Modelling of a pin-fin heat converter with fluid cooling for power semiconductor modules

This paper presents a way to design a finite-element computer model of cooling system with a complicated geometry. The computer model is developed on the basis of a commercial software package ABAQUS. The steady state forced-convective fluid cooling of a pin-fin heat converter for power (∼1 kW heat power) semiconductor module has been investigated on the basis of computer simulation. A phenomenological equation has been used for calculation of the local value of the heat transfer coefficient for the liquid-solid interface. The impacts of the thermal conductivity of the pin-fin sink material, volume flow rate of the cooling liquid and geometrical design of the pin-fin sink on the thermal resistance of the converter are shown. Copyright © 2003 John Wiley & Sons, Ltd.     

Thermal performance of high brightness LED array package on PCB

This paper presents a thermal analysis and experimental validation of natural convective air cooling of a high brightness 3 × 3 LED array package on a printed circuit board (PCB) during operation from 0 to 180° inclinations. Temperature distribution and heat flow of the LED package are assessed by thermal profile measurement using an IR camera and thermocouples. In addition, a design study on the thermal performance of the packaging structure is also performed. The analysis results reveal that the effect of position and inclination plays an important role in the heat dissipation of the LED package. The heat transfer process of the LED PCB package in natural convection is also modelled and simulated using computational fluid dynamics (CFD) method. The proposed thermal analytical study provides a detailed understanding of the thermal response of an open or enclosed LED array PCB unit under various operating conditions. The results provide criteria for setting up a LED array system and for adopting design features that would be beneficial to effective thermal management.     

Influence of the heat recovery steam generator design parameters on the thermoeconomic performances of combined cycle gas turbine power plants

This paper proposes a methodology to identify the most relevant design parameters that impact on the thermal efficiency and the economic results of combined cycle gas turbine power plants. The analysis focuses on the heat recovery steam generator (HRSG) design and more specifically on those operating parameters that have a direct influence on the economic results of the power plant. These results are obtained both at full and part load conditions using a dedicated code capable of simulating a wide number of different plant configurations. Two different thermoeconomic models aimed to select the best design point are proposed and compared: the first one analyzes the generating cost of the energy while the second one analyzes the annual cash flow of the plant. Their objective is to determine whether an increase in the investment in order to improve the thermal efficiency is worth from an economic point of view. Both models and the different HRSG configurations analysed are compared in the results section. Some parametric analysis show how the design parameters might be varied in order to improve the power plant efficiency or the economic results. Copyright © 2004 John Wiley & Sons, Ltd.     

Enhanced heat transfer by room temperature deposition of AlN film on aluminum for a light emitting diode package

Heat transfer is crucial to the fabrication of high efficiency light emitting diode (LED) packages. The effectiveness of the heat transfer depends on the package materials and design. This paper presents an application of high thermal conductivity aluminum nitride (AlN) films to replace low thermal conductivity epoxy resin or alumina substrates. The AlN film was directly deposited on an aluminum plate which enabled the removal of thermal interface materials (TIM) such as the adhesive thermal bonding sheets that are used in conventional metal printed circuit board (PCB)-based LED packaging process. A fully dense AlN ceramic film was successfully deposited at room temperature using the aerosol deposition method. The thermal resistance, a parameter of the heat transfer characteristic of an LED package, was measured using a thermal transient tester. The results showed that the thermal resistance of the LED package mounted on the AlN thick film was 28.5 K/W, while an LED package mounted on a conventional epoxy-based metal PCB and a PCB with thermal vias were 47.2 K/W and 36.5 K/W, respectively. This indicates that an aerosol-deposited AlN-based LED package exhibits greatly enhanced heat transfer compared to the conventional metal PCB.     

Numerical simulation of thermal runaway phenomena in silicon semiconductor devices

A mathematical model for heat production due to thermal excitation of conductive electrons and positive holes in a semiconductor pn junction is derived and discussed. The model is applied to simulate the thermal runaway phenomena in power electronics semiconductor devices. Our discussion focuses especially on the modeling of unexpected huge currents due to an excessive temperature increase. Calculated dynamics of temperature distributions of a silicon wafer while cooling performance decreases proved it is possible for a silicon wafer to be heated over its melting point in a few milliseconds. Our results indicate that if a local hot spot arises in a wafer, the thermal intrinsic excitation carries an increased diffusion current of minor carriers and a recombination current in the depletion layer of a pn junction. Also it appears to be important that cooling performance should be uniform on the wafer to avoid the growth of hot spots and thermal‐runaway itself. © 2002 Wiley Periodicals, Inc. Heat Trans Asian Res, 31(6): 438–455, 2002; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/htj.10044     

The heat transfer and pressure drop characteristics of finned tube banks in forced convection (comparison of the pressure drop characteristics of spiral fins and serrated fins)

In recent years there has been a growing need for reduction of energy consumption in an effort to solve problems of global warming and the shortage of petroleum resources. For example, in the power generation field, thermal power generation now occupies 60% of the power generation demand, and the need for improved thermal efficiency is thus considerable. In this paper, the pressure drop characteristics of the finned tube banks used for the heat exchanger in thermal power generation were clarified by testing the serrated finned tube banks for improvement of higher heat transfer and the conventional spiral finned tube banks under the same test conditions, and equations for predicting the pressure drop coefficient which is necessary to design the heat exchanger were proposed. © 2004 Wiley Periodicals, Inc. Heat Trans Asian Res, 33(7): 431–444, 2004; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/htj.20030     

Heat transfer enhancement by flexible printed circuit board's deformation

Flexible printed circuit board (FPCB) has started replacing rigid PCB in some electronic application. However, the deflection and heat transfer of FPCB caused by flow and thermal are far more crucial compared to rigid PCB. In the current study, effects of flow and thermal induced deflection were coupled in real time. The numerical modelling was executed using FLUENT and ABAQUS, coupled online by Mesh-based Parallel Code Coupling Interface (MpCCI). The numerical findings have been validated with experimental results. Rigid PCB with same thermal properties of FPCB has been compared. The findings showed that the deflection of the FPCB does help to increase the heat transfer of the PCB. Furthermore, models with different power of heat sources along with various Reynolds numbers (Re) had been studied. The results exhibited that the magnitude and the trend lines' pattern of deflection divided by characteristic length changes according to thermal power. It indicates both flow and heat have significant effect to the deflection and Nusselt number (Nu) of FPCB. Therefore, flow and thermal should be coupled at the same time for more realistic FPCB simulation under flow environment in operating condition.     

Reliability of power stations: Stochastic versus derated power approach

Consideration of the eventual forced outage of individual power stations leads to a large number of possible states of the power generating system, all with their own probability. It is possible to design a stochastic method to properly take into account all of these possibilities and to weigh them accordingly. In broader energy models, instead of these stochastic techniques that require a considerable amount of calculation time, mostly approximative static simplified methods are applied. Up till now, these simplified techniques have not been validated. The scope of this paper is to check their validity. Therefore, two approaches are compared: a complete stochastic approach and a method based on the derated power (which is the nominal power multiplied with the average availability) of the individual plants. The conclusion of this comparison is that derated power may be used in energy modelling instead of the complicated stochastic approach. The error made is very small and the correlation between the unserved load probability functions obtained by both methods is excellent. Copyright © 2004 John Wiley & Sons, Ltd.     

Internal radiation effects in semitransparent high‐temperature coatings

Internal thermal radiation in semitransparent coatings should be considered in the calculation of temperature and heat flux distribution in metal wall with a thermal barrier coating. In this paper, a ray tracing/node analysis method is used in the numerical simulation of a coupled transient radiative and conductive heat transfer in an absorbing‐scattering non‐gray coating. The present results show that the operating temperature is higher than the design temperature when the radiation is not considered. © 2004 Wiley Periodicals, Inc. Heat Trans Asian Res, 33(5): 271–278, 2004; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/htj.20021     

Efficiency of an Otto engine under alternative power optimizations

The proper optimization criterion to be chosen for the optimum design of the heat engines may differ depending on their purposes and working conditions. In this study, a comparative performance analysis is carried out for a reversible Otto cycle based on three alternative performance criteria namely maximum power (mp), maximum power density (mpd) and maximum efficient power (mep). The power density criterion is defined as the power per minimum specific volume in the cycle and the efficient power criterion is defined as multiplication of the power by the efficiency of the Otto cycle. Maximizing the efficient power gives a compromise between power and efficiency. Three different objective functions are defined and maximization of these functions is carried out under different design parameters of the Otto engine. The variations of power, power density and efficient power outputs are derived and presented with respect to the thermal efficiency of the cycle for various temperature ratios. It has been found that the design parameters at mep conditions lead to more efficient engines than that at the mp condition and the mep criterion may have a significant power advantage compared with mpd criterion. Copyright © 2009 John Wiley & Sons, Ltd.     

Maximum power point tracker for portable photovoltaic systems with resistive-like load

In this work we report on the design and realization of a maximum power point tracking (MPPT) circuit suitable for low power, portable applications with resistive load. The design rules included cost, size and power efficiency considerations. A novel scheme for the implementation of the control loop of the MPPT circuit is proposed, combining good performance with compact design. The operation and performances were simulated at circuit schematic level with simulation program with integrated circuit emphasis (SPICE). The improved operation of a PV system using our MPPT circuit was demonstrated using a purely resistive load.     

A comprehensive power loss,efficiency, reliability and cost calculation of a 1 MW/500 kWh battery based energy storage system for frequency regulation application

Battery based energy storage system (ESS) has tremendous diversity of application with an intense focus on frequency regulation market. An ESS typically comprised of a battery and a power conversion system. A calculation of performance parameters is performed in this research. The aim is to formulate an in-depth analysis of the ESS in terms of power losses of the semiconductor and electrical devices, efficiency, reliability and cost which would foster various research groups and industries around the globe to improve their future product. In view of this, a relation between the operating conditions and power losses is established to evaluate the efficiency of the system. The power loss calculation presented in this paper has taken into account the conduction and switching losses of the semiconductor devices. Afterwards, the Arrhenius Life Stress relation is adopted to calculate the reliability of the system by considering temperature as a covariate. And finally, a cost calculation is executed and presented as a percentage of total cost of the ESS. It has been found that the power loss and efficiency of the ESS at rated power is 146 kW and 85% respectively. Furthermore, the mean time between failures of the ESS is 8 years and reliability remains at 73% after a year. The major cost impact observed is for battery and PCS as 58% and 16% respectively. Finally, it has been determined that further research is necessary for higher efficient and lower cost system for high penetration of energy storage system in the market.     

Structural design considerations for micromachined solid-oxide fuel cells

Micromachined solid-oxide fuel cells (μSOFCs) are among a class of devices being investigated for portable power generation. Optimization of the performance and reliability of such devices requires robust, scale-dependent, design methodologies. In this first analysis, we consider the structural design of planar, electrolyte-supported, μSOFCs from the viewpoints of electrochemical performance, mechanical stability and reliability, and thermal behavior. The effect of electrolyte thickness on fuel cell performance is evaluated using a simple analytical model. Design diagrams that account explicitly for thermal and intrinsic residual stresses are presented to identify geometries that are resistant to fracture and buckling. Analysis of energy loss due to in-plane heat conduction highlights the importance of efficient thermal isolation in microscale fuel cell design.     

Simulation of the transient temperature distribution in a high-power semiconductor device cooling apparatus using heat pipes

This study describes the transient temperature distributions in a cooling apparatus for high-power semiconductor devices used in electric-railcar drive systems. The cooling apparatus is composed of heat pipes, air-cooled fin arrays, and a metal block which is used for attaching several semiconductor packages, In our numerical simulation model, we substituted solid elements for the heat pipes, and determined their thermal properties by experiment. As a result, we could obtain transient temperature distributions for the cooling apparatus through a heat conduction analysis. Calculated results showed that when the amount of heat generated in the devices changes, the temperature of the cooling apparatus changes more slowly than that of the devices. A comparison between the transient-temperature distribution calculations and the experiments confirmed the accuracy of the modeling and prediction method. Thus, these calculations can be used to provide data for packaging design, especially concerning thermal stress and fatigue in the packages. © 1998 Scripta Technica, Inc. Heat Trans Jpn Res, 26(2): 107–115, 1997     

Thermal and optical investigations of high power LEDs with metal embedded printed circuit boards

To improve the thermal and optical performances for high power LEDs, a metal embedded printed circuit board (MEPCB), with a columnar copper slug inside the low cost FR4 material, was introduced in this paper. This novel structure makes it possible to connect the LED component directly to the outside environment. The thermal performances, including thermal resistances and temperature distributions of the MEPCB were evaluated by employing the finite element analysis method (FEA) and transient thermal measurement. The luminous and chromatic characteristics were also measured and analyzed at transient state and steady state. Results showed that the maximum reductions in the total thermal resistance and junction temperature were 65.60% and 56.25% by using the MEPCB compared with the conventional metal core printed circuit board (MCPCB). Benefiting from the excellent thermal performance of the MEPCB, up to 24.14% increase in steady state luminous flux was obtained compared with the MCPCB. Moreover, the correlated color temperature (CCT) shift value between 150 mA and 900 mA could be controlled within 93 K. This work demonstrates that the MEPCB is more suitable for LEDs working at wide current ranges.     

Energy–exergy analysis and modernization suggestions for a combined‐cycle power plant

Energy and exergy analysis were carried out for a combined‐cycle power plant by using the data taken from its units in operation to analyse a complex energy system more thoroughly and to identify the potential for improving efficiency of the system. In this context, energy and exergy fluxes at the inlet and the exit of the devices in one of the power plant main units as well as the energy and exergy losses were determined. The results show that combustion chambers, gas turbines and heat recovery steam generators (HRSG) are the main sources of irreversibilities representing more than 85% of the overall exergy losses. Some constructive and thermal suggestions for these devices have been made to improve the efficiency of the system. Copyright © 2005 John Wiley & Sons, Ltd.     

Enhanced heat transfer analysis of latent functionally thermal fluid

A physical model has been developed to analyze the enhanced heat transfer process of the latent functionally thermal fluid with microencapsulated phase‐change material. The problem is solved by the combination of the finite difference method and the moving heat source method. The calculated results reveal that putting the phase‐change microcapsules into the fluids can enhance the heat transfer capabilities of the mixture. The effects of capsule radius and concentration of particles are numerically predicted. The numerical results provide the theoretical basis for the application and design of the latent functionally thermal fluid. © 2004 Wiley Periodicals, Inc. Heat Trans Asian Res, 33(6): 383–392, 2004; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/htj.20025     

一种功率因数校正电路在LED驱动器上的应用研究

论述了功率因数校正的原理,讨论了功率因数校正的一些方法,提出了一种应用于LED驱动器的新型功率因数校正电路.试制了一个用于100 W LED驱动电路的功率因数校正样机,实验表明,该样机的功率因数大于0.99,电流总谐波小于6％.     

Modeling and performance of microscale thermophotovoltaic energyconversion devices

We analyze the feasibility of energy conversion devices that exploit microscale radiative transfer of thermal energy in thermophotovoltaic devices. By bringing a hot source of thermal energy very close to a receiver fashioned as a pn-junction, the near-field effect of radiation tunneling can enhance the net power flux. We use the fluctuational electrodynamic approach to microscale radiative transfer to account for the spacing effect, which provides the net transfer of photons to the receiver as a function of the separation between the emitter and receiver. We calculate the power output from the microscale device using standard thermophotovoltaic device relations. The results for the performance of a device based on indium gallium arsenide indicate that a ten-fold increase in power throughput may be realized with little loss in efficiency. Furthermore, we develop a model of the microscale device itself that indicates the influence of semiconductor band-gap, energy, carrier lifetime and doping