最新刊期
卷 34 ， 期 6 ， 2013
- 摘要：In order to improve the working performance of vapor compression refrigeration/heat pump system, a new system named single machine two-chamber in-parallel compression refrigeration/heat pump system was provided. An analysis model was set according to the theory of thermodynamics. The variation of cooling and heating performance with side-stage suction pressure and the most favorable volume ratio of side-stage to main-stage have been calculated. The results show that, compared with conventional single-stage compression system, cooling and heating capacity can increase 29.6% and 29.2%; cooling EER and heating COP can increase 8.0% and 2.8%; the discharge temperature decrease 3～4℃. The most favorable volume ratio of side-stage to main-stage is 0.08～0.12.关键词：double-stage compression;parallel;volume ratio;cooling/heating performance;heat pump1779|2043|0发布时间：2024-07-18
- 摘要：The reasons for the problems of the existing absorption heat exchangers, such as excessively large size, high manufacture costs, and high return temperature of the primary network hot water, were attributed to the “triangular heat transfer processes” inside the absorption heat pumps. The structures of new Multi-stage Vertical Large Temperature Lift/Drop Generation-condensation And Evaporation-absorption Elementary Units were introduced, as well as their principles on how to eliminate the “triangular heat transfer processes” with a relatively compact structure. A new type of the absorption heat exchanger, called the Multi-stage Vertical Large Temperature Lift/Drop Absorption Temperature Transformer (ATT), was constituted by such elementary units. Simulation models for the ATT were built to compare its performance to the traditional single-stage absorption heat exchanger. Results showed that the ATT can reduce the minimum return temperature of the primary network hot water, from 26℃ to under 20℃. When return temperature of the primary network hot water is 26℃, the ATT can reduce the total KA (heat transfer areas multiplied by heat transfer coefficients) by 25%~32%, while the powers of solution pumps inside the ATT were only increased by 19%~48%, which were not remarkable. The ATT has obvious performance advantages over the traditional single-stage absorption heat exchanger.关键词：heat transfer areas;large temperature lift/drop;absorption heat pump;heat exchanger1802|1869|0发布时间：2024-07-18
- 摘要：A new type of consolidated composite adsorbent for CaCl2 is developed by the matrix of ENG-TSA(Expanded natural graphite treated by the sulphuric acid). Adsorption performance of consolidated composite CaCl2 was tested, and the results showed that for the sample with the density of 400kg/m3 and salt mass ratio of 80%, adsorption quantity ranges from 0.4015kg/kg to 0.4585kg/kg while the cooling temperature ranges from 25 to 35℃ and evaporating temperature ranges from -10 to 15℃,respectively. The cycle adsorption quantity of consolidated CaCl2 with ENG-TSA as matrix is similar with that of consolidated CaCl2 with ENG as matrix, whereas the addition of ENG-TSA can greatly reduce cycle time as well as improve the specific cooling performance per kilogram adsorbent(SCP).The cycle time for the composite adsorbent of CaCl2/ENG-TSA is around 3300 seconds, which is 33% reduced if compared with that for the adsorbent of CaCl2/ENG. When the condensing temperature is 30℃ , the maximum SCP for the adsorbent of CaCl2/ENG-TSA is 65.75W/kg which is increased by 48% if compared with the adsorbent of CaCl2/ENG.关键词：adsorption;consolidated composite adsorbent;adsorption quantity;specific cooling power1770|2009|0发布时间：2024-07-18
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Experimental Investigation on Heat Transfer of R22 during Condensation in a Rectangular Microchannel
摘要：The paper reported heat transfer coefficients of R22 during condensation in a horizontal stainless steel rectangular microchannel with the hydraulic diameter of 0.952 mm. Tests were conducted with saturation temperatures of 40-50℃, mass fluxes of 200-800 kg/m2 s and vapor qualities from 0 to 1. The results show that heat transfer coefficients of R22 increase with mass flux and vapor quality especially in high vapor quality regions while decrease with the saturation temperature. The data were compared with three existing heat transfer correlations. Heat transfer coefficients of R152a are larger than the data of R22 when compared with the same experimental conditions.关键词：condensation heat transfer;microchannel;experimental investigation;heat transfer coefficients1665|1795|0发布时间：2024-07-18 - 摘要：Liquid-vapor separation condenser (LSC) is a kind of parallel flow heat exchanger with liquid-vapor separation baffles in its headers, which can drain away the condensate in time during condensation process. This paper experimentally studied the performances of three refrigeration systems employing three parallel-flow condensers with different liquid-vapor separation baffles in the standard air enthalpy difference lab. The indoor dry bulb and wet bulb temperature fixed at 26.7℃ and 19.4℃, the outdoor dry bulb temperature varied from 29℃ to 41℃. The refrigerant tube wall temperatures and pressure drops of the three condensers were investigated, as well as their power consumption, cooling capacity and energy efficiency ratio. The results indicated the performance of the LSC may be the same or not with the different liquid-vapor separations. Once an excellent design for the LSC was done, its wall temperature kept quasi-constant, and pressure drop was also minimum. Further, the system with the LSC can obtain maximum system refrigerant mass flow rate, as well as the maximum cooling capacity and EER.关键词：liquid-vapor separation baffles;condenser;refrigeration system;flow distribution;system performance1583|1755|0发布时间：2024-07-18
- 摘要：According to double membrane mass transfer model of falling film absorption, change law and transport mechanism were analyzed on related physical quantities during ammonia’s heat, mass and momentum transfer process. Energy and mass conservation equations were established for ammonia gas falling film absorption, and equations discretization was made. Subsequently Gauss-Seidel iterative method was used to solve these equations. Variation curve of aqua ammonia solution mass fraction along falling film tube height was obtained about smooth tube(SMT) and transversally grooved tube(TGT). The temperature of aqua ammonia and cooling water at different dimensionless height was obtained for falling film absorption of transversally grooved tube. TGT has strong falling film absorption performance in the same conditions compared with that of SMT. Absorptive capacity in winter and summer season increased by 118.5% and 167.7% respectively. The experimental results showed that the predicted temperatures of aqua ammonia and cooling water agree well with the measured temperature in the falling film absorption process.关键词：aqua ammonia;falling film;absorption;temperature field;mass fraction;transversally grooved tube2057|1846|0发布时间：2024-07-18
- 摘要：In order to study the energy consumption law of water-loop heat pump system under nonstandard conditions, the circulating water was selected as the research foundation and on the basis of the circulating water energy equations, the system energy consumption equations were built by using a linear transfer function method. The theoretical results show that the change law is nonlinear between the system energy consumption and load rate, and it will more remarkable in winter; because the effect of load rate on the energy consumption, with the circulating water energy changing, the change law of system energy consumption will appear a distortion characteristic, which significantly affect system energy saving. In order to determine the range and lasting time of distortion condition point, an engineering was selected in Tianjin as the experiment object, and the test data was analyzed by energy gap method of circulating water. The experimental results show that for this building, the distortion condition point is in the range of 4~5 level, and its lasting time is less 10% of the total run time; the capacity of auxiliary heat source is reasonable with 55% of building heat load.关键词：water-loop heat pump;nonstandard condition;circulating water energy;linear transfer function;energy consumption;energy gap method of circulating water1605|1838|0发布时间：2024-07-18
- 摘要：The ozone depletion potential (ODP) and global warming potential (GWP) of HCFCs and HFCs are higher than hydrocarbons (HCs). R290 is perfect in environmental protection and energy saving performance. In order to determine the combustible region of leaked R290 from indoor unit of air-conditioner, a test room was established in this study. The distribution of R290 concentration was studied after it leaked in the room with different room area, installation height of indoor unit, location of the leakage and different leakage rate. The results showed that combustible region is limited only in the region very close to the indoor unit, and combustible region only exists during the leakage process, which will quickly disappear once the leakage stops.关键词：refrigerant;leak;split-type air-conditioner;connector;evaporator;R2901703|1734|0发布时间：2024-07-18
- 摘要：In order to solve the frost crack problem in winter and the tube corrosion problem of corrosive medium in closed cooling towers, engineering plastic capillary-network technology is introduced to the tower. A capillary-networked closed cooling tower was designed by theoretical calculation and the performance of real model has been tested. Research indicates that the heat-exchange ability of two capillary-networked closed cooling towers is similar to a normal closed cooling tower's with copper-tubes of the same size. The cost of the heat-exchanger for both towers is almost the same. On account of the capillary-networked closed cooling towers can prevent corrosion, frost crack, foreign matters, and reduce noise. The capillary-networked closed cooling towers have better technical and economic performance.关键词：closed cooling tower;capillary network;thermal properties;test1706|2049|0发布时间：2024-07-18
- 摘要：Life cycle assessment method was used to evaluate the full life cycle carbon emissions of a kind of hybrid-power gas engine heat pump. With the system boundaries and the accounting mode established based on the life cycle (LCA) assessment, the carbon equivalent emissions in the periods of production, transportation and installation, operation and recycling of the system are figured out respectively .The results show that the system CO2-eq emissions (35387.6kg) is the highest in running phase, accounting for approximately 84% of the entire life time, and the main source is from the usage of electricity and natural gas; followed by the production phase which are approximately 6178kg;the transportation-installation phase and disposal phase can be neglected because of their low carbon emissions. Therefore, in order to reduce the greenhouse gas emissions of the system in the full life time, more attentions should be paid to the rational use of electricity and natural gas and the development of new energy. Secondly, its carbon emissions are compared with separate power-driven heat pump, and the analysis results show that hybrid-power gas engine heat pump could reduce 20430.9kg carbon emissions. Finally, carbon emission reduction method and emission reduction potential of the system are further discussed.关键词：life cycle assessment;heat pump;carbon emissions;hybrid-power1596|1861|0发布时间：2024-07-18
- 摘要：R32 has a number of advantages compared to R410A, such as zero ODP and less GWP value. It is now regarded as a possible substitute refrigerant for R410a. This paper presents a comprehensive review of the application of R32 on air conditioners and heat pumps by comparing both operational performances, such as the system efficiency and the requirement of refrigerant charge, between systems using R32 and R410a, and physical characteristics, such as lubrication oil preference and flammability, between both refrigerants. The comparison indicates although systems using R32 have slightly higher energy consumption and discharge temperature of compressor, it has much larger cooling capacity than that using R410a. Hence, R32 is ideal to replace R410A. However, there are still limitations for spreading the application of R32, such as the possible deterioration of system performance caused by a high compressor discharge temperature and the restriction on the refrigerant charge amount due to the A2L level flammability of R32. Nonetheless, domestic and international legislations tend to set less restriction for the application of R32. This tendency will certainly promote researches on using R32 to replace R410A in domestic air conditioner and heat pump systems.关键词：refrigerant substitution;air conditioner;heat pump;R410A;R321728|1932|0发布时间：2024-07-18
- 摘要：Seasonal performance evaluation index is taken as the direction to evaluate multi-split air-condition (heat pump) units (Hereinafter referred to as: VRF) in the future. The challenge on unstable heating performance test for VRF unit is discussed when seasonal performance evaluation index is used. Advantages and disadvantages of unstable heating performance test methods in relevant standards are analyzed. The conclusion indicates that the unstable heating performance test methods in EN and ISO standards reflect the heating performance of VRF units more objectively, and are with good operability and repeatability. Potential effect of the unstable heating performance test method in EN and ISO standards on the development of VRF in China is investigated. The outline and issues of Chinese unstable heating performance test method for VRF units are suggested.关键词：multi-split air-condition (heat pump) unit;heating;performance test;unstable1621|1809|0发布时间：2024-07-18
- 摘要：A generalized algorithm called ALG-I as well as a companion algorithm called ALG-II, for simulation of variable refrigerant flow (VRF) systems were proposed. Firstly, the principles and methods to find the criteria of iterative calculation and choose the variables of iterative calculation were introduced. Then, the standard algorithm was organized by some proper combination between the iterative variables and the iterative criteria, and the critical steps of the algorithm were described in detail. ALG-I and ALG-II have very similar characteristics except time-consuming. Simulation results revealed that the models established are feasible and effective to simulate the VRF systems with different number of evaporators, which indicates the proposed system algorithms are generic and evaporator-number independent. For the VRF system with only one evaporator, the much larger time consuming of the ALG-I weakened the potential for control analysis applications, while for the multi-evaporator VRF system, the ALG-I has advantages over the ALG-II. Finally, tests also showed the proposed algorithms good ability responding to varying control variables including the openness of the throttling valves and speed of the compressor. It is concluded that the system model is feasible to be applied and lays solid foundation for the studies including performance and control analysis of the VRF systems.关键词：refrigeration system;variable refrigerant flow;simulation;generic algorithm;control analysis1855|1990|0发布时间：2024-07-18
- 摘要：In order to study the effects of tube type on vapor-gas condensation heat transfer and strengthen vapor-gas condensation heat transfer, the present paper establishes the integrated model of gas liquid film thickness and heat transfer coefficient along the wall when vapor-gas mixed fluid crosses vertically both circular tube and drop-shaped tube and condensation occurred. Through the finite difference method, the calculation and comparison are carried out with flue gas from natural gas combustion as an example. In the circumstance that the effective heat transfer area is same, compared with circular tube, diameter is smaller on upper half of drop-shaped tube and pressure gradient is greater, which is helpful for drainage; surface curvature is larger on lower half of drop-shaped tube, which is also helpful for drainage. Gas film on surface of drop-shaped tube is thinner, and liquid film is also thinner; drop-wise condensation area is larger and droplet size is smaller, so condensation heat transfer coefficient is greater. Besides, drop-shaped tube also has certain enhancement to sensible heat transfer. The calculation results are compared and verified by experiment, and this model is also suitable for oval tube and other kinds of vapor-gas mixed fluid.关键词：heat transfer enhancement;condensation heat transfer;finite difference;drop-shaped tube;gas liquid film thickness1708|1992|0发布时间：2024-07-18
- 摘要：A frost-free refrigerator with a variable capacity compressor(VCC) is studied based on the results from experiments and simulation. Analyses are conducted in terms of the system energy consumption, power and running percentage under several different compressor speeds. Moreover, the temperature variation in fresh food storage, freezer, fruit vegetable and the ice-making compartments is also discussed under different compressor running speeds respectively. The experimental results show that the temperature variation in all the compartments could be kept in a reasonable scope when the compressor is running at an optimal speed. The average temperature of the fresh food storage compartment is 4.1℃ with a maximum deviation of 3.4℃ and the average temperature in the fruit vegetable compartment is 6.1℃ with a max deviation of 1.0℃. With the help of VCC the energy consumption of this frost-free refrigerator can reach 0.908kWh/day when the temperatures in all the compartments reach the national standard requirement. What’s more, compared to the experimental result the simulated system energy consumption is higher by 16.2% when the compressor runs at 3000r/min, however it drops to 8.6% when the compressor speed is set at 1900r/min. The comparison results prove the reliability of the simulation software and also indicate the importance of further work on system model optimization .关键词：variable capacity compressor;frost-free refrigerator;energy saving;experimental analysis1598|2207|0发布时间：2024-07-18
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