最新刊期
卷 37 ， 期 6 ， 2016
- 摘要：The air-side pressure drop of fin-and-tube heat exchangers will increase when covered with dust particles. In this paper, a visual experimental rig was set up to investigate the particle deposition and pressure drop characteristics. The slit fin-and-tube heat exchangers were selected as the test samples. The air velocity ranged from 1.0 to 2.3 m/s and the particle concentration ranged from 2.1 to 10.8 g/m3. The results indicate that dust particles mostly deposited on the windward side of slit fins and the front part of tubes. High air velocity is beneficial to the particle deposition and can increase the air-side pressure drop; the maximum particle deposition weight and the maximum increase of air-side pressure drop increased up to 98.4% and 93.8% respectively in the experimental conditions. High particle concentration can promote the particle deposition and increase the air-side pressure drop; the maximum particle deposition weight and the maximum increase of air-side pressure drop increased up to 22.8% and 28.6% respectively in the experimental conditions. The air-side pressure drop tended to stability more quickly than particle deposition weight in the particle deposition process.关键词：fin-and-tube heat exchanger;particle deposition;pressure drop;slit fin;experimental investigation1989|2177|6发布时间：2024-07-18
- 摘要：Experiments are performed in rectangular micro-channels (dH =0.293 mm) under the condition of different mass flux and heat flux to evaluate the flow boiling heat transfer characteristics with deionized water and anhydrous ethanol. Research in micro-channels is aimed at studying the influence rule of state parameters of fluid properties, flow and heat transfer process of boiling heat transfer characteristics. According to the calculation and comparison of experimental data, the relationship between boiling heat transfer coefficient and thermal physical properties of fluid, mass flux, heat flux, vapor qualities, Boiling number are presented respectively. The results show that boiling heat transfer coefficient decreases with the increasing of heat flux, vapor qualities and Boiling number. Nucleate boiling is dominant in the process of heat transfer. Under the same condition the boiling heat transfer coefficient of deionized water is obviously higher than the boiling heat transfer coefficient of anhydrous ethanol. The heat transfer coefficient of deionized water increases with the increasing of mass flux, but anhydrous ethanol has no significant changes with mass flux. The results from heat transfer correlation taking scale effect and fluid properties into consideration have 14.2% and 16.6% MAE (Mean Absolute Error) for deionized water and anhydrous ethanol respectively. It proves that the heat transfer correlation has good applicability of predicting the boiling heat transfer coefficient in micro-channels.关键词：micro-channels;flow boiling;heat flux;experimental study;heat transfer coefficient correlation2090|2649|1发布时间：2024-07-18
- 摘要：Airflow distribution has significant impact on the performance of finned-tube evaporator. Simulation optimization and experimental study were carried out of fin-tube heater exchange flow path form with three typical air velocity distributions, when the heat exchanger structure size and inlet air state were under certain conditions. The optimization demonstrates that the capacity is increased by 10.3%, 3% under upper-triangular and middle-triangular air distribution. The analysis on upper-triangular optimized form show that the high air velocity profile is the key of improving heat transfer performance, and the COP is increased about 8% with upper-triangular air distribution. An experimental rig was built and verification was carried out. The results showed that relative error was in 5%, which indicates that the optimized and experimental results are basically consistent.关键词：finned-tube evaporator;nonuniform air distribution;optimization and analysis;experimental research1873|2701|4发布时间：2024-07-18
- 摘要：Based on REFPRO 9.0 and KW2 model parameters, the thermophysical properties of mixing refrigerant HFO-1234ze/HFC-32 were calculated in this paper, and the cycle performance of mixed refrigerant in different ratios was figured out according to the heat pump water heater test standard. The results showed that the optimal mixture ratio is 0.3/0.7. With this ratio, the performance of heat pump water heater in different operating conditions were conducted and compared with R410A. The results indicate that the mixed refrigerant’s compressor power consumption and discharge pressure are lower than R410A system, which is conducive to the safe and stable operation of the water heater; under the standard condition, the COP is 4.03 which is higher than R410A’s 3.6; meanwhile the decline rate of COP is lower than R410A when the temperature is higher than the standard condition. Therefore, the mixed refrigerant is feasible to replace R410A.关键词：heat pump water heater;mixed refrigerants;test conditions;COP2022|2563|1发布时间：2024-07-18
- 摘要：The accurate calculation of thermodynamic properties of refrigerant-oil mixture is the foundation to analyze and evaluate the influence of oil on compressor. Thermodynamic property models of R32/POE and R32/PVE are provided by explicit calculation method with the given experimental data and empirical formula. Simultaneously，the solubility and viscosity models of R410A/POE are given with the same method for comparative analysis. The maximum deviation of the predicted values of these models to experiment data is within 5 %，and these simple and reliable models provide accurate and reliable ways for the optimal design and performance analysis of compressors. Besides，the variations of solubility with temperature and pressure, and the variations of viscosity with solubility, temperature and pressure are analyzed at GX condition. In addition，the mixture properties are studied, the results show that PVE oil is better than POE when used with R32, and R32 is better than R410A when used with POE oil.关键词：refrigerant;lubricant oil;thermodynamic property;model2009|2959|3发布时间：2024-07-18
- 摘要：In order to improve the separation efficiency and decrease the pressure loss, the cyclone oil separators used in air conditioner system were designed with optimization. Based on the fluid simulation, the influences of different parameters on the separation efficiency and pressure loss of oil separator were researched, from which the optimum size ratios were obtained. The performances of the oil separator designed according to the optimum size ratio were tested in an air conditioning system. The experimental results show that in oil-return condition (lowest refrigerant velocity) the separation efficiency of new oil separator is increased from 95.5% to 99.0%, while in rated cooling capacity condition, the separation efficiency is increased from 97.3% to 99.6%, and the pressure loss is decreased from 55.2 kPa to 23.1 kPa. The distribution function of oil-particle is also obtained from experiment results.关键词：separation performance;CFD;cyclone oil separator2067|2500|4发布时间：2024-07-18
- 摘要：As to the typical air-distributions in subway platforms without screen doors, the temperature mathematical model of non-isothermal coupling airflows between the platform piston wind and air-conditioning jet is established. The dynamic natures of the mass average temperature and the axial temperature of the two coupling airflows are deduced. Both of them at some horizontal offset decrease at first(10-30 s), keep minimal value(40-70 s), and increase gradually later with train-in dynamic process(80-105 s). And the axial temperatures of the coupling airflows are lower than their mass average temperatures. Compared with the experimental results of the liquid scale model test, the maximum error between the theoretical value and the test results are within 5%. This is a good validation to support the correctness of the theory model.关键词：air-conditioning supply jet;platform piston wind;non-isothermal coupling;temperature field2122|2472|1发布时间：2024-07-18
- 摘要：The operational characteristics of ground source variable refrigerant flow (GSVRF) system in winter was investigated based on the measured data in GSVRF test rig. The variations of hourly heating capacity, hourly system power consumption and coefficient of performance (COP) of unit under different operation rate and part load ratio (PLR) were obtained. The results of the experiments indicate that the hourly heating capacity and hourly system power consumption increased substantially with the growing amount of operation rate, and the amount of hourly system power consumption is more sensitive to changes in the operating rate; regardless of the operation rate, hourly heating capacity increases with the rise of PLR; hourly system power consumption and COP of unit exhibits concave and convex trends with the rise of PLR, which shows that GSVRF system has more favorable energy efficiency at part load operating conditions .关键词：ground source variable refrigerant flow system;operation rate;part load ratio;operation in winter2065|2228|0发布时间：2024-07-18
- 摘要：Treated sewage source heat pump systems could reuse the large amount of wasted heat in the city sewage to refrigerate and heat the buildings. However, biofouling, which is the key problem in treated sewage heat pump systems, decreases the system efficiency and security. Ca2+, which is an important inorganic ion for bacteria metabolism, has a significant influence on biofouling formation. In this study, the effect and mechanism of calcium ions concentration on biofouling growth were investigated under flowing conditions. Model sewage was prepared, with the Ca2+ concentration ranging from 100 mg/L to 450 mg/L, and a rotating coupon device was used for biofouling formation. The total weight, dry weight and organic weight of biofouling grown under different Ca2+ concentrations were measured, the moisture content of the biofouling was calculated, and the microstructure of the biofouling was viewed. The results indicated that biofouling grown under higher Ca2+ concentrations have a more heterogeneous and porous structure, thus the moisture content and the total mass of the biofouling were increased. The results of this study could be used for predicting the biofouling formation under different operation conditions and improving the performance of treated sewage source heat pump systems.关键词：treated sewage source heat pumps;biofouling;Ca2+;microstructure1822|1912|2发布时间：2024-07-18
- 摘要：The experimental investigation on the phase change processes had been carried out. N-octadecane (C18) was used as latent heat storage phase change material (PCM), in which copper foams and carbon foams were embedded to enhance the heat transfer. The thermal properties of C18 were measured by differential scanning calorimetry(DSC). An experimental investigation on three thermal storage units (TSUs) with different kinds of materials filling state (C18, C18/carbon foam, C18/copper foam) had been carried out. The temperature data of TSUs had been recorded and analyzed. Compared to the results of pure C18 TSU, the effect of the foam materials on phase change heat transfer was very significant and made the temperature distribution more uniform.关键词：thermal storage;phase change;latent heat;n-octadecane;carbon foam2159|2819|4发布时间：2024-07-18
- 摘要：Dimethyl silicone oil and silane-coupler are chosen as oil phase and additive to form emulsion for slurry producing. The relation of Ice Packing Factor (IPF) and additive amount of dimethyl silicone oil and silane-coupler and environmental temperature was investigated using the mixing calorimetry method. The freezing point and the IPF of emulsion slurry are both reduced with the increase of dimethyl silicone oil mass fraction under the same crystallization time. Silane-coupler also reduces IPF, but it can prevent ice from adhering to the cooling surface and improve fluidity. The experimental results show that IPF is about 33.4% after 90 min crystallization under -8.5℃ temperature conditions when the mass fraction of dimethyl silicone oil and silane-coupler in emulsion are 4% and 10%, respectively. The slurry does not adhere to the cooling surface and is dispersed well. The slurry has a good fluidity.关键词：slurry;emulsion;phase change;cold storage1793|2223|4发布时间：2024-07-18
- 摘要：This paper presents a falling film generating apparatus for testing ammonia vapor generation rate with/without nanoparticles. The comparative experiments were conducted to study the influence of the nanoparticle and surfactant with their mass fraction varying from 0% to 0.5%, the ammonia-water with the concentration varying from 25% to 40%, and the temperature of the hot water on ammonia vapor generation rate. Adding the optimal mass fraction of Zinc Ferrite(ZnFe2O4) with sodium dodecyl benzene sulfonate(SDBS) into ammonia water can significantly improve the generation rate of ammonia vapor. The effective generation ratio can be increased by 60% with the mass fraction of 0.1% ZnFe2O4 and the mass fraction of 0.05% SDBS when the concentration of the base fluid ammonia-water varies from 25% to 40%. However, only adding the dispersant SDBS will weaken the generation rate of ammonia vapor. In order to achieve optimal result, both positive and negative effects of dispersant on generation process are need to be taken into account. In view of the enhancement of ammonia-water nanofluid on generation process, the development of AARS should have a more promising future for their commercial application.关键词：ammonia-water absorption refrigeration;nanofluids;falling film generation rate;Zinc ferrite (ZnFe2O4)1970|2080|1发布时间：2024-07-18
- 摘要：In adsorption refrigeration systems, adsorbent commonly used is in the form of powder or granular. The thermal contact resistance between adsorbent particles and the thermal contact resistance between the sorbent and heat transfer surface are large. Using consolidated adsorbent is an effective way to improve heat transfer performance. In this paper, expanded natural graphite treated with sulfuric acid (ENG-TSA) is employed as the host matrix of composite activated carbon (AC) and composite CaCl2 adsorbents. An adsorption prototype using separate thermosyphon heat pipe technology is established. Owing to the highly thermal conductive consolidated adsorbents, no fins are needed inside the adsorbers. In the experiments, the system performance is analyzed from three aspects: heat transfer performance, cycle time and evaporation/condensation temperature. The results show that the COP, SCP and volumetric refrigeration density of the system employing AC/ENG-TSA are 0.140, 86.1W/kg and 16.11 kW?h/m3, respectively, the COP, SCP and volumetric refrigeration density of the system employing CaCl2/ENG-TSA are 0.279，288.6 W/kg and 54.03 kW?h/m3, respectively. The refrigeration performances are improved significantly compared with conventional adsorbents.关键词：adsorption refrigeration system;consolidated adsorbent;activated carbon;calcium chloride;contrast experiment2138|2223|5发布时间：2024-07-18
- 摘要：With deionized water as working fluid, ultrasonic particle detection system is applied to two-phase heat transfer process. The ultrasonic attenuation spectrum method is used to measure flow boiling in vertical narrow rectangular channel. The ultrasonic attenuation spectrum, the bubble size distribution and export rate of gas (dryness) under different mass flux of 2.22 kg/(m2?s)，2.86 kg/(m2?s) and 3.49 kg/(m2?s) in the narrow rectangular are obtained by theoretical model and inversion algorithm, respectively. The experiment results show that when the mass flow rate is constant, with an increase of the heating power, ultrasonic attenuation coefficient will increase under the same ultrasonic frequency, the value of D50 will increase and the distribution of dimensions will broaden. Under the same operating conditions, with an increase of the mass flow rate, the value of D50 will decrease and the distribution of dimensions will heighten and narrow. The degree of dryness measured by ultrasonic testing system is higher than the theoretical value, and the measurement are closed to the theoretical values when the dryness is small. The error increases when the dryness increases and the theoretical model should be adjusted in this case.关键词：two-phase flow;ultrasonic;dryness;ultrasonic attenuation spectrum;bubble size distribution2075|2256|0发布时间：2024-07-18
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- 摘要：CO2 is a HCFCs substitution in HPMP of industrial and commercial refrigeration (ICR) sector in China. In this paper, the applicability of natural refrigerant CO2 application in ICR is analyzed by standards, testing, replacement cost and market prospect. The conclusion indicates that: 1) based on the leaking and suffocation risk charging limit, CO2 can be used in all refrigeration systems theoretically in relevant standards; 2) under ultra-low temperature condition and nominal condition in GB/T 21362—2008, the COP of CO2 heat pump water heater is 7.9% and 10.7% higher than R410A unit, and the performance of CO2 air-cooler evaporator is better than traditional unit; 3) the replacement cost from R22 heat pump and refrigeration system to CO2 system will increase 100%-200% and 20%-30%, respectively; 4) CO2 has well application potential in heat pump water heater and refrigeration equipment area of ICR, but the refrigeration cycle efficiency promotion, high efficiency components development and operation security protection under high pressure need further research.关键词：natural refrigerant;heat pump water heater;refrigeration equipment;coefficient of performance;CO2;applicability1914|2723|1发布时间：2024-07-18
- 摘要：Frost-free refrigerator is becoming more and more popular in the market. But the quality of frozen pork stored in the frost-free refrigerator decreased obviously with time. In this paper, the effect of three packaging types (no packaging，sealed packaging and air free packaging) on the quality of frozen pork was studied to find a effective and convenient method to maintain its quality. Weight loss rate, dripping loss rate, color-difference, texture, shear force and microstructure of frozen pork were taken as the factors to evaluate the effectiveness of packaging. The results showed that weight loss rate, L* value and b* value of the control group were significantly higher than that of sealed packaging and air free packaging. Dripping loss rate, a* value, texture, and shear force of the control group was significantly lower than that of sealed packaging and air free packaging. The microstructure of the control group was severely damaged with muscle fiber broken. After 60 days, weight loss rate of air free packaging was significantly smaller than that of sealed packaging. There were no significant differences in dripping loss rate, color-difference, texture and shear force between air free packaging and sealed packaging. The results of this study proved that the sealed packaging and air free packaging are feasible to maintain the quality of frozen pork, while air free packaging is better than that of sealed packaging, especially for long-term storage.关键词：frost-free refrigerator;frozen pork;packaging;quality;weight loss2476|2550|2发布时间：2024-07-18
- 摘要：Freezing time is an important index to evaluate the quality of frozen food, and the correct calculation of freezing time is the key to the optimal design and operation of food freezing equipment. In this paper, the freezing time is tested by the established frozen experiment platform with liquid nitrogen. After introducing existing models, several typical calculation methods are chosen to calculate the food freezing time. By comparing the theoretical results with the experimental results, the most accurate method to calculate the food freezing time is obtained. Taking the finite cyclical foodstuff as an example, the result shows that the International Institute of Refrigeration Model has the smallest difference with the experimental results, and the average deviation is 8.86%, while the Staging Model takes second place with an average deviation less than 15%.关键词：frozen food;freezing time;calculation model;experimental study2500|2900|2发布时间：2024-07-18
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