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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: 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: 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: 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: Tailoring the local flow field around a fin can substantially enhance the forced convection heat transfer from a conventional heat sink. A fin is set into oscillation leading to rupture of the thermal boundary layer developed on either side of the fin. This enhancement in heat transfer is demonstrated through an increase in the time-averaged Nusselt Number (Nu) on the fin surfaces. Nu has been found to be strongly dependent on the flow Reynolds Number (Re), the frequency and amplitude of the fin oscillations. A threshold amplitude and frequency is identified beyond which Nu improvements are observed for fixed Re. [Copyright &y& Elsevier]

Abstract: Experiments to evaluate heat transfer coefficient and friction factor for flow in a tube and with twisted tape inserts in the transition range of flow with Al2O3 nanofluid are conducted. The results showed considerable enhancement of convective heat transfer with Al2O3 nanofluids compared to flow with water. It is observed that the equation of Gleninski applicable in transitional flow range for single-phase fluids showed considerable deviation when compared with values obtained with nanofluid. The heat transfer coefficient of nanofluid flowing in a tube with 0.1% volume concentration is 23.7% higher when compared with water at number of 9000. Heat transfer coefficient and pressure drop with nanofluid has been experimentally determined with tapes of different twist ratios and found to deviate with values obtained from equations developed for single-phase flow. A regression equation is developed to estimate the Nusselt number valid for both water and nanofluid flowing in the transition flow Reynolds number range in circular plain tube and with tape inserts. The maximum friction factor with twisted tape at 0.1% nanofluid volume concentration is 1.21 times that of water flowing in a plain tube. [Copyright &y& Elsevier]

Abstract: Flow emerging from a combination of annular and conical nozzles and impinging onto a cylindrical cavity at elevated all temperature is considered, and the flow field and heat transfer rates from the cavity are computed. In the simulations, two cavity depths and four average jet velocities at nozzle exit are accommodated. Reynolds Stress Turbulence model is introduced to account for the turbulence. Air is used as working fluid while steel is considered as the cavity material. It is found that the Nusselt number attains high values in the neighborhood of the stagnation zone at the cavity bottom surface, which is more pronounced for 1 mm depth cavity. [Copyright &y& Elsevier]

Abstract  Pool boiling heat transfer characteristics on treated surfaces were investigated experimentally. Surface treatments were performed with sandpapers, building micro structures by etching, and micro-porous coating. Copper blocks of 20 mm × 20 mm were used as test sections and PF5060 was used as a working fluid. The effect of wall superheat (0–35 K), surface orientation (0°, 45°, 90°), and subcooling (0, 5, 10 K) on treated surfaces were also investigated. Heat transfer performance on inclined surface was better than that of horizontal surface in all test sections. Because bubble generation was suppressed by subcooling, higher wall superheat was needed to initiate boiling in all surfaces. Micro-porous coated surface showed the highest heat transfer enhancement among tested surfaces. [ABSTRACT FROM AUTHOR]

Abstract: Simulation is commonly used to develop control and diagnostic algorithms. Because vapor compression cycles are essentially heat management devices, transient and steady-state heat exchanger performance must be predicted accurately. However, for hardware- and software-in-the-loop purposes, the simulation must run in real-time. To reconcile these competing needs, a new lumped parameter or moving-boundary heat exchanger model was created. Accuracy concerns are addressed by including finned surfaces, nonlinear air temperature distributions, and non-circular passages. In its current form, the model is applicable to single pass, cross-flow heat exchangers. The mathematical basis of the model is given and shown to be consistent with integral forms of the energy and continuity equations. Although known to be more computationally efficient than finite volume models, moving-boundary models become singular and fail under certain conditions. To address this shortcoming, particular attention was focused on algorithms for switching between different representations and rezoning wall temperatures. Robustness to changing flow regimes is demonstrated through simulation test cases, and model application to a chiller system is shown. As such, the model provides improved accuracy, robustness, and operating range while maintaining real-time capability. [Copyright &y& Elsevier]

Abstract: The heat flux field for a single particle embedded in a graded material is derived by using the equivalent inclusion method. A linearly distributed prescribed heat flux field is introduced to represent the material mismatch between the particle and the surrounding graded materials. By using Green’s function technique, an explicit solution is obtained for the heat flux field in both the particle and the graded material. Comparison of the present solution with finite element results illustrates the accuracy and limitation of this solution. [Copyright &y& Elsevier]

Abstract: An experimental study of subcooled boiling heat transfer was conducted using R-134a in compact hypervapotron structures. The investigated flow and condition parameters in R-134a were: (1) inlet pressure of 5–8bar, (2) mass flux of 186–310kg/m2 s, (3) subcooling temperature of 10–30°C. Two distinctive zones were identified in the boiling process of the hypervapotron. It was found that the fully developed boiling curve has a slope range of 2.1–3.0 under tested conditions, which shows good agreement with Bjorge’s observations for flat surface channels. Shah and Kandlikar’s correlations are utilized to predict the heat transfer coefficient for fully developed boiling regions and some important parameters are suggested for hypervapotron applications based on the experimental results. [Copyright &y& Elsevier]

Abstract: The paper presents results obtained on the prediction of three-dimensional turbulent heat transfer to CO2 at supercritical pressure, flowing upward through heated vertical passages of non-circular cross-section. The problem is relevant to certain technical applications, including the cooling of fuel bundles in supercritical water nuclear reactors. Several k–ε turbulence models, implemented in the FLUENT code, are used; they include low-Reynolds number formulations and an RNG k–ε model with a two-layer near wall treatment. The reference experimental data are from a recent published study in which CO2 at supercritical pressure was used to cool uniformly heated channels of triangular and square cross sections. In keeping with previous work on circular ducts, the results obtained using the low-Reynolds number models were able to reproduce the trend of heat transfer deterioration due to buoyancy influence, but with a relatively large overestimation of measured wall temperatures. On the other hand, the RNG model with the two-layer approach was unable to capture even the expected qualitative trends. The results obtained in the current study are useful in confirming the mechanisms of heat transfer deterioration and also highlight interesting three-dimensional features related to flow redistribution under strong buoyancy forces. [Copyright &y& Elsevier]

Abstract: In this study, a design guideline for flow guides and dies is proposed for extrusion of complex cross-sectional shape products, such as CPU heat sinks. The plastic flow pattern of the billet inside the die cavity and the front-end shape of the extruded product are analyzed using a commercial finite element package “DEFORM 3D”. The configuration and dimensions of the flow guide and die for obtaining a straight product without curvature are investigated. The stress and deflection distributions of the die fin in the lateral and extrusion directions in the early non-steady state stage of the extrusion process are also discussed. Furthermore, experiments of extrusion using A6061 as the specimen with two different flow guide designs are conducted. The experimentally obtained front-end shape of product is compared with the simulation results, from which the simulation results are validated. [Copyright &y& Elsevier]

Abstract: A semi-analytical approach was presented to study the transient heat transfer of a single volatile drop evaporation in an immiscible liquid with bubble nucleation inside the drop. The solution was based on the energy equation included both convection and conduction heat transfer from the continuous liquid to the bubble with the concentric spheres model. The radius of the growing bubble had been found and the effect of Pr number, St number initial radius, initial velocity and ratio of density were examined. The Nu number derived as a function to the drop velocity was derived. The present results compared well with available data. [Copyright &y& Elsevier]

Abstract: In this paper, a general family of explicit algebraic tensor diffusivity functions based on the resolved temperature gradient vector and strain rate tensor is studied and applied to the construction of new constitutive relations for modelling the subgrid-scale (SGS) heat flux (HF). Based on Noll’s formulation, dynamic linear and nonlinear tensor diffusivity models are proposed for large-eddy simulation of thermal convection. The constitutive relations for these two proposed models are complete and irreducible. These two new models include several existing dynamic SGS HF models as special cases. It is shown that in contrast to the conventional modelling approach, the proposed models embody more degrees of freedom, permit non-alignment between the SGS HF and resolved temperature gradient vectors, reflect near-wall flow physics at the subgrid scale, and therefore, allow for a more realistic geometrical representation of the SGS heat flux for large-eddy simulation of thermal convection. Numerical simulations have been performed using a benchmark test case of a combined forced and natural convective flow in a vertical channel with a Reynolds number of and a Grashof number of Gr =9.6×105. The results obtained using the two proposed SGS HF models are compared with reported direct numerical simulation (DNS) data as well as predictions obtained using several conventional dynamic SGS HF models. [Copyright &y& Elsevier]

Abstract  Fluid flow and heat transfer characteristics around a semi-circular tube in cross flow were experimentally and numerically investigated. Three different tube-flow arrangements were considered. Firstly, the flat surface of the tube was placed parallel to the freestream flow; secondly, the flat surface of the tube was facing the upstream flow and thirdly, the curved surface of the tube was facing the upstream flow. For the second and the third arrangements, different angles of attack were studied. Flow visualization was carried out to illustrate streamlines around the tube and to verify flow patterns obtained from the numerical calculations. It was found that: (1) for any angle of attack, the arrangement of the curved surface facing the flow gave higher average Nusselt number than the arrangement of the flat surface facing the flow and (2) for all tube-flow arrangements, increasing the angle of attack slightly increases the average Nusselt number. Correlations of Nusselt numbers in terms of Reynolds number and angle of attack were deduced from the experimental results for the three arrangements. The comparisons between the experimental data, correlations’ predictions and numerical results showed reasonable agreements. [ABSTRACT FROM AUTHOR]

Mist cooling is expected to contribute to better steel products because it enables uniform and moderate cooling in steel-making processes. In this study, experimental data were obtained to understand the mist cooling process in a high-temperature cylinder. The wetting phenomenon on the cylinder surface was also observed with an installed CCD camera. Comparing these results with those from previous investigations, we found that our cooling curve corresponded to two distinct heat transfer regimes in mist cooling. A simplified model from the analysis was introduced to simulate the cooling curve in each heat transfer regime. The estimated cooling curves by this model agreed with the experimental data in one regime and had a similarity in the other regime. [ABSTRACT FROM AUTHOR]

Provides tips on possible problems that may be encountered in steam trap operation. Types of steam trap; Common problems of steam traps; Remedy when the valve set assemble is worn out.

Heat transfer enhancement in channel flow by using an inclined vortex generator has been numerically investigated. A square cylinder is located on the centerline of laminar channel flow, which is subject to a constant heat flux on the lower channel wall. As the cylinder is inclined with some angle of attack with respect to the main flow direction, flow characteristics change downstream of the cylinder, and significantly affect heat transfer on the channel wall. A parametric study has been conducted to identify the cause, and to possibly find the optimal inclination angle. It turns out that the increased periodic fluctuation of the vertical velocity component in the vicinity of the channel walls is responsible for the heat transfer enhancement. The large fluctuation is believed to be induced by the large-scale vortices shed from the inclined square cylinder, as well as by the secondary vortices formed near the channel walls. [ABSTRACT FROM AUTHOR]

We report a novel prototype of a two-dimensional micromachined accelerometer based on thermocapillary heat transfer. The only moving element in this accelerometer is a thermal bubble generated by vaporizing the working liquid in the microchamber. The accelerometer consists of two key components, a heating resistor for creating symmetrical temperature profiles and two pairs of temperature detectors placed symmetrically and orthogonally to each other. The prototype devices demonstrate that a sensitivity of 1.5°C/g for an operating power of 60 mW can be realized. The frequency response of the accelerometer containing deionized water is 200 Hz, and the corresponding noise equivalent acceleration is ∼1 mg/Hz1/2. [ABSTRACT FROM AUTHOR]