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The vertical condensers have advantages of small occupation area, convenient in assemble or dismantle tube bundle and simple structure etc. However, the low heat transfer performance limits their applications. To enhance the heat transfer, a novel type of vertical condensers was designed by introducing trisection helical baffles with liquid dams and gaps for facilitating condensate drainage. Four configurations of vertical condensers with trisection helical baffle are experimentally studied and compared to a traditional segment baffle condenser. The enhancement ratio of trisection helical baffle schemes is about 1.5–2.5 and the heat transfer coefficient of the dual-thread trisection helical baffle scheme is superior to that of the single-thread one by about 19%. Assistant by the theoretical study, the experimental data is simulated and the condensation enhancement mechanisms by applying trisection helical baffle in vertical condenser are summarized as condensate drainage, short tube construct and reduce steam dead zone functions of the helical baffles. [ABSTRACT FROM AUTHOR]

The widely used fin-and-tube heat exchangers have a low air-side heat transfer capacity. Enhancing the air-side thermo-hydraulic performance is a key point of the relevant research. Vortex generators have been proven to be one of the most promising techniques to improve the air-side heat transfer capacity of the fin-and-tube heat exchangers. Herein, this paper proposed an original sinusoidal wavy winglet type vortex generator to achieve high heat transfer performance with moderate increased pressure drop penalty. A three-dimensional numerical simulation was conducted to explore the air-side thermo-hydraulic performance with Reynolds number ranging from 1027 to 2054. The longitudinal vortex is generated in the channel so as to enhance the intensify of convective heat transfer. Especially, the wave-shaped vortex generators can produce many local small-scale secondary flows. And it is confirmed that the frontal area of the vortex generator can be effectively extended by such wavy shape and a more intensified disturbance can be caused in the air-side. Furthermore, the effects of the attack angle (α), dimensionless height (H p) and especially arrange position of the vortex generator were investigated. Additionally, the ranges of the Nusselt number ratio, friction factor ratio and surafece goodness factor in this study are 1.09–1.52, 1.09–2.31, and 1.06–1.24, respectively. Moreover, it is also very crucial to evalute the grade of energy and to explore the irreversible loss druing the heat tranfer process in view of the second law of thermodynamics. And the thermal dissipation can be reduced by up to 5.85% compared with the plain fins from the perspective of exergy analysis. [ABSTRACT FROM AUTHOR]

A unilateral ladder type helical baffle heat exchanger (ULHBHX) which is a novel countercurrent U-tube heat exchanger was proposed and investigated for better characteristics of high heat transfer coefficient, low resistance, anti-vibration and anti-fouling with a spiral flow pattern than those of the conventional segment one. The numerical model of ULHBHX was established and simulated by CFD software with 38 heat transfer tubes and 2 rod and spacing tube assemblies in the lower half cylindrical space under the parameters of subcooling of a high pressure feedwater heater in power plants. Different views such as on baffle-parallel slices and polygonal slices were presented to show the flow patterns of the main helical flow, secondary vortex flow and the leakage flow. The influences of geometrical parameters of baffle pitch and projection length of the inclined section on heat transfer and pressure drop were discussed quantitatively. The results show that the shell-side heat transfer coefficient h o of the ULHBHXs is 13.2%–18.2%, with an average of 16.0%, higher than those of the corresponding segment schemes, and the comprehensive index h o Δ p o −1/3 is 15.7%–46.4%, with an average of 28.3%, higher than those of the corresponding segment schemes with identical baffle pitches in the discussed range. [ABSTRACT FROM AUTHOR]

• A novel helical baffle with small inclined angle and folded structure is proposed. • The new helical baffles can be created by cheap 2D laser cutting and folding. • The leakage between two folded helical baffles can be greatly decreased. • The novel electric heaters have excellent flow and heat transfer performances. • Folded helical baffles are more excellent at large equivalent angles in this work. The difficult manufacturing of helical baffles hinders the widespread application of the enhancement technology and the shortcut leakage between adjacent baffles impairs the enhancement effects. To solve these two issues, the promising anti-leakage and easy-to-manufacture helical baffles with small inclined angle and folded structure are proposed, which can be produced by 2D laser cutting and simple mechanical folding. The influence of different helical baffle configurations, including three normal helical schemes, three axial separation helical schemes, three novel folded axial separation helical baffle schemes and a segmental scheme on the performance of electric heaters are numerically investigated. The equivalent angles of helical schemes adopted in this work are 15°, 20° and 25°, and the inclined angle of helical baffles under axial separation connection style is 10°. Compared with the corresponding axial separation scheme without folding, the leakage can be significantly decreased, the heat transfer coefficients h and the comprehensive indices h ⋅Δ p −1/3 of FH15(10)°, FH20(10)° and FH25(10)° are increased by 6.5%/2.3%, 12.2%/7.3% and 20.4%/13.0%, and the averaged tube wall temperatures T w are decreased by 12.5 K, 25.4 K and 54.7 K, respectively. This research can provide feasibility for the extended application of helical baffles in electric heaters or heat exchangers. [ABSTRACT FROM AUTHOR]

• A novel helical baffle with small inclined angle and folded structure is proposed. • The new helical baffles can be created by cheap 2D laser cutting and folding. • The leakage between two folded helical baffles can be greatly decreased. • The novel electric heaters have excellent flow and heat transfer performances. • Folded helical baffles are more excellent at large equivalent angles in this work. The difficult manufacturing of helical baffles hinders the widespread application of the enhancement technology and the shortcut leakage between adjacent baffles impairs the enhancement effects. To solve these two issues, the promising anti-leakage and easy-to-manufacture helical baffles with small inclined angle and folded structure are proposed, which can be produced by 2D laser cutting and simple mechanical folding. The influence of different helical baffle configurations, including three normal helical schemes, three axial separation helical schemes, three novel folded axial separation helical baffle schemes and a segmental scheme on the performance of electric heaters are numerically investigated. The equivalent angles of helical schemes adopted in this work are 15°, 20° and 25°, and the inclined angle of helical baffles under axial separation connection style is 10°. Compared with the corresponding axial separation scheme without folding, the leakage can be significantly decreased, the heat transfer coefficients h and the comprehensive indices h ⋅Δ p −1/3 of FH15(10)°, FH20(10)° and FH25(10)° are increased by 6.5%/2.3%, 12.2%/7.3% and 20.4%/13.0%, and the averaged tube wall temperatures T w are decreased by 12.5 K, 25.4 K and 54.7 K, respectively. This research can provide feasibility for the extended application of helical baffles in electric heaters or heat exchangers. [ABSTRACT FROM AUTHOR]

• Coupling-vortex triangular tube layout is proposed without extra manufacturing cost. • Concurrent flow, larger A / B and smaller S cause stronger secondary flow. • The Nu and Nu · f −1/3 of C14.2S50 is 132.8% and 47.1% higher than R10.8. • Smaller S and smaller A / B lead to greater advantage of TETHXs-AVRCV. • The averaged Nu / Nu · f −1/3 of C12.3S50 are 7.8%/4.9% higher than those of P12.3S50. An innovative alternating V-rows triangular tube layout was devised for the twisted elliptical tube heat exchangers to enhance heat transfer between adjacent tubes. Under the same tube circumference, altogether eleven twisted elliptical tube heat exchangers with two tube layouts, diverse aspect ratios of twisted elliptical tubes and different twisted pitches were constructed and simulated, including five coupling-vortex schemes, five parallel-vortex schemes and a smooth round tube scheme R10.8. Water with constant physical properties was adopted as the working fluid. Shell-side Reynolds number varies from 2000 to 10,000. The results show that the concurrent flow and the irregular channel in coupling-vortex schemes, and the larger aspect ratio and the smaller twisted pitch of twisted elliptical tubes help intensify turbulence and secondary flow. Compared with R10.8, the averaged Nu and Nu · f −1/3 of coupling-vortex scheme C14.2S50 are improved by 132.8% and 47.1%, respectively. Under shorter twisted pitch, smaller aspect ratio and lower Reynolds number, coupling-vortex schemes can acquire superior heat transfer capability than corresponding parallel-vortex schemes but will not increase manufacturing cost. Compared with P12.3S50, the maximum and averaged Nu of C12.3S50 are increased by 9.5% and 7.8% while the maximum and averaged Nu · f −1/3 are increased by 6.4% and 4.9%. [ABSTRACT FROM AUTHOR]