Time filter

Source Type

Yang R.,Zhejiang University | Yang R.,Key Laboratory of Refrigeration and Cryogenic Technology of Zhejiang Province | Wang Y.,Zhejiang University | Wang Y.,Key Laboratory of Refrigeration and Cryogenic Technology of Zhejiang Province | And 4 more authors.
Huagong Xuebao/CIESC Journal | Year: 2016

Thermoacoustic heat engine is a type of energy conversion machine with the merits of high reliability and environmental friendliness.The present work focuses on a looped travelling-wave thermoacoustic refrigerator with one thermoacoustic engine stage and one thermoacoustic refrigerator stage, connected by resonators.The required acoustic field for an efficient travelling-wave thermoacoustic system is featured by high acoustic impedance and appropriate phase relation close to travelling wave in the regenerator.In the presented thermoacoustic refrigerator, the installation positions of the regenerators could dramatically affect the acoustic field inside them, due to the fact that the acoustic field is highly sensitive to the variation in acoustic impedance.In order to investigate the effect of the installation locations of the thermoacoustic cores on the performance of the thermoacoustic refrigerator, the looped travelling-wave thermoacoustic refrigerator is simulated with DeltaEC, which is a software widely used for the simulation of thermoacoustic systems.In the simulation, the working fluid is helium at a mean pressure of 3 MPa, and the heating temperature and the cooling temperature are 227℃ and 0℃, respectively.The overall coefficient of performance of the whole system, the efficiency of the engine stage, the coefficient of performance of the refrigerator stage, the acoustic impedance and the phase difference in the two regenerators with different installation positions of the two regenerators have been analyzed.According to the simulation results, when the ratio of the distance from the engine's regenerator to the refrigerator's regenerator in the direction of the acoustic wave to the loop length is 0.24, the maximum overall coefficient of performance can be reached, corresponding to a relative Carnot overall coefficient of 0.13.When the ratio is within 0.21-0.26, the two regenerators can both achieve efficient thermoacoustic conversion, leading to high performance of the whole system.However, when it is larger than 0.26 or smaller than 0.21, the performance of the two regenerators will deteriorate, leading to poor performance of the whole system. © All Right Reserved.


Tang K.,Zhejiang University | Tang K.,Key Laboratory of Refrigeration and Cryogenic Technology of Zhejiang Province | Feng Y.,Zhejiang University | Jin T.,Zhejiang University | And 3 more authors.
Applied Thermal Engineering | Year: 2017

Gedeon streaming can cause a considerable deterioration in the efficiency of a double-inlet pulse tube refrigerator, which is usually ascribed to the thermal loss carried by the streaming in the conventional view. This paper addresses a different explanation of the mechanism behind the effect of Gedeon streaming on the efficiency of the double-inlet pulse tube refrigerator. Simulations of a typical double-inlet pulse tube refrigerator for various Gedeon streaming have been conducted to analyze the interaction between the enthalpy flow rate delivered by Gedeon streaming and the local temperature inside the regenerator and the pulse tube. The discussions are focused on the characteristics of acoustic field, the impact of Gedeon streaming on the temperature profiles, and the energy flows at the cold heat exchanger. The results indicate that different temperature profiles inside the regenerator and the pulse tube, caused by Gedeon streaming at various flow rate, can substantially change certain energy flow rates, e.g. equivalent conduction heat flow rate due to entropy transportation. This is the essential mechanism for Gedeon streaming affecting the efficiency of the double-inlet pulse tube refrigerator, instead of the thermal loss due to the enthalpy flow carried by the Gedeon streaming itself. © 2016 Elsevier Ltd


Jiao B.,Harbin University of Science and Technology | Yang D.,Harbin University of Science and Technology | Gan Z.,Zhejiang University | Gan Z.,Key Laboratory of Refrigeration and Cryogenic Technology of Zhejiang Province
Nuclear Engineering and Design | Year: 2017

The critical heat flux (CHF) of gas-liquid flow plays an important role in the safety of industrial equipment. At present, the liquid film dryout model is widely used for predicting CHF in gas-liquid annular flow. Most parameters in this model can be determined by some empirical correlations which are valid under different conditions. However, up to now, the entrainment fraction at the onset of annular flow is always assumed due to the lack of relevant experimental data. In this paper, the normalized data of the 2006 CHF look-up table (LUT) which has been adopted widely, especially in the nuclear industry, were used. Firstly, the empirical correlations, provided for the onset of annular flow and the limiting quality, were employed. In the valid pressure and mass flux range of these correlations, the selected database from LUT was confirmed. Secondly, the liquid film model was built. The entrainment fraction at the onset of annular flow was obtained when the calculated CHF by the model agreed with the corresponding value in LUT. A parallel look-up table for it was developed. Its correlation including the Weber and the liquid Reynolds number at outlet was proposed. The errors are mostly within ±30%. Finally, its reliability on the other conditions in LUT, which are beyond the valid range of the empirical correlations used for determining the database, was discussed. All the conditions whose errors are outside ±30% of the predictions by the provided correlation were marked in the tables. © 2017 Elsevier B.V.


Wang X.,Zhejiang University | Wang X.,Key Laboratory of Refrigeration and Cryogenic Technology of Zhejiang Province | Xu X.,Zhejiang University | Xu X.,Key Laboratory of Refrigeration and Cryogenic Technology of Zhejiang Province
Refrigeration Science and Technology | Year: 2015

In addition to indoor air temperature, indoor air humidity is also an important parameter for building up a thermally appropriate artificial indoor environment. However, introducing air humidity as a controlled parameter in addition to air temperature would significantly increase the difficulty to develop a controloriented model for building air conditioning systems. This is particular true for direct expansion (DX) air conditioning (A/C) systems, whose operational parameters are highly coupled and behave non-linearly and influenced by the controlled parameters, i.e., air temperature and humidity. Neither physical modelling approach nor artificial neural network (ANN) modelling approach could solely satisfy the requirement, in terms of accuracy and sensitivity, for simultaneous control of air temperature and humidity using a DX A/C system, without any inadequacies. In this paper, a hybrid modelling approach is proposed, which uses the physical modelling approach to simulate the performance of evaporator for accurately catching the cooling and dehumidification processes under various working conditions and uses ANN to simulate all other components of a DX A/C system for reduced calculation efforts. By such a hybrid modelling approach, the advantage of simplicity of an ANN-based sub-model could be utilized and the disadvantage of it that do not allow to accurately extrapolate beyond the range of the data used for training/estimating the model parameters could be avoided.


Guo Y.-X.,Zhejiang University | Guo Y.-X.,Key Laboratory of Refrigeration and Cryogenic Technology of Zhejiang Province | Gan Z.-H.,Zhejiang University | Gan Z.-H.,Key Laboratory of Refrigeration and Cryogenic Technology of Zhejiang Province | And 3 more authors.
Kung Cheng Je Wu Li Hsueh Pao/Journal of Engineering Thermophysics | Year: 2016

As a fundamental facility, helium liquefier is necessary to advanced scientific research. Yet, due to its complicated process and various variables, the optimization of helium liquefaction cycle has always been a bothering problem. Because of the limited computer technique in the early years, the design and optimization of a helium liquefaction cycle was primarily based on the properties of the fiuid, but such a method is actually a defective one. This paper has therefore presented a novel helium liquefaction design method based on component parameters with respective to Collins Cycle, which adopts a novel "Two Models" (Energy flow model & Double rhombus model) arithmetic and "EES Estimation-Aspen HYSYS Verification" design philosophy. This method could eventually help simplify the design procedure as well as produce reasonable results. © 2016, Science Press. All right reserved.


Jin T.,Zhejiang University | Jin T.,Key Laboratory of Refrigeration and Cryogenic Technology of Zhejiang Province | Yang R.,Zhejiang University | Yang R.,Key Laboratory of Refrigeration and Cryogenic Technology of Zhejiang Province | And 6 more authors.
Applied Energy | Year: 2016

To realize high normalized acoustic impedance and near travelling-wave acoustic field in the regenerator is the key issue for a thermoacoustic engine to be driven by low-grade heat (e.g., waste heat, geothermal energy and solar thermal energy, etc.), and a looped thermoacoustic system with the appropriate acoustic field is considered one of the promising techniques. The present work analyzes the conception and mechanism of the phase adjustment in a looped structure, based on which two phase adjustors (namely compliance tube and resistance tube) are introduced to build appropriate acoustic field. Systematic experiments have then been conducted on a looped thermoacoustic prime mover with compliance/resistance tube, and the results show that the system with appropriate compliance/resistance tube can be initiated to oscillate at quite low heating temperature, indicating the phase adjustor can help to build up proper acoustic field. The lowest onset temperature is 40 °C, with a compliance tube and using the CO2 of 2.37 MPa as working fluid. Features of the acoustic field, including pressure amplitude, volumetric velocity amplitude and their phase difference, have also been numerically analyzed to verify the phase adjustment mechanism. Besides, the influence of its installation position and length of the compliance tube on the performance of the prime mover has been experimentally and numerically studied. Finally, a comparison is made to analyze the similarity and difference between the performances of compliance tube and resistance tube for phase adjustment. © 2016 Elsevier Ltd


Tian F.-Y.,Zhejiang University | Huang L.-F.,Zhejiang University | Fan L.-W.,Zhejiang University | Qian H.-L.,Zhejiang University | And 3 more authors.
Powder Technology | Year: 2016

The knowledge on pressure drop over the packed layers of sintered ore particles (SOPs) is deemed essential to have a deep understanding on the flow and heat transfer in emerging vertically arranged sinter coolers for waste heat recovery. In this work, the wall effects on pressure drop over a packed bed of SOPs were studied experimentally. Experiments for SOPs with bed-to-particle diameter ratio ranging from 7 to 35 and glass beads with the ratio between 6 and 22 were performed. The results revealed that the voidage effect tends to be pronounced for relatively low ratio values, while the friction effect becomes more significant for relatively high ratio values when it is lower than 40. Comparing to the confining walls, the particle characteristics were shown to have a dominant effect on the flow regime in the voids of the SOP-filled beds, whereas an opposite comparison was observed for the smooth glass beads as a reference. The correlations for the wall corrected friction factor proposed in the literature (Exp. Heat Transfer 12 (1999) 309), with varying coefficients, fit well to predict the pressure drop through packed beds for both glass beads and SOPs with considering the wall effects. Improved correlations were also proposed for spherical particles, SOPs and their blends with fairly good predictive accuracy. © 2016 Elsevier B.V.


Tao X.,Zhejiang University | Tao X.,Key Laboratory of Refrigeration and Cryogenic Technology of Zhejiang Province | Liu D.L.,Zhejiang University | Liu D.L.,Key Laboratory of Refrigeration and Cryogenic Technology of Zhejiang Province | And 6 more authors.
IOP Conference Series: Materials Science and Engineering | Year: 2015

A precooled Joule-Thomson (J-T) cooler refrigerates at liquid helium temperature. Its third stage heat exchanger works below 20 K. Hot fluid cannot be sufficiently cooled due to nonidealism of the heat exchanger and helium-4 properties. In a J-T cycle of low pressure ratio, the heat exchanger with bypass and throttling improves the refrigeration capacity. Bypass and throttling reduces the temperature difference and entropy generation within the heat exchanger.


Deng H.R.,Zhejiang University | Liu Y.M.,Zhejiang University | Ma R.F.,Zhejiang University | Han D.Y.,Zhejiang University | And 3 more authors.
IOP Conference Series: Materials Science and Engineering | Year: 2015

The pulsating heat pipe (PHP) has been increasingly studied in cryogenic application, for its high transfer coefficient and quick response. Compared with Nb3Sn and NbTi, MgB2 whose critical transformation temperature is 39 K, is expected to replace some high-temperature superconducting materials at 25 K. In order to cool MgB2, this paper designs a Hydrogen Pulsating Heat Pipe, which allows a study of applied heat, filling ratio, turn number, inclination angle and length of adiabatic section on the thermal performance of the PHP. The thermal performance of the hydrogen PHP is investigated for filling ratios of 35%, 51%, 70% at different heat inputs, and provides information regarding the starting process is received at three filling ratios.


Zhang J.H.,Zhejiang University | Zhang J.H.,Key Laboratory of Refrigeration and Cryogenic Technology of Zhejiang Province | Bao S.R.,Zhejiang University | Bao S.R.,Key Laboratory of Refrigeration and Cryogenic Technology of Zhejiang Province | And 4 more authors.
IOP Conference Series: Materials Science and Engineering | Year: 2015

Dynamic visualization is of great significance in the research of flow conditions and mass transfer process of cryogenic fluids. In this paper, two common ways to measure the concentration of cryogenic fluids are introduced and compared. To improve the real-time monitoring of cryogenic fluid, a non-contact dynamic optical measurement system using laser interferometry is designed, which is sensitive to subtle changes of fluid concentration. A precise and dynamic interference pattern can be obtained using this system. Two-dimensional concentration distribution of the fluid can be calculated from the interference pattern. Detailed calculation process is presented in the paper.

Loading Key Laboratory of Refrigeration and Cryogenic Technology of Zhejiang Province collaborators
Loading Key Laboratory of Refrigeration and Cryogenic Technology of Zhejiang Province collaborators