Yuan Zhou

Experimental study of the oscillating flow characteristics for a regenerator in a pulse tube cryocooler

Abstract A dynamic experimental apparatus was designed and constructed to investigate oscillating flow characteristics in a regenerator subjected to a periodically reversing flow established by means of a self-made linear compressor. Detailed experimental data of oscillating pressure drops and phase shift characteristics for regenerators in a high frequency pulse tube cryocooler with an operating frequency of 50xa0Hz were given. The correlation equations for the maximum and cycle-averaged friction factors in terms of Reynolds numbers and dimensionless distance X were obtained. It was found that the value of the cycle-averaged pressure drop in the oscillating flow across the regenerator is two to three times higher than that of a steady flow at the same Reynolds numbers based on the cross-sectional mean velocity. In addition, the relationship of the phase shifts between the velocity and pressure wave is also discussed.

Development of a single-stage pulse tube refrigerator capable of reaching 49 K

Abstract The orifice pulse tube refrigerator is a new type of cryocooler which was reported to be capable of reaching 60 K. The present authors have achieved a temperature of 49 K for the first time with a single-stage orifice pulse tube refrigerator by improving the regenerator, the hot end heat exchanger and the insulation of the low temperature sections. A refrigeration power of 12 W could be obtained at 77 K at the cold end. The relation between the ratio of regenerator volume to pulse tube volume and the minimum temperature of the orifice pulse tube refrigerator was experimentally investigated. Methods for further improving the performance of the orifice pulse tube refrigerator are discussed.

FTIR spectroscopic studies of lithium tetrafluoroborate in propylene carbonate + diethyl carbonate mixtures

FTIR (Fourier transformed infrared) spectra have been collected and analyzed for solutions of lithium tetrafluoroborate in propylene carbonate (PC), diethyl carbonate (DEC), and PC+DEC mixtures. It has been shown that the carbonyl stretch bands of PC and DEC, the ring of PC and the ether oxygen stretch bands of DEC are all very sensitive to the interaction between Li(+) and the solvent molecules. New shoulders appear and the original bands split with the addition of LiBF4, indicating that a strong interaction between Li(+) and molecules of PC and DEC exists through the oxygen group of C=O and ring of PC and both C=O oxygen and ether oxygen atoms of DEC. In addition, no preferential solvation of Li(+) in LiBF4/PC+DEC solutions was detected.

Li+-molecule interactions of lithium tetrafluoroborate in propylene carbonate + N,N-dimethylformamide mixtures: An FTIR spectroscopic study

FTIR (Fourier transformed infrared) spectra have been collected and analyzed for solutions of lithium tetrafluoroborate in propylene carbonate (PC), N,N-dimethylformamide (DMF), and PC+DMF mixtures. The band splitting and symmetric ring deformation for PC and O=C-N deformation for DMF suggest that there is a strong interaction between lithium cations and solvent molecules. The solvent molecules have been assigned to two types, the free and complexed molecules. By a comparison of the intensity for the corresponding bands, it has been concluded that Li(+) cations are preferentially solvated by DMF molecules in the LiBF4/PC+DMF solutions. This has been explained by the difference in values of donor number (DN).

Sample-charged mode scanning polarization force microscopy for characterizing reduced graphene oxide sheets

A unique operation mode of scanning polarization force microscopy (SPFM) was developed for characterizing reduced graphene oxide (rGO) sheets that were individually charged, mainly by monitoring the change of the samples apparent height along with its surface potential. The principles and features of this sample-charged mode SPFM (SC-SPFM) were introduced. By comparing with other scanning-probe based techniques that characterize the surface electrical properties, including the traditional tip-biased mode SPFM, electrostatic force microscopy, and Kelvin probe force microscopy, it was found that the SC-SPFM has higher sensitivity and lateral resolution. Furthermore, by monitoring charge transfer between two rGO sheets with SC-SPFM, the “good” or “bad” contacts related to junction geometry at the nanometer scale can be visualized clearly.

Pulse Tube Refrigerator with low Temperature Switching Valve

Publisher Summary This chapter proposes a new method for achieving large refrigeration powers for some industrial applications. It proposes a new type of pulse tube refrigerator, termed pulse tube refrigerator with low temperature switching valve. Pulse tube refrigerator has been developing at an amazing speed Its refrigeration performance is now becoming comparable to that of G-M refrigerator or Stirling refrigerator. Therefore pulse tube refrigerator is finding more and more applications. It is suitable for industrial applications that require large refrigeration powers. In this kind of pulse tube refrigerator a recuperative heat exchanger instead of a regenerator is used and a switching valve is installed at the cold end of an orifice pulse tube. The adiabatic expansion efficiency of the orifice pulse tube with low temperature switching valve, which actually works as a new type of expander, has been experimentally investigated. Adiabatic efficiencies higher than 40% have been achieved in the preliminary experiments.

Enhanced thermal conductivity in a hydrated salt PCM system with reduced graphene oxide aqueous dispersion

The phase change enthalpy, thermal conductivity, thermal stability and thermal reliability of a novel reduced graphene oxide (r-GO) containing phase change material (PCM) r-GO/CaCl2·6H2O were investigated. The material was made by the aqueous dispersion of r-GO and calcium chloride dihydrate (CaCl2·2H2O) according to the mass ratio of CaCl2 and crystal water in CaCl2·6H2O. The thermal conductivity of the phase change material increased by ∼80% when using ∼0.018% (by weight) of r-GO with a ∼2.7% decrease of enthalpy (i.e., storage capacity), while using ∼0.018% of graphite led to an increase of thermal conductivity by ∼14% and a decrease of enthalpy by ∼5.6%. Additionally, the surface active agent for dispersing r-GO had the extra function of enhancing the system stability and reliability. The decomposing temperatures of r-GO/CaCl2·6H2O were higher than those of CaCl2·6H2O. After 100 cycles, the melting and crystallizing enthalpies of r-GO/CaCl2·6H2O decreased to 178.4 J g−1 and 150.7 J g−1 from 180.6 J g−1 and 153.7 J g−1, dropping by 1.2% and 2.0%, respectively, while for CaCl2·6H2O they decreased to 178.9 J g−1 and 147.8 J g−1 from 185.6 J g−1 and 161.8 J g−1, dropping by 3.7% and 8.7%, respectively. The thermal conductivity enhancement of CaCl2·6H2O with r-GO was markedly superior compared to that with graphite and other thermal conductive additives reported in previous literature, and the provided method (i.e., preparing aqueous dispersions of additives firstly and synthesizing hydrated salt PCMs with corresponding salts subsequently) was also applicable for other functional additives that cannot be directly dispersed well to modify the thermal properties of hydrated salt PCM systems.

Metabolomics insights into diabetes nephropathy and protective effects of Radix Scutellariae on rats using ultra-high performance liquid chromatography coupled with quadrupole time-of-flight mass spectrometry

Diabetic nephropathy (DN) is the most prevalent microvascular complication in diabetes contributing to high mortality. Radix Scutellariae is one of the most commonly used traditional Chinese medicines (TCM) and has played an important role in treating DN. In this study, a urine metabolomics method based on ultra-high performance liquid chromatography coupled with quadrupole time-of-flight mass spectrometry (UHPLC-Q-TOF-MS) has been established to explore the metabolic variations in DN rats and investigate the therapeutic effect of Radix Scutellariae on DN in the different stages (6th week and 10th week). Multivariate analysis approaches were applied to differentiate the components between a Radix Scutellariae-treated group, a model group and a normal group. A series of urinary endogenous metabolites were screened for DN rats, suggesting metabolic dysfunction in pathways of tryptophan, phenylalanine, tyrosine, purine, pyrimidine, and energy metabolism. Treatment with Radix Scutellariae could reverse urinary metabolite abnormalities, and subsequently influenced the above disordered pathways, which were remarkably involved in inhibition of oxidative stress, inflammation and attenuation of several enzymes altered in DN. Our results thus provide an overall view of the progression of DN, and nephroprotective effects of Radix Scutellariae against DN.

A novel Stirling type pulse tube cryocooler suppressing the third type of dc gas flow

This paper analyzes the zero and first order pressure drop along the pulse tube system and presents a simple but elegant way of eliminating the third type of DC gas flow which increases the efficiency of a Stirling type PTC. Since the optimization of a PTC depends sensitively on the adjustment of the phase angle between the pressure and mass flow because of its influence on the suppression of the third type of DC gas flow, we have done a series of experiments on a Stirling type multi-bypass PTC in order to attain the lowest refrigeration temperature. After the multi-bypass PTC reaches its lowest temperature, we open the metering valve to the best degree which connects the back pressure chamber of the linear compressor to the reservoir. For this novel type of PTC, the lowest refrigeration temperature drops from 38.8 K to 25.9 K after opening the metering valve. This approach offers a promising way for a compact single stage Stirling type PTC to reach liquid hydrogen temperatures.

Pulse tube refrigerator with low temperature switching valve: concept and experiments

The concept of a new type of pulse tube refrigerator, termed pulse tube refrigerator with low temperature switching valve, is proposed. It is suitable for industrial applications that require larger refrigeration powers. In this kind of pulse tube refrigerator a recuperative heat exchanger instead of a regenerator is used and a switching valve is installed at the cold end of an orifice pulse tube. The adiabatic expansion efficiency of the orifice pulse tube with low temperature switching valve, which actually works as a new type of expander, has been experimentally investigated. Adiabatic efficiencies higher than 40% have been achieved in the preliminary experiments. Methods for increasing the adiabatic efficiency are discussed.