U-tube Design Research Articles

Study on Measurement of Liquid Viscosity Coefficient

Based on the traditional falling ball method, the U-tube design is more suitable for measuring transparent or translucent liquids with a large viscosity coefficient. An electromagnetic relay is placed at the upper end of one side of the tube to ensure that the ball falls vertically through the axis of the tube. The other side is sealed with water to prevent the pollution of the liquid to be measured and improve the measurement accuracy. At the same time, it solves the problem of oil leakage in the existing device for a long time, which is convenient for device maintenance and cleaning.

Analysis of heat transfer characteristics and optimization of U-tube based solar evacuated tube collector system with different flow conditioning inserts

In the present study, the performance of a U-tube based evacuated tube collector (ETC) for a forced circulation system is tested. The collector tilt angle is varied to analyse the optimum tilt angle to get the higher thermal performance of the solar U-tube ETC regardless of the sun's location. Different flow conditioning inserts are introduced, and its feasibility study is accomplished for the ETC in the place of a conventional plain U-tube ETC to obtain higher system performance. Further, a computational fluid dynamics (CFD) based thermal model is developed in Ansys-fluent R14.5 platform and validated with in-house experimental datasets. Based on the developed CFD model, a detailed parametric study is carried out to optimize the model geometry and operating parameters of solar ETC. CFD results revealed that increasing U-tube diameter from 1/8“ to 3/8” enhances the net temperature gain by about 39%. Consequently, the proposed flow conditioning inserts models showed a better performance with higher net temperature gain and thermal efficiency under the same condition with acceptable pressure drop penalty. Among the different studied geometries, twisted taped with square holes proved to be the most effective design for obtaining a higher thermal efficiency compared to the plain U-tube design. The temperature contour with streamlines and pressure contour of the best flow conditioning model is also discussed. Furthermore, a trade-off study is accomplished to visualize the thermal efficiency in contrast to pressure drop and net temperature gain.

Analysis of the transient performance of coaxial and u-tube borehole heat exchangers

While coaxial borehole heat exchangers often have lower borehole thermal resistances than u-tubes, studies in the literature have mixed results as to whether the coaxial design always outperforms the u-tube. This study contributes a systematic comparison between the two designs, accomplished using a custom numerical model in OpenFOAM that provides detailed predictions of the heat transfer within the ground heat exchangers. The modelling and subsequent analysis of system thermal resistances demonstrated that the u-tube and coaxial heat exchanger performances differed the most during the early, transient phase of operation. Furthermore, modelling showed that the coaxial design does not necessarily exceed the u-tube performance long term; testing of coaxial heat exchangers with polyethylene piping showed small differences in outlet temperature compared to the u-tube after 72 h. Additional testing showed that using a steel coaxial outer tube could provide a 22% improvement to performance over the u-tube design. These findings are used to compare predictions of thermal resistance with available analytical models. The impact of the results on the potential for length reductions is also discussed.

Recent Moisture Separator Reheater Design Technologies

The moisture separator reheater (MSR) is a key piece of equipment in reheat systems in nuclear steam turbines that use saturated main steam, where it helps improve turbine efficiency and suppress flow-accelerated corrosion. Fundamental to achieving a compact, reliable MSR design are methods for predicting mist separator vane performance and suppressing tube drainage instability. First, we devised a method for predicting separator performance based on the observation of mist separation behavior under an air-water test. We then developed a method for predicting performance under steam conditions from air-water test data and verified it by means of a comparison with the actual results of a steam condition test. The instability of tube drainage associated with both subcooling and temperature oscillation at turbine partial load, which might adversely affect the seal welding of the tubes to the tube sheet due to thermal fatigue, was measured on an existing unit to clarify the behavior. We then developed a technique for increasing venting steam, which had been operating at a constant flow rate, to suppress instability and verified its effectiveness. Both methods were applied to current MSR models, which were adopted for nuclear power plant turbines commercially placed in service from 1984 to 2009, and the effectiveness of the methods was demonstrated. The separator vane mist carryover rate was less than 0.1%, and tube drainage instability was suppressed, demonstrating the effectiveness of the simple design concept of a two-flow U-tube instead of the prevailing four-flow U-tube design. We put forth a new concept in the design of MSRs for 1700 MW class advanced pressurized water reactor (APWR) units based on associated technologies, along with advanced technology for the compact design of pressure vessels and multidisciplinary optimum design for evaluating heat exchanger tube bundles.

Multiple Automated Reactor Systems (MARS). 2. Effect of Microreactor Configurations on Homogeneous Gas-Phase and Wall-Catalyzed Reactions for 1,3-Butadiene Oxidation

Wall-catalyzed and homogeneous gas-phase reactions for the gas-phase oxidation of 1,3-butadiene are studied using the Multiple Automated Reactor System (MARS) described in part 1 of this series of papers to assess reaction inertness for a typical parallel catalytic reactor system. The heterogeneous catalyzed version of 1,3-butadiene oxidation represents an alternate C4 hydrocarbon-based route for the manufacture of a tetrahydrofuran (THF) monomer. Polyether glycol polymers derived from THF are used to manufacture various commercial materials where elastic or flexible impact-resistant properties are desirable. Experiments were performed using parallel banks of the MARS U-tube and straight-through-tube reactor designs in both empty tube and packed-bed modes. Empty tube mode data using typical heterogeneous catalyst reaction conditions showed the presence of significant reactant conversion to combustion products for both reactor designs. The U-tube design generated different reactant conversion results when compared to the straight-through-tube design. These differences were attributed to the interaction between system design features and reaction conditions, such as the reactor tube geometry, the product transfer line design, and the contact times in various heated zones. Various materials of construction and catalyst bed retaining materials were also evaluated for inertness using the packed-bed mode. When a butadiene-rich feed gas was used, the O2 conversion was generally higher in the presence of various metals versus glass according to type 316 stainless steel > Ti > glass wool > glass beads. The results suggest that caution must be exercised when catalyst performance data are measured using parallel gas-phase reactor systems, especially for substrates with functional groups that may react in the gas phase and in the presence of various materials of construction. Each reactor unit in the parallel bank should be evaluated for reaction inertness before a catalyst development campaign is initiated to avoid incorrect conclusions on catalyst ranking and generation of biased data that contain false measures of catalyst performance.

Simplified Small-Break Blowdown Models

The behavior of the primary system coolant in a pressurized water reactor during a small-break loss-of-coolant accident (LOCA) is governed by the hydrostatic forces that develop in the system. Digital simulation of the hydrostatic interactions during a small-break LOCA can be achieved with simplified nodal representations that significantly reduce computer times. The simplification process can be successfully achieved by combining primary system regions that behave symmetrically while preserving the basic manometer or U-tube design of the system.The simplified nodal representations have the capability of assessing the hydrostatic effects on the blowdown for the spectrum of small breaks wherein detailed model computations become economically prohibitive for parametric analyses of emergency core cooling systems.