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For the problem of power generation turbine blade ablation in hypersonic vehicles, hydrocarbon fuel carried by the vehicle is used to cool the turbine blades. In order to fully utilize the cooling capacity of hydrocarbon fuel, the structure of the cooling channels needs to be optimized. In this study, a variable clearance hydrocarbon fuel cooling channel is applied for the first time to the rotating turbine blades of a hypersonic vehicle to enhance the heat transfer ability of hydrocarbon fuel. The effect of clearance size on the heat transfer performance of hydrocarbon fuel under rotating conditions is investigated. The accuracy of the calculations is verified by comparison with experimental data. The results of the study show that the heat transfer performance can be significantly improved by changing the clearance of the turning section. The clearance size 2.5 D channel has the highest thermal performance with a maximum improvement of 1.8 times. The law of change of thermal performance is affected by crossing the critical temperature point, as it is different before and after the crossing. Thermal performance changes from decreasing then increasing to increasing then decreasing as the clearance size increases for high rotation speed conditions as the temperature of the entrance straddles the critical temperature. The Nusselt number first increases and then decreases for all channels with different clearance sizes with an increasing rotational speed. The friction factor changes from first increasing and then decreasing to decreasing and then increasing as the clearance size increases for high rotation speed conditions as the temperature of the entrance straddles the critical temperature. [ABSTRACT FROM AUTHOR]

Uncontrolled atmospheric entry of meteors, satellites, and spacecraft components often leads to their partial or complete demise. In this destructive process, driven by hypersonic ablation, reentry objects fragment, interact, and alter each other's aerothermal environment. The effect of these interactions on the heat transfer to the fragments has not been investigated, despite the heat transfer's importance in hypersonic ablation and reentry demise. This study focuses on the numerical investigation of heat transfer to proximal circular cylinders in a thermochemically frozen flow and in two dimensions. First, binary body configurations at Mach numbers 2, 4, and 8 revealed that the heat load and peak heat transfer can be augmented for either or both proximal bodies by +20% to −90% of an isolated body. Second, different clusters of five proximal bodies showed that the heat load to any given body can range from +40% to −90% of an isolated body. Moreover, the average heat load in a cluster is found to vary between +20% and −60% of an isolated body. Intuitively, clusters which are thin in the direction perpendicular to free-stream velocity and long in the direction parallel to the free-stream velocity have their cluster-averaged heat load reduced. In contrast, thick and thin clusters, in directions perpendicular and parallel to the free-stream velocity, are subject to an increased cluster-averaged heat load. [ABSTRACT FROM AUTHOR]

In this paper, we study the ablation phenomena associated with the operation of a capillary discharge for an electrothermal gun. Electrothermal-chemical (ETC) guns are used for enhancement of ignition and combustion of an energetic propellant. One of the major components of the ETC system is a plasma source based on a capillary discharge. In this paper, a model of the capillary discharge is developed. In this model, primary attention is paid to the ablation phenomenon. Different characteristic subregions near the ablated surface, namely, a space-charge sheath, a Knudsen layer, and a hydrodynamic layer, are considered. In this formulation, the ablation rate is determined by the parameters at the edge of the Knudsen layer. The kinetic approach is used to determine the parameters at the interface between the kinetic Knudsen layer and the hydrodynamic layer. Coupling the solution of the nonequilibrium Knudsen layer with the hydrodynamic layer provides a self-consistent solution for the ablation rate. According to the model predictions, the peak electron temperature is about 1.4 eV, the polyethylene surface temperature is about 700 K, and the pressure is about 10 MPa. It is found that the ablation rate increases with the capillary length. The ablated mass and the predicted total pressure agree with previous experimental observations. [ABSTRACT FROM AUTHOR]

We discuss the ablation of aluminum plasma using picosecond pulsed laser in vacuum and in ambient atmosphere of nitrogen. The plume dynamics of picosecond and nanosecond laser-ablated plumes in ambient atmosphere is discussed. The degree of polarization is measured using optical emission spectroscopy for the Al III transition 4s 2S1/2-4p 2P3/2o at 569.6 nm. Strong anisotropy is observed using picosecond laser pulse as compared to nanosecond laser pulse. [ABSTRACT FROM AUTHOR]

Presents a study that examined thermal transport, mass ablation rates and preheat in six-beam ultraviolet irradiation of spherical targets. Functionality of the thermal transport in laser-target interaction; Discussion of mass ablation and ablation pressure; Possible sources of the discrepancy between spectral and charge-collector measurements.

Presents information on a study which proposed a thermal model for pulsewidth-dependent ablation of polyimide. Plume generation and associated screening of the laser pulse; Heat transfer and material removal model; Estimation of chromophore density.

Objective: Determining accurate intracardiac maps of atrial fibrillation (AF) in humans can be difficult, owing primarily to various sources of contamination in electrogram signals. The goal of this study is to develop a measure for signal fidelity and to develop methods to quantify robustness of observed rotational activity in phase maps subject to signal contamination. Methods: We identified rotational activity in phase maps of human persistent AF using the Hilbert transform of sinusoidally recomposed signals, where localized ablation at rotational sites terminated fibrillation. A novel measure of signal fidelity was developed to quantify signal quality. Contamination is then introduced to the underlying electrograms by removing signals at random, adding noise to computations of cycle length, and adding realistic far-field signals. Mean tip number N and tip density δ, defined as the proportion of time a region contains a tip, at the termination site are computed to compare the effects of contamination. Results: Domains of low signal fidelity correspond to the location of rotational cores. Removing signals and altering cycle length accounted for minor changes in tip density, while targeted removal of low fidelity electrograms can result in a significant increase in tip density and stability. Far-field contamination was found to obscure rotation at the termination site. Conclusion: Rotational activity in clinical AF can produce domains of low fidelity electrogram recordings at rotational cores. Observed rotational patterns in phase maps appear most sensitive to far-field activation. These results may inform novel methods to map AF in humans which can be tested directly in patients at electrophysiological study and ablation. [ABSTRACT FROM AUTHOR]

The quench protection system of the nonplanar coils of the Wendelstein 7-X stellarator was laid out over 15 years ago. At that time, the assessment of the hot-spot temperature by a basic adiabatic model was done using design values for material and operation parameters. After the operating experience in 2016, the hot-spot temperature is reassessed with the thermal-hydraulic program THEA, using the actual values for delay and dump time. The electrical resistivity of the conduit alloy ismeasured over the whole range of temperatures and in magnetic fields on relevant samples of a conductor, exposed to the hardening heat treatment after winding. The results were fed into THEA. Parametric variations are studied in the calculations, e.g., testing the effect of the quench initiation zone, delay time, and dump resistor. The results suggest that the hot-spot temperature of the conduit in the case of quench is safely within the allowable values even when the dump voltage is reduced compared to the initial design value. [ABSTRACT FROM AUTHOR]

The recent improvements of the commercial, general purpose Finite Element Analysis (FEA) software have allowed them to be used for modeling ablation problems. ABAQUS for example, provides a user-subroutine UMESHMOTION along with the Arbitrary Lagrangian-Eulerian (ALE) adaptive remesh algorithm that enable the users to couple the heat transfer with the progressive surface recession (i.e., ablation). However, such a numerical capability is limited to model ablation problems when the ablation front (i.e., receding surface) is confined within a single material domain (e.g., homogenous material). For ablation problems when the ablation front proceeds from one material domain to another (e.g., laminated composite materials that consist of multiple laminate layers with different material orientations), such a numerical capability is insufficient, since the mesh is not allowed to flow from one material domain to another when the UMESHMOTION subroutine is used. In this paper, a novel computational procedure that sequentially performs the general heat transfer analysis and the general static analysis in ABAQUS, is proposed enabling the capability of ABAQUS for modeling ablation of laminated composites. The proposed procedure is verified by comparing the predictions of temperature and ablation histories of a two-dimensional isotropic panel (i.e., with single material domain) with those obtained using the traditional UMESHMOTION + ALE method. In addition, a case study of applying the proposed procedure to predict the thermal and ablation response of a laminated carbon fiber reinforced epoxy matrix (CFRP) composite panel subjected to a high-intensity and short-duration radiative heat flux is demonstrated. [ABSTRACT FROM AUTHOR]

The thinning and miniaturization of components, such as liquid crystal display and solar cells, has increased the market demand for tempered ultra-thin glass. The physical tempering in glass, which is less than 2 mm thick, is difficult to achieve in air jet impingement. In this study, we propose the use of mist flow jet impingement cooling technology on ultra-thin glass. The effects of the mist flow droplets diameters, nozzle inlet temperature, and mass fraction on the heat transfer rate and uniformity are numerically studied. Our performance in terms of the heat transfer rate and the uniformity is accounted for through an evaluation of the surface-averaged temperature, averaged Nusselt number, surface-averaged Nusselt number, and surface standard deviation percentage of the Nusselt number. The empirical correlation for the surface averaged Nusselt number as a function of mist flow droplet diameters is provided. The droplet diameter is the major factor affecting the heat transfer rate, while the jet inlet temperature is a minor factor. We can obtain a better heat transfer uniformity by controlling the droplet diameter of the mist flow jet impingement. Using mist flow jet impingement, we would not only greatly reduce the amount of air and save energy, but also meet the needs of sudden cooling for tempered glass with a thickness of less than 2 mm. [ABSTRACT FROM AUTHOR]

This paper is aimed to restrain the defects such as fluff and ablation, which were often found in machining of the aramid fiber-reinforced composites (AFRP). The cooling method of spray liquid nitrogen was adopted in the orthogonal milling process. The processing parameters including cutting depth, cutting speed, cooling temperature, feed speed, and liquid nitrogen flow were considered in details, and their effects on the processing quality were researched and analyzed. The analysis optimization methods of processing parameter were employed for the influence on the machining surface quality. Meanwhile, the optimal machining surface quality was predicted and verified. The results show that the cryogenic way realizes a bigger improved role on machining quality than the conventional one for AFRP. As well as the influence order of processing parameters on the roughness is cutting depth, cutting speed, cooling temperature, feed speed, and liquid nitrogen flow. And the predicted result Ra = 0.557 μm of minimum surface roughness value is similar with the actual one Ra = 0.572 μm and verifies the feasibility of optimization method. For processing of AFRP, the cooling way of spray liquid nitrogen has a positive role with high quality and efficiency. [ABSTRACT FROM AUTHOR]

The spin-coupled interface (SI) resistance plays a crucial role in the interpretation of the giant magnetoresistance with current perpendicular to the plane. Recently, a theoretical work showed that its Joule heat also equals the total spin-dependent heat generation in a conceptual spin valve. Here we reexamine this conclusion in a practical spin valve with a finite nonmagnetic spacer layer and spin-selective interfaces. It turns out that this conclusion does not hold except for some special segments. The SI resistance has a more serious limitation: it may be negative in certain situation. In-depth analysis shows that its “Joule heating” should be interpreted actually as the extra energy supplied only in the ferromagnetic layers and at the interfaces. This extra energy is stored in the chemical-potential splitting due to spin accumulation and only part of it converts into heat locally. The rest flows to other layers, especially the nonmagnetic layer, in which the inflowing energy compensates exactly for the spin-dependent heat generation. In essence, this kind of energy transport makes the SI resistance unsuitable for a simple description of the heat generation, and thus we propose a new effective resistance as an alternative to it. [ABSTRACT FROM AUTHOR]

Microwave thermal ablation (MTA) is a minimally invasive therapeutic technique aimed at destroying pathologic tissues through a very high temperature increase induced by the absorption of an electromagnetic field at microwave (MW) frequencies. Open problems, which are delaying MTA applications in clinical practice, are mainly linked to the extremely high temperatures, up to 120 °C, reached by the tissue close to the antenna applicator, as well as to the ability of foreseeing and controlling the shape and dimension of the thermally ablated area. Recent research was devoted to the characterisation of dielectric, thermal and physical properties of tissue looking at their changes with the increasing temperature, looking for possible developments of reliable, automatic and personalised treatment planning. In this paper, a review of the recently obtained results as well as new unpublished data will be presented and discussed. [ABSTRACT FROM PUBLISHER]

The optimum design of a solid propulsion system consists of optimization of various disciplines including structure, aerothermodynamics, heat transfer, and grain geometry. In this paper, an efficient model of every discipline has been developed, and a suitable framework is introduced for these hard-coupled disciplines. Hybrid optimization algorithm is used to find the global optimum point including genetic algorithm and sequential quadratic programing. To show the performance of the proposed algorithm, the required correction factor values have been carefully derived using comparison between more than 10 real solid propulsion systems and the proposed algorithm results. According to the results, the derived correction factors are close to 1, with scattering level better than 0.97. In addition, it is shown that the proposed algorithm (errors < 8%) is more accurate in comparison with the conventional approach (errors < 17%). Then, for a case study, multidisciplinary analysis has been done based on 3 general objectives including dry mass, total mass, and specific impulse. It means that the optimum specific impulse is not the maximum value and the optimum dry mass is not the minimum value. Finally, the proposed algorithm can be used to directly derive the optimum configuration for every mission requirement. [ABSTRACT FROM AUTHOR]

KSLV-II (Korea Space Launch Vehicle II) planned to launch in 2020 is composed of three stages. The base of the 1st stage faces high heat fluxes with the reverse flow of 2200 K exhaust plume gas from clustered four engines. The base TPS (Thermal Protection System) is attached on the base of the 1st stage to protect the structure of the LV (Launch Vehicle). A cork insulator is selected as the TPS material and its thickness is determined by a numerical analysis. The insulation performance of the base TPS is qualified by a heating test and the adhesion performance on LV's body is verified by an environmental test. The research and development activities on the TPS in the space area are expected to be expanded because of planned heavy LVs. [ABSTRACT FROM AUTHOR]

The objective of this study was to determine and compare properties of laminated veneer lumber (LVL) panels manufactured from heat treated (212°C, 2h) and untreated pine veneer with melamine urea formaldehyde (MUF) adhesive. The results showed that, heat treatment considerably decreased all investigated physical properties of LVL. The reductions in density (D), moisture content (MC), and thickness swelling (TS) were 8.33%, 33.78% and 14.03%, respectively. The findings of this study demonstrated that heat treatment resulted in adverse effect on bending strength and hardness of LVL panels. Heat treatment caused a decrease in bending strength (MOR) by 31.85% and in hardness (HT) by 25.44%. However, modulus of elasticity (MOE) and compressive strength (CS) values of LVL panels were higher than those of untreated groups. Compressive strength and modulus of elasticity (MOE) of LVL panels made of heat treated veneer respectively were 11.17% and 7.46% higher than untreated LVLs. [ABSTRACT FROM AUTHOR]

Optimal design and performance of a combined infrared-convective drying system with respect to the energy issue is extremely put through the application of advanced engineering analyses. This article proposes a theoretical approach for exergy analysis of the combined infrared-convective drying process using a simple heat and mass transfer model. The applicability of the developed model to actual drying processes was proved using an illustrative example for a typical food. [ABSTRACT FROM AUTHOR]

The existence of large blood vessels seriously impacts the results of microwave ablation on heat transfer of surrounding tissue, and the research of influences about large blood vessels could be essential and significant. The temperature distribution in the tissue was analyzed with a microwave heating source by finite element method. The model, where the blood vessel is parallel to antenna, has different distances from antenna to blood vessel. As distance was greater than 20mm, the effect of blood vessel that was parallel to antenna was ignored and the ablation area was elliptical-like. When distance was less than 10mm, the part of asymmetrical coagulated area was on the right side of blood vessel. Therefore, the temperature contour by different conditions could provide numerical references, which is whether to block blood vessel or not, to achieve the aim of guiding the clinical practice, according to the locations of tumor and blood vessel. [ABSTRACT FROM AUTHOR]

An experimental analysis is presented to establish the thermal performance of a latent heat thermal storage ( LHTS) unit. Paraffin is used as the phase change material ( PCM) on the shell side of the shell and tube-type LHTS unit while water is used as the heat transfer fluid ( HTF) flowing through the inner tube. The fluid inlet temperature and the mass flow rate of HTF are varied and the temperature distribution of paraffin in the shell side is measured along the radial and axial direction during melting and solidification process. The total melting time is established for different mass flow rates and fluid inlet temperature of HTF. The motion of the solid-liquid interface of the PCM with time along axial and radial direction of the test unit is critically evaluated. The experimental results indicate that the melting front moves from top to bottom along the axial direction while the solidification front moves only in the radial direction. The total melting time of PCM increases as the mass flow rate and inlet temperature of HTF decreases. A correlation is proposed for the dimensionless melting time in terms of Reynolds number and Stefan number of HTF. © 2013 Wiley Periodicals, Inc. Heat Trans Asian Res; Published online in Wiley Online Library (). DOI 10.1002/htj.21120 [ABSTRACT FROM AUTHOR]

Ablation is one of the main means of thermal protection for hypersonic flight vehicles. In this paper, based on pyrogeneration-plane ablation model and temperature measurement at some specific locations, the surface heat flux estimation method is developed with adjoint equation analysis and validated by numerical examples. It is shown that the estimated heat flux agrees with the exact value well, and the difference between the estimated heat flux and the exact value grows as the measurement noise increases. It is also revealed that the measured noise in the ablated surface recession value may have a significant influence on the estimated heat flux. Furthermore, the estimation method is utilized to analyze the experimental ablation results of the blunt Carbon-phenonic material Narmco4028 in ceramic-heated tunnel, it is found that the estimated surface heat flux value is close to the heating power of the arc-heater. This result further verifies that the estimation method is effective and may have a bright prospect in engineering practice. [ABSTRACT FROM AUTHOR]

One of the most disputed issues raised by molten corium concrete interaction (MCCI) is how the 2D cavity ablation in an oxidic pool evolves: why is the ablation anisotropic with siliceous concretes and isotropic with carbonaceous concretes. The work performed in the frame of the SARNET2 WP6 group during the last 4 years has enabled significant progress on this topic. This paper summarizes this progress using the analysis of recent 2D real material experiments in an oxidic pool and from analytical simulant experiments on 2D heat convection in a bubbling pool, including calculations and recalculations with MCCI codes available in Europe. Firstly, the effective heat transfer coefficients from the bulk pool to the bottom and lateral pool interfaces deduced from MCCI experiments lead to a range of a few 100 W/m 2 /K. By contrast, a detailed review of possible 2D convection mechanisms shows that the individual heat convection mechanisms (without taking a crust into account) such as gas bubbling convection and solutal convection overestimates the overall heat transfer coefficient, and does not account for the main trends of 2D ablation deduced from MCCI tests, which are very dependent on the composition of concrete components and aggregates. This fact, in turn, points to the effect of more complex pool/concrete interface structures. On the basis of a thorough interpretation of the experimental database and of a detailed comparison of MCCI code predictions, a set of the most realistic and consistent assumptions are identified and major remaining uncertainties are listed. [ABSTRACT FROM AUTHOR]

In this paper a three-dimensional numerical model for cryosurgery is developed to study the effect of central probe on the cryosurgery process. The irregular boundary resulting due to the presence of cryoprobes is taken care by body-fitted multi-block non-orthogonal grids. The thermo-physical properties of biological tissue are considered as a function of temperature as phase change takes place over a wide temperature range for the biological tissue. It has been found that the cooling power requirement by the single offset cryoprobe is greater than that of the central cryoprobe. However, the presence of central cryoprobe markedly influenced the cryosurgery process, resulting in an increase in the ablation ratio by 57 % with an insignificant increase in cooling power by 4.5 %. This information can be utilised effectively in computerised planning of a cryosurgery protocol. [ABSTRACT FROM AUTHOR]

This paper is devoted to the stochastic optimization of the temporal shape of a laser pulse for material ablation. The temperature of the material subject to the laser pulse is modeled by a Stefan-like heat transfer equation. From the surface temperature is then determined the ablation depth of the studied material, which is the quantity to optimize for a given laser pulse fluence. Several numerical tests are presented for laser ablation of silicon, which is the material of interest here. [ABSTRACT FROM PUBLISHER]

Modified nanokaolinite was uniformly dispersed in acrylonitrile butadiene rubber using dispersion kneader and two roller mixing mill. In order to evaluate ablation characteristics of the fabricated composites, high-temperature ablation testing was carried out. The peak incorporation of nanoclay in the rubber matrix has enhanced the ablation resistance up to 97% and reduced the temperature elevation at the back face of the nanocomposite up to 51% during the 200s oxy–acetylene flame exposure on the surface of the ablator. Thermogravimetric and differential thermal analyses elucidate the thermal endurance improvement with increasing filler contents in the polymer matrix. Thermal conductivity and thermal impedance of the composite specimens were evaluated on the domestically manufactured thermal conductivity measuring apparatus. It is scrutinized that the former property reduced up to 49% at and the subsequent characteristic of the rubber composite is elevated up to 43% at 373 K with the 30 wt% incorporation of the nanoclay into the base rubber composition. Mechanical properties of the acrylonitrile butadiene rubber composite specimens were significantly enhanced with increasing filler introduction into the host matrix. Porous char morphology, polymer pyrolysis and composition of the ablated samples were analyzed using scanning electron microscopy and energy dispersive spectroscopy analyses. [ABSTRACT FROM AUTHOR]

The main goal of the work described in this paper was to set up a procedure for modeling a thermal protection system for a hypersonic reentry vehicle by extending earlier work done by the authors. A multiphysics framework has been setup for the simulation of hypersonic reentry vehicles using commercial codes FLUENT and LS-DYNA with user-defined programming. The computational fluid dynamics code (FLUENT) and the material thermal and structural response code (LS-DYNA) are loosely coupled to achieve the solution. The surface recession resulting from ablation in the reentry vehicle is simulated by implementing a mesh movement algorithm in LS-DYNA. The vehicle considered in the calculation is an axisymmetric vehicle flying at zero degree angle of attack. [ABSTRACT FROM AUTHOR]

Abstract: A simple modeling of the heat transfer through insulating bilayers of cryogenic reservoir subjected to surrounding environment or aerothermal flux is presented. The model permits to determine the instantaneous evolution of maximum fuel temperatures and the boil-off rate as well as the possible insulation ablation. To get a realistic estimation of the maximum fuel temperature and boil-off loss, the good knowledge of the internal convection coefficient, taking into account the possible fuel ebullition, is indispensable. The aerothermal flux provokes the insulation degradation and its ablation. Because of the ablation, the reservoir becomes less and less thermally protected, which may cause an important fuel boil-off. Compared to classical insulations with uniform density, those with spatially graded densities appear as potential insulations permitting to meet both light-weight and low boil-off requirements. [Copyright &y& Elsevier]

A procedure has been developed to couple a hypersonic reacting flow model, a radiative heat transfer model, and a surface ablation model to study the surface heat transfer and surface ablation rate of atmospheric reentry vehicles. The two-way loose-coupling algorithm is described for each of the models, as is the solution procedure to achieve convergence. Observations on the challenges of the loose-coupling strategy are given. Representative results are presented for two-dimensional benchmark examples and for three-dimensional flow at an angle of attack past a symmetric capsule based on the Crew Exploration Vehicle reentry vehicle. Effects due to the interaction with radiation and ablation are shown for two quantities of interest: the predicted peak surface heat flux and the ablation rate on the vehicle heat shield. Uncertain parameters are identified in each of the submodels, and a preliminary parameter sensitivity study is carried out by varying these values to examine their effects on the heat transfer and ablation rates in the coupled problem. [ABSTRACT FROM AUTHOR]

Abstract: The post-dryout heat transfer coefficients were analyzed by differentiating them into two regions, based on their observed trends. One is a transition region. The other is a fully dryout region. The effects of test conditions for heat flux and saturation temperature on the boundaries of the two regions were also investigated, and the existing models for post-dryout heat transfer coefficients were verified for both regions. To develop a prediction method for flow boiling of CO2, we applied the critical liquid film model, to predict the point of dryout vapor quality. The Yun et al. model and the Groeneveld model are used to estimate the heat transfer coefficients prior to and subsequent to the point of dryout vapor quality, respectively. The former shows a mean deviation of 38%, and the latter gives 36.4% for the three different data sources. [Copyright &y& Elsevier]

Abstract: Ice slurry flow through horizontal pipes is studied experimentally in order to find out its heat transfer and isothermal friction properties. Using 9% NaCl brine as the carrier fluid, different flow conditions are discussed with a view to analyse each involved variable. In this Part I, experimental data are directly correlated and easy-to-use expressions for the Darcy friction factor and the Nusselt number were obtained as functions of non-dimensional parameters expressing flow and geometrical properties. The most remarkable conclusion obtained is a clear influence of the ice particle–pipe diameter ratio in the pressure drop parameters, not previously taken into account, which must be confirmed in heat transfer process. The thermal and hydraulic performance of ice slurry flowing through corrugated pipes is also analysed showing, with regard to smooth pipe, the same behaviour in pressure drop and opposite behaviour in heat transfer. [Copyright &y& Elsevier]

Abstract: Experimental investigations on the effects of biofouling on air-side heat transfer and pressure drop for three biofouled finned tube heat exchangers and one clean finned tube heat exchanger were performed. Artificial accelerated method of microorganism growth on the fin surface was used for simulating the biofouled finned tube heat exchangers. Experimental results indicate that the effects of biofouling on the air-side heat transfer coefficient decreases 7.2% at 2.0m/s when the biofouled area ratio is 10%, while it decreases 15.9% at 2.0m/s when the biofouled area ratio is 60%, and biofouling causes a 21.8%∼41.3% increase in pressure drop when the air velocity is between 0.5 and 2.0m/s. The increase of inlet air velocity is helpful to improve the long-term performance of finned tube heat exchanger. Biofouling makes the hydrophilic coating failure, and the condensation water easily converges on the fin surface where biofouling grows. [Copyright &y& Elsevier]

Abstract: An experimental study has been carried out on the heat transfer enhancement and pressure drop characteristics in presence of twisted tape inserts, during flow boiling of R-134a, inside a horizontal evaporator. The test-evaporator was an electrically heated 1260mm long copper tube with 7.5mm inside diameter. The experiments were performed for plain flow and four tubes with twisted tapes of 6, 9, 12 and 15 twist ratios and four refrigerant mass velocities of 54, 85, 114 and 136kg/sm2 for each tape. It has been found that the twisted tape inserts enhance the heat transfer coefficient on relatively higher pressure drop penalty, in comparison to that for the plain flow. [Copyright &y& Elsevier]

Abstract: The performances of three types of heat exchangers that use the louver fin geometry: (1) parallel flow parallel fin with extruded flat tubes heat exchanger (PF2), (2) parallel flow serpentine fin with extruded flat tubes heat exchanger (PFSF) and (3) round tube wave plate fin heat exchanger (RTPF) have been experimentally studied under dry, wet and frost conditions and results are presented. The parameters quantified include air-side pressure drop, water retention on the surface of the heat exchanger, capacity and overall heat transfer coefficient for air face velocity 0.9, 2 and 3m/s, air humidity 70% and 80% and different orientations. The performances of three types of heat exchanger are compared and the results obtained are presented. The condensate drainage behavior of the air-side surface of these three heat exchanger types was studied using both the dip testing method and wind tunnel experiment. [Copyright &y& Elsevier]

Abstract: This study examined the two-phase flow boiling pressure drop and heat transfer for propane, as a long term alternative refrigerant, in horizontal minichannels. The pressure drop and local heat transfer coefficients were obtained for heat fluxes ranging from 5–20kWm−2, mass fluxes ranging from 50–400kgm−2 s−1, saturation temperatures of 10, 5 and 0°C, and quality up to 1.0. The test section was made of stainless steel tubes with inner diameters of 1.5mm and 3.0mm, and lengths of 1000mm and 2000mm, respectively. The present study showed the effect of mass flux, heat flux, inner tube diameter and saturation temperature on pressure drop and heat transfer coefficient. The experimental results were compared against several existing pressure drop and heat transfer coefficient prediction methods. Because the study on evaporation with propane in minichannels was limited, new correlations of pressure drop and boiling heat transfer coefficient were developed in this present study. [Copyright &y& Elsevier]

Abstract: This paper quantifies the influence of CuO nanoparticles on the boiling performance of R134a/polyolester mixtures on a roughened, horizontal, flat surface. A lubricant based nanofluid (nanolubricant) was made with a synthetic ester and CuO particles. For the 0.5% nanolubricant mass fraction, the nanoparticles caused a heat transfer enhancement relative to the heat transfer of pure R134a/polyolester (99.5/0.5) of between 50% and 275%. A smaller enhancement was observed for the R134a/nanolubricant (99/1) mixture, which had a heat flux that was on average 19% larger than that of the R134a/polyolester (99/1) mixture. Further increase in the nanolubricant mass fraction to 2% resulted in a still smaller boiling heat transfer improvement of approximately 12% on average. Thermal conductivity measurements and a refrigerant/lubricant mixture pool-boiling model were used to suggest that increased thermal conductivity is responsible for only a small portion of the heat transfer enhancement due to nanoparticles. [Copyright &y& Elsevier]

Abstract: An experimental research was conducted to investigate the effect of channel height on heat transfer enhancement of a surface affixed with arrays () of short rectangular fins of a co-angular type pattern in channels. An infrared imaging system with the camera (TVS 8000) measured the temperature distributions to calculate the local heat transfer coefficients of the overall surface (fin base and endwall) of the representative fin regions. Heat transfer experiments were performed for a co-angular type fin pattern varying the channel to fin height ratio () from 2 to 5. Friction factors of the finned surfaces were calculated from pressure drop measurements. Relatively larger friction occurs for the smaller channel to fin height ratios and the friction factor slowly decreases with increasing Reynolds number. For the larger channel to fin height ratios, friction factor slowly increases with Reynolds number. The area averaged heat transfer decreases with increasing the channel to fin height ratio and channel aspect ratio, while heat transfer increases with the mainstream velocity. This is because, separation space between the channel wall and the fin top surface has a great influence on the phenomena of flow separated from the fin edge and vortex formation. At a smaller separation space, generated vortex is strongly reflected and vortex structure formation is adequately completed having full strength to interact with fins and endwall surface which leads to larger friction and contributes heat transfer enhancement. A detailed heat transfer analysis and iso-heat transfer coefficient contour gives a clear picture of the heat transfer characteristics of the overall surface. A relative performance graph indicates that the lowest channel to fin height ratio () has the highest thermal performance out of the channels tested. In addition, significant thermal enhancement, 2.6–3 times the smooth surface value can be achieved at lower Reynolds numbers with a co-angular fin pattern in the channel. [Copyright &y& Elsevier]

Abstract: Microchannel heat exchangers (MCHE) can be made with channels of various geometries. Their size and shape may have considerable effect on the thermal and hydraulic performance of a heat exchanger. In this paper numerical simulation is carried out to solve 3D developing flow and 3D conjugate heat transfer of a balanced counter flow microchannel heat exchanger (CFMCHE) to evaluate the effect of size and shape of channels on the performance of CFMCHE for the same volume of heat exchanger. The effect of shape of the channels on its performance is studied for different channel cross-sections such as circular, square, rectangular, iso-triangular and trapezoidal. Results show that for the same volume of a heat exchanger, increasing the number of channels lead to increase in both effectiveness and pressure drop. Moreover circular channels give the best overall performance (thermal and hydraulic) among various channel shapes. New correlations are developed to predict the value of heat exchanger effectiveness and performance index as a function of relative size of channels with overall heat exchanger volume, Reynolds number and thermal conductivity ratio. [Copyright &y& Elsevier]

Abstract: This paper presents an experimental investigation of heat transfer enhancement capabilities of coolants with suspended nanoparticles (Al2O3 dispersed in water) inside a radial flow cooling device. Steady, laminar radial flow of a nanofluid between a heated disk and a flat plate with axial coolant injection has been considered. An experimental test rig was built. Results show that heat transfer enhancements are possible in radial flow cooling systems with the use of nanofluids. In general, it was noticed that the Nusselt number increases with particle volume fraction and Reynolds number and decreases with an increase in disk spacing. [Copyright &y& Elsevier]

Abstract: The correct sizing of the heat transfer surfaces is important to ensure proper operation, load turndown, and optimization of circulating fluidized beds (CFBs). From this point of view, in this study, the thermodynamic second law analysis of heat transfer surfaces in CFBs is investigated theoretically in order to define the parameters that affect the system efficiency. Using a previously developed 2D CFB model which uses the particle-based approach and integrates and simultaneously predicts the hydrodynamics and combustion aspects, second law efficiency and entropy generation values are obtained at different height and volume ratios of the heat transfer surfaces for CFBs. Besides that, the influences of the water flow rates and heat exchanger tube diameters on the second law efficiency are investigated. Through this analysis, the dimensions, arrangement and type of the heat transfer surfaces which achieve maximum efficiency are obtained. [Copyright &y& Elsevier]

Abstract: A predictive model is developed to describe heat transfer and fluid dynamic behavior of a helical double-pipe vertical evaporator used in an absorption heat transformer integrated to a water purification process. The evaporator uses water as working fluid connected in countercurrent. Heat transfer by conduction in the internal tube wall is considered; in addition the change of phase is carried out into the internal tube. The dynamic model considers equations of continuity, momentum and energy in each flow. The discretized governing equations are coupled using an implicit step by step method. The results of this model are compared with the experimental data in steady state, obtaining good agreement in the evaporation process. The model is also evaluated of form dynamic to determine the principal operation variables that affect the evaporator with the main objective to optimize and control the system. [Copyright &y& Elsevier]

Abstract: Linearized thermoacoustic model considering temperature oscillation in the solid wall is applied to analyze the heat transfer characteristics of compressible oscillating flow in parallel-plate and circular-tube regenerators. In particular, the study focus results of heat transfer analysis are applicable in lower cryogenic temperature ranges (<20K). Complete expression for Nusselt number is derived and it is shown to be the function of six nondimensional parameters when the shape of the regenerator is fixed. These parameters are discussed, respectively. Simplified expressions of the Nusselt numbers for both parallel plates and circular tubes structured regenerators are derived. Heat transfer characteristics can be evaluated via these simple expressions. Possible approaches of enhancing heat transfer in a thermoacoustic regenerator are discussed. [Copyright &y& Elsevier]

Abstract: Experiments were conducted to study the subcooled flow boiling heat transfer performance of FC-72 over silicon chips. For boiling heat transfer enhancement, two kinds of micro-pin-fins having fin thickness of 50 μm and fin heights of 60 and 120 μm, respectively, were fabricated on the silicon chip surface with the dry etching technique. The fin pitch was twice the fin thickness. The experiments were conducted at the fluid velocities of 0.5, 1 and 2 m/s and the liquid subcoolings of 15, 25 and 35 K. The micro-pin-finned surfaces showed a sharp increase in heat flux with increasing wall superheat and a large heat transfer enhancement compared to a smooth surface. The nucleate flow boiling curves for the two micro-pin-finned surfaces collapsed to one line showing insensitivity to fluid velocity and subcooling, while the critical heat flux values increased with fluid velocity and subcooling. The micro-pin-finned surface with a larger fin height of 120 μm provided a better flow boiling heat transfer performance and a maximum critical heat flux of 145 W/cm2. The wall temperature at the critical heat flux for the micro-pin-finned surfaces was less than 85 °C for the reliable operation of LSI chips. [Copyright &y& Elsevier]

Abstract: Heat transfer due to laminar natural convection of copper–water nanofluid in a differentially heated square cavity has been predicted by Artificial Neural Network (ANN). The nanofluid has been considered as non-Newtonian. The ANN has been trained by a resilient-propagation (RPROP) algorithm. The required input and output data to train the ANN has been taken from the results of numerical simulation that was performed simultaneously where the transport equations has been solved numerically using finite volume approach incorporating SIMPLER algorithm. Results from simulation and resilient-propagation (RPROP) based ANN have been compared. It has been observed that the ANN predicts the heat transfer correctly within the given range of training data. It is further observed that resilient-propagation (RPROP) based ANN is an efficient tool to predict the heat transfer than simulation, which takes much longer time to compute. [Copyright &y& Elsevier]

Abstract: The present study numerically investigated the effect of the geometry of flattened tube on the thermal performance of a high temperature generator (HTG) with the pre-mixed surface flame burner of the double effect LiBr–water absorption system. The heat transfer tubes of the HTG were consisted with a set of circular and flattened tubes in series. FLUENT, as a commercial code, was applied for estimating the thermal performance of the HTG. Key parameters were the aspect ratio of flattened tubes, rib transversal length, and the rib pitch ratio on the flattened tube of the HTG. The maximum heat transfer rate of the HTG was obtained at the aspect ratio of 6.8 for the flattened tube. The heat transfer rate for the flattened tube was increased by 4.2% as the rib transversal length was increased from 2mm to 3mm. The heat transfer rate of the flattened tube with the rib pitch ratio of 15.3 was higher by the maximum 5.8% than that without rib. The heat transfer rate of the HTG with the rib of the rib transversal length of 3mm and the rib pitch ratio of 15.3 was higher by 3.4% than that without the rib. It led that the exhaust gas temperature of the HTG with the rib was lower by 23°C than that without the rib. [Copyright &y& Elsevier]

Heat and mass transfer in a gas-droplet spray is investigated numerically using the Eulerian description of both phases. The system of averaged equations for the dispersed phase is based on the kinetic equation for the probability density function of the particle coordinates, velocity, and temperature. With increase in the particle concentration and size, the spray becomes narrower and longer. However, for evaporating sprays, particularly with small droplets, the turbulence suppression and mixing effects are less pronounced than for jets without phase transitions. The strongest turbulence suppression is detected in the initial spray region, where the droplet concentration is maximum and the droplet size is only slightly reduced due to vaporization. [ABSTRACT FROM AUTHOR]