Thermal performance of the chilled water spirally coiled finned tube in cross flow for air conditioning applications

AbstractThe thermal performance of spirally coiled finned tube in cross flow was investigated experimentally. The effects of curvature ratio, flow direction, fin pitch and flow rate of chilled water and air on thermal characteristics of spirally coiled finned tube have been studied. Six test sections with curvature ratios of 0.027, 0.03, 0.04, tube pitches of 18, 20, 30mm, and fin pitches of 33, 22, 11mm were used. The experiments were done using a pilot wind tunnel with air Reynolds number range 35,500–245,000. Innermost and outermost flow directions of chilled water with Reynolds number range 5700–25,300 have been investigated. The innermost flow direction has significant enhancement effect on the Nusselt number compared with outermost flow direction. The decrease of fin pitch enhances the Nusselt number on expense of pressure drop. Decreasing the curvature ratio increases air side Nusselt number on expense of pressure drop. A set of empirical expressions for predicting the friction factor and the Nusselt number for air flow across the spiral coils have been regressed based on the obtained data in the present experiments

Performance characteristics of shell and helically coiled tube heat exchanger under different tube cross-sections, inclination angles and nanofluids

The current research deals with an experimental and numerical inspection of the shell and helically coiled tube heat exchanger (SHCTHE) under various circular, elliptic, and square tube cross-sections. The research study strives to ameliorate the thermal-hydraulic performance with single nanofluids of Al2O3/H2O, MgO/H2O, and TiO2/H2O. Various factors were inspected to consider the heat exchanger performance under parameters, SHCTHE inclination angle, HCT diameter ratio, flow direction, the cross-section geometry shape, nanomaterials type, and nanomaterials concentration. The modeling engaging a numerical code tool of ANSYS-FLUENT 19 was accomplished with a 3D (RNG)/k–ϵ model. The mass flow rate and working fluid temperatures through the coil and shell sides were (0.05:0.2 kg/s at 80 °C and 0.05–0.2 kg/s at 10 °C, respectively. One of the most important results was that the SHCTHE with a circular tube cross-section gave the highest Nusselt number with an approximate percentage of 62.5%. The SHCTHE effectiveness and the number of transfer units were enhanced by around 19.35% and 30.78%, respectively, by the greater HCT diameter ratio and Al2O3 nanomaterials. Nusselt number, friction factor, and SHCTHE effectiveness were correlated through equations (52:55) with dimensionless factors and their limitations