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The construction of a lean operation and inspection integrated management system for substations is an important part of the development and maintenance of the power system. Forecasting the investment benefits of substation project development is an important issue in feasibility analysis. Therefore, we need to use a highly accurate method to make a prediction of the investment benefit of this project. Granger causation is a causal relationship based on "prediction", and inferring about its causality is a key task in time series analysis. In this paper, we propose a new estimation method, Granger causality estimation based on supervised learning. This method uses an eigenvalue representation of the distance between conditional distributions conditioned on past values. And for different time series, the method can give different feature vectors. Applying it to the prediction of the investment efficiency of the substation can achieve a good prediction effect. Therefore, we used granger causality to build a predictive model of the return on investment in substations. &nbsp

Objective: To develop a questionnaire and a scoring system for evaluating physicians’ knowledge of allergen immunotherapy (AIT). Methods: Questionnaire was designed using the Questionnaire Star tool. A total of 1024 physicians were assessed, and based on the score divided into accurate judgment and inaccurate judgment groups. Statistical analysis was done, and counting data were expressed as frequen-cies and percentage values. Chi-square test and multi-factor logistic analysis were used to determine influencing factors on the indications for AIT. Results: Physician’s age, grade of the hospital, and pediatric specialty influenced the accurate judgment of AIT indication after adjustment for independent variables (P < 0.05). In all, 80.5% physicians exercised accurate assessment for allergic rhinitis. Allergic conjunctivitis was judged accurately by 47.0% physicians. Bronchial asthma was judged accurately by 71.0% physicians, and atopic dermatitis by 61.3% physicians, with a higher accuracy rate for pediatricians than non-pediatricians for all the mentioned conditions (P < 0.05). There was no significant difference in the accuracy of judgment between pediatricians and non-pediatricians in terms of AIT for food allergy and dust mite sensitization (P > 0.05). Conclusion: The results of our study demonstrated a high accuracy judgment rate among clinicians for rhinitis, asthma, and dermatitis, and a low accuracy rate for desensitization of healthy people with allergic conjunctivitis, food allergies, and allergen sensitization.

Integral-fin tubes with high heat transfer capability are a promising solution for improving the compactness of condensers used in the exploitation of offshore natural gas at sea, and the sloshing motions including rolling and pitching would inevitably affect the performance of tubes. For applying integral-fin tubes offshore, the effects of rolling and pitching motions on condensation heat transfer characteristics of integral-fin tubes should be known. In this study, the condensation heat transfer characteristics of integral-fin tubes under rolling and pitching motions are experimentally investigated and the effects of motion angle and frequency are quantitatively analyzed. The results show that the sloshing motions have both positive and negative effects on the heat transfer of integral-fin tubes during a period, and the pitching motion has a greater influence than the rolling motion. As the sloshing angle increases from 0 deg to 12 deg, the maximum increase and reduction rates of the ratio of local wall subcooling temperature under pitching motion to that under static conditions are 10.9% and 12.5%, respectively, and the time-averaged condensation heat transfer coefficient (HTC) increases by 3.5% maximally. As the sloshing frequency increases from 0 to 0.25 Hz, the maximum increase and reduction rates of the ratio of local wall subcooling temperature under pitching motion to that under static conditions are 7.7% and 15.2%, respectively, and the increase rate of the time-averaged condensation HTC remains about 2%.

Multi-compartment indirect cooling household refrigerators (MIRs) have the advantage of multiple compartments with various storage temperatures, e.g. a freezing compartment (FC), a refrigerating compartment (RC) and a variable temperature compartment (VC). MIRs have difficulty in precise control of the temperatures of all compartments because they fail to independently deliver cooling capacities to each compartment. This paper presents a method to independently deliver cooling capacities by installing a novel air distributor in a MIR and changing the position of air supply dampers in this air distributor. The design method for the geometries of the novel air distributor, including the size and the opening angle of the damper as well as the size of the air openings, is detailed illustrated. To validate the proposed method, the novel air distributor was installed in a typical MIR, and the temperatures of all compartments of the MIR before and after the installation of the novel air distributor were measured and compared. It is found that the dynamic fluctuations of the temperatures of the FC in the MIR without the novel air distributor excess the preset range at the working conditions of only the RC or the VC need to be cooled, while those of the MIR with the novel air distributor are within the preset range at all working conditions. These results confirm the effectiveness of the proposed control method for precise temperature control.

To solve the problem of non-uniform refrigerant distribution among multi-tubes of micro-channel heat exchangers (MCHXs), a novel embedded-clapboard distributor is presented in this study, in which the embedded clapboards have a spray hole to transform the irregular flow pattern of inlet refrigerant into a dispersed bubble flow, and to form a cyclic channel to maintain the regular layout of dispersed bubble flow. The design method for the distributor is illustrated, including the calculation method for the spray hole diameter deduced from the transition criteria of dispersed bubble flow at both the horizontal and the vertical installations, and the calculation method for the hydraulic diameter of cyclic channel deduced based on the Bernoulli Equation for the circulation of dispersed bubble flow. The validation of refrigerant distribution performance includes the comparison of two-phase flow pattern between the proposed distributor prototype and conventional distributor prototype manufactured with transparent material, and the test of distribution unevenness among the outlet tubes for these two types of distributor prototypes. The experimental results show that the embedded-clapboard distributor forms the regular dispersed bubble flow at all installation patterns, and the average unevenness of the proposed distributor at the vertical, the sloped and the horizontal installations is 42.5%, 45.9% and 41.4% lower than that of the conventional cylinder-type distributor, respectively.

A typical room air conditioner uses fin-and-tube heat exchanger as evaporator, and its performance may be dramatically deteriorated by the dusty-bridge between fins, which is resulted from dehumidification and dusty particle adhesion. Design of a fin-and-tube heat exchanger to avoid dusty-bridge need to predict the forming process of dusty-bridge between fins. In this paper, a numerical model is developed to simulate the dusty-water bridge formation between fins, which can well predict the shape of dusty-water bridge and mass of the dusty particles adhered by water bridges. Prediction of the dusty-water bridge shape is realized by calculating the mean curvature of the water bridge interface at first and then predicting the effect of air flow and gravity on the water bridge shape. The prediction method of the mass of the dusty particles adhered by water bridges between fins is to simulate the motion trajectories of all particles in the air flow at first and then to choose those particles intersecting with the water bridge surface as adhered. The validation results show that, the water bridge shape predicted by the model agrees well with the experimental image, and the predicted adhered particle mass agree with 92% of the experimental data within the deviation of ±20% and the mean deviation is 14.8%.

Microchannel heat sink is commonly used as a high-efficiency heat exchanger type in electronic microchips cooling, and the parallel microchannels arranged on the heat sink not only enhance heat transfer area but also result in large pumping power. In this paper, a novel structure of microchannel heat sink with rhombus fractal-like units is proposed for improve the overall performance, and a geometry optimization approach is developed for the design of the new microchannel heat sink. The validation of the geometry optimization approach is performed, and the results show that the predicted pumping power can describe 93% of the experimental data within the deviation limit of ± 5% and the mean deviation is 1.95%. Compared to the conventional parallel microchannel heat sink, the microchannel heat sink with rhombus fractal-like units may increase the COP by 7.9%-68.7% under the same constrains of external size, specified heat flux and maximum temperature limitation, which indicates the rhombus fractal-like units may effectively improve the efficiency of microchannel heat sinks.

The annual performance factor (APF) is a new performance index of heat pump type air conditioners (HPACs) based on multiple testing conditions which may result in orders of magnitude larger workload in the product development for enhancing the APF to be close to the maximal value. The development process can be accelerated if the maximum APF can be predicted. The purpose of this study is to present a fast prediction method with a high precision for the maximum APF of HPACs based on a single group of experimental data. The idea of achieving fast prediction is to establish a simplified lumped parameter model for the calculation of capacities and efficiencies of HPACs, and to present a simplified approximate APF correlation by eliminating all the intermediate parameters from the complicated APF equations defined in standards of HPACs. A group of experimental data is applied in the prediction model to improve the precision of the fast prediction method. Application of this method for a typical HPAC shows that the predicted maximum APF of the HPAC agrees well with the tested maximum APF, the maximum deviation of predicted capacities and efficiencies from the experimental data is within ±1.4%; and the duration of prediction for maximum APF is within 12 s on a typical personal computer, significantly saving the time of HPAC development.

Dust removal by frosting-defrosting is a novel way to keep the cleanness of heat exchangers of air conditioners during long-term operation, and the effect depends on the fin surface wettability. The purpose of this study is to obtain the optimal choice of fin surface wettability for dust removal by testing dust removal characteristics on various surfaces, covering bare aluminum surface, bare copper surface, hydrophilic surface and hydrophobic surface. The temperatures of the air dry-bulb, air wet-bulb, the frosting surface and the defrosting surface in the experiments are 7 °C, 6 °C, -15 °C and 5 °C, respectively. The results show that, the hydrophobic surface has the best dust removal effectiveness; the remnant dust rates on the surfaces are 28.4%, 28.0%, 8.69% and 0.54% for bare aluminum plate, bare copper plate, hydrophilic copper plate and hydrophobic copper plate, respectively; the dust removal time on hydrophobic surface is much less than that on the other ones.

Vertical helically baffled shell-and-tube heat exchangers (HBHXs) occupy smaller ground areas compared to horizontal HBHXs and have been used as propane condensers in liquefied natural gas (LNG) plants. The heat transfer characteristics of propane in the shell side of vertical HBHX were investigated in the present study. The flow patterns and heat transfer coefficients in the shell side of a vertical HBHX test sample were obtained, and the results were compared with the existing data of the horizontal HBHX. The experimental conditions cover mass flux of 20–40 kg m−2 s−1, heat flux of 3.0∼7.0 kW m−1, and vapor quality from 0.2 to superheated. It is found that the variation trend of propane heat transfer coefficient with the increase of vapor quality in the vertical HBHX shell side is similar to that of the horizontal one. However, opposite to the horizontal HBHX, the heat transfer coefficient increases with the rise of heat flux for two-phase propane in the vertical HBHX shell side, probably arising from the influence of convection heat transfer in the liquid film. The heat transfer coefficient of two-phase propane in the vertical HBHX is 15–55% lower than that in the horizontal one, due to the thicker liquid film on tubes in the vertical HBHX. A correlation was developed to predict the heat transfer coefficient, and it agrees with 93% of experimental data within a deviation of ±20%.

Metal foams have great potential for improving the condensation heat transfer characteristics of shell-and-tube heat exchangers in FLNG plants, and the drainage characteristics in metal foam under sloshing conditions should be promoted through modifying the surface wettability. For revealing the liquid drainage mechanism of metal foam with different surface wettability, the influence of surface wettability on liquid drainage characteristics under sloshing conditions was experimentally investigated in the present study. The tested samples include the hydrophilic, uncoated and hydrophobic metal foams; the experimental conditions include foam pore density of 5–40 PPI (pores per inch), the sloshing frequency of 0–1 Hz and the angle from 0° to 25°. The experimental results show that, the decreasing wettability of metal foam promotes the liquid drainage characteristics, and the promotion effect is more significant for the metal foam with larger PPI. The liquid retention mass in metal foam with various surface wettability decreases maximally by 30% under the rolling motions, while it only decreases by 5% under the swaying and heaving motions. The wettability impact factors of the hydrophilic and hydrophobic metal foams under the sloshing conditions are within 0.96–1.33 and 0.26–0.97, respectively. A correlation for predicting the liquid retention mass in metal foam with various wettability under the sloshing conditions is developed within a deviation of 25%.

In order to efficiently use spiral wound heat exchangers (SWHEs) in the field of offshore natural gas liquefaction, the heat transfer mechanism in two-phase flow outside tube bundle should be known. In the study, the heat transfer characteristics of two-phase flow were numerically investigated based on the experimental results under offshore conditions using propane as medium. A comparison between the heat transfer of the proposed model and that of experimental data was analyzed. The validation results showed that the trends of simulation results were basically identical to those of the experimental ones, the deviation was generally within ±10%. It obtained that liquid film acted as a key role during the heat transfer procedure for two-phase flow outside tube bundle under offshore conditions, and increases of sloshing frequency would improve the velocity of liquid films escaping from tube surface, which resulted in an adverse effect on heat transfer. Furthermore, heave had the weakest effect on heat transfer procedure as well as the influence of roll was the strongest for the two-phase flow outside tube bundle. The results obtained by the numerical model could be the basis for design of liquefied natural gas spiral wound heat exchangers (LNG-SWHEs) installed on buoyant platforms.

The boiling liquid expanding vapor explosion (BLEVE) is a most severe hazard in liquefied gas storage and transportation, and its prevention depends on the suppression of the explosive boiling during tank depressurization. This paper proposes an idea of using micro-fin type surface to suppress the explosive boiling, and experimentally investigates the suppression mechanisms and quantitative effects on the explosive boiling. In the experiments, the bubble behaviors on a micro-fin and a smooth surface are observed for phenomenal analysis, and the explosive boiling consequences of the two surfaces are measured for quantitative evaluation. The results show that, the micro-fin surface brings forward the nucleation onset and reduces the boiling region, resulting in a weakened explosive boiling process. Among release pressures of 200 kPa-500 kPa and vent areas of 1.8 cm2-5.3 cm2, the adopted micro-fin surface reduces the boiling-induced pressure rise and the released energy by up to 24.5% and 35.6%, respectively.

Using the condensate water to remove the dust on fins is an economic way to maintain the heat transfer performance of a fin-and-tube evaporator, and the dust removal performance depends on the fin surface wettability. The purpose of this paper is to experimentally investigate the effect of surface wettability on dust removal by condensate water, covering the surfaces of hydrophilic coating, hydrophobic coating, superhydrophobic coating, and uncoated copper. The experimental conditions cover the inlet air temperature of 27 °C, the inlet air relative humidity of 50%, the inlet air velocity of 2 m s−1, the dust concentration of 10.8 g m−3, the dust deposition time of 30 min, and the sample surface temperature of 12 °C. The results show that, the superhydrophobic surface has the best dust removal performance, and the remnant dust weight on superhydrophobic surface is 69.9% lower than that on the uncoated copper surface, 61.1% lower than that on the hydrophilic surface and 3.59% lower than that on the hydrophobic surface.

Enclosing the controller in an inverter air conditioner can prevent the damage from insects and dusts in the ambience, but may decrease the efficiency of heat dissipation. The objective of this study is to propose a novel thermal management solution based on the heat pipe heat sink (HPHS) for cooling the enclosed controller. The heat flux of the chips in the controller is transferred to a HPHS by the forced convection supplied by an internal micro fan and then dissipated to the ambience. Two types of HPHSs (i.e. U-type and L-type) are designed, and the location of micro fan is optimized. The application of the proposed solution in a real inverter air conditioner shows that, the thermal management employing L-type HPHS is the better one and can reduce the average temperatures of small-power chips and large-power chips by 10.0 °C and 5.9 °C, respectively.

For optimizing the spiral wound heat exchanger (SWHE), the heat transfer mechanism of mixed hydrocarbon refrigerants flow boiling in shell side of SWHE should be known. In the present study, the heat transfer characteristics of the ethane/propane mixed refrigerants were experimentally investigated, and the ethane molar fractions of the mixed refrigerants cover 0–60%. As the vapor quality increases, the heat transfer coefficient (HTC) of the mixed refrigerant initially increases and then decreases sharply, presenting a maximum value at vapor quality of 0.6–0.8. As the ethane molar fraction increases from 0% to 60%, the HTC decreases maximally by 21% at vapor quality smaller than 0.7, while it increases maximally by 27% at vapor quality larger than 0.7. A heat transfer coefficient correlation for mixed hydrocarbon refrigerants flow boiling in shell side of SWHE was developed, and it agrees well with the experimental data.

For applying metal foam in enhancing the condensation heat transfer of shell-and-tube heat exchangers, the liquid drainage characteristics of metal foams under sloshing conditions are investigated experimentally. The experimental conditions include the pore density of 5-40 PPI and the porosity of 0.85–0.95. The results show that, the liquid drainage performance of metal foams is improved by sloshing motions; as the sloshing frequency and angle increase, the liquid retention of metal foam decreases by a maximum of 44%. A sloshing impact factor is employed to evaluate the influence of sloshing motions, and the impact factors of rolling, swaying and heaving motions are within 0.56–1.0, 0.93–1.0 and 0.92–1.0, respectively. With the increasing PPI, the shape of liquid retained in metal foam changes from droplet to scattered or full layer, which has significant effect on the drainage performance. A correlation for predicting the mass liquid retention was developed within a deviation of ±20%.

The resuspension of deposited nanoparticles within a boiling fluid is a nanoparticle behavior that may mitigate or even avoid the degradation of nanofluids, which is of great significance to the long-lasting heat transfer enhancement of nanofluids. In this study, the nanoparticle resuspension behavior during pool boiling was investigated experimentally and theoretically. Visualized pool boiling experiments were conducted for the nanoparticle-deposited surfaces which were prepared by boiling nanofluids. Various methods were employed to capture the resuspension phenomenon and characterize the morphology of nanoparticle deposition layer. The nanoparticle resuspension ratio was measured for various boiling durations, deposition area densities, and heat fluxes to elucidate the effects of these factors on the resuspension behavior. It was found that a part of deposited nanoparticles were resuspended to the bulk of the boiling liquid and then migrated with the internal flow during pool boiling, and the porous structure of nanoparticle deposition layer played a key role in the occurrence of resuspension. The measurement showed that heat flux was a main influential factor, and increasing heat flux can lead to a dramatical increase of resuspension ratio. A semi-theoretical model was developed to predict the resuspension ratio, which agreed well with the experimental results.

Magnesium (Mg) metal anode is a highly desirable candidate among various high energy density metal anodes, possessing higher volumetric capacity and better safety characteristic compared to lithium metal. However, most Mg salts in conventional Mg electrolytes easily react with Mg metal to form blocking layers, leading to inferior reversibility of Mg plating/stripping. Here, a stable Mg2+ -conducting solid electrolyte interphase (SEI) is successfully constructed on Mg metal anode by regulating the molecular-orbital-energy-level toward an aluminum(III)-centered anion Mg salt through anion-solvent coordination. Of which, the LUMO energy level of perfluorinated pinacolatoaluminate (Al(O2 C2 (CF3 )4 )2 - , abbreviated as FPA) anion has been adjusted by coordinating with solvent molecule (tetrahydrofuran) for facilitating the formation of advantageous SEI. The existence of SEI formed by FPA anion greatly improves the reversibility and long-term stability of Mg plating/stripping process. More importantly, based on this aluminum(III)-centered Mg electrolyte, the Mo6 S8 /Mg batteries can achieve a fantastic cycle performance of 9000 cycles, proving the beneficial effect of SEI on the cycling stability of Mg battery system. These findings open up a promising avenue to construct stable and compatible SEI on Mg metal anode, and lay significant foundations for the successful development of rechargeable Mg metal batteries.

For predicting the thermal performance of cold box with parallel plate-fin heat exchangers, a general distributed-parameter model based on graph theory was developed. In the present study, a mathematical description model of cold box based on graph theory was established, capable of describing the connection relations of multiple streams and components in cold box; a distributed-parameter thermal performance model of plate-fin heat exchangers based on approximate analytical method was developed, and the temperature gradients along both axial and transversal directions are reflected; a mass flow rate distribution model of parallel pipelines based on the pressure balance was presented to calculate the flow distribution of multiple streams in pipelines. A tailor-made iteration algorithm using graph-based traversal method was developed to solve the present model. The validation of the proposed model shows that the deviations of the calculated heat capacity and outlet temperature of natural gas from experimental data are −1.9% and +4.35 °C, respectively.

To resolve the problem of non-uniform refrigerant distribution in multi-path heat exchangers of air conditioners, a new distributor which distributes the two phase refrigerant uniformly is presented. The basic idea to develop the new distributor is firstly to construct a symmetric annular flow before distribution and then to allocate the annular flow evenly. The detailed design method, including an approach for computing the inlet tube geometry to construct the annular flow, and an approach for designing the connection structure between the inlet tube and the outlet tubes to allocate the annular flow evenly, is presented. The new distributor prototype is made of transparent material and the flow pattern inside it is observed visually. The experimental results show that the distribution unevenness of the proposed distributor under the horizontal and the vertical installations are respectively 19.8% and 60.9% lower than those of the most commonly used cone-type distributor.

The component proportion of ethane/propane mixture varies during the condensation process in shell side of helically baffled shell-and-tube heat exchangers of nature gas liquefaction plants, which significantly influences the heat transfer characteristics. In the present study, the heat transfer coefficients of ethane/propane mixtures with ethane mass fraction of 8–50% (covering practical conditions) were tested, and were compared with those of pure propane (0% ethane mass fraction) to analyze the influence of component proportion. The research results indicate that, the maximum heat transfer coefficient of ethane/propane mixture occurs at vapor quality around 0.8; as the ethane mass fraction increases from 0% to 15%, the heat transfer coefficient decreases dramatically by a maximum of 66.3%; as the ethane mass fraction further increases from 15% to 50%, the heat transfer coefficient keeps almost constant, and the fluctuation is within −26.4% to 29.1%. A new heat transfer correlation has been developed, and its prediction deviations are within ±25%.

In order to evaluate the performance of the hydrophobic metal foam heat exchangers under dehumidifying conditions, the effect of porosity on the heat transfer and pressure drop characteristics of wet air in hydrophobic metal foam was experimentally investigated and compared with that in uncoated ones. The test results show that, as the porosity decreases from 95% to 85%, the heat transfer coefficient and pressure drop in hydrophobic metal foams are increased by 6%–18% and 56%–162%, respectively. The heat transfer coefficient of wet air in metal foams is increased by the hydrophobic coating at most experimental conditions except for the porosity of 85% and relative humidity of 70%–90%, and the maximum increment is 33%. The pressure drop of wet air in hydrophobic metal foams is 3%–139% larger than that in uncoated ones. The comprehensive performance of hydrophobic metal foam is better than that of uncoated foams at porosity of 95% and relative humidity of 30%–50%, and it becomes worse than that of uncoated ones with the decreasing porosity and increasing relative humidity.

Wet particles have higher propensity to deposit on fin surfaces than dry particles, and may cause a more serious deterioration of the air-side performance of fin-and-tube heat exchanger. The purpose of this paper is to experimentally investigate the influence of deposited wet particles on the air-side heat transfer and pressure drop of heat exchangers. Test samples cover three types of fins, i.e., plate fin, wavy fin and louver fin. Experimental conditions cover the inlet air relative humidity of 50–90%, the inlet air velocity of 1.0–3.0 m s−1, and the particle concentration of 2.1–10.8 g m−3. The results show that wet particles mostly deposit on the leading edge of fins as well as the front part of tubes, and the louver fin is almost completely blocked by the wet particulate fouling. Moreover, the increase of inlet air relative humidity, particle concentration and the decrease of fin pitch reduce the air-side heat transfer and increase the air-side pressure drop after wet particle deposition; the increase of inlet air velocity firstly deteriorates and then enhances the air-side performance; and louver fin is the most conducive to the deterioration of air-side performance.

Fins of heat exchangers are gradually deposited by dust particles in most application scenarios, and so a model of particle-deposited fin efficiency is needed for heat transfer prediction. In this study, the expression of fin efficiency for a particle-deposited annular fin was developed by simplifying the fin as two two-dimensional coating layers on a one-dimensional clean fin firstly, and then this expression was extended to rectangular fins with circular holes by the equivalent radius transformation. The analytical solutions for a typical rectangular fin show that the attenuation rate of fin efficiency may increase up to 23.9% if the fin surface is covered by a fouling layer with an average thickness of 4.0 mm. This model can be used to predict the heat transfer rate of fouled heat exchanger with multi-fins, and the validation results show that the accuracy of the proposed model is acceptable in engineering applications.

The air permeation caused by the pressure difference at both sides of the magnetic seal accounts for a significant part of energy loss in a refrigerated room. The purpose of this study is to model the air permeation rate. Based on momentum equations of air flow along the permeation paths, the air permeation rate is deduced as a function of the average height of permeation paths and the flow factor. The average height is obtained by a resultant force of magnetic attraction and pressure difference under the assumption of parabolic asperity profile in the permeation paths; and the flow factor is calculated by semi-empirical correlations based on the average height of the permeation paths. An experiment is designed to validate the model, and the results show that the predicted air permeation rate can describe 98% of the experimental data within a deviation of ± 15% and the mean deviation is 5.6%.

Performance of a frost-free refrigerator may be deteriorated by frost accumulation on its evaporator surface. The objective of this study is to investigate the feasibility of using an enthalpy exchanger (EE) to reduce the frost accumulation on evaporator surface in frost-free refrigerator. The influence of EE on air circulation and the change process of air humidity is analyzed, and it is indicated that the application of EE is capable to decrease the amount of water vapor entering the evaporator and consequently reduce the frost accumulation on evaporator surface. The design process of EE in frost-free refrigerator is illustrated, and an optimal type of EE is presented. An experiment on a frost-free refrigerator shows that the application of EE decreases the frost accumulation by 18.8%. In addition, effects of EE on other main performances of frost-free refrigerator besides the frost accumulation are evaluated.

Nanorefrigerant–oil mixture is a promising energy-efficient refrigeration working fluid with superior thermophysical properties, and the prediction for its thermophysical properties requires the actual size of the particles in refrigerant–oil mixture. Due to the competitive adsorption of different liquid molecules on particle surface, the actual particle size of refrigerant–oil mixture cannot be predicted by the existing models developed for the nanofluids with single-component base fluid. This paper presents a model for predicting the particle size evolution during nanoparticle aggregation in refrigerant–oil mixture, considering the competitive adsorption behavior and its effects on particle movement and interaction. For model validation, the time-evolution of particle size distribution and the average size are calculated and compared with the existing experimental data. The model prediction agrees with 92% of the experimental data within deviation of ±10% and the mean deviation is 3.7%. In addition, the model can reflect the influences of oil mass fraction, initial particle concentration, primary nanoparticle diameter and temperature on particle size evolution. It is found that the adsorption layer has a significant effect on the aggregation behavior and the particle size evolution.

For designing helically baffled shell-and-tube heat exchangers (HBHXs) used liquefied natural gas (LNG) process, the condensation heat transfer mechanism in the shell side of HBHXs should be known. In the present study, the condensation heat transfer characteristics and flow patterns of propane spirally flowing in shell side of horizontal HBHXs were experimentally investigated. Experimental conditions cover mass flux of 20–40 kg (m2 s)−1, heat flux of 3.0–7.0 kW m−2, and vapor quality from 0.1 to superheated. The results show that, the heat transfer coefficient decreases with the increase of heat flux, and it initially increases and then decreases with the increase of vapor quality. As the vapor quality increases, the stratified flow, stratified-spray flow and spray flow were observed in sequence. A correlation was developed to predict the heat transfer coefficient, and it can agree with 86% of experimental data within a deviation of ±10%.

In order to optimize the parameters of metal foam heat exchanger operating under dehumidifying conditions, the influence of pore density and porosity on the heat transfer and pressure drop characteristics of wet air in metal foam under different conditions were investigated experimentally. The experimental conditions cover PPI (number of pores per inch) of metal foam from 5 to 40 and porosity from 85% to 95%. The results show that, as PPI increases, the global heat transfer coefficient always increases under low relative humidity conditions, while it initially increases then decreases under high relative humidity conditions, presenting a maximum increment of 12–21% at 20 PPI. As the porosity increases from 85% to 95%, the global heat transfer coefficient of wet air in metal foam decreases maximally by 32%, and the pressure drop of wet air in metal foam decreases by 47%.

For accurately and quickly predicting the performance of variable speed scroll compressors with vapor injection, a theory-based explicit calculation model should be developed. In the present study, the model of the compressor with vapor injection was proposed by developing the theory-based explicit equations for the compressor performance parameters. In the model, the suction mass flow rate was expressed as the function of normalized volumetric efficiency, and the injection mass flow rate was computed by partial linearization method; the total input power was linearized by the second-order Taylor expansion; the equation of discharge temperature was developed using the heat leakage factor to realize the explicit calculation by avoiding the iterative solution of thermal loss through the compressor shell. The model verification results show that, the proposed model has a good prediction accuracy, and the calculation speed of the present model is 102–103 times faster than that of the existing models.

The heat transfer and pressure drop characteristics of wet air flow in the metal foam with hydrophobic coating was investigated experimentally, and were compared with those in uncoated metal foam to analyze the influence of hydrophobic coating. The experimental conditions include the inlet air temperatures of 27–35 °C, the inlet air relative humidity of 30–90%, the air velocities of 0.5–1.0 m/s, the copper foam PPI of 5–40. The results show that, the heat transfer coefficient of wet air in metal foam with hydrophobic coating is 5–34% larger than that in uncoated metal foam under dehumidifying conditions, while the pressure drop in hydrophobic metal foam is larger by 1–95% than that in uncoated metal foam. The comprehensive performance of metal foam with hydrophobic coating under dehumidifying condition is better than that of uncoated metal foam at relative humidity of 30% and 50%, but is worse at relative humidity of 70% and 90%.