Parametric optimization and heat transfer analysis of a dual loop ORC (organic Rankine cycle) system for CNG engine waste heat recovery

In this study, a dual loop ORC (organic Rankine cycle) system is adopted to recover exhaust energy, waste heat from the coolant system, and intercooler heat rejection of a six-cylinder CNG (compressed natural gas) engine. The thermodynamic, heat transfer, and optimization models for the dual loop ORC system are established. On the basis of the waste heat characteristics of the CNG engine over the whole operating range, a GA (genetic algorithm) is used to solve the Pareto solution for the thermodynamic and heat transfer performances to maximize net power output and minimize heat transfer area. Combined with optimization results, the optimal parameter regions of the dual loop ORC system are determined under various operating conditions. Then, the variation in the heat transfer area with the operating conditions of the CNG engine is analyzed. The results show that the optimal evaporation pressure and superheat degree of the HT (high temperature) cycle are mainly influenced by the operating conditions of the CNG engine. The optimal evaporation pressure and superheat degree of the HT cycle over the whole operating range are within 2.5–2.9 MPa and 0.43–12.35 K, respectively. The optimal condensation temperature of the HT cycle, evaporation and condensation temperatures of the LT (low temperature) cycle, and exhaust temperature at the outlet of evaporator 1 are kept nearly constant under various operating conditions of the CNG engine. The thermal efficiency of the dual loop ORC system is within the range of 8.79%–10.17%. The dual loop ORC system achieves the maximum net power output of 23.62 kW under the engine rated condition. In addition, the operating conditions of the CNG engine and the operating parameters of the dual loop ORC system significantly influence the heat transfer areas for each heat exchanger

Batch Scheduling with Proportional-Linear Deterioration and Outsourcing

We consider the bounded parallel-batch scheduling with proportional-linear deterioration and outsourcing, in which the actual processing time is pj=αj(A+Dt) or pj=αjt. A job is either accepted and processed in batches on a single machine by manufactures themselves or outsourced to the third party with a certain penalty having to be paid. The objective is to minimize the maximum completion time of the accepted jobs and the total penalty of the outsourced jobs. For the pj=αj(A+Dt) model, when all the jobs are released at time zero, we show that the problem is NP-hard and present a pseudo-polynomial time algorithm, respectively. For the pj=αjt model, when the jobs have distinct m (<n) release dates, we provide a dynamic programming algorithm, where n is the number of jobs

Powder Technol.

Gas-solid interaction does exist both outside and inside particle clusters in gas-solid two-phase flow, but the penetrating flow through clusters was generally neglected in most mathematical models of clusters. As regards to what extent the penetrating flow exists in gas-solid flow and how the penetrating flow affects gas-solid interaction, there are still no universally accepted viewpoint and quantitative characterization until now. By utilizing both CFD (Computational Fluid Dynamics) simulations and PIV (Particle Image Velocimetry) measurements, this article quantitatively investigates the gas and dilute gas-solid penetrating flows through different pseudo two-dimensional clusters in a two-dimensional gas-solid fluidized bed. The solid penetrating flow through clusters seldom occurs, but the gas penetrating flow increases exponentially with increasing internal voidage of clusters, which is however affected little by superficial gas velocity under the tested operating conditions. These results imply that the effect of the gas penetrating flow through clusters must be taken into consideration when investigating particle clustering behavior in gas-solid two-phase flow. (C) 2012 Elsevier B.V. All rights reserved.Gas-solid interaction does exist both outside and inside particle clusters in gas-solid two-phase flow, but the penetrating flow through clusters was generally neglected in most mathematical models of clusters. As regards to what extent the penetrating flow exists in gas-solid flow and how the penetrating flow affects gas-solid interaction, there are still no universally accepted viewpoint and quantitative characterization until now. By utilizing both CFD (Computational Fluid Dynamics) simulations and PIV (Particle Image Velocimetry) measurements, this article quantitatively investigates the gas and dilute gas-solid penetrating flows through different pseudo two-dimensional clusters in a two-dimensional gas-solid fluidized bed. The solid penetrating flow through clusters seldom occurs, but the gas penetrating flow increases exponentially with increasing internal voidage of clusters, which is however affected little by superficial gas velocity under the tested operating conditions. These results imply that the effect of the gas penetrating flow through clusters must be taken into consideration when investigating particle clustering behavior in gas-solid two-phase flow. (C) 2012 Elsevier B.V. All rights reserved

Closed-Loop PI Control of an Organic Rankine Cycle for Engine Exhaust Heat Recovery

The internal combustion engine (ICE) as a main power source for transportation needs to improve its efficiency and reduce emissions. The Organic Rankine Cycle (ORC) is a promising technique for exhaust heat recovery. However, vehicle engines normally operate under transient conditions with both the engine speed and torque varying in a large range, which creates obstacles to the application of ORC in vehicles. It is important to investigate the dynamic performance of an ORC when matching with an ICE. In this study, the dynamic performance of an ICE-ORC combined system is investigated based on a heavy-duty diesel engine and a 5 kW ORC with a single-screw expander. First, dynamic simulation models of the ICE and the ORC are built in the software GT-Power. Then, the working parameters of the ORC system are optimized over the entire operation scope of the ICE. A closed-loop proportional-integral (PI) control together with a feedforward control is designed to regulate the operation of the ORC during the transient driving conditions. The response time and overshoot of the PI control are estimated and compared with that of the feedforward control alone. The results based on the World Harmonized Transient Cycle (WHTC) indicate that the designed closed-loop PI control has a shorter response time and a better trace capacity during the dynamic processes. The average output power and thermal efficiency during the WHTC cycle are improved by 3.23% and 2.77%, respectively. Compared with the feedforward control alone, the designed PI control is more suitable for practical applications

Operation Characteristics and Transient Simulation of an ICE-ORC Combined System

Currently, internal combustion engines (ICEs) are still the main power for transportation. Energy conservation and emission reduction for ICEs have become the driving force of the industrial R&amp;D in recent years. Organic Rankine cycle (ORC) is a feasible technology to recover the waste heat of an ICE so that the energy efficiency can be enhanced apparently. However, there are still many obstacles needed to be overcome for the application of an ORC together with an ICE. When a vehicle is driving, the operation conditions of the ICE vary in a large range. The operation of the ORC needs to be regulated accordingly to achieve maximum efficiency. In this study, the operation characteristics of an ICE-ORC combined system is investigated and the transient performance is analyzed. First, an integrated simulation model of the ICE and the ORC was built in GT-POWER software. A 5 kW single-screw expander was employed for the ORC system. The working characteristics of the ORC system were evaluated under various working conditions of the ICE. The matching principles of the ORC with the ICE were discussed and the optimal operation conditions of the ORC over the entire engine&#8217;s working range were obtained. Subsequently, a feedforward control strategy for the ORC system was designed in MATLAB/SIMULINK. Finally, the entire model was simulated under a transient driving cycle of a vehicle. The results indicate that the pump speed and the expander speed are two important parameters and must be adjusted according to the engine&#8217;s working condition. The speed of the single-screw expander maintains in the low-speed region and the pump speed is tuned to achieve a high evaporation pressure and a proper superheat degree of the working fluid at the inlet of the expander. Thus, the net power output can be maximized. The designed feedforward control strategy can adjust the working condition of the ORC automatically to match with the working condition of the ICE. The ORC operates intermittently and an impulse power is output under the urban driving conditions. However, the working time of the ORC is increased significantly and the power output is relatively higher under the highway conditions

SHORT-ROOT stabilizes PHOSPHATE1 to regulate phosphate allocation in Arabidopsis

International audienceThe coordinated distribution of inorganic phosphate (Pi) between roots and shoots is an important process that plants use to maintain Pi homeostasis. SHORT-ROOT (SHR) is well characterized for its function in root radial patterning. Here we demonstrate a role of SHR in controlling Pi allocation from root to shoot by regulating PHOSPHATE1 in the root differentiation zone. We recovered a weak mutant allele of SHR in Arabidopsis that accumulates much less Pi in the shoot and shows a constitutive Pi starvation response under Pi-sufficient conditions. In addition, Pi starvation suppresses SHR protein accumulation and releases its inhibition on the HD-ZIP III transcription factor PHB. PHB accumulates and directly binds the promoter of PHOSPHATE2 to upregulate its transcription, resulting in PHOSPHATE1 degradation in the xylem-pole pericycle cells. Our findings reveal a previously unrecognized mechanism of how plants regulate Pi translocation from roots to shoots.Plants confronted with nutrient deficiency allocate more resources to roots to maximize nutrient acquisition and growth. This study uncovers how plants repress phosphate uploading to curtail the long-distance transportation of phosphate to shoots

SHORT-ROOT stabilizes PHOSPHATE1 to regulate phosphate allocation in Arabidopsis

International audienceThe coordinated distribution of inorganic phosphate (Pi) between roots and shoots is an important process that plants use to maintain Pi homeostasis. SHORT-ROOT (SHR) is well characterized for its function in root radial patterning. Here we demonstrate a role of SHR in controlling Pi allocation from root to shoot by regulating PHOSPHATE1 in the root differentiation zone. We recovered a weak mutant allele of SHR in Arabidopsis that accumulates much less Pi in the shoot and shows a constitutive Pi starvation response under Pi-sufficient conditions. In addition, Pi starvation suppresses SHR protein accumulation and releases its inhibition on the HD-ZIP III transcription factor PHB. PHB accumulates and directly binds the promoter of PHOSPHATE2 to upregulate its transcription, resulting in PHOSPHATE1 degradation in the xylem-pole pericycle cells. Our findings reveal a previously unrecognized mechanism of how plants regulate Pi translocation from roots to shoots.Plants confronted with nutrient deficiency allocate more resources to roots to maximize nutrient acquisition and growth. This study uncovers how plants repress phosphate uploading to curtail the long-distance transportation of phosphate to shoots