最新刊期
卷 36 ， 期 1 ， 2015
- 摘要：An ideal process model based on real solution for absorption heat pump is obtained in this paper. First, temperature lift factor is derived for real solution with infinite solution flow rate, and a correction factor kr is used to consider the difference with ideal solution, which is mainly dependent on the activity coefficient of solution in the generator and the absorber. For absorption heat pump, kr is higher than 1 and the COP is lower than that with ideal solution; for absorption heat transformer, kr is lower than 1 and the COP is higher than that with ideal solution. Then for real solution with finite flow rate, temperature lifting factor is defined and compared with solution of infinite flow rate. The correction factor kr is lower for real solution with finite flow rate and influenced by the concentration difference of solution, and the higher the concentration difference, the lower the kr. The COP for solution with finite solution flow rate is lower than the COP with infinite solution flow rate. Whatever the flow rate of real solution is infinite or finite, it always meets thatφCOP1关键词：real solution;absorption heat pump;temperature lift factor;COP2135|2149|0发布时间：2024-07-18
- 摘要：The application of microchannel heat exchanger is becoming more and more widely. The application of microchannel heat exchanger (MCHX) on domestic air conditioning system was investigated experimentally. The results show that: (1) when only the indoor heat exchanger was changed into the microchannel heat exchanger, the system had the best performance when the fin pitch of the indoor MCHX was 1.4mm. The charge of refrigerant for the system reduced 15.9%. Meanwhile, the cooling capacity of the new system was 1% lower than the original system while the COP was 2.2% higher; when it worked in heating mode, the heating capacity of the new system was 3.9% higher than the original one while the COP was 11.2% higher than the original one; (2)when all the heat exchangers were changed into the microchannel heat exchangers, the charge of refrigerant for the system was reduced 54%. Meanwhile, the cooling capacity of the new system was 0.8% higher while the COP was 5.2% higher than the original one in refrigerating mode; when the refrigerant was changed into R290, the best refrigerant charge for the new system was 500 g.关键词：microchannel heat exchanger;domestic air conditioner;cooling capacity;R2902195|2095|0发布时间：2024-07-18
- 摘要：Hydrocarbons, whose environmental performance (ODP=0, GWP is extremely low) and thermophysical properties is excellent, can be selected as future alternative refrigerants. The research status of the application of HCs on large and medium-sized commercial equipment is introduced from aspects of commercial heat pumps, cascade system for supermarkets and other commercial equipment. Researches indicate that hydrocarbons behave well in the actual operation of the refrigeration system. Measures of reducing the refrigerant charge due to flammability, such as using micro-channel, plate heat exchanger, adopting indirect systems, are taken to make sure safe operation of refrigeration system.关键词：refrigerant substitution;large and medium-sized commercial equipment;HCs;reducing refrigerant charge1987|1950|0发布时间：2024-07-18
- 摘要：Influence of nanoparticles concentration, Reynolds number and heat flux on the convective heat transfer performance of MWNTs/H2O water-based nanofluid were investigated experimentally. The concentration of nanoparticles was 0.05 g/L, 0.1 g/L, 0.2 g/L and 0.4 g/L. The Reynolds number was changed from 500 to 900. The heat flux was changed from 10 kW/m2 to 20 kW/m2. The result indicated that, first, the convective heat transfer coefficient of nanofluids increases with increasing nanoparticles concentration, Re and heat flux. For example, the convection heat transfer coefficient of nanofluids is increased by 17.6% than base fluid when the Reynolds number is 631 and the concentration of nanoparticles is 0.4 g/L. Then, the rise of convection heat transfer coefficient of nanofluids is significantly higher than that of thermal conductivity. The convection heat transfer coefficient and the thermal conductivity of nanofluids is increased by 7.4% and 0.15%, respectively, than base fluid when the concentration of nanoparticles is 0.05 g/L. The convective heat transfer coefficient and thermal conductivity compared with base fluids is increased by 7.4% and 0.15%, respectively. Finally, an appropriate experimental correlation of mixed convection heat transfer is built on the basis of the Eubank-Proctor equation at the low Reynolds number.关键词：nanofluids;convective heat transfer;low Reynolds number;multi-walled carbon nanotubes;experimental correlation1724|1913|0发布时间：2024-07-18
- 摘要：The thermodynamic model to analyze the scroll compressor refrigeration with twice-vapor injection system has been set up and the calculation program is designed. The two suitable middle pressures are calculated, and the recommended empirical formulas are provided to calculate most suitable two stage middle pressure. Based on one scroll compressor, the method of how to make injection hole is developed. At last, the system performance is calculated, and the simulation results demonstrate that the cooling COP of new system with twice-vapor injection can be about 2.8% and 12.4% higher than that of the one hole vapor injection system and normal single stage system, the discharge temperature can decrease 3 - 4 ℃.关键词：scroll compressor;twice-vapor injection;cooling COP;discharge temperature2088|1987|0发布时间：2024-07-18
- 摘要：Based on the similarity theory, a box containing liquid aimed to model the indoor air distribution in a large space building was constructed, and the liquid experiments were taken to explore the pattern of the effect of the vertical developing plumes on the horizontal jets in large space buildings. The velocity ratio of the model to the prototype was taken to figure out the similarity between the cold jets and the thermal plumes. The results of the experiments show that, under the effect of the vertical developing plumes, the motion curve of the horizontal jets deviated upward. The single plume has little effect on the forepart before the countering point of the plume and jet. The raising of the jet curve is in the terminal of the cold jet. Under the effect of the two plumes, the deviation of a single jet increased. The deviation of the jet curve differs with the countering point of the plumes and the jet changing. In the forepart of the jet, the initial force of the jet predominates, thus the curve is not easy to deviate. However, in the terminal of the jet, the initial force of the jet weakens, and the curve is easy to be disturbed by the plume. Compared with the effect of different plumes, the effect of two plumes on the motion of the single jet weakens after two jets interact.关键词：large space;salt-bath experiment;thermal plume;cold jet;velocity distribution of the jet axis section1990|2131|0发布时间：2024-07-18
- 摘要：Aiming to the frosting problem of air-source heat pump (ASHP) at low temperatures, a novel frost-free air-source heat pump water heater (ASHPWH) system is proposed in the paper, in which dehumidification of solid desiccant is used to reduce the humidity ratios of ambient air to realize frost-free operation. In order to keep the system working continuously, phase-change thermal storage is used to recycle the condensation heat that acts as a low temperature resource to regenerate the solid desiccant. The novel system was compared experimentally with conventional defrost system at a temperature of 0 ℃ and relative humidity (RH) of 80%. The results show that the average COP of the system was increased by 7.25% and 46.3% in comparison with hot-gas bypass defrosting and electric resistance heating, which proves the feasibility of the novel system.关键词：frost- free ASHP;water heater;dehumidification;phase-change thermal storage2036|2143|0发布时间：2024-07-18
- 摘要：The radiant time factors are used to calculate radiant cooling load in the radiant time series method. Based on measurement data of hourly heat gain and cooling load collected within 24 hours, radiant heat gain and radiant cooling load can be calculated by separating convection with radiation . Transfer function is obtained and a 24 term radiant time factors can be calculated by transfer function coefficients matrix. By comparing the results with experiment, it shows that the calculation method of radiant time factors is feasible. The first value of radiant time factors decreases as supply air volume decreases and the sum of the first five factors is more than 0.75. For the radiant time factors calculated by ASHRAE software, the improvement method can be used to calculate radiant cooling load under different air circulation after correcting the first five factors.关键词：radiant heat gain;radiant cooling load;radiant time factors;improvement method1898|1998|0发布时间：2024-07-18
- 摘要：Low efficiency of PTC in electrical vehicles would cut down its travelled distance, so it’s necessary to design high efficiency heat pump system. Two kinds of heat exchangers were used as outside heat exchangers (HX) in four-way-valve heat pump system, and experimental study was finished under both heating and cooling modes. The results showed, under low face velocity in heating model, small diameter tube HX had higher capacity by 10.5%, and the same COP compared with parallel flow HX. Under low face velocity in cooling model, small diameter tube HX had higher capacity by 3.8%, and higher COP by 22.8% compared with parallel flow HX. With the increasing of wind velocity, capacity and COP with small diameter tube HX increased little; however, the one with parallel flow HX had a higher increasing. It is concluded that heat pump system used small diameter tube HX had a potential prospect under low wind velocity.关键词：electrical vehicles;capacity and COP;four-way-valve heat pump system;heat exchanger2165|2043|0发布时间：2024-07-18
- 摘要：An experimental investigation was performed on the oscillating characteristics and thermal resistances of the oscillating heat pipe(OHP) with water/methanol mixture under varied mixing ratios(i.e. 13:1,4:1,1:1,1:4 and 1:13) and filling ratios (i.e. 90%,70%,62% and 55%) , which is compared with the pure working medium, water and methanol. Experimental results showed that the amplitude of the OHP with mixture was larger than the pure working fluid. Generally, the thermal resistance of the OHP with the mixture working medium was mostly higher than that with pure one when the filling ratio was more than 62%.The OHP with mixture was easier to dry out than that with pure one. When the filling ratios were 55%, the thermal resistance of the OHP with mixture rises faster. Specially, the working medium with little methanol (13:1) and much water was ideal because of the high heating power when dry out in 55% filling ratio. The thermal resistance of the OHP was mainly determined by the viscosity of working medium, phase equilibrium and so on. The primary factor changes in different working conditions.关键词：heat transfer performance;oscillating heat pipe;mixture working fluids;experimental investigation1974|2070|0发布时间：2024-07-18
- 摘要：The existing moving-boundary models for evaporators are obtained by expanding the continuity and internal energy equations, and the error caused by the expansion results that the models are not intrinsically conservative on both mass and energy, resulting accuracy deterioration. To guarantee intrinsically conservative on both mass and energy in calculation, the mass and internal energy are selected as the state variables, and the continuity and internal energy equations are directly solved to avoid the expansion error. The equations and algorithms for refrigerant state and phase distribution in evaporator are developed when the mass and internal energy are given. The case study shows the new model is steady and intrinsically conservative on both mass and energy in the performance simulation of 48 hours, and the simulation results agree well with the experimental data.关键词：evaporator;transient simulation;moving-boundary model1989|2137|0发布时间：2024-07-18
- 摘要：Experimental investigation on the flow boiling of R134a in horizontal mini-channels was carried out in this study. The test sections are three different horizontal smooth stainless steel tubes with inner diameter of 1mm, 2mm and 3mm. The experiment was performed on the saturated temperatures ranging from 5 to 30 ℃, heat fluxes from 2 to 70 kW/m2 and mass fluxes from 200 to 1500 kg/(m2s). The results indicated that on the same conditions the pre-dryout heat transfer coefficients in 2-mm-ID tube increased 11.6% averagely than the 3-mm-ID tube, the coefficients in 1-mm-ID tube increased 26.3% averagely than the 2-mm-ID tube and the heat transfer coefficients in the 1-mm-ID tube were 40.8% greater in average than those in the 3-mm-ID tube. With decreasing tube diameter the coefficients started decreasing at lower vapor quality, the effect of mass flux and the contribution of forced convective evaporation on the local heat transfer coefficient decreased while the effect of heat flux was still strong in all three tubes, the zone of plug flow and slug flow decreased while the zone of bubbly flow and annular flow increased.关键词：R134a;mini-channel;flow boiling;dryout;heat transfer coefficient2169|2062|0发布时间：2024-07-18
- 摘要：Nucleate pool boiling outside the horizontal enhanced tube (Φ25 mm) with the refrigerant R134a was experimentally investigated. The inner heat transfer correlation has been obtained by using Wilson graphic method. Experiments were performed at evaporation temperatures of 5.6, 0, -2,-4,-6 and -8 ℃, heat fluxes from 4 to 55 kW/m2. Experimental results show that the pool boiling heat transfer coefficient outside the tube increases with the increase of heat flux and evaporation temperature. A new heat transfer correlation of pool boiling has been put forward. By comparison with test data, the relative deviation of 95% of the correlation value is within ± 20%.关键词：correlation;Wilson graphic method;enhanced tube;nucleate pool boiling1853|2025|0发布时间：2024-07-18
- 摘要：As gravity-fed recirculation evaporator is restricted by its principles, the structure of its flow path couldn’t be the same as that of the direct expansion cooling system. Firstly, in this paper, the flow path optimal principles of gravity-fed recirculation evaporator have been clarified, and two forms of flow path structures have been designed. The first is a flow path structure which is commonly used in the gravity-fed cooling system, and the second is an optimized flow path structure. A gravity-fed recirculation evaporator experiment platform is built based on the above. The evaporator performances before and after the optimization have been compared and analyzed. Results shows that, when the temperature of the insulation body keeps constant, the same circulation ratio and mean temperature difference can be guaranteed at the refrigerant-side of the four branches in parallel since the mean temperature of the air which contacts each of the branches of the optimized evaporator is the same.It is also shown that the optimized evaporation has a better performance, especially under the low-temperature condition. The second (ie. the optimized) evaporator has a greater heat transfer than the first (ie. the common) one based on per unit area, and the cooling capacity increased 60.3% and 44.1% respectively, and the COP increased 16% and 13.87% respectively for the condition of -25 ℃ and -20 ℃.关键词：gravity-fed recirculation evaporator;flow path;air evaporator performance;recirculation evaporator2127|2154|0发布时间：2024-07-18
- 摘要：The traditional oil cooler with smooth tube has low heat transfer coefficient and dead zone in shell side flow, and it easily produces dirt. The trefoil screwed expansion pipe is used to enhance the heat transfer of the traditional oil cooler. The heat transfer and pressure drop of the oil cooler with trefoil screwed expansion tube were tested in an experimental system and compared with oil cooler with smooth tube and oil cooler with outer finned tube respectively. The result shows that the oil cooler with trefoil screwed expansion tube improves heat transfer coefficient more significantly compared with oil cooler with outer finned tube, but is accompanied by a higher pressure drop. With Reynolds number increasing, the comprehensive performance of oil cooler with trefoil screwed expansion tube is better gradually than the oil cooler with outer finned tube , which means that oil cooler with trefoil screwed expansion tube has good application prospect.关键词：oil cooler;trefoil pipe;heat transfer enhancement;comprehensive performance1948|1994|0发布时间：2024-07-18
- 摘要：Based on the measured data of the ground source variable refrigerant flow system (GSVRFS) in the heating season, this research analyzes the variation of hourly system power consumption per square meter, coefficient of performance (COP) of unit and COP of system along with the change of part load ratio (PLR). The results show that the PLR is distributed mainly from 40% to 70%. Hourly power consumption per square meter varies with PLR in concave form. The COPs of the unit and system vs. the system part load ratio are within a convex performance domain.关键词：ground source variable refrigerant flow system;part load ratio;operation in winter;experiment research2047|2026|0发布时间：2024-07-18
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