Zhang Lenan

Zhang Lenan
Massachusetts Institute of Technology | MIT · Department of Mechanical Engineering

About

63
Publications
21,191
Reads
How we measure 'reads'
A 'read' is counted each time someone views a publication summary (such as the title, abstract, and list of authors), clicks on a figure, or views or downloads the full-text. Learn more
1,015
Citations

Publications

Publications (63)
Article
Full-text available
Jumping-droplet condensation is promising for various applications where the droplet size distribution plays a key role in the overall system performance. Despite being extensively studied in recent works, inconsistencies existed in previous size distribution models as the droplet growth and removal mechanisms were often not properly described. Her...
Article
Full-text available
Atomically thin two-dimensional (2D) materials have shown great potential for applications in nanoscale electronic and optical devices. A fundamental property of these 2D flakes that needs to be well characterized is the thermal expansion coefficient (TEC), which is instrumental to the dry transfer process and thermal management of 2D material-base...
Article
Full-text available
Solar desalination holds significant promise for the water-energy nexus. Recent advances in passive solar desalination using thermal localization show great potential for high-efficiency freshwater production, which is particularly beneficial for areas without well-established water and energy infrastructure. However, there is a significant knowled...
Article
Bubble growth and departure are ubiquitous phenomena in gas-evolving reactions, which govern the overall energy and mass transport. However, an in-depth understanding of the relationship between bubble dynamics and the electrochemical processes, in particular, the wettability effect on a gas-evolving porous electrode remains elusive. Here, we repor...
Article
The boiling crisis determines the maximum heat flux for the safe operation of boiling equipment, which is widely used in various applications including power generation, thermal management of electronics and water desalination. Here we present a mechanistic and predictive theory for the boiling crisis, combining the thermo-fluidic interaction betwe...
Article
Sorption and desorption with hygroscopic hydrogels hold significant promise for thermal management, passive cooling, thermal energy storage, and atmospheric water harvesting. However, a comprehensive understanding of the energy and mass transport mechanisms in hygroscopic hydrogels remains missing, impeding accurate modeling and optimization. In th...
Article
The efficiency of a heat engine can be significantly improved by operating in a high-temperature and high-pressure environment, which is crucial for a wide range of applications such as hybrid and electric aviation as well as power generation. However, such extreme operating conditions pose severe challenges to the heat exchanger design. Although r...
Article
Full-text available
Boiling is an effective energy transfer process with substantial utility in energy applications. Boiling performance is described mainly by the heat transfer coefficient (HTC) and critical heat flux (CHF). Recent efforts for the simultaneous enhancement of HTC and CHF have been limited by an intrinsic trade‐off between them — HTC enhancement requir...
Article
Full-text available
Flexible thermoelectric generators (f-TEGs) are promising solutions to power supply for wearable devices. However, the high fabrication costs and low output power density of conventional f-TEGs limit their applications. Here, we present a bulk-material-based f-TEG featuring multifunctional copper electrodes for heat concentration and dissipation an...
Article
Full-text available
Recent advances in thermally localized solar evaporation hold significant promise for vapor generation, seawater desalination, wastewater treatment, and medical sterilization. However, salt accumulation is one of the key bottlenecks for reliable adoption. Here, we demonstrate highly efficient (>80% solar-to-vapor conversion efficiency) and salt rej...
Article
Full-text available
Sorption and desorption with hygroscopic hydrogels hold significant promise for thermal management, passive cooling, thermal energy storage, and atmospheric water harvesting. However, a comprehensive understanding of the energy and mass transport mechanisms in hygroscopic hydrogels remains missing, impeding accurate modeling and optimization. In th...
Article
The critical heat flux during pool boiling has been investigated for a range of applications including electrical power generation and thermal management. Reported experimental CHF values during pool boiling of water on flat metallic surfaces, however, show a large discrepancy across studies. Here, we address this discrepancy in CHF values by accou...
Article
Boiling heat transfer is dictated by interfacial phenomena at the three-phase contact line where vapor bubbles form on the surface. Structured surfaces have shown significant enhancement in critical heat flux (CHF) during pool boiling by tailoring interfacial phenomena. This CHF enhancement has been primarily explained by two structural effects: ro...
Data
Supporting Information for "Toward optimal heat transfer of 2D-3D heterostructures via van der Waals binding effects"
Article
We describe a customized Capillary Breakup Extensional Rheometer (CaBER) with improved dynamic performance and added features for temperature control over the range from room temperature up to 250 °C. The system is aimed at characterizing the extensional rheological behavior of weakly rate-thickening fluids that are widely utilized in the automotiv...
Article
Full-text available
Non-thermalized electrons in metals, featured by deviation from the Fermi-Dirac distribution, have recently shown potential to facilitate realization of ultrafast photonic devices such as all-optical modulators. Dissection of non-thermalized electron dynamics and its influence on optical response of metals is therefore essential for optimization of...
Article
Full-text available
Antibubbles are fluid entities with the inverse phase of regular bubbles. While the structure and stability of antibubbles have been studied, a fundamental understanding of antibubble formation remains limited. We report a theoretical and experimental study of antibubble formation. In the experiment, pairs of surfactant-laden water drops impinged s...
Article
Full-text available
Nucleation site distribution is ubiquitous in many natural and industrial processes, such as liquid-to-vapor phase change, gas-evolving reactions, and solid-state material growth. However, a comprehensive understanding of nucleation site distribution remains elusive. These limitations are due to the challenge of probing micro/nanoscopic nucleation...
Article
Full-text available
Bubble nucleation is ubiquitous in gas evolving reactions that are instrumental for a variety of electrochemical systems. Fundamental understanding of the nucleation process, which is critical to system optimization, remains limited as prior works generally focused on the thermodynamics and have not considered the coupling between surface geometrie...
Article
Saturated steam (>121 oC and >205 kPa) is widely used in the medical sterilization process known as autoclaving. However, solar-driven steam generation at such high temperature and pressure requires expensive optical concentrators. We demonstrate a passive solar thermal device mostly built from low-cost off-the-shelf components capable of deliverin...
Article
The relationship between bubble departure frequency and diameter is fundamental to the boiling process and needs to be fully understood for prediction of overall boiling heat transfer performance. Hydrody-namic models for bubble departure were developed in previous studies. However, these models could not explain the dependence of bubble frequency...
Article
Recent work has demonstrated adsorption-based solar-thermal-driven atmospheric water harvesting (AWH) in arid regions, but the daily water productivity (L/m 2 /day) of devices remains low. We developed and tested a dual-stage AWH device with optimized transport. By recovering the latent heat of condensation of the top stage and maintaining the requ...
Article
Boiling is a ubiquitous process in many applications including power generation, desalination, and high-heat flux electronic cooling. At the same time, boiling is a complicated physical process involving hydrodynamics and interfacial heat and mass transfer on multiple scales. One of the key limiting factors of boiling is the critical heat flux (CHF...
Article
Full-text available
Environmental scanning electron microscopy (ESEM) is a powerful technique that enables imaging of diverse specimens (e.g., biomaterials, chemical materials, nanomaterials) in a hydrated or native state while simultaneously maintaining micro-to-nanoscale resolution. However, it is difficult to achieve high signal-to-noise and artifact-free secondary...
Article
Full-text available
Evaporation plays a critical role in a range of technologies that power and sustain our society. Wicks are widely used as passive, capillary-fed evaporators, attracting much interest since these devices are highly efficient, compact, and thermally stable. While wick-based evaporators can be further improved with advanced materials and fabrication t...
Article
Full-text available
The time-domain thermoreflectance (TDTR) technique has been widely used to measure thermal properties. The design and interpretation of the TDTR experiment rely on an in-depth understanding of the thermoreflectance signature for a given metal thermal transducer. Although the TDTR signals of several metal thermal transducers have been experimentally...
Article
Full-text available
During pool boiling, a significantly high heat flux leads to the transition from nucleate boiling to film boiling, where a vapor film forms over the boiling surface, drastically increasing thermal resistance. This transition at the critical heat flux (CHF) results in an abrupt increase in surface temperature and can lead to catastrophic failure of...
Article
Full-text available
The simultaneous imaging of magnetic fields and temperature (MT) is important in a range of applications, including studies of carrier transport, and semiconductor device characterization. Techniques exist for separately measuring temperature (e.g., infrared (IR) microscopy, micro-Raman spectroscopy, and thermo-reflectance microscopy) and magnetic...
Article
Full-text available
Passive vapor generation systems with interfacial solar heat localization enable high-efficiency low-cost desalination. In particular, recent progress combining interfacial solar heating and vaporization enthalpy recycling through a capillary-fed multistage architecture, known as the thermally-localized multistage solar still (TMSS), significantly...
Article
Full-text available
Recent progress in passive radiative cooling technologies has substantially improved cooling performance under direct sunlight. Yet, experimental demonstrations of daytime radiative cooling still severely underperform in comparison with the theoretical potential due to considerable solar absorption and poor thermal insulation at the emitter. In thi...
Article
Light propagation in random scattering media is a common phenomenon in many scientific and engineering fields. Because of light-matter interaction, part of the light transmitted through a random scattering medium is diffuse and causes haze. Previous approaches to manipulate haze in random media mainly focused on regulating scattering and paid littl...
Preprint
Full-text available
Inspired by non-Hermitian physics, Li et al. (Science 364, 170-173) theoretically predicted and experimentally demonstrated a stationary temperature profile in a diffusive heat transfer system-seemingly indicating that heat "stops" diffusing. By analogy to the wave physics framework, the motionless and moving temperature profiles are manifestations...
Article
High-flux evaporators are important for various fundamental research and industrial applications. Understanding the heat loss mechanisms, especially the contribution of natural convection during evaporation is thus a ubiquitous process to predict and optimize the performance of evaporators. However, a comprehensive analysis on natural convection he...
Method
Full-text available
In this study, we used the transport of intensity equation to reconstruct the phase of an electron wave. In this section, we provide the method to adapt the transport of intensity equation to electron-beam imaging. The propagation of the electron wave in a uniform medium can be described by the homogenous Helmholtz equation, ∇ 2 í µí±ˆ(í µí²“) + í...
Preprint
Full-text available
The simultaneous imaging of magnetic fields and temperature (MT) is important in a range of applications, including studies of carrier transport, solid-state material dynamics, and semiconductor device characterization. Techniques exist for separately measuring temperature (e.g., infrared (IR) microscopy, micro-Raman spectroscopy, and thermo-reflec...
Article
Full-text available
Recovering tiny nanoscale features using a general optical imaging system is challenging because of poor signal to noise ratio. Rayleigh scattering implies that the detectable signal of an object of size d illuminated by light of wavelength λ is proportional to d6/λ4, which may be several orders of magnitude weaker than that of additive and multipl...
Article
Full-text available
Recovering tiny nanoscale features using a general optical imaging system is challenging because of poor signal to noise ratio. Rayleigh scattering implies that the detectable signal of an object of size d illuminated by light of wavelength λ is proportional to d 6 /λ 4 , which may be several orders of magnitude weaker than that of additive and mul...
Article
Full-text available
Haze in optically transparent aerogels severely degrades the visual experience, which has prevented their adoption in windows despite their outstanding thermal insulation property. Previous studies have primarily relied on experiments to characterize haze in aerogels, however, a theoretical framework to systematically investigate haze in porous med...
Article
Full-text available
Environmental scanning electron microscopy (ESEM) is a broadly-utilized nanoscale inspection technique capable of imaging wet or insulating samples. It extends the application of conventional scanning electron microscopy (SEM) and has been extensively used to study the behavior of liquid, polymer and biomaterials by allowing for a gaseous environme...
Article
2020 American Chemical Society. The simultaneous imaging of magnetic fields and temperature (MT) is important in a range of applications, including studies of carrier transport and semiconductor device characterization. Techniques exist for separately measuring temperature (e.g., infrared (IR) microscopy, micro-Raman spectroscopy, and thermo-reflec...
Article
Full-text available
Thin film evaporation on microstructured surfaces is a promising strategy for high heat flux thermal management. To enhance fundamental understanding and optimize the overall heat transfer performance across a few microns thickness liquid film, however, requires detailed thermal characterizations. Existing characterization techniques using infrared...
Conference Paper
Full-text available
Jumping-droplet condensation has demonstrated promising heat transfer performance compared to dropwise condensation due to the high-efficient coalescence-induced shedding. Accurate modeling of the jumping-droplet condensation is crucial to provide in-depth understanding of the phenomenon. However, most models relied on extensions of traditional dro...
Conference Paper
Full-text available
Micro and nanostructures to enhance liquid-to-vapor phase change heat transfer for cooling high-performance electronics have attracted significant attention owing to their ability to generate capillary flow and thin-film area. Typically, heat transfer measurements are performed remotely (i.e., away from the three-phase contact line) due to limitati...
Article
Full-text available
Micro-EDM milling is an effective machining process for three-dimension micro-cavity of high hardness materials. Fix-length compensation method is an efficient compensation method for cavity milling by improving single layer thickness. A truncated cone shaped end is formed under fix-length compensation method by using tubular electrode. This paper...
Article
Full-text available
As semiconductor devices based on silicon reach their intrinsic material limits, compound semiconductors, such as gallium nitride (GaN), are gaining increasing interest for high performance, solid-state transistor applications. Unfortunately, higher voltage, current, and/or power levels in GaN high electron mobility transistors (HEMTs) often result...
Article
Due to inevitable wear of electrodes in micro electrical discharge machining (μEDM), compensation of tools is of great importance to maintain machining accuracy. Among all of the compensation strategies, fix-length compensation method is one of the most efficient ways for cavity milling because large single layer thickness can be achieved. However,...
Article
In electrical discharge machining (EDM) process, tool wear is an inevitable phenomenon that adversely affects the geometrical accuracy of machined features. A theoretical model accounting for tool wear during EDM process is hence the basis study for high precision machining. However, in most modeling studies on tool wear and electrode shape, the sp...
Article
Full-text available
Micro-EDM milling is an effective machining process for three-dimension (3D) micro-cavity of high hardness materials. Because of the sharp wear of the electrode, fix-length compensation method is proposed, thus results in a cone-shaped electrode. This compensation method can produce a slot with stable depth and conic cross-section. Because of layer...
Article
Full-text available
In a recent experimental study by Lau and Nathan [“Influence of Stokes number on the velocity and concentration distributions in particle-laden jets,” J. Fluid Mech. 757, 432 (2014)], it was found that particles in a turbulent pipe flow tend to migrate preferentially toward the wall or the axis depending on their Stokes number (St). Particles with...
Article
Full-text available
Micro-EDM milling is an effective machining process for three-dimension micro-cavity of high hardness materials. However, tools wear sharply in micro milling, thus several compensation methods are applied. The present study examines the fix-length compensation method, and the initial experiments show that a cone-shaped tool end is formed with this...

Projects

Projects (5)
Project
Develop new optical and imaging techniques and explore their applications in interdisciplinary researches
Project
Understand the fundamental mechanics of EDM and propose improved manufacture strategy for industrial applications.