Variable Volume Ratio Research Articles

Heat transfer enhancement of a multichannel flat tube-copper foam latent heat storage unit

In latent heat storage units, phase change materials are often combined with metal foams to enhance heat transfer due to their low thermal conductivity. However, the current metal foam structure cannot solve the problems of long melting time and uneven melting caused by natural convection. To obtain superior heat storage structures, this paper uses a multichannel flat tube as the heat exchange element and designs units with a variable volume ratio of gradient copper foam. This tube is divided into parts A and B and has a decreasing porosity along the vertical direction from top to bottom. Results of orthogonal tests show that low porosity, a large volume ratio of part A, and a large gradient can improve the performance. An average porosity of 0.84, gradient of 9%, and part A volume ratio of 80% are selected as the optimal structural parameters. Compared with a homogeneous porosity structure having a porosity of 0.96 under original working conditions, the optimal structure has 48.64% higher heat storage capacity and 54.13% shorter melting time. Meanwhile, compared with a homogeneous porosity structure having the same porosity of 0.84, the optimal structure has an 11.37% higher heat storage capacity and 4.09% shorter melting time.

A Novel Screw Compressor with a Shunt Enhanced Compression and Pulsation Trap (SECAPT)

Some positive displacement (PD) compressors are equipped with automatic discharge valves such as reed valves that open automatically whenever the cavity pressure is slightly larger than the outlet pressure to deal effectively with varying pressure ratio applications. Screw compressors today do not have such valves, resulting in off-design conditions known as the under-compression or over-compression when the cavity pressure at discharge is deviating from the outlet pressure. Compressor efficiency suffers and pulsation/noise becomes worse under these conditions. Some type of controls are desired such as a discharge pulsation dampener or a variable volume ratio (often called variable Vi) slide valve design to lessen or cure the discharge pressure mismatch problems.Injecting gas vapor into a screw compressor cavity during internal compression phase has been known to be beneficial in enhancing compressor performance and has been widely used in HVAC&R industry known as the Economizer. However, the underlining principle of the Economizer has thus far not been explored for optimizing compression schemes of a screw compressor in general. This paper introduces a self-sensing and self-correcting compression process that can be “derived or deduced” from the Perfect Gas Law by optimizing for multiple design criteria such as compressor efficiency, pulsation/noise abatement, and cost and footprint reduction for a screw operating over a wide range of pressures. The scheme, called SECAPT (Shunt Enhanced Compression And Pulsation Trap), is then investigated and optimized numerically by a new CFD code for one industrial case: a bulk truck loading application where compressor pressure varies from no pressure rise to maximum load. The numerical simulations illustrate that SECAPT is tentatively capable of achieving multiple targets as theorized.

Experimental and numerical analysis of variable volume ratio as additional optimization parameter in organic Rankine cycle expanders

In this paper, the use of a variable volume ratio expander for a 10 kWe organic Rankine cycle (ORC) to be integrated in a Carnot battery has been studied. The reciprocating piston expander used in this work has a built-in mechanism which allows changing the inlet valve timing of the expander and hence the expander internal volume - and pressure ratio. The experimental results of a 10 kWe ORC prototype are presented. A total of 58 steady state points has been collected by varying the heat source and cold sink temperature, the refrigerant mass flow rate, the expander speed and the expander inlet valve timing. The experimental results for the ORC are presented in terms of electrical power output and cycle efficiency and for the expander the isentropic and volumetric efficiencies are determined for different valve timings. Although the experimental results clearly show the effect of changing the internal volume ratio on the expander performance we here present a combined experimental-numerical approach which is necessary to evaluate the performance under varying external conditions. Therefore, an empirical quasi-steady state model of the ORC has been calibrated based on the experimental results. Subsequently, in a numerical analysis, the use of various valve timings has been evaluated under time-varying boundary conditions. A maximal difference of 14.2 % in the net power production has been observed between the most optimal and least optimal valve timing. However, for the presented numerical study the use of variable valve timing only increased the net power production maximally 1 % compared to the optimal fixed timing. Altogether, this study demonstrates the benefit of variable volume ratio reciprocating piston expanders for ORCs under varying external conditions.

The invisible arbiter of emulsion structure: insight from an examination of two types of 3-phase emulsions

It has long been established that the equilibrium properties of a water–oil–surfactant system governs the morphology of the emulsion formed—an inherently non-equilibrium system. In this work, we reinforce this concept and bring forward additional insights. Two types of 3-phase emulsions are examined, one obtained from suspension polymerization of silicone and acrylate in an aqueous phase and another obtained from mechanical dispersion of a silicone oil and a sunflower seed oil into an aqueous phase. We show that the specific emulsification process has an impact on the detailed structure of the final multiple droplets. In suspension polymerization, the complete miscibility of silicone with acrylate monomers prior to polymerization renders uniformity in the composition of the starting droplets; hence the final droplets after polymerization all have identical equilibrium tensions as well as relative volume ratios between the separated phases. Consequently, the final droplets have uniformly the same structure as predicted based on thermodynamics. On the other hand, the 3-phase emulsion formed from mechanical dispersion of two immiscible oils in water shows an overall morphology that is predicted by equilibrium tensions, however, a wide variation in the specific geometry is observed. This latter aspect reflects the randomness in drop break-up-and-recombination associated with the homogenization process, which results in variable volume ratio between the two immiscible oils among different droplets.

Development of a Reconfigurable Prototype Peristaltic Compressor

Traditional positive displacement compressors require valves, internal volume ratios or both to operate. These two features generate the majority of the losses in compressors. The peristaltic compressor is a novel compressor architecture that feature valve-less compression with variable volume ratios, which provides the potential for highly efficient compression. This paper will present a design of a reconfigurable prototype peristaltic compressor and illustrate how the structure of the compression chamber and actuation pattern affect the compressor efficiency. The prototype utilizes a flexible diaphragm constrained and sealed against a female die to make a compression chamber. Linear actuators with male dies press the diaphragm sequentially against the female die to move and compress the fluid. Preliminary experiments were performed using air as the working fluid for volume ratios ranging from 1.143 to 8 and operational frequencies ranging from 1.28 to 2.31 Hz. These results suggest that the actuation pattern has an impact on the major parameters such as mass flow, displacement volume, and pressure ratio which influence the overall efficiency of the compressor.

Experimental study on an injection-assisted air source heat pump with a novel two-stage variable-speed scroll compressor

Traditional air source heat pumps (ASHPs) with scroll compressors were limited in terms of variable volume ratio. An injection-assisted ASHP using a novel two-stage variable-speed scroll compressor with a variable volume ratio and direct current (DC) speed regulation motor, named IDCAHP, was proposed herein for improving heating performance in cold and/or severely cold regions over wide-range temperature conditions. Experiments focusing on the IDCAHP heating performance under different temperatures and various characteristics of the compressor frequency were performed. Results indicated that the IDCAHP performed well over wide-range temperature conditions. In particular, the discharge pressure decreased steadily with falling ambient temperature, and the discharge temperature of the IDCAHP increased with the rising pressure ratio by less than 82.6 °C at an ambient temperature of −20.0 °C. Additionally, gas injection and increasing the compressor frequency could improve the heating capacity of the IDCAHP. As the ambient temperature was −20.0 °C, the heating capacity reached 68.1% of the nominal condition, and the heating coefficient of performance (COP) and energy efficiency ratio (EER) of the IDCAHP could reach 2.0 and 1.8, respectively. Moreover, the decreasing intermediate pressure improved the heating performance. By contrast, with a common ASHP without gas injection, quasi-two-stage compression air-source heat pump with an economiser (QCAHP-E), quasi-two-stage compression air-source heat pump with a flash tank (QCAHP-F), and two-stage compression air-source heat pump (TCAHP) system, the COP of the IDCAHP increased to 35.0%, 4.2%, 37.6%, and 16.2%, respectively, whereas the discharge temperature decreased to 47.9 °C, 46.5 °C, 62.7 °C, and 40.7 °C, respectively.

Topography-induced variations of localized surface plasmon resonance in tip-enhanced Raman configuration

We report on topography-induced changes of the localized surface plasmon resonance (LSPR) enhanced luminescence of gold tip on SrTiO3 nanostructures with apertureless scanning near-field optical microscopy (aSNOM) in tip-enhanced Raman spectroscopy (TERS) configuration. Our experimental and simulated results indicate that the averaged refractive index of the dielectric environment of the tip apex containing both air and SrTiO3 in variable volume ratios, is dependent on the topography of the sample. This reveals that the local topography has to be taken into consideration as an additional contribution to the position of the LSPR.

Thermocapillary Convection Space Experiment on the SJ-10 Recoverable Satellite.

Thermocapillary convection is an important research subject in microgravity fluid physics. The experimental study on surface waves of thermocapillary convection in an annular liquid pool is one of the 19 scientific experimental projects on the SJ-10 recoverable satellite. Presented is a design for a payload for space experimental study on thermocapillary convection that includes the experimental model, measurement system, and control system. The specifics for the construction of an experimental model of an annular liquid pool with variable volume ratios is provided. The fluid temperatures are recorded by six thermocouples with a high sensitivity of 0.05 °C at different points. The temperature distributions on the liquid free surface are captured by means of an infrared thermal camera. The free surface deformation is detected by a displacement sensor with a high accuracy of 1 µm. The experimental process is fully automated. The research is focused on thermocapillary oscillation phenomena on the liquid-free surface and convective pattern transitions through analyses of experimental data and images. This research will be helpful to understand the mechanism of thermocapillary convection and will offer further insights into the nonlinear characteristics, flow instability, and bifurcation transitions of thermocapillary convection.

Experimental study of an improved air-source heat pump system with a novel three-cylinder two-stage variable volume ratio rotary compressor

Traditional air source heat pumps (ASHPs) only can work above about −20 °C to −25 °C, and have limitations in terms of performance. This paper proposes a novel three-cylinder two-stage variable volume ratio (TSVVR) rotary compressor to improve the performance of the ASHP. Utilizing the variation characteristics of the compressor optimal volume ratio under the different temperatures, the compressor volume can be switched for better performance. Experiments are conducted on the improved ASHP with the TSVVR rotary compressor and the two traditional ASHPs with the single-stage and two-stage compressor using the simulation of the residential building in the environmental laboratory. The results show that the TSVVR system operates in a stable manner with the COP of 1.52 W/W at −30 °C, and achieves a higher COP than the traditional ASHPs. The optimal volume ratio decreases with the decrease of the evaporation temperature. The TSVVR system works in the three-cylinder mode at low temperature and directly expands the heating capacity and compression efficiency because of the increase of the low-pressure volume and suction volume. When the water temperature varies between 40 °C and the maximum possible temperature, the COP of the TSVVR system is 18.4−22.3% higher and 6.6–7.3% higher than the single-stage and two-stage systems, respectively; when the indoor temperature varies between 12.5 °C and 18 °C, the COP of the TSVVR system is around 18.4−23.4% and 5.2–8.8% higher than the single-stage and two-stage systems, respectively. The two-cylinder mode of the TSVVR system has a larger volume ratio than the single-stage and two-stage ASHPs and is closer to the optimal volume ratio, which is more suitable for the high temperature and low load conditions. In the three-cylinder mode, the TSVVR system has a smaller volume ratio, and the compression efficiency and system refrigerant flow rate increase, when the evaporation temperature is low. Two modes ensure that the TSVVR system always work in the efficient states, especially in the low temperature environments.

Variable volume ratio free-piston expander: Prototyping and experimental campaign

This paper describes a dynamic model developed for control purposes of a novel free piston expander with a variable built-in volume ratio (BVR) for Organic Rankine Cycle (ORC) applications. In order to demonstrate the feasibility of the proposed concept and to validate the theoretical model, a test setup has been designed and built. An integrated two degree of freedom motor/alternator is substituted by a separate linear motor/alternator (LMA) and a rotary servo motor designed and made from standard industrial components. This approach gives a possibility to develop and to test the integrated alternator and the expander itself independently. The model has been validated by running the setup in compressor mode. The cogging force and the frictional force, which are difficult to obtain analytically, are identified and mapped. An estimation of the geometry and the mass of the piston of an integrated design has also been made. The obtained results are sufficient for the control algorithm development since all acting forces are calculated or estimated with a good accuracy.

Flexural performance of concrete beams containing engineered cementitious composites

Engineered Cementitious Composites (ECC) considers a type of ultra-ductile cementitious composites with fiber reinforcement. It is developed for applications for economic purpose in the construction industry. ECC characterizes by strain hardening and multiple cracking. This paper experimentally investigates the performance of ECC concrete beams reinforced with conventional reinforcement bars. Advanced Polyvinyl Alcohol Engineered Cementitious Composite (PVA-ECC) fibers were selected in this purpose. Twelve RC beams were poured and tested to study flexure behavior under four-point loading test. Two different longitudinal reinforcement percentages, variable volume ratios of (PVA) and polypropylene fibers (PP) were used. optimizing the usage of PVA material trails to put it in the lower layer of the section at point of maximum tension with variable thicknesses was conducted. Initial flexure cracking load, ultimate load, the ductility and the load-to-deflection relationship at various stages of loading were evaluated. Experimental outcomes revealed that the enhancement in maximum capacity is more significant in the case of using PVA rather than PP. The maximum load increases by 20% and 34% for 1.0% and 2.0% of PVA contents in total section respectively. The relative ductility factor increases by 30% and 45% for 1.0% and 2.0% of PVA content. Results also depicted that a reasonable considerable increasing in the load capacity when used limited layer thickness of PVA concrete. Nonlinear Finite Element Analysis (NLFEA) was conducted for the purpose of simulating the behavior of experimentally tested beams, regarding crack behavior and load-deflection response. Reasonable agreement was achieved between the experimental results and NLFEA results.

A rheological study of molecular and supramolecular organization of chitosan succinamide in a mixed water–etanol solvent

An approach based on quality reduction of the solvent, namely, the use of mixed water–ethanol solvents of variable volume ratio was used for control over the aggregation and formation of a physical net of bonds in chitosan succinamide solutions. A study of the molecular and supramolecular organization of chitosan succinamide in solution showed that this polymer, which does not aggregate in a dilute (to the crossover point) aqueous solution, aggregates in a mixed water–ethanol solvent even at high dilution. Polymer structurization in solution is accompanied by the formation of an additional net of physical bonds, whose nodes are aggregates of chitosan succinamide macromolecules formed in the mixed solvent. It leads to earlier formation of viscoelastic properties, which is ultimately reflected by the regularities of some physicochemical properties of materials formed from solution.

涡旋压缩机在低温热泵领域应用的发展趋势

为拓宽涡旋压缩机在低温热泵领域的应用，主要采用了几种技术手段。本文综述了涡旋压缩机在热泵系统中的几种发展趋势,即设置补气回路和经济器；结合制冷剂泄出技术和喷射技术对压缩机容量进行调节以及在压缩机上设置多个排气阀并将排气压力制冷剂引入背压腔；同时介绍了其技术原理和主要需要解决的技术问题，提高了涡旋压缩机的效率。 Some new technical methods are developed in order to increase the running scope of scroll compression heat pump systems. The most popular three ones are introduced in this article. They are 1) how to establish a heat pump sys-tem with economizer and auxiliary injection circuit; 2) how to adjust the system capacity through refrigerant release and injection; 3) how to get variable volume ratio by designing three discharge valves. The principles of these methods and solving technical problems are introduced and the scroll compressor efficiency has been improved.

Corrosion and electrochemical behaviors of pure aluminum in novel KOH‐ionic liquid‐water solutions

AbstractThe corrosion and electrochemical behaviors of pure aluminum in KOH‐ionic liquid‐water solutions with variable volume ratios of water and the ionic liquid 1‐butyl‐3‐methyl imidazolium tetrafluoroborate (BMIMBF4) were for the first time investigated by means of hydrogen collection, polarization curve, galvanostatic discharge, and electrochemical impedance spectroscopy (EIS). The results of hydrogen collection experiments showed that aluminum has a low corrosion rate in KOH‐BMIMBF4‐H2O solutions, and the corrosion rate decreases with increase in BMIMBF4 content in the electrolytes. The results of electrochemical experiments revealed that aluminum is electrochemically active over a very wide potential window in the KOH‐BMIMBF4‐H2O solutions, and its electrochemically kinetic mechanism is similar to that in the corresponding aqueous solution; the increase in KOH and water contents in the electrolytes may improve the anodic dissolution performance of aluminum. It was found that aluminum presents excellent galvanostatic discharge performance in the 2.0 M KOH BMIMBF4‐H2O mixed solution with 60% water.

A bending elasticity approach to the three-phase coexistence of microemulsions

In mixtures of water, oil, and surfactant, a microemulsion phase with a bicontinuous microstructure may coexist with water and oil excess phases. A common theoretical description of microemulsion properties is based on the energy of the curved bending elastic interface. The aim of the article in hand is to model the microstructures and phase behavior of microemulsions in the vicinity of the three-phase region. To this end, we compare the energy of several microstructures as function of volumetric constraints and preferred curvature parameters. Two major developments were necessary to do so: (i) A new bending energy function is introduced capable of explaining the coexistence of the bicontinuous microemulsion with both water and oil. (ii) An analytical geometric model of bicontinuous structures with variable volume ratios of the two domains is presented suitable for computing the local curvatures over the whole interface.

Geobarometry of ultramafic xenoliths from Loihi Seamount, Hawaii, on the basis of CO 2 inclusions in olivine

Abundant fluid inclusions in olivine of dunite xenoliths (∼1–3 cm) in basalt dredged from the young Loihi Seamount, 30 km southeast of Hawaii, are evidence for three coexisting immiscible fluid phases—silicate melt (now glass), sulfide melt (now solid), and dense supercritical CO 2 (now liquid + gas)—during growth and later fracturing of some of these olivine crystals. Some olivine xenocrysts, probably from disaggregation of xenoliths, contain similar inclusions. Most of the inclusions (2–10 μm) are on secondary planes, trapped during healing of fractures after the original crystal growth. Some such planes end abruptly within single crystals and are termed pseudosecondary, because they formed during the growth of the host olivine crystals. The “vapor” bubble in a few large (20–60 μm), isolated, and hence primary, silicate melt inclusions is too large to be the result of simple differential shrinkage. Under correct viewing conditions, these bubbles are seen to consist of CO 2 liquid and gas, with an aggregate ϱ = ∼ 0.5–0.75 g cm −3, and represent trapped globules of dense supercritical CO 2 (i.e., incipient “vesiculation” at depth). Some spinel crystals enclosed within olivine have attached CO 2 blebs. Spherical sulfide blebs having widely variable volume ratios to CO 2 and silicate glass are found in both primary and pseudosecondary inclusions, demonstrating that an immiscible sulfide melt was also present. Assuming olivine growth at ∼ 1200°C and hydrostatic pressure from a liquid lava column, extrapolation of CO 2 P-V-T data indicates that the primary inclusions were trapped at ∼ 220–470 MPa (2200–4700 bars), or ∼ 8–17 km depth in basalt magma of ϱ = 2.7 g cm −3. Because the temperature cannot change much during the rise to eruption, the range of CO 2 densities reveals the change in pressure from that during original olivine growth to later deformation and rise to eruption on the sea floor. The presence of numerous decrepitated inclusions indicates that the inclusion sample studied is biased by the loss of higher-density inclusions and suggests that some part of these olivine xenoliths formed at greater depths.