Search

Sugar alcohol slurries were proposed as a slurry heat medium for applications at low/medium temperatures (>100 °C). The flow characteristics of the sugar alcohol slurries were investigated experimentally. The solid fraction and the flow velocity were varied and the pressure drop in the sugar alcohol slurries flowing through a horizontal circular tube was measured. A power-law model, in which the viscosity coefficient and viscosity index were determined from the relationship between the shear rate and the shear stress, was discussed to describe the flow behavior of the slurries. For a mannitol slurry, the viscosity index decreased as the solid fraction increased. The slurry flow could be described as a pseudoplastic fluid. For erythritol slurries, there was no significant correlation between the viscosity index, the viscosity coefficient, and the solid fraction. Therefore, a power-law model could not be applied to erythritol slurry because the pipe friction coefficient could not be appropriately calculated. The differences of rheological behavior between the erythritol slurry and mannitol slurry seem to be occurred by the different flow patterns in each case. [ABSTRACT FROM AUTHOR]

Copyright of Larhyss Journal is the property of Biskra University, Research Laboratory in Subterranean & Surface Hydraulics and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Larhyss Journal is the property of Biskra University, Research Laboratory in Subterranean & Surface Hydraulics and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Annals of the University of Bucharest. Geography Series / Analale Universitatii Bucuresti. Seria Geografie is the property of Analale Universitatii Bucuresti. Seria Geografie and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

This paper presents a new method to measure the oil retention and oil circulation ratio (OCR) in the compressor discharge pipe based on oil film thickness, oil film average velocity, oil droplet size, oil droplet velocity, and system mass flow rate. Oil flow parameters are quantified based on visualization using high-speed camera and video processing techniques. The estimated oil retention and oil circulation ratio results are compared quantitatively with the results from sampling measurements under different compressor speed and compressor types. The agreement between video results and sampling measurements verify the accuracy of this innovative method, which can also be applied in other annular-mist flow analysis. It also shows that most of the oil exists in film by mass while oil droplets contributes more to the oil mass flow rate because oil droplets travel in a much higher speed. [ABSTRACT FROM AUTHOR]

Climate change, linked to global warming, acts directly on our natural environment, transforming it, and is accompanied by changes in the hydrological cycle. As a consequence, there is drastic reduction in available water resources due to the marked decrease in rainfall. In this study, we use the Mann-Kendall test to characterize the variability and trends of runoff in the Falémé basin over the period 1954–2014. The results of the analysis reveal a statistically significant downward trend in practically every month and in periods of high and of low flows. A trend was observed also in the years with low flow during which the periods of high and low flow were less noticeable. The Mann-Kendall test thus proved effective in identifying the negative trends of the flow in the Falémé basin. [ABSTRACT FROM PUBLISHER]

The present article deals with an experimental and numerical investigation of heat and mass infiltration rates during the opening of a refrigerated truck body. Experiments were carried out for different temperatures and different aperture ratios. The infiltration dynamics was found to involve two distinct phenomena: a buoyancy driven flow and a boundary layer flow. The first is a density-driven flow which gives birth to an important heat load peak. The second phenomenon is due to quasi steady-state natural convection over the inner wall of the truck. In the present work, the infiltration phenomenon was first analysed by means of a computational fluid dynamics model. The infiltration flow rate is well predicted except at the transition between both flow regimes. An analytical model using the ideal flow theory was also developed to model the buoyancy driven flow. The natural convection boundary layer flow is then well predicted using a classical method. [ABSTRACT FROM AUTHOR]

Abstract: Flow boiling heat transfer characteristics of refrigerant in tubes filled with metal foams were experimentally investigated at a saturation temperature of 7 °C, mass flux from 10 to 90 kg m−2 s−1, vapor quality from 0.1 to 0.8 and heat flux from 3.1 to 18.3 kW m−2. The refrigerant is R410A. The test sections are tubes with inner diameter of 23.4 or 13.8 mm, filled with 5 or 10 PPI copper foam. The experimental results reveal that, metal foam enhances the flow boiling heat transfer by a maximum of 220% and promotes the flow pattern transition from stratified flow to stratified-wavy flow and from stratified-wavy flow to annular flow. The heat transfer coefficient decreases with vapor quality under low mass flux, while it increases with vapor quality under high mass flux. A correlation for predicting the flow boiling heat transfer was developed and it agrees well with the experimental data. [Copyright &y& Elsevier]

The geomechanical modelling of failure and post-failure stages of rainfall-induced shallow landslides represents a fundamental issue to the proper assessment of failure conditions and recognizes the potential for long travel distances of the failed soil masses. Considering that these phenomena are among the most catastrophic natural hazards, as a contribution to the topic this paper discusses the potential of a hydromechanical coupled finite element model (FEM) to analyze the post-failure stage using an advanced constitutive model. In particular, simple undrained triaxial tests and experimental evidence of centrifuge tests are reproduced first, for both loose and dense soils. Then, two slope scale benchmarks are analyzed in the cases of vertical downward or horizontal water seepage and for both loose and dense soils. Compared with results obtained through standard limit equilibrium analyses, the coupled FEM provides a new comprehensive framework for failure and post-failure scenarios that includes a significant reduction of mean effective stresses, also in the case of a loose soil slope subjected to vertical downward water seepage. The obtained results are particularly encouraging because they outline the possibility to analyse both the failure and post-failure stages in a unique framework. Moreover, the numerical analyses indicate that the post-failure mechanisms are intimately tied to specific predisposing factors and boundary conditions, rather than to a single mechanical or state parameter of soil, such as, for instance, the soil relative density. [ABSTRACT FROM AUTHOR]

Experimental results on the nature-like fishway induced flow field and its relation to fish behaviour are presented. A rocky-ramp with 5% slope was built along a 8.9 m × 0.9 m × 0.6 m laboratory flume, and acoustic Doppler velocity measurements were taken in a grid with 186 points for low, middle, and high discharges. The flow is characterized applying spatial and point analysis techniques. Point analysis consistently shows that the boulder to boulder distance is small enough to disrupt turbulent coherent structures. At boulder wakes no predominance of sweep and ejection events occur, evidencing a good resting place for fish migration. The nature-like rocky-ramp offers a diversity of flow conditions controlled by the boulders geometry that might allow a variety of fishes to develop their preferred paths characterized by flow properties with different magnitudes depending on the particular species. Obtained results compare well with similar ones reported for other standard fishways. [ABSTRACT FROM AUTHOR]

Abstract: Interdependence between centrifugal stage pressure ratio, peripheral Mach number and impeller peripheral speed, as well the influence of the refrigerating capacity on the dimensions of the centrifugal compressor are determined to obtain the range of reasonable usage of R718 refrigerating/heat pump systems. The deep vacuum operating conditions, the low specific volumetric cooling capacity of the R718 and the small molecular mass of the water are the peculiarities which determined the main parameters of the centrifugal compressor and the range of rational application of the R718 refrigerating/heat pump systems. The high peripheral impeller speed, high Mach number and high pressure ratio cause separated jet-wake flow and transonic flow phenomena in the compressor flow field. Estimation of the flow characteristics and of the performance characteristics of the water vapor centrifugal compressors is presented, using results of CFD simulations and experimental investigations for high pressure ratio centrifugal compressors. [Copyright &y& Elsevier]

Abstract: This paper presents an experimental and numerical investigation of the flow of ice slurry, composed of monopropylene glycol (MPG) as an additive. The objective is to demonstrate the influence of initial concentrations of this additive and the ice fraction on the rheological behavior of the corresponding ice slurry. The ice slurry flow was modeled in a continuous approach, where the fluid is assumed to behave like a single-phase fluid. Complex fluid behavior is treated by an effective kinematic viscosity, which depends on several parameters. In the present study the rheological model of Ostwald-de Waele is applied. The results – which concern mainly the effect of velocity, ice mass fraction and solute concentration on the pressure drop – show an overall close agreement between the experimental and the numerical and analytical results. [Copyright &y& Elsevier]

Abstract: This paper presents flow imaging techniques developed for investigating flow in ejectors. These visualization techniques use the laser sheet method but differ from each other by the kind of the illumination source, the polarization direction of the incident light and the type of the scattering tracers. Each of these methods enables the visualization of specific phenomena (shock structure, flow instabilities, mixing process). Although the flow visualizations are primarily qualitative, they allow the determination of the flow regime, the measurement of the non-mixing length, can indicate suggestions for the design of ejectors and provide the possibility to validate numerical simulations. [Copyright &y& Elsevier]

Abstract: This paper describes the heat transfer and the pressure drop characteristics of CO2 mixed with small amounts of compatible lubricating oil at super-critical pressures inside horizontal tubes with inner diameters of 1.98 mm and 4.14 mm during cooling. The heat transfer coefficients and pressure drops were measured. The results show that for the oil-free cases, the correlation proposed by Dang and Hihara accurately predicted the heat transfer coefficients and Petukhov’s correlation was found to predict the frictional pressure drops reasonably. Entrainment of the lubricating oil reduced the heat transfer coefficients and increased the pressure drops. Analysis showed that the heat transfer coefficients of the CO2/oil mixture are strongly related to the density and viscosity ratios of the oil to the CO2. An empirical correlation was developed based on the measured data, which predicts most of the experimental data within a deviation of 20%. [ABSTRACT FROM AUTHOR]

Abstract: Flow characteristics of ice slurry were experimentally investigated using narrow tubes. Reynolds number, the diameter of the tubes and the ice packing factor (IPF) were varied as the experimental parameters. Theoretical analysis was carried out using the experimental results. For laminar flow, it was found that the ratio of the coefficients of pipe friction increases with the IPF, and the rate of increase is high in the case of a low Reynolds number. For turbulent flow, the ratio of the coefficients of pipe friction was 1 for each condition in the case of a low IPF. The ratio of coefficients of pipe friction then decreased slightly at a particular IPF and increased with the IPF in the high-IPF region. In theoretical analysis, it was found that the flow characteristics of ice slurry can be treated as those of pseudoplastic fluid and clarified using the apparent Reynolds number. [ABSTRACT FROM AUTHOR]

Abstract: Mal-distribution of airflow is an important factor for the performance of air-cooled multi-coil air-cooled condensers. This study is an attempt to investigate the effects of different included angles between the coils of the condenser. It has been found in this study that it can be a mean to improve the performance of multi-coil condensers without using larger heat transfer surfaces. A commercially used four-coil condenser of an air-cooled water chiller was used as the base case in the tests and analysis. The results show that the variation of the included angle can increase the airflow rate by 7.85%, which corresponds to 5.29% increase in heat transfer. The improvements were found to be due to the reduction of the stagnant flow regions of the heat exchanger coils, and more even flow distribution through the coils. Test data were used to verify the computer model of the four-coil heat exchanger. The same tested fan performance characteristic was used in all of the analyses. The research results are important as air-cooled condensing units can be designed to better performance merely by changing the configuration of the coil arrangements. [Copyright &y& Elsevier]

Abstract: This paper presents a novel strategy for predicting the performance of open vertical refrigerated display cabinets which is based on a modified two-fluid (MTF) model and an adaptive support vector machine (ASVM) algorithm. A MTF model (physical model) was built for open vertical refrigerated display cabinets, and then an ASVM algorithm (machine learning algorithm) was built. To verify the quantity of air leakage from the cabinet during operation, an important performance factor of display cabinets, an MTF model was built. After the training and validation data sets were constructed from the output of the MTF model, the problem was solved using an ASVM algorithm. The defrosting water quantity and total energy consumption / total display area (TEC/TDA), achieved from the experiments by using the predicted combination of the controlled parameters, were found to be reduced by 39.2% and 19.3%, respectively, from the experimental results of the original display cabinet. [Copyright &y& Elsevier]

Abstract: This paper presents an experimental investigation of coiling effect on the flow of R-407C in an adiabatic helical capillary tube. It has been observed that the coiling of capillary tube significantly influences the mass flow rate of R-407C through the adiabatic helical capillary tube. For the sake of comparison, the experiments have also been conducted for straight capillary tube and it has been observed that the mass flow rates in coiled capillary tube are 5–10 percent less than those in a straight one. The data obtained from the experiments have been analyzed and non-dimensional correlations for the prediction of mass flow rate of R-407C in straight and helical capillary tube have been developed. The proposed correlations predict our experimental data in an error band of ±10 percent. The predictions by developed correlations are also in good agreement with the data of other investigators. [Copyright &y& Elsevier]

Abstract: Small dimensions found in modern and novel heat exchanger (HX) designs encounter very challenging manufacturing issues. With current manufacturing techniques HXs in small dimensions will exhibit large tolerances relative to design variables. Hence, the anticipated variation in performance is a concern. Furthermore, small flow channel dimensions are very susceptible to severe fouling and even blockage. Therefore, flow distribution would be uncertain. These uncertainties in dimensions and flow distribution should be accounted for during the design and performance evaluation of new HX geometries with focus on ultra-compact designs. This paper outlines an effort to theoretically evaluate the performance of an air-to-water HX, assembled from tubes with non-conventional heat transfer surfaces. Vertical spacing within this HX is subject to a predefined statistical distribution compounded with uncertainty in water flow rate through each flow path (i.e., tube). A new implementation technique for ɛ-NTU is proposed in order to accommodate different air conditions on both tube sides. A Monte Carlo simulation approach is used to estimate the HX performance distribution. This approach is applied to three HX designs showing the performance degradation subject to geometrical and flow uncertainties. The simulation results under uncertainty provided useful insights into the reasons for the performance degradation and showed great impact to the uncertainty distribution. Overall, the proposed HX design with the smallest dimensions showed the least performance degradation due to manufacturing and operating conditions uncertainty. [Copyright &y& Elsevier]

Abstract: A multilayer two-dimensional model of beef carcass chilling using CFD-generated heat transfer coefficients was used to calculate the parameters of leg and shoulder cooling curves, assuming an exponential cooling model. A central composite experiment was designed to systematically vary air velocity, side weight and fat thickness. Comparison with experimental data suggests that the predicted characteristic time for the leg, and hence the cooling time to a given temperature, should be multiplied by a correction factor 1.07. The effects of airflow direction and of radiation heat transfer have been quantified. A correlation was proposed to estimate leg centre temperature from shoulder temperature. The shortcut formulae and methods presented here will be useful in the design and troubleshooting of industrial beef chillers. They could also be used in Monte Carlo simulations where a large number of samples are considered, to take into account random variations in product characteristics and operating conditions. [Copyright &y& Elsevier]

Abstract: The objective of this paper is to investigate the effect of nanoparticle on the frictional pressure drop characteristics of refrigerant-based nanofluid flow boiling inside a horizontal smooth tube, and to present a correlation for predicting the frictional pressure drop of refrigerant-based nanofluid. R113 refrigerant and CuO nanoparticle were used for preparing refrigerant-based nanofluid. Experimental conditions include mass fluxes from 100 to 200kgm−2 s−1, heat fluxes from 3.08 to 6.16kWm−2, inlet vapor qualities from 0.2 to 0.7, and mass fractions of nanoparticles from 0 to 0.5wt%. The experimental results show that the frictional pressured drop of refrigerant-based nanofluid increases with the increase of the mass fraction of nanoparticles, and the maximum enhancement of frictional pressure drop is 20.8% under above conditions. A frictional pressure drop correlation for refrigerant-based nanofluid is proposed, and the predictions agree with 92% of the experimental data within the deviation of ±15%. [Copyright &y& Elsevier]

Abstract: A hybrid method for optimizing refrigerant distribution in evaporators is presented that involves the use of small balancing valves in each circuit along with a primary expansion device to control the overall superheat from the evaporator. The flow balancing valves could be located upstream or downstream of the evaporator. This paper presents the results of a study to investigate the benefits of this hybrid scheme for both upstream and downstream flow balancing for the case of air flow mal-distribution. In order to perform this investigation, a simulation model was developed to consider evaporator flow mal-distributions for a 10.55kW residential R410A heat pump and then validated through comparisons of predicted results with measurements. Simulation results show that there are significant benefits in controlling the superheat of each circuit of evaporators through the hybrid–individual superheat control method. Furthermore, the upstream refrigerant flow control consistently outperforms the downstream refrigerant flow control, and recovers most of the loss in cooling capacity and COP due to non-uniform air flow distribution. [Copyright &y& Elsevier]

Abstract: Capillary tubes are extensively used in small refrigeration and air-conditioning systems with synthetic refrigerants and hydrocarbons. For CO2 transcritical applications, it has been shown that the capillary tube demonstrates an intrinsic capability of adjusting the upper pressure close to the optimal value in response to changes of gas-cooler heat sink temperature. The CO2 flow rate through four capillary tubes of various lengths, diameters and materials was measured in a test rig. Each capillary tube was tested with inlet pressure varying from 7.5MPa to 11MPa and inlet temperature from 20°C to 40°C. Outlet pressure varied from 1.5MPa to 3MPa. The experimental results were validated against different numerical and approximate analytical solutions of the capillary tube equations. These models give good predictions only if the friction factor of the capillary tube is calculated accounting for its dependence on the tube roughness. [Copyright &y& Elsevier]

Abstract: This paper outlines an algebraic model for simulating the transcritical expansion of carbon dioxide through adiabatic capillary tubes. The model was put forward based on the analytical solution of the momentum conservation equation assuming an isenthalpic expansion process. The theoretical model predictions were compared with 66 experimental data points covering different operating conditions and tube geometries. A good agreement between the experimental and calculated mass flow rates was achieved, with more than 94% of the data points lying within an error band of ±10%. [Copyright &y& Elsevier]

Abstract: This paper advances a study of the transcritical expansion of carbon dioxide (R-744, CO2) through adiabatic capillary tubes. The influence of both operating conditions (inlet and exit pressures, inlet temperature) and tube geometry (capillary diameter and tube length) on the CO2 mass flow rate was experimentally evaluated using a purpose-built testing facility with a strict control of the measured variables. A dimensionless correlation to predict the refrigerant mass flow rate as a function of tube geometry and operating conditions was developed. In addition, a theoretical model was put forward based on the mass, energy and momentum conservation principles. The model results were compared with experimental data, when it was found that the model predicts 95% of the measured refrigerant mass flow rate within an error band of ±10%. The model was also employed to advance the knowledge about the transcritical carbon dioxide flow through adiabatic capillary tubes. [Copyright &y& Elsevier]

Abstract: Upscaling is needed to transform the representation of non-additive space-dependent variables, such as permeability, from the fine grid of geostatistical simulations (to simulate small-scale spatial variability) to the coarser, generally irregular grids for hydrodynamic transport codes. A new renormalisation method is proposed, based on the geometric properties of a Voronï grid. It is compared to other classic methods by a sensitivity analysis (grid, range and sill of the variogram, random realisation of a simulation); the criterion is the flux of a tracer at the outlet. The effect of the upscaling technique on the results appears to be of second order compared to the spatial discretisation, the choice of variogram, and the realisation. [Copyright &y& Elsevier]

Abstract: The Note presents an unconventional computational method for irrotational and incompressible fluid flows over lifting bodies. At first, Laplace''s equation for the velocity potential is solved with internal Dirichlet conditions expressed at the nodes of the mesh rather than at smooth surface positions. Continuous distributions of surface normal doublets are used, and obtaining the surface velocity field with such distributions becomes straightforward. Secondly, an original Neumann type formulation of the Kutta conditions is proposed. Expressing the minimization of the velocity flux across the wall shows a significant reduction of the discretization impact upon the computed global efforts when compared to local no-load conditions. The method can be applied to 2 or 3-dimensional flows, steady or not. To cite this article: P. Ardonceau, C. R. Mecanique 337 (2009). [Copyright &y& Elsevier]

Abstract: During transport using refrigerated vehicles, this being a vital link in the cold chain, the maintaining of even temperature throughout the cargo is essential in order to preserve the quality, safety and shelf life of perishable food. Within the refrigerated container, the temperature level and its homogeneity are directly governed by airflow patterns. The design of the air-distribution system should allow these airflows to compensate heat fluxes exchanged through the insulated walls or generated by the products. In this paper, a reduced-scale model and CFD predictions were used to investigate experimentally and numerically the airflow patterns within a typical refrigerated truck configuration loaded with vented pallets filled with spherical objects. The experiments were carried out using a laser Doppler velocimetry and thermal sphere-shaped probes located inside the pallets. The aim was to investigate air velocity characteristics above and within pallets. The performance of ventilation was characterized with and without supply air duct systems. Both configurations are extensively used in refrigerated transport. Full-scale measurements were also performed within a load of fruit during transport in a refrigerated truck in order to evaluate the temperature distribution under given operating conditions. The numerical modelling of airflow was performed using the computational fluid dynamics (CFD) fluent code and the Reynolds Stress Model (RSM) turbulence model. Numerical and experimental data make it possible to evaluate the air ventilation levels and their heterogeneity between the pallets. The numerical predictions show reasonable agreement with experimental data. The studied supply air duct system improves significantly the homogeneity of ventilation in the vehicle. [Copyright &y& Elsevier]

Abstract: The present experimental investigation has been carried out to investigate the effects of various geometric parameters on the mass flow rate of R-134a through diabatic spiral capillary tube. In diabatic flow, the capillary tube is bonded with the compressor suction-line to form a counter-flow exchanger. The lateral type of diabatic capillary tube has been investigated in the present experimental study. The major geometric parameters investigated are capillary tube diameter, capillary tube length and coil pitch. In addition, effect of inlet subcooling on the mass flow rate through diabatic spiral capillary tube is also done. A comparison of the performance of diabatic spiral capillary tube has been made with adiabatic spiral capillary tube. Generalized empirical correlation for diabatic spiral capillary tube has also been proposed. It has been found that the predictions of the proposed correlation lie in the error band of ±7%. [Copyright &y& Elsevier]

Abstract: A comprehensive review of flow boiling characteristics and flow pattern visualization of refrigerant/lubricant oil mixtures is presented in this paper. First, various parameters influenced by the lubricant oil in convective boiling of refrigerants, such as mass velocity, vapor quality, oil concentration and geometric characteristics of the heat transfer tube are discussed. The effects of the unavoidable introduction of the lubricant oil on the thermodynamics properties of a refrigerant are described. Then, a review of the main experimental studies of flow boiling of refrigerant/lubricant oil mixtures is presented and also describes research with halocarbons, carbon dioxide, hydrocarbons and ammonia. There is no agreement among these studies regarding the effect of the oil in the evaporator, with studies showing an increase or decrease in the heat transfer coefficient. However, in relation to pressure drop, all the results presented the same trend, increasing the pressure drop with increasing oil concentration. Next, the flow patterns of refrigerant/oil mixtures are illustrated together with a selection of video images. It is possible to notice the difference in frothing formation with respect to the particular refrigerant and tube geometry. Some predictions of oil effects on the heat transfer coefficient and pressure drops based on the mixture physical properties are then presented and the trends compared to data. Finally, some suggestions for future work are given. [Copyright &y& Elsevier]

Abstract: The purpose of this work is to investigate the entropy generation in ice slurry pipe flow. Fully developed laminar flow is considered with uniform heat flux at the walls. The fluid behaves as a non-Newtonian fluid following the power-law model. Expressions for velocity, entropy generation number and average entropy generation number are obtained as function of mass fraction of ice and the dimensionless group parameter. [Copyright &y& Elsevier]

Abstract: This paper investigates the flow boiling heat transfer in a typical domestic refrigerator evaporator with horizontal flow, frequent bends and a non-circular cross-section. The mass flux was varied between 21 and 43kg/m2 s, the heat flux between 1 and 5kW/m2 and the vapour quality between 0.2 and 0.8. In spite of a predicted stratified to wavy-stratified flow pattern complete tube perimeter wetting was believed to occur except for the lowest mass flux and for positions upstream of the first bend. It was concluded that the bends helped wetting the tube perimeter. The experimental data revealed heat transfer coefficients higher than predicted with conventional correlations. This was suggested to be explained by thin film evaporation at a perimeter repeatedly wetted by liquid slugs. A simple correlation based on the pure convective part of the Shah correlation [3] was derived from the experimental data. The mean deviation of this was 16.9% compared to Shah''s 54.7%. [Copyright &y& Elsevier]

Abstract: This paper presents an experimental investigation for the flow of R-134a inside an adiabatic spirally coiled capillary tube. The effect of various geometric parameters like capillary tube diameter, length and coil pitch for different capillary tube inlet subcoolings on the mass flow rate of R-134a through the spiral capillary tube geometry has been investigated. It has been established that the coil pitch significantly influences the mass flow rate of R-134a through the adiabatic spiral capillary tube. The effect of providing pressure taps on the capillary tube surface has a negligible effect on the mass flow rate through the capillary tube. It has been concluded that the effect of coiling of capillary tube reduces the mass flow rate by 5–15% as compared to those of the straight capillary tube operating under similar conditions. The data obtained from the experiments are analyzed and a semi-empirical correlation has been developed. The proposed correlation predicts more than 91% of the mass flow rate which is in agreement with measured data in an error band of ±10%. [Copyright &y& Elsevier]

Abstract: A prototype liquid-to-refrigerant heat exchanger was developed with the aim of minimizing the refrigerant charge in small systems. To allow correct calculation of the refrigerant side heat transfer, the heat exchanger was first tested for liquid-to-liquid (water-to-water) operation in order to determine the single-phase heat transfer performance. These single-phase tests are reported in this paper. The heat exchanger was made from extruded multiport aluminium tubes and was designed similar to a shell-and-tube heat exchanger. The heat transfer areas of the shell-side and tube-side were approximately 0.82m2 and 0.78m2, respectively. There were six rectangular-shaped parallel channels in a tube. The hydraulic diameter of the tube-side was 1.42mm and of the shell-side 3.62mm. Tests were conducted with varying water flow rates, temperature levels and heat fluxes on both the tube and shell sides at Reynolds numbers of approximately 170–6000 on the tube-side and 1000–5000 on the shell-side, respectively. The Wilson plot method was employed to investigate the heat transfer on both the shell and tube sides. In the Reynolds number range of 2300–6000, it was found that the Nusselt numbers agreed with those predicted by the Gnielinski correlation within ±5% accuracy. In the Reynolds number range of 170–1200 the Nusselt numbers gradually increased from 2.1 to 3.7. None of the previously reported correlations for laminar flow predicted the Nusselt numbers well in this range. The shell-side Nusselt numbers were found to be considerably higher than those predicted by correlations from the literature. [Copyright &y& Elsevier]

Abstract: A modified two-fluid turbulence model is established to simulate the flow and heat transfer characteristics of air curtains in an open vertical display cabinet. The air exiting the back panel (AEBP), the inner air curtain and the outer air curtain are taken as the first fluid and described with the standard turbulence model (KE). The air outside the display cabinet is considered as the second fluid and calculated by the laminar model. Different from the existing two-fluid model, the mass transfer rate equation between the turbulent and the non-turbulent fluids is modified, and the face coefficient of honeycomb (the ratio of the effective area to the total area of honeycomb) is fetched with the volume fraction of air curtain in order to conveniently depict the blow characteristics of the honeycomb. The comparisons between the simulated temperatures and the experimental ones indicate that the modified two-fluid model (MTF) can give better agreement with the measurements than KE and two original two-fluid models (TF1 and TF2). [Copyright &y& Elsevier]

Abstract: We performed a study on the effect of the discharge airflow rate of the ceiling type air-conditioner on ventilation performance in the lecture room with the mixing ventilation. The experiments and CFD were conducted for analyzing ventilation performance. The concepts of mean air age and indoor CO2 concentration were used for evaluating ventilation performance. We made the CO2 generation model in the simulation and calculated a lot of cases with respect to the airflow rate of air-conditioner and the mechanical ventilation rate. And the selected experimental measurements were performed in the lecture room of the same layout as the numerical one for verifying simulation results. Mean air age is gradually increased, but CO2 concentration is oppositely decreased in the occupied zone with the increment of the discharge airflow rate of the ceiling type air-conditioner. This result shows that both mean air age and residual life time must be considered for evaluating ventilation performance when the contaminants are generated indoors. And the increment of discharge airflow of the ceiling type air-conditioner can induce the piston effect and push the contaminants out of the occupied zone. From this result, it is found out that ventilation performance can be increased when the momentum source like an air-conditioner is used in the room with the mixing ventilation. [Copyright &y& Elsevier]

Abstract: This paper presents the results of experiments and modelling carried out on ice slurries flowing in uninsulated steel pipes with a nominal diameter of 50mm. The slurries used were formed from 4.75% NaCl aqueous solution and had ice mass fractions in the range 18–42%, with a view to the use of thick ice slurry ‘pigs’ as a pipeline clearing technique. Of particular interest was the distance over which such slurries can survive as plug-like entities, before melting reduces them to ineffective thin two-phase suspensions. The experiments showed that for small volumes of slurry, survivability is directly proportional to the quantity of slurry used, but that increasing the ice fraction has a more marked effect. A simple one-dimensional numerical model that accounts for transportation, heat transfer and melting was developed that produces reasonable predictions. [Copyright &y& Elsevier]

Abstract: The applications of electronic expansion valves (EEVs) into multi-type heat pumps and inverter heat pumps in building air-conditioning systems have increased for comfort environmental control and energy conservation. However, test data and mass flow models of EEVs are very limited in open literature. The objectives of this study are to investigate the mass flow characteristics of R22 and R410A through EEVs and to develop an empirical correlation for the prediction of mass flow rates of R22 and R410A through EEVs. Mass flow rates through six EEVs were measured by varying the EEV opening, inlet and outlet pressures, and the subcooling. Mass flow rates of R410A were compared with those of R22 at the same test conditions. Based on the experimental data, an empirical correlation for mass flow predictions in EEVs was developed by modifying the orifice equation. The predictions of the present correlation showed good agreement with the measured data with average and standard deviations of 0.76% and 5.9%, respectively. Approximately 92% of the measured data were within ±10% of the predictions. [Copyright &y& Elsevier]

Abstract: Experiments were conducted to study the condensation flow pattern in silicon micro-condensers using water as the medium. Slug-bubbly flow was found to be one of the dominant flows in the micro-condenser and it was a major factor in determining the heat transfer and pressure drop properties of the fluid inside the micro-condenser. The transition from the slug-bubbly flow to a mixed flow pattern was studied. A correlation was obtained to predict when the transition of the flow pattern would occur. Only slug-bubbly flow existed under low steam mass flow rate and high heat transfer rate conditions. As the steam mass flow rate increased or the heat transfer rate dropped, the mixed flow pattern would then appear. In the slug-bubbly flow regime, the heat transfer coefficient and pressure drop in the micro-condensers were investigated in detail. It was found that micro-condensers with smaller channels could exhibit higher heat transfer coefficients with the same Reynolds number. The condensation heat transfer coefficient was higher than that in the tubes with the diameter of centimeter. Pressure drops in the micro-condensers with smaller channels were higher due to the increased transition loss. At the same time, the pressure drop in the micro-condenser was found to be lower than what could be predicted using the macro-scale correlation. Increasing the heat flux would create a longer bubble–film region and fewer unit cells in the micro-condenser resulting in an increased heat transfer coefficient and a decreased pressure drop. [Copyright &y& Elsevier]

Abstract: The pipe network generation proposed here assumes that flow in a 3D fracture field is highly channelled, and that there exist invariant crux nodes corresponding to crossroads connecting preferential flow paths whatever the mean head gradient''s direction. The method allows preferentially for these crux nodes by conditioning the simulated network first on a ‘seeding’ of nodes and second, in generating 1D pipes between these nodes. Note that usually, nodes are the consequence (the intersection) of the pipe generation. Pipes can be also conditioned on their length and other features, but this conditioning is not strict, since all pipes must pass by the nodes. In the end, the network is simple without dead ends; each cluster is flowing and connected to the boundaries of the system. This type of network is expected to facilitate further calculations, for instance solving inverse problems in deforming the network by simply moving the crux node locations. [Copyright &y& Elsevier]

Abstract: A dummy port plays an important role in the porting process and the improvement of the performance of a scroll compressor. This paper documents an investigation on the working mechanism of the dummy port in a scroll compressor. To characterize the dummy port effects on the different parts of the scroll compressor, two scroll compressors, one with and the other without a dummy port, are studied comparatively. The flow through the dummy port is examined in the background of an integrated compressor working process. The assembly of the compressor under investigation includes the upper bearing housing, scrolls, check valve, and discharge plenum. The Navier–Stokes equations with a k–ɛ turbulence model are solved at the standard operating conditions of a scroll compressor. Refrigerant-22 is used as the working fluid. The thermodynamic and transport properties of the refrigerant gas are modeled by the Martin–Hou equation of state and power laws, respectively. Global flow physics is investigated first to lay a foundation to understand the working mechanisms that control the porting process before averaging techniques are applied. The behavior of the gas pockets in the porting process is characterized in both geometric and dynamic nature. The time-dependent variation of volume, mass, energy, and volume-averaged field quantities inside the gas pockets are studied throughout the porting process. The impact of the dummy port on the compressor performance is defined. [Copyright &y& Elsevier]