ABSTRACT
Utilizing waste heat to drive thermodynamic systems is imperative for improving energy efficiency, thereby improving sustainability. A combined cooling and power systems (CCP) utilizes heat from a temperature source to deliver both power and cooling. However, CCP systems utilizing LNG cold energy suffers from low second law efficiency due to significant temperature differences. To address this, an "Advanced Power and Cooling with LNG Utilization (ACPLU)" system is proposed, integrating a cascaded transcritical carbon dioxide (TCO2)-LNG cycle with an Organic Rankine cycle (ORC) for improved power generation and an absorption refrigeration system (ARS) for simultaneous cooling. This study evaluates the second law efficiency, net work output, and exergy destruction performance through a sensitivity analysis, optimizing variables such as heat source temperature, superheater temperature difference, ORC and CO2 turbine inlet and condenser pressures, evaporator temperature, and pinch point temperatures of heat exchangers and generator. Compared to previous studies on CCP systems, the ACPLU shows a superior performance, with a second law efficiency of 27.3 % and a net work output of 11.76 MW. Cyclopentane as an ORC working fluid resulted in the highest second law efficiency of 29.06 % and net work output of 12.27 MW. Parametric analysis suggested that heat source temperature significantly impacts net power output. The exergy analysis concluded that a high-pressure ratio and good thermal match between the heat exchangers enhance overall performance. Utilizing artificial neural network (ANN) to produce a multiple-input-multiple-output (MIMO) objective function and performing multi-objective optimization (MOO) using genetic algorithm (GA), an improved second law efficiency and net power output by 28.11 % and 14.16 MW respectively, with pentane as the working fluid, is demonstrated. An average cost rate of 9.121 $/GJ was observed through a thermo-economic analysis. The ACPLU system is promising for medium temperature waste heat recovery, such as, pharmaceutical manufacturing plants.
ABSTRACT
The post-pandemic energy crisis and ever-increasing environmental degradation necessitate researchers to scrutinize refrigeration systems, major contributors to these issues, for minimal environmental impact and maximum performance. Thus, this study aims to comprehensively examine a triple cascade refrigeration system (TCRS) equipped with hydrocarbon refrigerants (1-butene/Heptane/m-Xylene). This system is specifically designed for ultra-low temperature applications, including vaccine storage, quick-freezing, frozen food preservation, cryogenic processes, and gas liquefaction. The investigation integrates conventional thermodynamic analysis with economic and environmental impact assessments, and finally multi-objective optimization (MOO) to ascertain optimal operating conditions for the system. The effect of (1) evaporator temperature, Tevap (2) condenser temperature, Tcond (3) Lower Temperature Circuit (LTC) condenser temperature, TLTC (4) Mid Temperature Circuit (MTC) condenser temperature, TMTC and (5) Cascade Condenser temperature difference, Δ T on three objective functions (COP, exergy efficiency, and overall plant cost) have been investigated employing a parametric analysis. Subsequently, quadratic equations for these objective functions are generated using the Box-Behnken method, and MOO utilizing the Genetic algorithm has been performed to maximize COP and exergy efficiency while minimizing the overall cost rate. The decision-making techniques TOPSIS and LINMAP are used to retrieve a unique solution from the Pareto Front, and the system performance has been assessed at the optimal point. The optimization result demonstrates that for the 10-kW capacity TCRS, COP, exergy efficiency, and total plant cost are 0.71, 0.51, and 38262.05 $/year respectively, at optimum condition (Tevap = -101.023 °C , Tcond = 36.545 °C , TLTC = - 69.047 °C and TMTC = - 34.651 °C ). Exergy analysis identifies HTC compressor (19.3 %) and throttle valve (15.5 %) as key contributors to total exergy destruction, while economic analysis underscores capital and maintenance costs (72 %) as the primary contributors to the overall cost, with evaporator (43 %) and condenser (20 %) accounting for 63 % of this cost.
ABSTRACT
A numerical investigation of a curved trapezoidal-corrugated channel with E-shaped baffles is conducted for thermal-hydraulic performance and flow behavior involving the use of single and hybrid nanofluids. This investigation introduces a unique integrated methodology for enhancing heat transfer efficiency by simultaneously combining geometric modifications and optimizing coolant utilization. To simulate turbulent, single-phase flow in three-dimensional corrugated channels, a computational model has been developed. The model considers a Reynolds number (Re) range of 5 × 103≤Re ≤ 35 × 103 and implies a uniform heat flux of 1000 W/m2. A commercial software, Ansys fluent was used in order to simulate the fluid flow by setting the inlet temperature at 300 K and velocity according to the Reynolds number. The continuity equation, momentum equation, and energy equations are discretized using a second-order upwind method. The equation's residual has been assigned a value of 1 × 106 for absolute criteria. The study evaluates the thermal-hydraulic performance of single nanofluids (Al2O3/water, CuO/water, SiO2/water) and hybrid nanofluids (Al2O3-Cu/water, TiO2-SiO2/EG-water) at varying volume fractions (1%≤φ ≤ 5%). Additionally, the investigation examines the effects of corrugations, baffles, and geometric parameter: blockage ratio (BR = 0.10, 0.15, 0.25). The findings demonstrate that the effects of baffles and corrugations can lead to the creation of vortex flow and greater turbulence, which can promote heat transfer enhancement. Various nanofluids demonstrated a significant rise in the Nusselt number, ranging from 35% to 60%, when compared to water in a curved corrugated channel. Additionally, a lower BR resulted in a smaller but still notable gain of 15%-19%. An effective heat exchanger that results in a significant energy dissipation is measured by the energy ratio (ER). The use of corrugated channels with narrow baffles has been found to consistently outperform smooth channels in terms of thermo-hydraulic parameters, leading to enhanced heat transfer. Using BR = 0.10 over 0.25 resulted in an increase in ΔP, HTC, and ER of 48.44%, 18.71%, and 45.86%, respectively. The implementation of a hybrid nanofluid consisting of 1% (20% TiO2-80% SiO2)/(60% Water-40% EG) volume fraction in a curved corrugated channel with baffles resulted in a significant improvement of 36.49% in thermal performance. This finding suggests that the aforementioned nanofluid composition and design parameter, characterized by a blockage ratio of 0.10, are the most effective in enhancing thermal performance.
ABSTRACT
With a population of 165 million, Bangladesh is undergoing rapid industrialization and urban development, and is well on track to move out from the group of least developed countries by 2024. This results in a significant increase in the urban energy needs and the amount of generated waste. Most of the municipal solid waste in Bangladesh is currently deposited in landfills, thereby contaminating nearby cultivable soils. It is desirable to have a system that recovers energy from the municipal solid waste in order to satisfy the increasing energy needs, while simultaneously addressing the land scarcity and pollution issues. This paper proposes using incineration to recover energy from municipal solid waste to produce electricity in the urban areas of Dhaka and Chattogram. A detailed technical analysis involving energy, exergy, exergoeconomic, and emission is presented. The power plants in these two cities show potential capacities of 169 MW and 83 MW respectively, with exergoeconomic factors of 61 %. The results indicate energy and exergy efficiencies of 32 % and 27 %, respectively, and a production cost in the range of 53.9-56.7 USD/MWh which is comparable to the production cost from the current power plants in Bangladesh. The proposed plants also result in a reduction in the greenhouse emissions and exhibit ecological efficiencies of over 87 %.