C. H. Peng

Heat Transfer Characteristics for a Confined Rotating MCM Disk With Round Jet Array Impingement

An effective method of design of experiments combined with Central Composite Design for exploring the heat transfer characteristics for a confined rotating Multi-Chip Module (MCM) disk with round jet array impingement has been successfully developed. The relevant parameters influencing heat transfer performance include the steady-state Grashof number (Grs ), ratio of jet separation distance to nozzle diameter (H/d), jet Reynolds number (Rej ) and rotational Reynolds number (Rer ). Their effects on heat transfer characteristics have been systematically explored. An axisymmetrical temperature distribution is ensured for various Grs , Rej , Rer and H/d ratios. As compared with the mutual effects of jet array impingement and disk rotation cause a more non-uniform distribution of chip temperatures. For heat transfer behavior, a new correlation of stagnation Nusselt number for jet array impingement at r/R = 0 in terms of Rej and H/d is presented. As compared with the experimental steady-state data of single round jet impingement, the average heat transfer enhancement at stagnation point r/R = 0 of jet array impingement is 607%. For the rotating MCM disk cases, the highest chip heat transfer occurs at the MCM disk rim, and decreases sharply along the distance from the surface edge toward the surface center.Copyright

An optimal approach with genetic algorithm for thermal performance of heat sink/TEC assembly

In the present study, a semi-empirical method that combines theoretical and experimental data for exploring the thermal performance of a heat sink with or without integrating TEC has been successfully established. By employing the genetic optimization technique, a series of constrained optimal designs have been performed. The independent variables for optimization search are the pumping capacity of the TEC (Q c), the electric current of the TEC (I) and the external thermal resistance between hot side of the TEC and ambient (Rext ). The present objective for the optimization search is the maximum temperature difference between heat sinks with and without integrating TEC. The results show that optimal value of DeltaTb-c is 21.3degC, with boundary limits of Qc =10W, I=10A and Rext=0.25 degC/W. However, this design results in a poor coefficient of performance (COP), say COP=0.17. Under a given constraint of COPsquare2, the optimal value of DeltaTb-c can be obtained to be 9.1 degC with the corresponding Qc=14.8W, I=3.4A and Rext=0.25degC/W. Comparisons between the results by the present optimal design and those obtained by the semi-empirical method have been made with a satisfactory agreement. The present optimal design shows that a heat sink/TEC assembly can provide an effective temperature reduction with high COP and extend the upper limits of air-cooled heat sinks

Cooling Performance of Plain-Plate-Fin Heat Sinks With Slot Jet Impingement

An experimental investigation on the thermal performance of slot jet impinging onto fully-confined and partially-confined heat sinks with plain-plate fins (ppf) is presented. The relevant parameters influencing the convective cooling performance with slot jet impingement include the ratio of heat sink height to jet separation distance (Hs /H), ratio of heat sink height to nozzle width (Hs /Wj ) and jet Reynolds number (Rej ). The thermal performance of fully-confined ppf heat sinks (Hs /H=1) is experimentally investigated. Besides, an effective theoretical model based on a developing channel flow with an impinging effect is successfully proposed to predict the average Nusselt numbers of fully-confined ppf heat sinks. Furthermore, a new correlation of average Nusselt numbers in terms of Hs /Wj and Rej is proposed for the cases of fully-confined ppf heat sinks. For partially-confined cases, a normalized Nusselt number, [Equation]Nuj /[Equation]Nuj,Hs /H=1 , is showed only dependent on Hs /H in the present study. A new correlation of [Equation]Nuj /[Equation]Nuj,Hs /H=1 in terms of Hs /H is proposed. This result manifests that the Nusselt numbers of partially-confined ppf heat sinks can properly be evaluated with the Nusselt numbers of fully-confined heat sinks and the normalized [Equation]Nuj /[Equation]Nuj,Hs /H=1 ratios. Finally, a generalized correlation of average Nusselt numbers in terms of Hs /H, Hs /Wj and Rej , which can be applied to both fully-confined and partially-confined heat sinks, is proposed. The maximum and average deviations between the correlations and the experimental data are 19.7% as well as 4.6%, respectively.Copyright

Convective Heat Transfer From a Stationary or Rotating MCM Disk With a Unconfined Round Jet Impingement

A series of experimental investigations with stringent measurement methods on the studies related to fluid flow and transient mixed convection from a horizontally unconfined stationary or rotating ceramic-based MCM disk with unconfined jet impingement have been successfully conducted. The relevant parameters influencing fluid flow and heat transfer performance are (1) mixed convection due to jet impingement and buoyancy: steady-state Grashof number, jet Reynolds number, and ratio of jet separation distance to nozzle diameter; and (2) mixed convection due to jet impingement, disk rotation and buoyancy: steady-state Grashof number, jet Reynolds number (Rej ), rotational Reynolds number (Rer ), ratio of jet separation distance to nozzle diameter (H/d). The thermal behavior explored includes the transient temperature distribution on the MCM disk surface, transient heat flux distribution of input power, transient convective heat flux distribution of chips, and transient chip and average heat transfer characteristics on the MCM disk surface. Besides, two new correlations of transient stagnation and average Nusselt numbers in terms of Rej , H/d and t are presented for the cases of stationary MCM disk. For the cases of rotating MCM disk, a new empirical correlation to classify two regimes of heat transfer modes such as disk rotation mode and jet impingement mode is presented; and a complete composite correlation of steady-state average Nusselt number for mixed convection due to jet impingement, disk rotation and buoyancy is proposed. As compared with the steady-state results, if the transient chip and average heat transfer behaviors may be considered as a superposition of a series of quasi-steady states, the transient chip and average Nusselt numbers in all the present transient experiments can be properly predicted by the existing steady-state correlations when t > 6 min in the power-on transient period.Copyright

Optimal Design for Thermal Performance of a Heat Sink Integrated With Thermoelectric Cooler

The demand for high execution speed and memory capacity for modern computers results in an increasing circuit density per unit chip and high power dissipation per unit volume. Consequently, traditional air cooling technology such as air-cooled heat sink is reaching the limits for electronic applications. Thermoelectric coolers are regarded as potential solutions for enhancing the performance of air-cooled heat sinks. In the present study, a semi-empirical method for exploring the thermal performance of a heat sink integrated with or without TEC has been successfully established. A concept of design of experiments (DOE) is applied, and a statistical method for sensitivity analysis of the influencing parameters is performed to determine the key factors that are critical to the design. By the statistical sensitivity analysis of ANOVA F-test for the temperature reduction (ΔTC−B ) and COP of the TEC, the factor contributions of QP , Rext and I are 31.66%, 33.73%, 34.61% as well as 14.9%, 0%, 85.1%, respectively. By employing the gradient-based numerical optimization technique, a series of constrained optimal designs have been performed. Under the given constraints of COP≧2, the optimal value of ΔTC−B (3.3°C) is obtained with the corresponding Qp (31.99W) and Qte (16W). Comparisons between the results by the present optimal design and those obtained by the semi-empirical results have been made with a satisfactory agreement. The present optimal design shows that a heat sink integrated with TEC can extend the upper limits of thermal management for traditional air-cooled heat sinks.Copyright

Fluid Flow Behavior for a Confined Rotating MCM Disk With Round Jet Array Impingement

A series of experimental investigations on the studies related to fluid flow characteristics of a confined rotating Multi-Chip Module (MCM) disk with round air jet array impingement have been performed. The relevant parameters influencing fluid flow characteristics include the ratio of jet separation distance to nozzle diameter (H/d), jet Reynolds number (Rej ) and rotational Reynolds number (Rer ). The parametric ranges are Rej = 712 – 4087, Rer = 0 – 2906, H/d = 0.83–14.4 and Z/d = 1–7. The potential core lengths of all the nozzle jets increases with increasing jet Reynolds number or H/d ratio and decreases with increasing rotational Reynolds number. New correlations of the ratio of potential core length to nozzle diameter at various nozzle jets in terms of relevant influencing parameters are proposed. Furthermore, the strengths on both streamwise velocity and turbulence intensity increase with increasing Z/d ratio. The turbulence intensity for the cases of jet array impingement growing up along the axial directions are significantly faster than the cases of single round jet impingement. The jet array impingement has a higher momentum flux in the flow interaction region between two adjacent nozzles; accordingly, it can achieve a more uniform thermal performance as compared with the cases of single round jet impingement. Near-surface fluid flow behavior including the streamwise velocity and turbulence intensity distributions can be employed to interpret the heat transfer characteristics for jet array impingement.Copyright

Thermal Optimal Design for Multichip Module Disks With an Unconfined Round-Jet Impingement

An effective method for performing the thermal optimization of stationary and rotating MCM disks with an unconfined round-jet impingement under space limitation constraint has been successfully developed. The design variables of stationary and rotating MCM disks with an unconfined round-jet impingement include: the ratio of jet separation distance to nozzle diameter (H/d), steady-state Grashof number (Grs ), jet Reynolds number (Rej ), rotational Reynolds number (Rer ). The total experimental cases for stationary and rotating MCM disks are statistically designed by the Central Composite Design (CCD) method. In addition, a sensitivity analysis, the so-called ANOVA, for the design factors has been performed. In the stationary MCM disk with an unconfined round-jet impingement, the contribution percentage of jet Reynolds number on the thermal performance is 95.86%. The effect of jet Reynolds numbers on chip temperature distribution is more significant than that of the H/d ratio and steady-state Grashof number. In rotating MCM disk with an unconfined round-jet impingement, the effect of jet Reynolds number, which has the contribution percentage of 91.81%, dominates the thermal performance. Furthermore, the comparisons between the predictions by using the quadratic Response Surface Methodology (RSM) and the experimental data are made. The maximum deviations for transient stagnation Nusselt number and transient average Nusselt number for the cases of stationary MCM disk are 10.05% and 11.82%, respectively; and 9.41% and 12.44% for the cases of rotating MCM disk, respectively. Finally, with the Sequential Quadratic Programming (SQP) technique, a series of thermal optimal designs under space limitation constraint H/d≤12 has been efficiently performed. Comparisons between the numerical optimization results and the experimental data are made with a satisfactory agreement.Copyright

Natural Convective Heat Transfer From an Unconfined or a Confined Heated Surface

A series of experimental investigations with a stringent measurement method on the natural heat transfer from an unconfined or confined smooth and extended surface have been successfully conducted. From the results, the maximum transient-/steady-state local Nusselt number exists in the region near the edge of the heated smooth or extended surface, and the transient-/ steady-state local Nusselt number decreases along the distance from the surface edge toward the surface center. The transient-/steady-state local and average Nusselt number increases with increasing Grs , H/W or Hes /W. The effects of Grs , H/W and Hes /W on the Nus /Nus,o distribution are not significant; and the Nus /Nus,o distribution can be expressed as a generalized bowl-shaped profile, which is independent of Grs , H/W and Hes /W. By the statistical sensitivity analysis of ANOVA F-test, the steady-state average Nusselt number for unconfined/confined smooth or extended surface is significantly affected by either one of Grs , H/W and Hes /W. Among them, Grs has the most significant effect. Four new correlations of steady-state average Nusselt number in terms of relevant influencing parameters for unconfined/ confined smooth or extended surfaces are proposed, respectively. Furthermore, two normalized steady-state average Nusselt numbers for confined smooth or extended surfaces are proposed, respectively. As compared with the steady-state average Nusselt numbers for unconfined/confined smooth surface, the steady-state heat transfer enhancement for unconfined/confined extended surface can be achieved between 93.99% and 254.65%.Copyright

Convective Heat Transfer From Confined Heated Surfaces With Slot Jet Impingement

A series of experimental investigations with a stringent measurement method on the transient-/steady-state heat transfer behavior for confined smooth surfaces with slot jet impingement have been successfully conducted. From the results, a generalized correlation is proposed to represent the distributions of normalized transient convective heat flux. The highest heat transfer during the transient period occurs at the surface center of confined heated smooth or extended surface. The transient local Nusselt number decreases along the distance from the surface center toward the surface edge. The transient-/steady-state local and average Nusselt numbers are almost independent of Grs , and they are more significantly affected by ReD as compared with H/W. They will increase with increasing ReD . Maximum local and average Nusselt numbers can be found between H/W = 3 and H/W = 5. The effects of Grs and H/W on the dimensionless local Nusselt number distribution are insignificant; and the distribution can be expressed as a generalized bell-shaped profile, which is only dependent of ReD . Finally, a new composite correlation of steady-state average Nusselt number for mixed convection from confined smooth due to slot jet impingement and buoyancy are presented.Copyright

Thermal Behavior of Silicon Heat Spreader Coated With Diamond Film

In the present study, an experimental setup with stringent measurement methods for performing the natural convection from a horizontal heated chip mounted with a silicon heat spreader coated with diamond film has been successfully established. The parametric studies on the local and average effective heat transfer characteristics for natural convection from a horizontal smooth silicon wafer, rough silicon wafer or silicon wafer coated with diamond film spreader have been explored. The influencing parameters and conditions include Grashof number and spreader material with different surface treatment conditions. From the results, an axisymmetric bowl-shaped Nu profile is achieved, and the highest heat transfer performance occurs at the location near the rim of the heated surfaces for various heat spreaders. The local Nusselt number for a specified convective heat flux decreases along the distance from the disk rim toward the center. The local or average Nusselt number increases with increasing Grashof number for various heat spreaders. As compared with the average Nusselt number for smooth water surface (Ra =5.69nm), the heat transfer enhancements for rough silicon surface (Ra =516.61nm) and rough diamond surface (Ra =319.51nm) are 10.42% and 7.69%, respectively. Furthermore, new correlations for local and average Nusselt numbers for various heat spreaders are presented, respectively. As compared with the smooth silicon surface, the external thermal resistance for rough silicon surface and rough diamond surface are reduced to 91.18% and 90.73%, respectively; and the maximum thermal resistances for rough silicon wafer and silicon wafer coated with diamond film are reduced to 90.43% and 92.61%, respectively.Copyright