Elbel S., Hrnjak P. Performance optimization of two-stage compressor system using transcritical R744 / trans. from Engl. M. A. Fedorova

The use of transcritical R744 systems has become increasingly popular in recent years in a variety of different applications. For applications that span a wide temperature range between the heat source and heat sink, the use of two-stage compressor results in numerous advantages in terms of efficiency and compressor discharge temperature. This paper presents experimental data for a transcritical R744 compressor system operating at high heat rejection temperatures. A comprehensive system model was developed and validated with the experimental results. Based on this, the simulation tool was used to further optimize the system design specifically to accommodate the two-stage compression process. The optimum heat transfer area distribution has been determined to simultaneously ensure efficient intercooling at intermediate pressure and gas cooling at the high-pressure level. Simultaneously, the system was also optimized with respect to optimal intermediate pressure and the results show that for this particular system, the optimum intercooler pressure deviated substantially from the standard design approach that uses the geometric mean between suction and discharge pressures

Alicyclobacillus acidoterrestris Strain Variability in the Inactivation Kinetics of Spores in Orange Juice by Temperature-Assisted High Hydrostatic Pressure

In this work, the inactivation kinetics of Alicyclobacillus acidoterrestris spores by temperature-assisted high hydrostatic pressure was assessed by means of the Weibull model. Spores from two A. acidoterrestris strains (a wild-type strain and a reference strain) were inoculated in commercial orange juice and subjected to high pressure levels (500 and 600 MPa) combined with four temperature regimes (25, 45, 60 and 70 °C) for time up to 30 min. Results showed that for a given high-pressure level spore inactivation was higher as temperature progressively increased. Furthermore, the Weibull model consistently produced satisfactory fit to the inactivation data based on the values of the root mean squared error (RMSE < 0.54 log colony-forming units (CFU)/mL) and the coefficient of determination (R2 > 0.90 in most cases). The shape of inactivation curves was concave upward (p < 1) for all temperature/high pressure levels tested, indicating rapid inactivation of the sensitive cells of the bacterium whereas the remaining ones adapted to high hydrostatic pressure (HHP) treatment. The values of the shape (p) and scale (δ) parameters of the Weibull model were dependent on the applied temperature for a given high pressure level and they were further described in a secondary model using first-order fitting curves to provide predictions of the surviving spore population at 55 and 65 °C. Results revealed a systematic over-prediction for the wild-type strain regardless of temperature and high pressure applied, whereas for the reference strain under-prediction was evident after 3 log-cycles reduction of the surviving bacteria spores. Overall, the results obtained indicate that the effectiveness of high hydrostatic pressure against A. acidoterrestris spores is strain-dependent and also underline the need for temperature-assisted HPP for effective spore inactivation during orange juice processing.

Experimental and Numerical Assessment of Water Leakages in a PVC-A Pipe

Nowadays, in the definition of effective approaches for the sustainable management of water pressurized systems, the assessment of water leakages in water supply and distribution systems represents a key aspect. Indeed, the large water volumes dispersed yearly provoke relevant environmental, technical and socio-economic costs. Worldwide, many water systems show alarming levels of water losses, due to both the poor sealing of joints and the presence of cracks, enhanced by a high pressure level greater than that strictly required for assuring a proper service level to users. With the aim of analysing the correlation between pressure and leakages, in this work the results of an experimental and a numerical Computational Fluid Dynamics (CFD) investigation are provided and discussed. With reference to a drilled PVC-A (Polyvinyl Chloride-Alloy) pipe, a new-generation plastic material for water systems use, an experimental investigation was first carried out at the Laboratory of Hydraulics of the University of Naples Federico II, aimed at assessing the leakage-pressure relation for transversal rectangular orifices. A CFD model was then implemented and calibrated with experimental results, to different geometric configurations of the orifice, with the aim of assessing the dependence of the orifice geometry and orientation on the calibration of leakage law parameters.

Auditory Warnings Invoking Startle Response Cause Faster and More Intense Neck Muscle Contractions Prior to Head Impacts

High-pressure level and sudden sound, especially during an elevated state of alertness can elicit a startle response. Startle response can induce sudden, intense muscle activations. Some studies have shown that increasing neck muscle activation during impact situations can reduce the risk of concussion and neck injury. This research aimed to study muscle coactivation patterns, contraction latency and the level of muscle activation in startle response compared to the voluntary response. To achieve this goal, a testbed capable of applying impacts to the head in four directions was created. Auditory (115 dB) startle stimulus was delivered and muscle activation measured using sEMG on neck muscles during startle and voluntary responses. We investigated a 1000 ms time period starting at the time that the sound is played to the time at impact. Results indicate that the first muscle activation in startle response is 2.1 times higher, 5.9 times faster and involved more muscles than in a voluntary response.

Advanced gas turbine performance modelling using response surface methods

ABSTRACTSurrogate models are widely used for dataset correlation. A popular application very frequently shown in public literature is in the field of engineering design where a large number of design parameters are correlated with performance indices of a complex system based on existing numerical or experimental information. Such an approach allows the identification of the key design parameters and their impact on the system’s performance. The generated surrogate model can become part of wider computational platforms and enable optimisation of the complex system without the need to run expensive simulations.In this paper, a number of design point simulations for a combined gas-steam cycle are used to generate a response surface. The generated response surface correlates a range of cycle’s key design parameters with its thermal efficiency while it also enables identification of the optimum overall pressure ratio and the high pressure level of the raised steam across a range of recuperator effectiveness, pinch temperature difference across the heat recovery steam generator and the pressure at the condenser. The accuracy of a range of surrogate models to capture the design space is evaluated using root mean square statistical metrics.

Second Law Analysis of an Organic Rankine Cycle Driven by Solar

In this paper, a thermal power system utilizing low-grade solar energy was proposed and analyzed. It can efficiently use the heat collected by the collector to provide electricity and also can provide some heat energy to satisfy the demand of heat. The system bases on the organic Rankine cycle. The evaporator employed in the system makes the organic working fluid turn to vapour phase at a high pressure level. Also a screw expander is employed in the system to conversion the heat energy to mechanical work. For the proposed system, a working condition was set and the performance of the system was calculated. When the temperature of the heat source is 95°C and the expander inlet pressure is 0.8MPa, the first law heat efficiency is 7.25% and the system exergetic efficiency is 10.14% for the system.

Dynamic Stability of Cylindrical Shells under Moving Loads by Applying Advanced Controlling Techniques—Part II: Using Piezo-Stack Control

The load acting on the actively controlled cylindrical shell under a transient pressure pulse propelling a moving mass (gun case) has been experimentally studied. The concept of using piezoelectric stack and stiffener combination is utilized for damping the tube wall radial and circumferential deforming vibrations, in the correct meeting location timing of the moving mass. The experiment was carried out by using the same stiffened shell tube of the experimental 14 mm gun tube facility which is used in part 1. Using single and double stacks is tried at two pressure levels of low-speed modes, which have response frequencies adapted with the used piezoelectric stacks characteristics. The maximum active damping ratio is occurred at high-pressure level. The radial circumferential strains are measured by using high-frequency strain gage system in phase with laser beam detection system similar to which used in part 1. Time resolved strain measurements of the wall response were obtained, and both precursor and transverse hoop strains have been resolved. A complete comparison had been made between the effect of active controlled and stepped structure cases, which indicate a significant attenuation ratio especially at higher operating pressures.

High Pressure and Flow Rate Measurements on Peroxide Dosing Pumps Under Laboratory and Site Conditions

The performance and reliability of peroxide dosing pumps are essential for every LDPE plant. The paper presents the results of measurement at an initiator injection pump under laboratory and site conditions. The recording was done with a flow meter and a high pressure transducer, both suitable for a maximum pressure of 400 MPa. It compares the results of hydraulic pressure inside the actuating cylinder at the intensifier with high pressure level and flow rate on the discharge connection of the pump. Direct measurement inside the high pressure cylinder and the possibilities to influence the fluctuations with a servo valve system round out the research work.

Critical Mass-Flow in Orifice-Nozzles at the Disintegration of Superheated Liquids

Flashing atomization is initiated when the superheated liquid is exposed to a sudden pressure drop below saturation vapor pressure at the prevailing temperature. Superheated atomization is used to enhance atomization where conventional pressurized liquid injection cannot achieve the desired fine sprays. Essentially flashing is initiated by in situ bubble nucleation followed by bubble growth. If the internal flow conditions are such that stable cavitation bubbles can form, then such bubbles promote the atomization of the base liquid already in the capillary of the nozzle. Bubble creation via cavitation can be achieved by changing the nozzle geometry such as the orifice length-to-diameter ratio, the inlet corner radius, the surface conditions of the nozzle material and the flow velocity in the orifice. In case of superheated atomization, the mass flow and thus the flow velocity in the orifice can just be indirectly set by the combination of superheat temperature upstream the nozzle and the difference between high pressure level upstream and ambient pressure downstream the orifice. Consequently the internal geometry and the material of the nozzle are of vital impact on the atomization process of the ejected liquid.