Abstract
Integrating air bubbles into the liquid phase of thermal exchangers serves as an efficient active strategy for improving convective heat transfer. This research examines the possibility of decreasing capital costs by incorporating tiny bubbles onto a Vertical - shell's shell side -and-helical-coiled-cylindrical thermal exchanger through a porous sparger. The thermal efficiency was assessed by altering the water flow rates on the shell side, the air injection flow rates, and the fluctuations in intake temperature. The comprehensive thermal transfer coefficient was determined by the experimental energy balancing and the logarithmic average temp discrepancy, whereas the thermal transfer area scaling, according to the six tenths rule, was employed to forecast the cost trajectory. Bubbling raised the total coefficient appreciably, with a maximum enhancement of approximately 119%. At a fixed heat duty, this implies a thermal transfer-area reduction of approximately 54.3% and, under the six-tenths rule, a predicted capital-cost reduction of approximately 37.5%. Shell-side bubbling therefore appears able to improve the economics of compact coiled-tube exchangers. The conclusion is conditional, however: compressor cost, air-injection power, pumping power, maintenance, and long-term reliability were left out of the present cost estimate.
Keywords: Helical coiled-cylindrical thermal exchanger; air-bubble injection; porous sparger; total coefficient of thermal transfer; capital-cost estimation; thermal transfer enhancement.
1. Introduction
Thermal exchangers appear throughout thermal systems, process plants, refrigeration equipment, energy-recovery units, and chemical processing, and in many installations, they represent a large share of the capital cost. A modest gain in heat transfer can thus shrink the surface area required, save material, and lower equipment cost โ which is why enhancement remains central to the design and optimisation of both compact and conventional exchangers
2. Results and Discussion
Figure 2 traces the total coefficient against Flow rates on the shell side for the various air-flow rates and inlet temp differences. In every case, shell-side bubbling raised the coefficient above the no-air reference. The gain is attributed to the rising bubbles, which stir the liquid, break up the thermal boundary layer around the coiled tube, and sharpen mixing near the thermal transfer surface.
3. Conclusion
This work assessed experimentally how shell-side bubbling affects the thermal performance and predicted capital cost of a Vertical - shell-and helical-coiled-cylindrical thermal exchanger. Fine bubbles were produced by a porous sparger, and the tests covered several water-flow rates, air-flow rates, and inlet temp differences..
References
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Full reference list available in the PDF version.