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• Asymptotic technique is applied to investigate the asymptotic behavior of fluid in near-critical region. • Thermal waves originated from the boundary with a characteristic diffusion coefficient scaled by exponent γ -0.5 α - x L. • Diffusion and wave modes show independent behaviors and the magnitude is proportional to boundary flux. • Divergence of bulk viscosity results in the extra pressure force (scaled by −0.5 α-x b) Abnormal transport phenomena are generally found in supercritical fluids heat transfer due to their unique thermophysical properties on the gas–liquid critical point. In the vicinity of the critical point, static or transport properties of fluids can be scaled by the critical exponents along any thermal path being defined. In this work, with such scaling on the critical isochore, the asymptotic technique is applied to investigate the behavior of the near-critical fluids by studying the response to the thermal perturbation in the acoustic time scale. The full asymptotic governing equations are found in both non-viscous and viscous cases that describe the wave mode in bulk and diffusion mode in the boundary layer. The analytical solutions for the mass transport correlation demonstrate the direct bond between the wave mode and boundary conditions regardless of the motion of boundary layers in both heating and cooling cases. Such correlation shows the asymptotic behavior characterized by exponent −0.5 α - x L = −0.625. Thus, the thermal waves that cause cooling and heating, respectively, can coexist and propagate independently due to the one-to-one bonding with respective boundaries (wave sources). This bonding is still valid even if the enlarged viscosity hinders the fluid flow out of the boundary layers. The viscosity leads to the extra pressure work, whose asymptotic behavior follows the exponent −0.5 α - x b = −1.875, to overcome the viscous stress as the boundary layers expand. [ABSTRACT FROM AUTHOR]

Oncolytic adenoviruses (OA) are promising therapeutics for glioblastoma (GBM) due to their unique capability of selectively lysing tumor cells and activating the immune response. However, their therapeutic potential is often impeded by limited cellular internalization caused by low expression of OA receptors, as well as restricted OA proliferation due to antiviral responses. In this work, a novel type of OA, named nanosynergist-engineered OA (nsOA), was developed by functionalizing the viral surface with siRNA-loaded hyperbranched polymers. The nanosynergist not only enhanced the infectivity of OA but also augmented virus replication, ultimately potentiating their oncolysis efficacy. We revealed that the enhanced replication of the virus was initiated by the downregulation of signal transducer and activator of transcription-3, which suppressed the transcription of interferon-stimulated genes, ultimately circumventing the antiviral defense of tumor cells. Furthermore, the innate ability of OA to disrupt endosomal membranes was found to improve the endosomal escape of the nanosynergist, creating synergistic effect that amplified the therapeutic benefits. A single dose of nsOA markedly increased the production of progeny viruses and prolonged the survival of mice. Collectively, these results provide an effective and valuable strategy to engineer OA, which may lead to innovative immunotherapies for various cancers. [Display omitted] • This nanosynergist favorably strengthened OA replication via siRNA mediated interruption of STAT3 gene. • The downregulation of STAT3 effectively bypassed the antiviral defense of tumor cells by inhibiting ISGs expression. • OA disrupted the endosomal membranes and facilitated the escape of nanosynergist from endosomes. • A single dose of nsOA increased viral titer, enhanced OA-mediated therapy, and prolonged the survival of mice with glioma. [ABSTRACT FROM AUTHOR]

The heat transfer and pressure drop (Δ P) of supercritical fluid are crucial for the safety of advanced power cycles. Here, experiments were performed for sCO 2 in a horizontal tube with inner diameter (d in) of 10 mm, covering in the ranges of (G): 496.7–1346.2 kg/m2, heat flux (q w): 97.4～400.3 kW/m2 and pressure (P): 7.53–23.51 MPa. Inspired by the similarity of the outer wall temperature (T ow) distributions between the sCO 2 flow and those of stratified-wavy-flow in subcritical pressures, the multiphase flow theory is introduced in subcritical pressures to deal with the sCO 2 heat transfer. In the two-phase-like (TPL) regime, heat transfer coefficients (HTC) and friction factors (f) of sCO 2 are found to significantly deviate from the correlations based on the single-phase flow theory. Further, the vapor-like Froude number Fr VL is proposed to develop new correlations for both the heat transfer and the flow resistance covering the whole data range. The present paper establishes a connection between the flow resistance and heat transfer in supercritical pressures, which is important for the design and operation of sCO 2 power cycles. • Supercritical heat transfer and flow characteristics of CO 2 is investigated in a horizontal tube. • Thick vapor-like film can reduce the frequency of negative temperature differences occurring. • Flow resistance and heat transfer in the two-phase-like regime both strongly deviates from the single-phase convection. • Fr VL was proposed to be the similarity criterion number to connect flow resistance and heat transfer for horizontal flow. • The new correlations with Fr VL number for heat transfer and friction factor are established. [ABSTRACT FROM AUTHOR]

Using the pseudo-boiling concept, supercritical heat transfer is analogized to the boiling at subcritical pressures. The proposed supercritical-boiling-number SBO represents the competition between the bubble expansion induced momentum force and the inertia force. Sudden changes between normal heat transfer and heat transfer deterioration are found when crossing critical SBO , which is experimentally determined for CO 2 , H 2 O, R134a and R22. The linear law of supercritical heat transfer is discovered. Our study supports the heterogeneous structure of supercritical fluids. • Supercritical-boiling-number SBO dominates supercritical heat transfer mechanism. • Sudden changes in heat transfer behaviors are found when crossing critical SBO. • Critical SBO values are experimentally determined for CO 2 , H 2 O, R134a and R22. • Our study supports the heterogeneous structure of supercritical fluids. Supercritical fluids such as CO 2 , water and organic fluids are frequently applied in power systems. The accurate prediction of heat transfer deterioration (HTD) is important to keep the safe operation of advanced power systems such as solar driven supercritical carbon dioxide Brayton cycle. As described in textbooks, it is impossible to identify liquid from gas beyond the critical point, thus supercritical fluid is assumed to have homogeneous structure with a single-phase. The single-phase assumption cannot explain and predict supercritical heat transfer (SHT). Instead, we investigate SHT by the pseudo-boiling concept. Heat transfer is analogized between supercritical pressure and subcritical pressure to create a new non-dimensional supercritical-boiling-number SBO , representing the bubble expansion induced momentum force against the inertia force when it is coupled with the ratio of liquid density with respect to vapor density. Our study reveals sudden changes from normal heat transfer (NHT) to heat transfer deterioration (HTD) with obvious temperature peak when crossing a critical SBO , which is 5.126 × 10−4, 2.018 × 10−4, 1.653 × 10−4 and 1.358 × 10−4 for CO 2 , H 2 O, R134a and R22, determined by a large quantity of database. Our work paves a new way to understand the SHT mechanism and supports the heterogeneous structure of liquid-like fluid and vapor-like fluid for supercritical fluids. [ABSTRACT FROM AUTHOR]

• Pseudo-boiling of supercritical fluid is investigated using Pt wire and NiCr wire. • Bubble-like interface is tracked by the grey extracting method based on image files. • Evaporation-like mode occurs for Pt wire, both evaporation-like and boiling-like modes occur for NiCr wire. • Intermittent boiling-like heat transfer is caused by the piston motion of the wire. • Continuous boiling-like heat transfer is caused by the temporal-spatial temperature variations of the wire. In this study, we identify whether evaporation-like (EL) mode and boiling-like (BL) mode occur under supercritical pressures by investigating the heat transfer of platinum (Pt) and nickel-chromium (NiCr) wires, with a length of 22.0 mm and diameter of 70 μm, in carbon dioxide liquid at 8 and 10 MPa. Using a direct photographic technique based on the light refractive principle, we analyse the brighter/darker pattern in a varied-density field. The vapor–liquid interface is quantified using the grey extraction method. Our results show that beyond the limit of natural convection (NC), only the EL mode is identified for the Pt wire. However, for the NiCr wire, the EL mode, the transition from EL to BL (TEB) mode, and the BL mode are observed. The opposing gravity and drag forces cause downward bending of the Pt wire and upward bending of the NiCr wire. In the TEB region, the varying importance of interfacial expansion velocity over the buoyancy velocity accounts for the piston motion of the NiCr wire. During falling of the wire, the lighter fluid penetrating the heavier fluid causes interfacial instability to trigger the intermittent BL heat transfer. Beyond the TEB region, continuous BL heat transfer is observed. We introduce the small-perturbation theory to achieve a new non-dimensional parameter, H 3. For the Pt wire, a smaller (either negative or positive) H 3 explains why only the EL mode appears. For the NiCr wire, the negative H 3 in the TEB region proves that the intermittent BL heat transfer is caused by the piston motion of the wire, but the positive and ∼30 times larger H 3 indicates that the continuous BL heat transfer is caused by the temporal-spatial temperature variations. Furthermore, we observe that the BL mode occurs in a vapor-like layer instead of wall cavities, which is different from subcritical boiling. The BL mode displays random and disordered features, like those of subcritical boiling. This work elaborately explores common and uncommon features between supercritical pseudo-boiling and subcritical boiling, and uncovers the secret of two modes of pseudo-boiling. [Display omitted] [ABSTRACT FROM AUTHOR]

• S-CO 2 coal fired power plant was investigated. • The overlap energy utilization (OEU) principle was proposed. • OEU increases the average heat absorption temperature for bottom cycle. • An external air preheater (EAP) recycles extra heat to the system for bottom cycle. • OEU and EAP reaches identical efficiencies for top and bottom cycles. For a coal fired power plant, a combined supercritical CO 2 cycle (S-CO 2) absorbs flue gas energy over entire temperature range. Because top/bottom cycles absorb high and moderate temperature flue gas energy respectively, there is an efficiency gap between the two cycles. To fill the efficiency gap, the overlap absorption of flue gas energy is proposed, using top cycle to absorb high temperature flue gas heat, but bottom cycle to absorb not only moderate temperature flue gas heat, but also a part of high temperature flue gas heat. The overlap energy absorption in a high temperature regime increases CO 2 heat absorption temperature to improve bottom cycle efficiency. A four steps roadmap guides us to construct a combined cycle with RC + DRH as top cycle and RC + DRH + EAP as bottom cycle to reach the maximum efficiency limit, where RC, DRH and EAP represent the cycles of recompression, double-reheating and external air preheater, respectively. The components sharing among top/bottom cycles ensures simple system layout, and EAP recycles extra heat of bottom cycle to the system, keeping a smallest heat dissipation to environment. The net power efficiency reaches 47.99% at the main vapor parameters of 620 °C/30 MPa. The overlap energy utilization can be extended for other systems. [ABSTRACT FROM AUTHOR]

Abstract A comprehensive analysis of enhanced condensation with phase separation concept is presented, for which mesh-membrane-tube (MMT) is suspended in a tube. A twill Dutch weaved mesh screen and two plain Dutch weaved mesh screens are used to fabricate MMT. Our study reveals that liquid leakage across MMT not only keeps better condensation on condenser wall, but also decreases pressure drop rise penalty. To modulate stratified-flow, the #1 MMT with smallest d p has the largest capillary force to pump liquid towards core region to expose more condenser surface with vapor, where d p is pore diameter. To modulate annular-flow, finest mesh wires of #1 MMT ensure the best wetting to liquid to prevent condenser wall from being impacted by satellite droplets. These mechanisms explain the best performance of #1 MMT, reaching a maximum heat transfer enhancement ratio of 1.82. The three MMTs share a single curve of nozzle discharge coefficient versus Reynolds number. The similar performance of #2 and #3 MMTs is due to identical d p / φ , where φ is mesh open porosity. Fine mesh wires and small mesh pores are suggested to enhance condensation heat transfer. MMT are recommended to be used in condenser tube upstream when vapor mass qualities larger than 0.1. Highlights • Mesh-membrane-tube (MMT) is suspended in tube to enhance condensation heat transfer. • MMT captures droplets with fine mesh wires to resist liquid accumulation on condenser wall. • MMT having smaller mesh pores enhances liquid suction from annular region to core region. • The ratio of mesh pore diameter to open porosity governs liquid flow across membrane. • An overall 82% improvement of heat transfer enhancement is observed, maximally. [ABSTRACT FROM AUTHOR]

Abstract The Organic Rankine Cycle (ORC) driven by low-grade energy can operate in off-grid mode. Here, we report the steady and transient characteristics of an ORC system. A single screw expander and a synchronous generator convert mechanical power to electricity. A lamp array simulates the variable external loads. The quality parameters including electric frequency, electric power and effective voltage are measured by a power meter. We show that at setting frequency of 50 Hz, the maximum system efficiency can be reached when the external load is not larger than the ORC power capacity. The expander isentropic efficiency is above 80% for the vapor superheating of 5–10 K at expander inlet. A control strategy is proposed to achieve better system performance under varied heat source and environment conditions. By use of residual frequency and adjusting pumping frequency, the vapor pressure at expander inlet can be automatically adjusted to reach the optimal value. Transient tests indicate that the electric quality is insensitive to the step change of external loads and heat/cold sources parameters. The thermohydraulic parameters are self-adapted to the change of external parameters. This work provides a self-adapting strategy for ORC operation at varied heat/cold source parameters. Highlights • The steady and transient operation characteristics of an ORC system are investigated. • A single screw expander and a synchronous generator are included in the system. • The electric frequency of 50 Hz is reached if external load is not larger than ORC capacity. • Electric energy quality parameters are insensitive to the step change of external parameters. [ABSTRACT FROM AUTHOR]

Abstract The challenge of the nanofluid solar energy harvesting lies in the strong coupling between nanoparticles generated heat and flow/temperature fields in various length and time scales. In this paper, the solar-driven evaporation of nanofluid droplet is investigated. The droplet evaporation rates behave a sharply increased regime and a constant regime when crossing a critical nanofluid concentration of c i,cr = 10 ppm. We decouple the total solar energy absorption into two parts in terms of the optical bands, and the whole droplet into two spatial domains. Our study reveals a small length scale starting from contact line to behave higher temperature and larger temperature gradient there, newly recognized as a boundary layer effect. Correspondingly, a contact line region CLR is defined, while the remain is the bulk volume region BVR. The observed coffee-ring behaves a self-assembly of nanoparticles in CLR. We found that even though CLR is two magnitudes smaller compared to the whole droplet, it dominates almost all of the electromagnetic energy absorption, while BVR contributes almost all of the infrared energy absorption. Our finding successfully explains the two regimes of droplet evaporations. With increase of initial nanofluid concentrations, the droplet evaporation rates are raised due to more heat generation induced by enhanced nanoparticles deposition in CLR. The increased evaporation rates stop at a critical concentration of 10 ppm, corresponding to sufficient nanoparticles deposition. Beyond the critical condition, extra nanoparticles are hidden beneath the effective nanoparticles layers to cause unchanged evaporation rate. The present work is useful to develop novel solar steam generation device. The evaporation induced coffee-ring can be regarded as a novel "fabrication" method of nanostructure for plasmonic heating. The pure water evaporation of liquid film or droplet on a prepared coffee-ring array offers great convenience for solar energy utilization. Graphical abstract fx1 Highlights • Solar-driven evaporation of nanofluid droplet is investigated. • A critical nanofluid concentration distinguishes two regimes of droplet evaporations. • The boundary layer effect is identified near droplet contact line during evaporation. • Coffee-ring nanoparticles dominate the light energy absorption in visible region. • The two regimes of drop dynamics correspond to insufficient and extra coffee-ring nanoparticles. [ABSTRACT FROM AUTHOR]

Abstract As a high-performance power cycle, S-CO 2 cycle has drawn a lot of attention in various energy utilization field. As one of the clean and efficient forms for coal utilization, coal-fired power plants still need novel power generation systems to have rational use of coal. So, it is necessary to explore the characteristic when a coal-fired power system integrated with S-CO 2 cycle. However, this application is confronted with many challenges related to boiler, such as pressure drop problem due to large mass flow rate and residual heat problem due to narrow CO 2 temperature difference. Focus on the residual heat problem, in this paper, a coupling analysis model between boiler and reheat S-CO 2 cycle is established. The proposed system consists of a thermal-hydraulic calculation module in boiler, a residual heat treatment module in tail flue and a thermodynamic calculation module of S-CO 2 cycle. The three modules can make the calculation results more credible for cycle characteristics. All the modules are programmed by Fortran. Base on the analysis result, the residual heat problem can be solved by raising turbine inlet pressure. But when turbine inlet temperature is higher, the turbine inlet pressure will be raised unacceptable. By adding a flue gas cooler (FGC), above limitation will be removed. So, in a certain temperature range, adding an FGC is a simple and effective way to solve residual heat problem. [ABSTRACT FROM AUTHOR]

Highlights • Condensation experiment on superhydrophobic nanograsses surface (NGS) is performed. • Fresh NGS behaves smaller drop but deteriorates heat transfer compared with polymer surface. • Collapse and breakage of nanograsses worsen heat transfer for long-term operation. • Three mechanisms to induce nanostructure failure are proposed. • There is a limit of decayed heat transfer after nanostructure failure. Abstract Dropwise condensation heat transfer (DWC) on superhydrophobic nanograsses surface (NGS) was investigated for long-term operation. For DWC of pure water-vapor on fresh NGS, two heat transfer regimes are identified: higher heat transfer coefficients with droplet jumping, and constant heat transfer coefficients with droplet rolling. The one-week operation not only deteriorates heat transfer performance, but also changes jumping or rolling mode to sliding mode. The condensation heat transfer coefficients are apparently decreased from first to third day, but they approach a limit value since the third day. In order to identify if the single-molecule-layer of polymer (SML) modified on nanograsses was destroyed, DWC on a smooth single-molecule-layer of polymer surface (SSML) was tested to display stable heat transfer with drop sliding for one-week operation, concluding no failure of the polymer layer. The collapse and breakage of nanograsses were observed to explain the decayed heat transfer versus time on NGS. Compared with SSML, the NGS has smaller droplet departure size but lower heat transfer coefficients, indicating positive and negative effects after introducing nanostructures. Three nanostructure failure mechanisms are proposed. This work suggests a new research field of the nanoscale fluid-wall interaction. [ABSTRACT FROM AUTHOR]

Abstract The objective of this paper is to develop a criterion to predict the onset of heat transfer deterioration (HTD) for supercritical CO 2 heat transfer. A new mechanism is proposed by assuming supercritical pseudo-boiling. Before bulk fluid reaches pseudo-critical temperature (T pc), the tube cross-section contains a vapor layer and a liquid-like fluid. The saturation temperature interface is defined at T = T pc , inside and outside which are a vapor layer (T > T pc) and a subcooled liquid (T < T pc). The subcritical boiling number is extended to supercritical "boiling" number, defined as SBO = q w /(Gi pc), where q w , G and i pc are heat flux, mass flux, and CO 2 enthalpy at T pc , respectively. SBO , by coupling the density ratio between "liquid" and "vapor", represents the competition between vapor expansion induced momentum force and inertia force. The experiment of supercritical CO 2 heat transfer is performed in a 10.0 mm inner diameter tube, covering ranges of P = 7.5–21.1 MPa, G = 488–1600 kg/m2s and q w = 74–413 kW/m2. Surprisingly, the onset of HTD is found to occur at a critical SBO which is 5.126 × 10 − 4 and the critical heat flux is expressed as q C H F = 5.126 × 10 − 4 G i pc . It is shown that our new criterion is also suitable for other experiments reported in literature, providing a general guidance to design and operate S CO 2 heaters to avoid HTD. Graphical abstract Image 1 Highlights • Similarity principle deals with heat transfer deterioration at supercritical pressure. • The analysis results in a new supercritical "boiling" number SBO. • SBO comprehensively considers the effects of a set of variables. • CO 2 heat transfer experiment is performed over wide parameter ranges. • The critical SBO of 5.126 × 10−4 distinguishes two regimes of heat transfer. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • Molecular dynamics simulation was performed in nano-Janus-interface system. • Temperature gradients can be steepened by lowering hot wall wettabilities. • Heat transfer is switched by varying wall wettabilities and applied forces to liquid. • The finding helps to develop temperature sensitive nano-energy-devices. Abstract Janus-interface-system is referred as liquid confined between hydrophilic and hydrophobic surfaces, nanoscale energy transfer in Janus-interface-system is not understood. Here, we investigate Poiseuille flow by non-equilibrium molecular dynamics (NEMD) using argon as the working fluid. The two solid walls hold different temperatures and wettabilities. It is found that for pure heat conduction, temperature jumps are negative on hot wall but positive on cold wall to create positive heat flow from hot wall to cold wall (called positive heat transfer). However, the convective energy transfer in Janus-interface-system always behaves positive temperature jumps on the two walls due to viscous heating. We show that, lowering hot wall wettabilities creates more significant velocity and temperature slippages on hot wall than those on cold wall to steepen liquid temperature gradients in nanochannel. We further show that heat flow sign can be switched between positive and negative, by (1) keeping super-hydrophilic hot wall but changing cold wall wettabilities, (2) keeping super-hydrophilic-hot-wall/hydrophobic-cold-wall but varying external forces applied to liquid, and (3) keeping super-hydrophilic-hot-wall/hydrophobic-cold-wall but varying hot wall temperatures. All the three cases yield non-symmetry velocity profile and more sensitive changes of temperature jumps on cold wall than those on hot wall for heat transfer switch. The transition between positive and negative heat transfer occurs at the zero temperature gradient in the channel. The findings not only enhance the understating of nanoscale energy transfer in Janus-interface-system, but also provide novel working principle for nano-devices behaving temperature sensitive nature. [ABSTRACT FROM AUTHOR]

Herein, the effect of the power capacity, W net , on the performance of supercritical carbon dioxide (sCO 2) coal-fired power plants is investigated, with W net in the range of (100–1000) MWe. A comprehensive model was established wherein the sCO 2 cycle was coupled with the models of various components. For the sCO 2 boiler, the total thermal load was assigned to various heaters, and the pressure drop in each heater was calculated. Owing to the strong penalty effect of the pressure drop, both total flow mode (TFM) and partial flow mode (PFM) were applied to the sCO 2 boiler. A fluid network integrating the recuperator units was established for heat recovery in the system. A thermal-hydraulic model was proposed for a single unit and an integration package. Various losses were considered in the prediction of the efficiencies of axial flow turbines and compressors. The thermal efficiency increases, attains a maximum, and then decreases with increase of W net. This parabolic distribution results from the tradeoff between the decreased efficiency owing to pressure drops in the heat exchangers and the increased efficiency of the turbomachinery. The maximum thermal efficiency occurred at W net of 300 MWe and 200 MWe when using the PFM and TFM, respectively. Based on the results, PFM is found to eliminate the penalty effect of pressure drops. Our study provides guidelines for the design and operation of sCO 2 coal-fired power plants. [ABSTRACT FROM AUTHOR]

Supercritical carbon dioxide (sCO 2) cycle can be driven by fossil energy and solar/nuclear energy. Available references maximize cycle efficiency by fixing turbine efficiencies η tt in advance. Here, we provide turbine efficiencies dependent on power capacities W T which are in the range of (50–450) MW. After examination of working mechanism and special characteristic of sCO 2 turbines, a comprehensive model was presented to predict characteristic sizes, irreversible losses and efficiencies of turbines. Characteristic size of turbines (l c) is found to obey the scale law of l c ∼ W T 0.5. Profile loss Y p , secondary loss Y s , clearance loss Y cl and trailing edge loss Y te obey the scaling laws of Y p ∼ W T − 0.075 , Y s ∼ W T − 0.075 , Y cl ∼ W T − 0.39 , Y te ∼ W T − 1 . These scaling laws agree with the correlations based on numerical simulations. With continuous increase of W T , η tt increases but the slope of the curves become gentle. Efficiency maps are provided based on inlet pressures P in and temperatures T in. By fixing W T , η tt decreases with increase of P in and T in. The scaling laws regarding irreversible losses provide the guidance to optimize the turbine design. The efficiency maps can be integrated in the cycle analysis for accurate estimate of system performance, and help to select suitable power capacity. • A comprehensive model is presented to predict the performances of sCO 2 axial turbines. • Scaling laws of characteristic sizes and irreversible losses are theoretically developed. • Turbine efficiencies quickly increase and then the slope of the curve decreases, with increase of W T. • Turbine efficiencies show parabolic variation with respect to expansion pressure ratios. • Efficiency maps are presented based on inlet pressures and temperatures. [ABSTRACT FROM AUTHOR]

For coal fired power plant, the supercritical carbon dioxide Brayton cycle (S-CO 2 ) is difficult to absorb flue gas heat in a wide temperature range of 120–1500 °C. Here, novel methods are developed to cascade utilize flue gas heat, in which energies in high, moderate and low temperature levels are extracted by top cycle, bottom cycle or flue gas cooler (FGC), and air preheater, respectively. The cascade utilization shall satisfy the criterion that CO 2 temperature entering boiler for top cycle equals to CO 2 temperature leaving boiler for bottom cycle . The separate-top-bottom-cycle (STB) is proposed, in which no any component is shared by top and bottom cycles. Six possible bottom cycles are studied. The thermodynamics analysis is coupled with heat transfer and pressure drop analysis for whole power plant. It is found that the main vapor pressure of bottom cycle can be the “best” parameter to be adjusted over a wide range of 15–35 MPa to couple and optimize top and bottom cycles. Then, the parameter coordination principle is proposed to share specific components for top and bottom cycles. Thus, the separate cycles are converted into a connected cycle to simplify the whole system layout. The connected cycle has a power generation efficiency of 51.82% at main vapor parameters of 700 °C/35 MPa, significantly higher than available supercritical water-steam Rankine cycle power plant. The findings in this paper give a clue to further raise the power generation efficiency for large scale S-CO 2 coal fired power plant. [ABSTRACT FROM AUTHOR]

When supercritical carbon dioxide (S CO 2 ) Brayton cycle is used for coal fired power plant, the significantly increased flow rate causes extremely large boiler pressure drops, and residual flue gas energy extraction becomes difficult. This paper contains two consecutive parts to resolve these issues. The first part deals with general analysis. Results show that, introducing intercooling and/or reheating into cycle apparently elevate thermal efficiencies, but cycle performance is obviously deteriorated by large pressure drops. Partial flow strategy was proposed in part 2 to yield boiler module design. Both flow rate and length for each module are cut to be half, reducing pressure drop to 1/8 of that with total flow mode. Surprisingly, we show that CO 2 boiler pressure drop can be equivalent to or even smaller than that for supercritical water-steam boiler. Three flue gas energy extraction schemes are proposed. The case A scheme not only keeps lower exit flue gas temperature (∼120 °C), but also maintains acceptable secondary air temperature. Finally, a 1000 MWe S CO 2 power plant design is given. With main vapor parameters 620 °C/30 MPa, thermal efficiency and power efficiency are 51.22% and 48.37% respectively, showing advantages over supercritical water-steam Rankine cycle. Future works are recommended on S CO 2 power plant design. [ABSTRACT FROM AUTHOR]

Onset of droplet motion is important for various applications, including dropwise condensation and water management in fuel cells. In order to determine critical conditions for onset of motion and specific motion mode, a general problem having a droplet sheared by a gas stream on inclined surface is investigated. Two criterion equations are theoretically established for onset of droplet sliding and rolling independently, including dimensionless parameters of Bond number ( Bn ), Ohnesorge number ( Oh ) and Weber number ( We ), inclination angle parameter and wettability parameters. The criterion equations predict critical gas velocity, maximum droplet radius, and “sliding angle” or “rolling angle”. Droplet sliding predictions agree well with experimental data in the literature. Criterion surfaces of sliding or rolling are constructed to verify if sliding or rolling can be initiated, influenced by both equilibrium contact angle and contact angle hysteresis. By coupling the criterion equations of sliding and rolling, we develop a mode selection criterion equation, which is only dependent on equilibrium contact angle θ e . Three regions are clarified: (1) for 126.3° <  θ e  < 147.0°, a droplet rolls if Bn  <  Bn t and slides if Bn  >  Bn t , where Bn t is the transition Bond number; (2) for θ e  < 126.3°, a droplet only slides; (3) for θ e  > 147.0°, a droplet only rolls. The theoretically determined 147.0° contact angle is newly recommended as the contact angle boundary between hydrophobicity and super-hydrophobicity. One of the applications of this work is to provide a general guideline for droplet detachment or retention in fuel cells and condensers. [ABSTRACT FROM AUTHOR]

Micro-condenser using the phase separation concept was investigated in this paper. Lined pin fin arrays generate liquid passages and vapor passages alternatively in chip width direction. The decreased Gibbs free energy with gas–liquid interface advancing pin fin throat location is the mechanism to induce liquid flow from vapor passages to liquid passages. The decreased energy dissipation due to decreased interfacial area between the two phases accounts for pressure drop reduction. Three micro-condensers were investigated: microchannel condenser (SWM), parallel phase separation condenser (PPS with constant cross sections of fluid passages) and conical phase separation condenser (CPS with varied cross sections of fluid passages). Micro-condensers had identical project condensation surface of 25.0 mm by 3.0 mm. The etched depth was 75 μm. Water-vapor was the working fluid. Compared with SWM, phase separation condensers increased mass flow rate by 15% at similar pressure drops. PPS condenser enhances heat transfer at moderate or smaller cooling intensity, but deteriorates heat transfer at large condensed liquid flow rate, at which over liquid expansion occurs to flood all pin fin side walls. CPS condenser self-adapts variations of flow rates of the two phases to stabilize vapor–liquid interface near pin fin membrane. Pin fin side walls facing vapor passage are covered by thin liquid film to eliminate over liquid expansion. CPS condenser enhances heat transfer over entire operating parameter ranges, increasing condensation heat transfer coefficients by 74% maximally while pressure drops are decreased. CPS condenser has the best performance among the three condensers. [ABSTRACT FROM AUTHOR]

Heterogeneous hydrophilicity/hydrophobicity surface involves many applications such as dropwise condensation, but droplet dynamics on such surface is not well understood. Here, droplet impacting on heterogeneous surface was described by non-dimensional conservation equations. The volume of fluid (VOF) method tracked the gas-liquid interface. A set of parameters such as impacting velocity, drop size etc. were combined to form three key non-dimensional parameters of We , Oh and β i (size ratio of hydrophilic dot to drop). Numerical simulations agreed with impacting outcomes on uniformly hydrophilic or hydrophobic surface in references. For drop dynamics on heterogeneous surface, the regime maps containing complete-drop, single-drop-pinching-off and multi-drops-pinching-off were demonstrated over a wide range of We = 1–100, Oh = 0.001–1 and β i = 0.5–10. The increased β i enlarges the complete drop regime. The single-drop-pinching-off mode involves combined wall adhesion and surface tension induced short wave mechanism, while the multi-drops-pinching-off mode is caused by the propagation and interference of capillary waves from both ends of an elongated liquid column. The superposition principle was found for the first time: drop patterns include an adhesion part on the wall, similar to that on a hydrophilic surface, plus a rebounding part, similar to that on a super-hydrophobic surface. Spreading diameters are increased by β i at smaller We and moderate or larger β i , but they are not influenced by hydrophilic dot sizes at large We , under which inertia force thoroughly suppress effects of surface tension and wall adhesion. The present findings of this paper are helpful to design hydrophilic/hydrophobic surface and ensure droplet completeness during the impacting process. [ABSTRACT FROM AUTHOR]

Solar energy-to-heat conversion for steam generation is an essential metrology for power generation, water purification and desalination. Harvesting light energy and converting it to heat as terminal energy by black photothermal sheets is a novel strategy to attain this goal. This technology rely on use of black nanomaterials as light absorber to increase the absorption and conversion efficiency of solar energy. Fundamental understanding of their structure-property has to be fully exploited for further developing efficient solar-to-heat systems. This report summarizes physical understanding and experimental advances in development of black photothermal sheets for solar water evaporation. We examine the popular photothermal systems with remarkable vapor generation performance to identify the state-of-the-art of the device design. Three groups of the photothermal sheet are discussed in terms of different light-harvesting materials, such as carbon-based sheets, plasmonic sheets as well as semiconducting sheets. The physical difference of these novel devices with their steam releasing property are also highlighted. [ABSTRACT FROM AUTHOR]

In the framework of modern thermodynamics, “thermodynamics flow” and “thermodynamics force” are introduced to develop a real thermal efficiency expression for heat engine, which receives heat from a heat source and dissipates heat to environment to yield a work output, for the first time. Enclosed area of T-Q curves of a counter-current heat exchanger is the dissipation for heat to power conversion, representing loss of thermal energy quality. The relationship between heat load and dissipation for heat to power conversion is quantified. Such connection is written for both heating and cooling processes. Linking the thermal couplings between heating and cooling processes yields the thermal efficiency expressed as η real = C η Carnot , where C = 1 η Carnot - R 1 - η Carnot , η Carnot is the Carnot efficiency, R = R h / R c is the ratio of resistance in heating process R h divided by that in cooling process R c . The thermal efficiency theory tells us that no matter how complex a heat engine is, the engine should reach a lower resistance ratio of heating process with respect to cooling process to raise its thermal efficiency. The guidelines for design and operation of general heat engines are provided. A link between heat transfer and thermodynamics is presented in this work. As an application example, the effect of critical temperatures of organic fluids on the performance of Organic Rankine Cycles is successfully explained by the newly developed theory. [ABSTRACT FROM AUTHOR]

Supercritical fluids (SFs) are widely used in power generation systems using nuclear, solar, geothermal, and fossil energies. The heat transfer deterioration (HTD) phenomenon during heat transfer of SFs is of great importance to the design and operation of the components in supercritical power cycles. The criteria for determining the onset of HTD has been reported in the literature, but the quantitative model to obtain the position of the wall temperature peak during HTD occurrence, and the correlation to accurately predict the heat transfer characteristics at the wall temperature peak, are both missing. In this work, to determine the position and to predict the characteristics of HTD at the wall temperature peak, we developed two correlations based on experimental results for supercritical CO 2 (sCO 2) in vertical upward tubes with wide range of experimental parameters. The first correlation to predict the location of the peak is developed using experimental data for sCO 2 , which can accurately determine the dimensionless bulk fluid temperature corresponding to the wall temperature peak. Moreover, a new heat transfer correlation is developed for the Nusselt number at the wall temperature peak, which has a simple form of N u H T D = 0.00796 R e b 0.7215 P r b − 0.1568 K − 0.115 , where Re b , Pr b , and K are Reynolds number, Prandtl number, and supercritical K number, respectively. This correlation shows smaller prediction error compared with five existing correlations in the literature for not only sCO 2 , but also various other working fluids. It also outperforms the recently proposed K number correlation in predicting characteristics at the wall temperature peak during HTD conditions. The two correlations developed in this work provides the quantitative models for the HTD phenomenon, and can benefit the engineering application of supercritical power cycles. • SCO 2 heat transfer deterioration (HTD) was experimentally studied coving wide parameter ranges. • The HTD phenomenon was quantitatively analyzed based on experimental databases. • New methods were proposed to predict the location and characteristics of wall temperature overshoot. • The new heat transfer correlation for HTD has significantly improved prediction accuracy. [ABSTRACT FROM AUTHOR]

A comprehensive model for organic Rankine cycle (ORC) was presented in this work. Several sub-models were included. Fewer empirical coefficients were needed in the improved expander model than the previous one as several parameters were obtained directly from the actual structure parameters of scrolls. The Dalton's law was used to simulate the pressure in the liquid tank, consisting of partial pressures of non-condensable gas and saturated vapor. A spray cooling tower model was built to take account of the influence of environment temperature and humidity on the ORC operation and performance. The simulations agree well with the tested data. Then, the model was used to analyze the mismatch among components of the cycle and evaluated the potential optimizations to the ORC prototype. For the present ORC system, the model predicts that the output power can be doubled after the optimization measures are taken. The environment temperature and humidity apparently influence the system performance. The effect of humidity becomes significant at high environment temperature. The expander power can be decreased by one third when the humidity is increased from 50% to 90% in summer season. The present work provides the guidance for design and operation of the ORC system. [ABSTRACT FROM AUTHOR]

A novel strategy was proposed for the improvement of vapor chamber heat pipe (HP) performance. The mastoid process array, wettability control of heat pipe and control of liquid charged into heat pipe are comprehensively used to manage the phase distribution. Thus, the two dominant heat transfer mechanisms of nucleation and convection can be switched. The objective of this strategy is to maintain nucleation mechanism but suppress convection mechanism. Holding the nucleation mechanism, our newly developed heat pipe behaves excellent thermal sensitivity with respect to heating loads. Our idea was thoroughly verified by experiments, in which three HP samples were fabricated and tested: #1 equal wettability sample, #2 moderate wettability difference sample and #3 opposite wettability sample. The wettability difference was generated with nano-structured surface. The #1 sample shows convection mechanism with heat transfer coefficients (HTCs) not changed versus heat fluxes, due to evaporator porous wick occupied by larger vapor content and liquid filmwise condensation on condenser surface. The super-hydrophilic evaporator and super-hydrophobic condenser (#3 sample) shows nucleation mechanism with HTCs significantly increased with increases in heat fluxes, due to large driving force to flood evaporator porous wick by water and expose condenser by vapor. Surprisingly, opposite wettability match HP had overall thermal resistances of only 1/3 to those of equal wettability HP. The comprehensive use of mastoid process array and controls of wettability and water amount charged into HP lowers heater temperatures by 30–40 °C at high heat fluxes such as ~100 W/cm 2 on a large heater area of 1.4 cm 2 , paving a new road for heat pipe performance improvement. [ABSTRACT FROM AUTHOR]

Condensation heat transfer of R245fa was investigated in a shell-tube condenser. The copper tube had an inner diameter of 14.70 mm with a 1600 mm heat transfer length. Mass fluxes and vapor mass qualities covered ranges of 198.8–504.7 kg/m 2 s and 0.291–0.976, respectively. Condensation heat transfer coefficients are increased with increases of mass fluxes and vapor mass qualities. The horizontal position yielded minimum condensation heat transfer coefficients. Deviating from the horizontal position enhances condensation heat transfer. The condenser is suggested to operate at weakly inclined flow to reach better thermal performance. Flow patterns and liquid height signals explored the condensation heat transfer mechanisms. The flow is stable for inclined down-flow but becomes unstable for inclined up-flow, which was caused by the vapor-liquid interface wave. Non-dimensional parameter analysis identified the competition between inertia force and gravity force. The vapor-liquid interface wave is the mechanism to enhance condensation heat transfer for inclined up-flow, while the decreased liquid film thickness on the tube bottom enhances heat transfer enhancement for inclined down-flow. A correlation based on the Froude number of vapor phase successfully matched the experimental data. This study is useful for the condenser design and operation such as applied in Organic Rankine Cycles. [ABSTRACT FROM AUTHOR]

Mesh screen membrane is a functional material for gas-water or oil-water separation. If a water drop impacts on the membrane at a sufficiently high velocity, a critical condition at which daughter droplets are generated and fall down below the membrane occurs, under which the separator is failure. The objective of this paper is to determine the critical condition. Six mesh screen membranes are used. The mesh wire diameter and mesh pore are on the same-scale (10–100 μm), involving apparent cross sectional area decrease of mesh pores in the membrane depth direction. Thus, drop impacting on the membrane yields significant liquid compression in ∼μs timescale to cause additional water hammer pressure. The analysis shows that the liquid compression is related to the number of mesh pores within drop project area ( N ). The water hammer pressure relative to dynamic pressure is found to be raised with N . The drop impacting process is governed by the dynamic pressure together with the additional water hammer pressure competed with the maximum capillary pressure at the throat location of the mesh pore. The modified Weber number − We w /cos( θ A ) was correlated with N in a single curve to predict the critical condition for droplet breakthrough, where We w is characterized by the mesh pore width and cos( θ A ) reflects the advancing contact angle effect. This paper is useful for membrane type gas-water or oil-water separator design. [ABSTRACT FROM AUTHOR]

The proposed gradient–porous-wall microchannels consist of bare channels and pin–fin array regions, fabricated by MEMS (microelectricalmechanicalsystem) technique. Boiling experiments were performed with acetone as the working fluid. Ultra-stable wall temperatures are achieved with oscillation amplitudes in the range of 0.02–0.18 °C. Bubble nucleation is found to happen in the porous wall. The generated vapor flows towards bare channels due to surface tension driving flow. The vapor ejection direction is periodically switched between neighboring channels, called the “bubble emission switch”. The bubble confinement ratio is newly defined. Bubbles become fat and slim in bare channels to generate high frequency “eye-blinking oscillation”. Bubble confinement ratios display sine function, and out-of-phase characteristic between neighboring channels. We confirm the “eye-blinking” oscillation as a density wave oscillation, propagating in the channel width direction. Because the porous-wall width is much smaller than the channel length, the “eye-blinking” frequencies are 10–100 times higher than that of the axially propagated density wave oscillation. The “integration parameter model” establishes the connection between “eye-blinking” oscillation and wall temperatures. The convective heat transfer intensity in bare channels is assumed to follow the bubble confinement ratio variation. The wall temperature oscillation amplitude is inversely proportional to the “eye-blinking” frequency. The phase angle between bubble confinement ratios and wall temperatures are 3 π /2, being the negative feedback mechanism to inhibit wall temperature oscillations. The porous-wall microchannels open a new way to eliminate flow instabilities for heat exchangers and thermal energy systems. [ABSTRACT FROM AUTHOR]

Supercritical heat transfer is important to design and operate advanced power generation system. Non-uniform heating is frequently encountered such as for sCO 2 boiler and solar receiver applications. Here, 3D numerical simulations are performed in turbulent regime, coupling solid wall and sCO 2 in tubes. Non-uniform heating is simulated by applying heat via a thin metal layer at the outer tube wall, covering half circumference of tube wall. Calculation results matched experimental data well. Heat transfer is compared between uniform heating and non-uniform heating. Numerical results are re-processed by the pseudo-phase transition theory, including a liquid-like region in tube core and a gas-like layer near the tube wall. The two layers of structure are interfaced by a terminating temperature T + which is determined by thermodynamics. Hence, supercritical heat transfer is evaluated based on the relative importance of thermal resistances induced by the liquid-like region and the gas-like film region. It is found that wall temperatures for uniform heating are higher than those for non-uniform heating, which is explained by larger thermal resistance of the gas-like film for uniform heating than that for non-uniform heating. This difference ensures better heat transfer for non-uniform heating than uniform heating. We conclude that in turbulent regime, the gas-like film dominates the magnitudes of wall temperature and the occurrence of heat transfer deterioration for both uniform and non-uniform heating. Our work is important for heat transfer facilities in supercritical domain, especially under non-uniform heating condition. • Heat transfer for sCO 2 in vertical tubes are comprehensively analyzed. • The heat transfer phenomenon for sCO 2 is analogous to the subcritical film heat transfer. • The thermal resistance mechanism is proposed to evaluate sCO 2 heat transfer. • Gas-like film is identified as the key factor affecting wall temperature, and even the HTD occurrence. [ABSTRACT FROM AUTHOR]

Dropwise condensation has much higher heat transfer efficiency than the filmwise condensation, hence it will be widely applied in power generation, waste heat recovery, refrigeration etc. The spontaneous coalescence-induced droplet jumping on superhydrophobic surfaces was an effective way to maintain highly efficient dropwise condensation. In our study, the coalescence-induced droplet jumping process was numerically studied through transient three-dimensional diffuse interface method. The effect of contact angle and its hysteresis, droplet size, viscosity and gravity on the jumping process was studied in details, energy conversions were also provided among the droplet surface energy, viscous dissipation, kinetic energy and gravitational energy. Our study showed that contact angle had negative effect on the jumping velocity, with the decreasing contact angle, both peak jumping velocities and radius range for droplet jumping would be reduced. For the capillary-inertial process the normalized droplet jumping velocity was at the order of 0.2. Although more than half of the released surface energy could be converted into the kinetic energy, only less than 10% of the released surface energy could be converted into the translational kinetic energy for droplet jumping. The contact angle hysteresis had significant effect on the droplet jumping, the larger advancing contact angle could help improve the droplet jumping velocity, while the lower receding contact angle could reduce the droplet jumping velocity. Our results might provide useful guideline for design of efficient dropwise condensation heat transfer through coalescence-induced droplet jumping on superhydrophobic surfaces. [ABSTRACT FROM AUTHOR]

We proposed a micro-pin-fin based membrane separator. An enclosed membrane with micron scale holes was symmetrically populated in a rectangular duct. When gas phase interacts with the membrane, the gas–liquid interface cannot break through the pin-fin holes due to the increased surface energy. A two-dimensional numerical model simulated the separation process. The volume of fluid (VOF) method tracked the gas–liquid interface. Multiscale grids were used. When a bubble attacks the pin-fin membrane, strong liquid circulation occurs at the membrane entrance. Pressures in the side region are larger than those in the core region. Liquid plugs are shortened due to the pressure driven flow from side region to core region to cause the bubble coalescence. The separation length was shortened while increasing the gas flow rates. The bubble lengths were weakly influenced by gas flow rates. Liquid plugs are quickly shortened following the membrane entrance. The frictional pressure drop of the two-phase mixture in the side region was larger than that of liquids in the core region, even at low gas flow rates. The ultra-large gas flow rates yielded quite large bubble pressure to exceed the capillary pressure limit, causing the separator failure. Ultra-low and large gas flow rates specified the separator operation range. [ABSTRACT FROM AUTHOR]

The integration temperature difference Δ T i considers the heat transfer routes, linking the heat transfer process with the thermodynamic behavior of heat exchangers. The first and second non-dimensional integration temperature differences are defined as Δ T i, h ∗ = Δ T i / T h, i and Δ T i, s ∗ = Δ T i / ( T h, i - T 0 ) respectively, where T h,i is the heat source temperature and T 0 is the environment temperature. This paper is the first to experimentally verify the significance of the non-dimensional integration temperature differences on organic Rankine cycle (ORC) systems. The first non-dimensional temperature difference is shown to have linear relationship with the revised entropy generation numbers ( N s ). With increases of the second non-dimensional integration temperature difference, the expander powers, system thermal and exergy efficiencies had parabola distributions. They simultaneously reached maximum at Δ T i, s ∗ = 0.282 , under which the vapor cavitation in the expander disappears and the exergy losses of heat exchangers are acceptable to elevate the expander efficiency. Beyond the optimal point, the ORC performance is worsened either due to the vapor cavitation in the expander, or due to the poor thermal matches in the evaporator and condenser. The second non-dimensional integration temperature difference comprehensively reflects the effects of heat source temperatures, heating powers and organic fluid flow rates and pressures, etc. It balances exergy destructions of various components to optimize the system. Thus, it can be an important parameter index to maximize the power or electricity output for a specific heat source. The usefulness of the integration temperature difference and the future work are discussed in the end of this paper. [ABSTRACT FROM AUTHOR]

We decouple a heat pipe into capillary pressure, flow resistance, condensation heat transfer, and assign specific length scale to adapt each function. We verify the synergy of various length scales to activate various functions. The strategy guides multiscale design to realize an enhancement of capillary pressure, a well management of flow resistance and an ultra-thin liquid thickness on condenser surface. The porous wick consists of a particle sub-layer and 3D mastoid process array. The tips of mastoid process directly contact the condenser wall. Four vapor chambers are formed by sintering d m = 73.8 μm without oxidation (#1), with oxidation (#2), d m = 556 nm without oxidation (#3) and with oxidation (#4), respectively. Liquid suction and heat transfer experiments were performed. Four types of evaporator temperatures versus inclination angles were observed. Small difference is found between bottom and top heating modes. The multiscale wick influences the vapor–liquid phase distribution to cause the difference between side and other heating modes. The d m = 73.8 μm particle sintering with nano-roughness successfully balance various conflicts among capillary pressure, vapor–liquid interface area, flow resistance and liquid removal from the condenser surface. Nano-roughness increases the vapor–liquid interface area to have 3–4 times of evaporation heat transfer coefficients compared with smooth particle surface. Nano-roughness increases the wettability to capture liquid from condenser, having ∼18 times of condensation heat transfer coefficients to those without nano-roughness. The d m = 556 nm particle sintering and nano-roughness are the poor match for heat pipes. This paper gives a clue to construct multiscale wicks for heat pipes and ensures better performance at varied gravity such as micro-gravity environment. [ABSTRACT FROM AUTHOR]

An ORC (organic Rankine cycle) was developed with R123 as the working fluid. The heat capacity is in ∼100 kW. The match between pump and expander is investigated. Lower pump frequencies ( f < 10 Hz) adapt the whole range of expander torques, yielding stable flow. Higher pump frequencies ( f > 10 Hz) adapt low expander torques only, and cause unstable flow and pump cavitation for larger expander torques. Ultra-low expander torques generate sufficiently high vapor superheatings to decrease expander efficiencies. Ultra-high expander torques achieve saturation vapor at the expander inlet, causing liquid droplets induced shock wave to worsen expander performance. An optimal range of expander torques exists to have better expander performance. A liquid subcooling of 20 °C is necessary to avoid pump cavitation. Expander powers and efficiencies show parabola shapes versus expander torques, or vapor superheatings at the expander inlet. The optimal vapor superheating is 13 °C. The cavitation mechanisms and measures to avoid cavitation are analyzed. This paper notes the overestimation of ORC performance by equilibrium thermodynamic analysis. Assumptions should be dependent on experiments. Future studies are suggested on organic fluid flow, heat transfer and energy conversion in various components. [ABSTRACT FROM AUTHOR]

This paper creates new method that uses microflows through mesh pores to modulate flow and temperature fields. Modulated heat transfer tube (MHTT) was constructed by suspending consecutive conical-mesh inserts in a tube. Because there are too many 3D mesh pores (10–100 μm size) for a conical mesh insert, numerical simulations in laminar flow regime were performed by an 3D to 2D conversion of mesh pores applying equal equivalent diameter criterion and total flow area criterion of mesh pores. The multiscale grid generation linked micron scale of mesh pores and macroscale of the tube. Covering the present data ranges, MHTT had Nusselt numbers which are 1.4–4.1 times of that in a bare tube, PEC (performance evaluation criterion) was up to 2.2, demonstrating excellent heat transfer enhancement at low flow rate pumping cost. The perfect MHTT performance comes from the distinct flow field: an attached hydraulic boundary layer having large velocity and its gradient near the tube wall, a weak circulating flow region upstream of the mesh insert and a weakly positive flow region downstream of the mesh insert. A thin thermal boundary layer on the tube wall was reached to enhance heat transfer. The periodic unit length S and diameter of the conical mesh insert δ were optimized. The varied slopes of Nu versus Re were found and explained while increasing Re . There are best matches of PPI (pores per inch) and Re (Reynolds number). Low PPI mesh insert was suggested at low Re , high PPI mesh insert deformed streamlines to deviate from the perfect flow and temperature fields. Meanwhile, high PPI mesh insert had better performance at high Re . Low PPI mesh insert had good performance, which can be further improved by raising PPI . Because metallic mesh screen is commercialized and cheap, MHTT has wide potential engineering applications. [ABSTRACT FROM AUTHOR]