Abstract
A mathematical model of a steady combined diesel-organic Rankine cycle with finite heat resistance and heat leakage is proposed. Performance of the studied combined cycle has been numerically analyzed based on the ecological criterion and endothermic rate optimization method. The variations of optimal power, optimal efficiency and optimal ecological criterion with the endothermic rate, and the relations between optimal ecological criterion, optimal efficiency and optimal power are studied by numerical calculation. Results show that the optimal power does not vary with the endothermic rate; optimal ecological criterion and optimal efficiency decrease with the increase of heat leakage. The efficiency under the optimal ecological criterion is larger than that under the optimal power while both of them are less than the optimal efficiency. The heat leakage brings the quantitative and qualitative impact on the power output and efficiency of the combined cycle. The power output, ecological criterion and efficiency of ORC increase with the increasing evaporation temperature and superheated temperature.
Highlights
With the emission regulations issued by the International Maritime Organization (IMO) becoming increasingly stringent and growing awareness of environmental protection requirements, waste heat recovery system and power generation systems are expected to furnish with large and mediumsized merchant ships
When Ci=0, The relation curve between optimal power, optimal efficiency and Q1 is still parabolic, optimal efficiency decreases monotonically with the increase of Q1. It can be concluded from the figure that under the same parameters, the optimal ecological function corresponding to the cycle efficiency is greater than the optimal power corresponding to the cycle efficiency, but both are less than the peak of the cycle efficiency
The relation curve of power and efficiency of the endoreversible heat engine without heat leakage are parabolic, have a peak power point, a zero power output corresponds to the peak efficiency point and a zero power, zero efficiency point
Summary
With the emission regulations issued by the International Maritime Organization (IMO) becoming increasingly stringent and growing awareness of environmental protection requirements, waste heat recovery system and power generation systems are expected to furnish with large and mediumsized merchant ships. Lingen Chen et al. established a class of generalized steady flow irreversible combined Carnot cycle models Jizhou He et al. studied the performance of combined power plant without intermediate heat source consisted of two Carnot heat engine. Ping Xie et al. established a steady flow Brayton-Rankine combined model with heat transfer, heat leakage, internal reversibility, and the ecological performance of combined cycle was analyzed by thermodynamic optimization theory. Large and medium merchant ships generally use waste gas boiler to recover part of the waste heat to generate low pressure saturated steam to meet the needs of daily life This is a low-level utilization means of the quantitative waste heat and cannot effectively recover the waste heat to fit stringent emissions regulations and enhanced environmental awareness. To analyze thermodynamic performance of the proposed combined cycle and make comparison to the former diesel cycle, optimization based on ecological criterion is performed and analyzed numerically
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