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We report a set of direct numerical simulation results on Rayleigh-Bénard-Marangoni (R-B-M) flow of cold water in the cylindrical pools. The heat transfer between the free surface and the environment is considered. The aspect ratio Г of the cylindrical pool varies from 2 to 8. Rayleigh (Ra) and Biot (Bi) numbers are respectively confined in Ra ≤ 104 and 0 < Bi ≤ 50. The flow onset critical Ra is determined and the influences of Bi and the density inversion parameter (Θm) on the critical Ra are analyzed. The primary bifurcation flow structures of R-B-M flow are shown and the evolution of the flow structures with Ra and Bi at different Θm is observed. Furthermore, the heat transfer ability is estimated by Nusselt number. The results indicate that the critical Ra of the flow onset increases with increasing Bi and Θm. But it decreases with the increase of Г. The primary bifurcation pattern is multicellular flow. With increasing Г, the number of flow cells in multicellular flow increases fast. With increasing Ra, the up-triangular and up-quadrilateral flow structures appear at Г = 4, and finally transits to the up one-torus. With increasing Ra and Г, and decreasing Θm, average Nusselt number increases monotonically. However, with increasing Bi, it first increases, and then decreases. [ABSTRACT FROM AUTHOR]

In order to understand the effect of the radius ratio on thermocapillary-buoyancy convection, a series of experimental observations on thermocapillary-buoyancy convection of 0.65cSt and 1cSt silicone oils have been conducted in annular pools with a smaller heating inner cylinder and the radius ratio of 0.25. The results show that the rotating petal-like structure or spoke pattern first appears on the free surface when thermocapillary-buoyancy convection destabilizes. As the Marangoni number increases, the spoke pattern becomes oscillating at the depth of 6–7 mm and the oscillating frequency is decreased compared with the results in the liquid pool with a radius ratio of 0.5. The wavenumber of the flow pattern decreases when the radius ratio decreases from 0.5 to 0.25. Especially at the liquid depth of 7–8 mm, a mode switching of the flow patterns has been observed and the flow pattern becomes more like cellular structures in cylindrical pools instead of the spoke pattern with the increasing Marangoni number. With the increase of the Prandtl number, this flow transition becomes difficult. Besides, the short spokes appear near the inner cylinder at a large Marangoni number and the deep fluid layer. Based on the experimental results, the general relationship of the threshold complex with the dynamic Bond number and the radius ratio is achieved. [ABSTRACT FROM AUTHOR]

This paper presented a set of direct numerical simulations on the thermocapillary flow instability of moderate-Prandtl number fluids in annular pools heated from inner cylinder. The emphasis is on the aspect ratio dependence of the critical Marangoni number of flow destabilization and the formation mechanism of the different flow patterns. It was found that the two-dimensional axisymmetric steady flow will bifurcate into three types of oscillatory flows, including the oscillatory concentric rings, the alternating straight spoke and the rotating wave patterns. The bifurcation process depends mainly on the aspect ratio of the annular pool when the radius ratio is fixed. With the increase of the aspect ratio, the first instability flow pattern is oscillatory concentric rings and the corresponding critical Marangoni number and the oscillatory frequency decrease first, and then increase slightly. When the flow pattern transits to the alternating straight spoke pattern at the aspect ratio of 0.415, there are an abrupt increase of the critical Marangoni number and a sudden decrease of the oscillatory frequency. Furthermore, when the rotating wave pattern appears, the critical Marangoni number decreases gradually, but the corresponding oscillatory frequency has only a slight decrease. [ABSTRACT FROM AUTHOR]

This paper presents a series of numerical simulations on the effect of heat dissipation on the thermocapillary convection of a low Prandtl number (Pr = 0.011) fluid in an annular pool heated from its inner cylinder. The radius ratio and the aspect ratio of the annular pool set as η = 0.5 and ε = 0.1, respectively. The results show that with the increase of Biot number, the isotherms of the two-dimensional basic flow are seriously compressed near the hot inner cylinder and the thermocapillary flow pattern will be impaired. With the increase of Marangoni number, the thermocapillary convection first evolves from the basic flow to a three-dimensional stationary flow with longitudinal stationary stripes on the free surface, and then to a three-dimensional oscillatory flow featured with the combination of stationary stripes and azimuthal waves, which is caused by the mutual effect of the radial convection, azimuthal local flow and heat dissipation. After the flow destabilization, the amplitude of temperature fluctuation increases and the wave number decreases with the increase of Marangoni number when the free surface is adiabatic. Furthermore, the temperature fluctuation pattern is changed due to the surface heat dissipation. In addition, with the increase of Biot number, the wave number almost keeps constant when Marangoni number is small, but it increases significantly at a large Marangoni number. [ABSTRACT FROM AUTHOR]

In order to understand the effect of surface heat dissipation on thermocapillary convection of moderate Prandtl number fluid in an annular shallow pool, we performed a series of three-dimensional numerical simulations by using the finite volume method. An annular shallow pool is full of 0.65cSt silicone oil with Prandtl number of 6.7. The radius ratio and the aspect ratio of the pool are respectively fixed at 0.5 and 0.1. Surface heat dissipation Biot number is varied from 0 to 50. Results indicate that the critical Marangoni number of flow destabilization mainly depends on the coupling effect of the thermocapillary force and surface heat dissipation on the free surface, which decreases first, and then increases gradually. When Biot number is small, the steady axisymmetric flow after the flow destabilization will bifurcate to the hydrothermal wave. With the increase of Marangoni number, the flow pattern evolution at a small Biot number is similar to that of an adiabatic free surface, and the fundamental oscillatory frequency increases gradually. With the increase of Biot number, the radial roll cells near the outer cylindrical wall gradually extend to the inner wall, and eventually occupy the whole liquid pool. When Biot number is large, the flow pattern after the flow destabilization is a radial rolling cell pattern with alternating azimuthal direction. Then it gradually evolves into azimuthal waves, and the fundamental oscillatory frequency has a slight decrease. [ABSTRACT FROM AUTHOR]

In order to understand surface heat dissipation dependence of thermocapillary convection for moderate Prandtl number fluid in a deep annular pool, a series of three-dimensional numerical simulations have been carried out by using the finite volume method. The radius ratio and the aspect ratio of an annular pool are fixed at 0.5 and 1.0, respectively. The working fluid is 0.65cSt silicone oil with Prandtl number of 6.7. Surface heat dissipation Biot (Bi) number is varied from 0 to 50. Results indicate that with the increase of Biot number, the radial temperature gradient near the inner cylindrical wall decreases, and near the outer cylindrical wall it increases, so the flow is enhanced. When 0 < Bi < 10, with the increase of Marangoni number, the axisymmetric steady flow first transits to the standing wave, and then to the azimuthal waves. The standing wave should be attributed to Marangoni-Bénard instability. However, the azimuthal waves should be corresponded to hydraulic instability, which is mainly driven by the azimuthal motion of temperature fluctuation from the sudden change of flow direction near the bottom and the inner cylindrical wall. When Bi ≥ 10, when the flow destabilizes, the axisymmetric steady flow transits directly to the azimuthal waves. With the increase of Biot number, the critical Marangoni number of the flow destabilization increases. Furthermore, the fundamental frequency and the wave number of three-dimensional oscillatory flow increase gradually with the increase of Biot number. [ABSTRACT FROM AUTHOR]

In order to understand the effect of Marangoni convection on the evaporation rate and the flow pattern, we performed a series of three-dimensional numerical simulations on evaporation process of sessile water droplet by introducing a kinetic model. Substrate temperature and the ratio of vapor pressure varied from 299 K to 308 K and from 0.92 to 0.99, respectively. The variation range of contact angle θ was between 9.15° and 120°. Results show that the axisymmetric ring-shape temperature distribution on droplet free surface transforms into a serrated temperature distribution because of the enhancing Marangoni convection with the increase of substrate temperature. In addition, with the decrease of vapor pressure, the total evaporation rate on free surface will be increased and the Marangoni effect will be enhanced. The flow pattern is axisymmetric at 90o ≤ θ ≤ 120o when the substrate temperature is fixed. However, it shifts to a multi-cellular pattern with the decrease of contact angle as a result of the competition between Marangoni flow and the evaporation. Additionally, the total evaporation rate increases with the increase of contact angle when contact angle is above 60o, but when the contact angle is below 60o, the trend is reverted. The temperature distribution becomes distinct at a small contact angle. [ABSTRACT FROM AUTHOR]

This study aims to improve the thermo-economic performance of the subcritical organic Rankine cycle (ORC). Accordingly, an economical evaluation and the simultaneous multiparametric optimization on the subcritical ORC system for recovering low-grade waste heat of flue gas were conducted using electricity production cost (EPC) as the evaluation indicator. Results show that the optimum evaporating and condensing temperatures are mainly influenced by the inlet temperatures of flue gas and cooling fluid, respectively. High critical temperature of working fluids indicates high thermal-economic performance of the ORC system for 19 kinds of selected working fluids. Furthermore, the optimum pinch point temperature difference of evaporator decreases and that of condenser increases with the variation in the critical temperature of working fluids, but the optimum condensing temperature is unchanged. On the basis of a large number of calculation data, the correlations among the optimum cycle and external operating parameters of the subcritical ORC are proposed. These correlations can guide the engineering design of the subcritical ORC system. [ABSTRACT FROM AUTHOR]

This paper presented a series of numerical simulations on thermocapillary convection for mixed toluene/hexane solution with mass fraction of c0 = 26.27% in a shallow annular pool. The Prandtl number of the binary solution is 5.54. Results indicate that when the annular pool subjects to a radial temperature gradient, the solute shifts toward the inner wall under the Soret effect, which leads to a concentration gradient with the opposite direction to the temperature gradient. With the increase of surface heat dissipation, thermocapillary convection is enhanced and the flow is more prone to destabilization. Therefore, the critical thermocapillary Reynolds number of the flow destabilization and the corresponding critical oscillation frequency all decrease, but the critical wave number increases. After flow destabilization, the concentration fluctuation similar to the temperature fluctuation on the free surface appears. No matter the free surface is adiabatic or not, the flow always undergoes a transition from two-dimensional steady axisymmetric flow to the hydrothermal waves, and then to chaos with the increase of thermocapillary Reynolds number. [ABSTRACT FROM AUTHOR]

In order to understand the characteristics of Rayleigh-Bénard convection of nanofluids in a rectangular cavity, a series of threedimensional numerical simulations were carried out by using the finite volume method. The working mediums were AlO-water and CuO-water nanofluids, and Rayleigh number varied from 1708 to 1.5×105. Results show that the critical Rayleigh number of the Rayleigh-Bénard convection onset increases with the increase of the volume fraction of nanoparticles, which hints that nanoparticles make the flow become more stable. Furthermore, the critical Rayleigh number decreases with the increase of the aspect ratio of the cavity. After convection appears, the average Nusselt number at the bottom wall increases, but the flow intensity and the oscillation frequency decrease with the increase of the volume fraction of nanoparticles. With the increase of Rayleigh number, there exist four bifurcation sequences, which are Steady flow (SF) → Periodic oscillatory flow (POF) → Chaotic flow (CF), SF → POF → SF → POF →CF, SF → POF → Multiple periodic oscillatory flow (MPOF) → POF →CF and SF → POF → MPOF →CF. [ABSTRACT FROM AUTHOR]

γ-Linolenic acid (GLA), stearidonic acid (SDA), and other polyunsaturated fatty acids (PUFAs) play important roles in human health, and Δ6 fatty acid desaturase (D6D) is a key enzyme for PUFA biosynthesis. Oenothera biennis is a traditional GLA-producing oil crop. Here we report the cloning, characterization, and metabolic engineering of its D6D gene family. The intronless 1922-bp ObD6D1 and 1752-bp ObD6D2 both have alternative transcription start sites, alternative polyadenylation sites, and repeated stop codons. Phylogenetic study revealed five large groups of front-end desaturases which are not simply correlated with desaturase types or organism origins. Any type of front-end enzyme has independently originated for multiple times. 'Higher plants,' 'higher animals,' and cyanobacteria each has front-end enzymes of single ancient origin, but other taxa are contrary. ObD6D1 and ObD6D2 are most abundantly expressed in bud and root, respectively. In yeast expression, ObD6D1 and ObD6D2 both catalyzed linoleic acid into GLA, and α-linolenic acid into SDA. Based on a newly constructed double-selection vector system, four constructs of ObD6D1 and ObD6D2 both individually driven by double CaMV35S promoter P and seed-specific promoter P were transformed into Brassica napus via Agrobacterium. T plants, T elite lines, and homozygous T elite lines accumulated average GLA + SDA levels of 6.04, 15.77, and 21.56% of seed fatty acids, respectively. ObD6D2 showed higher effect than ObD6D1. P-D6D engineering has little side effect but is weaker than P-D6D engineering in terms of GLA + SDA productivity. [ABSTRACT FROM AUTHOR]

We investigated the efficacy and safety of ultrasound (US)-targeted microbubble (MB) destruction (UTMD)-enhanced delivery of monomethoxypoly(ethylene glycol)-poly(lactic-co-glycolic acid)-poly- l-lysine (mPEG-PLGA-PLL) nanoparticles (NPs) loading Cy3-labelled platelet-derived growth factor BB (PDGF-BB) siRNA to rat retina in vivo. Eighty Wistar rats were divided into five groups (G). The right eyes, respectively, received an intravitreal injection as follows: normal saline (NS) (G1), NPs and NS (G2), NPs and MBs (G3), NPs and NS (G4) and NPs and MBs (G5). In G4 and G5, the eyes were exposed to US for 5 mins. Twenty-four hours after transfection, the uptake and distribution of Cy3-labelled siRNA in rat retina were observed by fluorescent microscope. The percentage of Cy3-labelled siRNA-positive cells was evaluated by flow cytometer. The levels of PDGF-BB mRNA in retinal pigment epithelium (RPE) cells and secreted PDGF-BB proteins were also measured. Hematoxylin and eosin staining and frozen sections were used to observe tissue damage. Our results showed that the number of Cy3-labelled siRNA-positive cells in G5 was significantly higher than those of the other groups ( P<0.05 for all comparisons). The maximum efficiency of siRNA uptake in neural retina was 18.22±1.67%. In G4 and G5, a small number of Cy3-labelled siRNA-positive cells were also detected in the pigmented cell layer of the retina. NPs loading siRNA delivered with UTMD could more effectively down-regulate the mRNA and protein expression of PDGF-BB than NPs plus US ( P=0.014 and P=0.007, respectively). Histology showed no evident tissue damage after UTMD-mediated NPs loading siRNA transfection. UTMD could be used safely to enhance the delivery of mPEG-PLGA-PLL NPs loading siRNA into rat retina. [ABSTRACT FROM AUTHOR]

In order to understand the onset of Rayleigh-Bénard convection of cold water near its density maximum in a vertical annular container heated from below and cooled from above, the instability of the static diffusive state was investigated by linear stability analysis. Two kinds of thermal boundary conditions, perfect insulating and conducting sidewalls, were used. The aspect ratio and radius ratio of the annular container varied from 0.5 to 4.5 and 0.1 to 0.8, respectively. Results indicate that the critical Rayleigh number and the critical wave number increase with the increase of density inversion parameter. There are some new flow modes with large azimuthal wave number near the convection onset for cold water with density maximum, which are not observed in Rayleigh-Bénard convection of the Boussinesq fluids. The stratified flow phenomenon in cold water with density maximum is certified. The larger the density inversion parameter is, the more obvious the stratified flow phenomenon becomes. With the increase of the aspect ratio, the critical Rayleigh number decreases, but the critical wave number increases. However, with the increase of the radius ratio, both the critical Rayleigh number and the critical wave number increase continuously. Furthermore, the effect of thermal boundary conditions at the sidewalls on the convection stability is also validated. [ABSTRACT FROM AUTHOR]

A novel chromene-type compound, with its trivial name shearene A, was obtained from the EtOH extract of Sheareria nana S. Moore. Its structure was elucidated as 2,2-dihydroxymethyl-2H-1-O-3,7-dihydroxy-6-acetylchromene. [ABSTRACT FROM AUTHOR]

In order to understand the effect of surface evaporation on thermocapillary convection in an annular pool, a series of numerical simulation on thermocapillary convection of the fluids with Prandtl number from 0.01 to 50 in the pure vapor environment were carried out. The results show that thermocapillary convection is always coupled with the evaporation process on the free surface. With the increase of evaporation Biot number, the surface temperature decreases, and the evaporation mass flux near the hot wall increases obviously. However, near the cold wall, the evaporation mass flux increases first, and then decreases. When Marangoni number is small, the total evaporation mass rate at free surface increases with the increase of evaporation Biot number; when Marangoni number is larger, it increases first and then approaches a constant value. The aspect ratio of the annular pool has a positive influence on the thermocapillary convection strength and the total evaporation mass rate. With the increase of Prandtl number, the surface temperature rises gradually and the evaporative mass flux increases, and the thermocapillary convection cell moves gradually toward the outer wall and the free surface. This effect decreases with the increase of evaporation Biot number When evaporation Biot number is smaller, the total evaporation mass rate increases with the Prandtl number; when Biot number is larger, Prandtl number has little impact on the total evaporation mass rate. [ABSTRACT FROM AUTHOR]

As possible candidate screening instruments for benign paroxysmal positional vertigo (BPPV), studies to validate the Dizziness Handicap Inventory (DHI) sub-scale (5-item and 2-item) and total scores are rare in China. From May 2014 to December 2014, 108(55 with and 53 without BPPV) patients complaining of episodic vertigo in the past week from a vertigo outpatient clinic were enrolled for DHI evaluation, as well as demographic and other clinical data. Objective BPPV was subsequently determined by positional evoking maneuvers under the record of optical Frenzel glasses. Cronbach's coefficient α was used to evaluate the reliability of psychometric scales. The validity of DHI total, 5-item and 2-item questionnaires to screen for BPPV was assessed by receiver operating characteristic (ROC) curves. It revealed that the DHI 5-item questionnaire had good internal consistency (Cronbach's coefficient α = 0.72). Area under the curve of total DHI, 5-item and 2-item scores for discriminating BPPV from those without was 0.678 (95 % CI 0.578-0.778), 0.873(95 % CI 0.807-0.940) and 0.895(95 % CI 0.836-0.953), respectively. It revealed 74.5 % sensitivity and 88.7 % specificity in separating BPPV and those without, with a cutoff value of 12 in the 5-item questionnaire. The corresponding rate of sensitivity and specificity was 78.2 and 88.7 %, respectively, with a cutoff value of 6 in 2-item questionnaire. The present study indicated that both 5-item and 2-item questionnaires in the Chinese version of DHI may be more valid than DHI total score for screening objective BPPV and merit further application in clinical practice in China. [ABSTRACT FROM AUTHOR]

In order to understand the characteristics of pure solutocapillary flow in a shallow annular pool subjected to a constant radial solutal gradient, a series of three-dimensional numerical simulations were performed. The annular pool was filled with the toluene/n-hexane mixture fluid with the Schmidt number of 142.8. The inner and outer cylinders were respectively maintained at low and high solutal concentrations. Aspect ratio of the annular pool is fixed at ε = 0.15 or 0.05. Results indicate that the solutocapillary flow is steady and axisymmetric at a small solutal capillary Reynolds number. The surface fluid flows radially from the inner cylinder toward the outer cylinder and a return flow exists near the bottom. With the increase of the solutal capillary Reynolds number, an axisymmetric oscillatory flow firstly appears and then becomes a three-dimensional oscillatory flow at ε = 0.15. Whereas at ε = 0.05 a direct transition from the steady and axisymmetric flow to the three-dimensional oscillatory flow is observed. Three types of the flow instabilities are the standing wave, hydrosolutal wave and source/sink type wave instabilities. Furthermore, the physical mechanism of the flow destabilization is analyzed. [ABSTRACT FROM AUTHOR]

In order to understand the characteristics of thermocapillary flow of a toluene/ n-hexane mixture with the Soret effect in a shallow annular pool, a series of three-dimensional numerical simulations were carried out. The shallow annular pool was heated from the outer cylinder and cooled at the inner cylinder. The initial toluene concentration in the toluene/ n-hexane mixture varied from 0 to 0.4467. Results indicate that the flow undergoes two transitions from the axisymmetric steady flow to the hydrothermal waves, and then to chaos with the increase of the thermocapillary Reynolds number. The critical thermocapillary Reynolds number for the incipience of the oscillatory flow decreases with the increase of the initial solute concentration. When the thermocapillary flow transits to a three-dimensional oscillatory flow, a concentration fluctuation is observed on the free surface, which is similar to the hydrothermal waves. However, compared with that of the temperature, the dimensionless fluctuation amplitude of the concentration is relatively weak. Furthermore, the fundamental oscillation frequency increases linearly with the initial solute concentration, but the wave number of the hydrothermal waves is almost unchangeable. [ABSTRACT FROM AUTHOR]

We present a novel coupled organic Rankine cycle (CORC) system driven by the low-grade waste heat, which couples a transcritical organic Rankine cycle with a subcritical organic Rankine cycle. Based on classical thermodynamic theory, a detailed performance analysis on the novel CORC system was performed. The results show that the pressure ratio of the expander is decreased in the CORC and the selection of the working fluids becomes more flexible and abundant. With the increase of the pinch point temperature difference of the internal heat exchanger, the net power output and thermal efficiency of the CORC all decrease. With the increase of the critical temperature of the working fluid, the system performance of the CORC is improved. The net power output and thermal efficiency of the CORC with isentropic working fluids are higher than those with dry working fluids. [ABSTRACT FROM AUTHOR]

Kushen (Radix Sophorae Flavescentis) has a long history of use for the treatment of tumors, inflammation and other diseases in traditional Chinese medicine. Compound Kushen Injection (CKI) is a mixture of natural compounds extracted from Kushen and Baituling (Rhizoma Smilacis Glabrae). The main principles of CKI are matrine (MT) and oxymatrine (OMT) that exhibit a variety of pharmacological activities, including anti-inflammatory, anti-allergic, anti-viral, anti-fibrotic and cardiovascular protective effects. Recent evidence shows that these compounds also produce anti-cancer actions, such as inhibiting cancer cell proliferation, inducing cell cycle arrest, accelerating apoptosis, restraining angiogenesis, inducing cell differentiation, inhibiting cancer metastasis and invasion, reversing multidrug resistance, and preventing or reducing chemotherapy- and/or radiotherapy-induced toxicity when combined with chemotherapeutic drugs. In this review, we summarize recent progress in studying the anti-cancer activities of MT, OMT and CKI and their potential molecular targets, which provide clues and references for further study. [ABSTRACT FROM AUTHOR]

Objective: To explore the influence of Chinese medicine constitution type on the susceptibility of hypertensive patients to intracerebral haemorrhage. Methods: Primary hypertensive patients were studied and divided into the hypertension and the hypertensive intracerebral haemorrhage groups, depending on whether or not the patients had intracerebral haemorrhage. The demographic characteristics, physiological characteristics, living habits, biochemical tests, other chronic diseases, Chinese medicine constitution type, etc. were collected and compared between the two groups. The neurological deficit in the hypertensive intracerebral haemorrhage group was also compared among the different constitution types. Results: A total of 304 patients participated in this investigation, including 213 cases in the hypertension group and 91 cases in the hypertensive intracerebral haemorrhage group. The percentages of dampness-heat and qi-depression types in the intracerebral haemorrhage group were greater than those with the same types in the hypertension group (20.9% vs 6.1%, 22.0% vs 8.0%; P<0.05). The percentages of each constitution type were different between genders in both groups. In addition, there were more male cases (14/20) with qi-depression type and more female cases (7/8) with phlegm-dampness type in the hypertensive intracerebral haemorrhage group than those with the same types (3/17 and 9/34, respectively) in the hypertension group ( P<0.05). The cases with phlegm-dampness and qi-depression types had greater levels of blood lipids in the intracerebral haemorrhage group than those with the same types in the hypertension group ( P<0.05). Furthermore, the cases with the qi-deficiency type presented with a more severe neurological deficit than those with the other types ( P<0.05). Conclusions: Chinese medicine constitution type might have an impact on the susceptibility of hypertensive patients to have an intracerebral haemorrhage. The heat-dampness and qi-depression types might lead to greater susceptibility than the other types. In addition, the patient's gender and blood lipids might also influence the susceptibility along with the constitution type. [ABSTRACT FROM AUTHOR]

This paper gives a special focus on the role of outlet temperature of flue gas ( T) in organic Rankine cycle (ORC) system for low temperature flue gas waste heat recovery. The variations of performance indicators: net work ( W), exergy efficiency ( η) and levelized energy cost (LEC) versus T are discussed. Considering the corrosion of low temperature flue gas, the necessity and reasonability of limiting T at its minimum allowed discharge temperature (355.15 K) are analyzed. Results show that there exist optimal T ( T) for W and LEC, while T for η does not appear under the investigated range of T. Moreover, the T for W is always lower than 355.15 K, the T for LEC, despite being greater than the one for W, is just slightly higher than 355.15 K when the inlet temperature of flue gas varies from 408.15 K to 463.15 K. For the waste heat recovery of low temperature flue gas, it is reasonable to fix T at 355.15 K if W or LEC is selected as primary performance indicator under the pinch point temperature difference of evaporator (Δ T) below 20 K. [ABSTRACT FROM AUTHOR]

In order to understand the transition characteristics of the thermal-solutal capillary convection in an annular pool, a series of two-dimensional numerical simulations were conducted. The bottom of the pool is adiabatic rigid wall and the top is adiabatic and non-deformable free surface. The inner and outer cylindrical walls maintain at constant temperature and solute concentration, respectively. The thermo-capillary force is supposed to equal to the solute-capillary force, but their directions are contrary. Results show that the thermal-solutal capillary convection is steady at a small Reylonds number. When the capillary Reynolds number exceeds a critical value, the steady flow transits into unstable thermal-solutal capillary convection. The transition from the steady to oscillatory flow undergoes a Hopf bifurcation. Furthermore, the effects of the liquid layer aspect ratio, the radius ratio, the Prandtl number and the Lewis number on the onset of flow pattern transition are discussed. The physical mechanism of the unstable thermal-solutal capillary convection is also analyzed. [ABSTRACT FROM AUTHOR]

In this paper, an exergo-economic criterion, i.e. the net profit per unit transferred heat load, is established from the perspective of exergy recovery to evaluate the performance of finned tube used in waste heat recovery. Also, the dimensionless exergy change number is introduced to investigate the effect of the flow (mechanical) exergy loss rate on the recovered thermal exergy. Selecting R245fa as a working fluid and exhaust flue gas as a heat source, the effects of the internal Reynolds number Rei, the external Reynolds number Reo, the unit cost of thermal exergy ɛq, the geometric parameter of finned tube ηoβ and the phase change temperature Tv etc. on the performance of finned tube are discussed in detail. The results show that the higher Tv and ηoβ, and lower Rei may lead to the negligible flow (mechanical) exergy loss rate. There exists an optimal value of Rei where the net profit per unit transferred heat load peaks, while the variations of Reo, ɛq and Tv cause monotonic change of the net profit per unit transferred heat load. The phase change temperature exerts relatively greater influence on the exergo-economic performance of finned tube in comparison with other parameters. And there exists a critical phase change temperature, where the net profit per unit transferred heat load is equal to zero. [ABSTRACT FROM AUTHOR]

Based on the heat transfer characteristics of absorber plate and the heat transfer effectiveness-number of heat transfer unit method of heat exchanger, a new theoretical method of analyzing the thermal performance of heat pipe flat plate solar collector with cross flow heat exchanger has been put forward and validated by comparisons with the experimental and numerical results in pre-existing literature. The proposed theoretical method can be used to analyze and discuss the influence of relevant parameters on the thermal performance of heat pipe flat plate solar collector. [ABSTRACT FROM AUTHOR]

By establishing an axial symmetric invariable temperature phase change interface model of porous wick evaporator based on alkali metal thermal-to-electric converter (AMTEC), a parametric study has been implemented to explore the impact of effective thermal conductivity model, working fluid, wick material, porosity and particle size of porous wick on the flow and heat transfer characteristics. The results indicate that the inner surface temperature profile of wick is closely dependent on effective thermal conductivity models; it is the minimum for series model while the highest for parallel model. The inner surface temperature of wick with Na-K alloy as working fluid is obviously lower than that with sodium or potassium as working fluid. The wick made of refractory ceramics makes the minimum of inner surface temperature, while the one with nickel appears the highest temperature. Increasing the porosity can reduce the pressure drop in the wick, but also increases the temperature of evaporator. [ABSTRACT FROM AUTHOR]

In order to understand the effect of the vertical heat transfer on thermocapillary convection characteristics in a differentially heated open shallow rectangular cavity, a series of two- and three-dimensional numerical simulations were carried out by means of the finite volume method. The cavity was filled with the 1cSt silicone oil (Prandtl number Pr = 13.9) and the aspect ratio ranged from 12 to 30. Results show that thermocapillary convection is stable at a small Marangoni number. With the increase of the heat flux on the bottom surface, thermocapillary convection transits to the asymmetrical bi-cellular pattern with the opposite rotation direction. The roll near the hot wall shrinks as the Marangoni number increases. At a large Marangoni number, numerical simulations predict two types of the oscillatory thermocapillary flow. One is the hydrothermal wave, which is dominant only in a thin cavity. The other appears in a deeper cavity and is characterized by oscillating multi-cellular flow. The critical Marangoni number for the onset of the oscillatory flow increases first and then decreases with the increase of the vertical heat flux. The three-dimensional numerical simulation can predict the propagating direction of the hydrothermal wave. The velocity and temperature fields obtained by three-dimensional simulation in the meridian plane are very close to those obtained by two-dimensional simulation. [ABSTRACT FROM AUTHOR]

In this study, numerical investigations are conducted for forced convective heat transfer in an annular helicoidal tube under uniform wall temperature condition for laminar flow including developing region. The numerical computations reveal the developments and distributions of heat transfer and flow fields in the annular helicoidal tube when the outer tube wall is heated and the inner tube wall is insulated. The effects of Reynolds number, curvature ratio, and coil pitch on the circumferential average friction factor and Nusselt number at different axial locations, and the non-dimensional entropy generation number of laminar convection in an annular helicoidal tube are investigated. In addition, the differences of flow and heat transfer characteristics between the annular helicoidal tube and circular helicoidal tube are also described. [ABSTRACT FROM AUTHOR]

Three-dimensional numerical simulation was developed to investigate thermocapillary flow induced by non-uniform evaporation on the meniscus in capillary tubes. Capillary tube radiuses ranging from 0.1 to 1 mm were considered and the working liquid was methanol. The effects of tube size, evaporation heat flux and buoyancy on thermocapillary flow were investigated. The results show that the non-uniform evaporation on the meniscus leads to two opposite temperature gradients along the radial direction, which generate two thermocapillary flow vortexes under the meniscus. For horizontal capillary tubes with r ≥ 0.32 mm, the path-lines in the vertical center plane are asymmetrical, which is attributed to the combined buoyancy and thermocapillary effects. For the vertical capillary tube, with increasing average evaporation heat flux, the steady axisymmetrical flow will gradually transit to a steady asymmetrical flow and eventually becomes a three-dimensional oscillatory flow. [ABSTRACT FROM AUTHOR]

In order to understand the characteristics of thermocapillary-buoyancy convection in the annular two-layer system of 5cSt silicone oil and HT-70 with a radial temperature gradient, a set of two-dimensional numerical simulations are carried out using the finite-volume method. The annular two-layer system is heated from the outer cylindrical wall and cooled at the inner cylindrical wall. The radius ratio and the aspect ratio of the system are 0.2 and 0.05-0.1, respectively. Results show that the flow is steady for sufficiently small Marangoni number. When the Marangoni number exceeds a critical value, the additional cells appear near the interface and the cold inner wall, and then an unsteady multi-cellular structure is developed. The temperature fluctuation wave propagates from the cold inner wall to the hot outer wall. And the critical Marangoni number decreases with the increase of the aspect ratio. [ABSTRACT FROM AUTHOR]

The linear-stability analysis of thermocapillary flow in the annular immiscible two-layer system of 5cSt silicone oil and HT-70 with a radial temperature gradient was carried out. The annular two-layer system is heated at the outer cylindrical wall and cooled at the inner wall, the bottom and top surfaces are bounded by two rigid and heat-insulated walls. The influences of the liquid layer depth and radius ratio between the cold inner wall and the hot outer wall on stability are thoroughly investigated. The critical Marangoni number, critical wave number and critical phase velocity are obtained. In addition, the mode of bifurcation for the hydrothermal wave is predicted at different liquid layer depth, and the temperature disturbance pattern of hydrothermal wave at interface is also exhibited. [ABSTRACT FROM AUTHOR]

Based on the experimental results of abnormal infrared effects (AIREs) for molecules adsorbed on transition-metal nanostructured surfaces, the interactions and the polarizability of the adsorbed molecules are analyzed theoretically. By numerical simulations, the normal absorption spectrum, the Fano-like bipolar spectrum and the anti-absorption spectrum of the adsorbed CO molecules are obtained respectively. The results show that the adsorbed molecules on a metal nanostructured surface can accumulate together dues to the effect of local external electric field, which leads to a change in imaginary part of the molecular polarizability within a certain range of frequency, and even a negative value may appear. [ABSTRACT FROM AUTHOR]

In order to understand the influence of the vertical heat flux on thermocapillary convection, we conducted a series of unsteady two-dimensional numerical simulations of thermocapillary convection in a differently heated shallow rectangular cavity with vertical heat flux on the bottom by means of the finite volume method. The cavity was filled with the 1cSt silicone oil (Prandtl number Pr = 13.9) and aspect ratio is 30. It is found that a small vertical heat flux has slightly influence on the flow pattern of stable or unstable thermocapillary convection. However, the critical Marangoni number increases first, and then decreases with the increase of the heat flux. And the flow pattern of the oscillatory thermocapillary convection transits from a series of the rolls rotating clockwise and moving from the cold wall to the hot wall to the single roll near the hot wall and a series of rolls near the cold wall, further, two series of rolls moving from the hot wall and cold wall towards the hot spot with the maximum temperature. With the increase of the Marangoni number, the period and the wavelength of the oscillatory thermocapillary convection increase, but the wave speed decreases. [ABSTRACT FROM AUTHOR]

In order to understand the effect of pool rotation on stability of thermocapillary convection, the critical conditions for the incipience of oscillatory flow in rotating shallow annular pools of silicon melt ( Pr = 0.011) are investigated by means of linear stability analysis (LSA) under different pool rotation rates ranging from Ta = 0 to 1,513.9 and under microgravity condition. The results indicate that with increase of Ta numbers, the critical Marangoni for the incipience of hydrothermal wave (HTW) increases, i.e., pool rotation stabilizes the steady axisymmetric thermocapillary convection of silicon melt. The critical azimuthal wave number m decreases linearly with increase of Ta number when Ta ≤ 378.5. However, when Ta > 378.5, m almost keeps constant with m = 34. When Ta < 550 the HTW propagates in the same direction as the pool rotation direction, while it is reversed when Ta > 550. [ABSTRACT FROM AUTHOR]

A set of two-dimensional numerical simulations of thermal convection of two immiscible liquid layers with a non-deformable interface was carried out in an annular cavity with the outer heated cylinder and the inner cooled cylinder using the finite-volume method. Bottom and top surfaces were bounded by two rigid and heat-insulated walls. The results show that the conversion of the thermal convection depends on the Marangoni number, the aspect ratio and the curvature of the annular cavity. For a sufficiently small Marangoni number, the flow is steady and there is one cell in each fluid layer. When the Marangoni number exceeds the critical value, the convective flow becomes instable and generates an unsteady multi-cell structure. In the case of the closed annular cavity, the value of the critical Marangoni number is higher than that in the infinite layer, and decreases with the increase of the aspect ratio. [ABSTRACT FROM AUTHOR]

In this paper, numerical simulations for natural convection of water near its maximum-density in horizontal annulus with isothermal walls are performed with the finite volume method. The results show that there are different steady-state flow patterns for different control parameters in the range of calculation for concentric horizontal annulus. Furthermore, the effects of the non-dimensional parameters, which include the radius ratio and density inversion parameter, on the temperature and flow fields are discussed, and the variation of the average Nusselt number is analyzed at different conditions. It is found that density inversion of water has a great effect on natural convective heat transfer in horizontal annulus. [ABSTRACT FROM AUTHOR]

In this paper, exergy effectiveness is defined to describe the thermodynamic performance of three-fluid heat exchangers with three thermal communications. It is systemically discussed that the effects of eight non-dimensional design parameters, which include the ratio of the thermal resistances between fluids, the ratio of thermal capacity between fluids, the number of transfer units, the dimensionless inlet temperature of fluid, and the ratio of the inlet temperature of fluids on exergy effectiveness of three-fluid heat exchangers. Furthermore, the exergy effectiveness of the parallel flow is compared with that of the counter flow. The obtained results are helpful for engineers to evaluate and improve the performances of three-fluid heat exchangers. [ABSTRACT FROM AUTHOR]

The thermocapillary convection instability in shallow annular pools with Prandtl numbers ( Pr) from 0.011 to 57.9, differentially heated at the outer wall and cooled at the inner wall, is investigated numerically. The critical Marangoni numbers ( Ma c), critical azimuthal wave numbers ( m c) and critical phase velocities ( ω c) for the incipience of oscillatory flow are determined by linear stability analysis. The results indicate that the Ma c increases steeply with increase of Pr number when Pr≤15.9, while it increases slightly with increase of Pr between Pr=23.9 and 57.9. The m c and ω c decrease with increase of Pr number. [ABSTRACT FROM AUTHOR]

The thermocapillary convection and buoyant-thermocapillary convection in the annular pool of silicon melt ( Pr=0.011) and silicone oil ( Pr=6.7) with depth d=10 mm differentially heated at the outer wall and cooled at the inner wall are investigated by 2-D numerical simulation. The numerical results exhibit that the thermocapillary flow is enhanced by buoyancy force for silicon melt while it is weakened for silicone oil. Linear stability analysis indicates that the buoyancy force destabilizes the thermocapillary convection, which is different from that for silicone oil. The detailed reason of different influence of buoyancy force on the thermocapillary flow with different Pr numbers is explained according to present numerical results. [ABSTRACT FROM AUTHOR]

By analyzing heat and exergy transfer processes of heat exchangers operating below the surrounding temperature, the effect of fouling on the low temperature heat exchangers performance has been conducted. Taking the parallel flow, counter flow, and cross flow low temperature heat exchangers as examples, the effects of some non-dimensional parameters on the low temperature heat exchangers performance under the fouling condition are given by introducing exergy transfer units number. [ABSTRACT FROM AUTHOR]

Abstract  In order to understand the characteristics of thermocapillary flow, we conducted a series of unsteady three-dimensional (3D) numerical simulations of thermocapillary flow for fluids with Prandtl number Pr = 0.011 and 1.0 in a shallow cylindrical pool with an azimuthal temperature non-uniform, an adiabatic solid bottom and free surface. The simulation results indicate that thermocapillary flow is steady 3D flow at the small temperature non-uniform. When temperature non-uniform exceeds some critical value, the flow will undergo a transition to 3D oscillatory flow, which is characterized by traveling oscillatory wave reversely along the flow direction on the free surface and diffusing to two sides at the same time. Further, the critical conditions for the flow transition are determined. [ABSTRACT FROM AUTHOR]

In order to understand the stability characteristics of thermocapillary convection in an annular pool with low Prandtl number ( Pr = 0.011) fluid, a linear stability analysis had been performed. The annular pool was heated from the outer cylindrical wall and cooled at the inner wall. Bottom and top surface were adiabatic. The results show that the critical Marangoni number and the critical wave number decrease with the increase of the aspect ratio, which is defined as the ratio of the depth to the gap width of the annular pool. When the aspect ratio exceeds 0.12, the critical wave number keeps almost constant. As the radius ratio increases, the critical Marangoni number decreases slightly, while the critical wave number increases. In the gravity condition, the effect of the buoyancy on the critical Marangoni number and wave number increases gradually with the increase of the aspect ratio. [ABSTRACT FROM AUTHOR]