scholarly journals Analysis of Heat Transfer Performance in a Brayton Cycle Recuperator

2021 ◽  
Vol 8 (3A) ◽  
Author(s):  
Elvis Falcão De Araújo ◽  
Guilherme Borges Ribeiro ◽  
Lamartine Nogueira Frutuoso Guimarães
Keyword(s):  
Heat Transfer ◽  
Heat Exchanger ◽  
Transfer Rate ◽  
Heat Transfer Performance ◽  
Power Conversion ◽  
Brayton Cycle ◽  
Transfer Performance ◽  
Convection Coefficient ◽  
Cold Side ◽  
Colburn Factor

Thermodynamic cycles are currently the most wanted means of converting nuclear power into available work due to the higher conversion efficiencies provided. Rankine cycles have been greatly applied for terrestrial reactors and nuclear submarines, while a lot of space projects have been using Brayton cycles for power conversion mainly due to mitigation in power-to-radiator area ratio. Regenerative Brayton cycles can present a considerable power conversion efficiency improvement when compared to the regular ones because of a reduction on the power demand from the hot heat exchanger of a cycle to achieve the same net output power. In this work, a cross-flow heat exchanger with He-Xe (40 g/mol) working fluid and Inconel 617 structural material used as the recuperator for the closed Brayton cycle of a nuclear reactor applicable for space systems is assessed in terms of heat transfer performance. The recuperator tubes are arranged in a staggered distribution around the exchanger axis. The matrix of tubes has a fixed count of 4 rows along the exchanger axis, while the number of tubes around the axis is variable, where the samples of 5, 7, 9, 12 and 16 are tested. The characteristic curves of heat transfer rate, effectiveness, convection coefficient and Colburn factor are built for each of the studied geometries in function of the Reynolds number. The obtained values for each of these parameters range between 1892.49 and 8493.21W (heat transfer rate), 0.165 and 0.325 (effectiveness), 60.3822 and 176.9682 W/m2K (cold side convection coefficient), 30.3276 and 104.3263 W/m2K (hot side convection coefficient), 0.0071 and 0.0109 (cold side Colburn factor), 0.0523 and 0.1370 (hot side Colburn factor).

scholarly journals Study on Surface Condensate Water Removal and Heat Transfer Performance of a Minichannel Heat Exchanger

Energies ◽  
2020 ◽  
Vol 13 (5) ◽  
pp. 1065
Author(s):  
Xiuli Liu ◽  
Hua Chen ◽  
Xiaolin Wang ◽  
Gholamreza Kefayati
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Heat Exchanger ◽  
Transfer Coefficient ◽  
Transfer Rate ◽  
Heat Transfer Performance ◽  
Transfer Performance ◽  
Air Velocity ◽  
Overall Heat Transfer Coefficient ◽  
Minichannel Heat Exchanger

The condensate on the surface of the minichannel heat exchanger generated during air cooling substantially reduces the heat transfer performance as it works as an evaporator in the air-conditioning system. This has received much attention in scientific communities. In this paper, the effect of operating parameters on the heat transfer performance of a minichannel heat exchanger (MHE) is investigated under an evaporator working condition. An experimental MHE test system is developed for this purpose, and extensive experimental studies are conducted under a wide range of working conditions using the water-cooling method. The inlet air temperature shows a large effect on the overall heat transfer coefficient, while the inlet air relative humidity shows a large effect on the condensate aggregation rate. The airside heat transfer coefficient increases from 66 to 81 W/(m2·K) when the inlet air temperature increases from 30 to 35 °C. While the condensate aggregation rate on the MHE surface increases by up to 1.8 times when the relative humidity increases from 50% to 70%. The optimal air velocity, 2.5 m/s, is identified in terms of the heat transfer rate and airside heat transfer coefficient of the MHE. It is also found that the heat transfer rate and overall heat transfer coefficient increase as the air velocity increases from 1.5 to 2.5 m/s and decreases above 2.5 m/s. Furthermore, a large amount of condensate accumulates on the MHE surface lowering the MHE heat transfer. The inclined installation angle of the MHE in the wind tunnel effectively enhances heat transfer performance on the MHE surface. The experimental results provide useful information for reducing condensate accumulation and enhancing microchannel heat transfer.

Heat Transfer in Serpentine Flow Passages With Rotation

1994 ◽  
Vol 116 (1) ◽  
pp. 133-140 ◽  
Author(s):  
S. Mochizuki ◽  
J. Takamura ◽  
S. Yamawaki ◽  
Wen-Jei Yang
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Rate ◽  
Transfer Rate ◽  
Heat Transfer Performance ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Transfer Performance ◽  
Flow Passage ◽  
Rotation Numbers ◽  
Straight Flow

Heat transfer characteristics of a three-pass serpentine flow passage with rotation are experimentally studied. The walls of the square flow passage are plated with thin stainless-steel foils through which electrical current is applied to generate heat. The local heat transfer performance on the four side walls of the three straight flow passages and two turning elbows are determined for both stationary and rotating cases. The throughflow Reynolds, Rayleigh (centrifugal type), and rotation numbers are varied. It is revealed that three-dimensional flow structures cause the heat transfer rate at the bends to be substantially higher than at the straight flow passages. This mechanism is revealed by means of a flow visualization experiment for a nonrotating case. Along the first straight flow passage, the heat transfer rate is increased on the trailing surface but is reduced on the leading surface, due to the action of secondary streams induced by the Coriolis force. At low Reynolds numbers, the local heat transfer performance is primarily a function of buoyancy force. In the higher Reynolds number range, however, the circumferentially averaged Nusselt number is only a weak function of the Rayleigh and rotation numbers.

Heat Transfer Performance of Different Nanofluids Flows in a Helically Coiled Heat Exchanger

2013 ◽  
Vol 832 ◽  
pp. 160-165 ◽  
Author(s):  
Mohammad Alam Khairul ◽  
Rahman Saidur ◽  
Altab Hossain ◽  
Mohammad Abdul Alim ◽  
Islam Mohammed Mahbubul
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Heat Exchanger ◽  
Pressure Drop ◽  
Transfer Coefficient ◽  
Friction Factor ◽  
Heat Exchangers ◽  
Heat Transfer Performance ◽  
Volume Concentration ◽  
Transfer Performance

Helically coiled heat exchangers are globally used in various industrial applications for their high heat transfer performance and compact size. Nanofluids can provide excellent thermal performance of this type of heat exchangers. In the present study, the effect of different nanofluids on the heat transfer performance in a helically coiled heat exchanger is examined. Four different types of nanofluids CuO/water, Al2O3/water, SiO2/water, and ZnO/water with volume fractions 1 vol.% to 4 vol.% was used throughout this analysis and volume flow rate was remained constant at 3 LPM. Results show that the heat transfer coefficient is high for higher particle volume concentration of CuO/water, Al2O3/water and ZnO/water nanofluids, while the values of the friction factor and pressure drop significantly increase with the increase of nanoparticle volume concentration. On the contrary, low heat transfer coefficient was found in higher concentration of SiO2/water nanofluids. The highest enhancement of heat transfer coefficient and lowest friction factor occurred for CuO/water nanofluids among the four nanofluids. However, highest friction factor and lowest heat transfer coefficient were found for SiO2/water nanofluids. The results reveal that, CuO/water nanofluids indicate significant heat transfer performance for helically coiled heat exchanger systems though this nanofluids exhibits higher pressure drop.

scholarly journals Effect of Magnetic Nanofluids on the Performance of a Fin-Tube Heat Exchanger

2021 ◽  
Vol 11 (19) ◽  
pp. 9261
Author(s):  
Yun-Seok Choi ◽  
Youn-Jea Kim
Keyword(s):  
Heat Transfer ◽  
Heat Exchanger ◽  
Magnetic Fields ◽  
Heat Transfer Performance ◽  
Permanent Magnets ◽  
Convective Heat Transfer Coefficient ◽  
Transfer Performance ◽  
Tube Heat Exchanger ◽  
Improve Heat Transfer ◽  
Fin Tube

As electrical devices become smaller, it is essential to maintain operating temperature for safety and durability. Therefore, there are efforts to improve heat transfer performance under various conditions, such as using extended surfaces and nanofluids. Among them, cooling methods using ferrofluid are drawing the attention of many researchers. This fluid can control the movement of the fluid in magnetic fields. In this study, the heat transfer performance of a fin-tube heat exchanger, using ferrofluid as a coolant, was analyzed when external magnetic fields were applied. Permanent magnets were placed outside the heat exchanger. When the magnetic fields were applied, a change in the thermal boundary layer was observed. It also formed vortexes, which affected the formation of flow patterns. The vortex causes energy exchanges in the flow field, activating thermal diffusion and improving heat transfer. A numerical analysis was used to observe the cooling performance of heat exchangers, as the strength and number of the external magnetic fields were varying. VGs (vortex generators) were also installed to create vortex fields. A convective heat transfer coefficient was calculated to determine the heat transfer rate. In addition, the comparative analysis was performed with graphical results using contours of temperature and velocity.

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