Wang Ruzhu

Pore structure of new composite adsorbent SiO2·xH2O· yCaCl2 with high uptake of water from air

A new composite adsorbent SiO2·xH2O·yCaCl2 which is composed of macro-porous silica gel and calcium chloride is introduced. In order to analyze its adsorption theory, adsorption and desorption isotherms, BET surface areas, pore volumes and average pore diameters of macro-porous silica gel and four composite adsorbent samples with different CaCl2 content are measured using SEM and Asap2010 apparatus. From the adsorption isotherms, desorption isotherms and lag loops, it can be deduced that the main pore structure in macro-porous silica gel and the new composite adsorbent have two shapes: taper with one top open and taper or hyperbolic taper with both ends open. Based on the analysis of pore diameter distribution and lag loop, a sketch map showing calcium chloride filled in pore of macro-porous silica gel is presented. The adsorption isotherms at 25°C are measured. Experimental results show that the new composite adsorbent can adsorb more water than common adsorbents (macro-porous silica gel, micro-porous silica gel and synthetic zeolite 13X). In the light of the results of pore structure, adsorption isotherms and lyolysis phenomenon are analyzed.

Adsorption performances and refrigeration application of adsorption working pair of CaCl2−NH3

The adsorption performance of CaCl2−NH3 is studied under the condition of different expansion spaces for adsorbent, and the relationships between adsorption performance of CaCl2−NH3 and the phenomena of swelling and agglomeration during adsorption are researched. It is found that the performance stability is related to the ratio of expansion space to the volume of adsorbent ras, and the performance attenuation is serious in the case of large ras. Severe adsorption hysteresis exists in the process of adsorption and desorption at the same evaporating and condensing temperatures, which is related to the stability constant of chemical reaction. This phenomenon cannot be explained by the theory of physical adsorption. Moderate agglomeration will be beneficial to the formation of ammoniate complex; the magnitude of expansion space will affect adsorption performance. Analysis shows that the activated energy needed in the process of adsorption for the sample with ras. of 2∶1 is less than that for the sample with ras of 3∶1. The refrigeration performance of CaCl2−NH3 is predicted from experiments. The cooling capacity of one adsorption cycle is about 945.4 kJ/kg for the adsorbent with an ras of 2∶1 at the evaporating temperature of 0°C.

Research on the chemical adsorption precursor state of CaCl2−NH3 for adsorption refrigeration

As a type of chemical adsorption working pair, the physical adsorption occurs first for CaCl2−NH3 because the effective reaction distance for van der Waals force is longer than that for chemical reaction force, and this physical adsorption state is named the precursor state of chemical adsorption. In order to get the different precursor states of CaCl2−NH3, the different distances between NH3 gas and Ca2+ are realized by the control of different phenomena of swelling and agglomeration in the process of adsorption. When the serious swelling exists while the agglomeration does not exist in the process of adsorption, experimental results show that the activated energy consumed by adsorption reaction increases for the reason of longer distance between Ca2+ and NH3, and at the same time the performance attenuation occurs in the repeated adsorption cycles. When the agglomeration occurs in the process of adsorption, the activated energy for the transition from precursor state to chemical adsorption decreases because the distance between NH3 gas and Ca2+ is shortened by the limited expansion space of adsorbent, and at the same time the performance attenuation does not occur. The adsorption refrigeration isobars are researched by the precursor state of chemical adsorption; results also show that the precursor state is a key factor for isobaric adsorption performance while the distribution of Ca2+ does not influence the permeation of NH3 gas in adsorbent.

Measurement of steady state heat transfer in a bath of sub-cooled superfluid helium

This paper reports a study of the peak and recovery heat flux densities (qP and qR) in a bath of subcooled superfluid helium (He lip). A RhFe wire (d=51 mu m, L=34.8 mm) was horizontally immersed in a He IIp cryostat, which served as sample, heater and temperature sensor. For steady state measurement a programmed voltage method with a triangle waveform of 20 s was applied. The measured qP and qR values cover the temperature range 1.81-2.1 K at a pressure of 0.1 MPa.

Transient Heat Transfer to Superfluid Liquid Helium

Transient heat transfer from thin superconducting and normal wires to saturated Hell and to pressurized Hell was investigated. Rectangular current pulses of 0.5 milliseconds duration and longer were applied to the sample while voltage and current were detected with a resolution in the microsecond range. For the determination of the sample temperature the temperature characteristic of the wire resistivity was used in the case of normal conductors and the temperature characteristic of the critical current in the case of superconductors. Data are reported for bath temperatures of 2 K and, in the case of the superconducting samples, transverse magnetic fields of 1.5 T.

Transient measurement of temperature oscillation during noisy film boiling in superfluid helium II

Noisy film boiling, which is characterized by a loud noise and severe mechanical vibration, is a particular phenomenon of superfluid helium II (He II). Experiments have been conducted under various thermal conditions by varying the heating timeth and the heat fluxq, and the temperature oscillation during noisy film boiling is measured by the superconductor temperature sensors in order to understand the physical mechanism of noisy film boiling.

Calculation of NARM’s equilibrium with Peng-Robinson equation of state

The liquid molar volumes of nonazeotropic refrigerant mixtures (NARM), calculated with Peng Robinson (PR) equation, were compared with vapor -liquid equilibrium experimental data in this paper. Provided with co-reaction coefficient kij, the discrepancies of liquid molar volume data for R22+R114 and R22+R142b using PR equation are 7.7% and 8.1%, respectively. When HBT (Hankinson-Brobst-Thomson) equation was joined with PR equation, the deviations are reduced to less than 1.5% for both R22+R114 and R22+R142b.

Specific Heat and Thermal Conductivity of a Single Crystal-Like Bi2Sr2CaCu2O8+x High-Tc Superconductor

The characteristics of specific heat and thermal conductivity for high — Tc superconductors are discussed. In order to understand the behaviors of a high-Tc superconductor, a single crystal-like Bi2Sr2CaCu2O8+x is selected as the sample, and its specific heat is measured by adiabatic calorimeter, while its thermal conductivity is measured by steady heat flow method via a stainless steel radiation shield. The measured specific heat C of the crystal shows a jump at Tc with ΔC/C ≈ 3.5%, while the measured thermal conductivity in the ab plane shows a minimum value at Tc which is qualitatively in good agreement with other work. The measuring skills are specially analyzed. In addition, the thermal expansion coefficient for the crystal-like high-Tc superconductor is also shown.

Normal zone propagation along superconducting wires in superfluid liquid helium

Abstract The propagation velocity of normal zones along bare technical NbTi-superconductors, cooled with saturated and pressurized HeII was measured at bath tempertures of 2.0 K and magnetic fields of 1.77 and 2.5 T. Although in saturated HeII propagation velocities up to 18 m/s were obtained, in pressurized HeII no propagation was observed up to transport currents close to I c . Furthermore transient heat transfer from thin bare wires to HeII was investigated with a time resolution in the μs-range. The results are discussed with regards to a theoretical model of quench dynamics.

Preparation and thermal performance of form-stable expanded graphite/stearic acid composite phase change materials with high thermal conductivity

Thermal energy storage plays an important role in improving the working reliability and utilization efficiency of renewable energy systems. Thermal energy storage includes sensible heat storage, latent heat storage using phase change material (PCM) and thermochemical heat storage. In comparison with sensible heat storage, latent heat storage has the distinct advantages of its high energy storage density and stable temperature during the energy storage and release processes. However, low thermal conductivity of PCM is the common drawback for various latent heat energy storage systems. The purpose of the research is to enhance the thermal conductivity of PCM by developing new form-stable composite phase change materials using expanded graphite matrix. Firstly, a preparation method “heating adsorption of liquid SA into expanded graphite (EG) matrix and compressing stable-shape composite” is employed to synthesis form- stable composite phase change material. Twenty samples with different EG contents and packed densities are prepared using stearic acid (SA) as phase change material and two kinds of EG with different dilatation as porous matrix. Secondly, the microstructures, thermal properties and thermal stabilities of different EG/SA samples are tested to analyze the influence of the dilatation of expanded graphite on the thermal performance of form-stable composite phase change materials. Moreover, EG/SA form-stable heat storage units with different EG contents and packed densities are fabricated to analyze the thermal storage/release performance through heating/cooling experiment. The microstructures of EG and EG/SA samples are observed using scanning electron microscopy (SEM) and the results show there exist obvious differences between two kinds of EG and SA distribution in the samples. The EG/SA samples with high dilatation EG are even more uniform because the high dilatation EG has larger pore size and pore volume. The data obtained from differential scanning calorimetry (DSC) show the addition of EG and compressing operation have negligible effect on the latent heat and slightly increase the phase transition temperature of pure SA. The form-stable EG/SA composite PCMs have lower supercooling degree than pure SA. LFA447 flash thermal diffusivity instrument is used to evaluate the effect of EG’s dilatation on the thermal conductivity of EG/SA samples. The results show that the use of high dilatation EG is more effective to improve the thermal conductivity of form-stable EG/SA composite PCMs when packed density is large. The radial thermal conductivity of form-stable 20 wt.%EG/SA phase change composite with packed density of 950 kg m−3 is as high as 19.6 W m−1 K−1 when high dilatation EG is utilized. This figure is more than 110 times higher than that of pure SA. Finally, the thermal stability of EG/SA samples is conducted by repeating the charging and discharging processes of SA. These samples prepared by high dilatation EG have better thermal stability than the samples prepared by low dilatation EG. The EG with high dilatation can assure the uniform distribution of SA inside EG/SA sample and thus prevent the leakage of liquid SA during the phase change transformation process due to its dilated microstructure. The heating/cooling test results show that the heat storage/release time of EG/SA composite units is about 1/8–1/4 of that of pure SA unit, and this means the heat transfer can be significantly enhanced. It suggests that the form-stable EG/SA composite phase change materials prepared by high dilatation EG has good comprehensive performance due to its high thermal conductivity, good thermal stability and no leakage problem.