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Abstract: The objective of this paper is to investigate the nucleate pool boiling heat transfer characteristics of refrigerant/nanolubricant mixture with surfactant. In the experiments, three types of surfactants including SDS, CTAB and Span-80 were used. Nanolubricant was formed from Cu nanoparticles and oil VG68. The results show that, the ratio of heat transfer coefficient of refrigerant/nanolubricant mixture with surfactant to that without surfactant (defined as surfactant impact factor, SIF) are within 0.85–1.58, 0.73–1.31, and 0.68–1.24 for SDS, CTAB and Span-80, respectively. The values of SIF increase with the increase of surfactant concentration and then decrease, and increase with the decrease of surfactant molecular weight, nanolubricant concentration and heat flux. A nucleate pool boiling heat transfer correlation for refrigerant/nanolubricant mixture was proposed, and it agrees well with the experimental data of refrigerant/nanolubricant mixture with surfactant and that without surfactant. [Copyright &y& Elsevier]

Abstract: 20 types of nanoparticles mixed pairwise orthogonally with 10 types of dispersants are added in ammonia-water, respectively, to observe the dispersion stability of suspension. Ratio of varying absorbency is defined to investigate the dispersion stability of nanofluids compared with the conventional methods of measuring the height of supernatant layer or just measuring the absorbency. The dispersion stabilities of nanoparticles employed are divided into three levels and the influence of boiling on the dispersion is investigated. The results show that the nanoparticles with better dispersive characteristics in dry condition can more easily disperse in ammonia-water directly or be strengthened dispersivity by dispersant. Ratio of varying absorbency is more practical than the height of supernatant layer to investigate the dispersion stabilities of some nanofluids which just fade or aren''t stratified clearly after storage, and is more efficient to contrast the dispersion stabilities of different types of nanofluid than absorbency. [Copyright &y& Elsevier]

Abstract: In this study, mono silver (Ag) nanoparticles are used to prepare binary nanofluids (NH3/H2O binary mixture with Ag nanoparticles) for application of NH3/H2O absorption in a bubble absorber. The measurements uncertainty in repeatability of absorption rate is yielded within 2.80%. The NH3/H2O bubble absorption experiments are carried out in two cases, with or without the coolant (water). The results show that the mass transfer in binary nanofluids with the coolant is enhanced more than that without the coolant. With the coolant, the highest absorption rate enhancement is observed to be 55% at 0.02 wt% Ag nanoparticles. In addition, the mass transfer enhancement by the binary nanofluids is discussed in detail. [Copyright &y& Elsevier]

Abstract: Various thermal conductivity models for nanofluid have been proposed, however, none have included the effect of the surfactant. In this paper, a thermal conductivity model which includes the effects of the interfacial layer formed by the surfactant and liquid molecules is proposed by upgrading Leong et al.''s model (2006). Based on the analysis of dispersion types, the thickness of the interfacial layer is defined by the length of the surfactant molecule for nanofluid under monolayer adsorption dispersion and double lengths of the surfactant molecule for nanofluid under electric double layer (EDL) adsorption dispersion. The length of the surfactant molecule is obtained by analyzing the stereo-chemical structure and assuming it is fully extended when adsorbed on the surface of the nanoparticle. The present model was compared with some experimental data for low concentrated nanofluid containing surfactants. The comparison results show the present model, in general, produces higher accuracies and precisions. [Copyright &y& Elsevier]

Abstract: In the present study, suspensions of Al2O3 and SiO2 nanoparticles in methanol (nanofluid) are produced and analyzed for the application of CO2 absorption in a tray column absorber. The absorber is an acrylic tray column with twelve plates. The column is a sieve tray type which has flat perforated plates where the vapor velocity keeps the liquid from flowing down through the holes and the CO2 gas and methanol liquid are brought in contact in a counter-current flow. The test section is equipped with two mass flow meters to measure the absorption rate. The results show maximum enhanced absorption rates of 9.4% and 9.7% for Al2O3 and SiO2 particles (compared to pure methanol), respectively. It is also found that SiO2 nanoparticle is a better candidate than Al2O3 nanoparticle and 0.05 vol% of nanoparticles is an optimum condition for CO2 absorption enhancement for the present experimental conditions. [Copyright &y& Elsevier]

Abstract: The objective of this study is to propose a model for predicting the migration characteristics of nanoparticles during the refrigerant-based nanofluid pool boiling. In establishing the present model, the departure and rising processes of bubble, as well as the movement of nanoparticles in the liquid-phase are firstly simulated; then the capture of nanoparticles by bubble and the escape of nanoparticles from the liquid–vapor interface are simulated; finally, the migration ratio of nanoparticles is obtained by flotation theory combining the analysis on the boiling process. The proposed model can predict the influences of nanoparticle type, nanoparticle size, refrigerant type, mass fraction of lubricating oil, heat flux and initial liquid-level height on the migration of nanoparticles. The migration ratio of nanoparticles predicted by the model can agree with 90% of the experimental data of within a deviation of ±20%, and the mean deviation is 12.1%. [Copyright &y& Elsevier]

Abstract: Influences of refrigerant-based nanofluid composition and heating condition on the migration of nanoparticles during pool boiling were investigated experimentally. The nanoparticles include Cu (average diameters of 20, 50 and 80nm), Al and Al2O3 (average diameters of 20nm), and CuO (average diameter of 40nm). The refrigerants include R113, R141b and n-pentane. The mass fraction of lubricating oil RB68EP is from 0 to 10wt%, the heat flux is from 10 to 100kWm−2, and the initial liquid-level height is from 1.3 to 3.4cm. The experimental results show that the migration ratio of nanoparticles during the pool boiling of refrigerant-based nanofluid increases with the decrease of nanoparticle density, nanoparticle size, dynamic viscosity of refrigerant, mass fraction of lubricating oil or heat flux; while increases with the increase of liquid-phase density of refrigerant or initial liquid-level height. [Copyright &y& Elsevier]

Abstract: Two types of nanofluids are obtained by adding the mixture of carbon black nanoparticles with emulsifier OP-10, and Al2O3 nanoparticles with sodium dodecyl benzene sulfonate (SDBS) in the ammonia-water solution, respectively. The dispersion stability of the prepared nanofluids in different mass fractions of surfactants is investigated by the light absorbency ratio index methods. The results show that with the increase of mass fraction of surfactant, the stability of carbon black nanofluid is improved firstly and then is exacerbated, while the stability of Al2O3 nanofluid is exacerbated firstly, then is improved, and then is exacerbated again. The influences of surfactant on the stability of ammonia-water nanofluids abide by the monolayer adsorption theory or electric double layer adsorption theory. Finally, the theoretical surfactant mass fractions required in the preparation of ammonia-water nanofluids are calculated by simplifying the dispersion models and the results are in accordance with experimental results. [Copyright &y& Elsevier]

Abstract: In this study, the nanoparticles (i.e. SiO2 and Al2O3 nanoparticles) and methanol are combined into SiO2/methanol and Al2O3/methanol nanofluids to enhance the CO2 absorption rate of the base fluid (methanol). The absorption experiments are performed in the bubble type absorber system equipped with mass flow controller (MFC), mass flow meter (MFM) and silica gel (which can remove the methanol vapor existing in the outlet gases). The parametric analysis on the effects of the particle species and concentrations on CO2 bubble absorption rate is carried out. The particle concentration ranges from 0.005 to 0.5vol%. It is found that the CO2 absorption rate is enhanced up to 4.5% at 0.01vol% of Al2O3/methanol nanofluids at 20°C, and 5.6% at 0.01vol% of SiO2/methanol nanofluids at −20°C, respectively. [Copyright &y& Elsevier]

Abstract: This paper quantifies the influence of Al2O3 nanoparticles on the pool-boiling performance of R134a/polyolester mixtures on a roughened, horizontal, flat surface. The nanoparticles enhanced the boiling heat transfer relative to that for R134a/polyolester mixtures without nanoparticles for the three lubricant mass fractions that were tested. 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) as large as 400% for the lowest heat flux. The average heat flux improvement for heat fluxes less than 40 kW m−2 was approximately 105%, 49%, and 155% for the 0.5%, the 1%, and the 2% mass fractions, respectively. A semi-empirical model was developed to predict the boiling enhancement as caused by the interaction of the nanoparticles with the bubbles. The model suggests that small particle size and large nanoparticle volume fraction improve boiling enhancement. [Copyright &y& Elsevier]

Abstract: The objective of the present work is to characterise, using an experimental microscopic observation device, the crystal size distribution (CSD) of ice and tetrahydrofuran (THF) hydrate slurries, which can be used as two-phase refrigerant fluids for cold transportation and storage in the field of secondary refrigeration. Three different solutes (ethanol, propylene glycol and sodium chloride) were used to form ice slurries. The studied hydrate was THF hydrate since it is stable at atmospheric pressure and in a temperature range suitable for refrigeration and air-conditioning applications. Experimental ice and THF hydrate slurry CSDs were compared to classical normal (Gaussian), log-normal, gamma, and Weibull (Rosin–Rammler) distributions. A comparison between ice and THF hydrate slurry CSD results showed that hydrate slurries were composed of crystals approximately 1.5 times smaller than ice crystals. The present results were shown to be useful input parameters for modelling thermophysical properties of slurry systems. [ABSTRACT FROM AUTHOR]

Abstract: The effects of metal piece additives on effective thermal conductivity and diffusivity of an unconsolidated adsorbent bed in which adsorbent is silica gel were investigated. The metal piece additives were copper, brass, aluminum and stainless steel with two different sizes as 1.0–2.8mm and 2.8–4.75mm. The effective thermal conductivity and diffusivity of the mixed bed were predicted by comparison of the experimental results with the solution of dimensionless heat conduction equation for the bed. The performed experiments showed that the addition 15wt% of aluminum pieces with sizes between 1.0 and 2.8mm enhances the effective thermal diffusivity and conductivity of a pure silica gel bed by 157% and 242%, respectively. [Copyright &y& Elsevier]

Abstract: Nucleate pool boiling heat transfer characteristics of refrigerant/oil mixture with diamond nanoparticles were investigated experimentally. The refrigerant is R113 and the oil is VG68. Experimental conditions include a saturation pressure of 101.3 kPa, heat fluxes from 10 to 80 kW m−2, nanoparticles concentrations in the nanoparticles/oil suspension from 0 to 15 wt%, and nanoparticles/oil suspension concentrations from 0 to 5 wt%. The experimental results indicate that the nucleate pool boiling heat transfer coefficient of R113/oil mixture with diamond nanoparticles is larger than that of R113/oil mixture by maximum of 63.4% under the present experimental conditions, and the enhancement increases with the increase of nanoparticles concentration in the nanoparticles/oil suspension and decreases with the increase of nanoparticles/oil suspension concentration. A correlation for predicting the nucleate pool boiling heat transfer coefficient of refrigerant/oil mixture with nanoparticles is proposed, and it agrees well with the experimental data of refrigerant/oil mixture with nanoparticles. [Copyright &y& Elsevier]

Abstract: The objectives of this paper are to examine the effect of nanoparticles on the pool type absorption heat transfer enhancement and to find the optimal conditions to design a highly effective compact absorber for NH3/H2O absorption system. The binary nanofluids which mean binary mixture with nano-sized particles are tested to apply nanofluids to the absorption system. Al2O3 and carbon nanotube (CNT) particles are added to make the binary nanofluids in the binary mixture of NH3/H2O. The effect of Al2O3 nanoparticles and CNT on the absorption performance is studied experimentally. The experimental ranges of the key parameters are 20% of NH3 concentration, 0–0.08vol% (volume fraction) of CNT particles, and 0–0.06vol% of Al2O3 nanoparticles. For the NH3/H2O nanofluids, the heat transfer rate and absorption rate with 0.02vol% Al2O3 nanoparticles were found to be 29% and 18% higher than those without nanoparticles, respectively. It is recommended that the concentration of 0.02vol% of Al2O3 nanoparticles be the best candidate for NH3/H2O absorption performance enhancement in the present conditions. It is expected that this study will give some basic idea to understand the heat and mass transfer enhancement mechanism in multi-components nanofluids. [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: The objective of this paper is to investigate the influence of nanoparticles on the heat transfer characteristics of refrigerant-based nanofluid flow boiling inside a horizontal smooth tube, and to present a correlation for predicting heat transfer performance of refrigerant-based nanofluid. For the convenience of preparing refrigerant-based nanofluid, R113 refrigerant and CuO nanoparticles were used. Experimental conditions include an evaporation pressure of 78.25kPa, 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 heat transfer coefficient of refrigerant-based nanofluid is larger than that of pure refrigerant, and the maximum enhancement of heat transfer coefficient is 29.7%. A heat transfer correlation for refrigerant-based nanofluid is proposed, and the predictions agree with 93% of the experimental data within the deviation of ±20%. [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: Migration characteristics of nanoparticles in the pool boiling process of nanorefrigerant and nanorefrigerant–oil mixture are fundamental knowledge for the application of nanorefrigerants in refrigeration systems. In this paper, migration characteristics of nanoparticles in the nanorefrigerant–oil mixture as well as in the nanorefrigerant were experimentally studied and numerically simulated. Experimental results show that the migrated mass of nanoparticles in the pool boiling process of both nanorefrigerant and nanorefrigerant–oil mixture, increase with the increase of the original mass of nanoparticles and the mass of refrigerant; the migration ratio decreases with the increase of volume fraction of nanoparticles; the migrated mass of nanoparticles and migration ratio in the nanorefrigerant are larger than those in the nanorefrigerant–oil mixture. A numerical model, which can qualitatively well predict the migrated mass of nanoparticles, was established, and the deviations between the model predictions and experimental data were in the range of 7.7–38.4%. [Copyright &y& Elsevier]

Abstract: Pressure drop experiments for a natural refrigerant vaporization of CO2 were performed in horizontal minichannels. The test section was made of stainless steel tubes with inner diameters of 1.5mm and 3.0mm and with lengths of 2000 and 3000mm. This test section was uniformly heated by applying electric current directly to the tubes. Experiments were performed at inlet saturation temperatures of −10, −5 and 10°C, mass flux ranges from 200 to 600kgm−2 s−1 and heat flux ranges from 10 to 30kWm−2. The current study showed the significant effect of mass flux, tube diameter, and saturation temperature on the pressure drop. The experimental results were compared against 13 existing two-phase pressure drop prediction methods. A new pressure drop prediction method based on the Lockhart–Martinelli method was developed with 9.41% mean deviation. [Copyright &y& Elsevier]

Abstract: PIV (particle image velocimetry) measurements of flow field due to natural convection in a parallelepipedic enclosure representing a domestic refrigerator model (scale 1) have been undertaken in order to determine the thickness of the hydrodynamic boundary layers and to study the flow motions depending on the boundary conditions applied on the vertical walls. One of the vertical walls is maintained at a negative and constant temperature either on the totality or on one part of its surface: this wall acts as the evaporator. The other walls are in contact with external air at constant temperature. The velocity measurements have been made in the symmetry plane of the enclosure. Unsteady recirculations have been observed at the bottom of the cavity. The influence of both the temperature and the dimension of the cold wall has been studied. Numerical simulations using CFD software (Fluent) have been then performed. In the numerical model, we assumed that the temperature of the evaporator is constant while an uniform global heat transfer coefficient has been used to describe the heat exchange with the external air at constant temperature. We considered laminar 3D flows and took into account the heat transfer by radiation between the different walls of the cavity. The results obtained with the 3D numerical simulations are in quite good agreement with the experimental airflow measurements using the PIV technique. [Copyright &y& Elsevier]

Abstract: The objectives of this study are to measure the vapor absorption rate and heat transfer rate for falling film flow of binary nanofluids, and to compare the enhancement of heat transfer and mass transfer under the same conditions of nanofluids. The key parameters are the base fluid concentration of LiBr, the concentration of nanoparticles in weight %, and nanoparticle constituents. The binary nanofluids are H2O/LiBr solution with nanoparticles of Fe and Carbon nanotubes (CNT) with the concentrations of 0.0, 0.01 and 0.1wt %. The vapor absorption rate increases with increasing the solution mass flow rate and the concentration of Fe and CNT nanoparticles. It is found that the mass transfer enhancement is much more significant than the heat transfer enhancement in the binary nanofluids with Fe and CNT. It is also found that the mass transfer enhancement from the CNT nanoparticles becomes higher than that from the Fe nanoparticles. Therefore, the CNT is a better candidate than Fe nanoparticles for absorption performance enhancement in H2O/LiBr absorption system. [Copyright &y& Elsevier]

Abstract: A nonintrusive flow measurement technique (particle image velocimetry) was used to determine the airflow field in a package with a container-to-product diameter ratio of less than 10. The complexity and uneven distribution of the measured flow field supported the requirement of a geometrical and mathematical model capable of describing the geometry and physics of flow within the package. Using novel computational fluid dynamics (CFD) codes, an accurate model of the packed structure was developed and the 3D Navier–Stokes equations were solved. A good agreement was obtained between experimental and predicted velocities. The detailed insight on the airflow pattern provided by the CFD analysis makes this approach an ideal tool to analyze the effect of different vent designs in the airflow field distribution in complex packaging systems. [Copyright &y& Elsevier]

Abstract: Thermodiffusion (Soret effect) and diffusionthermo (Dufour effect) effects on convective instabilities in nanofluids have been theoretically investigated. Thermodiffusion implies that mass diffusion is induced by thermal gradient, which is so-called the Soret effect. Diffusionthermo implies that heat transfer is induced by concentration gradient, which is so-called the Dufour effect. By using the linear stability theory under one-fluid model, a characteristic dimensionless parameter was newly obtained. From the instability analysis with given conditions, it is found that the convective motion in nanofluids sets in easily as the Soret and Dufour effects and the initial concentration of nanoparticles increase. [Copyright &y& Elsevier]

Abstract: The objectives of this paper are to visualize the bubble behavior during the NH3/H2O absorption process with chemical surfactant and nano-particles and to study the effect of nano-particles and surfactants on the absorption characteristics. Binary nanofluid which means binary mixture with nano-sized particles is tested to apply nanofluid to the absorption system. Cu, CuO and Al2O3 nano-particles are added into NH3/H2O solution to make the binary nanofluids, and 2-ethyl-1-hexanol, n-octanol and 2-octanol are used as the surfactants. The concentration of ammonia in the basefluid, that of nano-particles in the nanofluid, and that of surfactants in the nanofluid are considered as the key parameters. The results show that the addition of surfactants and nano-particles improves the absorption performance up to 5.32 times. It can be concluded that the addition of both surfactants and nano-particles enhances significantly the absorption performance during the ammonia bubble absorption process. [Copyright &y& Elsevier]

Abstract: This study examines the feasibility of using magnetic particles in liquid suspension as a working fluid to achieve room temperature refrigeration with a permanent magnetic field source. Potential advantages include facilitation of regenerative heat transfer while avoiding wear, drag, and leakage problems of mechanical sliding seals associated with the use of a solid magnetic working substance. Rheological properties are evaluated in defining an appropriate composition, and performance estimates developed for a conceptual embodiment. [Copyright &y& Elsevier]

Abstract: The objectives of this paper are to examine the effect of nano particles on the bubble type absorption by experiment and to find the optimal conditions to design highly effective compact absorber for NH3/H2O absorption system. The initial concentrations of NH3/H2O solution and the kinds and the concentrations of nano particles are considered as key parameters. The results show that the addition of nano particles enhances the absorption performance up to 3.21 times. Moreover, the absorption rate increases with increasing concentration of nano particles and the nano particles are more effective for lower absorption potential solution. The potential enhancement mechanism for binary nanofluid is suggested. The experimental correlations of the effective absorption ratio for each nano particles, Cu, CuO, and Al2O3, are suggested within ±10% error-band. [Copyright &y& Elsevier]

Abstract: One of the main advantages of ice slurry as secondary refrigerant is the possibility of cold storage, which enables load shifting and peak shaving. During cold storage, ice crystals are subject to mechanisms as attrition, agglomeration and Ostwald ripening causing changes in the crystal size distribution, which are of great importance for ice slurry systems since they influence other parameters such as pressure drop and heat transfer characteristics. Storage experiments with ice crystals in aqueous solutions of sodium chloride, ethylene glycol, ethanol and propylene glycol show that Ostwald ripening is the most important mechanism inducing an increase in average crystal size. The ripening rate strongly decreases as the solute concentration increases and the type of solute and the mixing regime also play an important role. The different ripening rates are caused by the fact that crystal growth and dissolution by means of Ostwald ripening are mainly limited by surface integration kinetics at low concentrations and by mass transfer at high solute concentrations. [Copyright &y& Elsevier]

Abstract: The present paper reviews the technologies on preventing the agglomeration and the growth of ice particles in water with a very small amount of suitable additives. This summarizes studies on the effects of anti-agglomeration of ice particles and suppression of ice growth by using anti-freeze protein and its substitutes or some kinds of surfactants, and on their applications to ice slurry making systems, and to the coupling technology with surfactant drag reduction of ice slurries. These anti-agglomeration additives are found to well disperse ice particles in water at a very low concentration without a serious depression of the equilibrium freezing temperature. This is concluded to improve the ability of ice slurries as a secondary refrigerant. [Copyright &y& Elsevier]

Particle deposition on ceilings close by ventilation outlets is a well-known and bothersome problem in the ventilation industry. This paper reveals the mechanisms causing the soiling of induction outlets and offers countermeasures. Experimentally verified CFD-calculations are performed to gain insight into the processes leading to particle deposition. It shows that the room air that is being induced by the entering airflow transports particles from the room to the ceiling where they deposit due to turbulent interaction forces. Other forces such as electro- and thermophoresis are negligible. An experimental technique is proposed to visualize the soiling patterns of an outlet by photographing deposited sodium chloride crystals. These tracer-particles stem from an atomizer and aerodynamically behave like the particles responsible for the soiling of ceilings in reality. Using image processing, suitable statistics describing the tendency of an outlet to attract particles can be derived from the pictures. [Copyright &y& Elsevier]