Papers by Keyword: Enhanced Heat Transfer

Abstract: This paper presents a numerical study on the passive cooling of an electronic component inside a rectangular enclosure filled with phase change material (PCM). The electronic component is centrally located on a substrate and generates volumetric heat. The study utilizes the enthalpy-porosity approach and the thermal equilibrium model. Its goal is to enhance the performance of the PCM by incorporating metal foam and nanoparticles. The investigation examines the impact of varying metal foam porosity while keeping the nanoparticle volume fraction constant. The results indicate that a lower porosity (0.85) significantly improves the thermal conductivity of the PCM by 3 times, which increases the cooling efficiency of the PCM-based heat sink. Meanwhile, nanoparticles have a negligible effect when metal foam is present.

Abstract: A two-phase mixture model is used to study natural convection in a square cavity filled with CuO+H₂O nanofluids, in the hypothesis of temperature-dependent physical properties, assuming that Brownian diffusion and thermophoresis are the primary slip mechanisms between solid and liquid phases. The cavity is heated at one side and cooled at the opposite side, whereas the horizontal walls are assumed either both adiabatic, or the bottom heated and the top cooled. A computational code based on the SIMPLE-C algorithm is used to solve the system of the mass, momentum and energy transfer governing equations. It is found that, owing to the effects of the slip motion occurring between solid and liquid phases, the rate of heat transferred across the cavity by the nanofluid in the heating-from-below configuration is remarkably higher than that transferred by the pure base liquid. Moreover, in this particular configuration the addition of nanoparticles to the base liquid generates periodicity in heat transfer. Additionally, the heat transfer enhancement is discovered to increase as the imposed temperature difference is increased, showing a smooth maximum at an optimal particle loading.

Abstract: In this paper, condensation mechanism of the Freon refrigerants outside spiral grooved tube is discussed. The heat transfer coefficient of Freon refrigerants condensation outside spiral grooved tube is obtained. A calculation example of heat transfer coefficient on the tube bundle of condenser with baffle bars is presented. It shows the excellent thermal performance of the spiral groove tubes compared to smooth tubes.

Abstract: Heat transfer and resistance characteristics of a tube inserted delta-winglet (inclination angle is 10 °) are studied by numerical simulation. The results show that the delta-winglet enhance the heat transfer of the enhancement tube inserted delta-winglet and improve the PEC with modest pressure drop penalties. Compared with based tubes, the delta-wings structure enhance the heat transfer 19.52%-31%.

Abstract: A new rectangular anti-icing structure with short pin fins is presented in this paper. Detailed experimental research is applied to discussing its heat transfer and enhancement characteristics. The results show that, heat transfer of this anti-icing structure enhances obviously, and the core factor for enhancement is the volume ratio occupied by pin fins in rectangular channel of anti-icing structure.

Abstract: This paper applies constructal design to obtain numerically the configuration that facilitates the access of the heat that flows through Y-shaped pathways of a high-conductivity material embedded within a square-shaped heat-generating medium of low-conductivity to cooling this finite-size volume. The objective is to minimize the maximal excess of temperature of the whole system, i.e., the hot spots, independent of where they are located. The total volume and the volume of the material of high thermal conductivity are fixed. Results show that there is no universal optimal geometry for the Y-shaped pathways for every value of high conductivity investigated here. For small values of high thermal conductivity material the best shape presented a well defined format of Y. However, for larger values of high thermal conductivity the best geometry tends to a V-shaped (i.e., the length of stem is suppressed and the bifurcated branches penetrates deeply the heat-generating body towards the superior corners). A comparison between the Y-shaped pathway configuration with a simpler I-shaped blade and with X-shaped configuration was also performed. For constant values of area fraction occupied with a high-conductivity material and the ratio between the high thermal conductivity material and low conductivity of the heat-generating body (φ = 0.1 and = 100) the Y-shaped pathways performed 46% and 13% better when compared to I-shaped and X-shaped pathway configuration, respectively. The best thermal performance is obtained when the highest temperatures (hot spots) are better distributed in the temperature field, i.e., according to the constructal principle of optimal distribution of imperfections.

Abstract: The array configuration of delta wing and elliptical cylinder vortex generator in the spiral surface channel was studied. By changing the assembly distance s, the triangle wing vortex generator angle of attack α, the elliptical cylinder vortex generator angle of attack β to research the heat transfer and resistance properties under different working conditions. The research model as follow: the heat-medium is water-vapor [H₂, the cold medium of flow is air, Steam temperature is 400K and air inlet temperature is 293K, the Reynolds number ranging from 4000 to 7000.The optimum structure was determined by using numerical simulation method and orthogonal experiment method. The result shows the optimization structure of the combination vortex generator: α=45°, β=45°, s=90mm. Compared with the normal structure, the heat transfer enhancement comprehensive effect of the optimization structure raised about 36.2%~47.6%.

Abstract: The effect of pulse flow on the performance of heat exchange tube with built-in spring was investigated using software FLUENT. The temperature field and pressure field under different pulse flow were obtained. Results presented that the average export pressure shows the same vibration period with that of pulse flow and the fluctuation amplitude increases with the increment of the frequency of pulse flow. Moreover, comparing with the case of steady flow, the thickness of velocity boundary layer decreases significantly and thus the heat transfer coefficient is enhanced greatly. Furthermore, the vibration amplitude of pulse flow has great effect on the heat transfer enhancement, while the frequency of pulse flow shows little influence on the heat transfer enhancement.

Abstract: At present, researchers pay close attention to heat transfer enhancement, and many new surface structures are developed. Two kinds of new condensation enhanced tubes with machined surface, namely NO.1 and NO.2, are put forward. The experimental results show that the enhanced tubes can improve condensation heat transfer evidently, which is due to the special internal and external surface structures. With water vapor as condensation medium, the enhancement ratios of total heat transfer coefficient (k) are 1.6-2.4 and 1.47-1.8 comparing with smooth tube, respectively, and the ratios of outside condensation heat transfer coefficient (ho) are 5.67-6.67 and 3-4 correspondingly. With alcohol vapor as condensation medium, the average enhancement ratios of k are 3 and 2 times as great as that of smooth tube, and the ratios of ho are 3-4.25 and 2.25-3.5 correspondingly.

Abstract: The pooling boiling plays an important role in the operation of the passive residual heat removal heat exchanger (PRHR HX). At present, smooth tubes are still widely used as boiling element in the PRHR HX; there is great extension to improve the security and miniaturize the size of PRHR HX if the smooth tubes were replaced by porous surface tubes. In this paper, the pool boiling heat transfer characteristics of porous surface tube was researched experimentally. The result shows that the porous surface tube can enhance the pooling boiling significantly: Compared with the smooth tube, the porous surface tube can greatly reduced the time before the water reached saturation; the wall superheat decreases about 1.5°C and the boiling heat transfer coefficient increases 68% to 75%. Besides, the enhanced mechanism of the porous surface tubes is also discussed in this paper.