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An improved momentum-exchanged immersed boundary-based lattice Boltzmann method (MEIB-LBM) is proposed for incompressible viscous flows in this paper. In present work, we come back to the intrinsic feature of LBM, which uses the density distribution function as a dependent variable to evolve the flow field, and use the non-equilibrium density distribution function correction at the neighbour Euler mesh points to satisfy the non-slip boundary condition on the immersed boundary. The improvements for the original MEIB-LBM are that the intrinsic feature of LBM is kept and the flow penetration is removed. Examples, including force convection over a stationary heated circular cylinder for heat flux condition, and natural convection with a buoyant circle particle in viscous fluid, are provided to validate the present method. [ABSTRACT FROM AUTHOR]

Abstract: Dry ice blockage in a CO2-solid–gas-flow-based ultra-low temperature cascade refrigeration system is investigated experimentally by a visualization test and a system study of the liquid CO2 blew into an expansion tube through a Throttle needle valve. The visualization test shows that dry ice sedimentation occurs in low flow velocity and the dry ice formation makes the heat transfer behavior of CO2 complicated. The sedimentation also occurs at low condensation temperature and low heating power input. Based on the present investigation, it is found that the present ultra-low temperature cascade refrigeration system is better to work at heating power input above 900 W and condensation temperature above −20 °C. At suitable operating condition, the present ultra-low temperature cascade refrigeration system has been shown the capability of achieving ultra-low temperature −62 °C continuously and stably. [Copyright &y& Elsevier]

Abstract: In this article, natural convections of a magnetic fluid in a cubic cavity under a uniform magnetic field are investigated experimentally and numerically. Results obtained from experiments and numerical simulations reveal that the magnetic field and magnetization are influenced by temperature. There exist relative larger magnetization and magnetic forces in the regions near the upper wall and center inside the cavity than in the region near the bottom and side walls. A weak flow roll occurs inside cavity under the magnetic force, and it brings the low temperature fluid downward in the center region, and streams the high temperature fluid upward along the regions near the sidewalls. With the magnetic field imposed, the heat transfer inside the cavity is enhanced significantly compared to that without the magnetic field, and increasing the strength of the magnetic field the heat transfer is increased further. [Copyright &y& Elsevier]

Abstract: The magnetic body force in boiling two-phase temperature-sensitive magnetic fluid (TSMF) flow is known to effectively increase the driving force of magnetic fluid in a non-uniform magnetic field. Based on this mechanism, in the present study, a binary TSMF, which is a mixture of the TSMF and a low-boiling-saturation-temperature organic solution, is proposed to be used in a heat transport device to enhance its circulation. In order to see its performance in the heat transport device, the pressure difference at different heated temperatures, magnetic fields and inclination angles of the heating section are investigated experimentally and theoretically. Results showed that the driving force increases remarkably due to more gas phase appearing in the test fluid and the magnetization of it decreasing. At low magnetic field the driving force is enhanced greatly when the inclination angle is close to 60°, while at high magnetic field the driving force is remarkably enhanced due to the effect of the magnetic force in the inclination angle range from 0° to 30° and 60° to 90°. [Copyright &y& Elsevier]

Abstract: Based on the preparation of Al2O3, Fe2O3 and ZnFe2O4 nanofluid, the comparative experiments on the falling film absorption between ammonia–water and ammonia–water with various kinds of nano-particles are carried out. Experimental results show that the sorts and mass fraction of nano-particles, the viscosity and stability of nanofluid, as well as the mass fraction of ammonia in the basefluid are considered as the key parameters. The absorption of ammonia is weakened by only adding surfactants or adding poorly dispersed nano-particles. The increase of mass fraction of nano-particles with matched surfactants can improve the absorption rate of ammonia under the condition that the viscosity of nanofluid does not increase remarkably, and there is an optimal mass fraction for each kind of nano-particles and surfactant. With the increase in ammonia mass fraction of initial nanofluid, the absorption potential capacity decline, but the enhancing effect induced by the nanofluid is more obvious compared to that without nano-particles. The effective absorption ratio can be increased by 70% and 50% with Fe2O3 and ZnFe2O4 nanofluid respectively when the initial ammonia mass fraction is 15%. The absorption enhancement by the nanofluid is attributable to the heat transfer enhancement and the decrease in viscosity of nanofluid, which are strongly proved by the temperature differences in cooling water and nanofluids as well as the falling film flowing time. [Copyright &y& Elsevier]

Abstract: Experiment and numerical study were conducted to investigate the heat transfer characteristics of a thermo-sensitive magnetic fluid (TSMF) filled in a cubic container with a heat generating square cylinder stick inside and under a uniform magnetic field. The experimental results show that, regardless of the heat generating object sizes, the heat transfer characteristic of the TSMF is enhanced when the magnetic field is applied to the TSMF. However, the heat transfer of the TSMF becomes poor as the size of the inside heat generating object increases because the space where the fluids go through becomes narrower and the flow is obstructed when the heat generating object size becomes bigger. Numerical simulation based on the Lattice Boltzmann method confirmed the experimental findings, and disclosed more flow details of the natural convection of the TSMF inside cavity. [Copyright &y& Elsevier]

• Test rig of heat exchanger in superfluid helium cryogenic system is constructed. • Flow and heat transfer process in spiral wound heat exchanger is simulated. • Influence of fins structure on the thermal performance is investigated. Spiral wound heat exchanger has compact structure, good thermal performance per volume and simple manufacture process. It is the key equipment for the superfluid helium cryogenic system, which is able to recover the cold capacity and improve the refrigeration effectiveness. To investigate the influence of fins structure on the thermal performance of spiral wound heat exchanger is essential for its structure design. This study combines experiment and CFD simulation methods, which means a performance test rig of heat exchanger in superfluid helium cryogenic system is designed and constructed, and a numerical simulation method of flow and heat transfer in heat exchanger is established with working medium as helium in the temperature range of 2 K~4.2 K. In this study, the heat transfer effectiveness and pressure drop in shell domain of spiral wound heat exchanger is obtained with the number of fins in the range of 40~135, area of single fin in the range of 669 mm2~1885 mm2, area ratio in the range of 0%~36%. Furthermore, the mechanics of fins structure affect the thermal performance of spiral wound heat exchanger is explored. This study provides reliable method and experimental data for the structure design and thermal performances analysis of spiral wound heat exchanger with helium in the temperature range of 2 K~4.2 K. It is significant for the design and experimental test of superfluid helium cryogenic system. [ABSTRACT FROM AUTHOR]

Temperature-sensitive magnetic fluid (TSMF) is a magnetic nanoparticle suspension with strong temperature-dependent magnetization even at room temperature. TSMF is a refrigerant that enables high heat transport capability and pumpless long-distance heat transport. To enhance the heat transport capacity of the magnetically-driven heat transport device using TSMF, it is effective to use a heating body with a very large heat exchange surface such as a heat sink or a porous medium. In the present study, the thermal flow of TSMF around a single heating pipe under a magnetic field was investigated. Visualization of the temperature field by infrared thermography showed that the application of the magnetic field dramatically developed the thermal boundary layer and improved heat transfer. It was clarified by numerical analysis that this dramatic variation in the thermal boundary layer was associated with several vortexes generated by magnetic force in the vicinity of the heating pipe. [ABSTRACT FROM AUTHOR]