Energy Saving Potential in Existing Volumetric Rotary Compressors

The issues of energy and Carbon saving in energy intensive sectors, along with that of energy generation from renewable sources, have been recently receiving a growing awareness, as they are perceived as the most effective ways to deal with global sustainability commitments. The Compressed Air Sector (CAS) accounts for a 10% worldwide electricity consumption, and thus is being re-thought as an area offering great opportunities for improvement. Considering that the compression is responsible for a 10-15% consumption, it is vital to pay attention to machines performances. An overview of present compressor technology is given and saving directions for Screw and Sliding Vanes machines are analysed: interesting source of information was the Compressed Air and Gas Institute (CAGI), whose data have been processed, in order to obtain consistency with fixed reference pressures, and organized as a function of main operating parameters. The overall efficiency has been split and all different sub-terms (adiabatic, volumetric, mechanical, electrical, organic) considered separately. This has allowed a term-by-term evaluation of the margin for improvement. The heat recovery from the oil into mechanical energy via an Organic Rankine Cycle (ORC), together with the thermodynamic improvement during compression phase opens the way to a step change concerning the specific energy consumption. The Authors acknowledge Ing. Enea Mattei S.p.A. and particularly its CEO, Dr. Giulio Contaldi, for continuous research funding and support. The work has been done also under the FP7 Project "Complete Vehicle Energy-Saving CONVENIENT" funded by the European Commission

performances of an orc power unit for waste heat recovery on heavy duty engine

Abstract Reciprocating internal combustion engines (ICE) are still the most used in the sector of the on-the-road transportation, both for passengers and freight. CO2 reduction is the actual technological driver, considering the worldwide greenhouse reduction targets committed by most governments. In ICE more than one third of the fuel energy used is rejected to the environment as thermal waste through the exhaust gases. Therefore, a greater fuel economy could be achieved, if this energy was recovered and converted into useful mechanical or electrical power. This recovery appears very interesting, in particular for those engines that run at almost steady working conditions, like marine, agricultural, industrial or long-hauling vehicle applications. In this paper, an ORC-based power unit was tested on a heavy duty diesel engine. Energetic and exergetic analyses have been carried out in order to assess the real performances of the ORC unit and to individuate differences with the theoretical ones. A single stage impulse axial turbine has been tested in this work, complete with an electric variable speed generator and an AC/DC converter. The tests demonstrated that the energy conversion chain is not negligible at all and an overall net efficiency of the power unit was around 2-3 % with respect to a 10% of thermodynamic efficiency

Theoretical modeling and experimental investigations for the improvement of the mechanical efficiency in sliding vane rotary compressors

Positive displacement compressors lead the market of compressed air production for industrial applications. Among them, sliding vane rotary compressors represent an energetically virtuous alternative to the current compression technologies. In the present work, the effects of compressor design parameters were investigated through a comprehensive approach that aimed at addressing more efficient machines to promote sliding vane compressors as the key enabling technology in compressed air systems. A comprehensive mathematical model was developed to study the main phenomena occurring in this kind of compressors. The model provides the cell volume evolution over a whole rotation during which filling, compression and discharge processes occur. The first and latter phases are described by the quasi-propagatory approach that represents the inertial, capacitive and resistive features of one-dimensional unsteady flows. The dynamics of the compressor blades led to four different arrangements inside the rotor slots while an analysis of the hydrodynamic lubrication established between blade tip and stator wall focused on the oil film thickness evolution to prevent dry contacts. An extensive experimental campaign on a mid-size industrial compressor allowed the model validation at different outlet pressure levels and revolution speeds using a direct measurement of mechanical power and the reconstruction of the indicator diagram from piezoelectric pressure transducers. The friction coefficient at the contact points between blades with stator and rotor was estimated in 0.065 and further improvements of the mechanical efficiency were eventually addressed considering the roles of compressor aspect ratio, revolution speed, and blade tilt. The first two theoretical optimizations might lead to an increase of the compressor efficiency of 2 and 9 percentage points respectively. On the other hand, acting on the blade tilt would not produce relevant improvements.The Authors acknowledge Ing. E. Mattei S.p.A. and particularly its CEO, Dr. Giulio Contaldi, for continuous research funding and support. The work has been done also under the FP7 Project ‘‘Complete Vehicle Energy-Saving CONVENIENT’’ founded by the European Commission

Experimental assessments on a pressure swirl oil atomizer for positive displacement vane compressors

The current work presents an experimental characterization of a pressure swirl nozzle that is used to spray the lubricant in positive displacement vane compressors such that the overall convective heat transfer between oil droplets and air is able to lower the specific energy consumption of the machine, bringing the closed volume compression phase towards an isothermal transformation. An experimental test bench was designed and built to reproduce the compressor operating conditions. Tests at different injection pressures and temperatures allowed to estimate some macroscopic features of the spray, namely break-up length and cone spray angle. In particular, measurements showed that while break-up length decreased at high pressure and temperature up to 3.1 mm at 65◦C and 10 barg, the cone aperture tended to diverge from the nominal value of 80◦ up to 106◦. Furthermore, measurements with a laser diffractometric particle size analyzer allowed to retrieve the droplet size distribution and to estimate a key parameter for the heat transfer capabilities of the spray, namely the Sauter Mean Diameter (SMD). At 55◦C and 9 barg the droplet size distribution fitted a Rosin Rammler function with shape parameter of 1.87 and scale parameter of 228 μm while the spray SMD was 122 μm. In these operating conditions, a series of nozzles equally distributed along the closed volume compression phase of a mid-size industrial vane compressor would lead to specific power savings up to 0.3 kW/(m3/min), that corresponds to 20-25% of the saving potential achievable considering an isothermal compression. This methodology will allow to calibrate a simulation platform of the sprayed injection technique such that further refinements of the energy saving strategy will be addressed

The Potential of Mixtures of Pure Fluids in ORC-based Power Units fed by Exhaust Gases in Internal Combustion Engines

Abstract ORC represents an effective challenge in the waste heat recovery from ICEs. In spite of technological aspects, its thermodynamic design still deserves attention. Mixtures of pure fluids show interesting properties able to improve exergetic efficiency of the Rankine cycle, thanks to the positive slope of the phase changing. They can reduce also ODP and GWP, helping the replacement trends of working fluids. The paper optimizes cycle exergetic efficiency considering mixtures of pure fluids. The use of hydrocarbons in mixtures is particularly suitable and when used in limited fractions with other organic fluids they loses the limits related to the flammability.R245fa is a fluid that obtains a large net power increase when used in mixtures with hydrocarbons, compared to pure fluid an optimized R245fa/benzene mixture, for instance, attains an 11% net power increase

Development of a Sliding Vane Rotary Pump for Engine Cooling

Abstract The efficiency of a pump for engine cooling system in automotive sector can be very low (15%-20%) during the homologation cycle which is more oriented to medium and low engine loads. Actual pump technology makes reference always to centrifugal pumps, which suffer in terms of efficiency when the speed changes as well as when head and flow rate delivered. In order to reduce the power absorbed by the pump, a different type is needed. A sliding vane rotary pump (SVRP) is a serious alternative having all the characteristics to fulfil the engine cooling circuit with high efficiency and reliability. In this work, a SVRP has been designed, built and tested for an existing engine cooling circuit: its performances were compared to the traditional (centrifugal) pump which today is mounted on that engine. The benefits over the homologation cycle in terms of mechanical energy and CO2 saving have been emulated thanks to a comprehensive mathematical model

Combined photodynamic therapy and intravitreal bevacizumab for idiopathic polypoidal choroidal vasculopathy: one-year follow-up

Abstract OBJECTIVE: To report the efficacy and safety of combined photodynamic therapy (PDT) and intravitreal bevacizumab (IVB) injection in the treatment of idiopathic polypoidal choroidal vasculopathy (IPCV). MATERIAL AND METHODS: A prospective case series of 10 eyes of 10 consecutive patients affected by IPCV with subfoveal involvement. PDT plus IVB (1.25 mg/0.05 mL) injection two weeks later was performed in all patients. Two adjunctive injections of bevacizumab were scheduled at four and eight weeks after the initial treatment. Best-corrected visual acuity (BCVA), fluorescein and indocyanine green angiographies, and optical coherence tomography were obtained at baseline, and at one, three, six, nine, and 12 months. RESULTS: The combined treatment led to an improvement of both neurosensory detachment and pigmented epithelial detachment in all eyes, with a decrease of exudation and regression of macular thickness, which remained stable to the end of follow-up. However, BCVA remained stable over the 12 months of follow-up. CONCLUSION: These findings demonstrate that PDT/IVB combined therapy is able to achieve morphologic stabilization of the IPCV lesion, through a rapid decrease of macular thickness and regression of the size of polypoidal vascular lesion

Scoring rules in experimental procurement

We report the results of an experiment where subjects compete for procurement contracts to be awarded by means of a scoring auction. Two experimental conditions are considered, depending on the relative weight of quality vs price in the scoring rule. We show that different quality-price weights dramatically alter the strategic environment and affect efficiency. Our evidence shows that each weighting better delivers against a matching objective function than using a scoring rule which misrepresents the buyer’s objective function. Nonetheless, there are large deviations in how each performs, with the higher weight on quality delivering much greater efficiency evaluated against its own objective function than a low weight on quality evaluated against its own objective function, despite the higher quality weight inducing higher deviations from equilibrium. We propose a “mediation analysis” to show that the “direct effect” (due to the different strategic properties of the induced game-forms) outweighs the “indirect” one (how the different game-forms affect out-of-equilibrium behavior). We also perform a structural estimation of the Quantal Response Equilibrium induced by subjects’ behavior, where we find that subjects are risk averse and noisy play affects behavior in the direction of underbidding

Uprighting impacted mandibular second molar using a skeletal anchorage: a case report

The aim of this case report is to present an innovative combined orthodontic-surgical technique to disimpact mandibular second molar (MM2) using an orthodontic miniscrew and an elastic chain. The impact on the Oral health-related quality of life (OHRQoL) was also evaluated. Using the present techinique, it is possible to expose the impacted tooth, insert a self-drilling miniscrew in the retromolar area, and remove the bud of third mandibular molar. At the same time the orthodontic force is applied with the use of an elastomeric chain that connects the head of miniscrew and vestibular and oral buttons bonded on MM2. A close traction is performed for the whole treatment time without the reactivation of the elastic force. The use of skeletal anchorage allowed the disimpaction of impacted MM2 in a short treatment time (about three months) avoiding the typical biomechanical side effects of traditional orthodontic appliance and increasing the effectiveness of the treatment. Further studies are necessary to evaluate the real advantages and disadvantages of this combined orthodontic-surgical approach