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Micro fins on the internal surface of the tube improves its heat transfer ability. This paper investigates the thermal performance of tube flow numerically by adding axial straight micro fins (ASMF) on internal tube surfaces. The numerical method is experimentally validated using a tube featuring ASMF. The effects of fin height e , fin number N f , and fin shape of the tube with ASMF on the thermal performance are numerically studied within the range of Reynolds number (Re) from 1280 to 7687. Compared to a smooth tube, the Nusselt number (Nu) for tube with ASMF is reduced over the entire range of Re. In order to assess the performance of heat transfer, the ratio of the heat transfer coefficient (h) multiplying the heat transfer area (F) of ASMF tube (hF) to that of the smooth tube (h s F s) is utilized. Parametric studies were performed. The optimal fin height, fin number are found to be 0.0429 and 32. The optimal fin profile is found to be quadratic function profile. By combining the optimal fin height, fin number and fin profile, the maximum value of hF /(h s F s) can reach 1.32. Besides, the heat transfer enhancement mechanism induced by ASMF is also disclosed in this paper. [ABSTRACT FROM AUTHOR]

This paper presents numerical simulation of graphe nanoplatelet (GNP) – sodium dodecylbenzene sulfonate (SDBS) – water nanofluid with volumetric mass fractions of ϕ equal to 0–0.1%. The new microchannel is made of 2 layers and has sinusoidal cavities along with the heat sink. The study was conducted for Re = 50, 300, 700 and 1000 (laminar flow). Based on the results, higher Re leads to more convective heat transfer coefficient. Therefore, the value of temperature gradients decreases and on the other hand the effect of cooling fluid temperature in warm areas near solid wall becomes important. Using a higher value of Re results in the penetration of heat in the fluid layer decreases which in general will reduce the temperature of the outlet section in larger Re values. Also, larger Re value results in larger development length which is also a cause for lack of thermal development and dominance of the temperature of the coolant flow in the heat sink resulting in decreased outlet section temperature for higher Reynolds numbers. For Re = 50 and 300 because of lower fluid velocity, the effect of surface geometry factors such as sinusoidal paths or hollow parts (cavities) has a smaller influence on the pressure loss or friction factor of the flow. [ABSTRACT FROM AUTHOR]

Corrugated tubes are extensively unitized in enhancing heat transfer within tubular heat exchange devices. The efficiency of these corrugated tubes is closely linked to the geometric characteristics of the surface corrugations. In this study, we conducted an extensive series of Large Eddy Simulations on a representative type of enhanced tube featuring periodic inward corrugations (PIC). Our goal was to compile a comprehensive and precise dataset of the thermal and hydraulic properties specific to this design. The key design parameters that define the corrugated patterns are corrugation height (H), corrugation width (W), and the length of the straight section (P). We systematically explored these parameters to understand their impact on heat transfer and fluid dynamics. Among these parameters, corrugation height (H) has been identified as the most influential factor affecting flow and heat transfer properties. As the corrugation height varies from 1/8D to 3/8D, we observed a substantial increase in the friction factor and Nusselt number by a factor of 209 and 5, respectively, at Re = 1000; while the critical Reynolds number decreased roughly from 800 to 100. These findings underscore the significant role of corrugation height in shaping the flow and heat transfer performance of PIC tubes. The other two parameters, corrugation width and straight section length, were also found to be crucial in determining the overall heat transfer coefficient and pressure drop. When Re = 1000, variations in W/D from 1 to 3 resulted in a 1.3-fold increase in both the f and the Nu. Furthermore, altering the P/D from 2 to 6 led to a 2.1-fold increase in f and a 2.2-fold increase in Nu. The results of our study suggest that when utilizing this type of corrugated tubes, careful consideration is required to strike an optimal balance between heat transfer efficiency and pressure loss. The large-sets LES results presented in this paper can serve as valuable inputs for optimizing the design of PIC tubes. [ABSTRACT FROM AUTHOR]

• The heat transfer characteristics of different horizontal wires immersed in both liquid and supercritical carbon dioxide were studied by visualization experiments with a schlieren system. • Pseudo film boiling shown the similar heat transfer characteristics and near-wall flow field structure with subcritical film boiling. A correlation based on an integral mean Raleigh number predicted the Nusselt number well. • Experiments with various metal wires revealed distinct self-propagating transition phenomena in boiling modes, driven by the axial heat conduction characteristics. Near-critical and supercritical fluid heat transfer exhibits unique heat transfer characteristics. Pool heat transfer experiments circumvent the drawbacks of traditional flow heat transfer experiments, characterized by numerous factors and challenges in observation, and can offer new insights for the study of heat transfer mechanisms. In this paper, the heat transfer characteristics of different horizontal wires immersed in both liquid and supercritical carbon dioxide were studied by visualization experiments with a schlieren system. The study showed that as approaching the critical point, the pool boiling weakened, resulting in a decrease in the peak heat transfer coefficient. In supercritical cases, heat transfer with low heat flux maintained natural convection, while the cases with high heat flux exhibited similar heat transfer laws and near-wall flow field structures with subcritical film boiling. Meanwhile, experiments with various metal wires revealed distinct self-propagating transition phenomena in boiling modes, driven by the axial heat conduction characteristics. Based on the experiments, a pool heat transfer mechanism of the near-critical and supercritical fluids was proposed. [ABSTRACT FROM AUTHOR]

This paper employs a computational fluid dynamics numerical framework integrating the Euler-Euler two-fluid model with the particle dynamics method to analyze the heat and mass transfer characteristics of water-based graphene nanofluid slurries in helical corrugated tubes. The results indicate that, with ice crystal content ranging from 10% to 30% at the inlet, the heat transfer performance is positively correlated with the slurry concentration, and the increase in nanofluid concentration has minimal impact on the pressure drop inside the tube. The helical structure results in the maximum flow velocity occurring in the groove area. Compared to straight tubes, the increase in heat transfer area does not only promote the generation of vortices but also enhances turbulent intensity, reduces the thickness of the thermal boundary layer, and improves heat transfer efficiency. Graphene nanofluid slurries exhibit superior heat transfer capability compared to pure water slurries, with surface heat transfer coefficient increasing with graphene concentration. The maximum HTC of helical corrugated tubes is 1.4 times that of straight tubes, with an average Nusselt number (Nu) 1.44 times higher than that of straight tubes. Lastly, an empirical correlation for Nu is established to predict the thermal performance of water-based graphene nanofluid slurries flowing through helical corrugated tubes. • Pressure drop, ice crystal concentration distribution, flow velocity, temperature distribution, and heat transfer performance are discussed. • Aqueous graphene nanofluid ice slurry demonstrates outstanding flow and heat transfer performance. • Helical structure significantly influences the flow and heat transfer of the ice slurry. • The average Nu of spiral bellows is 1.44 times that of straight pipe. [ABSTRACT FROM AUTHOR]

• The flow and heat transfer characteristics of single and multiple-synthetic jet impingement cooling is presented. • The equivalent Reynolds and Nusselt numbers were determined for the purpose of describing multiple orifice configuration. • The merging jet process is presented and the merging point is determined. In this paper, the comparison between synthetic jet actuator with single axisymmetric orifice and multiple axisymmetric orifices is presented. The aim of this paper is to compare the flow and heat transfer characteristics of single and multiple synthetic jet impingements cooling. The multiple orifice configurations had a central orifice and a satellite orifices placed in the pitch circle. The synthetic jet actuator had central orifice with 0, 3, 4, 5 and 6 orifices placed in the diameters of the relative pitch circle p / d = 2.5, 3 and 4. A total of 13 various geometric configurations were tested experimentally. In the multiple orifice configurations, the total cross-section area was approximately equal to the cross-section area of the single orifice configuration. The input power delivered to the synthetic jet actuator was maintained constant and equal to 3.00 W. The synthetic jet actuator energetic efficiency, Reynolds number, equivalent Reynolds number, radial and axial distributions of pressure coefficient, and heat transfer characteristic were presented. The synthetic jet issuing from multiple orifice plate merged at some axial distance, creating a single axisymmetric jet. The merging jet axial distances were determined for all investigated configurations. In the present paper, the integral quantities averaged over all orifices cross section area, or over impingement plate much larger than total orifices area, were analyzed for the purpose of objective comparison. From all various investigated parameters obtained from five different and independent experimental methods, the following conclusion may be made: if the total orifice cross section area in the case of single and multiple orifice synthetic jet is similar and real power deliver to the SJA is maintained at the same level the resulting equivalent Reynolds number and equivalent dimensionless stroke length achieved similar values and the impinging jet equivalent Nusselt number also achieved comparable values and distributions. [ABSTRACT FROM AUTHOR]

• Subcooled flow boiling heat transfer of water in the porous metal foam tubes was investigated experimentally. • Filling a tube with metal foam could improve the heat transfer and also pressure drop. • The thermal efficiency of metal foam tubes was investigated. • Based on experimental data, a correlation was presented to predict heat transfer in the metal foam pipes. This paper has investigated the effect of different porosities (0.80–0.90) of the metal foam pipes on heat transfer coefficient and pressure drop of subcooled flow boiling of water experimentally. The metal foam pipe with 0.80 porosity has increased the Nusselt number and pressure drop by 41 % and 21 % compared to the 0.90 metal foam pipe, respectively. The heat transfer of water phase change in a porous medium has received less attention due to the complexities of the problem. One of the challenges in this field is the absence of a correlation for predicting heat transfer in metal foams. In this paper, a systematic method based on dimensionless numbers considering the essential parameters, like mass flux, subcooling, and heat flux, was used to provide a correlation for calculating the Nu-number based on 106 experimental points. The mean absolute deviation (MAD) of the results predicted by the new correlation is 8.9 %, and it predicts 95 % of the database with ±20 %. [ABSTRACT FROM AUTHOR]

Particle-based moving bed heat exchangers are increasingly playing a significant role in industrial energy conservation and solar energy utilization. However, the moving bed heat exchanger used for cohesive granular materials still needs to be developed. This paper investigates the feasibility of indirect heat transfer of cohesive granular materials through a moving bed heat exchanger. A vibrating moving bed heat exchanger is developed for the metallurgical slag of vanadium-titanium (MSVT) from industry. The experiment demonstrates that the vibrating moving bed heat exchanger can establish an approximate mass flow regime of MSVT in the experimental section. The vibration device designed for the experimental and discharge section effectively resolves bridging and the intermittent collapse of arching in cohesive granular materials. The outer side of the tube is tightly wrapped by MSVT with vibration. Significant differences are observed in the flow and heat transfer behavior of MSVT between the aligned and staggered tubes. The local heat transfer coefficient at the top and bottom of the aligned tubes exhibits much lower sensitivity to flow velocity compared to the staggered tubes. The relationship between Nu −1 and Pe −0.5 or MSVT around the aligned and staggered tubes follows a linear correlation. Compared to aligned tubes, Nu −1 for MSVT in staggered tubes shows an average reduction of 28%. [Display omitted] • A vibrating moving bed heat exchanger is developed for cohesive granular materials. • Special experimental design can resolve bridging and arching between tubes. • Rheological properties of vanadium-titanium granular are quantitatively evaluated. • The heat transfer of granular flow is tested around different tube arrangements. • The heat transfer correlations are built to predict the heat transfer. [ABSTRACT FROM AUTHOR]

• Novel opening combination rotor blade is proposed to enhance heat transfer effect. • The effect of opening combination rotor blade is optimized for overall performance improvement. • Enhanced heat transfer is revealed by field synergy principle. • The characteristics of opening combination rotor blade are revealed by numerical simulation. • The applicable conditions of heat transfer strategies are determined. Based on the passive enhanced heat transfer mechanism, this paper proposes the new opening combination rotor blade, which aims to improve heat and mass transfer performance by changing internal structure of cracking furnace tube, thus achieving efficient production of ethylene. Through mathematical modeling and simulation of heat transfer properties of opening combination rotor blade, heat transfer performance and fluid flow characteristics of ordinary rotor blade tubes and opening combination rotor blade with axial widths of W (W = 0.25 R, 0.5 R, 0.75 R) are analyzed using field synergy principle and comprehensive heat transfer evaluation coefficient (PEC).The results demonstrate that the Nusselt number of opening combination rotor blade is 19%-23% lower than that of ordinary rotor blade. The resistance coefficient of opening combination rotor blade with axial width of 0.25 R is significantly lower by 33%-43%. Opening combination rotor blade with axial width of 0.25 R has a significantly lower resistance coefficient of 72%-78%. Its PEC value is between 1.23–1.28 with significantly improved overall heat transfer performance. In summary, opening combination rotor blade with axial width of 0.25 R has the most significant heat transfer effect and has a high reference significance for engineering design. [Display omitted] [ABSTRACT FROM AUTHOR]

In the applied mathematical modelling of heat transfer systems, the heat transfer coefficient (HTC) is one of the most important parameters. This paper proposes a combination of the Method of Fundamental Solutions (MFS) with particle filter Sequential Importance Resampling (PF-SIR) to estimate the time-dependent HTC in two-dimensional transient inverse heat conduction problems from non-standard boundary integral measurements. These measurements ensure the unique solvability of the boundary coefficient identification problem. Numerical results show high performance on several test cases with both linear and nonlinear Robin boundary conditions, supporting the synergy between the MFS and simulation-based particle filter sequential analysis methods. [ABSTRACT FROM AUTHOR]

Highlights • The effect of moisture content on natural convection flow in a cavity with differentially heated vertical and conducting horizontal walls was investigated. • Natural convection flow and heat transfer are very sensitive to the level of moisture present in the air and even at low temperature gradient between the cavity vertical walls. • The presence of moisture causes changes in the energy equation, which has a significant effect on the heat transfer coefficient and influences the weak natural convection flows inside the cavity. • The vertical walls have been found to show greater sensitivity for heat transfer with changes in moisture content, while both horizontal walls are almost insensitive to moisture content variation. • The heat transfer coefficient increases proportionally with increasing moisture concentration, while the average relative humidity inside the cavity significantly reduces with increasing temperature gradients between the vertical walls of the cavity. Abstract This paper reports a numerical investigation of low turbulence buoyancy-driven flow of moist air and heat transfer inside a rectangular cavity with differentially heated vertical walls. The variations of the flow, temperature and moisture inside the cavity has been analysed together with heat transfer coefficients for a range of mass fraction of water vapour and temperature gradients between the vertical walls of the cavity. The accuracy of the numerical methodology was also scrutinised by conducting a rigorous validation study of benchmark experimental data for the average Nusselt number for similar buoyancy driven cavity flow. The results of this investigation showed that during the natural convection process, the change in moisture content in the moist air has a significant influence on the flow and temperature fields inside the enclosure and the variation of the vertical wall temperature gradients have also shown to affect the moisture concentration inside the cavity. The percentage change in the average heat transfer varied significantly depending on the mass fraction of moisture in the air and the temperature gradient between the vertical walls. The results also showed a 3.5% increase in the average heat transfer for every 0.02 kg/kg increment in the mass fraction of water vapour. The findings from the study are significance to scientists and practitioners who are responsible for moisture management in enclosed space at the design threshold and for optimisation of energy used in buildings. [ABSTRACT FROM AUTHOR]

Highlights • The heat transfer and flow characteristics of two-turn ribbed serpentine channel were analyzed. • Heat transfer distribution is studied with the transient liquid crystal measurement technique. • The inlet Reynolds numbers are varied from 5,000 to 20,000. • Pressure coefficient distribution of two-turn ribbed serpentine channel was researched. Abstract This paper experimentally and numerically investigates the heat transfer and flow characteristics of a two-turn ribbed serpentine channel with lateral outflow. The heat transfer coefficient was measured by a transient liquid crystal technique. Experiments were carried out at Reynolds numbers between 5,000 and 20,000 and rotation numbers of 0 and 0.03. The results indicate that with increasing inlet Reynolds number, the high-Nusselt number regions of the middle and lateral outflow channels gradually move to upstream ribs. The inlet channel shows the highest increase rate of the Nusselt number; whereas, the rate is lowest at downstream turning area. The rotation increases the trailing surface Nusselt number of the inlet and lateral outflow channels, and the increase rate is more prominent for higher values of the Reynolds number. However, the rotation has negative effects on the averaged area Nusselt number of the middle channel in cases of Re ≤ 17,000. The pressure coefficients decrease the in inlet and middle channels along the flow direction; whereas, they slightly increase in the lateral outflow channel. There is a long low-velocity vortex formed in the lateral outflow channel, and the vortex size is considerably reduced by the rotation. Accordingly, the rotation has the most positive effects on the pressure coefficient of the lateral outflow channel. [ABSTRACT FROM AUTHOR]

Highlights • Anisotropic heat transfer and natural convection of a ferro-nanofluid are studied. • Based on frame indifference rule, anisotropic thermal conductivity tensor is derived. • Due to the magnetic field, the isotherms show significant anisotropy. • The Nusselt number increases significantly as the Rayleigh number increases. • The Hartmann number may enhance or diminish the thermal performance. Abstract In this paper, effects of anisotropic thermal conductivity and the Lorentz force in a ferro-nanofluid induced by external magnetic fields are investigated. The nanofluid is modeled as a non-linear single-phase fluid, where the viscosity is considered to depend on the nanoparticle concentration; the thermal conductivity shows anisotropy due to the existence of the magnetic field. The anisotropic thermal conductivity tensor, which depends on the magnetic field vector, is derived by considering the principle of material frame indifference of Continuum Mechanics. Numerical simulations are performed in a horizontal annulus enclosure. Effects of the nanoparticle concentration, magnetic distribution, and the dimensionless parameters, such as the Rayleigh number and the Hartmann number, are studied. The numerical results indicate that due to the anisotropic thermal conductivity, the isotherms become elliptic and deviate significantly from a circle which is a typical distribution with isotropic thermal conductivity; furthermore the elliptic shape changes as the direction of the magnetic field varies while the heat transfer is always much faster in the direction parallel to the magnetic field. For the range of the dimensionless parameters studied here, the Nusselt number increases significantly as the Rayleigh number (ranging from 2500 to 50,000) increases; depending on the situation, the magnetic field (the Hartmann number which ranges from 0 to 1) may enhance or diminish the thermal performance. In addition, the streamlines are more organized and less wavy when there exists a magnetic field; this could be attributed to the suppressive effect of the Lorentz force. [ABSTRACT FROM AUTHOR]

Abstract This paper deals with the modeling of weakly rarefied and dilute gas flows in micro channels by the continuum approach, valid for Knudsen numbers smaller than about 0.1. It particularly focuses on the modeling of the associated heat transfer. The models proposed in the literature for the forced convection of gas flows in long micro channels between two infinite plates are more specifically discussed. The complete model for such flows is reminded after a compilation and a brief description of their possible applications in industries. The compatibility of the pressure work and viscous dissipation in the energy equation with the power of the viscous stress at the walls is discussed in detail. A dimensional analysis is proposed in the context of long micro channels. Analytical solutions for the velocity and temperature fields and for the Nusselt number are provided in the case of compressible micro-flows in isothermally heated flat plate channels, with pressure work and viscous dissipation included. The choice of an appropriate Nusselt number, including the power of the viscous stress at the wall, is particularly discussed. It is shown analytically and numerically, by solving the complete model for an isothermal wall micro-channel, that the Nusselt number tends to zero when the hydraulic diameter decreases, that is when the Reynolds number decreases and the Knudsen number increases. This could theoretically explain the very small values of the Nusselt number obtained in the experiments by Demsis et al. (2009, 2010). Highlights • Isothermally heated gas slipping flows in long plane micro-channels are considered. • Analytical solution of flow and heat transfer established from an asymptotic analysis. • Viscous stress power at the wall must be included in the total wall heat flux. • Wall Nusselt number tends to zero or to very small values for this flow type. • The very small values of the Nusselt number obtained in experiments are explained. [ABSTRACT FROM AUTHOR]

Jet impingement cooling is usually used in zones with extremely high thermal loads. The major factor that limits impingement heat transfer uniformity is the crossflow. The impingement cooling with return hole is applied to reduce the negative effect of crossflow on the target surface heat transfer in present paper. The influences of jet-to-plate spacing (H / D), impingement target surface curvature (α), temperature ratio (TR) and Reynolds number on flow field and heat transfer performance are investigated in detail. The results indicate that the correlation between the overall area average Nusselt number of target surface and H / D , the overall area average Nusselt number decreases by approximately 5.76% with H / D increases by one unit. Increasing the impingement target surface curvature is beneficial to expand the spanwise heat transfer. The overall area average Nusselt number increases by 295.5% for Reynolds number varying from 10,000 to 50,000 at TR = 0.910, and the overall area average Nusselt number increases by 8.68% for the TR varying from 0.668 to 0.910 at Re = 30,000. The results indicate that impingement cooling with return hole can achieve high heat transfer coefficient and uniform heat transfer distribution. [ABSTRACT FROM AUTHOR]

In the present paper, a numerical and experimental study has been performed to investigate the heat transfer and pressure drop properties of Al 2 O 3 and SiO 2 /Base oil nanofluid flow in a helical tube under constant heat fluxes. The nanofluids were prepared by using SN-300 base oil as a working fluid for 0.05%, 0.1%, 0.3%, and 0.5% mass concentrations. The experiments were carried out with two constant heat fluxes of 3950 W/m2 and 5280 W/m2 at 30, 40, 50, and 60 °C. The impact of various parameters, including flow Reynolds number, fluid temperature, two different nanoparticles, and various weight concentrations, on the heat transfer factor and pressure drop of the flow, are investigated. To examine the impact of different geometries on the heat transfer rate, simulations were conducted over four different helical tubes by changing the pitch circle diameter and steps. The results indicated that the heat transfer factor and pressure drop were increased by utilizing nanofluid instead of the base fluid. In addition, in the same mass concentration, the Al 2 O 3 nanofluid increased the heat transfer coefficient more than the SiO 2 nanofluid. The maximum heat transfer rate corresponds to 0.5% mass concentrations of Al 2 O 3 and SiO 2 nanofluids, which are 41.4% and 27.3% more than base oil, respectively. The helical tube compared to the straight tube increased heat transfer by 19.5%. Moreover, heat transfer was improved by 6% and 16.5%, respectively, by reducing helical pitch and pitch circle diameter. [Display omitted] [ABSTRACT FROM AUTHOR]

Abstract: In this paper the method used in a recently published paper to measure the latent heat of the martensite transformation during quenching of a steel is analysed. The arrangement of the experiment made it possible to obtain reasonable values for the latent heat of transformation, but cannot be expected to produce reasonable values for the heat transfer coefficient. Improved methods are discussed, including the novel probe design of the present authors. [Copyright &y& Elsevier]

This paper investigates a Taylor-Couette-Poiseuille flow in an annular channel of a slotted rotating inner cylinder, corresponding to a salient pole hydrogenerator. The purpose of this study is to improve the understanding of flow and thermal phenomena in electrical machines using a simplified scale model. The validation of the numerical model for a specific configuration is first shown by comparing the results with the experimental data. A parametric study is also performed to investigate all main flow regimes and to derive correlations in terms of the Nusselt number distribution on the rotor pole face and sides. The results show that the Nusselt number is proportional to the tangential Reynolds number to the power 1/7 in the pole and inductive faces trailing side. This relationship is similar to the one encountered in classical Taylor-Couette-Poiseuille flows between two concentric and smooth cylinders. [ABSTRACT FROM AUTHOR]

In this work, a three-dimensional analysis is used to study the heat transfer and entropy generation inside a helically coiled tube-in-tube heat exchanger in laminar flow regime using two different types of nanofluids. Overall heat transfer coefficient, effectiveness, Nusselt number, and entropy generation of helically coiled tube-in-tube heat exchanger were investigated considering the nanoparticle volume concentrations between 0 and 2.0 vol.%. The mass flow rate of the nanofluid from the inner tube was kept and the mass flow rate of the water from the annulus was set at either half, full, or double the value. The present contribution is a companion paper of Huminic and Huminic [1]. The numerical results reveal that the use of nanofluids in a helically coiled tube-in-tube heat exchanger improves the heat transfer performances. Thus, the maximum effectiveness was 91% for 2% CuO nanoparticles and 80% for 2% TiO 2 nanoparticles. Also, the increase of nanoparticles volume concentration leads to the Nusselt number increase and the reduction of the entropy generation due heat transfer effects, the viscous effects to entropy generation being negligible. [ABSTRACT FROM AUTHOR]

• The effect of pulsating flow on heat transfer efficiency of ice slurry is studied. • The cycle-averaged heat transfer coefficient can be increased by 34%. • Heat transfer is more efficient for large particles and high ice volume fraction. • The prediction correlation for the time-averaged nusselt number is proposed. In this paper, the heat transfer enhancement of ice slurry in a horizontal pipe with constant heat flux has been investigated numerically. The model is validated with the experimental results from the literature. Then the axial distribution of the heat transfer coefficient, the bulk and wall temperature and the ice volume fraction are obtained. The factors that affect the heat transfer coefficient are analyzed. Furthermore, the heat transfer efficiency of ice slurry in pulsating flow is compared with that in steady state. It is found that the heat transfer efficiency of ice slurry can be significantly improved by pulsating flow. The maximum increment of cycle-averaged heat transfer coefficient reaches 34.32%. Moreover, the degrees of heat transfer enhancement increase with increasing pulsating frequency, relative amplitude of velocity, ice particle diameter and ice volume fraction, and decrease with increasing cycle-averaged velocity. And the heat transfer is more efficient to ice slurry with large particles and ice volume fraction under the pulsating flow conditions. The pulsating frequency is suggested to be not more than 10π Hz. Finally, the correlation for predicting cycle-averaged Nusselt number of ice slurry in pulsating flow is established, and obtaining the reasonably good prediction results. [ABSTRACT FROM AUTHOR]

• A cross-corrugated triangular flow channel with trapezoidal baffles is proposed. • The flow and heat transfer characteristics of the proposed flow channel are studied. • The heat transfer in the flow channel is analyzed using the field synergy principle. Heat recovery ventilator (HRV) with cross-corrugated triangular flow channels has the advantages of high heat transfer coefficient and high mechanical strength, but it also has the disadvantages of uneven internal temperature distribution and large pressure loss. In this paper, a kind of cross-corrugated triangular flow channel with trapezoidal baffle is proposed, and the influence of the trapezoidal baffle on the flow and heat transfer characteristics of the cross-corrugated triangular flow channel is comprehensively studied by numerical simulation. The Nusselt number (Nu), friction factor (f) and Performance Evaluation Criteria (PEC) value of the flow channel with trapezoidal baffles and the original flow channel were compared. The synergistic effect of the trapezoidal baffle on the flow and heat transfer in the flow channel was analyzed. The results show that the trapezoidal baffle can promote fluid mixing and momentum exchange, thus enhancing the field synergistic effect and improving the comprehensive heat transfer performance of the flow channel. The Nu and f of flow channels with trapezoidal baffles are more than 1.7 and 3.5 times of those without baffles, and the PEC value can be increased by 30%. The data and empirical formulas of this study can provide a guideline for HRVs design. [ABSTRACT FROM AUTHOR]

Abstract: Heat transfer coefficients for thermal design of heat exchangers are taken from equations in laminar or turbulent flow. The equations used to calculate the Nusselt numbers in tubes do not agree in the transition region between laminar and turbulent flow. There is a gap at Re=2300. A linear interpolation between the Nusselt numbers at Re=2300 and Re=4000, each resulting from well-known equations is presented. The linear interpolation is based on the results of a paper published recently. New experimental findings about the Nusselt numbers in tubes at turbulent flow again confirm the respective equation. [Copyright &y& Elsevier]

• Lattice Boltzmann simulations have been conducted to study the heat transfer in particle-fluid beds. • The effects of flow condition, material properties and bed structure on the heat transfer are quantified. • The underliying mechanisms are analysed in terms of spatial and statitiscal distributions of relevant transport properties. • New correlation is formulated to describe, more accurately and generally, the heat transfer in particle-fluid beds. Non-isothermal fluid flows through packed beds are common in many industries. Such a system is very complicated because heat transfer is associated with the interaction between fluid and particles. Our current understanding of the phenomenon is still limited. For example, the effect of the Prandtl number on thermal flow and the significant inconsistency between experimental data and predictions at a low Peclet number remain unclear. To overcome these problems, this paper presents a comprehensive study of this system on a sub-particle scale. This is done by conducting about five hundred Lattice Boltzmann simulations under different conditions, covering a wide range of Reynolds number (Re), Prandtl number (Pr), and bed porosity (ε). The results show that the effects of Re, Pr , and ε on the thermal behavior of fluid flows are strong, varying significantly with the flow condition and fluid/bed properties. Based on the simulation data, a new correlation to calculate the heat transfer coefficient is established and validated against the experimental data in the literature. This correlation is more accurate and general than those reported in the past and is recommended for simulations of non-isothermal fluid-particle flows in the future. [Display omitted] [ABSTRACT FROM AUTHOR]

Abstract: This paper presents a methodology for the estimation of temperature dependent heat transfer coefficient for a vertical rectangular fin by using the inverse heat transfer method with Liquid crystal thermography (LCT) data. Steady state, laminar natural convection experiments have been done on a vertical rectangular fin of size 150×250×4, (L × w × t, all dimensions are in mm). The variation of heat transfer coefficient is considered as a power law function of temperature excess (h = a o θ b ) and is derived from the basic Nusselt number equation used for laminar natural convection, Nu = aRa b . With this functional form, the one dimensional fin equation in finite difference form is repeatedly solved using the Gauss–Seidel iterative method. Treating this as a one parameter estimation in ‘a’ the sum of the squares of the difference between the simulated and Thermochromic Liquid Crystal (TLC) measured temperatures is minimized with the Golden section search algorithm to retrieve ‘a’. Estimate of ‘a’ and the accompanying uncertainties are first reported for synthetically generated temperature distribution for assumed values of ‘a’. The effect of noise on the estimate of ‘a’ is discussed. This is followed by retrievals with experimentally obtained TLC temperature distribution for a range of heat inputs to the fin base. The required temperature distributions for accomplishing the retrievals over the surface are obtained using calibrated R40C5W Thermochromic Liquid Crystal (TLC) sheets. As an additional proof of the accuracy of the method, the retrieved value of ‘a’ is used to simulate the temperature distribution in the fin which is then compared with the actual TLC measured temperature distribution. [Copyright &y& Elsevier]

Abstract: This paper presents an experimental study on the convective boiling heat transfer and the critical heat flux (CHF) of ethanol–water mixtures in a diverging microchannel with artificial cavities. The results show that the boiling heat transfer and the CHF are significantly influenced by the molar fraction (xm ) as well as the mass flux. For the single-phase convection region except for the region near the onset of nucleate boiling with temperature overshoot, the single-phase heat transfer coefficient is independent of the wall superheat and increases with a decrease in the molar fraction. After boiling incipience, the two-phase heat transfer coefficient is much higher than that of single-phase convection. The two-phase heat transfer coefficient shows a maximum in the region of bubbly-elongated slug flow and deceases with a further increase in the wall superheat until approaching a condition of CHF, indicating that the heat transfer is mainly dominated by convective boiling. A flow-pattern-based empirical correlation for the two-phase heat transfer coefficient of the flow boiling of ethanol–water mixtures is developed. The overall mean absolute error of the proposed correlation is 15.5%, and more than 82.5% of the experimental data were predicted within a ±25% error band. The CHF increases from xm =0–0.1, and then decreases rapidly from xm =0.1–1 at a given mass flux of 175kg/m2 s. The maximum CHF is reached at xm =0.1 due to the Marangoni effect, indicating that small additions of ethanol into water could significantly increase the CHF. On the other hand, the CHF increases with increasing the mass flux at a given molar fraction of 0.1. Moreover, the experimental CHF results are compared with existing CHF correlations of flow boiling of the mixtures in a microchannel. [Copyright &y& Elsevier]

Abstract: In this paper, heat transfer of single cylindrical particle affected by wall has been investigated numerically and experimentally for Reynolds number range 2000 to 6000. The heat transfer in two different orientations, axial and cross flow over the particle has been considered in simulation with MultiPhysics Software FEMLAB version 2.3. The heat and mass transfer analogy technique has been applied for validation of the simulation results. The coated particle with naphthalene was sublimated to obtain the corresponding Sherwood numbers. The results show that the CFD model can predict the particle-to-fluid heat transfer for two situations due to trivial error (an average error of 6%) compared to experimental values. Influence of wall on heat transfer of particle in seven different bed-to-cylinder diameter ratio (N=1.66, 2.65, 2.75, 5, 6.66, 12, and 18) have been discussed in different velocities. According to obtaining results, with increasing the bed-to-cylinder diameter ratio over the 12 wall have no significant consequence on Nusselt number. Due to this fact, a CFD based correlation has been proposed to consider the wall effects on particle-to-fluid Nusselt number with an average error of 2.19%. [Copyright &y& Elsevier]

Abstract: The numerical modeling of the conjugate heat transfer and fluid flow of Al2O3/water nanofluid through the microchannel heat sink is presented in the paper. The laminar flow regime was considered along with viscous dissipation effect. The microchannel heat sink with square microchannels and Dh =50μm is considered. The heat flux was fixed to q =35W/m2 with heating and cooling cases. The water based Al2O3 nanofluid was encountered with various volume concentrations of Al2O3 particles and three diameters of the particle dp =13, 28 and 47nm. The analysis is performed on the results obtained for the local heat transfer coefficients based on a fixed pumping power. The results reveal a different local heat transfer behavior compared to the analysis made on a basis of the constant Re. [Copyright &y& Elsevier]

Abstract: Twisted tape is a widely used technique for heat transfer enhancement. In the present paper, we proposed a center-cleared twisted tape aiming at acxhieving good thermohydraulic performance. A comparative study between this type and the short-width twisted tape was performed numerically in laminar tubular flows. The computation results demonstrated that the flow resistance can be reduced by both methods; however, the thermal behaviors are very different from each other. For tubes with short-width twisted tapes, the heat transfer and thermohydraulic performance are weakened by cutting off the tape edge. Contrarily, for tubes with center-cleared twisted tapes, the heat transfer can be even enhanced in the cases with a suitable central clearance ratio. The thermal performance factor of the tube with center-cleared twisted tape can be enhanced by 7–20% as compared with the tube with conventional twisted tape. All these demonstrated that the center-cleared twisted tape is a promising technique for laminar convective heat transfer enhancement. [Copyright &y& Elsevier]

Abstract: In this study, forced convection flows of nanofluids consisting of water with TiO2 and Al2O3 nanoparticles in a horizontal tube with constant wall temperature are investigated numerically. The horizontal test section is modeled and solved using a CFD program. Palm et al.''s correlations are used to determine the nanofluid properties. A single-phase model having two-dimensional equations is employed with either constant or temperature dependent properties to study the hydrodynamics and thermal behaviors of the nanofluid flow. The numerical investigation is performed for a constant particle size of Al2O3 as a case study after the validation of its model by means of the experimental data of Duangthongsuk and Wongwises with TiO2 nanoparticles. The velocity and temperature vectors are presented in the entrance and fully developed region. The variations of the fluid temperature, local heat transfer coefficient and pressure drop along tube length are shown in the paper. Effects of nanoparticles concentration and Reynolds number on the wall shear stress, Nusselt number, heat transfer coefficient and pressure drop are presented. Numerical results show the heat transfer enhancement due to presence of the nanoparticles in the fluid in accordance with the results of the experimental study used for the validation process of the numerical model. [Copyright &y& Elsevier]

Abstract: In this paper, we consider an inverse problem of heat equation with Robin boundary condition for identifying heat transfer coefficient. Combining the method of fundamental solutions with discrepancy principle for the choice of the locations for source points, we give a method for solving the reconstruction problem. Since the resultant matrix is severe ill-conditioning, Tikhonov regularization with L-curve method is employed. Some numerical examples are given for verifying the efficiency and accuracy of the presented method. [Copyright &y& Elsevier]

Abstract: This paper presents new experimental flow boiling heat transfer results in micro-scale tubes. The experimental data were obtained in a horizontal 2.3mm I.D. stainless steel tube with heating length of 464mm, R134a and R245fa as working fluids, mass velocities ranging from 50 to 700kgm−2 s−1, heat flux from 5 to 55kWm−2, exit saturation temperatures of 22, 31 and 41°C, and vapor qualities ranging from 0.05 to 0.99. Flow pattern characterization was also performed from images obtained by high-speed filming. Heat transfer coefficient results from 1 to 14kWm−2 K−1 were measured. It was found that the heat transfer coefficient is a strong function of heat flux, mass velocity and vapor quality. The experimental data were compared against ten flow boiling predictive methods from the literature. Liu and Winterton , Zhang et al. and Saitoh et al. worked best for both fluids, capturing most of the experimental heat transfer trends. [Copyright &y& Elsevier]

Abstract: This paper presents the heat transfer coefficients and the pressure drop measured during HFC refrigerants 236fa, 134a and 410A saturated vapour condensation inside a brazed plate heat exchanger: the effects of saturation temperature (pressure), refrigerant mass flux and fluid properties are investigated. The heat transfer coefficients show weak sensitivity to saturation temperature (pressure) and great sensitivity to refrigerant mass flux and fluid properties. A transition point between gravity controlled and forced convection condensation has been found for a refrigerant mass flux around 20kg/m2s that corresponds to an equivalent Reynolds number around 1600–1700. At low refrigerant mass flux (G r <20kg/m2s) the heat transfer coefficients are not dependent on mass flux and are well predicted by the Nusselt analysis for vertical surface: the condensation process is gravity controlled. For higher refrigerant mass flux (G r >20kg/m2s) the heat transfer coefficients depend on mass flux and are well predicted by Akers et al. equation: forced convection condensation occurs. In the forced convection condensation region the heat transfer coefficients show a 25–30% increase for a doubling of the refrigerant mass flux. The frictional pressure drop shows a linear dependence on the kinetic energy per unit volume of the refrigerant flow and therefore a quadratic dependence on mass flux. HFC-410A shows heat transfer coefficients similar to HFC-134a and 10% higher than HFC-236fa together with frictional pressure drops 40-50% lower than HFC-134a and 50–60% lower than HFC-236fa. [Copyright &y& Elsevier]

Abstract: This paper reports on the investigation of pool boiling heat transfer of γ-Al2O3/CMC non-Newtonian nanofluids. To prepare nanofluids, γ-Al2O3 nanoparticles were dispersed in CMC solution (carboxy methyl cellulose in water) using ultrasonic mixing and mechanical mixer. Different concentrations of CMC non-Newtonian fluids and γ-Al2O3/CMC non-Newtonian nanofluids were tested under nucleate pool boiling heat transfer conditions. Experiments were carried out at atmospheric pressure. Results show that the pool boiling heat transfer coefficient of CMC solutions is lower than water. The decrease in boiling heat transfer is more pronounced at higher CMC concentrations and, as a result, higher solution viscosity. Adding nanoparticles to CMC non-Newtonian solutions results in an improved boiling heat transfer performance. The enhancement in the boiling heat transfer coefficient increases with the nanoparticle concentration; at a concentration of 1.4wt.%, the boiling heat transfer coefficient increases by about 25% when compared to the base fluid. [Copyright &y& Elsevier]

Abstract: Carbon dioxide is gaining renewed interest as an environmentally safe refrigerant. In order to improve the energy efficiency of R744 systems, an accurate knowledge of heat transfer coefficients is fundamental. In this paper experimental heat transfer coefficients during flow boiling of R744 in a smooth, horizontal, circular, 6.00mm inner diameter tube are presented. We obtained 217 experimental points in 18 operating conditions commonly encountered in dry-expansion evaporators investigating the effect of the mass flux within the range from 200 to 349kg/m2 s, the saturation temperature within the range from −7.8 to 5.8°C, the heat flux within the range from 10.0 to 20.6kW/m2 and the vapor quality within the range from 0.02 to 0.98. An interpretation of the experimental trends based on the local circumferential distribution of heat transfer coefficients, the flow regimes and the thermophysical properties is proposed. Besides the measured data are compared with those predicted by the Cheng et al. [L. Cheng, G. Ribatski, J.R. Thome, New prediction methods for CO2 evaporation inside tubes: Part II – An updated general flow boiling heat transfer model based on flow patterns, International Journal of Heat and Mass Transfer 51 (2008) 125–135] and Yoon et al. [R. Yun, Y. Kim, M.S. Kim, Y. Choi, Boiling heat transfer and dryout phenomenon of CO2 in a horizontal smooth tube, International Journal of Heat and Mass Transfer 46 (2003) 2353–2361] correlations to determine the best predictive method for the tested operating conditions. [Copyright &y& Elsevier]

Abstract: The paper presents the results of experimental investigation of heat transfer and hydrodynamics during condensation of moving steam in a narrow channel of square cross-section 2mm×2mm. The channel had a serpentine shape, the channel length was 660mm. An experimental cell simulated conditions of heat transfer in the condenser of loop heat pipes. The steam velocity at the channel inlet ranged from 13 to 52m/s, the pressure was 1atm. The temperature of the cooling water varied from 70 to 95°C. The annular flow pattern was noted in the whole range of the regime parameters. There was a clear boundary between the condensation zone and the zone occupied by the condensed phase downstream. Temperature has measured along the channel, and the heat-transfer coefficients have been determined. The coefficient values varied from 10,000 to 55,000W/Km2 depending on the steam velocity at the channel inlet and the cooling temperature. The efficiency of the condenser – heat exchanger has been investigated. [Copyright &y& Elsevier]

Abstract: This paper presents the heat transfer coefficients and the pressure drop measured during HFC-410A condensation inside a commercial brazed plate heat exchanger: the effects of saturation temperature, refrigerant mass flux and vapour super-heating are investigated. The heat transfer coefficients show weak sensitivity to saturation temperature and great sensitivity to refrigerant mass flux and vapour super-heating. At low refrigerant mass flux (<20kg/m2 s) the saturated vapour condensation heat transfer coefficients are not dependent on mass flux and are well predicted by Nusselt [W. Nusselt, Die oberflachenkondensation des wasserdampfes, Energy 60 (1916) 541–546, 569–575] analysis for vertical surface: the condensation process is gravity controlled. For higher refrigerant mass flux (>20kg/m2s) the saturated vapour condensation heat transfer coefficients depend on mass flux and are well predicted by Akers et al. [W.W. Akers, H.A. Deans, O.K. Crosser, Condensing heat transfer within horizontal tubes, Chem. Eng. Prog. Symp. Series 55 (1959) 171–176] equation: forced convection condensation occurs. In the forced convection condensation region the heat transfer coefficients show a 30% increase for a doubling of the refrigerant mass flux. The condensation heat transfer coefficients of super-heated vapour are 8–10% higher than those of saturated vapour and are well predicted by Webb [R.L. Webb, Convective condensation of superheated vapor, ASME J. Heat Transfer 120 (1998) 418–421] model. A simple linear equation based on the kinetic energy per unit volume of the refrigerant flow is proposed for the computation of the frictional pressure drop. [Copyright &y& Elsevier]

Abstract: This paper presents experimental results on evaporation heat transfer for flow boiling of ammonia and of R134a in a chevron-pattern corrugated plate heat exchanger (PHE). The measurements enable the evaluation of a quasi-local heat transfer coefficient along the plate, which in turn allows discussing the two-phase distribution and the heat transfer mechanism during evaporation in a plate channel. The saturation temperature varied between for ammonia and for R134a. The heat transfer coefficient is discussed in relation to the vapor quality, mass flux, heat flux and the type of refrigerant. The secondary fluid is a water/ethylene glycol mixture flowing in counter flow or parallel flow arrangement within the PHE. It is shown that the parallel flow case yields better overall performance than the counterflow case, and that plates with low chevron angle corrugations increase the evaporation heat transfer. Comparison with the limited data available from the literature shows good agreement. The Danilova equation and the Steiner boiling correlation are adapted to PHEs and show the need for further theoretical development. [Copyright &y& Elsevier]

Abstract: The application of new standards of pollutant gas emission restrictions has forced the motor-car industry to improve their level of knowledge on heat transfers occurring between intermittent gas flows and exhaust system pipes. In this paper we present a study that we carried out in order to estimate the heat transfer coefficient in exhaust pipes. We developed an experimental device which re-creates engine working conditions. This experiment set up has been designed in order to check all assumptions of the theoretical model. Measurements are carried out with heat flux sensor, gas temperature probes and pressure sensor in the entrance zone of a cylindrical exhaust pipe. First results show that the heat transfer coefficient estimated in the case of an intermittent gas flow is higher than the one measured on a continuous flow with identical inlet conditions: same mass flow and inlet temperature. Measurements show that, for a given flow rate, the intensification of the heat transfer due to the flow intermittency corresponds to the eigen frequency of the exhaust pipe. [Copyright &y& Elsevier]

• Study the effect of condenser temperature on the performance of a wickless heat pipe. • Performance in microgravity declined as the condenser temperature decreased. • Temperature data was used to extract a heat transfer coefficient in the evaporator. • Nusselt number was found to scale with Marangoni number to the -1/3 power. • A single correlation using the Marangoni number collapsed all the experimental data. The Constrained Vapor Bubble (CVB), a simple, wickless, heat pipe design that depends on interfacial forces to drive corner flow in a square cuvette, was studied in the microgravity environment aboard the International Space Station (ISS). In this paper, we consider the effects of different condenser temperatures on the heat transfer and fluid flow behavior using pentane as the working fluid. As the condenser temperature was decreased, the performance of the system decreased. This performance decrease using the pure working fluid was opposite to the behavior observed when using a mixture of 94 vol% pentane and 6 vol% isohexane. The mechanism for the decline in performance as the condenser temperature was lowered was a stronger than expected increase in the apparent strength of Marangoni flows at the heater end of the system. A simple mathematical model was fit to the experimental data and used to extract an evaporator heat transfer coefficient for experiments where we held the condenser temperature constant while increasing the heater power and where we held the heater power constant while decreasing the condenser temperature. All the results could be collapsed onto a single Nusselt number vs. Marangoni number curve. In this formulation, the Nusselt number was found to decrease with increasing Marangoni number to the 1/3 power. [ABSTRACT FROM AUTHOR]

• Water pool boiling in high porosity aluminum foams is studied. • The 10 mm thick foams show the best performance. • The 40 PPI foam showed the highest heat transfer performance. • The developed ANN model showed excellent predicting capabilities. This paper shows the promising capabilities that the aluminum metal foams offer in enhancing the water pool boiling on flat surfaces. Different metal foam samples, with pore density ranging between 5 and 40 Pore Per Inch (PPI), with similar porosity values, around 0.92, and two different thickness values, 5 and 10 mm, were tested to investigate their pertinent pool boiling performance. The saturated boiling curves at atmospheric pressure were obtained. Furthermore, using a high speed camera, heat and fluid flow inside and above the porous layer were investigated. The results showed that boiling heat transfer can be greatly enhanced by the use of metal foams partly because of an earlier onset of the nucleate boiling. Moreover, over a wide range of operating conditions foams lead to remarkably higher heat transfer coefficients, compared with a smooth aluminum reference surface. For a more comprehensive understanding of the problem, we tried to correlate the existing data in the literature for different foam geometries and base materials. However, the existing correlations and independent test data in the literature do not agree well; not even within the same order of magnitude. Hence, in order to offer a generic solution, predictions based on the results of an artificial neural network (ANN) are sought. A large database, comprising 758 experimental data points available in the open literature, was collected and then used to develop, train and validate a model based on ANN to estimate the heat transfer performance of metal foams during water pool boiling. Our data show that the predicted Nusselt number is within 10% of the measured experimental data. Moreover, we demonstrate that the developed ANN tool can be successfully implemented to predict the intrinsic complexity of water pool boiling inside metal foams that in most cases cannot be articulated by merely relying on conventional semi-empirical methods. [ABSTRACT FROM AUTHOR]

Abstract: An experimental apparatus for evaluating carbon dioxide local heat transfer coefficients during flow boiling has been set up at University of Naples Federico II. In this paper, the local heat transfer coefficient measured is evaluated relative to the measurement error, varying the type and costs of the instrumentation. The analytical analysis has been performed prior to construction of the test facility. The main aim of the work is to provide a methodology that allows one to reach the best compromise between measurement accuracy and financial resources in the selection of the instrumentation. [Copyright &y& Elsevier]

Abstract: This paper presented the characteristic of liquid desiccant dehumidification based on NTU–Le model. The results showed that the Lewis number Le had little effect on air outlet humidity ratio during desiccant solution dehumidification process. A new method called h D–Le separative evaluation method was developed for determining coupled heat and mass transfer coefficients between air and liquid desiccant, through which the heat and mass transfer coefficients between air and liquid desiccant were calculated to obtain from experimental inlet and outlet parameters of air and desiccant solution. The effects of the air volume flow rate, temperature, humidity ratio and the solution concentration, temperature on the Lewis number, heat and mass transfer coefficient were analyzed according to experimental data and the h D–Le separative evaluation method. Based on the computation results, it was concluded that the Lewis number greatly depended on the operation parameters and conditions of the air and desiccant. In addition, the correlations of the heat and mass transfer coefficients were developed. The additional 74 groups of experiments validated the developed correlations by comparison of air/solution parameters change with the calculation data. [Copyright &y& Elsevier]

Abstract: Two- and three-dimensional CFD modeling of heat transfer from discrete circular cylindrical particles in four different situations including A) infinite cylinder in cross-flow, B) cross-flow on finite cylinder with different aspect ratio in a rectangular duct, C) axial-flow on finite cylinder and D) axial-flow on finite cylinder with upstream turbulence have been investigated with the commercial CFD software, FEMLAB. The results were validated using experimental data from different research papers and also experimental correlations and show good quantitative and qualitative agreement with each other. In case B, a correction term has been proposed from CFD work which is applied to an experimental correlation to consider the aspect ratio influence on predicting the Nusselt number with an average error of 3.7%. [Copyright &y& Elsevier]

Abstract: In this paper, the thermal characteristics of suspended platinum (Pt) nanofilm sensors have been investigated experimentally. The Pt nanofilm sensors with the thickness of 28–40nm, the width of 260–601nm, and the length of 5.3–5.7μm were fabricated by electron beam lithography, electron beam physical vapor deposition and isotropic/anisotropic etching processes. Based on the one-dimensional heat conduction model, the in-plane thermal conductivity of the nanofilm sensors was obtained from the linear relation of the volume-averaged temperature increase and the heating rate measured in vacuum. Furthermore, natural convection heat transfer coefficients of air around the suspended nanofilm sensors at the pressures ranging from 1×10−2 Pa to 1atm were also investigated. The experimental results show that the in-plane thermal conductivities of the nanofilm sensors are much lower than those of the bulk values, the natural convection heat transfer coefficients are, however, very high at the atmospheric pressure. [Copyright &y& Elsevier]

Abstract: In this paper a computational approach is employed to derive a dimensionless heat transfer correlation for forced convection over a sphere. This correlation is applicable to fluids with a wide range of Prandtl numbers. The lower end of this range includes the Prandtl number for liquid sodium (Pr ≈0.003), whereas the upper end includes the Prandtl number for water (Pr ≈10).The model predictions derived from this research were validated extensively. First, the model was tested in two liquid metals, and subsequently it was compared with existing experimental data involving water. Both verification procedures have shown very good agreement between experimental results and model predictions. Multiple regression was employed to derive the above mentioned correlation. A detailed description of various steps used is described here. [Copyright &y& Elsevier]

In this paper, heat transfer performance was experimentally tested in a helically coiled pipe using three types of nanofluids, TiO 2 , ZnO and Ag water-based nanofluids. TiO 2 , ZnO and Ag nanoparticles were characterized by X -ray powder diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscope (TEM). The XRD results showed that the purity of ZnO and TiO 2 were obtained. TEM and SEM results showed that the mean particles size of TiO 2 , ZnO and Ag are 14, 20 and 16 nm respectively. The three types of nanofluids, TiO 2 /water, ZnO /water and Ag /water were prepared with a volume concentration of 0.25%. To ensure a good mixture and measure particles distribution in each nanofluid, Zetsizer test was performed and showed a good distribution of nanoparticles in all tested nanofluids. The three different nanofluids have been thermally tested in helical coil with a flow rate from 1 to 3.5 L/s with different inlet temperatures in the range of 30 °C and 60 °C. The experimental results showed an enhancement in Nusselt number up to 27.31%, 16.03%, and 10.38% with augmentation in the heat transfer coefficient up to 32%, 21% and 16% utilizing TiO 2 , ZnO and Ag nanoparticles respectively. [ABSTRACT FROM AUTHOR]

The paper presents the specific wavy heat exchange surfaces in order to intensify convective heat transfer in the channel. The study is focused on the analysis of local and average heat transfer coefficients and Nusselt numbers by experimental method of the holographic interferometry and numerical simulations. The results are presented for temperatures of the heat exchange surfaces T s = 318.15 K, 328.15 K, 338.15 K, and 348.15 K, Reynolds numbers Re = 1386–4203, and height between the surfaces H = 30, 35, 40, 45, and 50 mm. New correlating equations for average Nusselt number for the in-line and the offset wavy channels are determined. The total heat transfer and pressure drop j / f and thermal performance η are calculated for the wavy channels compared with the smooth one. It is observed that the offset wavy channel achieves a higher j / f values compared with the in-line wavy channel for all H and T s values. The thermal performance η increases with Re and decreases with height H. The offset wavy channel achieves higher thermal performance η by 5.7%–15.7% when changing Re and H compared with the in-line one. [ABSTRACT FROM AUTHOR]

• Obtain exact solutions for fluid and solid temperatures and Nu number under LTNE model together with different thermal interface conditions and no-slip interface condition. • Show the effect of stress jump at the interface on heat transfer under different thermal interface conditions. • Compare temperature fields and Nu numbers under three thermal interface conditions. This paper analytically investigates a fully developed forced convection in a channel partially filled with two porous layers symmetrically arranged at inner walls. The local thermal non-equilibrium (LTNE) model and Brinkman-extended Darcy model are employed as energy and momentum equations respectively in porous region. Three thermal boundary conditions (models A, B and C) and no-slip condition are adopted at porous-fluid interface. Explicit expressions of solid and fluid temperatures and Nusselt number are derived under each thermal boundary condition and variances between the three thermal boundary conditions in predicting thermal behaviors are discussed. It is shown that with present parameters, the temperature bifurcation phenomenon occurs in most cases under model B, while this phenomenon cannot be observed under models A and C. The LTNE model holds in almost any conditions under model B, but under models A and C the LTNE model holds with a low hollow ratio (S) and Biot number (Bi), a large effective thermal conductivity ratio (K) and Darcy number (Da). The increase of interfacial convective heat transfer coefficient (H s) makes the Nusselt number (Nu) of model C more close to but not exceed the Nu of model A, while the Nu under model B is lower than which under models A and C. By using different thermal boundary conditions, the stress jump coefficient (β) effect on heat transfer can be ignored, and with a high Da , a low β and S the Nu number predicted by stress jump interface condition has slight difference from that by stress continuity interface condition. [ABSTRACT FROM AUTHOR]

In this paper, 3D analysis of forced convection of Newtonian and non-Newtonian nanofluids through a horizontal pipe using single- and two-phase mathematical models is performed. The models include the Newtonian single-phase model, non-Newtonian single-phase model, Newtonian two-phase mixture model and finally non-Newtonian two-phase mixture model. The geometry of the problem is a horizontal pipe that is filled with Al 2 O 3 /water nanofluid. The effects of particle volume fraction and the Reynolds number on the heat transfer and hydrodynamic characteristics of the flow are examined. Results indicate that for the volume fraction of 0.01, the non-Newtonian mixture model gives more accurate results in comparison with the other models. By increasing the solid volume fraction, the mixture models give a higher heat transfer coefficient in comparison with that of the corresponding single-phase model; however, by comparing the results of Newtonian and the corresponding non-Newtonian models, no meaningful relationship can be obtained. Furthermore, for all the investigated models, the Nusselt number is increased with increasing the Reynolds number. [ABSTRACT FROM AUTHOR]

In this paper, an industrial-scale experiment with ten testing heat exchangers is conducted to study the influences of structures and working conditions on the tube-side heat transfer and flow characteristics of spiral-wound heat exchangers. The experimental results show that, with the increase of the winding angle, the tube-side heat transfer coefficients increase because of the enhanced secondary flow and slightly larger velocity. The compactness of the whole heat exchanger changes with the variations of the layer and tube pitch. When layer pitch and tube pitch decrease, the flow channel in the shell side is narrowed down, which makes the overall heat transfer temperature difference decrease and finally results in deterioration of the heat transfer in the tube side. For the friction factors, they decrease when the winding angle decreases due to the different turbulence status and velocities in the tube. As a parameter of working condition, the tube-side inlet temperature has a slightly negative effect on the heat transfer. Based on the experimental data, the correlations of Nusselt number and friction factor are developed. Comparing the experimental data and the correlations, the average errors of the Nusselt number and friction factor are 8.04% and 6.28%, respectively. [ABSTRACT FROM AUTHOR]