•The effect of header and channels’ orientations on phase distribution in parallel micro-channels was clarified.•The flow behaviors of three inlet flow patterns in the header were visually analyzed.•The suitable orientation of header and channels for each flow pattern was obtained.An experimental investigation was conducted to study the effect of header and channels orientations on the two-phase flow distribution in parallel micro-channels. The parallel micro-channels was composed of a header with hydraulic diameter of 0.667 mm and three parallel channels with hydraulic diameter of 0.500 mm, all with rectangle cross sections. Nitrogen and 0.03 wt% sodium dodecyl sulfate (SDS) solution were used as the test working fluids. The inlet superficial velocities of gas and liquid varied from 0.200 to 16.0 m/s and from 0.0246 to 0.650 m/s, respectively. The fluid dynamics of two-phase flow splitting in parallel micro-channels was captured by high speed recording technique and three flow patterns were observed at the inlet. It was found that the phase distribution characteristics of two-phase flow in parallel channels highly depended on the inlet flow patterns and the orientations of header and channels. For slug flow, a uniform phase distribution was achieved in horizontal header with vertically downward channels, whereas the distribution of slug-annular flow was improved in vertically upward header and horizontal channels. For annular flow, two-phase inhomogeneous distribution reached the highest when the header was vertically downward.

•Structure of parallel air-cooled BTMS is optimized to improve cooling performance.•Widths of divergence plenum and convergence plenum are optimized using Newton method.•Fixed inlet flow rate, temperature difference of battery pack is reduced remarkably.•Fixed consumed power, temperature difference of battery pack is reduced remarkably.•For unsteady situation, temperature difference of battery pack is reduced remarkably.Battery thermal management system (BTMS) is critical to battery packs in electric vehicles, which significantly influences the service life of the battery packs and the performance of the electric vehicles. In this paper, the structure optimization of the parallel air-cooled BTMS is investigated to improve the cooling performance of the system. The flow resistance network model is introduced to calculate the velocities in the cooling channels of the system. The numerical results show that the velocities in the cooling channels calculated by the flow resistance network model are in good agreement with the ones calculated by CFD method, validating the effectiveness of the model. Furthermore, the model can save much calculation time, which is applicable to combine with the optimization approaches for structure optimization of BTMS. Subsequently, the structure of the BTMS is optimized through arranging the widths of the inlet divergence plenum and the outlet convergence plenum without changing the layout of the battery cells. Newton method is introduced to combine with the flow resistance network model to obtain the optimal plenum widths, with the target of minimizing the standard deviation of airflow velocities in the cooling channels. The optimization with fixed inlet flow rate and the one with fixed power consumption are both conducted. Three-dimensional CFD calculations for both the original BTMS and the optimized BTMS are performed, respectively. The results show that the cooling performance of the BTMS can be improved significantly after optimization using the proposed method. For the situation with fixed inlet flow rate and constant heat generation of the battery pack, the maximum temperature difference of the battery pack is reduced by 45% after optimization. For the situation with fixed power consumption and constant heat generation of the battery pack, the maximum temperature difference of the battery pack is reduced by 41% after optimization. Moreover, the maximum temperature of the battery pack is also reduced slightly after optimization. For the situation with fixed power consumption and unsteady heat generation of the battery pack, the maximum temperature differences of the battery pack are still reduced by 35% and 32% respectively for 4C and 5C discharge processes after optimization. It can be concluded that Newton method combined with the flow resistance network model is an effective method to optimize the structure of the parallel air-cooled BTMS and to improve the cooling performance of the system.

•Configuration optimization of battery pack in air-cooled BTMS is conducted.•Simplified models are used to calculate the battery cell temperature.•An optimization strategy is proposed to optimize the battery cell spacings.•Temperature difference of battery pack is reduced remarkably after optimization.Battery thermal management system (BTMS) is essential for heat dissipation of the battery pack to guarantee the safety of electric vehicles. Among the various BTMSs, the parallel air-cooled system is one of the most commonly used solutions. In this paper, the configuration of the battery pack in parallel air-cooled BTMS is optimized through arranging the spacings among the battery cells for cooling performance improvement. The flow resistance network model is introduced to calculate the velocities of the cooling channels. The heat transfer model is used to calculate the battery cell temperature. Combining these two models, an optimization strategy is proposed to optimize the configuration of the battery pack under the constant cell heat generation rate. The numerical results of typical cases show that the optimization strategy can obtain the final solution in only several times of adjustments of cell spacings. The cooling performance of the BTMS is improved remarkably after optimization. The maximum temperature difference is reduced by 42% and the maximum temperature of the battery pack is reduced slightly after optimization, with no increment on the total pressure drop of the system. Furthermore, the optimized BTMS still performs much better than the original one for various inlet flow rates and for the situation of unsteady heat generation rate.

•Quantify the relationship between the heat transfer capability and the confined bubble behaviors.•Capture distinct heat transfer features in the confined microchannels.•Explore the exact effect of the flow patterns on the heat transfer mechanisms.•Propose a novelty theoretical model based on Chen's model.•91.3% of the experimental data is within ±15% deviation with the present prediction.Bubble behavior in horizontal ultra-shallow microchannels displays distinct features in flow boiling heat transfer process, which is embodied as the fast elongation and deformation. It expands the range of the microlayer region and causes effective disturbances to the main flow, and therefore contributes to the enhancement in heat transfer. However, too fast deformation of the confined bubbles also results in rapid reducing of the liquid film thickness, causing the early appearance and short span of the annular flow. The enhancement in the heat transfer capability is then limited or even weakened. These distinct features lead to unsuitable predictions of classic correlations for the experimental data. The average error of the classic correlations exceeds 50% and the largest deviation reaches 125%. On the ground of the visualization experimental results, a theoretical model based on Chen’s model is proposed to calculate the flow boiling heat transfer coefficient in horizontal ultra-shallow microchannels. The presented model can be applied for both the elongation bubble flow and the annular flow as the heat transfer mechanism for these two flow patterns are specially considered respectively. Verified by the measured data, the average error of the model successfully drops to ±15%, from ±52.4% of the Chen’s model whose prediction fitted experimental data the best among the classic correlations.

•Heat source layout problem is optimized using simulated annealing method (SA).•Mathematical analysis is conducted to illustrate the applicability of SA.•The solutions are improved by SA compared to the ones of random distribution.•SA needs more calculation to obtain the solution than bionic optimization (BO).•SA performs better than BO for the case with asymmetric boundary conditions.Heat source layout optimization is an effective way to enhance heat transfer for electronic cooling. In this paper, the heat source layout optimization in two-dimensional heat conduction is investigated using simulated annealing (SA) method. Mathematical analysis is conducted to transform the heat source layout problem into a combinatorial optimization problem, which can be solved by SA. Three typical cases with various boundary conditions are introduced to validate the effectiveness of SA for heat source layout optimization. The solutions of SA are compared to the ones of random distribution (RD) and the ones of bionic optimization (BO). The results indicate that the maximum temperature of the domain can be remarkably reduced after optimizing the heat source layout using SA compared to RD. Compared to BO, it needs more computational time for SA to obtain the solution. Furthermore, the maximum temperature after optimizing by BO is lower than the ones by SA for the cases with symmetric boundary conditions. While for the case with asymmetric boundary conditions, SA performs better and the maximum temperature lower than BO is obtained. It can be concluded that simulated annealing method is effective to optimize the heat source layout problem in heat conduction.

•SA-AC/EG CPCM was obtained with optimum mass ratio of 90 wt.% SA-AC eutectic mixture.•The intrinsic latent heat of SA-AC was enhanced due to the EG porous filler.•The thermal conductivity of CPCM was significantly enhanced by a factor of 17.59.•CPCM possessed favorable heat storage capacity with appropriate melting temperature.•The second law of thermodynamics was used to explain phase change characteristics.Condensation heat of air-conditioner in household and public is a kind of indispensable waste heat, which is necessary to recover and reuse it. Herein, phase change material is widely used in exhaust heat recover and storage. In the present work, expanded graphite(EG) was introduced to stearic acid-acetamide(SA-AC) eutectic mixture, aiming at obtaining composite phase change material(CPCM) with high thermal conductivity, large heat storage capacity and favorable thermal repeatability for efficient heat recover. DSC results exhibited its remarkable energy storage capacity with a latent heat of CPCM of 186.8 J g−1 compared to most of the organic eutectic composite. The second law of thermodynamics was used to explain the phase change characteristics of the SA-AC/EG CPCMs corresponding to the pristine SA-AC eutectic mixture. The thermal conductivity of the CPCM was enhanced by 17.59 times comparing to pristine SA-AC. The results of thermal conductivity and infrared thermal images confirmed the CPCM possessed prominent heat storage efficiency. The thermo-physical properties of the SA-AC/EG CPCM after 500 accelerated thermal cycles were slightly decreased which did no distinct influence on heat storage. Due to the low cost and remarkable properties, the SA-AC/EG CPCM was a promising candidate for energy conservation by condensation heat recovery of air-conditioner.

•Pyrolytic graphite sheets-enhanced composite PCM based battery module was designed.•Composite PCM with 15–20 wt% EG is recommended to be used for battery thermal management.•Dynamic cycles and failure mode were conducted for PCM/PGS and PCM modules.•PGS forms a thermal conductive network for module to improve the thermal homogeneity.•PCM/PGS module can prevent thermal runaway propagation with less PCM consumption.Thermal management is a crucial strategy that needs to be carefully considered for lithium-ion batteries under extreme operating conditions. One promising approach is the use of phase change material (PCM), which can bring benefits such as passively thermal buffering and extending lifespan. In this paper, a paraffin/expanded graphite (EG) composites based battery module (PCM module), as well as the two dimensional thermal model is proposed. The effects of different EG mass fractions associated with different phase change enthalpy and thermal conductivity are investigated firstly under high-rate discharge condition. The results show that an optimal mass fraction of EG is needed to achieve the best thermal performance and the EG mass fraction of 15–20% is recommended to be used for battery thermal management. In order to further improve the overall performance, we also design a novel pyrolytic graphite sheets (PGS)-enhanced paraffin/EG composites based battery module (PCM/PGS module). EG with porous structure can create the primary thermal conductive network for PCM to increase the heat absorption rate. PGS forms the secondary thermal conductive network for the module to improve the whole thermal homogeneity. As a result, the as-designed PCM/PGS module presents much better heat dissipation performance and temperature uniformity compared with the PCM module during discharge–charge cycles. Also, the introduction of PGS is beneficial for thermal fluctuations and energy saving, for instance, the thermal performance of PCM/PGS module with a convective heat transfer coefficient of 50 W m−2 K−1 is comparable to PCM module with 200 W m−2 K−1. In the case of failure mode, to achieve the prevention of thermal runaway propagation, the spacing between cells for PCM module is up to 14 mm. However, the use of PGS lowers the spacing (i.e. less composite PCM consumption) by a decreasing rate of ∼71.4% in comparison with PCM module.

•The pressure drop exiting in three hybrid modules were comparatively analyzed.•The cooling performance of three hybrid modules were comparatively analyzed.•The cause of the difference in the cooling performance were analyzed.•The cooling performance of trapezoid channel module was further improved by changing the geometrical parameters.This paper investigates the effect of channel shape on the micro-channel and slot-jet module with the realizable k-ε turbulent model. Cooling performance of three channels with a same cross-section area but different shapes (rectangular, trapezoid and circular) are comparatively discussed. The hybrid module with circular channel has the maximum pressure drop at the same flow rate. While the hybrid module with trapezoid channel achieves the best cooling performance. Its superiority in the cooling performance enlarges with the heat flux rising and the pump power increasing, as compared with the other two hybrid modules. The local thermal resistance in the trapezoid channel exhibits peak-shape distribution, which is very different from the other two shapes channel. In addition, the cooling performance of the trapezoid channel module can be further improved by the optimization of the three geometric parameters (channel height, channel bottom width, and channel corner angle). When the optimal value for the three parameters is respectively adopted, the temperature on the bottom surface of the module can be reduced by 12.22%, 14.85% and 7.15% as compared with the worst design, and the temperature difference can also be reduced by 63.60%, 74.86% and 57.16%. What's more, the influence level of these parameters is also compared. Before the reference value, the channel height has the greatest influence on the module bottom surface temperature, whereas after the reference value, the corner angle becomes the largest influence factor. As for the temperature difference on the module bottom surface, it is just opposite.

•The formation and effects of porosity in phase change composites were analyzed.•A denser carbon network structure was detected with 24 wt.% expanded graphite.•The composites thermal conductivity and thermal stability were significantly enhanced.•Experimental data is about 9.6% deviation with the present prediction of modified model.As for thermal energy storage (TES) with phase change materials (PCM), thermal conductivity is a crucial property for heat storage/release rates and energy storage efficiency. In this study, a sort of new microcapsules based phase change composites (PCC) with carbon network to enhance the thermal conductivity and thermal stability was developed. The effective thermal conductivities of the as-prepared PCC were investigated by experiments and theoretical models. The influencing factors of PCC thermal conductivity were analyzed systematically. The morphology of PCC with carbon network structure was detected by energy dispersive spectroscopy using a scanning electron microscope. The experimental thermal conductivities were measured by the transient plane source method, while the theoretical ones were calculated by effective medium theory (ETM). Additionally, an effective theoretical model was proposed and modified to predict the thermal conductivity of such kind of composites with different mass fractions of expanded graphite (EG). As a result, obvious denser carbon network structure of PCC was further confirmed with 24 wt.% EG, the corresponding thermal conductivity was increased by as much as 24 times of the pristine paraffin. The predictions of modified Agari-Uno model were in good agreement with the experiments. Negligible change in thermal conductivity of the PCC was proved after 500 heating and cooling cycles. Hence, the enhancement on thermal properties of PCC can be promising for further applications in TES system.A sort of new microcapsules based phase change composites (PCC) with carbon network to enhance the thermal conductivity and thermal stability was developed. An effective modified model was presented based on the thermal conductivity of PCC with different mass fraction of EG. Verified by the measured data, the average error of the modified model is successfully limited within ±9.6%. This indicating the theoretical model proposed in this study can be generalized to predict the thermal conductivity of such kind of composites.Download high-res image (376KB)Download full-size image

•Designed three ULHP prototypes with various groove configurations.•Experimentally studied the start-up process and the gravity instability of the ULHPs.•Analyzed the effect of configurations on the density wave instability and the dry-out limit.•Divided instability boundary with Nsub-Npch figure.•Shape factor is proposed to effectively quantize the function of the groove configuration.Aims to solve the increasingly serious safety issue in thermal management system applied for power sources, the typical thermo-hydraulic devices—heat pipe, has been widely adopted. In this paper, the start-up characteristics at low heat load as well as the dry-out limits at high heat load of the Ultra-Thin (1.5 mm in thickness) Looped Heat Pipes (ULHPs) with three various groove configurations are investigated via experiments. Gravity instability and density instability are considered as the two main types of flow instability occurred in the ULHP system and have significant influences on the stable operation. The effects of the groove configurations on suppressing the flow instability and stabilizing the operation of two-phase flow in the ULHPs are both analyzed. The boundaries and the corresponding areas of the two types of instability for different configurations are plotted with well-known Nsub-Npch figure. The shape factor ξ and the contribution effect φ are proposed to effectively quantify the function of the groove configuration on stabilizing the system operation. The effectiveness of the method is verified with the experimental results and the theoretical analysis, providing possible tools for the further design and optimization in heat pipe systems.

•The phase distribution of two-phase slug flow in three parallel micro-channels was visually investigated.•The behavior of two-phase slug flow at the entrance of branch channels was analyzed.•The effects of inlet gas slug length and inlet real velocity on phase distribution were studied.•A relatively good phase distribution was obtained with short inlet gas slug length and high inlet real velocity.A visualization experimental study was conducted to investigate the phase distribution of two-phase slug flow in horizontal multi-parallel micro-channels, which was composed of a header with hydraulic diameter of 0.667 mm and three parallel channels with hydraulic diameter of 0.500 mm, all with rectangle cross section. Nitrogen and 0.03 wt% sodium dodecyl sulfate (SDS) solution were used as the test working fluids. The inlet superficial velocities of gas and liquid varied from 0.130 to 1.47 m/s and from 0.128 to 0.900 m/s, respectively. The high speed recording technique was utilized to elucidate the fluid dynamics of two-phase flow in parallel micro-channels. It was found that the phase distribution characteristics of two-phase flow in parallel channels highly depended on the inlet gas slug length and the inlet real velocity, and the channels in the front of the header can influence the phase distribution of the adjacent channel in the rear. Moreover, a uniform phase distribution was achieved at high real velocity with short gas slugs.

•Single factor analysis is performed for the heat dissipation performance.•CFD simulation results are validated by comparing with the experimental results.•Orthogonal design method is used to optimize the structure of the battery pack.The forced air cooling system is of great significance in the battery thermal management system because of its simple structure and low cost. The influences of three factors (the air-inlet angle, the air-outlet angle and the width of the air flow channel between battery cells) on the heat dissipation of a Lithium-ion battery pack are researched by experiments and computational fluid dynamics (CFD) simulations. Then the three structure parameters are optimized by using single factor analysis and orthogonal test method. It is shown that the layout of the air flow channels has great impacts on the maximum temperature and the temperature difference. The best cooling performance is obtained under the condition of 2.5° air-inlet angle, 2.5° air-outlet angle and equal channels width. With the optimization method, the maximum temperature and the temperature difference are decreased by 12.82% and 29.72% respectively. Therefore, the presented approach in this paper is able to optimize the battery thermal management system for electric vehicles.

•A heat pipe assisted phase change material based battery thermal management system is proposed.•The proposed system is compact and efficient from a view of practical application.•Cycling conditions are experimentally simulated for practical working environment.•The proposed system presents better thermal performance in comparison to other systems.•Combining forced air convection with heat pipe further enhances the cooling effect.In this paper, a heat pipe-assisted phase change material (PCM) based battery thermal management (BTM) system is designed to fulfill the comprehensive energy utilization for electric vehicles and hybrid electric vehicles. Combining the large heat storage capacity of the PCM with the excellent cooling effect of heat pipe, the as-constructed heat pipe-assisted PCM based BTM is feasible and effective with a relatively longer operation time and more suitable temperature. The experimental results show that the temperature maldistribution of battery module can be influenced by heat pipes when they are activated under high discharge rates of the batteries. Moreover, with forced air convection, the highest temperature could be controlled below 50 °C even under the highest discharge rate of 5C and a more stable and lower temperature fluctuation is obtained under cycling conditions. Meanwhile, the effectiveness of further increasing air velocity (i.e., more fan power consumption) is limited when the highest temperature continues to reduce at a lower rate due to the phase transition process of PCM. These results are expected to provide insights into the design and optimization of BTM systems.

•Proposed a novel LB model for the solid–liquid phase change with the convection in the porous media at the REV scale.•An effective total enthalpy energy conservation equation is derived.•An LB evolution equation without a phase change source term and a newly modified equilibrium distribution function are constructed.•Temperature and heat flux continuity conditions at the interface are inherently satisfied.•Numerical diffusion across the phase interface can be reduced by the MRT scheme.A novel lattice Boltzmann (LB) model with double distribution functions is proposed to simulate the solid–liquid phase change problems with the convection heat transfer in the porous media at the representative elementary volume scale. A generalized LB model is adopted to simulate the velocity field of the liquid region in the presence of the porous media. Based on the framework of a LB model for nonlinear convection–diffusion equation, an LB evolution equation without a phase change source term, as well as a newly modified equilibrium distribution function including the effective total enthalpy and thermal capacity ratio, are constructed to solve the effective total enthalpy energy conservation equation for the porous media. The macroscopic effective total enthalpy energy conservation equation can be exactly recovered from the present LB model by the Chapman–Enskog procedure. As compared with the most previous models, the present model can provide a higher computational efficiency, because the iterative step or linear equations solving procedure for the latent heat source term can be avoided. Furthermore, the temperature and heat flux continuity conditions at the interface between phases of different thermophysical properties are inherently satisfied for the present model. In such a case, the differences in both thermal conductivity and specific heat between phases, as well as the variation of porosity can be tackled by independently adjusting the relaxation time and the thermal capacity ratio included in the equilibrium distribution function, respectively. Additionally, the numerical diffusion across the phase interface for temperature, induced by solid–liquid phase change, can be dramatically reduced in the present model through the MRT collision scheme with a special configuration for the relaxation matrix. Numerical tests for several benchmark problems are carried out to validate the wide practicability and the accuracy of the present model. Very good agreements with analytical solutions or previous experimental and numerical results can be achieved, demonstrating the present model can be served as a promising numerical technique for simulating the transient solid–liquid phase change problems in the porous media.

The present work experimentally investigated the phase splitting characteristics of gas–liquid two-phase flow passing through a horizontal-oriented micro-channel device with three parallel micro-channels. The hydraulic diameters of the header and the branch channels were 0.6 and 0.4 mm, respectively. Five different liquids, including de-ionized water and sodium dodecyl sulfate (SDS) solution with different concentration were employed. Different from water, the surface tension of SDS solution applied in this work decreased with the increment of mass concentration. Through series of visual experiments, it was found that the added SDS surfactant could obviously facilitate the two-phase flow through the parallel micro channels while SDS solution with low concentration would lead to an inevitable blockage of partial outlet branches. Experimental results revealed that the two phase distribution characteristics depended highly on the inlet flow patterns and the outlet branch numbers. To be specific, at the inlet of slug flow, a large amount of gas preferred flowing into the middle branch channel while the first branch was filled with liquid. However, when the inlet flow pattern was shifted to annular flow, all of the gas passed through the second and the last branches, with a little proportion of liquid flowing into the first channel. By comparison with the experimental results obtained from a microchannel device with five parallel micro-T channels, uneven distribution of the two phase can be markedly noticed in our present work.

A novel nanencapsulated phase change material (NEPCM) was fabricated via the self-assembly method with n-dodecanol as the core and SiO2 derived from sodium silicate as the shell. The as-prepared nanocapsules with different core/shell ratios were investigated systematically. Scanning electron microscopy and transmission electron microscopy photographs indicated that the products had a nearly spherical and compact surface with nanometer size. Fourier transform infrared spectroscopy and X-ray diffraction confirmed that SiO2 was successfully encapsulated upon n-dodecanol. Differential scanning calorimetry results showed that the NEPCMs exhibited similar phase change characteristics to pristine n-dodecanol, which melted at 21.03 °C with a latent heat of 116.7 J/g and solidified at 19.58 °C with a latent heat of 114.6 J/g. Thermogravimetric analysis and thermal cycle tests revealed that the nanocapsules had good thermal stability. In conclusion, the prepared nanocapsules have great potential for thermal energy storage and building energy conservation as a result of their facile synthesis process, low cost, and excellent thermal properties.

An experimental investigation has been undertaken to understand the phase split of nitrogen gas/non-Newtonian liquid two-phase flow passing through a 0.5 mm T-junction that oriented horizontally. Four different liquids, including water and aqueous solutions of carboxymethyl cellulose (CMC) with different mass concentrations of 0.1, 0.2 and 0.3 wt%, were employed. Rheology experiments showed that different from water, CMC solutions in this study are pseudoplastic non-Newtonian fluid whose viscosity decreases with increasing the shear rate. The inlet flow patterns were observed to be slug flow, slug–annular flow and annular flow. The fraction of liquid taken off at the side arm for nitrogen gas/non-Newtonian liquid systems is found to be higher than that for nitrogen gas/Newtonian liquid systems in all inlet flow patterns. In addition, with increasing the pseudoplasticity of the liquid phase, the side arm liquid taken off increases, but the increasing degree varies with each flow pattern. For annular flow, the increasing degree is much greater than those for slug and slug–annular flows.Highlights► The features of gas/non-Newtonian fluid flow splitting at a 0.5 mm T-junction are studied. ► Increasing pseudoplasticity of the liquid phase increases side arm liquid taken off. ► Effect of properties of non-Newtonian fluid on phase split of three typical flow patterns is presented.

In this paper, a novel design of heat collecting component for a flat plate solar collector is presented and a numerical study on this solar collector collection efficiency by computational fluid dynamics (CFD) method is conducted. The new heat collecting component consists of a corrugated upward surface and a flat downward surface. The significant influences of the tilt of solar collector, the mass flow rate of inlet water and the distance of air gap on the solar collector collection efficiency are investigated by CFD-simulation. Simulation results reveal that the optimum values of the three factors are the tilt of 10° for April to September, 30° to 35° for the rest months (in Guangzhou of China), the mass flow rate of inlet water 0.15 kg/s and the distance of air gap 20 mm, respectively. Finally, the maximum instantaneous efficiency of 85.1% and the total heat loss factor of 3.127 are obtained by fitting the instantaneous efficiency curve of this solar collector.

A complete three-dimensional model is developed to investigate the flow and thermal transport in the flat evaporator of a miniature loop heat pipe. The model is involved in flow and heat transfer in the wick and vapor groove, which is conjugated with heat conduction in the wall. The pressure and temperature of boundary conditions are coupled with the operating status of the LHP. Effect of structural parameters of vapor groove in the flat evaporator is investigated in details under the specific heat flux. The results show that heat transfer coefficient of evaporator with vapor groove inside the sintered wick is greater than that inside the solid wall when the wick is in fully saturated operating status. The results predict that the optimum of form factor(α) of vapor groove is 1, and when ratio(β) between interval of vapor grooves and width of vapor groove is the less, wall temperature of evaporator (i) is the lower. The suitable range of β is from 0.5 to 1.Highlights► A complete 3-D model is developed to study the performance of the flat evaporator. ► Pressure and temperature of boundary conditions are coupled with operation of LHP. ► Structural effects of vapor groove are investigated under the specific heat flux. ► The results predict effect of location and structural parameters of vapor groove.

An experimental investigation has been conducted to study the effect of surface tension on phase distribution of gas–liquid two-phase flow through a T-junction with diameter 0.5 mm. It is found that the decrease in liquid surface tension makes the liquid taken off reduce when inlet flow pattern is slug flow, slug-annular and annular flow. These results highlight that phase distribution is remarkably influenced by surface tension in micro-T-junctions. To be specific, the surface tension contributes positively to liquid taking off. High surface tension seems to make the liquid capture more kinetic energy transported from the gas and dissipate it in form of vortexes. It is suggested that phase distribution in micro-T-junctions can be partly controlled by adjusting liquid surface tension.