A study on investigating the thermal and energy saving performances of flat plate heat exchanges (FPHE) with different corrugated channels configurations

Du to scarce conventional energy resources, energy consumptions in the buildings occupied a large proportion of the overall energy consumptions. Therefore, many researchers pay more attentions to energy conservation in the buildings, including the heat recovery of air ventilation systems. Previous studies investigated the application of the plate heat exchangers in the heat recovery of air ventilation systems. The objective of this paper is to offer new methods to improve the thermal performance of heat recovery system and provide a guidance for the optimization design of a novel plate heat exchanger. This paper firstly compared the relevant results of numerical simulations with previous experimental results and verified the validation of the numerical simulations. Then, this paper used the Computational Fluid Dynamics (CFD) method to investigate the heat transfer characteristics and the pressure drop as well as the flow distributions in plate heat exchangers with two different corrugated surfaces (triangular and trapezoidal) and different heights of the channel spacing. In the paper, the numerical studies were carried out at a uniform wall heat flux, 580W/m2, for air as the working fluid. The Reynolds (Re) number varied from 500 to 2500 under three different channel heights and corrugated surfaces. The numerical results showed that, corrugated surfaces not only had a significant positive impact on heat transfer enhancement, but also led to an increase in the pressure drop through the channel. It can be seen that the effects of the corrugation patterns on the heat transfer and pressure drop were various for different channels with different Re numbers. In addition, the comparisons of comprehensive heat transfer factors identified that when the height of the channel spacing is larger, it is more appropriate to choose a triangular corrugated channel at a lower Re number. However, at a higher Re number, selecting the trapezoidal corrugated channel may be more suitable. Based on this study, it can be found that the plate heat exchangers with corrugated surfaces are of high efficiency and compactness. Therefore, a large amount of energy can be saved by using corrugated plate heat exchangers to recover heat

A PD Law Based Fuzzy Logic Control Strategy For Simultaneous Control Of Indoor Temperature And Humidity Using A Variable Speed Direct Expansion Air Conditioner

In small to medium scale buildings located in the subtropics, such as Hong Kong, direct expansion air conditioning (DX A/C) systems are widely applied. This is because, as compared to chilled water based central air conditioning systems, DX A/C systems are compact, flexible for multi-room services, energy efficient and cost less to maintain and operate. However, traditionally, a DX A/C system is equipped with a single-speed compressor and supply air fan, and employs ON / OFF control strategy to maintain indoor air temperature only, leaving the indoor moisture content (or relative humidity) uncontrolled. With the introduction of variable speed technology, the speeds of compressor and supply air fan can be varied continuously so as to realize the simultaneous control of the indoor temperature and humidity. In this paper, the development of a novel control strategy based on PD law and fuzzy logic is reported. The compressor speed was adjusted directly according to the indoor air moisture content and supply air fan speed according to the indoor air temperature, respectively, to realize the simultaneous control of indoor air temperature and humidity. Controllability tests for the novel control strategy were carried out and the test results suggested that, although two control loops for temperature and humidity were significantly coupled, the simultaneous control of indoor temperature and humidity was achieved with respect to control accuracy and sensitivity

Increase in neuroexcitability of unmyelinated C-type vagal ganglion neurons during initial postnatal development of visceral afferent reflex functions

BACKGROUND: Baroreflex gain increase up closely to adult level during initial postnatal weeks, and any interruption within this period will increase the risk of cardiovascular problems in later of life span. We hypothesize that this short period after birth might be critical for postnatal development of vagal ganglion neurons (VGNs). METHODS: To evaluate neuroexcitability evidenced by discharge profiles and coordinate changes, ion currents were collected from identified A- and C-type VGNs at different developmental stages using whole-cell patch clamping. RESULTS: C-type VGNs underwent significant age-dependent transition from single action potential (AP) to repetitive discharge. The coordinate changes between TTX-S and TTX-R Na(+) currents were also confirmed and well simulated by computer modeling. Although 4-AP or iberiotoxin age dependently increased firing frequency, AP duration was prolonged in an opposite fashion, which paralleled well with postnatal changes in 4-AP- and iberiotoxin-sensitive K(+) current activity, whereas less developmental changes were verified in A-types. CONCLUSION: These data demonstrate for the first time that the neuroexcitability of C-type VGNs increases significantly compared with A-types within initial postnatal weeks evidenced by AP discharge profiles and coordinate ion channel changes, which explain, at least in part, that initial postnatal weeks may be crucial for ontogenesis in visceral afferent reflex function

Measurement of the Cotton-Mouton effect in nitrogen, oxygen, carbon dioxide, argon, and krypton with the Q & A apparatus

Experiments for vacuum birefringence and vacuum dichroism have been set up with high-finesse high magnetic experimental apparatuses, which seem to be ideal for small gaseous Cotton-Mouton effect (CME) measurements. PVLAS Collaboration has measured CMEs in krypton, xenon and neon at the wavelength of 1064 nm. In this Letter, we report on our measurement of CMEs in nitrogen, oxygen, carbon dioxide, argon, and krypton at the same wavelength in a magnetic field B = 2.3 T at pressure P = 0.5-300 Torr and temperature T = 295-298 K. Our results agree with the PVLAS results in the common cases.Comment: 8 pages, 2 tables, 5 figures, submitted to Chemical Physics Letters. Some modifications are made in the revision according to the referee's comments: Donotations in equations are unified. Error in quoting numbers in 2 places in Table 2 is corrected. Uncertainty in modulation depth is included in the total systematic error. References are order re-arrange

Analysis of Changes in Hydration Products During Solidification/Stabilization Process of Heavy Metals in the Presence of Magnesium Potassium Phosphate Cement

Abstract To study the changes in hydration products over time during the solidification/stabilization process of magnesium potassium phosphate cementing material (MKPC) and to reveal the solidification mechanism of heavy metal elements in MKPC, methods, such as scanning electron microscope-energy spectrum (SEM-EDS), X ray diffraction (XRD), Fourier Transform Infrared Spectroscopy (FTIR) etc., were used to analyze the composition and microstructure of MKPC solidified body products with different production time, which are further adulterated with heavy metals, such as Zn, Cu, Ni, Cd and Cr, as well as changes in phases of hydration products. The results showed that the preliminary, intermediate and the final hydration products were MgHPO 4 ×7H 2 O, Mg 2 KH(PO 4 ) 2 ×15H 2 O and MgKPO 4 ×6H 2 O(MKP), respectively on day 7, day 15, day 30, day 45 and day 60 after the curing of the solidified body, which was adulterated with heavy metals. Based on the analysis of the result of Cu 2+ solidification test through FTIR, Mg 2+ was replaced by Cu 2+ in MKPC hydration products to generate CuKPO 4 , and the structure of the original hydration products did not have a crystal lattice change. The scanning electron microscope image (SEM) showed that cracks and harmful voids in the MKPC solidified body decreased gradually during the curing period between day 7 and day 60, and the effect of heavy metal solidification was strengthened. Based on energy spectrum analysis, heavy metal ions existing in the hydration products and MKPC could be used to solidify heavy metals. It was thus concluded that MKPC could solidify heavy metals, primarily due to the fact that heavy metals are capable of replacing Mg 2+ . Also, they participate in a variety of chemical reactions to generate heavy metal phosphate, which could react with heavy metal ions and precipitate them. Such sediments cement and the cemented body can seal partial heavy metal ions, and the combined actions could further solidify and stabilize heavy metals

Radiative viscosity of neutron stars

We study non-linear effects of radiative viscosity of $npe$ matter in neutron stars for both direct Urca process and modified Urca process, and find that non-linear effects will decrease the ratio of radiative viscosity to bulk viscosity from 1.5 to 0.5 (for direct Urca process) and 0.375 (for modified Urca process). Which means that for small oscillations of neutron star, the large fraction of oscillation energy is emitted as neutrinos; but for large enough ones, bulk viscous dissipation dominates.Comment: 11pages, 4 figure

Parametric analysis for underwater flapping foil propulsor

This paper researched into the harmonic and anharmonic underwater flapping foil propulsion systems to improve the efficiency of these bioinspired propulsors. The angle of attack, the pitching angle, the heaving amplitude, and the phase difference are parametrically investigated in this paper. A rigid two-dimensional NACA (National Advisory Committee for Aeronautics) 0012 airfoil is modeled with the aid of a commercial computational fluid dynamics software, FINE™/Marine. Unsteady Reynolds Average Navier-Stokes (URANS) equation is solved together with dynamic mesh to simulate the foil motion. The investigation first verifies the reliability of the developed modeling method against the benchmark data. Then, the systematic investigation is conducted and identifies that the heaving amplitude is most influential factor for the propulsion efficiency. Secondly, phase difference also has a significant influence on efficiency, but this effect is related to the reference working condition, which needs further study. Then, the pitching amplitude has little effect on the maximum efficiency value of flapping foil, while it will affect its optimal speed range. When the heaving amplitude ratio reaches 3 and the corresponding maximum angle of attack is about 9°, the maximum efficiency can reach 87%. The effect of anharmonic motion on the efficiency is very small and varies with the St number, but in summary, it can maintain the peak efficiency over a wider range of operations. In addition, the force and flow field characteristics of different efficiency points are compared and analyzed to distinguish their corresponding relationship with the propulsion efficiency

Integrated application of uniform design and least-squares support vector machines to transfection optimization

<p>Abstract</p> <p>Background</p> <p>Transfection in mammalian cells based on liposome presents great challenge for biological professionals. To protect themselves from exogenous insults, mammalian cells tend to manifest poor transfection efficiency. In order to gain high efficiency, we have to optimize several conditions of transfection, such as amount of liposome, amount of plasmid, and cell density at transfection. However, this process may be time-consuming and energy-consuming. Fortunately, several mathematical methods, developed in the past decades, may facilitate the resolution of this issue. This study investigates the possibility of optimizing transfection efficiency by using a method referred to as least-squares support vector machine, which requires only a few experiments and maintains fairly high accuracy.</p> <p>Results</p> <p>A protocol consists of 15 experiments was performed according to the principle of uniform design. In this protocol, amount of liposome, amount of plasmid, and the number of seeded cells 24 h before transfection were set as independent variables and transfection efficiency was set as dependent variable. A model was deduced from independent variables and their respective dependent variable. Another protocol made up by 10 experiments was performed to test the accuracy of the model. The model manifested a high accuracy. Compared to traditional method, the integrated application of uniform design and least-squares support vector machine greatly reduced the number of required experiments. What's more, higher transfection efficiency was achieved.</p> <p>Conclusion</p> <p>The integrated application of uniform design and least-squares support vector machine is a simple technique for obtaining high transfection efficiency. Using this novel method, the number of required experiments would be greatly cut down while higher efficiency would be gained. Least-squares support vector machine may be applicable to many other problems that need to be optimized.</p

Topological Hall Effect Driven by Short-Range Magnetic Orders in EuZn2_2As2_2

Short-range (SR) magnetic orders such as magnetic glass orders or fluctuations in a quantum system usually host exotic states or critical behaviors. As the long-range (LR) magnetic orders, SR magnetic orders can also break time-reversal symmetry and drive the non-zero Berry curvature leading to novel transport properties. In this work, we report that in EuZn$_2$As$_2$ compound, besides the LR A-type antiferromagnetic (AF) order, the SR magnetic order is observed in a wide temperature region. The magnetization measurements and electron spin resonance (ESR) measurements reveal the ferromagnetic (FM) correlations for this SR magnetic order which results in an obvious anomalous Hall effect above the AF transition. Moreover the ESR results reveal that this FM SR order coexists with LR AF order exhibiting anisotropic magnetic correlations below the AF transition. The interactions of LR and SR magnetism evolving with temperature and field can host non-zero spin charility and berry curvature leading the additional topological Hall contribution even in a centrosymmetric simple AF system. Our results indicate that EuZn$_2$As$_2$ is a fertile platform to investigate exotic magnetic and electronic states.Comment: 6 pages, 4 figure