Dual-loop System Research Articles

Thermodynamic performance analysis of air-to-air hybrid heat recovery unit driven by pump combined with booster

The air conditioning energy consumption for fresh air handling in buildings increases yearly, especially in low energy buildings. This energy consumption can be greatly reduced when exhaust air is recovered for preheating or precooling fresh air. Then, significant savings in the total energy consumption in buildings will be achieved, which in turn helps achieve the carbon peak in the building field. In this paper, a booster/pump coupled energy recovery ventilator is proposed for energy recovery in buildings. The system performance, which depends on the loop number and combination strategies were analyzed and compared through model simulations. Results indicate that the heat transfer rate of different coupling systems increases with the temperature difference. In summer, the pump/booster driven dual-loop system has the highest average temperature effectiveness of 47.3% and average heat transfer rate of 4.97 kW. The booster/booster-driven dual-loop system has the highest average heat transfer rate of 5.07 kW and average temperature effectiveness of 47.1%. The average temperature effectiveness of the pump/booster/booster driven triple-loop system reaches up to 45% and average heat transfer rate of 4.73 kW. The booster/booster/booster-driven triple-loop system has the highest average heat transfer rate of 4.82 kW and average temperature effectiveness of 44.7%. In winter, the maximum average heat transfer rate and temperature effectiveness of the pump/booster driven dual-loop system are 8.54 kW and 44.44%, respectively. The maximum average heat transfer rate and temperature effectiveness of the pump/booster/booster driven triple-loop system are 7.90 kW and 41.5%, respectively. Throughout the year, the best coupling scheme of the dual-loop system is the pump/booster driven dual-loop system, and its average heat transfer rate and temperature effectiveness are 6.755 kW and 45.85%, respectively. The best coupling scheme of the triple-loop system is the pump/booster/booster-driven triple-loop system, and its average heat transfer rate and temperature effectiveness are 6.315 kW and 43.25%, respectively.

Simulation research of a dual-loop booster heat pump system on district heating under ultra-low temperature

ULTDH (ultra-low temperature district heating) system improves the shortcoming of significant loss of heating network in traditional district heating systems. This work proposes a dual-loop booster heat pump for ULTDH to improve the heating capacity and COP. The system is modeled by MATLAB, and the water temperature between the two loops is solved by the NSGA-II algorithm (Non-dominated Sorting Genetic Algorithm-II algorithm). The simulation results show that when the heat source temperature changes from 20 °C to 40 °C, the COP and heating capacity of the dual-loop system increase by 43.79% and 90.30%, respectively, which are higher than those of the single-loop system. When the temperature difference between the inlet and outlet of the evaporator is increased, the heating capacity of the dual-loop system is still 7.31–33.47% higher than that of the single-loop system. When the hot water supply temperature is 60 °C, the COP of the dual-loop system is 3.34, which is 23.70% higher than that of the single-loop system. During the whole heating period in Beijing, the dual-loop system can save 17.67 % of the electric energy than the single-loop system. The dual-loop system shows excellent advantages in heating capacity and COP.

Study on anti-disturbance capacity of LBE cooled double loop natural circulation system under asymmetric conditions

Heat exchangers in natural circulation LBE-cooled fast reactors are used in harsh conditions such as extreme temperatures, significant pressure differences, high density, and corrosive environments. Therefore, heat transfer tube rupture and flow blockage accidents are common and result in an asymmetric heat load or asymmetric resistance thereby significantly impacting the safe and stable operation of the reactor.In this study, SNCLFR-10 has been used as the reference reactor and FLUENT simulation is used to establish the LBE-cooled dual-loop natural circulation system. Consequently, a theoretical solution of the natural circulation flow of a dual-loop system (TSNCD) is deduced using dimensionless analysis.The TSNCD theoretical solution is verified by using a dual-loop natural circulation system established via FLUENT simulation. Subsequently disturbance characteristics of the natural circulation system under different heat load differences or resistance differences are analyzed. The characteristic parameters representing the anti-disturbance capacity of natural circulation are determined using fitting approximation, and the best anti-disturbance interval is obtained.The results show that the TSNCD theoretical calculation formula of dual-loop natural circulation flow is extremely reliable, and the error between the calculations and the FLUENT simulation result is less than 5 %.When an asymmetric heat load disturbance and asymmetric resistance disturbance are incorporated into the system together or alone, the loop flow changes insignificantly in a certain interval; the anti-disturbance capacity of the system is strong in this interval. The resistance of the system to heat load disturbance is 0.2<k1<0.8, and the resistance disturbance is 0.6<B<4.8. When an asymmetric heat load and asymmetric resistance disturbance are simultaneously introduced into the system, an optimal resistance disturbance is achieved (k1∈[0.40,0.60] and B∈[0.7,2.9]).

Supercritical CO2 Power Cycle and Ejector Refrigeration Cycle for Marine Dual Fuel Engine Efficiency Enhancement by Utilizing Exhaust Gas and Charge Air Heat

Dual fuel engines with LNG as fuel have become a feasible solution for ship power units in the current situation, but their fuel efficiency needs to be further enhanced to meet the increasingly stringent emission requirements. This paper designs a dual-loop system, including a supercritical CO2 power cycle and a thermally driven ejector refrigeration cycle, for recovering the exhaust gas and charge air heat of a marine dual fuel engine. The models of the waste heat recovery system, the evaluation indicators of the combined system, and the genetic algorithm optimization program are developed. Compared to the standalone machine, the waste heat recovery system can improve by about 9.3% of the engine’s fuel efficiency. The performance analysis shows that the ejector contributes to the highest share of exergy destruction and accounts for approximate 53% of the refrigeration cycle. There are optimal values for the compressor inlet temperature of about 8.1 MPa and for the turbine inlet temperature of about 305 °C. Finally, after optimization, the specific fuel consumption, fuel efficiency, and CO2 emissions of the combined system are around 137.9 g/kWh, 53.3%, and 537.4 g/kWh, respectively. It provides a feasible solution in which the charge air cooler can be wholly replaced by the ejector refrigeration cycle.

Power Sharing Control Strategy of High-Frequency Chain Matrix Converter Parallel System Based on Adaptive Virtual Impedance

In the high frequency link matrix converter parallel system, the impedance parameters on each line are unequal so that the output power of each converter is not equal. To solve this problem, the reason why the power cannot be divided equally under the droop control strategy is analyzed, and a power sharing strategy based on adaptive virtual impedance is proposed. This strategy introduces virtual impedance in a voltage-current dual-loop system with droop control, and uses the converter’s power information and output power factor to adaptively adjust the amplitude and phase of the virtual impedance, so that different branches have the same equivalent output impedance to compensate The voltage drop on the line impedance, while adding the droop control fine-tuning compensation link, so as to realize the load power sharing. Simulation results show that the proposed strategy can effectively improve the accuracy of output power sharing and ensure the stability of the system output voltage amplitude.

Thermo-economic multi-objective optimization of an innovative Rankine–organic Rankine dual-loop system integrated with a gas engine for higher energy/exergy efficiency and lower payback period

Thermo-economic multi-objective optimization of an innovative Rankine–organic Rankine dual-loop system integrated with a gas engine for higher energy/exergy efficiency and lower payback period

Influences of compressor displacement ratio on dual-loop heat pump system for ventilation heat recovery

The performance of heat pump ventilation heat recovery system can be effectively improved using multiple-loop independent compression cycle. The influence of the DR change on the performance of dual-loop system was predicted through calculation to explore the influence of the change in displacement ratio (DR) on the performance of the system and the direction of further improving the performance of the system. The optimum DR in dual-loop system was calculated. The performance differences of two dual-loop heat pump systems with different DR values were compared by experiments. Results show that the optimum DR is between 0.8040 and 0.9206, and this optimum DR maximizes the COP of the system. Experimental results show that, compared with the COP of the system with the DR of 2, that of the system with the DR of 0.5 can be increased by 14.8%. Compared with the overall COP of the triplex loop system with the same displacement in each loop, that of the system with the DR of 0.5 is even higher under certain test conditions. The comparison results of COP changes are in accordance with the prediction of simulation calculation. Therefore, a reasonable increase in the displacement of the low-pressure loop in the multi-loop heat recovery heat pump system will improve the system performance.

Experimental investigations on a heat pump system for ventilation heat recovery of a novel dual-cylinder rotary compressor

To simplify the dual-loop heat pump ventilation heat recovery system, a new type of dual-cylinder rotary compressor with two independent suction ports and two independent discharge ports was designed and used to drive the heat recovery system in this paper. Thus, a system cycle approaching the Lorentz cycle was formed by dual-loop compression cycles. A test bench of heat pump system for ventilation heat recovery with a novel compressor was built to carry out system performance experiment. Experimental results showed that the COP of the dual-loop system under winter test conditions could be increased by 17.1% compared with that of the traditional heat pump system with a single loop. The COP of the dual-loop system could reach 10.21 under the outdoor temperature of −5 °C and the indoor temperature of 20 °C. Under summer test conditions, the COP of the dual-loop system was up to 33.47% higher than that of the traditional system. Under the outdoor temperature of 40 °C and the indoor temperature of 27 °C, the COP of the dual-loop independent compression system could reach 4.69. The performance level of the heat pump system for ventilation heat recovery could be greatly improved using the novel compressor with independent suction and discharge ports.

Theoretical analysis of a regenerative supercritical carbon dioxide Brayton cycle/organic Rankine cycle dual loop for waste heat recovery of a diesel/natural gas dual-fuel engine

Supercritical carbon dioxide Brayton cycle is considered one of the most promising systems for waste heat recovery of engines because of its compactness and high energy efficiency. To further improve the fuel utilization ratio and solve the difficulties of waste heat recovery of high temperature exhaust gas, a regenerative supercritical carbon dioxide Brayton cycle/organic Rankine cycle dual loop is proposed for cascade utilization of exhaust heat from a dual-fuel engine. The regenerative supercritical carbon dioxide Brayton cycle of the proposed system is powered by the waste heat contained in the exhaust gas. The working fluid in the organic Rankine cycle is pre-heated by CO2 exiting the regenerator and then further heated by the residual heat of the exhaust gas. The flow rates of the working fluids in both sub cycles are adjusted to match the waste heat recovery system to respond to the changing conditions of the dual-fuel engine. The results revealed that the maximum net power output of this system is up to 40.88 kW, thus improving the dual-fuel engine power output by 6.78%. Therefore, such a regenerative supercritical carbon dioxide Brayton cycle/organic Rankine cycle dual loop system design enables the thorough recovery of high temperature exhaust heat, leading to higher energy efficiency and lower fuel consumption of the engine.

Performance of a coupled dual-loop refrigerator under different control strategies

The coupled dual-loop refrigerator has great energy-saving potential in the large-capacity domestic refrigerator field. However, the traditional on-off control strategy is not suitable to this type refrigerator. This study introduced a semi-compulsive control strategy to improve its performance. The experimental test is carried out based on the semi-compulsive control strategy simulation results. From the experiment, the system using the semi-compulsive control shows a 2.2% decrease in energy consumption compared with the compulsive control strategy refrigerator. The semi-compulsive strategy can guarantee that the coupled dual-loop system is under the coupled operating most of the time.

Potential of a thermofluidic feed pump on performance improvement of the dual-loop Rankine cycle using for engine waste heat recovery

The dual-loop Rankine cycle system is considered as the most effective way to recover the multi-grades waste heat of engine. However, the power consumption of mechanical pump is relative high, especially for that in the low-temperature loop of dual-loop Rankine cycle, which will influence the system efficiency and power output. Therefore, a thermofluidic pump driven by the engine coolant heat instead of electric energy is used to replace the mechanical pump of low-temperature loop in this paper. The effect of the design parameters on the performance of thermofluidic pump are analyzed firstly. There is always a reasonable height distribution among the components that makes the mass flow rate of thermofluidic pump achieve to maximum, which contributes to a smaller volume and less pressure fluctuation of pump. Then several working fluids are selected as the candidates for systems with thermofluidic pump and mechanical pump. Based on the comprehensive analysis (utilization rate of engine coolant, the energy and exergy efficiency, and output power), the R1234ze is regarded as the most suitable working fluid for both system with thermofluidic pump and system with mechanical pump. Afterwards, a comparison analysis between systems with thermofluidic pump and mechanical pump is implemented in the low-temperature loop. Results indicate that R1234ze based low-temperature loop with the thermofluidic pump has improvement of 7.6%, 9.1% and 7.7% on net power, thermal efficiency and exergy efficiency respectively compared with that of low-temperature loop with the mechanical pump. In addition, the mass flow rate will decrease by 8.6% in low-temperature loop, which conduces to reduce the size of component of cycle. All the results indicate that thermofluidic feed pump is an effective way to improve the performance of dual-loop system.

Grid-Current-Feedback Control for LCL-Filtered Grid Converters With Enhanced Stability

This paper proposes a second-order-generalized-integrator (SOGI)-based time-delay compensation method for extending the stable region of a dual-loop grid-current-feedback (GCF) control system. According to the analysis, stable region of the dual-loop system should be designed below a certain critical frequency, before time-delay compensation method can be applied. To always meet the requirement, relationship between single-loop converter-current-feedback and dual-loop GCF control is clarified, before a robust inner-loop gain for the dual-loop GCF scheme is determined. Enforcing this gain allows the converter to remain in its stable region, regardless of how its LCL -filter parameters and grid impedance vary. The SOGI-based delay compensation method can then be applied for widening the stable region of the dual-loop GCF scheme, as proven through s-domain Bode diagrams and z -domain root loci. These theoretical proofs are eventually validated by experimental results obtained in the laboratory.

Demonstrating Improved Fuel Economy Using Subsystem Specific Lubricants on a Modified Diesel Engine

ABSTRACTFuel economy performance in modern internal combustion engines is of increasing importance to lubricant formulators due to regulations targeting global greenhouse gas emissions. Engines typically employ a single lubricant, with a common sump, to service all components. As a result, base oil and additive selection for fuel economy performance is a compromise among competing demands for different engine subsystems. Opportunities for significant fuel economy improvement through targeted formulation of lubricants for specific engine subsystems are presented, with specific emphasis on segregating the lubricant supplies for the valve train and the power cylinder subsystems. A working prototype was developed in a lab environment by modifying a commercially available twin-cylinder diesel engine. Motored valve train and whole-engine fired test results were obtained and compared to model data. Fuel economy benefits were demonstrated using market representative heavy-duty diesel lubricants, including mineral oil and polyalphaolefin (PAO) blends. The fuel economy benefits of a dual-loop lubricant system are demonstrated through significant viscosity reduction in the power cylinder subsystem, achieving overall engine friction reductions of up to 8% for the investigated operating condition. Results suggest that additional gains may be realized through targeted base oil and additive formulation. Implications for incorporation in larger diesel engines are also considered.

Performance analysis of zeotropic mixtures for the dual-loop system combined with internal combustion engine

To reveal whether organic mixtures perform better in the aspect of matching two heat sources of different grades, this paper presents a dual-loop system for waste heat recovery from internal combustion engine which has two heat sources of different temperature. The high temperature loop with water as working fluid is employed to recover waste heat from engine exhaust gas. And in the low temperature loop, organic mixtures RC318/R1234yf, butane/R1234yf and RC318/R245fa are selected as working fluids to recover the heat from jacket cooling water and heat released from condensation process in the high temperature loop. The organic mixtures in the low temperature loop present a better system performance than pure working fluids because of better temperature matching in condensation and better matching two heat sources of different grades. The influence of high temperature loop condensing temperature on the whole system is also analyzed in this research. The simulation results reveal that the appropriate mixture does not only improve the thermal efficiency but also the absorbed heat from heat sources in the low temperature loop. With RC318/R1234yf as working fluid in the low temperature loop, the engine output can be improved by nearly 14.4%.

Electro-mechanical hybrid PLL for MEMS oscillator temperature compensation system

This paper describes the design and measurement of a dual Phase-Locked Loop system that utilizes a MEMS VCO with a DC-controlled silicon resonator as the frequency-setting element. System-level considerations are given for the use of such structure in temperature compensation system for MEMS reference oscillators. Micromachining process and circuit design challenges of the particular implementation are also discussed. The PLL has been implemented using a 0.35 μm CMOS process and operates with a nominal supply of 3 V. The nominal supply voltage for the MEMS VCO is 24 V with 15 V bias applied to the silicon resonator.

Adaptive neural network visual servo control for dynamic positioning of underwater vehicles

Dynamic positioning is an important technique to ensure the capability of a next generation underwater vehicle to fulfill complex intervention and observation tasks. This work proposes an adaptive neural network image-based visual servo (IBVS) controller for positioning an underwater vehicle with respect to a fixed target in camera-in-hand configuration. The visual servoing error is defined by projecting the image error to the vehicle space using a pseudo inverse of the estimated Jacobian matrix. In the proposed dual-loop system architecture, the velocity command is designed to stabilize the visual servoing error in the kinematic loop, and the desired acceleration is derived to track the velocity command in the dynamic loop. A single hidden layer (SHL) feedforward neural network, in conjunction with a conventional proportional-integral (PI) controller, is applied to the cascaded systems to compensate for the uncertainties in both the Jacobian matrix and the vehicle dynamics. The thruster control signals are obtained by using the approximate dynamic inversion (ADI) of the vehicle. The uniform ultimate boundedness of the visual servoing error and the neural network weight matrices are proved by Lyapunov theory. Simulation results are provided to verify the effectiveness of the controller with two candidate methods of estimating the image Jacobian matrix.

The Dual-Loop Model and the Human Mirror Neuron System: an Exploratory Combined fMRI and DTI Study of the Inferior Frontal Gyrus

The inferior frontal gyrus (IFG) is active during both goal-directed action and while observing the same motor act, leading to the idea that also the meaning of a motor act (action understanding) is represented in this "mirror neuron system" (MNS). However, in the dual-loop model, based on dorsal and ventral visual streams, the MNS is thought to be a function of the dorsal steam, projecting to pars opercularis (BA44) of IFG, while recent studies suggest that conceptual meaning and semantic analysis are a function of ventral connections, projecting mainly to pars triangularis (BA45) of IFG. To resolve this discrepancy, we investigated action observation (AO) and imitation (IMI) using fMRI in a large group of subjects. A grasping task (GR) assessed the contribution from movement without AO. We analyzed connections of the MNS-related areas within IFG with postrolandic areas with the use of activation-based DTI. We found that action observation with imitation are mainly a function of the dorsal stream centered on dorsal part of BA44, but also involve BA45, which is dorsally and ventrally connected to the same postrolandic regions. The current finding suggests that BA45 is the crucial part where the MNS and the dual-loop system interact.

The ventral fiber pathway for pantomime of object use

The current concept of a dual loop system of brain organization predicts a domain-general dual-pathway architecture involving dorsal and ventral fiber connections. We investigated if a similar dichotomy of brain network organization applies for pantomime (P) and imitation of meaningless gestures (I). Impairments of these tasks occur after left hemispheric brain lesions causing apraxia. Isolated impairments and double-dissociations point towards an anatomical segregation. Frontal and parietal areas seem to contribute differently. A special role of the inferior frontal gyrus and underlying fiber pathways was suggested recently.Using a combined fMRI/DTI-approach, we compared the fiber pathway architecture of left hemispheric frontal, temporal and parietal network components of pantomime and imitation. Thereby, we separated object effects from pantomime-specific effects. P and I both engage a fronto-temporo-parietal network of cortical areas interconnected by a dorsal fiber system (superior longitudinal fascicle) for direct sensory–motor interactions. The pantomime-specific effect additionally involved the triangular part of the inferior frontal gyrus, the middle temporal gyrus, the inferior parietal cortex and the intraparietal sulcus, interconnected by ventral fibers of the extreme capsule, likely related to higher-order conceptual and semantic operations. We discuss this finding in the context of the dual loop model and recent anatomical concepts.

Thermodynamic analysis of a dual loop heat recovery system with trilateral cycle applied to exhaust gases of internal combustion engine for propulsion of the 6800 TEU container ship

A dual loop waste heat recovery power generation system that comprises an upper trilateral cycle and a lower organic Rankine cycle, in which discharged exhaust gas heat is recovered and re-used for propulsion power, was theoretically applied to an internal combustion engine for propulsion in a 6800 TEU container ship. The thermodynamic properties of this exhaust gas heat recovery system, which vary depending on the boundary temperature between the upper and lower cycles, were also investigated. The results confirmed that this dual loop exhaust gas heat recovery power generation system exhibited a maximum net output of 2069.8 kW, and a maximum system efficiency of 10.93% according to the first law of thermodynamics and a maximum system exergy efficiency of 58.77% according to the second law of thermodynamics. In this case, the energy and exergy efficiencies of the dual loop system were larger than those of the single loop trilateral cycle. Further, in the upper trilateral cycle, the volumetric expansion ratio of the turbine could be considerably reduced to an adequate level to be employed in the practical system. When this dual loop exhaust gas heat recovery power generation system was applied to the main engine of the container ship, which was actually in operation, a 2.824% improvement in propulsion efficiency was confirmed in comparison to the case of a base engine. This improvement in propulsion efficiency resulted in about 6.06% reduction in the specific fuel oil consumption and specific CO2 emissions of the main engine during actual operation.

Application of Continuous 222Rn Monitor with Dual Loop System in a Small Lake

To estimate the spatial distribution of groundwater discharge from the bottom of a small lake of Kumamoto in Japan, we applied continuous radon measurements with a dual loop system and verified the results obtained using the radon method by visual diving surveys. Time-shifting correction in the dual-loop system is reasonable to obtain the true radon activity in water. Distributions of radon activity and water temperature in the study area reveal the effects on groundwater discharge and mixing situation of lake water. The estimated discharge zone ascertained using the radon method agrees with the groundwater discharge distribution observed through diving surveys. Although the data resolution of the radon method is much greater than the width of observed discharge zones, the general distribution of groundwater discharge is recognizable. The dual loop system of radon measurement is useful for smaller areas.