Effects of PAA and PBTCA on CaCO_3 Scaling in Pool Boiling System

Formation of mineral scales on heat exchangers is a persistent and expensive problem. In the presentpaper, the calcium carbonate scale inhibition by two inhibitors, polyacrylic acid (PAA) and 2-phosphonobutane-1,2,4-tricarboxylic acid (PBTCA) has been studied in a pool boiling system. It is found that PBTCA has abetter inhibition effect than PAA under the identical conditions. X-ray diffraction(XRD) and Fourier transform-infrared(FTIR) analyses demonstrate that the content of vaterite increases as inhibition effects increase. Themetastable crystal forms of vaterite and aragonite are stabilized kinetically in the presence of inhibitors. Therelationship between the inhibition effect and the fractal dimension has also been investigated. The result showsthat the fractal dimension is higher in the presence of inhibitors. The better the inhibition effect, the higher thefractal dimension. The step morphology was observed by atomic force microscopy (AFM) images. It is shown thatthe step space on the calcium carbonate surface increases in the presence of inhibitors. Moreover, with the increaseof inhibition effect, both the step space and the fractal dimension increase. The step bunching is found on thecalcium carbonate by AFM. The better the inhibition effect of the inhibitor, the slower the step velocity in theunbunched location. As a result, the step space becomes wider in the presence of PBTCA than that in the presenceof PAA.

Thermal Structure of Glass Fiber Reinforce Plastic Support Structure

The assembled form of thick-wall glass fiber reinforced plastics (GFRP) tube and 0Cr18Ni9 austenitic stainless steel pipes was designed as the radius thermal-insulating and load-supporting structure in cryogenic vessels. In order to study the thermal leakage and gap changes on the support structure, as well as radius temperature and stress distribution on GFRP tube, an experimental investigation has been taken. The results indicate that the support structure is proved to fit well as thermal-insulating and load-supporting part in cryo-genic vessels, furthermore has high security during cryogenic applications.

Metal hydride work pair development and its application on automobile air conditioning systems

Aiming at developing exhaust gas driving automobile air conditioning systems, a hydride pair LaNi4.61Mn0.26A10.13/ La0.6Y0.4Ni4.8Mn0.2 was developed working at 393-473 K/293-323 K/263-273 K. Property tests showed that both alloys have flat plateau slopes and small hystereses; system theoretical coefficient of performance （COP） is 0.711. Based on this work pair, a function proving automobile metal hydride refrigeration system was constructed. The equivalent thermal conductivities of the activated reaction beds were merely 1.1-1.6 W/（m-K）, which had not met practical requirement. Intermittent refrigeration cycles were achieved and the average cooling power was 84.6 W at 423 K/303 K/273 K with COP being 0.26. By altering cycling parameters, experiment data showed that cooling power and system COP increase with the growth of heat source temperature as well as pre-heating and regeneration time while decrease with heat sink temperature increment. This study confirms the feasibility of automobile metal hydride refrigeration systems, while heat transfer properties of reaction beds still need to be improved for better performance.

Modeling cavitation flow of cryogenic fluids with thermodynamic phase-change theory

Cavitation is the formation of vapor bubbles within a liquid where the flow dynamics causes the local static pressure to drop below the vapor pressure. The so-called full cavitation model (FCM) developed by Singhal has been widely used in numerical modeling of the cavitation flow for thermosensible and non-thermosensible fluids. Within the FCM, the bubble size is taken to be equivalent to the maximum possible value to forego the calculation of bubble number density. We developed a new cavitation model by recalculating the bubble radius in FCM to account for the effects of local pressure. The new model was obtained by combining the thermodynamic phase-change theory and the Young-Laplace equation with the assumption of thermodynamic equilibrium during the cavitation process. The cavitation calculations were performed based on the mathematical framework of the homogeneous equilibrium flow model and the transport-equation-based model for vapor phase mass fraction. The model was validated by modeling the cavitating flow of liquid nitrogen and liquid hydrogen through NASA hydrofoil and Ogive with consideration of the phase-change thermal effects. The temperature and pressure distributions with the new model are found to agree well with data from existing experimental studies, as well as the simulations with the FCM.

Liquid film dryout model for predicting critical heat flux in annular two-phase flow

Gas-liquid two-phase flow and heat transfer can be encountered in numerous fields, such as chemical engineering, refrigeration, nuclear power reactor, metallurgical industry, spaceflight. Its critical heat flux (CHF) is one of the most important factors for the system security of engineering applications. Since annular flow is the most common flow pattern in gas-liquid two-phase flow, predicting CHF of annular two-phase flow is more significant. Many studies have shown that the liquid film dryout model is successful for that prediction, and determining the following parameters will exert predominant effects on the accuracy of this model: onset of annular flow, inception criterion for droplets entrainment, entrainment fraction, droplets deposition and entrainment rates. The main theoretical results achieved on the above five parameters are reviewed; also, limitations in the existing studies and problems for further research are discussed.

Experimental study on a -60 °C cascade refrigerator with dual running mode

In this study,an experimental setup is designed and built to investigate the feasibility and performance of the proposed dual-mode cascade refrigeration cycle.The apparatus can be operated in two modes:dual-stage mode and single-stage mode such that the low temperature cycle(LTC) can be operated together with the high temperature cycle(HTC) or can run independently.Experimental results validate the feasibility of independent operation of LTC.The performance of the independent operation of LTC mode is theoretically investigated using experimental data as bases.Detailed suggestions are made for the improvement of the coefficient of performance(COP) of the experimental system.Theoretically,high COP of the cycle provides excellent application for the presented refrigeration cycle.