最新刊期
卷 34 ， 期 1 ， 2013
- 摘要：Pulsating heat pipe (PHP), which is also called oscillating heat pipe (OHP), is a novel type of highly efficient heat transfer component. It is widely applied in many fields, including aerospace technology, cooling of electronic devices and energy-saving technology, etc. In the present paper, the characteristics and working principles of PHPs are first introduced, and then the current research in the field is described from experimental study, theoretical study and practical application achievements. The experimental investigations are mainly focused on the flow visualization and the applications of nano-fluids and other functional fluids to enhance heat transfer performance of the PHPs. It is also pointed out that the current theoretical analyses of the PHP are restricted by further development of two-phase flow theory, and are concentrated in the non-linear analysis. Numerical simulations will become another research focus, especially the combination of the nano-fluids and functional fluids.关键词：pulsating heat pipe;nano-fluid;nonlinear analysis;visualization1750|2290|0发布时间：2024-07-18
- 摘要：Two-dimensional mathematical model of the heat and mass transfer process among refrigerant, cooling water and air in the plate evaporative condenser was established on the basis of energy and mass conservation. Distributions of cooling water temperature, air temperature and air humidity ratio are obtained. And then studies on influencing factors of plate evaporative condenser heat flux, i.e., air flow rate, cooling water spray density, air dry bulb temperature, wet bulb temperature and the condensing temperature were conducted. Simulation results were verified through experiments, and the error was less than 10%. The results showed that heat flux increased with increasing air flow rate, increasing condensing temperature and decreasing air wet bulb temperature, and is not relevant to air dry bulb temperature. With the increasing cooling water spray density, heat flux gradually increased and then kept constant. These conclusions are instructive for optimization design of plate evaporative condenser.关键词：evaporative condenser;heat and mass transfer;numerical simulation;heat exchanger1945|2178|0发布时间：2024-07-18
- 摘要：According to analysis on the energy efficiency standards of the constant speed room air conditioner and the variable speed type, differences between the two kinds of air conditioners exist in division standard, grades of energy efficiency and outdoor temperature starting refrigeration. Therefore, a survey was made about cooling capacity and EER as well as energy efficiency grades of the constant and variable speed room air conditioners. The thermodynamic perfectibility of the two types of room air conditioners was calculated for the performance evaluation. The calculation results show that energy efficiency standard of variable speed room air conditioners in 2008 is lower than that of constant room air conditioners. A new energy efficiency standard of the variable speed air conditioner is suggested in accordance with the consistent thermodynamic perfectibility.关键词：room air conditioners;energy efficiency standard;thermodynamic perfectibility;SEER;EER1946|2289|0发布时间：2024-07-18
- 摘要：The heat transfer characteristics of refrigerant-oil mixture flow boiling inside circular tubes filled with metal foam were experimentally investigated. The metal foams are 5 ppi / 95% porosity and 10 ppi / 95% porosity copper foams. The experimental conditions include saturation pressure of 995 kPa, mass flux from 10 to 30 kg/(m2.s), heat flux from 3.1 to 9.3 kW/m2, inlet vapor quality from 0.175 to 0.775, and oil concentration from 0% to 5%. The experimental results show that: metal foam enhances the flow boiling heat transfer coefficient of refrigerant by a maximum of 185% at oil free conditions, while the enhancement effect of metal foam is weaken at oil presence conditions; the flow boiling heat transfer coefficient for the circular tube filled with high ppi metal foam is higher than that for the tube filled with low ppi ones. A new correlation of heat transfer coefficient for refrigerant-oil mixture flow boiling inside circular tubes filled with metal foam is developed based on the flow pattern, and it can agree with 98% of the experimental data within a deviation of ±30%.关键词：flow boiling;heat transfer characteristics;metal foam;refrigerant;oil1860|1941|0发布时间：2024-07-18
- 摘要：Ice slurry storage in the storage tank often occurs in practical projects. The ice slurry storage characteristics have an important influence on the ice slurry application. The main problem of ice slurry storage is the nonuniformity and the low utilization of ice slurry storage tank. The research achievements about ice slurry storage reported in domestic and international literatures were collected and summarized from the aspects of characteristics, model and experimental study. It is found that image method is often used to analyze ice slurry storage characteristics and the main influence factors on the storage characteristics are solution, additives, ice slurry IPF (ice packing factor) and flow rate at the entrance and storage time. The analysis of the present situation of ice slurry storage provides references to the further research.关键词：ice slurry storage;characteristics;model;experimental study1856|2056|0发布时间：2024-07-18
- 摘要：The parallel flow microchannel (PFM) heat exchanger is widely used in automotive air conditioning system, but it has the disadvantage of easy-frost and difficult in water-drain in defrost . The traditional tube and fin heat exchanger can overcome the frost and defrost problem but has low efficiency. In this paper a ?5 tube and fin heat exchanger is developed for the automotive heat pump. Performances of small diameter tube-and-fin heat exchanger and PFM heat exchanger are compared based on benchmark test. Results show that the system with small diameter tube-and-fin heat exchanger has 17.4%~23.7% higher COP in air conditioning mode, 12.6%~35.8% higher COP and 15~28℃ lower compressor discharge temperature in heat pump mode, which indicates that small diameter tube-and-fin heat exchanger is a promising solution to the automotive heat pump system of electric vehicle.关键词：electric vehicle air conditioning;heat pump;small diameter tube-and-fin heat exchanger;electric compressor;COP1773|2472|0发布时间：2024-07-18
- 摘要：The main shaft rotor is the core component of the vane compressor in automotive air conditioning, and its natural frequency and mode shape have direct impacts on the motion stability of the compressor. By means of theoretical and experimental modal analysis, as well as NX Nastran modal computation, the natural frequency and mode shape of the main shaft rotor are obtained. The results show that the natural frequency of the rotor system is greater than 3300Hz, much higher than its working frequency, which indicates high reliability of the motion of the main shaft rotor. Vibration test results prove that the vibration acceleration of the compressor shell is much lower than the upper limit specified value of the GMW standards of the U.S. General Motors Corporation, which ensures that the resonance and the resulting noise and large deformation would not occur in its working process. The analytical results also provide an important reference for fault diagnosis and vibration control of the main shaft rotor system.关键词：vane compressor;automotive air conditioning;modal analysis;main shaft rotor;experimental modal;NX Nastran FEA1657|2093|0发布时间：2024-07-18
- 摘要：Horizontal-base and vertical-base heat sinks are simulated and optimized geometrically in order to improve performance of heat sink in natural convection heat transfer with software ICEPAK. At first, the numerical model is validated through comparison of results between the experiments which has already existed and the numerical simulation herein. Then, a series of heat sinks with different geometric parameters are simulated. The optimal geometric parameter will be found through comparing their performance. Fin thickness varied from 1 to 15 mm, fin spacing varied from 6.75 to 33.75 mm and fin height varied from 55 to 1395 mm. The result indicates that there are optimal fin thickness t and optimal fin space s at every fin height. The smallest thermal resistance of horizontal-base heat sinks for certain fin height tends to be a constant value as fin height is over 720 mm. The smallest thermal resistance of vertical-base heat sinks for certain fin height always decreases as fin height increases.关键词：engineering thermophysics;plate fin heat sink;numerical simulation;natural convection;geometric optimization2061|2245|0发布时间：2024-07-18
- 摘要：A heat pump with economizer is studied by experiment under the conditions: dry-bulb temperature of inlet air is from -15℃ to +20℃, while inlet water is from 33℃ to 55℃.By change the opening of the electronic expansion valves in the main pipe line as well as in the injection pipe line, it shows that the main pipe line valve optimum opening is getting smaller when inlet water is getting warmer,and optimum opening is getting larger when inlet air is getting warmer,while the injection pipe line valve optimum opening goes oppositely . Some analysis and explanation on the rule is carried out. The rule can be used to guide to product optimization.关键词：heat pump;economizer;electronic expansion vlave;operation rule2134|2362|0发布时间：2024-07-18
- 摘要：The efficiency requirement of room air conditioner (RAC) has became stricter and stricter with the development of global environment consciousness. The efficiency evaluation method of RAC has been updated from single working condition to aunnal performance factor (APF) with multiple working condition. Performance evaluation method of compressors must be changed accordingly which account for main energy consumption of RAC. Compressor efficiency of annual performance (COAP) is proposed to evaluate the efficiency level of inverter compressor which is applied in variable speed RAC with multiple working conditions. Actual operation efficiency can be indicated by COAP because inverter compressor performance is considered according to COAP. In order to simplify test procedure of COAP, standard test conditions and its weight are generated .Then the effect of efficiency curve of inverter compressor on COAP is discussed . Finally examples with this method are illustrated for compressor matching and design optimization.关键词：compressors for air conditioner;coefficiency of annual performance (COAP);variable speed room air condtioner;inverter compressors;efficienty evaluation1937|2648|0发布时间：2024-07-18
- 摘要：A single-side heating apparatus is set up to study the flow boiling and heat transfer in vertical narrow rectangular channel together with high speed video camera to get the flow images in the channel. The experiment results show that: the heat transfer coefficient exists a maximum value; Heat transfer coefficient gradually decreases with increasing thermodynamic vapour quality (heat flux increasing), and flow type turns to liquid film evaporation, at this case it necessarily needs to control heat flux to avoid the occurrence of dry-out.关键词：flow boiling;rectangular narrow channel;liquid film vaporization;dry-out;visual1814|2684|0发布时间：2024-07-18
- 摘要：In order to increase the coefficient of performance (COP) of the refrigeration system , the expansion valve is replaced by a two-phase ejector in the two-phase ejector refrigeration cycle to recover the potential energy of the high pressure refrigerant. The performance of two-phase ejector refrigeration system with refrigerant R134a as working fluid is experimentally investigated. The effects of the throat diameter of the nozzle and the diameter of the mixing chamber on the performance of the ejector and the two-phase ejector refrigeration cycle system were analyzed. The experimental results indicate that there is an optimal combination of the nozzle throat diameter and the mixing chamber diameter to maximize the entrainment ratio under a fixed working condition. The entrainment ratio of the ejector reaches to the maximum value with the throat diameter of 2.0mm and the mixing chamber diameter of 16mm under the conditions of 3℃ evaporating temperature and 55℃ condensing temperature. Under a fixed working condition, the optimal combination of the nozzle throat diameter and the mixing chamber diameter for maximum of the entrainment ratio is not consistent with the one for maximum of the COP of the refrigeration system. This may be caused by the shocks in the ejector, which should be investigated deeply.关键词：two-phase ejector cycle;two-phase ejector;geometric parameter;experiment2027|1998|0发布时间：2024-07-18
- 摘要：The energy conservation in chiller exchangers are analyzed in this paper, the formula of limit of coefficient of performance (COP) is then deduced. According to the working condition of GB/T 18430.1—2007 and AHRI 550/590—2011, the limits of COP and IPLV are calculated for water cooled chiller and air cooled chiller respectively. The results show that, the COP limit and IPLV limit of water cooled chiller is 10.01/14.51 at GB/T 18430.1—2007 condition and 10.07/17.3 at AHRI 550/590—2011 condition. For air cooled chiller, those values are 7.37/10.25 and 7.30/16.11. The air temperature increase through condenser coil and the condensing temperature is decided by its heat transfer area and effectiveness. If the former temperature in full load at rated condition can’t be achieved to be less than 10℃ by means of improving coil configuration, enlarging heat transfer area and improving the heat transfer effectiveness, the limit of COP of air cooled chiller in full load will be no more than 7.37, IPLV can’t be higher than 10.25.关键词：chiller;efficiency;limit1964|3380|0发布时间：2024-07-18
- 摘要：A new heat and mass transfer model was presented on the basis of Navier-Stokes equation. One-dimensional transformation was conducted on the function of liquid film flow in the process of falling-film, and the Grank-Nicholson Method was used to solve falling-film characteristics. The simulation result of theoretical model was validated with the experiment, and its error is within 17%. Heat and mass transfer coefficient formula was fitted based on the experimental data, and the biggest flow volume of liquid film was obtained in different diameters.关键词：falling-film absorption;heat and mass transfer;horizontal bare tube;numerical simulation1880|2167|0发布时间：2024-07-18
- 摘要：The heating and cooling capacity of two different radiant ceilings are tested. Testing results show that the cooling performance of the radiant ceiling with parallel capillary coil is better than the series-connected coil type, when the temperature difference between the room and the average temperature of the supply and return water is 8℃, the cooling capacity of the capillary type radiant ceiling is 64.4W/m2, and the coil type is 55.0 W/m2. For the same radiant ceiling in the same temperature difference between the room and the average temperature of the supply and return water, the difference between cooling and heating capacity is no more than 10%. In addition, the radiant ceiling with parallel capillary tubes has less flow resistance than the series-connected coil ceiling.关键词：heat transfer performance;radiant ceiling;experimental investigation1786|2049|0发布时间：2024-07-18
- 摘要：Copper tubes covered by Ni-P-PTFE composite coating can mitigate fouling adhesion on the heat exchange surface. However, the impact of composite coating on the thermal conduction of copper tubes should be considered. A thermal resistance method was utilized to measure the heat transfer coefficient of copper tubes with Ni-P-PTFE composite coatings. The thermal conductivities of these Ni-P-PTFE composite coatings were gained by means of Wilson plot in the end. The effects of Ni, PTFE, C and P contents were discussed on the thermal conductivity of Ni-P-PTFE composite coating. The results showed the thermal conductivity of these Ni-P-PTFE composite coatings were weakened by the increases of PTFE and P contents, but enhanced when the C content increased. It reached a peak value 23.12 W/(m.K) when w(PTFE)=1.76%, w(C)=3.82% and w(P)=10.81%, respectively. Although the thermal conductivities of the composite coatings were lower, their thermal resistances in the total heat transfer process were from 9.91×10-5 to 1.6×10-4(m2.K)/W due to their small thickness. Therefore, the tubes with Ni-P-PTFE composite coatings still kept high thermal conductivities 314.88~357.55W/(m.K).关键词：thermal conductivity;thermal resistance method;Ni-P-PTFE composite coating1852|2021|0发布时间：2024-07-18
- 摘要：Stainless steel 304 and 316 are widely used in heat exchangers, and get the precipitation characteristic of CaCO3 is the first step to research anti-fouling technology. CaCO3 precipitated on stainless steel 304 and 316 coupons from 1.0mmol/l CaCO3 solution at 35℃. By weighing the coupon before and after experiment and using scanning electron microscope (SEM), the amount of fouling and the morphology can be obtained. The results show that at the same conditions there are more fouling on stainless steel 304 than 316; high pH not only makes more new crystal nucleation but also promotes square aragonite and calcite, and recrystallization of square aragonite into calcite, the most thermodynamically steady crystal type; high pH makes both homogeneous and heterogeneous nucleation rate increasing, but the former increases more, which results in more fouling at low pH under high supersaturation degree; fouling first grows at the place with high surface energy and then extend to more place, and when the number increases and crystal grows to connect each other, fouling layer is formed.关键词：CaCO3 crystallization fouling;Coupon test;precipiation characteristics;Crystal morphology;crystal size distribution1810|1978|0发布时间：2024-07-18
- 摘要：An Ice storage refrigeration system is proposed for application in coal mine rescue capsule. Performance test of the refrigeration system is developed in the reality survival condition. The temperature change curves are acquired for the different positions in the rescue capsule. The result shows that the refrigeration system works reliably with good performance, and the refrigeration system is able to provide a comfortable living environment. This paper provides a reference for subsequent research on the coal mine rescue capsule.关键词：rescue capsule;ice storage;refrigeration system;performance test1871|1923|0发布时间：2024-07-18
- 摘要：The water properties of frozen dough were measured by NMR over the temperature range from -70℃ to 5℃.The thawing process of dough was also studied by MRI.The water in dough can be divided into two portions ,that are the half-bound water, the T2 of which is ≈ 10ms, and the deep-bound water, the T2 of which is ≈ 2ms. During freezing,the half-bound water partly form to ice and the other change to unfreezale water. The deep-bound water did not change or move. So improving the ratio of deep-bound water in dough is benefit to frozen dough production and inhibiting ice crystals generating. According different NMR data, it is confirmed that the glass transition of dough occurs at -30℃ and the ice melting at -9℃. The water in frozen dough can be classified into three parts and they are the solid ice (29.71%), the real unfreezable water (22.2%), the deep-bound water (33.81%).关键词：NMR;frozen dough;water mobility;half-bound water;deep-bound water;glass transition1810|2105|0发布时间：2024-07-18
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