The present article reports on experimental investigation of heat transfer and pressure drop characteristics of multi tubes in tube helically coiled heat exchanger. The study aims to investigate the effects of heat exchanger geometric parameters and fluid flow parameters; namely, number of inner tubes, annulus hydraulic diameter, Reynolds numbers and input heat flux, on performance of the heat exchanger. Different coils with different numbers of inner tubes, namely, 1, 3, 4 and 5 tubes, were tested. Results showed that: (a) coil with three inner tubes has bitter heat transfer characteristics as compared with other coils, (b) coils with 3 and 4 inner tubes, respectively, have higher values of (the parameter used to measure performance and compactness of compact heat exchanger) as compared to other coils, (c) for all coils and at the tested ranges of Reynolds number and heat flux, input heat flux has no effect on heat transfer coefficients, and (d) pressure drop increases with increasing both of Reynolds number and number of inner tubes. Correlations of average Nusselt number were deduced from experimental data in terms of Reynolds number, Prandtl number and coil hydraulic diameter. Correlations prediction was compared with experimental data and the comparison was fair enough. |
