at the same time. The experiment was performed under a constant he at flux condition. Two types of single straight tapes, two types of cross t apes, a wire mesh, a delta wing tape, a ribbon tape and a conic coil used c onventionally were investigated. Even though several vortex generators were investigated previously, a ribbon tape and a delta wing tape designed spec ially in this research were also tested (Fiebig (1994:)). The performance p arameter for a heat exchanger with insert was defined as the ratio of the h eat transfer coefficient of a heat transfer tube with inserts to that of a smooth tube under the same pumping power. Even though the performance values varied with the Reynolds number, the con ic coil and the ribbon tape were generally shown to have better performance than the others. Their heat transfer performance was enhanced 30% relative to than the smooth tube, The mesh type insert and the delta wing tape were also useful for the heat transfer augmentation.