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Phytochemical investigation of the aerial parts of Chimonanthus salicifolius resulted in the isolation of two sesquiterpenoids, 8 α -hydroxy-T-muurolol and (1 α ,6 β ,7 β )-cadinane-4-en-8 α ,10 α -diol, together with 13 known compounds. The 15 structures were established by means of 1D and 2D NMR spectroscopy. The relative and absolute configurations of 8 α -hydroxy-T-muurolol and 8 α ,11-elemodiol were achieved by NOESY experiments and X-ray crystallography using CuK α radiation. 8 α -hydroxy-T-muurolol and (1 α ,6 β ,7 β )-cadinane-4-en-8 α ,10 α -diol showed immunosuppressive activities in a dose-dependent manner. [ABSTRACT FROM AUTHOR]

Abstract: The increasing industrial applications of boiling heat transfer call for high fidelity and efficient numerical predictions, of which a hybrid scheme simulation combining CFD and boiling model is a promising candidate. To this end, the current research put forth a dynamical boiling model. The model dynamically integrates the sub-processes associated with a boiling cycle, including those of the formation of a thermal boundary layer, the evaporation of a sublayer film, the growth and detachment of a bubble as well as the concomitant heat transfer. In the bubble growth period the growth rate is given by summing the evaporation over the vapor-liquid interface surrounded by a micro sublayer film, a macro film in the thermal boundary layer, and bulk fluid respectively. The computation solves transient governing equations for the instantaneous distribution and heat transfer of the micro sublayer film. It also works out automatically an apparent contact angle. The bubble detachment is processed in a new way that calculates the various forces acting on the bubble to trace the detaching process. Numerical results of the boiling from single nuclei agree with experimental data with reasonable accuracies. Comments are given about the possible improvement of the model and the further development toward practical hybrid simulations of the boiling phenomena. [Copyright &y& Elsevier]

Abstract: This article presents a two-step procedure for the computation of radiative heat transfer with anisotropic scattering and reflection. It is based on a concept that the coincident processes of absorption and scattering/reflection can be separated factitiously. All medium elements and wall surfaces are supposed to be pure-absorbing when receiving incident radiation. Afterwards they emit the scattered/reflected radiations. The absorption of both the initial and the secondary radiations can be assessed by the direct exchange area. It is needed to repeat the processes for a few times until the radiations are substantially absorbed. For anisotropic scattering/reflection, a vector summation obtains the directional distribution of emissive power. The method is validated by several benchmark computations in terms of emissive power and heat transfer coefficients. It is shown that the method gives more accurate solution than the isotropic scaling for the heat transfer in anisotropically scattering media. [Copyright &y& Elsevier]

The toroidal thermosyphon is widely used in solar water systems, nuclear reactors and geothermal energy systems, etc. The flow stability has been the main research topic but little attention was paid to the influence of boundary conditions. An experiment was performed on a copper torus. The Lorenz-like chaotic flow was not observed in clear contrast to that in the usual glass torus. Numerical simulation showed that the axial heat conduction in the tube wall deformed the heat flux distribution. A one-dimensional model generally formulated the boundary condition effects on the Hopf bifurcation. The model suggested that the metal wall could efficiently eliminate temperature perturbation, decrease the driving force and hence stabilize the global flow. The model was also used to analyze the effect of torus tilt angle on flow stability, whose conclusion agreed with previous experiment. [Copyright &y& Elsevier]

This paper presents a new simulation method with lower computation consumption for microtube heat exchangers (MSTEs) used for supercritical CO 2 cooling, which maintains high precision. The heat transfer characteristics in the shell pass and tube pass and the relationship between them are both analyzed. Baffles lead to various regions with different follow patterns and heat transfer features in the shell pass. Furthermore, higher heat transfer performance in the shell pass leads to heat transfer enhancement in the tube pass due to the CO 2 near-pseudocritical characteristics. The optimization method based on the eigenfunction of Δ P i = F(A i) which characterizes the influence of baffles on the comprehensive performance of MSTEs focuses on the difference among local heat exchange and pressure loss in multiple segments and guides to reduce the pressure loss while the heat transfer load and area remain unchanged. The optimized baffles arrangement is found according to the numerical results and the optimization method. The comparison between the simulation results of the original and optimized MSTEs shows that the optimization method is effective for heat exchangers with variable local heat exchange features and pressure loss performances. [ABSTRACT FROM AUTHOR]

• The MSTEs consisting of tubes with an inner diameter of 1.6 mm are experimentally investigated as the pre-cooler of S-CO 2. • The effect of baffles on the heat transfer and pressure drop performance of the MSTEs is analyzed. • The accuracy of different correlations of the supercritical CO 2 heat transfer coefficient is verified. • The pressure drop of CO 2 in the MSTEs is tested and the pressure loss coefficient is fitted. The characteristics of heat transfer and pressure drop of supercritical CO 2 and water in microtube heat exchangers with and without baffles are studied experimentally. The tube bundle of the microtube heat exchanger consists of 37 stainless steel tubes with an inner diameter of 1.6 mm and an outer diameter of 2 mm. The length of the tube is 500 mm. The experiments are divided into hot water–cold water heat transfer experiments and supercritical CO 2 –water heat transfer experiments. The results of hot water–cold water experiments are shown to produce a large discrepancy with the conventional heat transfer correlation and new correlations of water convective heat transfer coefficient in the shell side are fitted according to the experimental results. The comprehensive performance of the heat transfer and pressure drop of the microtube heat exchanger with baffles is better than that without baffles. The results of CO 2 –water experiments show that the prediction of the design program based on Dang's heat transfer correlation of supercritical CO 2 is relatively in better agreement with the experimental results than others. The overall pressure drop of CO 2 in microtube heat exchangers is small. However, the pressure drop at the inlet and outlet of microtube heat exchangers is larger than that of conventional shell and tube heat exchangers. The pressure loss coefficient is modified according to the experimental results. [ABSTRACT FROM AUTHOR]

More and more fixed geometry structures are being manufactured to enhance the boiling heat transfer (BHT). However, they usually perform well at a special heat load and don't always have good BHT properties. Applying shape memory alloy (SMA) material to change the geometry is a new solution to achieve optimal effect at different boiling condition. Pool boiling heat transfer on deformable structures made of SMA in three fluids (ethanol, FC-72, water) with different thermal properties was explored. Comparing heat flux versus wall superheat and heat transfer coefficient (HTC) at different fluxes with fixed geometry, it was found that deformable structure combines the merits of closed-tunnel and open-tunnel. At low heat fluxes, it can increase the number of nucleation sites inside the closed tunnels with bent fins and after reverting to the original shape, the nucleation sites are activated and the bubble growth and departure is accelerated to enhance the HTC significantly. So by choosing the appropriate time and opportunity for different fluids to open the tunnels, the deformable structures can be used to achieve adaptive-control of boiling heat transfer. In terms of theoretical analysis, the existing correlations for fixed structures have not been fit for deformable structures, because large-scale deformation make the heat transfer mechanism different from the fixed geometry structure. Thus experimental results are compared with fitting curves and a new correlation was deduced. [ABSTRACT FROM AUTHOR]

The permeability of porous media is a significant parameter that determines the upper limit of heat transfer in heat pipes. Mesh screens, as a standard structure, offer many advantages such as simple fabrication, a wide range, and high controllability of permeability. However, there is no common and accurate theoretical formula to predict the permeability of the multilayer mesh screen superposition structure due to its randomness. In this paper, through a combination of experimental methods, numerical simulations, and microscopic observations, a statistical law regarding the superposition structure is identified. Specifically, the complex superposition forms can be simplified to the combination of three basic compact configurations. Based on this statistical law, a unified mathematical relationship between permeability and screen structure was derived. [ABSTRACT FROM AUTHOR]

The permeability of porous media is an important parameter in designing ultra-thin vapor chambers, while there was a little researched on the ultra-thin mesh wick with a free liquid-gas interface. In the paper, the permeability of single layer mesh screen with different mesh numbers and diameters was investigated using experimental and numerical simulation methods. Experimentally, according to the Bernoulli equation with the resistance term, the flow resistance could be balanced by gravity in a sloping placed wick. And when the flow reaches the equilibrium state, the permeability can be obtained through the flow rate and the incline angle based on Darcy's law. In order to further explore the relationship between permeability and mesh structure, scanning electron microscope (SEM) and optical microscope were used to observe the microstructure. Based on the scanning picture, numerical simulation was carried out to study the source of flow resistance. And then the relationship between permeability and structure parameters was obtained. The result shows that there is an approximately linear relationship between fRe (the product of loss coefficient and Reynolds number) and the hydraulic diameter in the position where the longitudinal and horizontal wires intersect. The work can support the calculation of the capillary limit in design of ultra-thin vapor chamber. [ABSTRACT FROM AUTHOR]

• Heat transfer behavior between the supercritical carbon dioxide and water in the microtube heat exchanger is numerically investigated. • The effects of pressure, mass fluxes and buoyancy on the heat transfer of CO 2 flowing at low reynolds numbers are obtained. • The flow patterns of water in the shell side influence the secondary flow intensity of CO 2. • Separate correlations should be used to get a better prediction of heat transfer due to different flow forms of CO 2 in the microtube heat exchanger. A numerical study on the heat transfer between supercritical carbon dioxide and water in the microtube heat exchanger at low mass fluxes of CO 2 is reported in this paper. The inner diameter of the tube used in the heat exchanger was 1.6 mm. Four sections with different heat transfer performance are found during the heat exchange process between CO 2 and water. The operating pressure, mass fluxes of CO 2 and water, buoyancy effect are considered to analyze the heat transfer characteristics of sCO 2. The heat transfer coefficient is found to be the maximum when the temperature is near pseudocritical point and the peak value increases when the pressure is getting closer to the critical point. The heat transfer coefficient increases with the increase of mass flux of CO 2. The buoyancy effect is found to have a significant influence on the heat transfer at the different locations of the tube. The secondary flow of CO 2 results in the enhancement of heat transfer on the top side of the tube and weakens the heat transfer on the bottom side. Different flow patterns of water in the shell side are compared in this study. The counter-current flow achieves the best heat transfer effect, while the downward flow is slightly better than the upward flow on the total heat transfer due to the different intensity of secondary flow. Existing different correlations should be used to get a better prediction of heat transfer depending on the state of CO 2 in the microtube heat exchanger, especially when CO 2 flows at a low mass flux. [ABSTRACT FROM AUTHOR]