Jianying Du

Bio: Jianying Du is an academic researcher from Xiamen University. The author has contributed to research in topics: Waste heat & Electricity generation. The author has an hindex of 3, co-authored 6 publications receiving 24 citations.

Quantum-dot heat engines with irreversible heat transfer

Abstract: This work establishes a quantum heat engine considering qubits as the external heat transfer mediums. The authors find that the efficiency and the power output of the quantum heat engine are closely dependent on the microproperties of qubits, and consequently relate the irreversible heat transfer with quantum effects. The equivalent conditions between the quantum heat engines and the classical endoreversible Carnot heat engines are revealed

Designing high-performance nighttime thermoradiative systems for harvesting energy from outer space.

Abstract: Energy harvesting using thermoradiative systems has been extensively explored in recent years as a novel strategy for further reducing our energy footprint. However, the nighttime application, thermodynamic limit, and optimal design of such a system remain largely unaddressed so far. Here we propose an improved nighttime thermoradiative system (NTS) for electrical power generation by optically coupling Earth's surface with outer space. Our theoretical model predicts that the NTS operating with Earth (deep space) at 300 K (3 K) yields a maximum power density of 12.3Wm-2 with an efficiency limit of 18.5%, which is potentially more advantageous than previous nighttime energy harvesting systems, such as a nighttime thermoelectric generator. We find that optimizing the thickness of the active layer, enhancing thermal infrared emission, and employing a silver backreflector for photon recycling are crucially important in improving system performance. This Letter provides new insights for the optimal designs of NTSs and paves the way toward practical nighttime power generation.

Efficiency at maximum power: An analytically solvable model for stochastic heat engines

Abstract: We study a class of cyclic Brownian heat engines in the framework of finite-time thermodynamics. For infinitely long cycle times, the engine works at the Carnot efficiency limit producing, however, zero power. For the efficiency at maximum power, we find a universal expression, different from the endoreversible Curzon-Ahlborn efficiency. Our results are illustrated with a simple one-dimensional engine working in and with a time-dependent harmonic potential.

Space–charge limited current in nanodiodes: Ballistic, collisional, and dynamical effects

Abstract: This Perspective reviews the fundamental physics of space–charge interactions that are important in various media: vacuum gap, air gap, liquids, and solids including quantum materials. It outlines the critical and recent developments since a previous review paper on diode physics [Zhang et al. Appl. Phys. Rev. 4, 011304 (2017)] with particular emphasis on various theoretical aspects of the space–charge limited current (SCLC) model: physics at the nano-scale, time-dependent, and transient behaviors; higher-dimensional models; and transitions between electron emission mechanisms and material properties. While many studies focus on steady-state SCLC, the increasing importance of fast-rise time electric pulses, high frequency microwave and terahertz sources, and ultrafast lasers has motivated theoretical investigations in time-dependent SCLC. We particularly focus on recent studies in discrete particle effects, temporal phenomena, time-dependent photoemission to SCLC, and AC beam loading. Due to the reduction in the physical size and complicated geometries, we report recent studies in multi-dimensional SCLC, including finite particle effects, protrusive SCLC, novel techniques for exotic geometries, and fractional models. Due to the importance of using SCLC models in determining the mobility of organic materials, this paper shows the transition of the SCLC model between classical bulk solids and recent two-dimensional (2D) Dirac materials. Next, we describe some selected applications of SCLC in nanodiodes, including nanoscale vacuum-channel transistors, microplasma transistors, thermionic energy converters, and multipactor. Finally, we conclude by highlighting future directions in theoretical modeling and applications of SCLC.

Performance optimization of thermionic refrigerators based on van der Waals heterostructures

Abstract: In this paper, an irreversible thermionic refrigerator model based on van der Waals heterostructure with various irreversibilities is established by utilizing combination of non-equilibrium thermodynamics and finite time thermodynamics. The basic performance characteristics of the refrigerator are obtained. The effects of key factors, such as bias voltages, Schottky barrier heights and heat leakages, on the performance are studied. Results show that cooling rates and coefficients of performances (COPs) can attain the double maximum with proper modulation of barrier heights and bias voltages. Increasing cross-plane thermal resistance as well as decreasing electrode-reservoir thermal resistance and reservoir-reservoir thermal resistance can enhance the performance of the device. The optimal performance region is the interval between the maximum cooling rate point and the maximum COP point. By modulating the bias voltage, the working state of the device can fall into the optimal performance region. The optimal performance of the refrigerator when using single layer graphene and a few layers graphene as electrode material is also compared.

Progress Toward High Power Output in Thermionic Energy Converters

Abstract: Thermionic energy converters are solid-state heat engines that have the potential to produce electricity with efficiencies of over 30% and area-specific power densities of 100 Wcm-2. Despite this prospect, no prototypes reported in the literature have achieved true efficiencies close to this target, and many of the most recent investigations report power densities on the order of mWcm-2 or less. These discrepancies stem in part from the low-temperature ( 1 Wcm-2 and employing emitter temperatures of 1300 K or higher. With this result in mind, this review provides an overview of historical and current design architectures and comments on their capacity to realize the efficiency and power potential of thermionic energy converters. Also emphasized is the importance of using standardized efficiency metrics to report thermionic energy converter performance data.