Abstract An experimental investigation of subcooled flow boiling in a large width-to-height-ratio, one-sided heating rectangular mini-gap channel was conducted with deionized water as the working fluid. The super-hydrophobicity micro-porous structured copper surface was utilized in the experiments. High speed flow visualization was conducted to illustrate the effects of heat flux and mass rate on the heat transfer coefficient and flow pattern on the surfaces. The mass fluxes were in the range of 200–500 kg/m 2 s, the wall heat fluxes were spanned from 40–400 kW/m 2 . With increments of imposed heat flux, the slopes of boiling curves for superhydrophobic micro-porous copper surfaces increased rapidly, indicating the Onset of Nucleate Boiling. Heat transfer characteristics were discussed with variation of heat fluxes and mass fluxes, the trends of which were analyzed with the aid of high speed flow visualization.

Abstract Higher energy densities and the potential for nearly instantaneous recharging make microscale fuel cells very attractive as power sources for portable technology in comparison with standard battery technology. Heat management is very important to the microscale fuel cells because of the generation of waste heat. Waste heat generated in polymer electrolyte membrane fuel cells includes oxygen reduction reaction in the cathode catalyst, hydrogen oxidation reaction in the anode catalyst, and Ohmic heating in the membrane. A novel microscale fuel cell design is presented here that utilizes a half-membrane electrode assembly. An ANSYS Fluent model is presented to investigate the effects of operating conditions on the heat management of this microscale fuel cell. Five inlet fuel temperatures are 22°C, 40°C, 50°C, 60°C, and 70°C. Two fuel flow rate are 0.3 mL/min and 2 mL/min. The fuel cell is simulated under natural convection and forced convection. The simulations predict thermal profiles throughout this microscale fuel cell design. The exit temperature of fuel stream, oxygen stream and nitrogen stream are obtained to determine the rate of heat removal. Simulation results show that the fuel stream dominates heat removal at room temperature. As inlet fuel temperature increases, the majority of heat removal occurs via convection with the ambient air by the exposed current collector surfaces. The top and bottom current collector removes almost the same amount of heat. The model also shows that the heat transfer through the oxygen channel and nitrogen channel is minimal over the range of inlet fuel temperatures. Increasing fuel flow rate and ambient air flow both increase the heat removal by the exposed current collector surfaces. Ultimately, these simulations can be used to determine design points for best performance and durability in a single-channel microscale fuel cell.

Abstract Thermal management has become an important issue to be solved in the miniaturization and weight reduction of electronic equipment, especially in the aerospace field. The doped BaTiO 3 , as a self-regulating heating material, exhibits an attractive application perspective on the thermal control of electrical devices, resulting from its positive temperature coefficient (PTC) property. However, the Curie temperature of most of the doped BaTiO 3 material at present is much higher than the operating temperature of the electrical equipment. On this basis, this paper focuses on the controlling of the Curie temperature and thermal control performance of the BaTiO 3 -based heating component. The polycrystalline Ba 1-x Sr x TiO 3 was synthesized by solid solution reaction. The Curie temperature is tuned by the content of the strontium element, simultaneously the elements Y and Mn are doped to reduce the room temperature resistivity and improve the PTC effect. The X-ray diffraction demonstrates that the bulk phase of the Ba 1-x Sr x TiO 3 generates in the presintering process, while the crystallization of composition has completed during the sintering. Importantly, the Curie temperature of doped Ba 1-x Sr x TiO 3 for x = 0.3 with average particle size of 4.86 μm has shifted to around 38°C, beyond that exhibiting a 2.8-orders magnitude of PTCR jump. Results of the thermal control experiment show that, in contrast to the ordinary resistor heater, the heating element based on the BaTiO 3 PTC material can achieve lower equilibrium temperature without any auxiliary control methods. Compared to the traditional thermal control system composed by the ordinary resistor, sensor and controller, the novel thermal control system based on PTC heating unit possesses simple structure, lightweight and excellent reliability.

Abstract Due to the small size of low-dimensional materials, traditional experimental methods can hardly meet the requirements of accurate measurement. This paper presented a method for measuring the thermal conductivity of low-dimensional materials based on DC heating. This method adopted a micro-machining process to prepare a measuring electrode in advance, and only needed to suspend the object (one-dimensional wire or two-dimensional film) on the electrodes and maintain close contact. Finally, a standard diameter of 20 μm platinum wire was used to verify the measurement accuracy of this method. The application and future development of thermal conductivity testing structures for low-dimensional materials were also prospected.

Abstract Recent microCT imaging study has demonstrated that local heating caused a much larger nanoparticle distribution volume in tumors than that in tumors without localized heating, suggesting possible nanoparticle redistribution/migration during heating. In this study, a theoretical simulation is performed to evaluate to what extent the nanoparticle redistribution affects the temperature elevations and thermal dosage required to cause permanent thermal damage to PC3 tumors. Two tumor groups with similar sizes are selected. The control group consists of five PC3 tumors with nanoparticles distribution without heating, while the experimental group consists of another five resected PC3 tumors with nanoparticles distribution obtained after 25 minutes of local heating. Each generated tumor model is attached to a mouse body model by microCT scans. A previously determined relationship between the nanoparticle concentration distribution and the volumetric heat generation rate is implemented in the theoretical simulation of temperature elevations during magnetic nanoparticle hyperthermia. Our simulation results show that the average steady state temperature elevation in the tumors of the control group is higher than that in the experimental group when the nanoparticles are more spreading from the tumor center to tumor periphery (control group: 64.03±3.2°C vs. experimental group: 62.04±3.07°C). Further we assess the thermal dosage needed to cause 100% permanent thermal damage (Arrhenius integral Ω = 4) to the entire tumor, based on the assumption of unchanged nanoparticle distribution during heating. The average heating time based on the experimental setting from our previous studies demonstrates significantly different designs. Specifically, the average heating time for the control group is 24.3 minutes. However, the more spreading of nanoparticles to tumor periphery in the experimental group results in a much longer heating time of 38.1 minutes, 57° longer than that in the control group, to induce permanent thermal damage to the entire tumor. The results from this study suggest that the heating time needed when considering dynamic nanoparticle migration during heating is probably between 24 to 38 minutes. In conclusion, the study demonstrates the importance of including dynamic nanoparticle spreading during heating into theoretical simulation of temperature elevations in tumors to determine accurate thermal dosage needed in magnetic nanoparticle hyperthermia design.

Advancements in the field of microfluidics has led to an increasing interest to study laminar flow in microchannel and its potential applications. Understanding mixing at a microscale can be useful in various biological, heating and industrial applications due to the space and time reduction that micro mixing permits. This work aims to study mixing enhancement due to curved microchannel and the influence of varying microchannel cross sectional shape through numerical and experimental investigations. Unlike prior studies which use channel dimensions in the lower microscale range, this work has been conducted on channels with dimensions in the higher end of micrometer range. Using a cross sectional hydraulic diameter of 600 μm enables introduction of flow into the curved channel at a Reynolds Number ranging from 0.15 to 75, the findings of which show considerable improvement in the mixing performance as compared to that of equivalent straight channels, due to the development of secondary flows known as Dean Vortices.

A mathematical model has been developed in previous work to optimize the parameters of the biporous structures with micro channels among pillars to reduce the viscous force by shortening the liquid prorogation length inside porous media. In this paper, an experimental rig has been built to test the performance of the designed samples at ambient conditions according to the previous derived mathematical model. The pillar areas of the samples have been fabricated by photolithograph and Deep Reactive-Ion Etching (DRIE) with varied parameters for further comparisons. To simulate the concentrated heating of a working device and measure its temperature, a Pt heater and four Resistance Thermal Detectors (RTDs) have been fabricated by the electron beam deposition and lift-off process. The sample has been mounted horizontally to a water-proof sample holder, and the de-ionized water has been pumped into the evaporator through a reservoir by a syringe pump. By fine tuning the pumping rate, one can reach the minimum pumping rate while maintaining the water levels of the reservoir and the evaporator without drying out for a certain heating power. The mathematical model has be partially verified by the experimental results, which paves the way for the final design of the silicon vapor chamber.

With the development of metamaterials, microscale thermal cloak attracted many researchers’ attention. It was found that a thermodynamic cloak has unique characteristics of heat transfer transformation, with fundamental principle of transformation optics applied in thermodynamic field. An overview of thermal cloak related studies have not explained the physical mechanism in view of energy aspect. In the current work, two-dimensional heat transfer model of a multilayer thermal cloak was investigated through simulation according to Schittny’s microstructured model as well as an only polydimethylsiloxane protected layer model and plate model as control groups. Numerical simulations were developed with ANSYS FLUENT software for three models respectively in the process of heating to analysis the heat transfer and stealth protection during transient heat transfer process. The simulation results were agreed well with other’s previous experiment results on temperature distribution. The cloaking mechanism was analyzed by entropy generation approaches, and deriving the thermodynamics explanation at the aspect of the energy transfer. Thermodynamic cloak structure has a good heat stealth effect on the process of heat transfer, without the effecting outside the protected object on the distribution of both temperature and energy. Thermodynamic cloak control the energy dissipation inside the multi-layer structure, but the maximum dissipation position was shifted along the heat transfer processing.

Magnetic nanoparticle hyperthermia has attracted growing attentions recently due to its ability of confining nanoparticle-induced heating in targeted tumor region. Our recent studies have identified an injection strategy to achieve repeatable and controllable nanoparticle deposition patterns in PC3 tumors using microCT scans. Based on the injection strategy, simulation of temperature elevations in tumors is conducted to design heating protocols to induce irreversible thermal damage to the entire tumors. In this study, in vivo heating experiments are performed on PC3 tumors implanted on mice following the designed heating protocols. The tumors in the control group without heating triple their sizes over a period of eight weeks. The tumors in the heating groups are heated for either 25 minutes or 12 minutes, representing that the Arrhenius integral is equal to or larger than 4 or 1 in the entire tumors, respectively. The tumors in the heating group of 25 minutes disappear completely after the 3 rd days, and the site maintains the disappearance for over eight weeks. The sizes of the tumors in the heating group of 12 minutes decrease in the first ten days, however, the tumors re-grow afterwards, and by the end of the 8 th week, they are approximately 60% larger than their initial size. This study demonstrates the importance of imaging-based design for individualized treatment planning. The success of the designed heating protocol in complete damaging PC3 tumors validates the theoretical models used in planning the heating treatment in magnetic nanoparticle hyperthermia.

In present work, Al2O3/H2O nanofluid was prepared by ultrasonic oscillation. Furthermore, nanofluid flow boiling heat transfer in a vertical cube is experimentally studied, with 0.1% and 0.5% volume concentration and 20nm diameter. Some factors are under consideration, including heat flux on the heating surface (48∼289kW·m −2 ), pressure (0.2∼0.8MPa) and mass flow rate (400∼1100 kgm −2 s −1 ). The results confirm that the flow boiling heat transfer of Al 2 O 3 /H 2 O nanofluid is improved mostly about 86% compared with pure water. And the average Nusselt number enhancement rate of nanofluid compared with deionized water is 35% in the range of this work. Moreover, the heat transfer capacity of nanofluid increase with the heat flux on the heating surface, pressure and the volume concentration of nanoparticle. It is proved that nanoparticle deposited on the heating surface by SEM observations, and TEM observations for nanoparticle confirm that nanoparticle have not obviously changed after boiling. In addition, the enhancement rate of nanofluid flow boiling heat transfer capacity increase with the pressure, and the influence of mass flow rate is negligible. In conclusion, this work is a supplement for nanofluid flow boiling heating transfer, especially for the influence of pressure.

The graphene-based nanomaterial has great potential as catalyst and supercapacitors. In this paper we study the pyrolysis of polymers in a nanosecond time scale with the reactive molecular dynamics (MD) simulations using ReaxFF potential. It is found that the confined heating will produce graphene-like nanostructures out of two kinds of polymers: polyimide and polyether ether ketone. The peak pressure achieves above 3GPa with a processing temperature of 3000K. It indicates that the local high temperature and pressure can convert polymer to graphene-based nanomaterials without metal catalyst, which may enable large scale production of high performance electrical devices and microreactors with laser scribing method.

The confined jet array impingement cooling using NEPCM (nano-encapsulated phase change material) slurry was investigated numerically using a homogeneous model based on effective heat capacity method. The nanofluids consists of the carrier fluid of polyalphaolefin (PAO) and the NEPCM particles of Polystyrene shell and paraffin core. The distributed slot jet array with the jet width W=100 μm, confinement height H=300 μm, jet-to-jet distance S=400 μm was investigated at first under different jet velocity, inlet temperature and NEPCM volumetric concentration. It was found that for a fixed jet velocity, there is an optimal NEPCM volumetric concentration and an optimal inlet temperature to achieve the maximum average heat transfer coefficient. The larger the jet velocity, the higher the optimal NEPCM concentration and the closer the optimal inlet temperature to the midpoint of melting temperature range of PCM where the peak of effective heat capacity achieves. The local heat transfer on the heating surface under the exit slot is the weakest, because of stagnant zone formed by the head-to-head collision of the two adjacent jets. The pressure drop and average heat transfer coefficient of six jet arrays with different H/W (=2, or 3) and S/W (=3, 4 or 5) were also compared.

2D nanomaterials have been attracting extensive research interests due to their superior properties and the accurate thermophysical characterization of 2D materials is very important for nanoscience and nanotechnology. Recently, a noncontact technique based on the temperature dependent Raman band shifts has been used to measure the thermal conductivity of 2D materials. However, the heat flux, i.e. the absorbed laser power, was either theoretically estimated or measured by a laser power meter with uncertainty, resulting in large errors in thermal conductivity determination. This paper presents a transient “laser flash Raman spectroscopy” method for measuring the thermal diffusivity of 2D nanomaterials in both the suspended and supported forms without knowing laser absorption. Square pulsed laser instead of continuous laser is used to heat the sample and the laser absorption can be eliminated by comparing the measured temperature rises for different laser heating time and laser spot radii. This method is sensitive for characterizing typical 2D materials and useful for nanoscale heat transfer research.

The heat transfer performance of fluid flowing in a microchannel was experimentally studied, to meet the requirement of extremely high heat flux removal of microelectronic devices. There were 10 parallel microchannels with rectangular cross-section in the stainless steel plate, which was covered by a glass plate to observe the fluid flowing behavior, and another heating plate made of aluminum alloy was positioned behind the microchannel. Single phase heat transfer and fluid flow downstream the microchannel experiments were conducted with both deionized water and ethanol. Besides experiments, numerical models were also set up to make a comparison with experimental results. It is found that the pressure drop increases rapidly with enlarging Reynolds number (200), especially for ethanol. With comparison, the flow resistance of pure water is smaller than ethanol. Results also show that the friction factor decreases with Reynolds number smaller than the critical value, while increases the velocity, the friction factor would like to keep little changed. We also find that the water friction factors obtained by CFD simulations in parallel microchannels are much larger than experiment results. With heat flux added to the fluid, the heat transfer performance can be enhanced with larger Re number and the temperature rise could be weaken. Compared against ethanol, water performed much better for heat removal. However, with intensive heat flux, both water and ethanol couldn’t meet the requirement and the temperature at outlet would increase remarkably, extremely for ethanol. These findings would be helpful for thermal management design and optimization.

The open system of visual loop heat pipe experimental rig driven by phase change of the refrigerant is established, which is used to research the effect of parameters of the volume, supplementary of refrigerant, properties of wick, height of evaporation cavity and heating power on the performance of this system quantitatively, also the heat transfer characteristics of refrigerant flow in the evaporator visually is studied. We observed and researched the whole process of system from the start up to the stable condition in the evaporator, the changes of refrigerant which is from boiling to the gas-liquid separation. From the experimental point of view, it provides a basis for the establishment of the closed system and for the creation of new mathematical model of the driving mechanism.

In this article, the heat transferring property of the copper-water nanofluids in self-exciting mode oscillating flow heat pipe under different laser heating power is experimented, as well as is compared with that of the distilled water medium in self-exciting mode oscillating flow heat pipe under same heating condition. The objective of this article is to provide the heat transfer characteristics of Cu-H 2 O nanofluids in self-exciting mode oscillating-flow heat pipe under different laser heating input, and to compare with the heat transfer characteristics of the same heat pipe with distilled water as working fluids. The SEMOS HP used in this experiment is made of brass tube with 2mm interior diameter, which is consisted of 8 straight tubes with 4 turns’ evaporation section and 12 turns’ condensation section. The heat resource for the evaporation zone is eight channel quantum pitfall diode array semi-conductor laser heater with 940nm radiation wave length, while the radiation power of each channel is changeable within 0–50W and the facular size is 1×30mm 2 . The condensation section is set in a cooling water tank in which water is from another higher tank. The actual transferring rate could be calculated by the flow rate of the cooling water and the change of the temperature. The change of the temperature of the heat pipe wall is measured by those thermo-couple fixed in different section in the heat pipe and data is collected by a data acquisition. In the heat pipe the fluid filling rate is 43%, the pressure is 2.5×10 −3 Pa, and the heat pipe inclination angle is 55° while the size of the brass particle in the nanofluids is less than 60nm and volume proportion is 0.5%. In this paper, the particularity of heat transfer rate of the SEMOS heat pipe with Cu-H 2 O fluid has been experimentally confirmed by changing the proportion of working fluid and Cu nonsocial particles in the heat pipe. By comparing the experimental result of these two different medium in the SEMOS HP, it is shown that the heat transferring rate with brass-water nanofluids as medium is much better than that with distilled water as medium under same volume proportion.

Flow boiling in Silicon Nanowire microchannel enhances heat transfer performance, CHF and reduces pressure drop compared to Plainwall microchannel. It is revealed by earlier studies that promoted nucleate boiling, liquid rewetting and enhanced thin film evaporation are the primary reasons behind these significant performance enchantments. Although flow regime plays a significant role to characterize the flow boiling Silicon Nanowire microchannel performances; surface characteristics, hydrodynamic phenomena, bubble contact angle and surface orientation are also some of the major influencing parameters in system performances. More importantly, effect of orientation (effect of gravity) draws a great attention in establishing the viability of flow boiling in microchannels in space applications. In this study, the effects of heating surface orientation in flow boiling Silicon Nanowire microchannels have been investigated to reveal the underlying heat transfer phenomena and also to discover the applicability of this system in space applications. Comparison between Nanowire and Plainwall microchannels have been performed by experimental and visual studies. Experiments were conducted in a forced convection loop with deionized water at mass flux range of 100kg/m 2 s – 600kg/m 2 s. Micro devices consist of five parallel straight microchannels with Nanowire and without Nanowire (Plainwall) (200μm × 250μm × 10mm) were used to investigate the effects of orientation. Two different orientations were used to perform the test: upward facing ( 0° Orientation ) and downward facing ( 18 0° Orientation ). Results for Plainwall show sensitivity to orientation and mass flux, whereas, little effects of mass flux and orientation have been observed for Nanowire configuration.

In modern microprocessors, thermal management has become one of the main hurdles in continued performance enhancement. Cooling schemes utilizing single phase microfluidics have been investigated extensively for enhanced heat dissipation from microprocessors. However, two-phase fluidic cooling devices are becoming a promising approach, and are less understood. This study aims to examine two-phase flow and heat transfer within a pin-fin enhanced micro-gap. The pin-fin array covered an area of 1cm × 1cm and had a pin diameter, height and pitch of 150μm, 200μm and 225μm, respectively, (aspect ratio of 1.33). Heating from two upstream heaters was considered. The working fluid used was R245fa. The average heat transfer coefficient was evaluated for a range of heat fluxes and flow rates. Flow regime visualization was performed using high-speed imaging. Results indicate a sharp transition to convective flow boiling mechanism. Unique, conically-shaped two-phase wakes are recorded, demonstrating 2D spreading capability of the device. Surface roughness features are also discussed.

Room temperature liquid metal has been widely used in many MEMS applications, such as integrated heaters, sensors, electrodes and stretchable wires. Injecting the liquid metal into microchannels provides a simple, rapid and low-cost way to fabricate micro heaters and sensors. The liquid-metal-filled microstructures can be designed in any shape and easily integrated into micro devices. In this study, a liquid-metal based thermal micro-system was proposed for on-chip cell culture purpose. The thermal micro-system consisted of two same microchannels filled with the liquid metal as electrical heaters. At the same time, the heater also worked as a resistance temperature sensor to control the heating process. The temperature sensor was calibrated from 20 °C to 70 °C to give an accurate temperature control for the microsystem. To justify whether this micro-system is capable of providing a uniform temperature distribution, Rhodamine B was filled into the micro cell culture chamber of interest to monitor the temperature distribution. Thermal analysis was numerically carried out to reveal the temperature field of the chip. This thermal micro-system has great potential use in many microfluidic applications, such as on-chip PCR, temperature gradient focusing, protein crystallization or chemical synthesis.

Aiming at providing a detailed disclosure on the thermal effects of EM (electromagnetic) hyperthermia on the liver tumor underneath the ribs, this paper has numerically provided comprehensive interpretations on the heating effects of magnetic nano-particles induced hyperthermia for target tumor treatment. The results revealed the following factors: (1) The existing of bone structure, i.e. ribs has an inevitable effect on the distribution of EM field; specifically, due to its lower dielectric property, the bone structure seemingly acts as a barrier to attenuate the access of EM energy into the tissue, especially the tumor in the deep body. (2) Using higher dosage or bigger size magnetic nano-particles have greatly enhanced the temperature elevation of targeted tumor tissue and thereby obtain good performance of hyperthermia. (3) Further parametric studies indicated that a worse heating effect would be obtained when utilizing external EM field with a higher frequency of 10MHz; while higher strength of EM field would evidently enhance the heating effects of such EM hyperthermia. The present study would promote the understandings of thermal effects on the specific organs in EM hyperthermia, and the findings are expected to provide valuable guidance for planning an accurate dosage in clinical liver tumor thermal ablation.