Design and fabrication development of a micro flow heated channel with measurements of the inside micro-scale flow and heat transfer process

The current work provides a design and fabrication technique for a micro channel system that can provide a uniform heat flux boundary condition on the channel wall and a well insulation on the wall to prevent heat loss from the channel to the outside ambient. Therefore, detailed micro-scale flow and heat transfer process and information along the channel can be studied. Semiconductor sensor material was selected to fabricate both the heaters and the arrays of temperature sensors on a silicon substrate. These heaters and sensors were then moved to a low thermal conductivity epoxy-glass substrate for fabrication of the channel. Design consideration and fabrication techniques involved in this processes will be discussed. A final measurement for the validation of the heaters and the sensors fabricated and a study of the flow friction behavior and the heat transfer coefficient distributions inside the micro channel will be presented. The local Nusselt number distrubution inside the micro channel is reported the first time in the open literature.     

Fabrication of titanium based MALDI bacterial chips for rapid, sensitive and direct analysis of pathogenic bacteria

For the first time, we report the fabrication of a titanium bacterial chip for MALDI-MS produced from a simple, cost effective and rapid heat treatment process. This bacterial chip can be reused many times and is highly versatile. These bacterial chips serve dual roles: (1) They can be applied as MALDI-MS target plates for direct and highly sensitive bacterial analysis. (2) They can be used as bacterial sensors for direct analysis of the captured bacteria using MALDI-MS. The sensitivity of these chips when used as bacterial sensors is <10(3)cfu/mL. The lowest detectable concentration for direct MALDI-MS analysis was found to be 10(4)cfu/mL. The results were further justified by using standard plate counting method combined with Tukey-Kramer statistical analysis and fluorescence imaging followed by image processing for fluorescence quantification using ImageJ software to substantiate the MALDI-MS results.     

Rapid nested-PCR for tyrosinase gene detection on chip

The availability of non-invasive, fast and sensitive technologies for detection of circulating cancer cells is still a critical need of clinical oncology, particularly for diagnosis of aggressive and highly metastatic tumors, like malignant melanoma. Here we present the first nested polymerase chain reaction process carried out by a microfabricated, hybrid plastic-glass microfluidic chip on the tyrosinase gene, a predictive marker for melanoma diagnosis. The device is a hybrid system consisting of a glass microchannel embedded in an elastomeric matrix, and operating in flow-oscillating modality on a droplet of biological sample. The convection heat transfer and the temperature distribution inside the carrier fluid in the device are investigated. The oil responds to temperature changes with a characteristic time around 53 s, and exhibits three different thermal gradients along the capillary, with temperature variations below 4°C in correspondence of heater electrodes. The sample heating/cooling rates in the chip are as high as 16°C/s, allowing rapid processes. The nested polymerase chain reaction process is performed in less than 50 min, namely more than four times faster than in a standard thermocycler. The rapidity of the analysis method, combined with the simple and low-cost fabrication, reduced sample evaporation, and flexibility of the overall microfluidic platform, make it promising for the detection of events of tumor spreading.     

Frontal impingement of nanojets: formation,disintegration and mixing of nano liquid sheets

We investigate nano liquid sheets formed by frontal impingement of two cylindrical nanojets using the molecular dynamics method. The results show that only with a high enough velocity can a stable liquid sheet be formed because of the strong surface tension effect in nanoscale. In relatively low jet velocity range, the relationship between the intact sheet radius and the jet velocity takes on the power function form with the power being ? 0.502. This relationship is explained by considering the thermal fluctuation effect, thus confirming the dominating role of the thermal fluctuation effect in the disintegration process. The influence of the jet velocity on the time-domain evolution of mixing of the system and the spatial mixing distribution of the liquid sheet are also investigated. Our results suggest that nanojets do not coalesce at the impingement point, the mixing occurs mainly through diffusion. And there is recoil that happens at the stagnation plane.     

Containment sensors for the determination of L-lactate and glucose

This paper reports some new results on enzyme based silicon containment sensors. For the first time an L-lactate sensor in containment technology is presented. Through optimization of the buffer system the stability of the lactate sensor was enhanced and the linear response of over 10 mM was achieved. The glucose sensor has also been optimized for a large linear measurement range exceeding 30 mM. A two-enzyme chip with glucose and lactate sensor elements which were integrated on one silicon chip is presented. The response behaviour of the two-enzyme chip was very similar to the single chip behaviour. No cross-talking effects could be observed. A fabrication process for mass-production is described.     

Biomaterial-based infrared detection

This effort is focused on the use of crustacyanin protein extracted from the lobster shell in IR detection and imaging applications. In addition to the protein's excellent reversible thermo-active response in the IR region of interest, electrical characteristics versus temperature showed that the protein can be used as an electro-optic thermal sensing device as well. The high sensitivity and fast response of the protein layer were further enhanced by the deposition process we used. The thin coatings were prepared by Langmuir-Blodgett and self-assembly techniques. Furthermore, the protein exhibited temperature variation under Ti:sapphire laser excitation at different wavelengths in ambient environment. We have also shown that the protein exhibits fluorescence properties after exposure to IR heat. Stability of the protein, which is important in this type of application, was also demonstrated using the different characterization techniques after repeated heating/cooling cycles. We can conclude that this protein represents a formidable candidate for the fabrication of IR sensors and microbolometers for uncooled IR imaging applications.     

Numerical Modeling and Analysis of Grooved Surface Applied to Film Cooling

In order to improve the efficiency of film cooling,numerical investigation was carried out to study the effects of different film-cooled plates on surface heat transfer.Both grooved and non-grooved surfaces were concerned.The modeling was performed using Fluent software with the adoption of Shear-Stress Transport (SST) k-co model as the turbulence closure.The coolant was supplied by a single film cooling hole with an inclination angle of 30°.The Mach numbers for the coolant flow and the mainstream flow were fixed at 0 and 0.6,respectively.At three blowing ratios of 0.5,1.0 and 1.5,the aerodynamic behaviour of the mixing process as well as the heat transfer performance of the film cooling were presented.The numerical results were validated using experimental data extracted from a benchmark test.Good agreements between numerical results and the experimental data were observed.For the film cooling efficiency,it shows that both local and laterally averaged cooling effectiveness can be improved by the non-smooth surface at different blowing ratios.Using the grooved surface,the turbulence intensity upon the plate can be reduced notably,and the mixing between the two flows is weakened due to the reduced turbulence level.The results indicate that the cooling effectiveness of film cooling can be enhanced by applying the grooved surface.     

Longitudinal distribution of canine respiratory heat and water exchanges

We assessed the longitudinal distribution of intra-airway heat and water exchanges and their effects on airway wall temperature by directly measuring respiratory fluctuations in airstream temperature and humidity, as well as airway wall temperature, at multiple sites along the airways of endotracheally intubated dogs. By comparing these axial thermal and water profiles, we have demonstrated that increasing minute ventilation of cold or warm dry air leads to 1) further penetration of unconditioned air into the lung, 2) a shift of the principal site of total respiratory heat loss from the trachea to the bronchi, and 3) alteration of the relative contributions of conductive and evaporative heat losses to local total (conductive plus evaporative) heat loss. These changes were not accurately reflected in global measurements of respiratory heat and water exchange made at the free end of the endotracheal tube. Raising the temperature of inspired dry air from frigid to near body temperature principally altered the mechanism of airway cooling but did not influence airway mucosal temperature substantially. When local heat loss was increased from both trachea and bronchi (by increasing minute ventilation), only the tracheal mucosal temperature fell appreciably (up to 4.0 degrees C), even though the rise in heat loss from the bronchi about doubled that in the trachea. Thus it appears that the bronchi are better able to resist changes in airway wall temperature than is the trachea. These data indicate that the sites, magnitudes, and mechanisms of respiratory heat loss vary appreciably with breathing pattern and inspired gas temperature and that these changes cannot be predicted from measurements made at the mouth. In addition, they demonstrate that local heat (and presumably, water) sources that replenish mucosal heat and water lost to the airstream are important in determining the degree of local airway cooling (and presumably, drying).     

Heat transfer during cryopreservation by perfusion through the vascular system

An analytical study was performed to determine whether it is possible to uniformly freeze or thaw biological tissue by perfusion with a fluid that transfers heat along the vascular system. A simple criterion was developed to evaluate the thermal performance of heat transfer fluids. The results show that fluids that have been considered in the past for heating or cooling by perfusion are unable to transfer heat uniformly through the tissue.     

Biomimetic MXene Textures with Enhanced Light‐to‐Heat Conversion for Solar Steam Generation and Wearable Thermal Management

2D materials are of particular interest in light‐to‐heat conversion, yet challenges remain in developing a facile method to suppress their light reflection. Herein, inspired by the black scales of Bitis rhinoceros, a generalized approach via sequential thermal actuations to construct biomimetic 2D‐material nanocoatings, including Ti₃C₂T_x MXene, reduced graphene oxide (rGO), and molybdenum disulfide (MoS₂) is designed. The hierarchical MXene nanocoatings result in broadband light absorption (up to 93.2%), theoretically validated by optical modeling and simulations, and realize improved light‐to‐heat performance (equilibrium temperature of 65.4 °C under one‐sun illumination). With efficient light‐to‐heat conversion, the bioinspired MXene nanocoatings are next incorporated into solar steam‐generation devices and stretchable solar/electric dual‐heaters. The MXene steam‐generation devices require much lower solar‐thermal material loading (0.32 mg cm^?2) and still guarantee high steam‐generation performance (1.33 kg m^?2 h^?1) compared with other state‐of‐the‐art devices. Additionally, the mechanically deformed MXene structures enable the fabrication of stretchable and wearable heaters dual‐powered by sunlight and electricity, which are reversibly stretched and heated above 100 °C. This simple fabrication process with effective utilization of active materials promises its practical application value for multiple solar–thermal technologies.     

Emerging Materials and Strategies for Personal Thermal Management

In this decade, the demands of energy saving and diverse personal thermoregulation requirements along with the emergence of wearable electronics and smart textiles give rise to the resurgence of personal thermal management (PTM) technologies. PTM, including personal cooling, heating, insulation, and thermoregulation, are far more flexible and extensive than the traditional air/liquid cooling garments for the human body. Concomitantly, many new advanced materials and strategies have emerged in this decade, promoting the thermoregulation performance and the wearing comfort of PTM simultaneously. In this review, an overview is presented of the state‐of‐the‐art and the prospects in this burgeoning field. The emerging materials and strategies of PTM are introduced, and classed by their thermal functions. The concept of infrared‐transparent visible‐opaque fabric (ITVOF) is first highlighted, as it triggers the work on advanced PTM by combining it with radiative cooling, and the corresponding implementations and realizations are subsequently introduced, followed by wearable heaters, flexible thermoelectric devices, and sweat‐management Janus textiles. Finally, critical considerations on the challenges and opportunities of PTM are presented and future directions are identified, including thermally conductive polymers and fibers, physiological/psychological statistical analysis, and smart PTM strategies.     

Application of Bioinspired Superhydrophobic Surfaces in Two-phase Heat Transfer Experiments

This paper addresses the potential to use Lotus leaf bioinspired surfaces in applications involving heat transfer with phase change,namely pool boiling and spray impingement.Besides describing the role of bioinspired topographical features,using an innovative technique combining high-speed visualization and time-resolved infrared thermography,surface durability is also addressed.Water is used for pool boiling and for spray impingement systems (simplified as single droplet impact),while HFE7000 is used in a pool boiling cooler for electronic components.Results show that surface durability is quickly compromised for water pool boiling applications,as the chemical treatment does not withstand high temperatures (T ＞ 100 ℃) during long time intervals (3 h-4 h).For HFE7000 pool boiling (depicting lower saturation temperature-34 ℃),heat transfer enhancement is governed by the topography.The regular hierarchical pattern of the bioinspired surfaces promotes the heat transfer coefficient to increase up to 22.2％,when compared to smooth surfaces,while allowing good control of the interaction mechanisms until a distance between micro-structures of 300 μm-400 μm.Droplet impingement was studied for surface temperatures ranging between 60 ℃-100 ℃.The results do not support the use of superhydrophobic surfaces for cooling applications,but reveal great potential for other applications involving droplet impact on heated surfaces (e.g.metallurgy industry).     

Review of biomaterial thermal property measurements in the cryogenic regime and their use for prediction of equilibrium and non-equilibrium freezing applications in cryobiology

It is well accepted in cryobiology that the temperature history and cooling rates experienced in biomaterials during freezing procedures correlate strongly with biological outcome. Therefore, heat transfer measurement and prediction in the cryogenic regime is central to the field. Although direct measurement of temperature history (i.e. heat transfer) can be performed, accuracy is usually achieved only for local measurements within a given system and cannot be readily generalized to another system without the aid of predictive models. The accuracy of these models rely upon thermal properties which are known to be highly dependent on temperature, and in the case of significant cryoprotectant loading, also on crystallized fraction. In this work, we review the available thermal properties of biomaterials in the cryogenic regime. The review shows a lack of properties for many biomaterials in the subzero temperature domain, and especially for systems with cryoprotective agents. Unfortunately, use of values from the limited data available (usually only down to −40 °C) lead to an underestimation of thermal property change (i.e. conductivity rise and specific heat drop due to ice crystallization) with lower temperatures. Conversely, use of surrogate values based solely on ice thermal properties lead to an overestimation of thermal property change for most biomaterials. Additionally, recent work extending the range of available thermal properties to −150 °C has shown that the thermal conductivity will drop in both PBS and tissue (liver) due to amorphous/glassy phases (versus crystalline) of biomaterials with the addition of cryoprotective additives such as glycerol. Thus, we investigated the implications of using approximated or constant property values versus measured temperature-dependent values for predicting temperature history during freezing in PBS (phosphate-buffered saline) and porcine liver with and without cryoprotectants (glycerol). Using measured property values (thermal conductivity, specific heat, and latent heat of phase change) of porcine liver, a standard was created which showed that values based on surrogate ice properties under-predicted cooling times, while constant properties (i.e. based on limited data reported near the freezing point) over-predicted cooling times. Additionally, a new iterative numerical method that accommodates non-equilibrium cooling effects as a function of time and position (i.e. crystallization versus amorphous phase) was used to predict temperature history during freezing in glycerol loaded systems. Results indicate that in addition to the increase in cooling times due to the lowering of thermal diffusivity with more glycerol, non-equilibrium effects such as the prevention of maximal crystallization (i.e. amorphous phases) will further increase required cooling times. It was also found that the amplified effect of non-equilibrium cooling and crystallization with system size prevents the thermal history to be described with non-dimensional lengths, such as was possible under equilibrium cooling. These results affirm the need to use accurate thermal properties that incorporate temperature dependence and crystallized fraction. Further studies are needed to extract thermal properties of other important biomaterials in the subzero temperature domain and to develop accurate numerical methods which take into account non-equilibrium cooling events encountered in cryobiology when partial or total vitrification occurs.     

Thermal time constant estimation in warming and cooling ectotherms

(1) Measurement of physiological control of warming and cooling in reptiles requires calculating the thermal time constant (tau) of the animal. (2) Previously reported methods of estimating tau are sensitive to multiple problems including measurement error in operative environmental temperature and equilibrium body temperature, drift of environmental temperatures, requirements for extremely simple thermal environments, and ill conditioning of the estimation techniques themselves. (3) We propose a physiologically based heat transfer model which is less sensitive to common experimental errors, more numerically robust, and can provide physiologically meaningful estimates of time constants. (4) The method presented here allows time constants to be measured for animals subjected to the traditional step change experiment as well as to shorter periods of warming and cooling such as during shuttling.     

Analysis of electric and magnetic fields leaking from induction heaters

Results are presented of an investigation on electric and magnetic fields leaking from inductive (magnetic) heaters that are used for thermal processing of high-power electron tubes and lasers in an industrial plant. Measurements of electric and magnetic fields were done using both commercially available and laboratory-developed instrumentation. Isotropic H-field sensors were developed to allow quantitative evaluation of high-intensity magnetic fields. Ten induction heaters with nominal A.C. power ranging from 2.5 kW to 15 kW and operating at frequencies between 300 kHz and 790 kHz were surveyed. Electric field strengths up to 8 kV/m and magnetic field strengths up to 20 A/m were measured.     

Numerical analysis of the cooling effect of blood over inflamed atherosclerotic plaque

Atherosclerotic plaques with high likelihood of rupture often show local temperature increase with respect to the surrounding arterial wall temperature. In this work, atherosclerotic plaque temperature was numerically determined during the different levels of blood flow reduction produced by the introduction of catheters at the vessel lumen. The temperature was calculated by solving the energy equation and the Navier-Stokes equations in 2D idealized arterial models. Arterial wall temperature depends on three basic factors: metabolic activity of the inflammatory cells embedded in the plaque, heat convection due to luminal blood flow, and heat conduction through the arterial wall and plaque. The calculations performed serve to simulate transient blood flow reduction produced by the presence of thermography catheters used to measure arterial wall temperature. The calculations estimate the spatial and temporal alterations in the cooling effect of blood flow and plaque temperature during the measurement process. The mathematical model developed provides a tool for analyzing the contribution of factors known to affect heat transfer at the plaque surface. Blood flow reduction leads to a nonuniform temperature increase ranging from 0.1 to 0.25 degrees Celsius in the plaque/lumen interface of the arterial geometries considered in this study. The temperature variation as well as the Nusselt number calculated along the plaque surface strongly depended on the arterial geometry and distribution of inflammatory cells. The calculations indicate that the minimum required time to obtain a steady temperature profile after arterial occlusion is 6 s. It was seen that in arteries with geometries involving bends, the temperature profiles appear asymmetrical and lean toward the downstream edge of the plaque.     

Elastic-plastic finite elements analysis of transient and residual stresses in ceramo-metal restorations

Transient and residual stresses occurring in partially fixed dental prostheses after the firing process can be calculated with elastic or elastic-plastic finite element analyses (FEA). In this study, firstly, the mechanical and thermal properties at various temperatures of the materials used in a porcelain fused metal (PFM) system were obtained by experimental and literature studies. The effects of viscoelastic and viscoplastic behaviours of the dental porcelain at the elevated temperatures were reflected onto its elastic properties. The equivalent heat transfer coefficients were determined experimentally by measuring temperatures and the results were supplied as input to the 3D finite elements analysis. It has been observed that the maximum stresses occur within a short time period after cooling begins and that stresses decrease during the cooling process and remain at a constant value at the end of cooling; these are the thermal residual stresses.     

Analysis of oscillatory flow disturbances and thermal characteristics inside fluidic cells due to fluid leakage and wall slip conditions

The effects of both fluid leakage and wall slip conditions are studied analytically and numerically on the fluctuation rate in the flow inside non-isothermal disturbed thin films supported by soft seals within a fluidic cell. Flow disturbances due to internal pressure pulsations and external squeezing are considered in this work. The main controlling parameters are found to be the dimensionless leakage parameter, softness of the seal, squeezing number, dimensionless slip parameter, the thermal squeezing parameter and the power law index. Accordingly, their influences on the fluctuation rate and heat transfer characteristics inside disturbed thin films are determined and discussed. It is found that an increase in the dimensionless leakage parameter, softness of the seal-upper plate assembly and the wall slip parameter result in more cooling and an increase in the fluctuation level in the flow. However, an increase in the squeezing number and the fluid power index decrease flow fluctuations. Finally, a suggested design to alleviate a number of problems in fluidic cells is presented.     

Potentials and limitations of miniaturized calorimeters for bioprocess monitoring

In theory, heat production rates are very well suited for analysing and controlling bioprocesses on different scales from a few nanolitres up to many cubic metres. Any bioconversion is accompanied by a production (exothermic) or consumption (endothermic) of heat. The heat is tightly connected with the stoichiometry of the bioprocess via the law of Hess, and its rate is connected to the kinetics of the process. Heat signals provide real-time information of bioprocesses. The combination of heat measurements with respirometry is theoretically suited for the quantification of the coupling between catabolic and anabolic reactions. Heat measurements have also practical advantages. Unlike most other biochemical sensors, thermal transducers can be mounted in a protected way that prevents fouling, thereby minimizing response drifts. Finally, calorimetry works in optically opaque solutions and does not require labelling or reactants. It is surprising to see that despite all these advantages, calorimetry has rarely been applied to monitor and control bioprocesses with intact cells in the laboratory, industrial bioreactors or ecosystems. This review article analyses the reasons for this omission, discusses the additional information calorimetry can provide in comparison with respirometry and presents miniaturization as a potential way to overcome some inherent weaknesses of conventional calorimetry. It will be discussed for which sample types and scientific question miniaturized calorimeter can be advantageously applied. A few examples from different fields of microbiological and biotechnological research will illustrate the potentials and limitations of chip calorimetry. Finally, the future of chip calorimetry is addressed in an outlook.     

哺乳动物毛被传热性能及其影响因素

毛被能够加强或减弱动物向周围环境的热量散失,毛被的形态结构和颜色是传热性能的决定因素,其传热过程往往是传导、对流和辐射3个过程的耦合。以往研究发现环境因子中,风可增加机体向环境中的散热速率,且散失量与风速正相关,且动物通过调节在风场中的姿态来适应不同风向。动物体与环境间的温差是影响散热速率的另一因素,不同环境中的动物通过改变毛被结构来适应温差变化。毛被含水率上升会引起导热和蒸发冷却作用加强,动物通过行为或毛被结构变化来调节毛被含水率。毛色决定毛被吸收和反射热辐射的能力。毛被传热性能直接把动物的生理特点与环境因子关联起来,这对揭示动物的适应、进化都具有重要意义。同时提出,毛被结构和传热性能的研究还有助于仿生学意义的挖掘。因此,今后应重点在毛被结构和物理性能、研究技术与方法以及毛被生物学和仿生学意义等方面开展研究。