最新刊期
卷 35 ， 期 1 ， 2014
- 摘要：A novel type of LiBr/water absorption refrigeration cycle with the self-adjustable effect between 0.5 and 1.0 (0.n) have been proposed and analyzed. A pair of medium pressure evaporator/absorber is added into the single effect cycle to form this novel cycle. Cooling water into the cycle is precooled by this evaporator. Precooling makes the solution concentration out of the absorber weaker, which lifts the highest generation temperature limited by crystallization and drops the generation starting temperature. Calculation is given based on several assumptions. Results show that 0.n-effect cycle has generation temperature ranges twice and six times larger than single effect cycle under cooling water temperature of 32 ℃ and 40℃ respectively. Meanwhile a COP of 0.3~0.75 is obtained.关键词：LiBr/water;absorption refrigeration;single effect;multi effect;generation temperature2081|2270|0发布时间：2024-07-18
- 摘要：Regeneration of solid desiccants by electro-osmostic effect caught more and more attentions due to its energy saving and simplicity. The surface area and pore size analyzer was used to test the adsorption performance of the zeolite and the macroporous silica gel firstly. The possibility of electro-osmosis regeneration for the zeolite and the macroporous silica gel has been analyzed combined with different desiccants adsorption and electro-osmosis effect. The adsorption mechanism of the zeolite is monolayer adsorption or porous filler. The water exists in the micro pore of the zeolite in molecular state, thus it can’t form electro-osmosis effect. Capillary condensation happens for macroporous silica gel. The liquid water exists when it is saturated, so it is possible for macroporous silica gel to be regenerated by the electro-osmosis effect. The experiment results show the critical moisture content existing electro-osmosis effect of zeolite is between 40%~55% when the voltage is 30V which is higher than its saturated moisture content. This result verifies that there is no electro-osmosis effect for the zeolite when it is unsaturated. As for the macroporous silica, there is no electro-osmosis effect when the moisture content is 95% and the voltage is 60V. And electro-osmosis effect exists for 105% moisture content and 40V, 50V and 60V voltage. Electro-osmosis effect can reduce the moisture content of the macroporous silica gel when it is unsaturated.关键词：solid desiccant;electro-osmostic;regeneration;adsorption1820|2301|0发布时间：2024-07-18
- 摘要：Ionized water was used to investigate the heat transfer characteristics of vertical rectangular narrow channels experimentally. The distribution characteristics of wall-temperature and the local heat transfer coefficient were analyzed by using single-side heating and various parameters of the working fluid. The experiment results show that the heat transfer coefficient is increased with the increase of the mass flow rate but the inlet temperature substantially has no effect on the heat transfer coefficient for convection boiling flow. When the dryness χ <0.1, the heat transfer coefficient is increased with decreases of the dryness; when the dryness χ >0.1, the heat transfer coefficient keeps constant with increases of dryness. The results also show that the heat transfer coefficient has a slight increase with the increases of dryness and is increased with the increases of inlet temperature for nucleate boiling flow.关键词：heat transfer characteristics;local heat transfer coefficient;rectangular narrow channels;experimental study1875|2233|0发布时间：2024-07-18
- 摘要：Effect of anti-fouling capacity of Ni-P-PTFE composite coating was tested in the hard water. It is found that anti-fouling capacity of the Ni-P-PTFE coatings is determined by the PTFE concentration in the coating. The induction period is lengthened and fouling deposition is dropped with the increase of PTFE content in the coating. In addition, the thermal conductivities of the Ni-P-PTFE coatings were measured by thermal resistance method in the paper. It is shown that the thermal conductivity is declined with the increase of PTFE content, and the PTFE content of the Ni-P-PTFE coatings is influenced by the PTFE concentration of the solution. The anti-fouling efficiency and thermal conductivity reduction rate are then defined to evaluate the performance of coating. It is found that the sample formed at the PTFE concentration 11ml?L-1 in the solution behaved the best integrated performance of anti-fouling capacity and thermal conductivity under the conditions in the paper.关键词：Ni-P-PTFE composite coating;anti-fouling capacity;thermal conductivity;PTFE concentration1824|1972|0发布时间：2024-07-18
- 摘要：The frost on the heat exchanger of air-source heat pump has a great influence on the operating performance. The frosting experiment based on a cascade type air-source heat pump water heater is carried out in the enthalpy-difference chamber in this paper, and the outdoor evaporator of the unit is a finned-tube heat exchanger. The experiment is conducted under the conditions that the outdoor temperature is from -18℃ to 6℃ and outdoor relative humidity is from 70% to 90%. Experimental results show that: First of all, the amount of frosting almost changes linearly with the frosting time which is of maximum in the outdoor temperature range of -3~3℃, and the lower outdoor temperature, the more frosting amount; Secondly, the outdoor relative humidity has a great influence on the quantity of frost, and the more humidity, the more frosting quantity; Finally, the frosting factor is proposed based on the relationships of the area and form of evaporator coil, the time of frosting, the difference of the dew point temperature and the temperature on the evaporator coil and the frosting quantity, and is from 6.51 to 10.31kg/(m2?℃?min) with the average value 8.58×10-4 kg/(m2?℃?min).关键词：air-source heat pump;finned-tube heat exchanger;outdoor temperature;outdoor humidity;frosting amount1929|2210|0发布时间：2024-07-18
- 摘要：As a new phase-change cold storage materials, the thermal properties of nano-fluids are important for its further application. The effect of diameter, mass fraction and cooling rate to solidification point, freezing point, melting temperature, specific heat capacity and latent heat of Al2O3 was measured by Differential Scanning Calorimetry (DSC). The diameter of nanoparticle is 10nm, 20nm, 50nm, 100nm, 500nm. The mass fraction is 5%, 10%, 12%, 15%, 20%.The cooling rate is 2℃/min, 3℃/min,5℃/min,7℃/min,9℃/min. The results show that the nanoparticle plays a critical role on cool storage. The solidification point and freezing point of nanofluids are higher than the deionized water. With the increase of nanoparticle sizes, mass fraction and cooling rate, the solidification point and freezing point of nanofluids will increase, and the specific heat capacity of nanofluids will decrease. The melting temperature will increase with the increase of nanoparticle sizes, mass fraction, and also decrease with the increase of cooling rate. The latent heat of deionized water is higher than the nanofluids’. The latent heat of nanofluids will increase with the increase of diameter of nanoparticle and decrease with the increase of mass fraction and cooling rate.关键词：DSC;nano-fluids;phase change characteritics;mass fraction;diameter;cooling rate1815|1828|0发布时间：2024-07-18
- 摘要：For the cascade air-source heat pump operated under different environment temperature, the proper control of intermediate pressure is important. In this paper the principle that two stage compression ratio is approximately equal is used to determine the intermediate pressure at the optimal middle temperature. The proposed method and control strategy were implemented by highly applicable Proportion Integration Differentiation (PID) algorithm and Programmable Logic Controller(PLC).A test was conducted, and it showed that the control method was sensitive, stable and accurate with various outside conditions and indoor loads.关键词：air-source heat pump;cascade;PID;PLC;control;stability1805|2237|0发布时间：2024-07-18
- 摘要：To describe the heat and mass transfer performance of the cross-flow dehumidifier, this paper measures the dehumidifier’s moisture removal rate and dehumidifier effectiveness on the test bed with liquid desiccant evaporative cooling air-conditioning system, which is driven by solar energy and uses LiCl solution as liquid desiccant. The effect of air and solution inlet parameters on the dehumidifier is analyzed by the experiment. The new empirical correlation is developed with the experimental data, and the error of the calculation is within 15% compared with the test value. It can be used to calculate the performance of the cross-flow dehumidifier and design the cross-flow dehumidifier. Compared with other results available in the literature, the impacts of air and solution inlet parameters show similar tendency among different desiccant.关键词：cross-flow dehumidifier;heat and mass transfer;LiCl solution;experimental investigation1884|1963|0发布时间：2024-07-18
- 摘要：As a type of renewable energy, solar energy has attracted more and more attention in recent years. The solar energy can be collected by the solar collectors with the temperature lower than 100°C efficiently. The Organic Rankine Cycle that transforms the low temperature heat source with the temperature lower than 100°C into electricity has been recognized and developed by the academics. Considering that the expander is a key component of an ORC, firstly, this paper selected R600 as working fluid for ORC system, then the thermodynamic performance is analyzed, and simultaneously the performance of scroll expander is simulated by the experiments with the compressed air. Through the theoretical analysis of ORC, when the heat source temperature and ambient temperature are 78-97°C and 30°C, respectively, 0.7-1kW electricity can be obtained. Correspondingly, exergy efficiency is from 0.84 to 0.89. Compressed air is used to simulate R600. Inlet temperature of the expander changes from 75°C to 95°C while corresponding pressure changes from 0.8MPa to 1.2MPa, and outlet pressure is controlled at 0.28MPa. Isentropic efficiency is maintained at about 0.7. The work-power efficiency decreases when the ideal output power increases.关键词：organic Rankine cycle;scoll expander;isentropic efficiency;exergy efficiency;solar energy1880|2007|0发布时间：2024-07-18
- 摘要：A literature review on bubble pump using in refrigeration technology and a brief introduction the principle of bubble pump are provided. A number of bubble pumps that apply to diffusion-absorption refrigeration, Einstein refrigeration cycle, absorption refrigeration and solar refrigeration are provided and discussed. Configuration, operating parameter and working fluid are presented as the important parameters influencing the performance of the bubble pump. Finally, the fundamental theory of bubble pump, working characteristics and the performance of bubble pump improvement are proposed to be researched preferentially.关键词：refrigeration technology;bubble pump;reviews;absorption refrigeration1925|2424|0发布时间：2024-07-18
- 摘要：Heat pump water heaters are more energy efficient than the conventional ones using electricity or gas. A wrap-around micro-channel condenser was proposed to reduce the system charge of refrigerant, improve the heat transfer efficiency, reduce cost of heat pump water heaters, and improve safety. A quasi-steady-state system modeling approach to performance simulation of the air source heat pump water heater using wrap-around micro-channel condenser was developed. The refrigerant components were described by steady-state models, while the water tank was described by a dynamic lumped-parameter model. The model was well validated with the laboratory test data of the dynamically cumulative power consumption, time-variant water temperature rise, and the overall time-average COP of heat pump water heaters. Parametric analysis revealed that the insulation layer of water tank can reduce the heating time and improve the system COP around 9.2%, while a bigger condenser can improve the system COP but has negligible impact on the heating time. At last, pass number of the micro-channel condenser was optimized and three-pass design were recommended for higher performance and less chance of refrigerant maldistribution.关键词：heat pump water heater;micro-channel heat exchanger;model;simulation;experiment1788|2361|0发布时间：2024-07-18
- 摘要：Electric vehicles don’t have enough waste heat for heating in winter, so the introduction of heat pump system to electric vehicles is of great significance. Two kinds of heat pump system with three heat exchangers and four-way valve are researched in the article, and the result shows that: in most conditions, the two systems’ ability are similar, the difference between them is only 10W to 50W, but the COP of four-way valve system is 15% ~ 18% higher than that of three heat exchanger system, and the compressor power of four-way valve system is 50 to 150W lower than that of three heat exchanger system.关键词：electric vehicle air condition system;heating capacity;cooling capacity;COP1869|2177|0发布时间：2024-07-18
- 摘要：An experimental study was carried out in order to investigate the heat transfer performance of falling film outside a single horizontal tube with a new test facility. Two types of commercial evaporation tubes were tested: a plain tube and an enhanced tube, which have the same outer diameter of 19 mm and the same effective test length of 2500 mm. Refrigerant 404A was used as working fluid to transfer heat with heating water inside the tube. Spraying feeding method was adopted by using 21 spray nozzles with the equivalent diameter of 2 millimeters. Experiments were performed at saturation temperatures of 0, 5, 10 and 15 oC, heat fluxes from 8 to 30 kW/m2 and mass flow rate per unit length of tube from 0.07 to 0.11 kg/ms. The regularity of falling film heat transfer performance of R404A outside a horizontal tube was obtained which is meaningful for the design and application of falling film evaporator.关键词：falling film evaporation;heat transfer enhancement;horizontal tube1964|2033|0发布时间：2024-07-18
- 摘要：A new type of aluminum clad copper tube is proposed to substitute traditional copper tube used in heat exchanger of air-conditioner, and the cost of exchanger with the aluminum clad copper tube can be reduced by 29.5%. Firstly the airside heat transfer and flow characteristics of heat exchanger with copper tube and aluminum clad copper tube (ACC) are studied by numerical simulation. Computation results show that the performance of fin with ACC tube drops 3.12% compared with that of fin with copper tube while the pressure distribution is almost the same at inlet velocity of 2.5m/s. At the other hand, the performance of heat exchanger with copper and aluminum clad copper tube is experimentally investigated. According to the experimental results, heat transfer amount of the heat exchanger with ACC tube decreases by 3.58% compared with that of heat exchanger with copper tube, being in line with the heat exchanger standards. The numerical and experimental results are basically consistent, both of them indicate that this new type of aluminum clad copper pipe has little negative effect on the performance of heat exchanger. As a result, the aluminum clad copper pipe can be applied in air conditioner .关键词：numerical simulation;air conditioner;heat exchanger;aluminum clad copper tube (ACC)1971|1931|0发布时间：2024-07-18
- 摘要：An experimental study on the air-side resistance characteristics for micro channel heat exchanger has been performed. A series of tests were conducted at a constant surrounding temperature of 20℃ for the air velocity of 1-4m/s, Reynolds numbers of 100–500 and surface dimension of 600mm×550mm. The data were compared with different general correlations. The results show that there is a big difference between different correlations. Davenport’s predication is the best one, but the experimental data was only 55%-66% of predicted result. The data were compared with the plain fin and round tube heat exchanger with same surface dimension and capacity. The results show that they are near. The flat tube and lesser depth are two effective ways to reduce the air resistance.关键词：micro channel heat exchanger;exchanger air resistance;louver fin1798|2129|0发布时间：2024-07-18
- 摘要：Condensation of refrigerant R404A on doubly-enhanced tubes and convection heat transfer of water inside tube were measured and analyzed. The experimental data were processed by Wilson graphical method and Gnielinski method. Theoretical analysis and experimental studies show that the Gnielinski method is more appropriate to process the experiment data of doubly-enhanced tubes inside and outside surface heat transfer coefficients than the Wilson graphical method which will engender great error. The correlations of convective heat transfer inside tube and condensation heat transfer outside tube were obtained. The heat transfer enhancement ratios of inside and outside tube are 2.17 and 7.91, respectively. The condensation surface heat transfer coefficients of non-azeotropic refrigerant R404A on enhanced tubes increase with increasing wall subcooling degree which present a different variation trend from pure refrigerants condensation on smooth tubes. That is mainly due to the vapour diffusion layer formed between the liquid film and the vapour bulk.关键词：heat transfer enhancement;condensation heat transfer;R404A;data processing1867|2058|0发布时间：2024-07-18
- 摘要：The characteristics of ice-rich layer formed during ice slurry storage and the ice slurry storage homogeneity were investigated experimentally based on the self-built experiment table, which focused on the period of ice slurry accumulation from the start that ice slurry enters the ice storage tank to the end of ice-delivering. The ice slurry inlet IPF, ice slurry inlet flow and initial water level of ice storage tank were varied in order to get the significance of influence and influence on the ice slurry storage homogeneity using the orthogonal experiment and variance analysis.关键词：ice slurry storage;homogeneity;orthogonal experiment;variance analysis1799|2031|0发布时间：2024-07-18
- 摘要：The vapor compression/ejection refrigeration system (VCERS) is an energy-saving system which can reduce the loss of throttling expansion and the pressure ratio of compressor to improve the efficiency of the refrigeration system. The structure of ejector related with the evaporating and condensing temperature is researched and the energy-saving effects are compared with the compression refrigeration system from the refrigerating capacity, the compressor work and COP on five working conditions. The results indicate that the VCERS is more suitable for the low temperature working condition, the maximum increase of refrigerating capacity is about 29%, the maximum decrease of the compressor work is about 65% and the maximum increase of COP is about 63%.关键词：VCERS;ejector;structure design;energy-saving analysis1763|2622|0发布时间：2024-07-18
- 摘要：In this article, Cu-H2O, Co-H2O, MWCNT-H2O nanofluids were prepared through two-step method. The transmittance of nanofluids over solar spectrum (250 to 2500nm) was measured by the UV-Vis-NIR spectrophotometer based on integrating sphere principle. The factors of various particle size, mass fraction and optical path influencing transmittance of nanofluids were investigated. The experimental results show that the transmittance of the three nanofluids is much less than that of deionized water. The transmittance decreased with the nanoparticle size and mass fraction increasing, but increased with the optical path length reducing. With the same mass fraction, the transmittance of MWCNT-H2O nanofluids is the minimum. The transmittance of Co-H2O nanofluids is higher than that of Cu-H2O during 250～775nm wavelength, while inverse during 775～1370nm wavelength. It indicates that different particle has diverse light absorption properties during different wavelength.关键词：nanofluids;solar energy;radiation;transmittance1861|2008|0发布时间：2024-07-18
- 摘要：Adding nanoparticles into cryoprotectant may be an important means of cryopreservation in future. The oocytes were cryopreserved using cryoprotectant containing hydroxyapatite (HA), and the morphology of crystal and oocytes in the process of crystallization, recrystallization and thawing were observed using cryomicroscope system. In the mean time, the temperatures were recorded when every phase change occurred. It is found that cryoprotectant with 0.05%HA recrystallized implicitly with narrow danger zone during rewarming and hence little harm was done to oocytes. In contrast, the group without any HA nanoparticles tended to get harmed. In conclusion, the mechanism that nano-cryoprotectant promoted the survival rate of oocytes was that nanoparticles hindered the recrystallization of cryoprotectant in the process of rewarming.关键词：cryobiology;crystallization;cryomicroscope;nano-cryoprotectan1874|2098|0发布时间：2024-07-18
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