Heat transfer enhancement is an important factor in obtaining energy efficiency improvements in all heat transfer applications. A numeric study was performed that compares the performance of heat exchangers using the Vipertex enhanced heat transfer tubes (model 1EHT) to the performance of heat exchangers that use smooth surface tubes and other enhanced tubes. Surface enhancement of the 1EHT tube is accomplished through the use of the primary dimple enhancement and a secondary background pattern made up of petal arrays. Utilization of enhanced heat transfer tubes is an effective method that is utilized in the development of high performance thermal systems. Vipertex™ tubes, have been designed and produced through material surface modifications that produce flow optimized heat transfer tubes that increase heat transfer performance. Current energy demands and the desire to increase efficiencies of systems have prompted the development of optimized enhanced heat transfer surfaces. Enhanced heat transfer tubes are widely used in many areas (refrigeration, air-conditioning, process, petrochemical, chemical, etc.) in order to reduce cost, create a smaller application footprint or increase production. A new type of enhanced heat transfer tube has been created; therefore it is important to investigate relevant heat exchanger designs using the Vipertex enhanced surface tube in industrial applications and compare that performance to smooth tubes and other enhanced tubes. Results include design characteristics and performance predictions using the design simulations produced using HTRI Exchanger Suite (2016). Performance for all cases considered using the Vipertex tube predicted over design when compared to a smooth tube design. Vipertex 1EHT tubes produced enhanced heat transfer and cost efficient designs. In some of the case studies the 1EHT tubes produce an overdesign that is more than 35%, while smooth tubes produce an underdesign and other low fin tubes produce overdesign but not as large as the 1EHT tubes.

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.

This paper presents a visualization of condensation droplet distribution affected by the electrowetting-on-dielectric (EWOD) approach. A single-side double-layer-electrode design (grid wire, thin wire, and thick wire) and coplanar-electrode design (zigzag) are discussed. Side-by-side experiments with applied 40V DC electric potential are carried out to compare droplet distribution between charged and uncharged devices with the identical design. The uncharged devices show a random droplet distribution, whereas charged devices have a regulated distribution based on the designed patterns. As droplets on the electrode boundaries become larger, they are likely to slide away and stay in electrode-free regions. The droplets ‘sit’ inside the grid wires and distribute vertically along thin and thick wires. On the coplanar-electrode zigzag device, droplets cover the electrode gaps and are distributed vertically. The charged surfaces lead to a faster droplet growth rate, resulting in larger droplet size and more dispersed droplet distribution. This phenomenon accelerates droplets’ shedding frequency and frees up more condensing areas for small droplets to nucleate and grow. The first shedding moment of the charged surfaces occurs earlier than the uncharged ones for all types of EWOD devices. The detected droplet shedding diameter ranges from 1.2 mm to 2 mm in this study. The work presented in this paper introduces a novel approach to actively influence droplet distribution on microfabricated condensing surfaces and indicates great potential for improving condensation heat transfer rate via EWOD.

Polymers have been widely used due to low cost, light weight, chemical inertness and easy of processing. However, bulk polymers are usually considered as thermal insulators owing to their low thermal conductivity. In this paper, the 3D polyethylene (PE) structure based on knitting method is proposed. We investigate the thermo-mechanical property of 3D PE and make a comparison with the amorphous PE. The results show that the 3D PE has a higher thermal conductivity, elastic modulus, and shear modulus than amorphous PE, which provides a novel perspective on designing high thermal conductivity polymers. In the past decades, although the strain effect on the thermal conductivity of PE has been intensively studied, little research has been focused on the impact of shear. In this work, the thermal conductivity of PE under different shear strain is calculated by molecular dynamics simulation. Unexpectedly, the impact of shear on the amorphous PE and 3D PE is different. For amorphous PE, the average thermal conductivity is insensitive to the shear strain. However, the thermal conductivity of 3D PE can be slightly enhanced when the shear strain is large enough. The underlying mechanism is related to the specific morphology. Our findings can deliver new insights on designing high thermal conductive polymers.

To allow a better adsorption performance inside a novel magnetic adsorption device designed in the process of hemodialysis, the mechanical properties of magnetic absorbents trapped inside a two-phase system are studied in this paper. A gradient magnetic coil field was assumed to produce the magnetic driving force that balances other hydraulic forces for the adsorbents. Applying this field, a complement practical form of winding equation for the solenoid coil is obtained. The case studies are also made in this paper to explore the design of the field.

Recently in our research studies, ferroferric oxide magnetic micro particles were used as magnetic seeds combining with adsorbent materials during post hemodialysis (HD) nutrition recovery process. The combined particles were designed as magnetic adsorbents to selectively take back nutritional substances from waste dialysate solution, and then, these substances can be further chemically released to blood. To allow a better adsorption performance, these particles should be trapped inside their working area. So, a gradient magnetic field was designed accordingly. Instead to use a permanent magnet which could accumulate magnetic particles, the field was produced by multiple-level magnetic solenoid coils. This paper outlined the design method for the multiple-level solenoid field. And then, the measurement results for the magnetic intensity at different axis locations inside the solenoid field were compared with the numerical computation results. The computation results also showed that, near the axis area of the multiple-level solenoid, the magnetic intensity is smoothly developed. This feature allows the easy movement of magnetic particles since an abrupt gradient tends to accumulate the particles.

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.

Indoor air pollution seriously threats the life and health of human beings. The improvement of indoor air quality has become a focus that people pay more and more attentions to. The photocatalytic of pollutants based on TiO 2 is a promising air purification technology. In order to overcome the disadvantages of nanometer powder TiO 2 catalyst and to enhance the photocatalytic activity of TiO 2 , series of glass plates covered with doped-TiO 2 were prepared and the photocatalysis them were studied. The glass plates covered with TiO 2 which was doped in advance with N, F, or/and Fe were prepared by a sol-gel method. The doping content of N, F, Fe and heat treatment temperature were determined using the orthogonal array of the Taguchi quality design. The prepared gel was coated on the glass by spin-coating method. The effects of doping level of N, F and Fe and heat treatment temperature on the photocatalytic capabilities were investigated. The photocatalytic capabilities of prepared glass plates were investigated by degrading the solution of methylene blue (MB,C 16 H 18 ClN 3 S). The results show that appropriate addition of N, F and Fe and temperaturae are effective for improving the photocatalytic activities of TiO 2 under visible light. The optimal TiO 2 was prepared under the condition that the doping amount of F element was 9at %, that of N is 7at %, and none of Fe under 400 °C calcination temperature. The degradation rate of the sample for methylene blue solution reaches 23.49% under visible light irradiation for 5 hours. The influence order of the factors was the calcination temperature > F > N > Fe.

Cooling technique in mini-scale heat sink is essential with the development of high power electronics such as electronic chip. As heat transfer techniques, jet impingement cooling and convective cooling by roughened surface are commonly adopted. To obtain good cooling efficiency, the cooling structure within the heat sink should be carefully designed. In the present study, mini-scale heat sink with feature size of 1∼10 mm is set up. Arrangement of jet impingement and dimple/protrusion surface are designed as heat transfer augmentation approaches. The effect of dimple/protrusion configuration is discussed. From the result, the Nu distribution of on heat sink surface is demonstrated for each case. The pressure penalty due to the arrangement of roughened structure is evaluated. Also, thermal performance TP and performance evaluation plot are adopted as evaluations of cooling performance for each configuration. Comparing all cases, optimal cooling structure considering the energy saving performance is obtained for the mini-scale heat sink. Referencing the statistics, new insight has been provided for the design of cooling structure inside mini-scale heat sink.

As the rapid growing of the semiconductor logic gate number and operation speed, the heat dissipated from electronic devices increases drastically. Moreover, most of the heat flux can reach about 100 W/cm 2 , therefore efficient removal of the heat from the electronic devices is essential to ensure the reliable operation of the electronic devices. The traditional direct cooling system, such as air cooling, liquid cooling, would not be able to transfer the high heat flux owing to their heat transfer limits, so advanced cooling solutions are necessary. The flat heat pipes have some advantages, such as small scale, strong heat transfer capacity, low weight penalty and low environmental requirements, therefore, in recent years, researchers have shown great interest for the flat heat pipe. But most of them played the important on the structure design of the flat heat pipes, and few of them focused on the study of the effect of the working fluid on the heat transfer performance. In this paper, a flat heat pipe with rectangular channel is designed and manufactured, and an experimental set up was built to study working fluid on the effects of the flat heat Pipe thermal performance. The flat heat pipe is heated via a 35mmx20mm rectangular electrical resistance (the evaporator side), and the other side (the condenser side) is cooled by convection of a heat sink. In the experimental work, three types of working fluid are used in the heat pipe: (A) deionized water, (B) deionized water-based Fe3O4 nano fluid (1, 1.5wt%). A comparison is performed for the thermal performance of different size flat heat pipe. Finally, the experimental results showed that nano fluid could improve the thermal performance of the FHP. With the same charge volume, the heat transfer coefficient of the FHPs filled with nano fluid were higher than that of DI water. There was an optimal mass concentration which was estimated to be 1.5 wt% to achieve the maximum heat transfer enhancement.

In order to improve the possibility of successful bonding and performance of structures, the new method for multi-depth silicon etching is required. This paper aims to design and create a new method for one-time multi-depth silicon etching in manufacturing complex structures based on SiO 2 masking layer. The core idea of this method is that: Firstly, all patterns are transferred into photo resist through photo etching; Then etch pattern will be transferred in the SiO 2 masking layer by multi-time shallow etching with different time etching control; Finally, patterns will be transferred to the silicon wafer with uniform ratio based on the measured etching selectivity of SiO 2 -Si with one time. In the experiments, the process is completed in the silicon wafer with SiO 2 masking layer whose thickness is elaborately designed. Firstly, the etching rate of SiO 2 and the etching selectivity of SiO 2 -Si were measured accurately. Secondly, the shallow structure based on the designed structure, the etching rate of SiO 2 and the etching selectivity of SiO 2 -Si is etched on the SiO 2 masking layer. The second step forms different thickness version of SiO 2 masking layer. At last, the SiO 2 masking layer is etched until final structure and consequently different depth of groove accomplish due to various thickness of SiO 2 etched by previous step. The experimental results indicated that the new methods has at least three advantages compared to traditional method: That is faster efficiency, higher cleanness and more complex structure. Fast work efficiency owes to only SF 6 etching rather than two gases of SF 6 and C 4 F 8 to reduce half of time. Also high cleanness comes from being not exposed to air and researchers directly. The largest benefit of new method may be that can create more complex structure for higher required machine design and for higher mechanical function. It is because that normal etching method could only build few different depth of grooves due to multi-process limitation and contrary to normal one, new method can create more different depth of groove. And more different depth of groove means that more complex structure can be designed.

The efficiency of conventional heat exchangers is restricted by many factors, such as effectiveness of convective heat transfer and the cost of their operation. The current research deals with these issues by developing a novel method for building a lower-cost yet more efficient heat sink. This method involves using a specially designed curved microchannel to utilise the enhanced fluid mixing characteristics of Dean vortices, and thus transferring heat efficiently. Numerical models have been employed to investigate the heat transfer enhancement of curved channels over straight equivalents, with the aim of optimising the heat exchanger design based on the parameters of maximising heat transfer whilst minimising pressure drop and unit cost. A range of cross-sectional geometries for the curved channels were compared, showing significantly higher Nusselt Numbers than equivalent straight channels throughout, and finding superior performance factors for square, circular and symmetrical trapezoidal profiles. Due the difficulty and expense in manufacturing circular microchannels, the relatively simple to fabricate square and symmetrical trapezoidal channels are put forward as the most advantageous designs. These results take into account both constant wall temperature and constant heat flux conditions. For a given set of channel dimensions, an optimal input flow rate condition is also determined.

The dimension of electronic devices becomes smaller and smaller and, thus, it is of crucial importance to enhance the heat dissipation from such tiny devices. The present study investigates the boiling heat transfer in a minichannel heat sink with saw-tooth structure on channel surface. The heat sink is comprised of four minichannels with hydraulic diameter of 0.8 mm and made of copper. The dimensions of the base area of the heat sink are 90 mm (length) × 5 mm (width). The saw-tooth topology on the bottom surface of minichannel was manufactured by wire-cut electrical discharge machining (EDM). The height, tip angle, and pitch of the saw-tooth structure are 0.5 mm, 45°, and 1mm, respectively. This study employed refrigerant HFE-7100, which is of low global warming potential (GWP), as a working fluid to investigate the boiling heat transfer in three kinds of surface structures (i.e., plain, parallel saw-tooth, and counter saw-tooth). The mass flux of the HFE-7100 ranged from 64 to 285 kg/m 2 s. The experimental results showed that the critical heat flux (CHF), compared to the plain minichannel, is improved by 46.7% and 40.2%, respectively, in the parallel and counter saw-tooth minichannels for a low mass flux of 127 kg/m 2 s. This result indicated that the CHF is considerably enhanced by the saw-tooth structure with both parallel and counter flow designs for the low mass flux. However, the CHF in the parallel and plain minichannels is nearly the same for a large mass flux of 285 kg/m 2 s. But for a saw-tooth structure with counter flow design, the CHF increases by 17.1% compared to the plain minichannel. Consequently, the experimental results demonstrated that the CHF can be enhanced by using saw-tooth structure on the channel surface.

Particulate fouling at elevated temperature is a crucial issue for microchannel heat exchangers. In this work, a microfluidic system is designed to experimentally study on the deposition of micro-particles suspended in microchannels, which simulates the working fluid in microscale heat exchangers. We have directly measured the deposition rate of microparticles and found that the number density of deposited particles was monotonically increased with solution temperature when constant flow rate of samples was maintained. Moreover, our results show that pulsatile flow, which was generated by a piezoelectric unit, could mitigate the particulate fouling in microchannels, and the deposition rate was decreased with increasing the frequency of pulsation within a low frequency region. Our findings are expected to gain better understanding of thermally driven particulate fouling as well as provide useful information for design and fabrication of microchannel heat exchangers.

We present a 2D square loop-shaped nanostructure, which is made of a square loop aluminum array on Al 2 O 3 spacer and Al substrate. High absorption peaks are obtained at 3.5μm and 9μm when the incident wave is vertically. In the design of dual-band or multi-band structure, the two high absorption bands are designed to stimulate the outer magnetic excitation of the first-order and the high-order magnetic resonance wavelength. For structure design with two absorption peaks or multiple absorption peaks, the expectation bands with high absorption would be obtained in the cooperation between first-order and higher-order magnetic resonance due to the outer structure. The main absorption peak due to the inner structure may be coupled the second absorption peak due to the outer structure. Then the absorption bandwidth could be broadened and the dual-band perfect absorption effect could be obtained in this loop-shaped structure.

Multiphase flow phenomena in single micro- and minichannels have been widely studied. Microchannel heat exchangers offer the potential for high heat transfer coefficients; however, implementation challenges must be addressed to realize this potential. Maldistribution of phases among the microchannels in the array and the changing phase velocities associated phase change present design challenges. Flow maldistribution and oscillatory instabilities can severely affect heat and mass transfer rates as well as pressure drops. In components such as condensers, evaporators, absorbers and desorbers, changing phase velocities can change prevailing flow regimes from favorable to unfavorable. Geometries with serpentine passages containing pin fins can be configured to maintain favorable flow regimes throughout the length of the component for diabatic phase-change heat and mass transfer applications. Due to the possibility of continuous redistribution of the flow across the pin fins along the flow direction, maldistribution can also be reduced. These features enable the potential of high heat transfer coefficients in microscale passages to be fully realized, thereby reducing the required transfer area, and achieving considerable compactness. The characteristics of two-phase flow through a serpentine passage with micro-pin fin arrays with diameters 350 μm and height 406 μm are investigated here. An air-water mixture is used to represent two-phase flow through the serpentine test section, and a variety of flow features are visually investigated using high-speed photography. Improved flow distribution is observed in the serpentine geometry. Distinct flow regimes, different from those observed in microchannels are also established. These observations are used to obtain void fraction and interfacial area along the length of the serpentine passages and compared with the corresponding values for straight microchannels. Models for the two-phase frictional pressure drops across this geometry are also developed.

With the rapid development of the supersonic aircraft technology, tremendously, the aircraft Mach numbers get higher and higher, but on the other hand, the working condition become worse and worse. The photonic crystal material which is formed by the periodic micro/nanoscale structures can generate the photonic band gaps, and the photonic band gaps could reflect the energy of the electromagnetic wave effectively. Consequently, the photonic crystal material turns into the newly-developing hotspot on the field of thermal protection for the supersonic aircraft. In this paper, the aircraft states of Mach 6 are set as the target operating condition, and 5 optimum proposals are presented for the structures of typical photonic crystal material. The energy which gets into the body material is calculated; Based on the theory of the electromagnetic field, using the method of transmission matrix and Plane Wave Expansion (PWE), the characteristics of the photonic band gaps for one-and-three dimensional photonic crystals are calculated. Finally, the characteristics of the photonic band gaps are discussed, and optimal design for the performance of the photonic crystal material thermal protection are proposed.

Transparent insulating materials combine high visible light transmission and excellent thermal insulation, and have potential applications in solar energy utilization, building energy conservation and commercial freezers. As a medium of low absorption and low thermal conduction, introducing gas bubbles into transparent mediums such as glass and polycarbonate (PC) may improve simultaneously their light transmission and thermal insulation performances through decreasing the absorption and thermal conduction in the materials. However, gas bubbles can also enhance the scattering which is a competition to the effect of the absorption decrease. Moreover, the material design should also consider the balance between the visible light transmittance and effective thermal conductivity. Therefore, a radiative transfer model for the transparent medium containing large gas bubbles (with a diameter much larger than the wavelengths concerned) with the assumption of independent scattering and the Maxwell–Eucken thermal conduction model were adopted to calculate the transmittance, reflectance and effective thermal conductivity. Subsequently, the effects of the volume fraction of gas bubbles ( f v ) and bubble radius ( r ) were discussed, and the two balances mentioned above were analyzed. The results showed that the transmittance always decreases when f v increases with fixed r or when r decreases with fixed f v . The transmittance includes two components, named as the collimated transmittance and bulk transmittance due to the forward scattering. The collimated transmittance depends on the effects of absorption decrease and scattering increase, whereas in the weak absorption region, the effect of the scattering increase dominates, making the collimated transmittance decrease, and the decreasing rate is larger than the increasing rate of the bulk transmittance as only the forward scattering contributes to the bulk transmittance. Therefore, the transmittance decreases when f v increases with fixed r or when r decreases with fixed f v . In addition, as f v increases from 0 to 0.5, the effective thermal conductivity ( k e ) of the glass decreases from 1.4 to 0.58 W/(m·K), and k e of the PC decreases from 0.236 to 0.113 W/(m·K). At the same time, the transmittances of both materials at 0.55 μm can be kept larger than 50% for f v =0.5 as long as the bubble radius is larger than 0.7 mm. To elucidate the application performance, a heat transfer model of a freezer adopting glass or PC as a cover was analyzed. Although the decrease percentage of k e for glass is higher than that of PC, the effect of the energy saving is more significant for PC, as the cooling load can be saved by 9.6% when f v increases from 0 to 0.5, while the corresponding value for glass is only 2.7% because that the decreasing rate of the cooling load with k e is higher at a lower k e .

The efficiency of conventional heat exchangers is restricted by many factors, such as effectiveness of convective heat transfer and the cost of their operation. The current research deals with these issues by developing a novel method for building a lower-cost yet more efficient heat sink. This method involves using a specially designed curved microchannel to utilise the enhanced fluid mixing characteristics of Dean vortices, and thus transferring heat efficiently. Numerical models have been employed to investigate the heat transfer enhancement of curved channels over straight equivalents, with the aim of optimising the heat exchanger design based on the parameters of maximising heat transfer whilst minimising pressure drop and unit cost. These studies examined the variation of Nusselt Number over the length of the channel, for a range of different curvatures (and hence Dean numbers). The results showed significantly higher heat transfer occurring in curved channels, especially in areas where the generated Dean vortices are strongest, with the variation in Nusselt Number forming the shape of an ‘arc’. In this way, a relationship between the Dean Number and the Nusselt Number is characterised and discussed, leading to suggestions regarding optimal microfluidic heat transfer design.

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.