Multi-Layer Thermionic-Tunneling Structures for Power Generation

2005 ◽  
Author(s):  
Taofang Zeng
Keyword(s):  
Heat Transfer ◽  
Power Generation ◽  
Electron Transport ◽  
Heat Source ◽  
Heat Sink ◽  
Interface Design ◽  
Thermionic Emission ◽  
Power Generator ◽  
Layer Structures ◽  
Substantial Temperature

A new method for power generation based on nano-engineered interface design with partially filled gap is proposed. The device combines electron thermionic emission and tunneling to enhance electron transport. Thermal radiation and tunneling contribute to heat transfer in the device, which can be minimized using selected materials. The largely reduced heat transfer coupled with use of multi-layer structures enable a substantial temperature difference between heat source and heat sink or two electrodes, thereby maximizing heat source utilization. Detailed analyses are provided for the solid device operating either as a power generator or as a cooler.

Mixed Convection of Impinging Air Cooling Over Heat Sink in Telecom System Application

2004 ◽  
Vol 126 (4) ◽  
pp. 519-523 ◽  
Author(s):  
Siddharth Bhopte ◽  
Musa S. Alshuqairi ◽  
Dereje Agonafer ◽  
Gamal Refai-Ahmed
Keyword(s):  
Heat Transfer ◽  
Heat Source ◽  
Mixed Convection ◽  
Heat Sink ◽  
Three Dimensional ◽  
Source Surface ◽  
Air Cooling ◽  
Transfer Rates ◽  
Nusselt Numbers ◽  
Air Jet

The current numerical investigation will examine the effect of an impinging mixed convection air jet on the heat transfer rate of a parallel flat plate heat sink. A three-dimensional numerical model was developed to evaluate the effects of the nozzle diameter d, nozzle-to-target vertical placement H/d, Rayleigh number, and the jet Reynolds number on the heat transfer rates from a discrete heat source. Simulations were performed for a Prandtl number of 0.7 and for Reynolds numbers ranging from 100 to 5000. The governing equations were solved in the dimensionless form using a commercial finite-volume package. Average Nusselt numbers were obtained, at H/d=3 and two jet diameters, for the bare heat source, for the heat source with a base heat sink, and for the heat source with the finned heat sink. The heat transfer rates from the bare heat source surface have been compared with the ones obtained with the heat sink in order to determine the overall performance of the heat sink in an impingement configuration.

Micro-Feature Heat Exchanger Using Variable-Density Arrays for Near-Isothermal Cold Plate Operation

2015 ◽  
Author(s):  
Noris Gallandat ◽  
Danielle Hesse ◽  
J. Rhett Mayor
Keyword(s):  
Heat Transfer ◽  
Heat Source ◽  
Flow Rate ◽  
Heat Sink ◽  
Convective Heat Transfer Coefficient ◽  
Water Flow Rate ◽  
Variable Density ◽  
Flow Path ◽  
Cold Plate ◽  
Reduced Pressure

The purpose of this paper is to demonstrate the possibility to selectively tune the convective heat transfer coefficient in different sections of a heat sink by varying the density of micro-features in order to minimize temperature gradients between discrete heat sources positioned along the flow path. Lifetime of power electronics is strongly correlated to the thermal management of the junction. Therefore, it is of interest to have constant junction temperatures across all devices in the array. Implementation of micro-feature enhancement on the convective side improves heat transfer due to an increase in surface area. Specific shapes such as micro hydrofoils offer a reduced pressure drop allowing for combined improvement of heat transfer and flow performance. This study presents experimental results from an array of three discrete heat source (20 × 15 mm) generating 100 W/cm2 and positioned in line along the flow path with a spacing of 10 mm between each of the sources. The heat sink was machined out of aluminum 6061 and micro-hydrofoils with a characteristic length of 500 μm were embedded in the cold plate. The cooling medium used is water at a flow rate of 3.6–13.4 g/s corresponding to a Reynolds number of 420–1575. It is demonstrated that the baseplate temperature can be maintained below 90°C and the difference between the maximum temperatures of each heat source is less than 6.7 °C at a heat flux of 100 W/cm2 and a water flow rate of 4.8 g/s.

Energy Payback Optimization of Thermoelectric Power Generator Systems

2010 ◽  
Author(s):  
Kazuaki Yazawa ◽  
Ali Shakouri
Keyword(s):  
Power Generation ◽  
Heat Source ◽  
Thermal Resistance ◽  
Thermoelectric Power ◽  
Output Power ◽  
Heat Sink ◽  
Generation System ◽  
Thermoelectric Power Generation ◽  
Energy Payback ◽  
Power Generation System

An analytic model for optimizing thermoelectric power generation system is developed and utilized for parametric studies. This model takes into account the external thermal resistances with hot and cold reservoirs. In addition, the spreading thermal resistance in the module substrates is considered to find the impact of designing small fraction of thermo elements per unit area. Previous studies are expanded by a full optimization of the electrical and thermal circuits. The optimum condition satisfies both electrical load resistance match with the internal resistance and the thermal resistance match with the heat source and the heat sink. Thermoelectric element aspect ratio and fill factor are found to be key parameters to optimize. The optimum leg length and the maximum output power are determined by a simple formula. The output power density per mass of the thermoelectric material has a peak when thermo elements cover a fractional area of ∼1%. The role of the substrate heat spreading for thermoelectric power generation is equally significant as thermoelement. For a given heat source, the co-optimization of the heat sink and the thermoelectric module should be performed. Active cooling and the design of the heat sink are customized to find the energy payback for the power generation system. The model includes both the air cooled heat sinks and the water cooled micro channels. We find that one can reduce the mass of thermoelement to around 3∼10% of that in commercial modules for the same output power, as long as the module and elements are designed properly. Also one notes that higher heat flux sources have significantly larger energy payback and reduced cost per output power.

scholarly journals Experimentation of a Wearable Self-Powered Jacket Harvesting Body Heat for Wearable Device Applications

2021 ◽  
Vol 2021 ◽  
pp. 1-22
Author(s):  
Atif Sardar Khan ◽  
Farid Ullah Khan
Keyword(s):  
Heat Transfer ◽  
Power Generation ◽  
Heat Transfer Coefficient ◽  
Thermal Resistance ◽  
Transfer Coefficient ◽  
Heat Sink ◽  
Energy Harvester ◽  
Wearable Devices ◽  
Cold Side ◽  
Self Powered

The development of special wearable/portable electronic devices for health monitoring is rapidly growing to cope with different health parameters. The emergence of wearable devices and its growing demand has widened the scope of self-powered wearable devices with the possibility to eliminate batteries. For instance, the wearable thermoelectric energy harvester (TEEH) is an alternate to batteries, which has been used in this study to develop four different self-powered wearable jacket prototypes and experimentally validated. It is observed that the thermal resistance of the cold side without a heat sink of prototype 4 is much greater than the rest of the proposed prototypes. Besides that, the thermal resistance of prototype 4 heat sinks is even lower among all proposed prototypes. Therefore, prototype 4 would have a relatively higher heat transfer coefficient which results in improved power generation. Moreover, an increase in heat transfer coefficient is observed with an increase in the temperature difference of the cold and hot sides of a TEEH. Thus, on the cold side, a heat flow increases which benefits heat dissipation and in turn reduces the thermal resistance of the heat sink. Besides that, the developed prototypes on people show that power generation is also affected by factors like ambient temperature, person’s activity, and wind breeze and does not depend on the metabolism. A different mechanism has been explored to maximize the power output within a 16.0 cm2 area, in order to justify the wearability of the energy harvester. Furthermore, it is observed that during the sunlight, any material covering the TEEH would improve the performance of prototypes. Prototypes are integrated into jacket and studied extensively. The TEEH system was designed to produce a maximum delivering power and power density of 699.71 μW and 43.73 μW/cm2, respectively. Moreover, the maximum voltage produced is 62.6 mV at an optimal load of 5.6 Ω. Furthermore, the TEEH (prototype 4) is connected to a power management circuit of ECT310 and LTC3108 and has been able to power 18 LEDs.

scholarly journals Maximum work output of multistage continuous Carnot heat engine system with finite reservoirs of thermal capacity and radiation between heat source and working fluid

2010 ◽  
Vol 14 (1) ◽  
pp. 1-9 ◽  
Author(s):  
Jun Li ◽  
Lingen Chen ◽  
Fengrui Sun
Keyword(s):  
Heat Transfer ◽  
Heat Source ◽  
Heat Sink ◽  
Heat Engine ◽  
Thermal Capacity ◽  
Working Fluid ◽  
Work Output ◽  
Maximum Work ◽  
Engine System ◽  
Maximum Work Output

Optimal temperature profile for maximum work output of multistage continuous Carnot heat engine system with two reservoirs of finite thermal capacity is determined. The heat transfer between heat source and the working fluid obeys radiation law and the heat transfer between heat sink and the working fluid obeys linear law. The solution is obtained by using optimal control theory and pseudo-Newtonian heat transfer model. It is shown that the temperature of driven fluid monotonically decreases with respect to flow velocity and process duration. The maximum work is obtained. The obtained results are compared with those obtained with infinite low temperature heat sink.

scholarly journals Using Graphene-Based Grease as a Heat Conduction Material for Hectowatt-Level LEDs: A Natural Convection Experiment

Processes ◽  
2021 ◽  
Vol 9 (5) ◽  
pp. 847
Author(s):  
Chih-Neng Hsu ◽  
Keng-Wei Lee ◽  
Chun-Chih Chen
Keyword(s):  
Heat Transfer ◽  
Heat Conduction ◽  
Natural Convection ◽  
Heat Source ◽  
Thermal Performance ◽  
Contact Surface ◽  
Heat Sink ◽  
Heat Sources ◽  
Light Emitting ◽  
Performance Capacity

In this study, a self-adjusting concentration of graphene thermal grease was developed to reduce the contact surface thermal resistance of 50 W light-emitting diodes (LEDs). The purpose was to identify an important type of heat conduction material with a high thermal conductivity coefficient, which can be applied to the contact surface of various high-heat sources or concentrated heat sources to achieve seamless heat transfer with an extremely low thermal resistance state. The contact heat conduction material conductivity reached the highest K value of 13.4 W/m·K with a 15 wt.% self-adjusting concentration of graphene grease. This material could continuously achieve a completely uniform and rapid thermal diffusion of heat energy. Therefore, we performed an analysis of chip-on-board light-emitting diodes (LEDs) with a highly concentrated heat source, which showed excellent heat dissipation under natural convection heat transfer. As such, this study achieved the natural convection mechanism and a heat sink volume thermal performance capacity of 473,750 mm3 for LEDs under 50 W, but those over 50 W require an enhanced forced convection solution and a heat sink volume thermal performance capacity between 473,750 mm3 and 947,500 mm3. If the heat source dissipation reaches 100 W, the volume capacity must be at least 947,500 mm3 for lighting equipment applications. In the experimental study, we also verified and analyzed the research data, including an analysis of the measured data, grease component wt.%, heat sink material selection, increase in heat sink volume, heat transfer path, and contact surface, a discrimination analysis of infrared thermal images, and an analysis of flow visualization, which were conducted to ensure quantitative and qualitative improvement, provide a mechanism for judging the technical performance, and provide research results to enable discussion.

Direct Power Generation Using Tunneling and Thermionic Emission

Volume 4 ◽  
2004 ◽  
Author(s):  
Taofang Zeng
Keyword(s):  
Electron Transport ◽  
Work Function ◽  
High Efficiency ◽  
Experimental Studies ◽  
Thermionic Emission ◽  
Single Layer ◽  
Phonon Transport ◽  
Parallel Plates ◽  
Power Generator ◽  
Daunting Task

Thermionic emission in vacuum could be a highly efficient cooler or power generator if the work function, the minimum work for electrons to go into vacuum, is around 0.3–0.4 eV for heat source at a temperature below 500C [Mahan, 1994]. Unfortunately, the work function of existing materials is currently above 1 eV. Theoretical and experimental studies have shown that the work function can be reduced to 0.3–0.4 eV if the distance between the two electrodes (cathode and anode) of the thermionic emission cooler/power generator is below 10 nm [Hishinuma, et al, 2001, 2003]. At this nanometer scale, electron transport between the two electrodes takes two paths: electron tunneling and thermionic emission. The combined physical processes result in a desired work function. However, maintaining a nanometer gap for two parallel plates within an area larger than 1 cm2 is a daunting task, if not impossible, especially if the power generator is mounted on a moving or vibrating device. Even a slight vibration or thermal expansion of the two plates (electrodes) could cause direct contact between the two plates (electrodes), and thus shorten the circuits. Thus vacuum thermionic power generator based on difficult to make and to operate [Tavkhelidze, et al., 2002]. In this study, we propose to use a solid insulating spacer for preventing the shortening and for feasibility of manufacturing. The spacer is less than 5nm, and electron transport as thermionic emission and tunneling concurrently. In this study, we first investigate electron and phonon transport in single-layer (spacer) double heterostructures by including the tunneling effects. It is found that single-layer generator can have a high efficiency, but small power intensity due to the small temperature difference between the two electrodes. We then investigate the efficiency of multilayer-layer power generator. Calculations show that the solid power generator operating at a temperature below 500°C, can have an efficiency of larger than 40% of the Carnot efficiency.

scholarly journals Research on Performance Test Characteristics of Solar Energy ORC Generator Set

2018 ◽  
Vol 232 ◽  
pp. 04007
Author(s):  
Yongkang Zhang ◽  
Jinghui Song ◽  
Yunfeng Xia
Keyword(s):  
Heat Transfer ◽  
Power Generation ◽  
Heat Source ◽  
Organic Rankine Cycle ◽  
Rankine Cycle ◽  
Working Fluid ◽  
Source Condition ◽  
Power Cycle ◽  
Solar Powered ◽  
Regenerative Cycle

In order to study the performance of low-temperature solar-powered ORC generator sets, a solar-powered ORC power generation test bench was designed and built. In the experiment, R-123 was used as the organic Rankine cycle working fluid, and the solar ORC power generation system was experimentally studied. The research results show that when the direct solar radiation intensity is about 400W, the temperature of the heat transfer oil at the outlet of the collector can reach 140 °C. When the temperature of the heat transfer oil at the outlet of the collector is around 110°C, the collector efficiency of the collector can reach about 60%. Under the heat source condition, when the power cycle part is switched from the basic cycle to the regenerative cycle mode, the collector heat collection efficiency can reach about 60%. Under the heat source condition, when the power cycle part is switched from the basic cycle mode to the regenerative cycle mode, the measured efficiency is increased from 9.3% to 10.8%, and the measured cycle efficiency is increased from 1.57% to 1.67%, which is an increase of 6.07%. The measured cycle system efficiency is about 10%, and the heat recovery mode is slightly higher than the basic cycle mode. The organic Rankine cycle performance under different working fluid flows was also investigated in the experiment. The maximum measured average power was 386.27 W when the working fluid flow was 6.88 kg·s. At a certain heat source temperature, as the flow rate of the working fluid increases, the inlet pressure of the expander increases, and the circulating output work also increases. Under a certain working fluid flow rate, as the temperature of the heat source increases, the temperature of the inlet of the expander increases, and the inlet pressure increases. the cycle output work also increased.

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