Heat Sink Temperature Research Articles

Flicker Modeling of White Light Emitting Diode With Sinusoidal Waveform

Based on the properties of light emitting diode (LED) source and driver, this article proposes a prediction model for the dynamic optical properties of LED sources. With a series of parameters for LED device (heatsink temperature, thermal resistance of LED source, heat dissipation coefficient, coefficients of luminous efficacy, and LED numbers) and driver (frequency and power amplitude), it is possible to accurately quantify dynamic light output of LED source and then to predict the flicker index and percent flicker. Optical and thermal evaluations are included in the modeling, which makes it easy for LED designers to comply with the regulations. Experimental validation of the proposed prediction model has been carried out using LED samples. It appears that the agreement between measured and calculated results of LED sources is fairly good with an average relative error of 5.3%.

Effects of working fluid mixtures on the exergetic sustainability of a solar-biomass organic Rankine cycle power plant

This study assessed the effects of working fluid mixtures on the exergetic sustainability of a solar-biomass organic Rankine cycle (ORC) plant. The design features of a real ORC plant operational at Ottana (Italy) were employed for analyses. Although a lot of studies exist in the literature on thermo-economic implications of mixture working fluids in ORC plants, the aspect of sustainability is often left out. The desire to bridge this gap is the key motivation for this study. Zero-dimensional models were implemented in MATLAB for the design of all the hybrid plant units. The ORC design considered as working fluids the existing pure MM, and mixtures 0.1MM/0.9MDM, 0.8MM/0.2MDM, and 0.9MM/0.1MDMselected actively from the REFPROP database. Furthermore, established off-design models were incorporated into the ORC simulations. The exergetic sustainability index (ESI), the environmental effect factor (EEF), the exergetic improvement potential rate (IP), and the exergetic recoverability ratio (RECR) were adopted as sustainability performance indicators. Additionally, the destruction factor (DF) was used to assess the effects of a working fluid mixture on the sustainability performance of the ORC at the component level. Results showed that under design conditions, the mixture 0.1MM/0.9MDM had worse ESI than pure MM by about 1.5%, while the mixtures 0.8MM/0.2MDM and 0.9MM/0.1MDM improved ESI by about 1.6% and 2%, respectively. At off-design conditions, the optimum HTF mass flow rate with the highest ESI was obtained as about 7 kg/s for all the fluids. For the HTF temperature, 260 o C was obtained as the optimum for the mixture 0.8MM/0.2MDM, and 250 o C for all the other fluids. Also, decreasing the heat sink temperature in all fluids increases linearly the system ESI. Moreover, the ORC condenser showed the highest DF of over 70% for all the fluids, and the use of the best mixture (0.9MM/0.1MDM) as the ORC working fluid would increase the condenser DF by about 2 percentage points relative to pure MM. Future studies should seek to derive a set of general criteria that would aid the selection of cycle and working fluid mixture designs in favor of sustainability.

방열판의 온도를 이용한 IGBT 모듈 및 공랭시스템의 상태 모니터링

The insulated gate bipolar transistor (IGBT) is one of the weakest components in the converter. Therefore, high reliability is very important in terms of price. However, it is very difficult to monitor IGBT’s condition because it is not easy to directly measure the junction temperature in practice. And cooling system also important element of converter, but additional method should be used to monitor cooling system. This paper proposes a method of monitoring the condition of IGBT module and cooling system at once by heatsink temperature that is easy to measure. Advantage of proposed method is very easy to implement without interfering operation of IGBT. Simulation tests were conducted to verify the effectiveness and accuracy of this proposed method. The results show that the proposed method can improve accuracy of the reliability of power converter.

High power density thermal management of discrete semiconductor packages enabled by additively manufactured hybrid polymer-metal coolers

Discrete-packaged wide bandgap (WBG) semiconductor devices provide a flexible and cost-effective solution for scalable highly dense power electronics. However, their utilization at high power levels is limited due to various challenges, while the effective thermal management if one of them. We develop a liquid cooled thermal management solution for discrete semiconductor packages using polymer-metal hybrid cooling structure design and integration. Coolant flowing through an additively manufactured polymer manifold is guided to finned metal heat sinks having low thermal resistance and overall mass. Here, we study a number of prototypes designed for integration of silicon carbide (SiC) MOSFETs in TO-247 package. The cooling integration is benchmarked with a baseline design having an aluminum heat sink with square inline pin fins. The cooling strategy is tested experimentally with results used to validate a finite element numerical approach. Fin design parameters including fin height, thickness, spacing, and arrangement are studied to assess their impact on heat sink temperature and pressure drop. Zigzag fins showed the most promising performance when compared to straight fins, inline fins, and staggered pin fins. The zigzag design showed lower maximum temperatures at comparable pressure drop with the baseline design. The impact of thermophysical properties of the cooling fluid (water, ethylene glycol, and Novec 7300), heat sink (copper and aluminum), and electrical isolation (gap pad, aluminum nitride) are also reported. The optimal design employing zigzag fins with a copper heat sink and an aluminum nitride heat spreader achieved 32.5 % improvement in thermal performance over the baseline design with a modest 60 % increase in pressure drop and 68 % higher mass. The optimized design enables a maximum heat rejection capability of 225 W per single MOSFET package, an equivalent to 75 W/cm2 heat flux dissipation using single phase cooling.

Power Plant Cycles: Evolution towards More Sustainable and Environmentally Friendly Technologies

The scarcity of energy and water resources and rising temperatures due to climate change has set the focus on improving the energy efficiency of power plant thermodynamic cycles to adapt to higher heat sink temperatures and use fewer resources for energy production. In this work, a review of power production thermodynamic cycles is presented: from Brayton to Rankine and combined cycles, alongside particular cycles such as Organic Rankine Cycles, Kalina, Goswami or the more recently developed Hygroscopic Cycle. The efficiency of these cycles and their possible improvements are considered, as well as their environmental impact. Costs associated with existing power plants found in the literature have also been included in the study. The main existing facilities for each cycle type are assessed, and the most sustainable options in terms of resource consumption (fuel, water, etc.) and future perspectives to ensure both their energy efficiency and sustainability are identified.

Topology Optimization Design of Micro-Channel Heat Sink by Considering the Coupling of Fluid-Solid and Heat Transfer

To investigate the effect of the target weight coefficient on the structure design of the micro-channel heat sink, an innovative method for the topology optimization design of micro-channel structures with different bifurcation angles is adopted. In this study, the improved interpolation function, density filtering, and hyperbolic tangent projection methods are adopted to obtain a clear topological structure of the micro-channel heat sink. The heat transfer of the micro-channel heat sink under different bifurcation angles is compared. At the same time, the influence of the two different objective functions, heat transfer, and flow energy consumption, is analyzed in the topology optimization of micro-channel heat sinks. The results show that when the bifurcation angle is 135°, both the heat transfer and the average outlet temperature of the micro-channel heat sink obtain the maximum value, and the heat transfer effect is the best. With the increase of the heat transfer weighting coefficient, the distribution of solid heat sources in the main channel increases, and the refinement of the branch channels also increases. On the other hand, although the heat transfer effect of the micro-channel heat sink is the best, the corresponding flow energy consumption is larger.

2.7 μm GaSb-based distributed feedback lasers with laterally coupled gratings

We report on a high-performance GaSb-based quantum well laterally coupled distributed feedback laser emitting at wavelength of 2.7 μm. The first-order grating structure of chromium(Cr) is designed to obtain the maximum coupling coefficient, and is defined alongside the ridge waveguide by electron beam lithography. The DFB laser emits an output power of 4.3 mW in a single-mode operation at a heat-sink temperature of 20 °C. Continuous wavelength tuning has been obtained by varying the injection current at a tuning rate of 0.012 nm mA−1. The mixmum side mode suppression ratio is as high as 54.9 dB, which is the highest value ever reported at the wavelength region of 2.7 μm. In addition, the loss margin introduced by Cr gratings is estimated to be 5.02

Sensitivity analysis of avoidable and unavoidable exergy destructions in a parallel double‐effect LiBr–water absorption cooling system

AbstractA parametric study has been carried out based on advanced exergy assessment for a parallel double‐effect LiBr–water absorption chiller. The advanced exergy method provides the real potential of the equipment for improvement in the system by recognizing the avoidable irreversibilities. The sensitivity analysis of various parts of the exergy destruction (endogenous avoidable, endogenous unavoidable, exogenous avoidable, and exogenous unavoidable) in system components and the overall performance (coefficient of performance, exergy efficiency, and modified exergy efficiency) of the system has been done to identify the actual potential of different components of the system to improve the overall performance of the system relative to operational parameters. Operational parameters include the heat source temperature, heat sink temperature, and the difference between the absorption and condensation temperature. The results showed that by modifying and improving the performance of components, 18.5% of the total exergy destruction of the system could be reduced. The modified exergy efficiency reduces sharply (nearly 40%) with the rising heat sink temperature. The endogenous exergy destruction increases in all system components except the condenser and evaporator by the heat source temperature increase. With the increase in the heat sink temperature, the avoidable part of the total exergy destruction in the system increases due to the significant rise in the avoidable exogenous exergy destruction in the components, and the unavoidable endogenous exergy destruction decreases (more than 200%) in the absorber. Increasing the condensation temperature reduces the unavoidable endogenous exergy destruction in the components except for the low‐temperature heat exchanger.

48 W Continuous-Wave Output From a High- Efficiency Single Emitter Laser Diode at 915 nm

Improving the power and efficiency of 9xx-nm broad-area laser diodes has a great help in reducing the cost of laser systems and expanding applications. This letter presents an optimized epitaxial structure with high power and conversion efficiency. Laser diodes with 230 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mu \text{m}$ </tex-math></inline-formula> emitter width and 5 mm cavity length deliver continuous-wave output power up to 48.5 W at 48 A, 30 °C, the highest power reported for 9xx-nm single emitter lasers so far. The slope efficiency is as high as 1.23 W/A due to a low internal optical loss of 0.31 cm−1 and a high internal efficiency of 96%. The maximum power conversion efficiency reaches 72.6% at 15.3 W and 67.3% at the operating power of 30 W under a heatsink temperature of 25 °C. Life test results show no failure in 1000 hours for 55 laser diodes.

Investigation of the Thermal Performance of a Nanofluid-filled Grooved Cylindrical Heat Pipe for Electronics Cooling

Thermal management of electric and electronic components is a critical issue and needs to consider enhanced cooling systems such as heat pipes. This study deals with the theoretical modeling of a nanofluid-filled copper cylindrical heat pipe for electronics cooling applications. The heat pipe includes helicoidal and trapezoidal capillary grooves. The model can predict the capillary limit as well as the heat transfer in the different sections of the heat pipe. The thermal resistances of the evaporation and condensation sections are calculated based on correlations for heat transfer, which are determined from experiments. Two working nanofluids are considered: water/CuO and water/Al2O3. The thermal performances are predicted for different concentrations and heat sink temperatures, and the heat pipe is positioned horizontally. For both nanofluids, the results indicate that augmenting the concentration of the nanoparticles leads to a capillary limit increase reaching up to 14 % and 25 % for water/Al2O3 and water/CuO, respectively, and an overall thermal resistance decrease reaching up to 51 % and 68 % for water/Al2O3 and water/CuO. Moreover, decreases up to 24 %, and up to 18 % in the evaporator wall temperatures are obtained for water/CuO and water/Al2O3 nanofluids, respectively. The nanofluid water/CuO gives the best thermal performance whatever the nanoparticle concentration and heat sink temperature.

Temperature control of a heat source using a loop heat pipe integrated with a thermoelectric converter

The paper presents the results of experimental studies of automatic temperature control of a heat source cooled by a loop heat pipe integrated with a thermoelectric converter. The power supply of the thermoelectric converter was regulated by a PID controller having feedback on the heat source temperature. The tests were carried out under conditions of varying the heat load value of the heat source from 10 to 320 W at the set points of the heat source temperature of 20, 40 and 60 °C, of the heat sink temperature from −10 to +30 °C and of the slope angles of 0° and +90°. It was shown that the control system makes it possible to control the heat source temperature with an accuracy of ±0.2 °C in the stationary mode and with a short-term deviation from the set value of no more than 2.5 °C with a sharp change in the heat load. Additional logical conditions were also tested, which were included in the controller program and ensured the operability of the loop heat pipe when starting from low heat loads and exiting the control mode at maximum heat loads.

Thermodynamic Analysis and Working Fluid Selection of a Novel Cogeneration System Based on a Regenerative Organic Flash Cycle

Recently proposed organic flash cycles maintain lower irreversibility in the evaporator than traditional organic Rankine cycles. This study presented a novel combined heat and power system that was based on a regenerative organic flash cycle, in order to improve thermal efficiency. Parametric analyses for the proposed combined heat and power system were carried out, using six working fluids, and performed with heat source temperatures and heat sink temperatures that ranged from 130 °C to 170 °C, and from 20 °C to 40 °C, respectively. The results showed that the preferable working fluid was altered, with a change in the operating condition. Isopentane, R1234ze(Z), R1233zd(E), and R245fa performed better at a cooling water temperature of 20 °C. The system that used R245fa showed more promising performance when the heat source temperatures were set to 150 °C and 160 °C. R365mfc was determined to be the best working fluid at a heat source temperature of 150 °C, and at cooling water temperatures of 30–40 °C. Finally, the analyses evaluated the year-round system performance on the basis of monthly ambient and water temperatures in Daegu, Korea, as the system’s parameters. Compared to the single regenerative organic flash cycle, the thermal efficiency of the novel system improved significantly, from 8.37 % to 32.80% in August, and to 74.34% in February.

Performance analysis of heat pumps with zeotropic mixtures at different load conditions

Heat pump cycles with zeotropic mixtures as working fluids and temperature glides on both heat sink and heat source sides are analyzed. Five binary zeotropic mixtures, selected based on previous studies in the literature, are examined. The cycles are initially optimized for each binary mixture at three different heat source temperature glides (10–30 K) and fixed heat sink temperature glide (30 K). The variation in the heating COP of the optimized designs is then computed and compared for five different part load scenarios down to 40% of the design point heating load. The design point optimization is performed for different single and double-compression cycle layouts, based on which the standard vapor compression cycle with a suction gas heat exchanger is adopted as the most economical option for the rest of the study. The part load cycle simulations demonstrate that, when the heat source temperature glide is large, two of the studied part load scenarios can lead to increased COP; these are when the reduction in the heating load is due to (1) an increase in both the heat sink (e.g. district heating water) inlet and heat source (e.g. process water) outlet temperatures, and (2) a decrease in both heat sink and source flow rates. Moreover, it is observed that different mixtures show different levels of sensitivity to a decrease in heating load. Among the studied mixtures, DME/Iso-Pentane while outperforming others in all studied cases, has the most unfavorable trend at part load, hence losing its benefit margin over other candidates.

CFD analysis and environmental assessment on the heat transfer and flow of the pure water or water/silver Nano fluid coolants in a plate-fin heat sink applying two-phase mixture model

Environmental impacts are the consequences caused by the elementary flows on human health, plants, and animals (ecological health) or by the future availability of natural resources (resource depletion). The heat transfer characteristics of a plate-fin heatsink were investigated using a 3-dimensional numerical analysis based on the two-phase mixture model. The effect of using NF, fin spacing, and fin height on the performance of the system were studied considering the constant heat flux of 100 kW/m2 at the bottom of heatsink and NF inlet temperature of 300 K. The results showed that the increase in the secondary fin height (hsf) from 5 mm to 17.5 mm leads to increase in the pressure drop by 11.6%, 52%, to improve the heat convection coefficient (h) by 32.92%-23.84%, and consequently reduces the central processing unit (CPU) mean temperature by 4.31% and 2.34% for Re=500-2000. The maximum performance evaluation criterion (PEC) was obtained as 1.11-1.05 at Re numbers of 500-2000 for heatsink with hsf=12.5 mm. In addition, the optimum location for the secondary fin was determined to be at the mid-space of two primary fins (dsf=0.5 mm) which leads to improving h by 18%-5% at Re numbers of 500-2000 as compared to other fin spacing scenarios. Moreover, the intensification of nanoparticle concentration (ψ) leads to improve h by 15.71%-17.21% for Re=500-2000. Besides, the escalation of ψ decreases the pressure drop by 14.18% for all Re numbers. The PEC of the system with hsf=12.5 mm, ψ=1%, at Re=2000 was obtained as the highest PEC of 1.226 among the other studied cases. According to the design, the heat sink has an environmental impact of 0.5233.

Analysis of a New Super High Temperature Hybrid Absorption-Compression Heat Pump Cycle

Utilization of high-temperature energy in industrial production processes is often exhausted by huge low-temperature waste heat without recovery. Thus, energy efficiency is quite limited. Heat pumps are widely used as a high-efficiency waste heat recovery system and are divided into vapor compression cycle, driven by electricity, and absorption type, driven by steam or hot water. However, compression heat pumps are quite difficult to reach more than 100 °C due to the temperature and compression limits of compressors and the working medium. Meanwhile, the COP (coefficient of performance) of an absorption heat pump is quite low due to the thermodynamic cycle characteristics. In order to increase the outlet temperature and COP significantly, a new type of compression-absorption hybrid heat pump cycle is presented and simulated. Compared with traditional cycles, this heat pump can reach the heat sink temperature of 200 °C with a highly satisfactory COP. This heat pump could reach the optimal COP of 3.249 when the pressure ratio of the compressor is 6.5, the coupling temperature of the low-pressure stage is 55 °C and the coupling temperature of the high-pressure stage is 73 °C. Exergy analysis shows that evaporators and condensers show better efficiency. This heat pump could be promising in different kinds of heat recovery.

A novel compression-assisted energy storage heat transformer for low-grade renewable energy utilization

Thermal energy storage is a promising method to balance the timing mismatch between the intermittent energy sources and time-variable user loads but cannot address the low-grade issue, which results in the underutilization of low-temperature renewable energy. An absorption-based energy storage heat transformer (ESHT) can achieve temperature upgrading with satisfactory storage performance. To further improve the system performance, a novel compression-assisted ESHT (CESHT) is proposed. The dynamic characteristics of the basic ESHT and CESHT cycles are analyzed and compared. Then, the effects of heat output, heat input, and heat sink temperatures on the cycle performance are investigated. Results show that significant enhancements are achieved by the CESHT cycle for both energy storage performance and temperature upgrading ability. With auxiliary compression, the temperature lift is increased from 30 °C to 65 °C, and the required input temperature is decreased from 60 °C to 45 °C. Moreover, the performance indexes are greatly improved, e.g., the energy storage efficiency, energy storage density, and exergy efficiency are respectively increased from 0.24 to 0.43, from 35.2 kWh/m3 to 282.7 kWh/m3, and from 0.32 to 0.54 with a temperature lift of 30 °C. The proposed cycle demonstrates the advantages of enhanced storage performance and large temperature lift.

Investigation of a loop heat pipe to achieve high heat flux by incorporating flow boiling

• A loop heat pipe incorporating flow boiling is proposed for high heat flux dissipation. • The device combines the virtues of LHPs as self-driven and flow boiling as high heat transfer limit. • An injector serves as a pump and provides liquid for a boiling chamber. • The boiling chamber achieves a heat dissipation capability several times higher than the evaporator. A loop heat pipe incorporating flow boiling (LHPFB) was proposed to meet the heat dissipation requirement of high heat flux devices. A boiling chamber was arranged for high heat flux dissipation, where flow boiling was realized. An injector was designed to serve as a pump without introducing any moving parts and extra energy consumption. Moreover, the heat transfer performance of the LHPFB was investigated under various operating conditions, and its operation mechanism was revealed by visualization study. The results indicated that the vapor coming from the evaporator was the driving source of the injector, whose entrainment characteristics provided a large amount of liquid for the boiling chamber. The boiling chamber performed satisfactorily and achieved a heat dissipation capability several times higher than the evaporator. It was also found that higher heat sink temperature resulted in higher operating temperature and lower heat transfer limit of the boiling chamber, with the maximum heat flux of 103.3 W·cm −2 and 87.8 W·cm −2 at heat sink temperature of 5 °C and 35 °C respectively. Compared with the conventional loop heat pipes, the LHPFB had substantially higher heat transfer limit. Therefore, it is a promising device for high heat flux dissipation.

Lumped Thermal Coupling Model of Multichip Power Module Enabling Case Temperature as Reference Node

Insulated gate bipolar transistor (IGBT) modules with multiple chips have wide range of applications, and the correct estimation for the thermal behaviors inside IGBT modules is becoming crucial. Thermal impedance matrix is one of the most adopted approaches to describe the thermal-coupling effect of IGBT module. For simplicity of analysis, the heatsink or ambient temperature is typically chosen as the reference node for the thermal-coupling impedance term, while the case temperature is simplified or ignored. This letter provides a thermal coupling model enabling case temperature as reference node. This proposed model decouples the thermal coupling impedances of IGBT module itself and external cooling condition, so that the modeling of cooling conditions outside device and inside the power module, can be separately considered. The characterization method and advantages of the proposed model are verified by an experimental demonstration, and the potential applications are further discussed.

P‐4.6: High‐efficiency and high‐power 660 nm laser diode

A highly reliable and high-power laser diode with 110 um stripe width is designed and fabricated. At 25 °C, the lasing wavelength is 660.2 nm at 1.5 A and low threshold current of 506.4 mA can be obtained. At the output power of 2.5 W, the wall-plug efficiency (WPE) can achieve 48.7%. In addition, it can produce as high as 5.1 W at 25 °C and the maximum power can still reach over 4.2 W at 40 °C under CW. Attributed to the non-absorbing mirror, the catastrophic optical degradation (COD) power of this device can reach 6.5 W at 20°C. Till now, the laser diodes have stably operated for 510 hours at the operation current of 2.0 A and heatsink temperature of 40 °C.

Continuous-wave distributed Bragg reflector quantum cascade lasers with fine single-mode tuning up to 102 °C at [formula omitted

We have demonstrated an 8.4μm stable single-mode quantum cascade laser using a two-section distributed Bragg reflector design. Output power of 252 mW, a threshold current density of 1.04 kA/cm2, and a characteristic temperature of 206 K were achieved during continuous-wave operation at room temperature. Robust single-mode emissions with all side-mode suppression ratios exceeding 25 dB were obtained at injection currents ranging from 420 mA to 900 mA and heat-sink temperatures ranging from 10 °C to 102 °C. Benefiting from the physical isolation of the two sections and from being mounted epilayer-side down on patterned submounts, the tiny tuning coefficients of the device are −0.003014 cm−1mA−1 and −0.0762 cm−1K−1. This type of single-mode quantum cascade laser with fine tuning characteristics is required to perform accurate detection of trace gases.