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Benefiting from the electrification, using energy efficient high temperature heat pump is the key technology to tackle the challenges towards decarbonization of process heat. This work aims to upgrade district heating at 85 °C to process heating of supplying 1 MW steam at 160 °C using high temperature heat pump (HTHP) technology. Two different concepts of open and closed steam systems are considered. The former, which directly delivers steam from the compressor to the end user, proposes two layouts of cascade butane/steam and two-stage steam/steam. While the latter-including a two-stage flashed cyclopentane cycle-provides the opportunity, if the customer can't accept steam directly from the compressor, due to the pollution concerns. In the corresponding layouts, the use of either dry or oil injected gas compressor is examined. In addition, projecting various fuel prices till 2045, a comprehensive techno-economic analysis is developed for a case study. The results reveal that eventhough, the HTHP or HTHP involved integrated systems own higher investment costs, thanks to lower fuel costs, they can compete closely to the conventional natural gas and electric boilers. Specially, when the heat source is free, then an HTHP involved system demonstrates a better business case. [Display omitted] • Three new open/closed HTHP concepts to supply process heat at 160 °C are proposed. • District heat at 85 °C is used as available heat source for the proposed HTHPs. • Maximum COP of about 3 is achieved by the two-stage steam/steam HTHP layout. • Economic study is done for standalone/integrated systems based on HTHP or boilers. • Despite high CAPEX, in case of using free heat source, HTHPs are cost-effective. [ABSTRACT FROM AUTHOR]

To address the limitations of existing stall/surge warning methods—including variations in research subjects, sensor configurations, computational complexity, and the universality of thresholds—this study proposes a novel incipient instability warning approach utilizing adaptive wavelet synchrosqueezed transform. Each detection cycle begins with the acquisition of a low-pass filtered and downsampled total pressure signal from the compressor outlet, captured via a sliding window to represent the pressure sample. Then, the adaptive wavelet synchrosqueezed transform (AWSST), employing dynamic discretization with scales and synchrosqueezing technology, analyzes the real-time pressure sample to extract precise instantaneous frequency changes at low computational costs. Features of instability severity are derived from the amplitude, phase, and pressure drop within the time-frequency spectrum, leading to the formulation of a warning logic. The proposed method's effectiveness and universality are validated through hardware-in-loop (HIL) tests using multiple surge test data. Results show that the proposed method outperforms traditional real-time warning methods, which rely on the pressure change rate, by enhancing accuracy and advancing warning times by 15 ms–50 ms. Notably, the threshold is universal for compressors or engines of the same model. By increasing the acceptable performance decline criteria, compressors, turbofan engines, and turboshaft engines can employ a common set of thresholds. • Novel AWSST method enhances real-time detection of gas turbine engine instabilities. • AWSST offers superior accuracy and earlier warnings compared to traditional methods. • Validated through hardware-in-loop tests on various engines and surge inducements. • Effective implementation on embedded platforms with low computational costs. • Universal threshold settings applicable across different engine types and speeds. [ABSTRACT FROM AUTHOR]

Small-scale refrigeration centrifugal compressors hold the potential for superior efficiency compared to currently used positive displacement compressors. However, traditionally, centrifugal compressors have been employed in large refrigeration systems with cooling capacity of several hundred kilowatts or more. Conversely, the application of small-scale centrifugal compressors in smaller refrigeration systems, with cooling capacity in the tens of kilowatts, has largely remained theoretical, lacking practical experimental studies. For a better understanding of the operational characteristics of such systems, this study constructed a 45 kW R245fa refrigeration system test bench based on the small-scale oil-free centrifugal compressor utilizing gas foil bearings. The experimental investigation analyzed the impact of refrigerant charge amount, compressor speed, and coolant flow rate on system performance. Results indicate that the system achieves its peak cooling capacity of 49.73 kW with a system COP of 3.64 at 65,000 rpm. Moreover, at 50,000 rpm, the system demonstrates its highest system COP of 4.23 with a cooling capacity of 26.07 kW. In comparison to traditional positive displacement compressor refrigeration systems, it exhibits higher energy efficiency. Additional simulation studies were conducted to evaluate the effects of substituting R1233zd(E) for R245fa on the system performance and to assess the feasibility of such a substitution. • An Oil-Free centrifugal compressor with 45 kW cooling capacity was developed. • The maximum cooling capacity of the system is 49.73 kW with a COP of 3.64. • The maximum isentropic efficiency of the compressor is 0.83. • The performance and characteristics of this system are comprehensively analyzed. • R1233zd(E) is one of the most suitable alternatives to R245fa in the system. [ABSTRACT FROM AUTHOR]

The electric superchargers driven by a high-speed motor instead of exhaust gas to operate the compressor have excellent transient characteristics and can effectively reduce the turbo lag of diesel engines. To develop an optimal control strategy for the electric superchargers, it is necessary to explore the combined effects of the electric supercharger and turbocharger under transient processes. Therefore, this study investigated the influence of different intervention speed and time of the electric supercharger on the transient performances of a turbocharged diesel engine. The combined effects of the electric supercharger and turbocharger were analyzed to optimize control strategy through simulations. Effects of the optimization in control strategies were tested through engine experiments. According to the results, the optimized control strategy (slope control strategy) was able to effectively balance transient responsiveness and stability since the rise time of intake pressure were reduced by 52.5 % compared to the base engine and the fluctuations in intake pressure and engine torque were significantly eliminated. Besides, the slope control strategy achieved the lowest PM and NOx emissions during the transient loading process. • The transient characteristics are greatly improved by the electric supercharger. • The combined effects of the electric supercharger and turbocharger are investigated. • An advanced control strategy of the electric supercharger is developed. • Emissions during the transient process are reduced by the electric supercharger. [ABSTRACT FROM AUTHOR]

This study investigates the effects of different bleed air CFD modelling methods on the aerodynamic simulation of a heavy-duty gas turbine multistage compressor with bleed airflow. Two methods, the local source term method and the simplified bleed off-take geometry method, are compared. The results reveal that while overall compressor performance shows minimal variation between the methods, significant differences are observed near the blade tip region. The bleed source term method predicts a more uniform flow field in the bleed cavity, leading to a larger surge margin for the compressor. Therefore, in the analysis of multistage compressors, it is advisable to adopt simplified geometric modeling method for simulating bleed air extraction. Moreover, when utilizing this approach, careful consideration should be given to the choice of the slot inclination angle. This design parameter presents a crucial trade-off between losses within the exhaust structure and those arising from the entry of mainstream flow into the exhaust slot cavity. • Comparison of bleed simulation methods: the local source term method and a simplified bleed structure method. • Impact of bleed slot angles: impact of three bleed slot angles on the outlet flow field parameters of the compressor. • Analysis of internal bleed losses: decomposes the bleed slot based on flow lines and velocity distribution. • Significance for industrial applications: valuable insights for industrial gas turbine compressors and bleed systems. [ABSTRACT FROM AUTHOR]

Natural Gas (NG) is constantly increasing its importance and widening its penetration in the world energy mix, so that the topic of its reliable and efficient transportation represents an enduring challenge of utmost importance. Within this framework, the design and operation of NG compression stations is a key aspect, significantly influencing the operation expenses of gas transport companies. Such plants are characterized by an increasing level of complexity both for the choice of the technology to adopt for gas compression and for the plant layout and integration, facing a combination of diverse energy demands including electric power, thermal and cooling demands. The present study is developed mining the data provided by the Italian natural gas infrastructure company, Snam Rete Gas, for a key compression station in the North-East of Italy. A feasibility study to increase the capacity of the compressor station has been carried out and an innovative trigenerative application has been proposed to fulfill the overall plant energy requirements, reducing primary energy needs by nearly 30%. Thanks to the outcome of the study, such trigenerative solution has been deployed by Snam Rete Gas. • A case study of a North Italian compression station owned by Snam Rete Gas. • A solution to increase efficiency and reliability of natural gas compression stations. • A comprehensive analysis of the diverse energy demands of the compression station. • Feasibility study of a trigenerative application to fulfill overall energy loads. • The trigenerative plant allows the reduction of primary energy needs by nearly 30%. [ABSTRACT FROM AUTHOR]

Hydrocarbons in the form of natural gas can be used in long-term energy production and could strengthen the defossilisation of the energy sector. However, operational reliability will decrease due to gas shortages in integrated energy systems. Correlations exist among the multiple failure patterns such as overloads of the transmission lines, overloads of the combined heat and power generator, and over-limit operations of gas compressors. The energy reliability assessment problem becomes more difficult to resolve for integrated energy systems than for power systems. This paper proposes an analytical method to address the multiple correlated risks that are caused by the energy network interactions in an integrated energy system. Three case results in MATLAB demonstrate the accuracy and computational efficiency of the proposed method. Compared to the Monte Carlo algorithm, which required approximately 550 s to obtain a precise failure probability with 50 thousand samples, the proposed method takes approximately 12.7 s to obtain an exact failure probability. The advantage is that, different from wide-bound theory and narrow-bound theory, the proposed method can offer a certain value rather than two bounds with respect to the failure probability. • The correlations among different failure patterns are established for integrated energy systems. • Theoretical analysis and statistical experiments are presented to estimate IES reliability. • Network constraints are modelled to fully analyse the nonlinearity of the IES failure estimation. • Both the estimation accuracy and efficiency are ensured using the proposed analytical method. [ABSTRACT FROM AUTHOR]

The global rising demand for civil air travel shows good prospects for the industry, however, this growth is inevitably matched with higher levels of emissions and fuel consumption. In this study, demineralised water injection is presented as an alternative to reduce NO x emissions and enhance engine performance. The experimental study firstly presents the droplet size characterisation of a spray nozzle. This is done for varied injection pressure, water temperature and at varied axial and radial locations using an impaction pin nozzle. The single-shaft Artouste engine is used in conducting the compressor water injection test with water-to-air ratios of 0.5, 1 and 2%. The water droplet diameter, engine gas path and exhaust emissions are all monitored in real time. For the engine tests, droplets are measured at the spraying point and correlations are used to account for the droplet size at the inlet of the compressor due to measurement difficulties in this region. The test showed a reduction in compressor discharge temperature by up to 34 K and a NO x decrease by 25%. Nevertheless, the higher reductions in NO x at higher water-to-air ratios are attributed to a predominant cooling in the combustor because of unevaporated water in the compressor. At 0.5% water-to-air ratio, the drop in NO x is mainly due to compressor cooling and signified by the only case in which the fuel-to-air ratio reduces. The study presents evidence of the combined effects of compressor and combustor water ingestion. The CO is seen to increase significantly and associated with reduced combustor efficiency. • Droplet size sensitivity study is conducted. Factors affecting these are quantified. • Spraying nozzles are used to inject water into the compressor of a gas turbine. • Compressor water injection at 2% leads to a drop in compressor temperature of 37 K. • The reduced cycle temperature results in a 25% reduction in NOx emissions. • Droplet size, engine performance and emissions are all monitored simultaneously. [ABSTRACT FROM AUTHOR]

Abstract Natural gas compressor stations represent a huge potential in terms of waste heat recovery. Typical installations consist of multiple gas turbine units, in mechanical drive arrangement, operated most of the time under part-load conditions. The paper investigates the feasibility of Organic Rankine Cycle application as bottomer recovery technology in natural gas compressor facilities. The aim of the performed analysis is to obtain a detailed techno-economic and environmental scenario of the integrated system on yearly base. Different commercial gas turbine models, in the size range from 3 to 30 MW, have been taken into account as representative of mechanical driver units. Bottomer configurations (with & without intermediate loop) are modelled and compared assuming two different organic fluids. A sensitivity analysis of the bottomer cycle is carried out aimed at maximizing ORC shaft power output for each investigated layout. Off-design part-load operation of the integrated cycles have been simulated with reference to one minute data typical GT operation on a yearly base. The goal of this work is: (i) to assess the actual performance of merging gas turbines and ORC units for efficient power generation under variable operating conditions; (ii) to analyze the real potential of state-of-the art technology in the proposed innovative application. Highlights • Techno-economic investigation of ORC potential, in a real NG compression stations. • Retrofit with ORC commercial GTs, widely diffused in compression facilities. • Simulate part-load of selected GTs according to different control load strategies. • Investigate different organic fluids and topper-bottomer integrated layouts. • Define, for each GT-ORC layouts, optimal design and estimate off-design behavior. [ABSTRACT FROM AUTHOR]

Abstract An industrial highly loaded gas compressor with the large turning angles in gas turbines always causes the serious flow separations, which leads to the significant increase in aerodynamic losses and the evident deterioration of the pressure rise ability. In order to solve this issue, a novel active flow control technique inspired by the Coanda effect is introduced in this study. Here, the Zierke & Deutsch airfoil with the camber angle of 65° is selected for the reference profile of the highly loaded compressor cascade. Design of Experiment (DOE) is firstly used to obtain the sensitivity information of the geometric parameters in building the Coanda jet flap. The cascade shape with the optimal aerodynamic performance is then figured out based on the optimization method. The comparison of the flow details between the optimization result and the prototype is performed to further understand the flow mechanisms behind the performance enhancement. Finally, the experimental measurements are conducted to validate the effectiveness of the well-designed Coanda jet flap in the wind tunnel. The numerical and experimental results show that the Coanda jet can effectively improve the aerodynamic performance of the highly loaded cascade. A tradeoff exists between the increased mixing losses near the slot and the decreased shearing effects near the trailing edge when the mass flow rate of the Coanda jet is increased. The total pressure losses can be reduced by up to 18.4% when the normalized mass flow rate of the jet flow is equal to 1%. Meanwhile, the static pressure rise coefficient can be increased by 8.8% when the mass flow rate of the Coanda jet is equal to 1.5%. Highlights • Coanda jet flap efficiently enhances the performance of industrial gas compressors. • Flow control mechanisms of Coanda jet in highly loaded compressor are summarized. • Optimal Coanda jet flap design is obtained by employing the optimization method. • Experimental measurements validate the effectiveness of Coanda jet flap. • Some design criterions are proposed to guide the further Coanda jet flap designs. [ABSTRACT FROM AUTHOR]

Abstract Employing the systems which make use of waste heat for upgrading its temperature is of great importance for their energy saving potential. In this research, the thermoeconomic analysis of a novel ejector boosted hybrid heat pump (EBHP) is evaluated and compared with three other types of heat pumps namely the absorption, compression, and absorption/compression heat pumps. The analysis uses the exergy costing method that combines the exergy concept with the economic analysis to evaluate the unit cost of final product at the wide operating range. The results reveal that the advantages of the proposed heat pump from the thermoeconomic view point are clear in higher upgraded temperatures. A detailed analysis of the different thermoeconomic variables is also conducted and the contributions of each component in the overall cost of the heat pumps are evaluated. In addition, effects of various decision variables on the economic performance of the systems are studied. The investigations demonstrate that the concentration of ammonia in hybrid heat pumps and the pinch point temperature difference in all of the studied heat pumps affect the final unit product cost of the systems considerably. Highlights • An ejector boosted hybrid heat pump is compared with three other types of heat pumps. • Thermoeconomic variables are used to analyze the economic performance of each component. • For low temperature lifts, the absorption heat pump has lower unit product cost. • As the temperature of upgraded heat increases, the EBHP shows better performance. • The effect of operating parameters on the product cost of the systems is investigated. [ABSTRACT FROM AUTHOR]

Abstract In this paper, a method for improving the efficiency of the cascade mechanical compression–ejector cooling cycle is described. The considered cooling cycle is the combination of the electrically driven carbon dioxide (CO 2) subcritical mechanical compression cooling cycle as a bottoming cycle, and the heat driven ejector cooling cycle as a topping cycle. This cooling cycle is proposed to use superheated CO 2 vapor to preheat the working fluid supplied to the vapor generator, thus improving the whole system's efficiency. This paper provides thermodynamic analysis results for the cascade cooling system in a wide range of evaporating temperatures. Refrigerants R245ca, R600, and R601b were investigated as the working fluids for the ejector cooling cycle, and the results show that the proposed cooling cycle is the most effective at low evaporating temperatures. Highlights • A cascade CO 2 mechanical compression–ejector cooling cycle is studied. • Refrigerants R245ca, R600 and R601b are used for the ejector cooling cycle. • Performance improvement regarding COP, COP THERM and exergy efficiency is evaluated. • The refrigerant preheating has considerable influences on the cascade cycle performance. • The proposed cascade cooling cycle is compared with conventional cycle. [ABSTRACT FROM AUTHOR]

Abstract In this study effects of compression ratio on HCCI combustion, performance and emissions was investigated parametrically. In addition to parametric investigation and as a novel way of the paper engine BSFC maps were obtained for RON20 andRON40 fuels and each compression ratios of 9:1, 10:1, 11:1 and 12:1. The parametric experiments were carried out at 800 rpm engine speed. In both parametric and mapping experiments were conducted at intake temperature of 353 K. In-cylinder pressure, ROHR, combustion duration, start of combustion, indicated mean effective pressure, thermal efficiency and CO, HC and NO x emissions were examined. It was determined that in-cylinder pressure and rate of heat release decreased while the mixture getting leaner. The increase of octane number of fuel led to extension of combustion duration. On the contrary, combustion duration decreased along with the increase of compression ratio. It was found that the CO and HC emission were high while NO x emissions were low at lower CR. With the increase of CR, CO and HC emissions decreased however NO x emissions increased. The maximum thermal efficiency was obtained as 38.2% at 800 rpm and 12:1 CR with RON40 fuel. The widest operational region was obtained with RON20 fuel at CR of 10:1 with a minimum BSFC value of 210 g/kWh. Highlights • RON20 and RON40 fuels were tested in A HCCI engine at different compression ratios. • RON, lambda and compression ratio effects on HCCI engine was examined parametrically. • Additionally BSFC and operation maps were determined for each compression ratio. • RON40 seems more suitable fuel due to controlling the HCCI combustion in all compression ratios. • Largest operation map in terms of engine load and speed was obtained with RON20. [ABSTRACT FROM AUTHOR]

Abstract As known that the cooling technology is commonly used in the turbine to protect the turbine blade. The mixing and heat transfer between the high pressure cooling air from the compressor and the turbine main flow would cause energy loss, and it will influence the gas turbine cycle performance. However, the existing definitions of the cooled turbine efficiency always take no account of the work which is added to the cooling air to product high pressure in the compressor, thus, the cooling influence on the gas turbine cycle performance cannot be indicated by using the existing cooled turbine efficiency. In this paper, a definition of cycle based comprehensive efficiency for a cooled turbine is presented, in which the work added to the cooling air during its compression process is considered. The existing efficiency definitions are first reviewed, then, the definition of the cooled turbine comprehensive efficiency is presented and validated numerically to show its capacity. Finally, the redesign of a high-pressure turbine is provided. The result shows that the new efficiency can evaluate a cooled turbine performance comprehensively, and can be used as a reliable evaluation criterion for the optimal design of a turbine or a gas turbine cycle. Highlights • Provide a definition of cycle based comprehensive efficiency for cooled turbines. • Compare the new definition with the existing efficiency definitions. • Capable of considering the influence of coolant fraction on cycle performance by affecting turbine efficiency directly. • Capable of providing a more reliable method to evaluate the optimization design of cooled turbines. [ABSTRACT FROM AUTHOR]

Abstract This paper presents a hybrid power generation system comprising of Photovoltaic (PV) panels, Molten Carbonate Fuel Cell (MCFC), Gas Turbine (GT), Thermal Energy Storage (TES), Battery (Bat) and a Compressed Air Energy Storage (CAES) system. The CAES pressure was considered to be regulated using a water reservoir system located at a suitable height place. The described system was designed to supply the electricity needs of 500 households with peak electricity demand of 500 kW. A set up MCFC/GT with power generation rate of 500 kW was considered in the calculations, and the PV system capacity was considered to be changed from 100 kW to 600 kW. The optimal configuration and operational conditions of the system were conducted based on the Levelized Cost of Electricity (LCOE) definition as well as the total annual emission that is occurred by the auxiliary fossil fuel boiler and MCFC systems. The results showed that the overall system efficiency would be increased by about 25%, when the CAES is used and the compressor is switched off. Also, the optimal operational pressure of MCFC was found to be 6 bar for 2000 number of PVs, 1500 kWh of battery storage and CAES capacity of 685 m3. Highlights • Investigate the combination of MCFC/PV/GT system for generating a determined electricity load. • Using of the storage systems to obtain the high reliability. • Consider the effect of different parameters on operation of the hybrid system. • Suggestion of using a water reservoir with CAES to generate a constant pressure supply air. • Using a hybrid electrical energy storage to reduce the waste of PVs generated power. [ABSTRACT FROM AUTHOR]

Abstract Electric power and natural gas networks are coupled through several types of network facilities. These interdependencies are getting stronger and should be considered at both the operational and the planning stage. Hence, it is necessary to have a powerful simulation model that is capable to simultaneously analyze these two coupled networks in a single simulation environment. This can be done by an equivalent electrical model of the whole multi-energy system. In this study, the behavior of an ideal, as well as a real natural gas compressor station, has been analyzed and electric analogy steady state models are given. The verification of the presented model is obtained by two case studies. In the first, the presented model is verified through a wide range of input data by comparing its simulation results with the results obtained by SIMONE - commercial software package for gas network simulation that is widely used in Europe. In the second, a real natural gas compressor station is modeled with the presented approach and the obtained results are compared with the measurements. In both cases, the results have shown a very high precision of the presented model and confirmed the proposed modeling principles and the approach. Highlights • Electrical analogy approach has been employed to model a gas compressor station. • Steady-state electrical equivalent models of gas compressor station are proposed. • Verification has shown a very high precision of the presented model. • The sensitivity of the calculation process on the main variables has been performed. [ABSTRACT FROM AUTHOR]

In oil and gas industry, the performance prediction of gas compressors is approaching criticality. Usually, maintenance engineers rely on recommendations set by the original equipment manufacturer (OEM) for maintenance activities. Since compressors are operated in offshore conditions, OEM recommendations may over predict or under predict the maintenance schedule. An improper verdict on compressor maintenance interventions may increase the equipment downtime because of unavailability of the resources and poor readiness of the spare parts. The aim of the presented research was to develop a diagnostic model for gas compressors by using the genetic programming (GP). The OEM isentropic and actual isentropic heads were compared, and the maintenance activity of a gas compressor was predicted by calculating the performance degradation. The computational codes were developed separately for OEM isentropic and actual isentropic heads through GP. Hereinafter, the empirical equations were derived from the developed computational codes to predict the optimum time for the routine maintenance. For rotational speed between the tested regions, GP predicted 92% accurate interpolation between the curves. It reveals that using the developed GP model, the operators can accurately predict the compressor's health and plan ahead the equipment maintenance at any time. [ABSTRACT FROM AUTHOR]

In a vehicle with a CI (compression ignition) engine, the power of the latter rotates an electric generator to produce a mixture of hydrogen (H 2 ) and oxygen (O 2 ) gas (hydrooxile – HHO, later just HHO) by water electrolysis. Low HHO content levels in air (0.14–0.18% of the volume) combined with air in cylinders of the CI engine affect the energy and environmental performance of the engine. It was found through stand tests and numerical modeling that chemically active hydrogen starts to ignite at the end of the compression stroke when the pressure and temperature rise prior to fuel injection into the cylinder. Early hydrogen ignition and supplemental energy consumption for HHO gas production worsen the energy performance of the engine and increase concentrations of carbon dioxide (CO 2 ) and nitrogen oxide (NO x ) in the exhaust gas. However, H 2 and O 2 additives reduce concentrations of incomplete combustion products (carbon monoxide (CO) and hydrocarbons (HC)) as well as the smokiness of the exhaust. When diesel fuel is replaced with biodiesel and when HHO gas is added, the indicated efficiency of the engine changes insignificantly; however, concentrations of CO and HC in the exhaust gas and smoke levels are reduced markedly. [ABSTRACT FROM AUTHOR]

Supercritical helium has been considered as an ideal working fluid in a number of design studies for closed Brayton cycle due to its thermal properties. But the low density level of supercritical helium, the characteristics of the small flow channel in the turbomachine and the variable working condition method of the system determine that the compressor may run at low Reynolds number. In this paper, the influence of Reynolds number on supercritical helium compressor rotor is investigated under different conditions by numerical simulation program. Effects of specific heat ratio on Reynolds number sensitivity of supercritical helium compressor rotor are also investigated by comparing the calculated results of different working fluids. Special attention is paid to the relationship between properties of working fluids and efficiency. Then, the equations of efficiency and total pressure ratio for different working fluids are established. The results show that the Reynolds number sensitivity of supercritical helium compressor rotor decreases with the increase of tip clearance and increases with the increase of the specific heat ratio. [ABSTRACT FROM AUTHOR]

One of the challenges in cooling science today is the development of vapour compression system that is compact, scalable and highly energy-efficient. In order to achieve this goal, the novel cross vane expander-compressor (CVEC) has been introduced. This device amalgamates the working principle of the compressor and expander into a single unit, permitting fluid compression and expansion energy recovery to be accomplished simultaneously. In this paper, we describe theoretically the frictional losses of the CVEC and predict its net power input per cycle. CO 2 is used as the working fluid for simulation purposes. The mechanical efficiency of CVEC is found to be 95.9% where the largest loss is caused by end-face friction which accounts for 81.2% of the total losses. The proposed CVEC system improves the overall coefficient of performance (COP) by 36.6% as compared to that of the basic vapour compression system. An experimental investigation is conducted for the measurement of torque and speed of a CVEC prototype to verify its operational characteristics. For initial testing purposes, air is used as the working fluid in an open circuit. The average discrepancy between the predicted and measured net power input was found to be 10.5%. [ABSTRACT FROM AUTHOR]

A new thermoacoustic-Stirling engine is introduced, composed of a compressor, regenerative assemblies, displacers and an alternator. The regenerative assemblies are coupled to displacers to successively multiply the acoustic power input by the compressor. The amplified acoustic power is converted into electric power in the alternator. This new configuration overcomes the limitations of traditional thermoacoustic or Stirling engines, including losses in long resonant tubes, response hysteresis and current inversion. The design method of the displacers and alternators is presented. Numerical simulations are carried out to investigate the characteristics of this system. Results show that the overall efficiency of this system could reach 47% with heating temperature of 900 K. Changing alternator load is the most plausible factor in piston or displacer exceeding the displacement limit. These parts can be effectively protected as long as the voltage of the compressor can be instantaneously adjusted. The working frequency, charging pressure and mechanical resistance do not substantially influence the efficiency and power capacity, when varied within a limited range. This allows the proposed engine to work stably when these parameters deviate from the design. [ABSTRACT FROM AUTHOR]

Carbon dioxide capture, utilization, and storage (CCUS) is an attractive method to reduce carbon dioxide (CO 2) emissions originating from fossil fuels burned from large single-point sources. CO 2 separation from a CO 2 -laden gas stream is the first stage of CCUS. In this investigation, a cryogenic distillation-based CO 2 separation process (CCSP) is developed. CCSP is modified to utilize waste heat obtained in the process for reducing the energy consumption of CO 2 separation. Two modifications are carried out in the process which include (i) heat integration (HI) with CCSP (CCSP + HI) of the reboiler with the heat from hot streams available in the process and further, (ii) energy recovery by using the organic Rankine cycle (ORC) operating between gas compressor temperature and ambient temperature (CCSP + HI + ORC). The parametric and 4 E (energy, exergy, economic, and environmental) analysis results obtained for the CCSP + HI, CCSP + ORC, and CCSP + HI + ORC processes are compared with those of CCSP. The net electrical energy required to operate the compressor for CCSP is 2.7%, 7%, and 21.8% higher than that for CCSP + HI, CCSP + ORC, and CCSP + HI + ORC, respectively. • Cryogenic distillation process for CO 2 separation is examined. • The heat integration of the stream with the reboiler would reduce the energy penalty of the distillation process. • Waste heat available in the compressor would reduce the energy penalty of the process by using ORC. [ABSTRACT FROM AUTHOR]

Considering the need for a reliable and environmentally friendly energy storage solution for addressing renewable energy intermittency issue and following the developments on Isothermal Compressed Air Energy Storage (I-CAES) systems, a new finned piston compressor which is characterized by increased heat transfer area and coefficient has been designed, analyzed, manufactured and experimentally tested. This compressor includes two sets of concentric annular fins with different diameters: the mobile fins are pushed into the space between the stationary fins through a driver shaft and compress the air trapped in the interconnecting annular chambers while keeping the air temperature close to ambient. Modeling of heat transfer and fluid flow in such a complicated geometry with a transient, non-linear, multi-layer, multi-dimensional nature can be best done by equivalent electric analogies with variable resistances and capacitors and employing a lumped method. Using bond graph representation method and based on a previously developed model for a classic reciprocating compressor, energy conversion has been modeled using a conjugate heat transfer and fluid flow model. Results of the simulation are presented and have been validated using an experimental test bench and to provide contrast to current technology, compared to a classic reciprocating compressor. The heat transfer along one cycle has increased in the finned compressor by 32 times compared to a classic piston compressor. The results also reveal that however the volumetric efficiency is decreased slightly in the finned compressor (−8%), the exergetic efficiency has increased from 55.1% in a classic piston to 78.4% in the finned piston. [ABSTRACT FROM AUTHOR]

Sensors play essential roles in the refrigeration and air conditioning systems. The faults of sensors may result in the decrease of system performance and waste of energy. It is not easy to discover the sensor bias, since its occurrence is always random and unpredictable. The data-driven based evaluation logic is proposed to assess the measurement reliability of sensors in the refrigeration and air conditioning systems. The subtractive clustering is presented to classify and recognize the various operation conditions adaptively. The principal component analysis models constructed upon the known conditions are developed to detect the measuring faults of sensors. Two statistics of T 2 and SPE are combined to evaluate the measurement reliability of variables, which are divided into monitoring-type and controlling-type according to their attributes in the control loops. Ten fault cases, which include the fixed and drifting biases of various temperature and pressure sensors, are tested in a real vapor compression system. [ABSTRACT FROM AUTHOR]

Compression and purification unit (CPU) is a common industrial process for capturing CO 2 from oxy-fuel combustion where high energy requirement is one of its disadvantages. This study focuses on analyzing of the sensitivity and optimizing multi-objectively the operating conditions of CPU, using response surface methodology (RSM). The main objective was to increase the efficiency of CO 2 removal from the oxy-fuel combustion power plant. Statistical analysis reveals that reducing the first separator temperature, not only, plays a major role in CO 2 separation, but also, it decreases the total work and heat duty of the process. It was found that the optimal multi-stage CO 2 compressor discharge pressure was 25.34 bar while regular pressure for this process was reported as 30 bar. Furthermore, the optimal flue gas temperature before, between and after compression, and the first and second flash separator temperatures were 20 °C, 20 °C, 20.6 °C, −38.2 °C, and −55 °C, respectively. with the previous works carried out in a constant amount of CO 2 separation, the proposed process leads to lower pressure, and therefore lower operating and capital costs. [ABSTRACT FROM AUTHOR]

Fuel efficiency of aircraft and helicopter becomes greater concern in recent years caused by rising fuel costs and as well as environmental impact of aviation emissions. Modern helicopters, however, highly complex systems with especially turboshaft engines that produce energy and power. So it is important to gain deeper understanding energy and exergy use throughout turboshaft engine and its components. Concurrently, in this study, energy and exergy-based computational approach applied to a turboshaft engine and its components. Exergy efficiency of the axial, centrifugal compressors and power turbine is found to be between 83.8% and 88.6%, while for the combustor, the corresponding value is to be 80.60%. For the components, the greatest exergy efficiency is calculated to be 91.4% at the gas generator turbine unit. As a result of the study, the exergetic efficiency of the turboshaft has been calculated as 27.5% with 1500 kW product exergy. It is expected that numerical formulation based on energy and exergy is beneficial for assessing turboshaft performance for future rotorcraft development. [ABSTRACT FROM AUTHOR]

A scheme of the DME-diesel dual-fuel PCCI (premixed charge compression ignition) combustion is an attractive option of relatively high thermal efficiency, low emission and operating costs as well as availability of wide DME (dimethyl ether) resource. However, one of the main problems in the DME-diesel dual-fuel PCCI operation is that an early start of combustion easily leads to detonation due to high cetane number and better auto-ignition property of DME, and above-mentioned phenomenon is especially pronounced with a large DME energy ratio or at higher loads. Thus, LPG (liquefied petroleum gas), as a kind of ignition inhibitor, is added into DME for changing the property of port premixed fuel, and the effects of LPG quantity on the combustion and exhaust performance of a DME-diesel dual-fuel PCCI engine is investigated in this paper. Experimental results show that the appearing positions of the maximum cylinder pressure and mass-averaged temperature shift towards later crank angles and their peak values decline slightly when LPG mass fraction in DME/LPG mixture (f L ) increases. The start of combustion postpones, and the combustion duration shortens with a rise of f L. Simultaneously, brake thermal efficiency and NO x emission reduce slightly; whereas the number concentration of particles firstly increases but then decreases with a rise of f L . [ABSTRACT FROM AUTHOR]

In this work, a freezing desalination unit is integrated into a conventional combined power plant to improve the plant performance and produce desalinated water. A mathematical model is developed to simulate the modified cycle. The effect of compressor inlet air temperature on thermal performance, desalinated water production capacity and specific fuel consumption is examined. Results of the modified cycle were compared to that of the conventional cycle. The results show that the proposed system is capable of producing up to 2.74 million m3of desalinated water annually from a brackish water source (TDS of 2000 mg/l) with an increase in the Energy Utilization Efficiency (EUE) by 15% as compared to the designed value under ISO standard conditions. Furthermore, operation cost for fresh water production is also examined, results show that the fuel cost of 1 m3 of desalinated water varies between (0.56–0.58) $/m3 compared with 0.66 $/m3 and 0.93 $/m3 for desalination technologies of R. O and MED, respectively. • A novel modification to a combined power plant is introduced. • Freezing desalination unit is integrated for power plant performance improvement and desalinated water production. • The effect of gas turbine compressor inlet temperature on the proposed system performance has been examined. • An economic study for the suggested cogeneration system is performed based on sensitivity analysis. [ABSTRACT FROM AUTHOR]

Syngas produced from gasification of solid fuels can serve best as transition fuel from the carbon-based to the hydrogen-based fuels in the internal combustion engines. The lone drawback is its low calorific value being between one tenth and one fifth of that of CNG (Compressed Natural Gas). This results in higher BSFC (brake specific fuel consumption) and limitation on the injection duration at late injection timings in the DI (direct-injection) SI (spark-ignition) engine. Recently, there have been efforts to enrich the syngas with methane so that the calorific value can be improved. This paper presents experimental results on the effect of methane-enrichment of syngas on the combustion, performance and emissions in the DISI engine. The result shows that the MES (methane-enriched syngas) has extended the operation excess air ratio (λ) compared to syngas and CNG at the same engine speed. Methane-enrichment has maintained the faster and smoother combustion, the lower brake emissions of carbon monoxide and total hydrocarbon, and higher brake emissions of nitrogen oxides observed with syngas. Besides, MES improved the maximum brake thermal efficiency and the BSFC of the syngas by 30.2% and 21.3%, respectively. Therefore, MES can be better replacement to CNG in the DISI engine at all load conditions. [ABSTRACT FROM AUTHOR]

The IHX (internal heat exchanger) is introduced in some refrigeration systems in order to achieve higher energy performances. Results obtained vary greatly depending on the refrigerant used and working conditions. This paper describes a drop-in analysis of IHX effects on the performance of a vapour compression system using R1234ze(E) and R450A (R134a/R1234ze(E) commercial mixture) as R134a low-GWP replacements. The tests were carried out in a completely monitored vapour compression system varying the condensing and evaporating temperature, with and without a counter-current flow tube-in-tube IHX. Because the cooling capacity rises and the power consumption remains similar, the conclusion is that the IHX has a positive influence on the energy efficiency for all refrigerants tested. The COP (coefficient of performance) gain using R1234ze(E) is the highest observed (overcomes the R134a COP for the same conditions). The R1234ze(E) and R450A discharge temperature increments are lower than those of R134a so does not reach dangerous values and the IHX pressure drops are also below than that of R134a. [ABSTRACT FROM AUTHOR]

Six stroke engine presented by Conklin and Szybist is an effective way to recover energy of exhaust gas by adding a partial exhaust stroke and steam expansion stroke. Characteristics of the engine are analyzed and its disadvantages are pointed out. A new six stroke diesel engine is presented here. It refers rankine cycle inside cylinder. Total exhaust gas is recompressed and at a relatively low back pressure in the fourth stroke water is injected to which maintains liquid phase until the piston moves to the TDC. At c′ 720 °CA (crank angle) the water becomes saturated. An ideal thermodynamics model of exhaust gas compression, water injection and expansion is constructed to investigate this modification. Properties at characteristic points are calculated to determine the increased indicated work. Results show that the work increases with the advance of water injection timing and the quality of water. The cycle is more efficient and the new engine has potential for saving energy. Moreover, it is forecasted that HC and PM emissions may reform with steam in reality and H 2 is produced which will react with NO X . [ABSTRACT FROM AUTHOR]

T-ORVC (Transcritical organic Rankine vapor compression) refrigeration system for intercity bus air-conditioning using engine exhaust heat is investigated. Wet refrigerant R134a and dry refrigerant R245fa are considered as refrigerants. Typical efficiencies for pump, turbine and compressor utilized in literature (namely LV (low values), MV (medium values) and HV (high values)) are compared for the influence on COP (coefficient of performance) of the system analyzed. The results are strongly dependent upon the efficiencies. COPH (coefficient of performance for heat energy) used for the heating of the refrigerant, coefficient of performance for electrical energy (COPW) needed for the pump and coefficient of performance for both heat energy and electrical energy (COPT) needed together for the heating of the refrigerant and for the pump (COPT) are calculated. Besides the isentropic efficiencies, mechanical, electromotor and electric energy production efficiencies are also taken into account. Using MV efficiencies, COPT values at 8 MPa pressure can be as high as 0.54 and 0.66 at 180 and 200 °C temperatures for R134a and R245fa, respectively. COPW values are very high and therefore electrical energy need is very low as compared to exhaust heat energy need. Assuming 30 kW of cooling load for an intercity bus and under different engine loads, all heat exchanger properties are determined. The results for a cooling load of 30 kW show that using T-ORVC (organic Rankine vapor compression cycle) system, air-conditioning of the intercity buses can be realized using waste heat energy of engine exhaust gases. [ABSTRACT FROM AUTHOR]

In this study, a thermodynamic comparison of five supercritical carbon dioxide Brayton cycles integrated with a solar power tower was conducted. The Brayton cycles analyzed were simple Brayton cycle, regenerative Brayton cycle, recompression Brayton cycle, pre-compression Brayton cycle, and split expansion Brayton cycle. A complete mathematical code was developed to carry out the analysis. A heliostat field layout was generated and then optimized on an annual basis using the differential evolution method, which is an evolutionary algorithm. The heliostat field was optimized for optical performance and then integrated with the supercritical CO 2 Brayton cycles. Using the results of the optimization, a comparison of net power outputs and thermal efficiencies for these cycles was performed. The findings demonstrated that the highest thermal efficiency was achieved using the recompression Brayton cycle, at June noontime. The maximum integrated system thermal efficiency using this cycle was 40% while the maximum thermal efficiency of this cycle alone was 52%. The regenerative Brayton cycle, although simpler in configuration, shows comparable performance to the recompression Brayton cycle. This analysis was carried out for Dhahran, Saudi Arabia. [ABSTRACT FROM AUTHOR]

The study focuses on the effect of CR (compression ratio) on the emission, performance and, combustion characteristics of a gasoline engine fueled with iso-butanol (10%, 30% and 50%) blended gasoline fuel. The tests were conducted for three different CRs (9:1, 10:1 and 11:1) at 2600 rpm and wide-open throttle. The results indicate that the BSCF (brake specific fuel consumption), BTE (brake thermal efficiency) and the emissions of CO 2 (carbon dioxide) increased while UHC (unburned hydrocarbon) and CO (carbon monoxide) emissions decreased with the increase in the amount of iso-butanol in the fuel mixture at all CRs. The best results for BSFC, BTE, the emissions of CO and UHC were observed at increased the CR. Moreover, the ICP (in-cylinder pressure) generally increased with the increase in the amount of iso-butanol in the fuel mixture and the ICP and HRR (heat release rate) rose earlier than those values in gasoline. [ABSTRACT FROM AUTHOR]

Several studies carried out with the aim of improving the RCCI (reactivity controlled compression ignition) concept in terms of thermal efficiency conclude that the main cause of the reduced efficiency at light loads is the reduced combustion efficiency. The present study used both a 3D computational model and engine experiments to explore the effect of the oxygen concentration and intake temperature on RCCI combustion efficiency at light load. The experiments were conducted using a single-cylinder heavy-duty research diesel engine adapted for dual fuel operation. Results suggest that it is possible to achieve an improvement of around 1.5% in the combustion efficiency with both strategies studied; the combined effect of intake temperature and in-cylinder fuel blending as well as the combined effect of oxygen concentration and in-cylinder fuel blending (ICFB). In addition, the direct comparison of both strategies suggests that the combustion losses trend is mainly associated to the in-cylinder equivalence ratio stratification, which is determined by the diesel to gasoline ratio in the blend since the injection timing is kept constant for all the tests. Moreover, the combined effect of the intake temperature and ICFB promotes a slight improvement in the combustion losses over the combined effect of the oxygen concentration and ICFB. [ABSTRACT FROM AUTHOR]

Reactive absorption of CO 2 with MEA (monoethanolamine) has been established as the preferred reference technology in benchmark studies of novel post combustion CO 2 capture technologies. However, recent advances in solvents tailored for CO 2 capture warrant an updated reference for consistent performance comparisons. Moreover, as innovative solvent concepts require desorption heat at varying temperatures, SRDs (specific reboiler duties) are not directly comparable. This paper estimates the specific capture and compression work for two different solvents with varying SRD as a method to rapidly assess the CO 2 capture energy penalty. To confirm the results, full process simulations are presented for the NGCC (Natural Gas Combined Cycle) with post combustion capture using a novel amine-based solvent and compared to MEA. Desorber pressure, exhaust gas recirculation ratio and reboiler approach temperature is varied. For identical operating conditions, the novel solvent increases the net plant efficiency from 49.4% to 50.4% compared to MEA. However, although an increased desorber pressure reduces SRD by 8%, the net efficiency is virtually constant. This illustrates the difference between reduced SRD and improved net plant efficiency and the importance of systems level analysis. The best net efficiency, with EGR (Exhaust Gas Recirculation) and 5 °C reboiler approach temperature, for the novel solvent corresponds to a 6.2%pt capture penalty. [ABSTRACT FROM AUTHOR]

An analytical model has been developed to evaluate "displacer gap losses" in the clearance between the displacer and the cylinder in both β and γ configurations of Stirling engines. Displacer gap losses are the sum of the "shuttle heat transfer" and the "enthalpy pumping". The present model takes into account the pressure gradient in the gap, the gas compressibility and real gas effect. Gas velocity and temperature distributions in the displacer, in the gap and in the cylinder were determined by solving momentum and energy balances in a concentric tubes geometry. Our model is then introduced in a whole engine model and the effect of the clearance thickness and engine's speed on total displacer gap losses are investigated. Novel tendencies of the solution are observed and new ways for optimization are demonstrated. [ABSTRACT FROM AUTHOR]

Abstract: The experimental work presents a comparative study of performance and emission using Pongamia pinnata methyl ester (PPME) and Diesel as pilot fuel in a CI (compression ignition) engine with compressed natural gas (CNG) as the primary fuel. The results show that PPME–CNG dual fuel operation is more effective than Diesel–CNG dual fuel operation in improving the performance and emission characteristics of the engine. CNG is found to share higher quantity of input energy with PPME pilot operation than pilot Diesel operation. Low amount of CNG injection also increases the brake thermal efficiency of the engine. PPME–CNG operations with low amount of CNG injections are also more instrumental in reducing CO (carbon monoxide) emission and smoke opacity than Diesel–CNG operations. NOx emission from the engine is found to increase a bit for PPME–CNG operations in comparison to Diesel–CNG operation. PPME–CNG operation is also more effective in reducing hydrocarbon emission than Diesel–CNG operations. The study also shows that CNG injected at 10° ATDC (after top dead center) for a duration of about 4500 μs with PPME as pilot fuel can produce better performance and emission signatures than Diesel–CNG operation. The tradeoff study also consolidates the fact that PPME–CNG dual fuel operation is instrumental in resolving the high performance–low emission paradox. [Copyright &y& Elsevier]

Abstract: This paper has shown the development of a theoretical model to determine the operating parameters and consumption of a domestic hot water (DHW) installation, which uses a direct-expansion solar assisted heat pump (DXSAHP) with refrigerant R-134a, a compressor with a rated capacity of 1.1kW and collectors with a total area of 5.6m2. The model results have been compared and validated the experimental results obtained with the equipment installed at the University Carlos III, South of Madrid. The analysis was conducted over the course of a year, and the results have been represented depending on the meteorological and process variables of several representative days. Taking into account the thermal losses of the installation and the dependency on the operating conditions, the acquired experimental coefficient of performance is between 1.7 and 2.9, while the DHW tank temperature over the course of the study is 51°C. [Copyright &y& Elsevier]

Abstract: This paper reports on a specific phenomenon, noticed during steam injection experiments on a microturbine. During the considered experiments, measurements indicated an unsteady inlet air temperature of the compressor, resulting in unstable operation of the microturbine. Non-continuous exhaust air recirculation was a possible explanation for the observed behaviour of the microturbine. The aim of this paper is to investigate and demonstrate the effects of exhaust recirculation on a microgasturbine. Depending on wind direction, exhaust air re-entered the engine, resulting in changing inlet conditions which affects the operating regime of the microturbine. For this paper, a series of experiments were performed in the wind tunnel. These series of experiments allowed investigation of the effect of the wind direction on flue gasses flow. Next to the experiments, steady-state simulations of exhaust recirculation were performed in order to study the effect of exhaust recirculation on thermodynamic performance of the microturbine. Dynamic simulations of the non-continuous recirculation revealed the effects of frequency and amplitude on average performance and stability. Results from simulations supported the important impact of exhaust recirculation. Wind tunnel tests demonstrated the influence of the wind direction on recirculation and revealed the necessity to heighten the stack, thus preventing exhaust recirculation. [Copyright &y& Elsevier]

Abstract: Alcohol blends with hydrocarbon fuels for spark-ignition engine increase fuel octane rating and power for a given engine displacement and compression ratio. In this work, the influence of butanol addition to gasoline was investigated. The experiments were performed in a ported fuel injection single cylinder SI engine with an external boosting device. The optically accessible engine was equipped with the head of a commercial SI turbocharged engine with the same geometrical specifications. The effect on the spark ignition combustion process of 40% of n-butanol blended in volume with 60% pure gasoline (BU40) was investigated by cycle resolved visualization. The engine worked at low speed, medium boosting and WOT. Changes in the spark timing and fuel injection phasing were considered. Comparisons between flame luminosity and combustion pressure data were performed. The fuel was injected at closed (CV) and open intake valves (OV). Butanol blend allowed working in more advanced spark timing without occurrence of abnormal combustion. For the blend BU40, the duration of injection (DOI) was increased to obtain a stoichiometric mixture. BU40 granted performance levels similar to gasoline and in open valve injection allowed to minimize the abnormal combustion effects including the emission of ultrafine carbonaceous particles, NOx and HC. [Copyright &y& Elsevier]

Abstract: One of the most promising technologies for coal-to-electricity conversion considering CO2 removal is coal gasification process integrated with a combined cycle (IGCC). One of the ideas for IGCC efficiency increase is process integration including well-known ASU-GT coupling by compressed air and nitrogen streams. In this case, the integration idea is based on supplying of the compressed air from the GT compressor to ASU where it replaces air compressed in electrical-driven compressors. From the energy effectiveness point of view, the integration should reduce the electricity consumption in ASU and energy losses in auxiliary transformer. It should also be noted, that the polytropic efficiency of large compression stages like for GT compressor is usually higher than for smaller units as for ASU compressors. The main goal of the present paper is to check if the air-side ASU-GT integration has a positive impact on the IGCC efficiency, assuming that the GT unit is a syngas-dedicated machine and massive CO2 removal is applied. The general conclusion is that in case of dedicated GT unit, where the compressor pressure ratio is relatively high, the ASU-GT integration is not recommended from the efficiency point of view. [Copyright &y& Elsevier]

Flutter instability because of the blade vibrations is a major problem in axial compressor cascades. This paper investigates the effects of blade oscillations on aerodynamic performance and turbulent flow characteristics of modern gas-turbine compressors. Highly accurate direct numerical simulations (DNS) are performed based on the spectral-hp element method to predict the flow instabilities, pressure fluctuations and vortex generation on the surface of the compressor blades by considering all complex physical parameters at different vibration frequencies (0 < f < 8.28 Hz). The main novelty of this study is to consider the aeroelastic vibrations of the compressor blades in DNS analysis. The novel proposed method enables the detailed analysis of complex structure fluid interactions, which cannot be obtained using other methods such as RANS models. The simulations revealed that the blade oscillations have a huge impact on the vortex generation and laminar separation bubble on the suction side of the blade. Moreover, the amplitude of unsteady pressure distribution is greater at 90% span, with the phage angle deviating between 100° and 350°. Strong fluctuations are observed at the centre of the wake region of the vibrating blade cascade. These fluctuations are activated by the flow disturbances resulting from the blade oscillation. Moreover, intense pressure fluctuations happen in the wake region of the oscillating compressor blade compared with the stationary one. The separating point occurred 8.28% sooner on the suction surface of the vibrating blade with k = 0.4 (X sep /C = 0.288) compared to the stationary blade with X sep /C = 0.314. • The vibration effects on flow structure over axial compressor blades are studied. • Separation occurred 8.28% faster over vibrating blade compared to stationary one. • Oscillations have huge impact on vortex generation and LSB in compressor cascade. • Strong pressure fluctuations are observed in the wake region of vibrating blade. • Additional flow disturbance is detected due to higher vibration frequencies. [ABSTRACT FROM AUTHOR]

Abstract: This paper describes the optimization of the distribution of heat transfer (cooling) during the process of gas compression. The coolant is a stream of cold liquid. There is a fundamental tradeoff between the savings in compressor power, which are due to distributed cooling, and the pumping power required to circulate the coolant. The tradeoff is revealed on the basis of a combined model of multi-stage gas compression, resistance to fluid flow, and area-constrained counter- or co-current heat exchange between the gaseous stream and the liquid stream. The results are illustrated for the compressor of an actual ammonia refrigeration plant, for which the distributed-cooling design is highly recommended because the compressor discharge temperature in such units is high. It is shown that there is an optimal coolant (water) flow rate such that the total power requirement is minimized. The optimized distribution of gas compression and cooling is robust with respect to the selection of the water flow rate. [Copyright &y& Elsevier]