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International journal of heat and mass transfer 122건

  1. [해외논문]   Editorial Board   SCI SCIE


    International journal of heat and mass transfer v.121 ,pp. ii - ii , 2018 , 0017-9310 ,

    초록

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  2. [해외논문]   Analytical modeling of oscillatory heat transfer in coated sorption beds   SCI SCIE

    Bahrehmand, Hesam (Corresponding author at: School of Mechatronic Systems Engineering, Simon Fraser University, 250-13450 102 Avenue, Surrey, BC V3T 0A3, Canada.) , Ahmadi, Mehran , Bahrami, Majid
    International journal of heat and mass transfer v.121 ,pp. 1 - 9 , 2018 , 0017-9310 ,

    초록

    Abstract A novel analytical model that considers the thermal contact resistance (TCR) at the interface between the sorbent layer and heat exchanger (HEX) is developed to investigate the oscillatory heat transfer and performance of coated sorption beds. The governing energy equation is solved using an orthogonal expansion technique and closed-form relationships are obtained to calculate the temperature distribution inside the sorbent coating and HEX. In addition, a new gravimetric large pressure jump (GLAP) test bed is designed to measure the uptake of sorption material. Novel graphite coated sorption beds were prepared and tested in the GLAP test bed. The model was successfully validated with the measurements performed in the GLAP test bed. It is found that specific cooling power (SCP) of a sorption cooling system (SCS) enhances by increasing the sorbent thermal diffusivity and decreasing the TCR. For example, SCP of the sorption cooling system (SCS) can be enhanced from 90 to 900 (W/kg) by increasing the sorbent thermal diffusivity from 2.5e−7 to 5.25e−6 (m 2 /s) and decreasing the TCR from 4 to 0.3 (K/W). Moreover, the results show that SCP increases by reducing the HEX to sorbent thickness ratio (HSTR). Therefore, the proposed graphite coated sorption beds with high thermal diffusivity and low thickness are suitable for sorption cooling applications. Highlights Analytical modeling of oscillatory heat transfer in sorber beds considering TCR. Closed-form relationships for temperature distribution in sorbent and HEX. Remarkable enhancement of SCP by improving α sorb and TCR. Improvement of SCP using graphite coated sorption beds. Graphical abstract [DISPLAY OMISSION]

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  3. [해외논문]   High anisotropy metamaterial heat spreader   SCI SCIE

    Hamed, Ahmed (Corresponding author.) , Ndao, Sidy
    International journal of heat and mass transfer v.121 ,pp. 10 - 14 , 2018 , 0017-9310 ,

    초록

    Abstract The ability to manipulate heat flow has numerous promising benefits in thermal energy applications such as in heat spreader design. This paper introduces a novel thermal functional metamaterials heat spreader with high anisotropy. The metamaterial heat spreader consists of alternating layers of copper/VHTC and PDMS thin films. The effects of the number of bilayers, bilayers’ thermal conductivity ratio, and thermal spreader thickness on the metamaterial lateral heat spreading have been investigated numerically. In comparison to a simple copper heat spreader, results show significant enhancements of the lateral heat spreading with both the copper and VHTC based metamaterial heat spreaders. Highlights We designed a novel metamaterial heat spreader with high anisotropy. The proposed spreader consists of alternating thin layers of copper/VHTC and PDMS. Higher thermal conductivity ratio of the bilayers’ materials leads to higher spreading. Increase in spreader thickness allows for more lateral heat spreading.

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  4. [해외논문]   Atomization and surface heat transfer characteristics of cryogen spray cooling with expansion-chambered nozzles   SCI SCIE

    Wang, Xin-Sheng (Corresponding author.) , Chen, Bin , Zhou, Zhi-Fu
    International journal of heat and mass transfer v.121 ,pp. 15 - 27 , 2018 , 0017-9310 ,

    초록

    Abstract Cryogen spray cooling (CSC) is commonly applied in laser dermatology to protect the epidermis from thermal damage. Many efforts have attempted to improve the cooling capacity of CSC, among which the use of expansion-chambered nozzles is an effectively simple method with considerable potential. This study examined the influences of the expansion-chambered nozzle structure, including the ratios of inlet nozzle diameter to discharge nozzle diameter and of chamber diameter to discharge nozzle diameter on R134a and R404A spray cooling. Fifteen transparent expansion-chambered nozzles with the expansion chamber aspect ratio of 1.0, chamber diameter to discharge nozzle diameter ratios of 5.0–10.0, and inlet nozzle diameter to discharge nozzle diameter ratios of 0.6–1.4 were tested. The internal flow pattern inside the expansion chamber, external spray pattern, and surface heat transfer characteristics of cryogen spray using different nozzles, including the straight-tube nozzle, were investigated. The structure of the expansion chamber was found to have an important effect on the spray patterns and cooling characteristics. The spray radius obviously decreased when the expansion-chambered nozzles were used, and the spray pattern became narrower as the ratio of chamber diameter to discharge nozzle diameter increased. By contrast, the increase in ratio of two nozzle diameters enlarged the spray radius. Surface temperature and heat flux with different nozzles and cryogens showed a similarity, and correlations of surface temperature and heat flux were proposed. The introduction of expansion-chambered nozzles could effectively improve the spray cooling capacity. The minimum average surface temperature during the fully developed spray period could be reached for both R134a spray and R404A spray by an expansion-chambered nozzle with a chamber diameter to discharge nozzle diameter ratio of roughly 5.0 and an inlet nozzle diameter to discharge nozzle diameter ratio of roughly 0.6. Highlights Nozzle structure has great impact on cryogen spray cooling characteristics. The introduction of expansion-chambered nozzles yields a small spray radius. The expansion-chambered nozzle can increase the spray cooling capacity. Dimensionless heat flux shows self-similarity for different nozzles. The optimized nozzle structure is recommended as d c / d e of 7.0 and d i / d e of 1.0.

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  5. [해외논문]   Heat transfer enhancement in suddenly expanding annular shear-thinning flows   SCI SCIE

    Hammad, Khaled J.
    International journal of heat and mass transfer v.121 ,pp. 28 - 36 , 2018 , 0017-9310 ,

    초록

    Abstract Heat transfer enhancement in suddenly expanding annular pipe flows of Newtonian and shear-thinning non-Newtonian fluids is studied within the steady laminar flow regime. Conservation of mass, momentum, and energy equations, along with the power-law constitutive model are numerically solved. The impact of inflow inertia, annular-diameter-ratio, k, power-law index, n, and Prandtl numbers, is reported over the following range of parameters: Re = {50, 100, 150}, k = {0, 0.5, 0.7}; n = {1, 0.8, 0.6}; and Pr = {1, 10, 100}. Heat transfer enhancement downstream of the expansion plane, i.e., Nusselt numbers greater than the downstream fully developed value, Nu / Nu fd > 1, is only observed for Pr = 10 and 100. In general, higher Prandtl numbers, power-law index values, and annular-diameter-ratios, result in more significant heat transfer enhancement downstream of the expansion plane. Heat transfer augmentation, for Pr = 10 and 100, increases with the annular-diameter-ratio. For a given annular-diameter-ratio and Reynolds numbers, increasing the Prandtl number from Pr = 10 to Pr = 100, always results in higher peak Nu values, Nu max , for both Newtonian and shear-thinning flows. All Nu max values are located downstream of the flow reattachment point, in the case of suddenly expanding round pipe flows, i.e., κ = 0. However, for suddenly expanding annular pipe flows, i.e., κ = 0.5 and 0.7, Nu max values appear upstream the flow reattachment point. For Pr = 10 and 100, shear-thinning flows display two local peak Nu / Nu fd values, in comparison with one peak value in the case of Newtonian flows. The highest heat transfer enhancement, Nu max / Nu fd ≈ 5, is observed at κ = 0.7, n = 0.6, and Pr = 100. Highlights Heat transfer enhancement in suddenly expanding annular shear-thinning flows is numerically studied. Heat transfer enhancement increases with Prandtl numbers, power-law index, and annular-diameter-ratio. Peak Nu values appear downstream the flow reattachment point, for suddenly expanding pipe flows. Peak Nu values are located upstream the flow reattachment point, for suddenly expanding annular flows. Annular shear-thinning flows display two peak Nu values, while Newtonian flows display one peak only.

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  6. [해외논문]   Nonlinear convection regimes in superposed fluid and porous layers under vertical vibrations: Positive porosity gradients   SCI SCIE

    Kolchanova, E.A. (Institute of Continuous Media Mechanics UB RAS, 1 Academ. Koroleva, Perm 614013, Russian Federation ) , Kolchanov, N.V. (Perm State University, 15 Bukireva, Perm 614990, Russian Federation)
    International journal of heat and mass transfer v.121 ,pp. 37 - 45 , 2018 , 0017-9310 ,

    초록

    Abstract We investigate the onset of average convection and its nonlinear regimes in a single-component fluid layer overlying a fluid-saturated porous layer. A heated from below cavity with a superposed fluid and a porous medium undergoes high-frequency and small-amplitude vertical vibrations in the gravitational field. Porosity of the medium decreases linearly with depth at a positive porosity gradient. Thermal vibrational convection equations are obtained by the averaging method and solved numerically. The shooting method, Galerkin method and finite-difference method are applied. It is shown that for small vibration accelerations, a convective flow is generated as short-wave rolls in the fluid layer overlying a porous medium. The heat flux undergoes abrupt changes as the supercriticality increases. It is due to the fluid flow penetrating into pores. A magnitude of the jump grows with the growth of vibration intensity. For sufficiently large vibration accelerations, the average convection is excited in the form of long-wave rolls that penetrate both layers. Here, the Nusselt number is 2–3 times higher than its value in the static gravity field. Highlights Studying the vibration effect on nonlinear convection in fluid and porous layers. Porosity decreases with depth for glass spheres partially filling a water layer. For small vibration accelerations, short-wave convection occurs in the fluid layer. Heat flux undergoes jump changes with the growth of supercriticality. For intensive vibration, heat flux enhances due to flow penetration into the pores.

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  7. [해외논문]   Saturated pool boiling enhancement using porous lattice structures produced by Selective Laser Melting   SCI SCIE

    Wong, K.K. (Corresponding author.) , Leong, K.C.
    International journal of heat and mass transfer v.121 ,pp. 46 - 63 , 2018 , 0017-9310 ,

    초록

    Abstract Pool boiling heat transfer of saturated FC-72 under atmospheric pressure was studied for porous lattice structures fabricated using the Selective Laser Melting (SLM) technique. The substrates possess repeating geometry of octet-truss unit cell and were varied with unit cell sizes of 2.0 mm, 3.0 mm and 5.0 mm and structure heights of 2.5 mm, 5.0 mm and 10.0 mm. In comparison with a plain surface, the porous structures show significant enhancement in nucleate boiling heat transfer coefficients and delay of Critical Heat Flux (CHF). The enhancement is attributed to the increased surface area, increased nucleation site density and capillary-assisted suction of the porous structure. The porous structure allows sustained liquid replenishment which delayed the hydrodynamic choking and CHF significantly. The best performing substrate with the 3-mm unit cell size and 5-mm structure height has an average nucleate boiling heat transfer coefficient of 1.35 W/cm 2 ·K, which is 2.81 times that of the plain surface at 0.48 W/cm 2 ·K. Heat transfer mechanisms are proposed for the different heat flux levels of the porous structures based on visual observations. The boiling patterns are classified as low, mid, high and very-high heat flux levels. At high heat flux level, two separate modes of stable and unstable boiling patterns are observed. For the stable boiling pattern, there are distinct bubble departure and liquid replenishment pathways, thus allowing a good convection flow. However, for the unstable boiling pattern, there is major liquid–vapor counter-flow, which disrupts the orderly liquid replenishment pathway. Highlights Pool boiling of porous substrates of different unit cell sizes and heights were investigated. The substrates were fabricated using Selective Laser Melting technique. Heat transfer coefficient enhancement of up to 2.81 times was achieved. Porous substrates allowed sustained liquid replenishment and delayed CHF significantly. Heat transfer mechanisms were proposed for different boiling regimes.

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  8. [해외논문]   Regulating solar absorptance for remedying thermal asymmetry of a roadway embankment   SCI SCIE

    Zhang, Xingui (Corresponding author at: College of Civil Engineering and Architecture, Guangxi University, 100 University Road, Nanning, Guangxi 530004, China.) , Yan, Li-E , Qin, Yinghong
    International journal of heat and mass transfer v.121 ,pp. 64 - 71 , 2018 , 0017-9310 ,

    초록

    Abstract Roadways in permafrost regions are laid upon embankments because permafrost stratum is highly sensitive to the thermal disturbance at the ground surface. The south-facing slope of the embankment is exposed to longer insolation than the north-facing one annually, differing the solar absorption of the side slopes and thus developing differential settlement across the embankment. A simple, economical strategy is to reduce the solar absorptance of the southern side slope to a critical level such that the solar absorption of both slopes is equalized. However, it is unknown this critical absorptance of a specific embankment and it is also unknown if this critical absorptance can be achieved by using existing techniques. This study mimics the solar radiation falling on the side slopes of embankments with different configurations, and subsequently it estimates the solar absorption of the side slopes. We found that in sunny weather when the thermal asymmetry of an embankment is maximum, reducing the southern side-slope absorptance from 0.80 to 0.40 can eliminate the thermal asymmetry. By analyzing the solar absorptance of a rough surface such as a crushed-rock layer, we can ascertain that this critical absorptance can be achieved by coating the side slope with nonwhite high-reflective pigment. Highlights We simulate solar absorption at side slopes of an embankment with different configuration. Thermal asymmetry of an embankment can be remedied by regulating the side slope absorptance. It is possible to reduce a crushed rock layer absorptance to 0.40 and even lower.

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  9. [해외논문]   Transient and steady state heat transport in layered materials from molecular dynamics simulation   SCI SCIE

    Liu, Chenhan (Corresponding author.) , Chen, Weiyu , Tao, Yi , Yang, Juekuan , Chen, Yunfei
    International journal of heat and mass transfer v.121 ,pp. 72 - 78 , 2018 , 0017-9310 ,

    초록

    Abstract In this paper, both transient and steady state heat transfer in graphite are investigated with molecular dynamics (MD) simulations. The simulation results demonstrate that elastic anisotropy controls heat transfer in the transient state, which makes the outermost isothermal surface of temperature distribution similar to the phonon group velocity surface that has a shape of very flat ellipse in layered materials. In steady state, with the help of phonons engaging in sufficient scattering, the basal plane phonon modes determine the thermal conductivity along all directions except those very close to the cross plane. Our simulation results confirm that the classical theoretical model can accurately predict the thermal conductivity along arbitrary directions in layered materials. Highlights The thermal conductivity of layered materials along arbitrary direction is first time obtained by molecular dynamics simulation. In transient state only elastic anisotropy controls the heat transfer, while in steady state both elastic anisotropy and phonon scattering control the heat transfer. In steady state, with the help of phonons engaging in enough scattering, the basal plane phonon modes of layered materials determine the thermal conductivities along all directions except ones very close to the cross plane.

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  10. [해외논문]   The influence of interface contaminated degree on the wake characteristics of a spherical bubble at moderate Reynolds number under the condition of isothermal flow   SCI SCIE

    Fei, Yang (Corresponding author at: School of Mechanical Engineering, Changzhou University, Changzhou 213164, China.) , Pang, Mingjun
    International journal of heat and mass transfer v.121 ,pp. 79 - 83 , 2018 , 0017-9310 ,

    초록

    Abstract The wake flow characteristics of a spherical bubble against the interface contaminated degree are deeply investigated at moderate Reynolds number ( Re = 25–200) based on the 3D rear stagnant cap model. The interface contaminated degree is controlled by changing the magnitude of the cap angle, for θ = 0&nda 0–180°. It is found that the vortex size does not change obviously when θ = 0&nda 0–67.5°; when θ > 67.5°, it decreases until it is equal to zero when θ > 135°. The variations of vortex size and separation angle are related to the deceleration of fluid near the lee face of the bubble. The vortexes display the 3D characteristic due to the skip of pressure coefficient component in the flow direction at the leading edge of the stagnant cap when θ = 45°, 45°, 67.5°, 112.5° and 135°. Highlights A 3D rear stagnant cap model for a contaminated bubble is used. The vortex characteristics against the interface contaminated degree are discussed. The physical explanations of vortex size and its separation angle are presented. The physical explanation of vortex 3D characteristic is presented.

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