Effect of pulse frequency on heat transfer at the stagnation point of an impinging turbulent jet

Heat transfer in an impact pulsed air jet is numerically studied using the Reynolds stress model. It is shown that both enhancement and suppression in the heat transfer are possible in an impinging pulsed jet as compared with a steady flow. The heat transfer intensifies with the pulse frequency at a stagnation point in the region of small distances between a pipe exit cross section and an obstacle (H/D ≥ 6), while an increase in the pulse frequency causes a decrease in the heat transfer for H/D > 8. An increase in the Reynolds number causes a deintensification of the heat transfer, and the data for all frequencies approach the single-phase flow mode. A comparison with available data by other authors is made, and satisfactory agreement is obtained with respect to the pulse frequency effect on the heat transfer between a gas jet and the impact surface.     

脉动冲击射流的传热特性研究

为了深入理解脉动冲击射流的传热传质特性,研究脉动流的温度相关热物理性质对于靶面局部努塞尔数分布的影响,分别对正弦和方波非稳态脉动冲击射流进行了数值模拟.结果显示单个正弦脉冲的强化传热并不明显,而方波脉冲的强化传热效果却十分明显.对于脉动冲击射流中的流场分析表明,靶面上的瞬态换热效率与非线性热力学和水力学边界层随时间的发展密切相关.     

射流冲击凸台时传热与流动的数值模拟研究

针对冲击射流应用中经常会遇到不平整表面的情况(如各种电子元件),采用RNG的κ-ε模型,对处在半封闭板内凸台的冲击传热和流动进行了数值模拟.研究了冲击凸台表面、侧面及平板上的传热特性,分析了冲击高度H/D、流动Re数等参数对传热和流动的影响.结果表明,冲击高度较小时凸台上表面的传热Nu数沿径向的分布有一个先抑后扬的特征,在凸台边缘处达到最大.数值模拟还较好地给出了射流冲击凸台后流体分离、再次冲击平板等复杂的流动特征.     

旋转射流冲击凸台换热特性的数值模拟

运用重整化(RNG)的κ-ε模型对半封闭板内带旋流的射流冲击凸台的传热及流动进行仿真,研究了旋转射流冲击凸台时的流场特性以及凸台表面、侧壁和平板上的传热特性.分析了旋流强度(旋转数)、流动Re数、冲击高度H/D对传热与流动的影响.结果表明,不同Re数下旋流会削弱驻点处的冲击作用,从而使得驻点处的传热Nu数减小.在雷诺数Re=25 000时,在旋转数0相似文献   

突扩膨胀射流冲击换热与流动的数值模拟

采用大涡模拟模型对突扩膨胀射流冲击平板的传热特性及喷嘴内部流场进行数值模拟,得到不同进口Re数,不同膨胀比情况下喷嘴内部流场和射流冲击平板时的换热效果,分析了不同进口Re数、膨胀比E、冲击高度H/d对换热和流动的影响.研究表明,与直喷嘴进行对比,由于膨胀喷嘴射流与周围介质的掺混、渗透作用使射流的流速大大降低,最大速度偏离几何中心,使得换热效果减弱,对加热平板的冷却具有不对称性,但使得整个换热板的平均冷却效果更加均匀.     

Radiation heat transfer in an air plasma

Integrated radiation characteristics with respect to the spectrum are described for the rapid analysis of heat transfer in systems containing hot air with variable temperature and pressure fields.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 47, No. 2, pp. 294–300, August, 1984.     

Effect of the nonisothermicity of the wall on heat transfer in jet wetting

A method for solving a conjugate periodic convective-conductive problem for a "heat-transfer agent-wall" developed earlier system is used for calculation of the effect of the wall parameters on heat transfer under conditions of jet wetting.     

Confined jet impingement of liquid nitrogen onto different heat transfer surfaces

Jet impingement of liquid nitrogen owns many applications in the cryogenic cooling aspects, such as, cooling of high-power chips in the electronic devices and cryoprobes in the cryosurgery. In the present study, we systematically investigated the confined jet impingement of liquid nitrogen from a tube of about 2.0 mm in diameter onto the heat transfer surfaces of about 5.0 mm in basement diameter with different heat transfer surface geometries and conditions, i.e., flat surface, hemispherical surface and flat surface with a needle. The effects of many influential factors, such as, the geometry of the heat transfer surface, jet velocity, distance between the nozzle exit and heat transfer surface, heat transfer surface condition, and some other, on the heat transfer were investigated. The heat transfer correlations were also proposed by using the experimental data, and it was found that the heat transfer mechanism of liquid impingement in the confined space was dominated by the convective evaporation rather than the nucleate boiling in the present case. The critical heat flux (CHF) of the confined jet impingement was measured and the visualization of the corresponding flow patterns of the confined jet impingement of liquid nitrogen was also conducted simultaneously to understand the heat transfer phenomena.     

Convective heat transfer enhancement produced by secondary heat sources in a liquid nitrogen pool

This paper studies the influence of secondary heat sources on the convective heat transfer from a vertical cylindrical heater immersed in a LIN pool. Two types of secondary heat source have been used. In the first case, the heat leak through the vessel walls into the pool was varied without causing nucleation, so as to retain convective heat transfer. It was found that the convective flow loops induced in the pool produced a small enhancement of the heat transfer from the cylindrical heater. In the second case, a small horizontal heater loop was introduced into the pool below the cylindrical heater. The secondary heat flux used was such that boiling occurred at the loop to give rising bubbles surrounding the cylindrical heater. This produced a large enhancement of the convective heat transfer from the cylindrical heater. The enhancement ratio is presented as a function of the power supplied to the loop heater.     

Effect of corona discharge on heat transfer in natural air convection

Results are presented of an experimental and theoretical investigation of the effect of a corona discharge on heat transfer from a thin wire under natural air convection conditions.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 15, No. 5, pp. 922–930, November, 1968.     

Effect of mass transfer on heat transfer in liquid evaporation from a free surface in an evacuated gaseous medium

Evaporation of a liquid from a free surface is considered for pressures in the surrounding medium of 1.33 · 10³ and 2.67 · 10³ N/m². On the basis of an experimental study, a mechanism was established for the effect of mass transfer on heat transfer during evaporation under conditions of free convection.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 20, No. 3, pp. 405–410, March, 1971.     

Flow and heat transfer in coaxial jet flow around an obstacle

Results are presented of an experimental investigation of the gasdynamics and heat transfer in the reverse flow zone near an obstacle during coaxial jet flow on it along the normal.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 38, No. 1, pp. 38–43, January, 1960.     

Investigating corrosion effects and heat transfer enhancement in smaller size radiators using CNT-nanofluids

Nanofluids have been extensively studied in the past to enhance the heat transfer performance and efficiency of systems. However, corrosion effects have been paid very little attention and thus this work presents an experimental study on the effect of carbon nanotubes (CNT) on corrosion of three different metals under study such as aluminium alloy, stainless steel and copper, respectively. The work was further extended to study the heat transfer performance in a car radiator of two different sizes. Both the studies were performed using four different fluids such as water, ethylene glycol, 0.02 % CNT-nanofluid and 0.1 % CNT-nanofluid, respectively. It was observed that among the three metals, the highest rate of corrosion occurs to aluminium, followed by stainless steel and copper, irrespective of the fluid used. The rate of corrosion increased with the increase in temperature (27–90 °C) in all cases. The experimental results showed that the stable CNT-nanofluids prepared in this work showed better heat transfer performance in both engines. Moreover, the smaller radiator using the CNT-nanofluids depicted enhanced heat transfer rates compared to the standard radiator using water and ethylene glycol.     

Influence of stream vorticity on friction and heat exchange in application to the case of a supersonic jet impinging on an obstacle

The flow in the neighborhood of the stagnation point of a stationary plane stream of viscous incompressible fluid with harmonic components superposed on the velocity components is investigated. Such a flow corresponds to a stream containing periodic eddies perpendicular to the flow plane. The results of the investigation can be applied to estimate thermal fluxes.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 17, No. 4, pp. 633–638, October 1969.     

不同空气侧风速下微通道蒸发器换热特性实验研究

搭建微通道蒸发器性能实验台,采用控制变量法研究不同空气侧风速下微通道蒸发器表面温度分布、制冷剂进出口压力的变化规律,计算换热量和换热系数,从而分析空气侧风速对微通道蒸发器的流量分配特性和换热效果的影响。结果表明,随着风速增大,微通道蒸发器制冷剂流量分配不均匀性增大,进出口压力波动振幅和周期增加,压降增大,风速2 m/s时微通道蒸发器换热效果最佳。     

Hydrodynamic structure and heat transfer in the initial region of an argon plasma jet

The relationship between the hydrodynamic structure of a turbulent argon plasma jet and the intensity of heat transfer between the flow and the wall normal to it is analyzed.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 33, No. 4, pp. 648–655, October, 1977.     

Investigation of the hydrodynamic conditions of jet heat transfer

An impact jet model that can be used to explain the regularities of heat transfer is proposed.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 33, No. 2, pp. 210–212, August, 1977.     

Unsteady-state heat transfer in the region of interaction between a turbulent jet and an obstacle

Unsteady-state heat transfer is considered in the region of interaction between a round turbulent jet and a normally positioned flat obstacle. The Navier-Stokes equations filtered over space are closed by the RNG-model of eddy viscosity which takes into account the curvature of the lines of flow in the region of turning of flow. The calculations are performed for different relative distances from the nozzle exit section to the obstacle and for different values of Reynolds number. The correlation between the distribution of characteristics of heat transfer over the obstacle surface and the eddy structure of the jet is discussed.