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Liquefied natural gas (LNG) is a clean energy source that shows great potential for further development. In the production and transportation process of LNG, heat exchanger is an essential device that conducts the liquefaction and vaporization operations. With the booming development of floating LNG (FLNG) technology, higher requirements have been...
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Printed Circuit Heat Exchangers (PCHEs) are considered an excellent alternative for the main cryogenic heat exchanger of Floating Liquefied Natural Gas (FLNG) facilities due to their compact structure and strong heat transfer performance. However, it is unclear how to configure the geometry of the PCHE channels to achieve its optimal performance in...
Citations
... However, the actual flow length was a zigzag channel of 216 mm and a straight channel of 209 mm. Therefore, the criterion ζ = ( / 0 )/( / 0 ) was applied to investigate the pressure drop and heat transfer performance for a given pumping power [7,[23][24][25]. Where the subscript 0 represents the comprehensive minimum performance value of the straight channel at a mass flow rate of 5.10810 -5 kg/s as a basis. ...
Mini-channel heat exchanger are widely used due to their compact structures and high efficiency. Integrating heat exchangers with triply periodic minimal surfaces (TPMS) has shown great potential to optimize the flow and heat transfer performance. In this study, Gyroid (G), Diamond (D) and IWP type TPMS based heat exchangers are constructed in three dimensions. The thermal hydraulic, entropy production and flow-induced noise characteristics of TPMS based heat exchangers are numerically investigated. The results indicate that the TPMS channels with larger viscosity entropy production have smaller thermal entropy production due to the greater flow disturbance. The G-channel has the highest friction factor and the lowest sound source intensity, while the D-channel obtains the strongest sound source intensity due to frequent cross-collisions of the fluid. The sound source intensity of the IWP channel is 10% lower than the D-channel. The wall dipole sound source plays a dominant role in TPMS channels. This study provides different perspectives to evaluate the performance of a TPMS heat exchanger, and provides references for the design and optimization of TPMS heat exchangers.
Surface heat exchanger is extensively used for sustainable development in energy systems. In the surface heat exchanger, the heat transfers from hot flow to cold flow through separating solid surface. The heat transfer area of surface heat exchanger is usually constant when it is performing in energy system. Similarly, fixed plate heat exchanger is applied in electronic outdoor cabinet. In this paper, a novel approach to vary the heat transfer surface in heat exchanger is proposed. A blown plate heat exchanger is introduced for cabinet cooling system. The blown and fixed plate heat exchangers are compared. The heat transfer performances of the blown plate heat exchangers are the same with fixed plate heat exchanger for the same Reynolds numbers. For different Reynolds numbers, the blown plate heat exchanger with all mixed plates has the best performance and the temperature reduction of hot air is arrived 15.185 K, when the maximum temperature difference is 20 K.
Graphical Abstract
The liquid air energy storage assisted by liquefied natural gas is a promising large-scale storage method, but its development is limited by the lack of thermo-hydraulic data on the cryogenic printed circuit heat exchanger. A simplified model for conjugate heat transfer was built and solved by a commercial code FLUENT 14.5. Model validation was conducted by comparing results with experimental data. The nature of flow and heat transfer was revealed by quantifying the vortex strength and visualizing the vortex core. The influence of the inclined angle was investigated, and the Nusselt number and friction factor correlations for the best angle were developed. The minimum internal temperature approach for optimum system operation is approximately 6 K, located in the middle of the heat exchanger. Results indicate that the evolution of Dean vortices plays a crucial part in the augmentation of heat transfer. The secondary flow caused by elbows forces the fluid cores to strike the windward side periodically, which disturbs the boundary layer and enhances the fluid mixing. Entropy production analysis shows that the thermal entropy generation has a dominant share of total irreversibility. The best performance is achieved at an inclined angle of 45° since the irreversibility is reduced by augmenting the heat transfer.
The printed circuit heat exchanger(PCHE) is often utilized for the supercritical CO2(SCO2) Brayton cycle. This study proposed a assessed method with the dual effects of temperature and pressure to investigate the heat transfer performance(HTP) for PCHE derived from theoretical analysis and numerical validation. The influence of various operating conditions on total and hot-side heat transfer coefficient(HTC) was analyzed. The results showed that the PCHE may achieve better HTP when the critical index was near 1. The assessed way had been verified by utilizing the existing experimental data. The total and hot-side HTC for SCO2-Water PCHE were higher than that of SCO2-SCO2 PCHE, which may increase as cold-side Reynolds number increases. The effect of entropy generation rate for heat transfer on the irreversibility was larger than that of entropy generation rate for viscosity. This study may offer theoretical guidance for optimization of heat exchangers.
The discontinuous airfoil-fin printed circuit heat exchanger is a leading candidate due to its high compactness, high efficiency, and ability to endure extreme conditions. In this paper, an unusual asymmetric airfoil-fin heat exchanger is experimentally investigated using the supercritical carbon dioxide and water experimental system. The effects of working parameters and flow direction on the heat transfer performance are analyzed based on the average thermal-resistance ratio. Meanwhile, the effects of flow directions on the comprehensive performance are quantitatively evaluated. Compared with the overall thermal resistance, the average thermal-resistance ratio is more sensitive in evaluating the heat transfer performance. The reverse flow hardly improves the heat transfer, while significantly amplifies the pressure drop. Compared with the reverse flow, when the bulk temperature of CO2 is 38 °C, 41 °C and 47 °C, the comprehensive performance of forward flow increases by 6.1%, 4% and 1.8%, respectively. Finally, the unified heat transfer correlation for two opposite flow directions is proposed within applicable ranges.
To solve the shortcomings of small cooling capacity of the current Joule-Thomson (J-T) cryocooler, a multi-layer microchannel J-T cryocooler is designed and fabricated by printed circuit board technology. The characteristic of the cryocooler is that there exists heat transfer while throttling. The coupling effect of heat transfer and throttling affects the overall performance of cryocooler. Therefore, the steady-state model was established for each part of the cryocooler. The P-h diagram of N2 was calculated by the model. Considering the variation of J-T coefficient (μjt) in the process, the coupling performance of heat transfer and throttling in the J-T cryocooler were analyzed. A new parameter, J-T efficiency (ηjt), was proposed to evaluate the J-T effect. Additionally, according to the dependence of μjt with temperature and pressure, the refrigeration performance of the cryocooler under different working conditions was simulated. The results show that the heat transfer in the throttle can enhance the throttling effect. When the inlet temperature is 285.0K and the inlet pressure increases to 18.00MPa, the N2 temperature at the cold end reaches 116.3K, and the gross cooling capacity is 4.55W. When the inlet pressure is 6.00MPa and the inlet temperature reduces to 195.0K, the temperature at the cold end can reach to the saturated temperature of 103.2K, and the maximum gross cooling capacity is 7.68W. For the two groups of working conditions, the heat transfer in the throttle can enhance the J-T effect. ηjt reaches 95.87% and 94.76%, the proportion of temperature drop caused by J-T effect is 56.10% and 68.03% of the total temperature drops, respectively. Finally, the variation laws of inlet temperature and ηjt are analyzed when N2 reaches saturated temperature under different pressures to guide the selection of inlet parameters.
