Study on forced air convection cooling for electronic assemblies

The slotted fin concept was employed to improve the air cooling performance of plate-fin in heat sinks. Numerical simulations of laminar heat transfer and flow pressure drop were conducted for the integral plate fin, discrete plate fin and discrete slotted fin heat sinks. It is found that the performance of the discrete plate fin is better than that of the integral continuum plate fin and the performance of slotted fin is better than that of the discrete plate fin at the same pumping power of the fan. A new type of heat sink characterized by discrete and slotted fin surfaces with thinner fins and smaller spaces between fins is then proposed. Preliminary computation shows that this type of heat sink may be useful for the next generation of higher thermal load CPUs. The limit of cooling capacity for air-cooling techniques was also addressed. __________ Translated from Journal of Xi’an Jiaotong University, 2006, 40(11): 1241–1245 [译自: 西安交通大学学报]     

Development of new correlations for forced convection heat transfer during cooling of products

This paper presents the new, simple but powerful effective Nusselt–Reynolds correlations for estimating the effective convective heat transfer coefficients of spherical and cylindrical products cooled in water and air flows. In this respect, both experimental and theoretical works were obtained. In the experimental case, several spherical and cylindrical products, namely, tomatoes, pears and cucumbers were cooled in water and air flow and their centre temperature variations were measured. In the theoretical case, the effective convective heat transfer coefficients for the individual spherical and cylindrical products were determined using the centre temperature data in the present approach including Dincer's models. Therefore, the new Nusselt–Reynolds correlations were developed using the effective convective heat transfer coefficient values and a general diagram of Nu/Pr^1/3 against Reynolds number was drawn. This study indicates that the present effective Nu–Re correlations are capable of estimating the effective convective heat transfer coefficients of any spherical and cylindrical shaped products exposed to water and air cooling in practical applications in a simple and accurate manner.     

Study of mixed-mode forced convection solar drier

In the current paper presented investigations of the developed mixed-mode forced convection solar drier (SD). Developed design of the unit can be used as a greenhouse in winter time and as a solar drier during of the other times of the year. Studied of the technical parameters of the system by using of the developed mathematical model of operation mode. The model was developed in parallel with experimental work. 1 The article is published in the original. The article is published in the original.     

高空飞行器舱内强制对流换热随压降的衰减变化

在理论分析了气压下降与舱内强制对流换热关系的基础上,利用实验的方法对理论分析进行了验证。结果表明,低气压下,处于连续介质流的流体对流换热仍然可以利用常规情况经验准则关系式进行分析计算;舱内对流换热能力随气压下降不断衰减,气压越低,衰减越快。研究结果对飞行器设备舱热控制有一定的参考作用。     

Turbulent natural convection cooling of electronic components mounted on a vertical channel

The paper presents a numerical simulation of conjugate, turbulent natural-convection air cooling of three heated ceramic components, which are identical and mounted on a vertical adiabatic channel. A two-dimensional, conjugate heat transfer model and the standard k–ϵ turbulence model were used to obtain the dynamic and thermal fields. The finite-volume method has been used to solve the model equations throughout the entire physical domain (solid and fluid). After validation of the method with available measurements for a single source, it was applied to investigate the effects on cooling of spacing between the heated electronic components and of the removal of heat input in one of the components. The former modification led to better cooling while the latter can be partially advantageous only when the non-powered components are mounted between the powered ones: this reduces the temperature of the powered components situated downstream from the non-powered component.     

Natural convection cooling process from two identical porous-covering electronic components

In the present work, we focus to study numerically the natural convection cooling process from two identical electronic components located on the bottom wall of a two-dimensional cavity. Each electronic component is covered by a porous medium with finite thickness. The conservation equations governing the problem are discretized using the finite volume method and the SIMPLER algorithm is used to handle the nonlinear character of conservation equations. Calculations were carried out for the following control parameters: the porous/fluid thermal conductivity ratio (1 ≤ Rk_P1 ≤ 100), the Darcy and Rayleigh numbers (10⁻¹ ≤ Da ≤ 10⁻⁶, 10³ ≤ Ra ≤ 10⁶), the first porous-cover thickness (0.05 ≤ e₁ ≤ 0.3), and the separation distance between components (0.2 ≤ S ≤ 1) to highlight their influence on the cooling process. The results show that under specific values of the Darcy and Rayleigh numbers and in the limiting case of a high value of the porous/fluid thermal conductivity ratio (Rk_P1 = 100), a decrease in the maximum components temperature, up to 95%, is observed by increasing the porous-cover thickness from 0.05 to 0.3. In addition, by increasing the permeability, the Rayleigh number or the separation distance, an improvement in the cooling process of the two components greater than or equal to 22% is achieved.     

Effect of metal plate barrier without holes in forced convection of electronic equipment

Two rectangular block‐like elements as in an electronic module are positioned in a parallel‐walled channel and cooled by forced convection airflow. A metal plate without holes as a barrier protrudes above the plane of the modules. It is intended to function as a cover for protecting them from mechanical or electromagnetic damage, or as a thermal control device. Per‐module heat transfer coefficients in the presence of the barrier of various gaps, G, between the barrier and the channel and distance, L, between the module and the barrier were measured. In the presence of the barrier, the heat transfer coefficient at the 2nd row module is enhanced, but it is diminished at the 1st row module. Nusselt numbers are correlated as a function of Reynolds number and G/L. © 2008 Wiley Periodicals, Inc. Heat Trans Asian Res; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/htj.20224     

A brief survey and economical analysis of air cooling for electronic equipments

The techniques used in the cooling of electronic equipments vary widely depending on the particular application. Cooling with liquids and impinging air jets become important where classical cooling techniques may be insufficient, while a single or array jet is employed where highly localised cooling is desired. This paper provides a comparative survey of advanced methods of cooling for electronic systems and an economical analysis of cooling electronic equipments using slot and circular jets.     

Heat transfer of combined forced and natural convection from horizontal cylinder to air

Experimental investigations have been carried out for combined convective flows of air induced around uniformly heated, horizontal cylinders. Three cases of aiding, opposing, and cross flows were examined. The experiments covered the ranges of the Reynolds and modified Rayleigh numbers of Re_d=50 to 900 and Ra_d^*=5×10⁴ to 3×10⁶. The flow fields around the cylinders were visualized with smoke. The results showed that separation points gradually shift from those of the forced convection to the top edge of the cylinder with increasing wall heat fluxes. The local heat transfer coefficients of the cylinders were also measured. Although the local coefficients show complex variations with the forced flow velocities and the wall heat fluxes, the overall coefficients become higher than those estimated from pure forced and natural convections throughout the cases of aiding, opposing, and cross flows. Moreover, it was confirmed that the overall Nusselt numbers as well as the separation points can be predicted with the non‐dimensional parameter (Gr_d^*/Nu_dRe_d²). © 2007 Wiley Periodicals, Inc. Heat Trans Asian Res, 36(8): 474–488, 2007; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/htj.20180     

The forced air cooling heat dissipation performance of different battery pack bottom duct

Due to the requirement of the battery for the thermal management system, based on the coupling relationship between the velocity field and the thermal flow field of the field synergy principle, the flow paths of the forced air cooling system for different battery packs were analyzed. First, the thermodynamic parameters of the battery were collected through experiments and verified by simulation. Secondly, based on the collected thermodynamic parameters of the battery, the heat generation model of the battery, the heat conduction model of the gas, and the coupled heat dissipation model of the battery and air were established. Determine the boundary conditions, calculation methods and evaluation indicators required for simulation; Finally, based on four different driving conditions, the forced air cooling performance of the double “U” shape duct and double “1” type duct is simulated. Through the analysis of the results, the dual “U” air ducts have a more heat dissipation effect on the battery pack than the double “1” shape duct. The results conform to the definition of the field synergy principle for the coupling relationship between the velocity field and the heat flow field. Then research provide references for the design of battery packs and matching of cooling systems.     

Limitations of the lumped model for in‐tube laminar forced convection interacting with cross forced convection flows

The short communication addresses forced convection heat transfer of a viscous fluid flowing in a tube with fully developed laminar velocity and uniform entrance temperature that exchanges heat convection with a surrounding fluid. The idea is to implement the lumped model following the footsteps of the potent lumped model within unsteady heat conduction, instead of the differential model. The computed mean bulk temperatures of the viscous fluid expressed by a simple exponential function agrees well with the baseline numerical mean bulk temperatures when the internal fluid is air, water or crude oil and the external fluid is air for small values of the modified Biot numbers and maximum Reynolds numbers are satisfied.     

Mixed convection air cooling of protruding heat sources mounted in a horizontal channel

A numerical study of laminar mixed-convection heat transfer to air from two identical protruding heat sources, which simulate electronic components, located in a two-dimensional horizontal channel, is presented in this paper. The finite volume method and the SIMPLER algorithm are used to solve the conservation equations of mass, momentum, and energy for mixed convection. Results show that the heat transfer increases remarkably for Pr = 0.71 and 5 ≤ Re ≤ 30. It was also found that the increase of separation distance, the height and the width of the components has a considerable enhancement of the heat removal rate from the components, and therefore, on the improvement of the heat transfer inside the channel.     

Natural convection in a triangular cavity filled with air under the effect of external air stream cooling

Natural convection in a triangular cavity filled with air is investigated numerically. In this paper, the cavity is exposed to air stream cooling exerted on its sides and it is heated by a fixed heat flux from the base. The air inside the cavity is assumed to be laminar and obeying Boussinesq approximation. The governing equations are solved numerically using the finite volume technique with SIMPLE algorithm. The results are achieved with a range of Rayleigh number (10⁴ < Ra < 10⁷), free stream Reynolds number (10³ < Re_∞ < 1.5 × 10⁴), four aspect ratios (AR = 0.25, 0.5, 0.866, and 1) and five inclination angles (? = 0°, 30°, 45°, 60°, 90°). The influence of these parameters is displayed on the stream function, isotherms lines, local and average Nusselt numbers. The results reveal that the heat transfer rate increases as Rayleigh number, free stream Reynolds number and AR increase. The highest heat transfer rate is obtained at ? = 0° while the lowest one is obtained at ? = 90°. Furthermore, as the AR augments, the local and average Nusselt numbers are enhanced and the stream function is formed of two symmetric counter‐rotating vortices.     

Evaporation of a thin binary liquid film by forced convection into air and superheated steam

<正>This paper deals with a numerical analysis of the evaporation of a thin binary liquid film by forced convection inside a channel constituted by two plates.The first plate is externally insulated and wetted by a thin water ethylene glycol film while the second is dry and isothermal.The first part is concerned with the effects of inlet ambiance conditions and the liquid concentration of ethylene glycol on the distribution of the velocity,temperature,concentrations profiles and the axial variation of the evaporation rate.The second part is focused on the inversion temperature point of the evaporation of binary liquid film.Results show that the inversion temperature phenomenon for the evaporation of binary liquid mixture is observed for high liquid concentration of ethylene glycol.The present results show that in the inlet temperature range considered here,the inversion temperature does not exit for the evaporation of pure ethylene glycol.     

Laminar forced convection in eccentric annuli

Forced convection to hydrodynamically and thermally fully developed laminar flow in eccentric annuli is studied. Following Reynolds et al. [1], we determine the solutions of the energy equation which satisfy certain fundamental boundary conditions. These fundamental solutions can be superposed to satisfy a wide variety of boundary conditions. Exact solutions of the energy equation could not be found, so an approximate solution was determined. Nusselt numbers, wall temperature and heat fluxes, wall-fluid temperature differences, and mean fluid temperatures are presented for a wide range of eccentricities and radius ratios. It is believed that these results are accurate to within 1 per cent.     

Improving efficiency of high‐concentrator photovoltaics by cooling with two‐phase forced convection

The potential of increasing high‐concentrator photovoltaic cell efficiency by cooling with two‐phase flow is analyzed. The governing energy equations were used to predict cell temperature distributions and cell efficiencies for a photovoltaic cell under 100 suns' concentration. Several design conditions were taken into consideration in the analysis, including cooling channel height, working fluid type (between water and R134a), working fluid inlet temperature, pressure, and mass flow rate. It was observed that the dominant parameter for increasing cell efficiency was the working fluid saturation temperature, which itself is affected by a number of the aforementioned design parameters. The results show R134a at low inlet pressures to be highly effective in this two‐phase cooling design. Copyright © 2010 John Wiley & Sons, Ltd.     

轴向通流旋转盘腔内类Rayleigh-Benard对流稳定性研究

利用数值模拟的方法对冷气轴向通流旋转盘腔的流动过程进行了研究。研究发现。对应一进口冷气的冒诺教，存在一临界瑞利敷(Rαc)，高于该瑞利教(Rα)。流动出现不稳定现象。且Rα越大，不稳定行为越严重。对于特例，盘腔内的流动可以看成是由类Rayleigh—Benard对流和强迫对流两个区域构成，两个区域通过能量和质量交换相互影响。流动随着Rα的增加从稳态发展为非稳态；采用频谱图分析的方法对数值解的不稳定性进行定性分析。结果显示随着Rα的增大。教值解经历了从稳定解到分贫的周期性不稳定和准周期不稳定的发展过程，离心浮升力引起的类Rayleigh—Benard对流是造成流动从稳定到不稳定发展的重要原因，哥氏力的存在恶化了不稳定过程。     

Thermal boundary condition effects on forced convection heat transfer

We propose a numerical solution of an adjoint problem of forced convection heat transfer to evaluate the mean heat transfer characteristics under arbitrary thermal boundary conditions. Using the numerical solution of the adjoint problem under the Dirichlet condition, which can be computed by slightly modifying a conventional heat transfer code, we obtain an influence function of local surface temperature on total heat transfer. As a result, the total heat transfer for arbitrary surface temperature distributions can be calculated by the influence function. Similarly, using the numerical solution of the adjoint problem under the Neumann condition, we can also obtain an influence function of the local heat flux on the mean surface temperature. The influence functions for a circular cylinder and for an in-line square rod array are presented to illustrate the capability of this method. © 1999 Scripta Technica, Heat Trans Asian Res, 28(3): 227–238, 1999