Jenn-Tsong Horng

Thermal Optimal Design for Plain Plate-Fin Heat Sinks by Using Neuro-Genetic Method

An effective artificial neural network together with a genetic algorithm have been demonstrated for predicting the optimal thermal performance of plain plate-fin heat sinks in a ducted flow under multi-constraints such as pressure drop, mass, and space limitations. A series of constrained optimal designs can be efficiently performed. Comparisons of the optimal results between the artificial neural network with genetic algorithm (ANN-GA) and the response surface methodology with sequential quadratic programming (RSM-SQP) methods are made. Although more training patterns are needed for the ANN-GA method as compared to that for the RSM-SQP method, the ANN-GA method which has randomly uniform-distributed training patterns in the whole solving domain can be applied to the global region of interest, not just in the region of operability. Consequently, a globally precise optimal solution can be achieved with the ANN-GA method; while the solution obtained with the RSM-SQP method may cause a significant error if the optimal values of the design variables happen to be located beyond the region of operability.

Thermal Design Optimization for Strip-Fin Heat Sinks with a Ducted Air Flow

An effective method for performing the thermal optimization of strip-fin heat sinks with a ducted air flow under constraints of pressure drop, mass, and space limitations has been successfully developed. The thermal and hydrodynamic models for strip-fin heat sinks have been developed. The design of experiments approach is performed to explore the relationships between design variables and responses with the minimal number of experimental runs. A statistical method for sensitivity analysis of the design factors, including the size of heat sink footprint, conductivity of sink base, thickness of sink base, stream wise and span wise fin pitch, fin thickness, fin length, fin height, and upstream air velocity, is performed to determine the key factors that are critical to the design; and a response surface methodology is then applied to establish regression models for the thermal resistance and pressure drop in terms of the design factors with an central composite design. Diagnostic analysis of the residuals from the regression model may reveal errors that were not in Gaussian distribution, which is one of the most important assumptions of experimental analysis; in the case of this work, a log-transformation is applied to make the response variance closer to the normal distribution. Furthermore, to screen out the insignificant model terms for the better modeling accuracy, the statistical skill, F-test, is applied. By employing the gradient-based numerical optimization technique, a series of constrained optimal designs have been efficiently performed

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

A Semi-Empirically Thermal Optimization for Heat Sink/TEC Assemblies With Various External Thermal Resistances

An effective semi-empirical method that combines thermal network models and empirical correlations for exploring the thermal performance of heat sinks and HS/TEC assemblies under different external thermal resistances is successfully established. A series of parametric studies, including the effects of external thermal resistance, input current of TEC and pumping heat capacity, on thermal performance improvements of HS/TEC assemblies have been performed. The Response Surface Methodology (RSM) is applied to establish explicit models of the thermal performance of HS/TEC assemblies under various external thermal resistances in terms of the design variables through statistical fitting method. Furthermore, the numerical optimization results for HS/TEC assemblies under different constraints are obtained. With constrained optimal designs of HS/TEC assemblies, the HS/TEC assemblies can provide excellent thermal performance improvements on (1) the reduction of thermal resistance, (2) the enhancement of module heat loads and (3) the improvement of external thermal resistance.© 2007 ASME

Thermal Optimal Design for Heat Sinks or Heat Sink/TEC Assemblies in a Ducted Flow

A series of experimental studies on the heat transfer characteristics from heat sinks or Heat Sink/TEC assemblies in a ducted flow have been performed. Their effects on heat transfer characteristics in ducted flow have been systematically explored. From the results, new performance correlations of the temperature difference (ΔT) and terminal voltage (V) of the TEC modules are proposed. Besides, two new correlations of steady-state average Nusselt number and external thermal resistance in terms of relevant influencing parameters for confined ppf heat sinks in a ducted flow are also proposed, respectively. The statistical sensitivity analysis of ANOVA F-test is employed to estimate the contributions of relevant parameters. Furthermore, a series of RSM models for evaluating heat transfer characteristics including average Nusselt number, average external thermal resistance and T c −Ta are established. A Sequential Quadratic Programming with multi-starting-point method is successfully employed to automatically and efficiently seek a globally optimal thermal performance. An optimal design of HS/TEC assemblies under both COP ≥ 2 and pumping power limitation larger than 30 W can be achieved with a reduction of 75% on thermal resistance.Copyright

Thermal Optimal Design for Partially-Confined Compact Heat Sinks

An effective method for predicting the optimal thermal performance of partially-confined compact heat sinks under multi-constraints of pressure drop and heat sink mass has been successfully developed. The design variables of PPF compact heat sinks include: heat sink fin and base material, thickness of heat sink base, heat flux, channel top bypass and inlet flow velocity. A total of 108 experimental cases for confined forced convection are designed by the Central Composite Design (CCD) method. According to the results in ANOVA, a sensitivity analysis for the design factors is performed. From the analysis, the effect of inlet flow velocity, which has the contribution percentage of 86.24%, dominates the thermal performance. The accuracies of the quadratic RSM models for both thermal resistance and pressure drop have been verified by comparing the predicted response values to the actual experimental data. The maximum deviations of thermal resistance and pressure drop are 9.41% and 7.20% respectively. The Response Surface Methodology is applied to establish analytical models of the thermal resistance and pressure drop constraints in terms of the key design factors with a CCD experimental design. By employing the Sequential Quadratic Programming technique, a series of constrained optimal designs can be efficiently performed. The numerical optimization results for four cases under different constraints are obtained, and the comparisons between these predicted optimal designs and those measured by the experimental data are made with a satisfactory agreement.Copyright

Forced Convective Heat Transfer for Partially-Confined Compact PPF Heat Sinks With Top-Bypass Effect

A series of experimental investigations with a stringent measurement method on the study of the fluid flow and heat transfer for confined compact heat sinks in forced convection have been successfully conducted. From the results, the thermal capacity of the heat sink and the convective heat dissipation play the major roles for dominating the transient thermal behavior in the beginning of power-on transient period; while, the convective heat dissipation finally becomes the solely dominating term at the end of power-on transient period. The transient/steady-state local and average Nusselt numbers increase with increasing Grs, H/Hc ratio or Re. As compared with the steady-state average Nusselt number for non-compact heat sink (Fin-Al/ Base-Al), the steady-state heat transfer enhancement for compact heat sinks (Fin-Al/Base-Al) is 185.74%. Furthermore, a new correlation of steady-state average Nusselt number in terms of relevant influencing parameters for confined compact PPF heat sinks in forced convection is proposed. As compared with two existing correlations of steady-state average Nusselt numbers for unconfined and confined non-compact PPF heat sinks, the heat transfer enhancements for the present confined compact PPF heat sinks of H/Hc = 0.47 are 423.29% and 219.93%, respectively.Copyright

Thermal performance measurement for confined heat sinks

The convective heat transfer characteristics for confined heat sinks by using two experimental methods such as the improved transient liquid crystal method and thermal testing method have been systematically investigated. The trends of average effective heat transfer coefficients measured by using transient liquid crystal method are consistent with that by using thermal testing method. The deviation of the results evaluated by transient liquid crystal method from the data measured by thermal testing method will become more significant when the air flow velocity increases. For exploring the parameters influencing the thermal and fluid friction performances, the average effective heat transfer coefficient increases with increasing flow velocity or decreasing channel porosity; the highest and lowest effective heat transfer coefficients can be found for the cases close to fully-confined and unconfined heat sinks at a specific channel inlet velocity, respectively. The overall channel pressure drop increases with increasing flow velocity. The highest and lowest pressure drops can be found for the cases close to fully-confined and unconfined heat sinks at a specified air flow velocity, respectively. Furthermore, two new correlations of average effective heat transfer coefficient in terms of flow velocity and channel porosity for confined heat sinks are proposed for transient liquid crystal method and thermal testing method, respectively. Finally, a concept of the amount of enhanced heat transfer (AEHT) defined as the ratio of j/f for heat sink analysis is introduced. The j/f ratio is almost independent of Reynolds number for a specific confined heat sink; and it increases with decreasing channel porosity. All the present experimental data for partially confined heat sinks are reasonably bounded between 0.0124 for unconfined heat sinks and 0.0603 for fully-confined heat sinks.

Optimal Thermal Design for PPF Heat Sinks

An effective method for predicting and optimizing the thermal performance of Parallel-Plain Fin (PPF) heat sinks that satisfy given design constraints has been successfully developed in the study. The thermal and hydrodynamic performance analyses for PPF heat sinks have been conducted. The Response Surface Methodology (RSM) is applied to establish analytical models of the thermal resistance and pressure drop in terms of the design variables with a Central Composite Design (CCD) experimental design. A constrained optimization technique, Sequential Quadratic Programming (SQP), is employed to efficiently seek the optimal designs; and the comparisons between these predicted optimal designs and those evaluated by the theoretical calculations are made with a satisfactory agreement.Copyright