Rapid Heat Exchange Research Articles

La-Fe-Si magnetocaloric composite with anisotropic microstructure prepared by hot pressing

In this study, we have proposed an anisotropic microstructure in La-Fe-Si magnetocaloric composites for thermal management. This is vital to the rapid heat exchange and high working efficiency in magnetic refrigerator system. We demonstrate the anisotropic microstructure in composites can be fabricated via powder metallurgy in this work. By adjusting the particle size of the 1:13 phase, the introduced reinforcing phase with rheological property can effectively deform and anisotropic microstructure can be obviously observed. This can be attributed to the tailored stress distribution in cubic-anvil-type pressure apparatus. The element diffusion between the two phases was also discussed in this paper, taking into account the influence of particle size. Such anisotropic microstructure causes some other anisotropic physical properties in the composite, such as mechanical strength. The compressive measurements along the axial direction exhibit superior mechanical properties (~ 3.5% for strain and ~ 350 MPa for strength) compared to those along the radial direction. Attributed to the stress buffer-effect provided by the introduced ductile phase, magnetocaloric effect (magnetic entropy change ~ 7.8 J/kg K) can be maintained in the La-Fe-Si composite.

Insights into the tiger stripe phenomenon of polypropylene and its blend in injection molding with a rapid heat exchange mold

AbstractTo examine the formation of tiger stripes (TS) phenomenon on the surface of the injection molding parts, a home‐made injection mold with a rapid heat exchange system and in situ measurement of pressure and temperature was designed and manufactured. Based on this special mold, the TS diagrams as a function of mold temperature and injection pressure for isotactic polypropylene (iPP) and its blend with a type of polyolefin elastomer (iPP/POE) were explored for the first time. It is found that there exists a critical mold temperature and a critical injection pressure for the TS appearance or disappearance in both systems. The critical temperatures of TS disappearance for iPP and iPP/POE are ~50 and ~ 120°C, respectively. As evidenced by the correlation between melt pressure drop and TS appearance, the wall slip mechanism is regarded as the main cause of TS formation. Compared with the critical shear stress of wall slip (σw) in totally molten PP, the lower σw value in this study further indicates that the wall slip could be facilitated by the crystallization of iPP during injection. Combined with white light interferometer, micro‐area x‐ray diffraction nanoindentation and scanning electron microscopy, it is demonstrated that the cloudy and glossy region of TS in pure iPP system could be distinguished by surface crystallinity. In the blend system, however, the rubber phase orientation as a dominant factor contributes to the glossiness of TS.

Effects of Shot Peening and Electropolishing Treatment on the Properties of Additively and Conventionally Manufactured Ti6Al4V Alloy: A Review.

This literature review indicates that the basic microstructure of Ti6Al4V is bimodal, consisting of two phases, namely α + β, and it occurs after fabrication using conventional methods such as casting, plastic forming or machining processes. The fabrication of components via an additive manufacturing process significantly changes the microstructure and properties of Ti6Al4V. Due to the rapid heat exchange during heat treatment, the bimodal microstructure transforms into a lamellar microstructure, which consists of two phases: α' + β. Despite the application of optimum printing parameters, 3D printed products exhibit typical surface defects and discontinuities, and in turn, surface finishing using shot peening is recommended. A literature review signalizes that shot peening and electropolishing processes positively impact the corrosion behavior, the mechanical properties and the condition of the surface layer of conventionally manufactured titanium alloy. On the other hand, there is a lack of studies combining shot peening and electropolishing in one hybrid process for additively manufactured titanium alloys, which could synthesize the benefits of both processes. Therefore, this review paper clarifies the effects of shot peening and electropolishing treatment on the properties of both additively and conventionally manufactured Ti6Al4V alloys and shows the effect process on the microstructure and properties of Ti6Al4V titanium alloy.

Experimental study on combustion behaviors of thin-layer methanol with lateral continuous leakage

Fire accidents caused by liquid fuel leaks occur at times. In this paper, the combustion behavior of thin layers formed by the free spread of methanol at six continuous leakage rates was studied. The results show that methanol combustion with continuous leakage can be divided into four stages according to the change of burning area. The quasi-steady burning rate of thin-layer fuel is lower than that of pool fire at the same scale, due to the rapid heat exchange between the fuel layer and the substrate. As measured and calculated, the average fuel layer thickness gradually decreases in the spread burning stage, rises in the shrink burning stage, and finally reaches stability. The average fuel layer thickness of the quasi-steady burning stage of each case is used to calculate the heat loss by substrate reflection. Based on the law of energy conservation, a heat equilibrium model of the quasi-steady burning stage of a thin layer combined with fuel flow heat transfer was established. This model explains the uneven substrate temperature found by experimental measurements. The calculation results show that the effect of flow heat transfer is more significant within 20% of the burning area near the leakage port.

Numerical study on effects of nozzle hole spacing distance on steam submerged jet condensation from triangular holes spray nozzle

Steam-water direct contact condensation (DCC) is a phenomenon which is frequently found in the industrial sector due to its rapid and efficient heat and mass exchange rates. In this work, three dimensional numerical study of steam injection from triangular hole nozzles (with different holes pitch circle diameter, PCD = 6, 8,10 and 12 mm) into subcooled water tank has been carried out using Eulerian multiphase flow model along with realizable k-epsilon turbulence model. The thermal phase change model as User Defined Function (UDF) was employed in Fluent software for capturing submerged steam jet condensation. The simulation results were validated using experimental results as well as previously published numerical study and a fairly good agreement was observed. The effects of nozzle hole spacing distance on distributions of various thermal hydraulics parameters including velocity, pressure, temperature, heat and transfer characteristics have been studied. The axial distribution of the velocity, temperature, heat transfer coefficient and mass transfer computed at the centerline of the nozzle was found weaker than observed at the centerline of the nozzle holes. However, these distributions were not weak at nozzle centerline for nozzle with PCD 6 mm. The heat transfer coefficient has been found in the ranges of 1.75–2.3 MW/m2 K. The results reveal that the heat transfer coefficient for nozzle PCD 8 mm is higher than rate obtained for other nozzles. The rate of mass transfer at the holes centerlines has been found increasing with the holes PCD. The axial distribution of the mass transfer curve shifts downstream for nozzle with smaller PCD. Additionally, the mutual shielding effect of the jets weakens as holes PCD increases.

Numerical Analysis for Supercavitation Characteristics around Underwater Vehicle according to Ventilated Gas Temperature

Supercavitation is a phenomenon in which the cavity covers the entire underwater vehicle. The purpose of this paper is to compare and analyze the thermal effect on the cavity characteristics by changing the ventilated gas temperature through computational analysis. For this study, a homogeneous mixture model based on the 3D Navier-Stokes equation was used. As a phase change model, it is its own code considering both pressure change and temperature change. A dimensionless number <i>T<sub>m</sub></i> was presented to analyze the numerical results, and as the <i>T<sub>m</sub></i> increased, the cavity length increased by about 3.6 times and the cavity width by about 3.3 times at 393.15 K compared to room temperature. Analyzing these thermal effects, it was confirmed that rapid heat exchange and heat transfer between the gas phase and the liquid phase occurred at the location where the ventilated gas was sprayed, affecting the cavity characteristics. In addition, it can be confirmed that the initial cavity surface becomes unstable as the ventilated gas temperature increases, and it can be confirmed based on the numerical analysis results that the critical temperature at which the cavity surface becomes unstable is 373.15 K.

Effect of Flue Gas on Steam Chamber Expansion in Steamflooding

Summary The expansion of the steam chamber is very important for the recovery performance of steamflooding. In this paper, we discuss 1D and 2D sandpack experiments to performed analyze the effect of flue gas on steam chamber expansion and displacement efficiency in steamflooding. In addition, we examine the effect of flue gas acting on the steam condensation characteristics. The results show that within a certain range of injection rate, flue gas can significantly enlarge the swept volume and oil displacement efficiency of steam. However, when the flue gas injection rate is excessively high (the ratio of gas injection rate to steam injection rate exceeds 4), gas channels may form, resulting in a decline of oil recovery from steamflooding. The results of the 2D visualization experiments reveal that the swept volume of the steam chamber during steamflooding was small, and the remaining oil saturation in the reservoir was high, so the recovery was only 28%. The swept volume of the steam chamber for flue-gas-assisted steamflooding was obviously larger than that of steamflooding, and the recovery of flue-gas-assisted steamflooding in 2D experiments could reach 40.35%. The results of the steam condensation experiment indicate that flue gas could reduce the growth and coalescence rates of steam-condensed droplets on the cooling wall and increase the shedding period of the droplets. Macroscopically, flue gas could reduce the heat exchange rate between the steam and the reservoir and inhibit the rapid condensation and heat exchange of the steam near the injection well. As a result, flue gas could expand the steam chamber into the reservoir for heating and displacing oil.

Heat release characteristics of a latent heat storage heat exchanger by scraping the solidified phase change material layer

Latent heat storage (LHS) is one of the key methods to level renewable energy and utilize waste heat. In this method, heat is stored as latent heat of the phase change material (PCM) during melting. Releasing the stored heat in PCM consumes considerable time because the heat release rate is slow when a solidification layer of PCM is formed on the heat transfer wall during the heat release period. The authors have proposed a new mechanism for rapid heat exchange in LHS, i.e., by scraping the solidified PCM layer on the heat transfer wall. In this mechanism, the heat transfer wall is a rotating cylindrical tube to which a fixed blade is attached. During the heat release period, PCM is solidified on the tube, and the solidified layer is immediately removed using the fixed blade. In this study, a laboratory-scale setup with 1 kg of sodium acetate tri-hydrate as PCM was developed, and the effect of rotation rate on the heat release rate was experimentally examined. The results showed that the heat release rate during rotation accelerated by more than 100 times compared with the rate without rotation, and it increased with the rotation rate of the cylindrical tube.

Thermal mechanical analysis of porous granite asperities in contact using probabilistic damage model

Contacting asperities play an important role in stabilizing the existing fracture networks in the geothermal system. In such a system, the rapid heat exchange occurs when cold water is injected into existing fractures with high reservoir temperatures. The deformation mechanisms of the porous asperities in contact under the coupled thermal-mechanical loading are complex and critical to engineering operations. The present study models the deformation process using a probabilistic damage model (PDM) incorporating the porosity effect. The results revealed the coupled deformation mechanisms, which are the contact induced damage and the radial cracking of the asperities. The interaction between two processes was characterized based on both of the analytical and computational models. It was also found that the porosity distribution affects two mechanisms and their interaction significantly. The field data were input to predict the deformations of fracture apertures during the normal range of operation conditions. A critical overburden pressure was discovered, which draws the line between the increasing or decreasing trend of porosity effect as the temperature increases.

Temperature and convection velocities in two-component liquid droplet until micro-explosion

The micro-explosion of slurries and emulsions droplets under heating contribute to a significant increase in efficiency of a large group of promising technologies, in particular, in the production of heat carriers based on flue gases, vapors, and water droplets, in flame and thermal water purification from unspecified impurities, and in environmentally friendly combustion of fuels, including those prepared from abundant industrial waste containing sewage and service water. In this paper, we study the consistent patterns of partial fragmentation and micro-explosion of two-liquid droplets consisting of a flammable (oil) and non-flammable (water) liquids. The consequences of rapid convective heat exchange have been researched between a droplet and heated air flow. The Planar Laser Induced Fluorescence optical technique was used to measure the droplet temperature field, and the Micro Particle Image Velocimetry – the convection velocities in the droplet. We focus on the structure of convective flows, centers of vortex formation, velocities, and the influence on the temperature in different droplet sections (especially, at the inter-component interface, whose destruction triggers the micro-explosive breakup of droplets). The tracer particles were used to simultaneously measure the convection velocities in the flammable and non-flammable liquids making up two droplet parts. We have determined the velocities and temperatures near the inter-component interface sufficient for micro-explosion of a rapidly heated two-liquid droplet. The experimental findings provide a deeper insight into the mechanism and main stages of inter-component interface destruction in heated heterogeneous droplets.

Thermal and rheological performance of asphalt binders modified with expanded graphite/polyethylene glycol composite phase change material (EP-CPCM)

Phase change materials (PCMs) can be used as thermal regulation units to prevent thermal diseases of asphalt pavements. However, the effects of PCMs on the thermal and rheological properties of asphalt binders still need to be further studied. Therefore, the influence of an expanded graphite/polyethylene glycol composite phase change material (EP-CPCM) on the thermal and rheological performance of a Pen 60/80 base binder and a SBS modified binder were investigated in this research. Various experiments were conducted, and the thermal constants analyses show that the thermal conductivity gaps of the EP-CPCM modified base and SBS asphalt binders are lower than 8%, indicating a favorable compatibility between EP-CPCM and the asphalt binders. The thermal conductivity and thermal diffusivity of base and SBS binders are doubled after the incorporation of EP-CPCM, which ensures a rapid heat exchange with the ambient environment. Differential scanning calorimeter (DSC) results indicate that the melting and crystallization enthalpies of the EP-CPCM modified base binders are 13.77 J/g and 10.22 J/g respectively, meanwhile, the melting and crystallization enthalpies of the SBS binders are 14.63 J/g and 13.59 J/g respectively. The heating and cooling rate of the modified binders are separately reduced at the temperature range of 40–50 °C and 35–25 °C because of the phase transition of EP-CPCM. Dynamic shear rheometer (DSR) results reveal that both the rutting parameter G*/sinδ and the fatigue parameter G*sinδ of the modified binders are increased when the EP-CPCM is added, indicating the rutting resistance is improved while the fatigue resistance is damaged. Bending beam rheometer (BBR) tests show that the addition of EP-CPCM results in the decrease in the creep rate and the increase in the creep stiffness of the modified binders, and both effects are detrimental to the prevention of low-temperature cracking.

Plastically deformed Gd-X (X = Y, In, Zr, Ga, B) solid solutions for magnetocaloric regenerator of parallel plate geometry

Despite significant progress in the study of materials undergoing first-order magnetic phase transitions accompanied by the so-called giant magnetocaloric effect (MCE), Gd metal still remains the most widely used material in prototypes of magnetic refrigerators due to its significant MCE, good machinability and reasonable mechanical and chemical stabilities. Alloying of Gd enables fine-tuning the Curie temperature of Gd-based solid solutions (all show second-order phase transitions), for graded magnetocaloric materials. Commonly, Gd packed spheres are used as a magnetocaloric working substance in the active magnetic regenerator (AMR) cycle. In this work, we show that the optimized stacking parallel-plate geometry of AMR bed made of Gd is more effective for application at frequencies 1–10 Hz then the packed spheres. We also give a short review on magnetocaloric properties of cold-rolled Gd-X (X = Y, In, Zr, Ga, B) solid solutions. These materials can be produced in the form of thin (∼100 μm) foils/plates to ensure rapid heat exchange between to the heat transfer fluid. Although the magnetocaloric effect decreases in the as-rolled foils, it can be recovered by thermal treatment of the final stacked-plates regenerators. Gd-Y, Gd-In and Gd-Zr solid solutions have magnetocaloric properties, comparable to the MCE of pure Gd in a wide temperature working span up to 37 K, 36 K, and 16 K respectively, which makes them suitable magnetocaloric material systems for testing the fundamental heat exchangers geometries at ambient temperature and in frequencies of 1–10 Hz.

Temperature of gases in a trace of water droplets during their motion in a flame

The paper experimentally investigates the integral characteristics of the processes involved in the reduction of gas temperature by injecting the aerosol flow of water droplets into a counter flow of combustion products (period of steady low gas temperature Tg’ compared to the initial Tg, range of temperature decrease (ΔTg=Tg-Tg’), rate of temperature recovery, the geometric dimensions of the temperature traces and their lifetime). We use the following recording devices: fast-response thermocouples (heat inertia less than 0.1 s), a multichannel recorder, a high-speed video camera (up to 105 frames per second), as well as a cross-correlation hardware and software package (with optical methods for recording the front and trace of the aerosol). The temperature trace of an aerosol is defined as the area with the temperature Tg’ lower than the initial Tg by at least 10 K. We determine how the following group of factors affects the characteristics of temperature traces of water droplets: size (0.04-0.4 mm) and concentrations (3·10-5- 11·10-5 m3 of droplet/m3 of gas) of droplets in a pulse, the initial temperature of water (280-340 K), the duration of a pulse (1-5 s), the temperature (350- 950 K) and velocities (0.5-5 m/s) of combustion products. The temperature in a trace of water droplets during their motion in a flame can be reduced due to rapid vaporization or heat exchange between the gases and water. The conditions are identified, under which the low temperature of gases in a trace of droplet aerosol can be preserved for a long time (20–30 s). Finally, we forecast the parameters of temperature traces under the conditions of actual fires with combustion product temperatures over 1000 K.

Optimal Heat Transfer and Optimal Exit Times

A heat exchanger can be modeled as a closed domain containing an incompressible fluid. The moving fluid has a temperature distribution obeying the advection-diffusion equation, with zero temperature boundary conditions at the walls. Starting from a positive initial temperature distribution in the interior, the goal is to flux the heat through the walls as efficiently as possible. Here we consider a distinct but closely related problem, that of the integrated mean exit time of Brownian particles starting inside the domain. Since flows favorable to rapid heat exchange should lower exit times, we minimize a norm of the exit time. This is a time-independent optimization problem that we solve analytically in some limits, and numerically otherwise. We find an (at least locally) optimal velocity field that cools the domain on a mechanical time scale, in the sense that the integrated mean exit time is independent on molecular diffusivity in the limit of large-energy flows.

High‐Performance Thermomagnetic Generators Based on Heusler Alloy Films

Recent developments on Heusler alloys including Ni–Mn–X and Ni–Co–Mn–X (X = Ga, In, Sn,…) demonstrate multiferroic phase transformations with large abrupt changes in lattice parameters of several percent and corresponding abrupt changes in ferromagnetic ordering near the transition temperatures. These materials enable a new generation of thermomagnetic generators that convert heat to electricity within a small temperature difference below 5 K. While thermodynamic calculations on this energy conversion method predict a power density normalized to material volume of up to 300 mW cm−3, experimental results have been in the range of µW cm−3. Challenges are related to the development of materials with bulk‐like single‐crystal properties as well as geometries with large surface‐to‐volume ratio for rapid heat exchange. This study demonstrates efficient thermomagnetic generation via resonant actuation of freely movable thin‐film devices of the Heusler alloy Ni–Mn–Ga with unprecedented power density of 118 mW cm−3 that compares favorably with the best thermoelectric generators. Due to the large temperature‐dependent change of magnetization of the films, a periodic temperature change of only 3 K is required for operation. The duration of thermomagnetic duty cycle is only about 12 ms, which matches with the period of oscillatory motion.

Geo- and biogeochemical processes in a heliothermal hypersaline lake

Water chemical variations were investigated over three annual hydrologic cycles in hypersaline, heliothermal, meromictic Hot Lake in north-central Washington State, USA. The lake contains diverse biota with dramatic zonation related to salinity and redox state. Water samples were collected at 10-cm depth intervals through the shallow lake (2.4m) during 2012–2014, with comprehensive monitoring performed in 2013. Inorganic salt species, dissolved carbon forms (DOC, DIC), oxygen, sulfide, and methane were analyzed in lake water samples. Depth sonde measurements of pH and temperature were also performed to track their seasonal variations. A bathymetric survey of the lake was conducted to enable lake water volume and solute inventory calculations. Sediment cores were collected at low water and analyzed by X-ray diffraction to investigate sediment mineralogy.The primary dissolved salt in Hot Lake water was Mg2+-SO42− whereas sediments were dominated by gypsum (CaSO4·2H2O). Lake water concentrations increased with depth, reaching saturation with epsomite (MgSO4·7H2O) that was exposed at lake bottom. At maximum volume in spring, Hot Lake exhibited a relatively dilute mixolimnion; a lower saline metalimnion with stratified oxygenic and anoxygenic photosynthetic microbiological communities; and a stable, hypersaline monimolimnion, separated from above layers by a chemocline, containing high levels of sulfide and methane. The thickness of the mixolimnion regulates a heliothermal effect that creates temperatures in excess of 60°C in the underlying metalimnion and monimolimnion. The mixolimnion was dynamic in volume and actively mixed. It displayed large pH variations, in-situ calcium carbonate precipitation, and large evaporative volume losses. The depletion of this layer by fall allowed deeper mixing into the metalimnion, more rapid heat exchange, and lower winter lake temperatures. Solubility calculations indicate seasonal biogenic and thermogenic aragonite precipitation in the mixolimnion and metalimnion, but the absence of calcareous sediments at depth suggests dissolution and recycling during winter months. Dissolved carbon concentrations [dissolved organic carbon (DOC) and dissolved inorganic carbon (DIC)] increased with depth, reaching ∼0.04mol/L at the metalimnion–monimolimnion boundary. DIC concentrations were seasonally variable in the mixolimnion and metalimnion, and were influenced by calcium carbonate precipitation. DOC concentrations mimicked those of conservative salts (e.g., Na+-Cl−) in the mixolimnion and metalimnion, but decreased in the monimolimnion where mass loss by anaerobic microbial processes is implied. Biogenic reduced solutes originating in monimolimnion (H2S and CH4) were biologically oxidized in the metalimnion as they were not observed in more shallow lake waters. Multi-year solute inventory calculations indicated that Hot Lake is a stable, albeit seasonally and annually dynamic feature, with inorganic solutes cycled between lake waters and sediments depending on annual recharge, temperature, and lake water dilution state. With its extreme geochemical and thermal regime, Hot Lake functions as analog of early earth and extraterrestrial life environments.

Enzymatic microreactors in biocatalysis: history, features, and future perspectives

AbstractMicrofluidic reaction devices are a very promising technology for chemical and biochemical processes. In microreactors, the micro dimensions, coupled with a high surface area/volume ratio, permit rapid heat exchange and mass transfer, resulting in higher reaction yields and reaction rates than in conventional reactors. Moreover, the lower energy consumption and easier separation of products permit these systems to have a lower environmental impact compared to macroscale, conventional reactors. Due to these benefits, the use of microreactors is increasing in the biocatalysis field, both by using enzymes in solution and their immobilized counterparts. Following an introduction to the most common applications of microreactors in chemical processes, a broad overview will be given of the latest applications in biocatalytic processes performed in microreactors with free or immobilized enzymes. In particular, attention is given to the nature of the materials used as a support for the enzymes and the strategies employed for their immobilization. Mathematical and engineering aspects concerning fluid dynamics in microreactors were also taken into account as fundamental factors for the optimization of these systems.

Mechanical Properties and Tensile Fracture Mechanism of Rheocast A356 Al Alloy Using Cooling Slope

A356 aluminium alloy has a wide applicability in the manufacturing of automotive parts. Cooling slope (CS) rheocasting process has been used in the present work to produce A356 billets having near spherical morphology of primary Al phase. Absence of dendritic primary phase, observed in case conventionally cast A356 alloy, and finer distribution of secondary eutectic Si phase within the matrix establishes the usefulness of the CS casting route. Near spherical primary phase in the rheocast alloy ensures better strength, elongation properties and structural integrity in the produced billets. The liquid melt is allowed to flow through the cooling slope after pouring at 6500C. Rapid heat exchange between the flowing melt and slope wall and the atmosphere facilitates heterogeneous nucleation of α-Al phase on the cooling slope wall. Shear driven flow of the solidifying melt is found responsible for separation of α-Al phase from the slope wall and generation of nearly spherical morphology of the primary phase in the microstructure. Grain refiner addition in the melt leads to enhance the primary α-Al percentage in the microstructure and also aids to the improvement of degree of sphericity and reduction of spheroid size. So, grain refining helps to improve the strength, elongation and fracture properties of rheocast billets further.

Chemical Reaction Engineering and Catalysis Issues in Distributed Power Generation Systems

Three issues are most critical in fuel processors which are integrated with polymer electrolyte membrane (PEM) fuel cells for power generation: the steam reformer configuration, which must ensure very rapid heat transfer to the reformation zone, the development of highly active catalysts for the water−gas shift (WGS) reaction and the development of highly selective catalysts for the methanation reaction. The heat-integrated wall reactor (HIWAR), in either the tubular or the plate form, which offers very rapid heat exchange between a combustion and a reformation zone, is proposed. This configuration results in high efficiency and compact design. Platinum catalysts supported on a “reducible” metal oxide such as TiO2 exhibit high WGS activity, which can be further improved with the addition of alkali or alkaline earth promoters. Titania-supported ruthenium catalysts are capable of completely and selectively methanate CO in the presence of excess CO2, provided that catalyst characteristics are optimized and operating conditions are properly selected. Integration of the three developments can result in efficient power generation systems.

Development of a High-Speed Real-Time Polymerase Chain Reaction System Using a Circulating Water-Based Rapid Heat-Exchange

Polymerase chain reaction (PCR) is a powerful technique to detect microorganisms, viruses, or cells by amplifying a single copy or a few copies of a fragment of a particular DNA sequence. To reduce acquisition time, it is necessary to decrease the temperature transition time between denaturation and extension. We have developed a simple rapid real-time microlitter-sample droplet PCR system accomplished by the rapid liquid-based heat-exchange of sample droplets by quick switching of two circulating hot waters of denaturation and extension, a microlitter-sized droplet and a thin-film aluminum chip. Using this system, rapid PCR amplification of a set of droplets lined up on an aluminum chip was conducted successfully as shown by the increase in fluorescence intensity, and was accomplished within 3.5 min in 40 cycles of 1 s denaturation and 3 s extension reaction, which is one magnitude faster than conventional fast PCR systems. This method allows the rapid detection of DNA fragments and has a possibility for measuring multiple samples simultaneously in a miniaturized microfluidic chip.