Thermal Efficiency Of System Research Articles

Assessing the performance of geothermal pavement constructed using demolition wastes by experimental and CFD simulation techniques

This paper studies the possibility of harnessing renewable thermal energy from road pavement constructed using construction and demolition (C&D) materials in Australia. This research study aims to evaluate the efficiency and heat gain capacity of geothermal pavement system with constant inlet water temperature and closed-loop approach. An experimental model was developed using copper pipe and C&D materials as pavement structure and the tests were conducted during summer-time in Melbourne, Australia. Numerical computational fluid dynamic (CFD) simulation was used to study the capacity of simulation in modeling heat transfer and the temperature field in the geothermal pavement. The results showed that the geothermal pavement system with constant inlet water temperature can gain almost 450 (kJ/m2) of thermal energy while subsequently decreasing the surface temperature of the pavement, hence increasing the service life of the geothermal pavement. The pipe burial depth of 40 mm to 60 mm was found to lead to the best efficiency of the geothermal pavement. The thermal efficiency of the geothermal pavement could increase and reach 25% during the day for a geothermal pavement system with constant inlet water temperature. Thermal conductivity and surface albedo would also increase the thermal efficiency of the system. Results showed that increasing thermal conductivity from 1 (W/m.K) to 3.5 (W/m.K) led to an increase in thermal efficiency from 20% to 34%. Also, increasing surface albedo magnitude equal to 0.1 would decrease efficiency by approximately 5%. The experimental results of the closed-loop geothermal pavement system demonstrated that the maximum hourly heat gain capacity of the system was 1000 (kJ/m2), which is twice higher than this value for a system with a constant inlet water temperature. The thermal efficiency of geothermal pavement system increased to its peak value equal to 30% throughout the day.

Natural convection heat transfer in PCM suspensions in a square enclosure with bottom heating and top cooling

Research on the use of phase change material (PCM) suspensions to improve the natural convection efficiency of thermal systems is booming; however, there are few studies on the transient behavior of PCM suspensions. In this study, numerical simulations were used to investigate transient and steady-state natural convection in a square enclosure containing a PCM suspension. The implicit finite-difference method was adopted. The left and right walls of the enclosure were adiabatic sections, the bottom was an isothermal heating, and the top was an isothermal cooling. The following parameters were considered: PCM = n-octadecane (C18H38), enclosure aspect ratio = 1, buoyancy ratio for mass-to-heat transfer = 1, Rayleigh number (RaT) = 103–104, Stefan number (Ste) = 0.005–0.05, subcooling factor (Sb) = 0–10, and initial mass fraction (cm,i) = 0–20%. The results show that all the parameters (RaT, Ste, Sb, and cm,i) affect the flow pattern, and convection oscillations occur at Sb = 0.5–1. The heat transfer rate increases with RaT. Both cm,i and Sb affect the heat transfer rate but in a case-specific manner, and no well-defined correlations are observed.

A novel design of power-cooling cogeneration system driven by solid oxide fuel cell waste heat in ocean-going vessels

Among many global energy and environmental problems, the ocean and air pollution caused by ocean-going vessels cannot be ignored. Cleaner and more efficient power generation systems should be used to replace traditional diesel generators on ships. To this problem, the combination of fuel cell and waste heat recovery technology can become a better choice. In this paper, a novel power-cooling cogeneration system is designed and analyzed, which is mainly composed of solid oxide fuel cell, preheating subsystem, homogeneous charge compression ignition engine and double-effect absorption refrigeration cycle. The study mainly includes mathematical modeling, reliability verification of each subsystem, numerical simulation and results analysis in energy, exergy and economics. The results show that the system thermal efficiency and exergy efficiency can reach 64.01% and 61.83%, respectively, which are 18.76% and 12.62% higher than those of simple cell. Compared with traditional combined system, the payback time of the proposed scheme is about 2.59 years, which not only proves that the cost can be recovered in a short time, but also shortened by about half. By improving energy efficiency and reducing costs, the proposed scheme can ensure the demand of electricity and cold energy in daily life of the crew, and provides a new choice for the marine auxiliary power generation equipment.

Numerical analysis of the photovoltaic system inspection with active cooling

<span>The use of solar energy may replace the present fossil fuel or gas to produce electricity. The goal of this study is to set up a simulation model to survey the performance of a photovoltaic thermal system (PV/T) based on the computational fluid dynamics (CFD) method. Ansys fluent software has been used for the simulation procedure. The electrical panel output and its efficiency were investigated numerically. In addition, the effect of variations in absorbed radiation on inlet fluid and absorber panel temperature on the system performance was investigated. The study was conducted for three cases, in a first case, where there is no refrigerant in the system and in the latter case, at constant fluid rate of the pump, whereas the third case with optimal pump operation. The numerical findings obtained from CFD simulators have been compared with the test records of the experimental results of the literature. The two results have a good agreement. From the obtained results, it can be noted that the system shows a good improvement for the electric net efficiency level of 3.52% with a lower reduction of the thermal system efficiency of 1.96% in comparison to the system when using the constantly high flow rate.</span>

Thermo-economic analysis and optimization of the very high temperature gas-cooled reactor-based nuclear hydrogen production system using copper-chlorine cycle

An improved very high temperature gas-cooled reactor (VHTR) and copper-chlorine (Cu–Cl) cycle-based nuclear hydrogen production system is proposed and investigated in this paper, in order to reveal the unknown thermo-economic characteristics of the system under variable operating conditions. Energy, exergy and economic analysis method and particle swarm optimization algorithm are used to model and optimize the system, respectively. Parametric analysis of the effects of several key operating parameters on the system performance is conducted, and energy loss, exergy loss, and investment cost distributions of the system are discussed under three typical production modes. Results show that increasing the reactor subsystem pressure ratio can enhance the system's thermo-economic performance, and the total efficiencies and cost of producing compressed hydrogen from nuclear energy are respectively lower and higher than that of generating electricity. When the system operates at the maximum hydrogen production rate of 403.1 mol/s, the system's net electrical power output, thermal efficiency, exergy efficiency, and specific energy cost are found to be 38.77 MW, 39.3%, 41.26%, and 0.0731 $/kW·h, respectively. And when the system's hydrogen production load equals to 0, these values are respectively calculated to be 177.25 MW, 50.64%, 53.29%, and 0.0268 $/kW·h. In addition, more than 90% of the system's total energy losses are caused by condenser and Cu–Cl cycle, and about 50–60% of the system's total exergy destructions occur in VHTR. About 60% and 30% of the system's specific energy cost are respectively caused by the equipment investment and the system operation & maintenance, and the investment costs of VHTR and Cu–Cl plant are the system's main capital investment sources.

Thermal Efficiency and Economics of a Boil-Off Hydrogen Re-Liquefaction System Considering the Energy Efficiency Design Index for Liquid Hydrogen Carriers

This study analyzes the thermodynamic, economic, and regulatory aspects of boil-off hydrogen (BOH) in liquid hydrogen (LH2) carriers that can be re-liquefied using a proposed re-liquefaction system or used as fuel in a fuel cell stack. Five LH2 carriers sailing between two designated ports are considered in a case study. The specific energy consumption of the proposed re-liquefaction system varies from 8.22 to 10.80 kWh/kg as the re-liquefaction-to-generation fraction (R/G fraction) is varied. The economic evaluation results show that the cost of re-liquefaction decreases as the re-liquefied flow rate increases and converges to 1.5 $/kg at an adequately large flow rate. Three energy efficient design index (EEDI) candidates are proposed to determine feasible R/G fractions: an EEDI equivalent to that of LNG carriers, an EEDI that considers the energy density of LH2, and no EEDI restrictions. The first EEDI candidate is so strict that the majority of the BOH should be used as fuel. In the case of the second EEDI candidate, the permittable R/G fraction is between 25% and 33%. If the EEDI is not applied for LH2 carriers, as in the third candidate, the specific life-cycle cost decreases to 67% compared with the first EEDI regulation.

Influence of glass cover on the characteristics of PV/trombe wall with BI-fluid cooling

A practical investigation was conducted to demonstrate the effect of a glass cover on the efficiency of the Photovoltaic/Trombe wall using Nano-fluid (water/Al2O3) as a coolant. Two concentrations of nan-particles (0.5% and 1%) were tested. Using the glass cover on the front of the modified Trombe wall causes an increase in the solar cell temperature, which decreases the system's electrical efficiency but increases the room temperature, leading to improved thermal system efficiency. The highest recorded thermal efficiency value was 80% when using glass cover and 0.5% Nano-fluid at 2 p.m. Moreover, the implementation of a Nano-fluid as a coolant was increased the electrical efficiency. The maximum electrical efficiency was 14% at 1 p.m. In the absence of the glass cover and by using 0.5% Nano-fluid as a coolant. In general, using low concentration Nano-particles with cooling water improves the system efficiency, and increasing the Nano-particles concentration causes a negative influence on the system performance. The maximum total efficiency was 88% at 2 p.m. for the operation conditions (with a glass cover and using 0.5% Nano-fluid at the discharge of 300 L daily).

Transient behavior investigation of a regenerative dual-evaporator organic Rankine cycle with different forms of disturbances: Towards coordinated feedback control realization

This study utilizes an innovative regenerative dual-evaporator organic Rankine cycle (RDORC) with R1234ze to recover solid bulk waste heat by using air as heat transfer medium. A comprehensive transient model for RDORC is constructed based on finite volume method. Furthermore, a novel coordinated feedback control system for RDORC including two PI controllers is proposed to remain turbine inlet main vapor and resupplied vapor superheat degrees constant. The transient behaviors of RDORC and simple ORC (SORC) are compared under external disturbances of heat source inlet temperature. The results indicate that under 10 °C step decrease disturbance, the RDORC presents a 0.5 °C larger undershoot and a 164s longer setting time of superheat degree than that of SORC. Compared with SORC, the exergy efficiency enhancement of RDORC increases from initial value 4.13% to final value 4.51% after the step disturbance. Under sinusoidal disturbance with amplitude of 10 °C in RDORC, the peak amplitude of turbine main vapor inlet pressure (3.6%) is far higher than that of turbine resupplied vapor inlet pressure (0.82%). Besides, under random disturbance with variance of 1, the system exergy efficiency and thermal efficiency fluctuate around the design values of 35.67% and 7.65% with maximum deviations of 2.2% and 0.37%, respectively.

Graph-based configuration optimization for S-CO2 power generation systems

Configuration optimization for energy conversion systems is still under-researched compared with that in the chemical process area. As the basis of design and operation optimization, configuration optimization helps generate more advanced thermodynamic configurations and dramatically promotes the efficiency of thermal systems. However, the variable in configuration optimization involves discrete variables to make optimization more complicate when mixed with continuous design variables. Current configuration optimization research focuses on task-orient methods, superstructure, and heuristic algorithms. These methods tend to screen out candidates based on high levels of knowledge from researchers. In this paper, we first developed a graph-based configuration representation with minimum thermodynamic knowledge requirements. Therefore, the searching space shrinks without losing any possible optimum point. The representation is embedded in a simulated annealing-based optimizer. This optimization framework was validated by optimizing the S-CO2 power generation system's configurations with simple and complex component number limitations. This framework has an over 99% generation rate of feasible configurations. The simple and complex case study results show that the optimization framework converges to a recuperated system with an efficiency of 38% and a recompression system with 44% under maximum and minimum temperature of 850 K and 310 K. Moreover, the result of the simple case study was further justified with an exhaust search. Moreover, both case studies' convergence stabilities are confirmed by multiple and independent framework executions. Finally, the initial configuration's influence shows that the best configuration on lower volume searching space will significantly help with computational efficiency and whole converge process on high volume search space problem.

Gray and non-gray simulations of the combined conduction and radiation heat transfer in a complex enclosure utilizing FSK method considering the scattering influences

This research simulates the conduction-radiation problem in a complex enclosure for the gray/ non-gray assumptions with the presence of scattering influences to improve energy efficiency of thermal systems. The enclosure bottom wall includes an inclined recess with two diagonal walls. To convert these diagonal surfaces to the regular rectangular surfaces in Cartesian coordinates, the Blocked-off method is used. The air containing 10% CO2 and 20% H2O is regarded as participating medium in the enclosure. The absorption coefficient of this mixture is obtained across the spectrum using the information of HITRAN2008 database. Simulating the non-gray medium is done by employing the full-spectrum k-distribution (FSK) approach, whilst the gray medium simulation is performed utilizing the Planck mean absorption coefficient. The finite volume and discrete ordinates methods are respectively applied to calculate the energy and radiation transport equations. Impacts of surface emissivity on conductive, radiative and total heat fluxes are examined in details.

Design and optimization of reforming hydrogen production reaction system for automobile fuel cell

Mathematical modeling and simulation analysis of the dimethyl ether steam reforming reaction system were carried out in the study. The numerical results of simulation and experiment were consistent. The effects of reaction conditions on the conversion of dimethyl ether and hydrogen production were analyzed. The internal structure of the reforming reactor was adjusted to obtain higher hydrogen production efficiency. The study established the reforming hydrogen production industry system, and analyzed the thermal efficiency of the system. The results show that when the temperature of the conversion bed is 673 K, the inlet flow rate of the mixture gas is 0.5 ms−1 and the ratio of water to ether is 3, the dimethyl ether steam reforming reaction system could obtain the dimethyl ether conversion rate of 90%, the hydrogen production rate of 88% and system thermal efficiency of 74%.

System modification and thermal efficiency study on the semi-closed cycle of supercritical carbon dioxide

Supercritical carbon dioxide (sCO2) semi-closed cycle is an advanced, efficient, and economical power generation system that can meet the needs of low cost and efficient utilization of coal and low carbon emissions. The Advanced System for Process Engineering software (Aspen Plus) was used to simulate different sCO2 systems. In the simplified sCO2 closed cycle, multi-stage compression and inter-cooling of CO2 compressors together can increase the system efficiency by about 5%. The system thermal efficiency increases by 0.5% with every 10 bar increase of the combustion chamber pressure between 200 bar and 500 bar, and increases by 0.35% with every 10 °C increase of the combustion temperature between 800 °C and 1500 °C. In the typical sCO2 semi-closed cycle--Allam cycle, the gas temperature in the combustion chamber decreases with the increase of CO2 backflow, and it would decrease with increase of the excess O2 ratio. The system thermal efficiency could be improved by 3% by adding reheat and graded expansion, and by 2% with ASU coupling and CO2/O2 mixing. Adding heat exchangers and proper stream distribution can improve the system efficiency by up to 10%. When the combustion chamber temperature is 1300 °C, turbine inlet pressure is 300 bar, turbine outlet pressure is 30 bar, and the split ratio of CO2 is 5:95, the sCO2 semi-closed cycle with precompression, recompression or partial cooling reaches the highest thermal efficiency (~64%). Depending on the results of the system modification and sensitivity analysis, ideas can be provided for the improvement and demonstration of the system.

Entropy optimization for Darcy–Forchheimer electro-magneto-hydrodynamic slip flow of ferronanofluid due to stretching/shrinking rotating disk

The flow of ferronanofluid due to a rotating disk finds its significant place in biomedical sciences, pharmaceuticals, electronics, aerodynamics etc. Entropy generation appears in the systems/processes where its minimization is needed because it prohibits the decay of available energy which in turn boosts the efficiency of the associated thermal systems where it matters the most. In view of these added advantages, the flow and heat transfer behavior of ferronanofluid subject to slip, suction, electromagnetic field, Darcy–Forchheimer effect, and viscous dissipation, Ohmic heating and thermal radiation has been explored within this research. In addition, the role of entropy minimization associated with the flow concern has been analyzed. The apposite governing equations are numerically treated via shooting method. The important outcome of the study include infusion of more porous matrix develops controlled rotating flow due to both deformed disks. Rise in slip parameter augments flow velocity for stretched RD while that shows the adverse effect for shrunk RD. Controlled rate of heat transportation due to enhanced convective heating is significant for shrunk RD than that of stretched RD. Further, low Prandtl fluids, low molecular heat conduction and liquid friction yield entropy minimization thereby leading to uplift efficiency of thermal systems.

Study on a new cascade utilize method for ship waste heat based on TEG‐ORC combined cycle

AbstractIn order to achieve the efficient cascade utilization of various ship's waste heat, improve the energy efficiency of ships and meet the strict requirements of the new international carbon emission regulations, this article proposes a of TEG‐ORC (thermoelectric power generation/organic Rankine cycle) combined cycle, and designs the experimental system. Coupling characteristics of each bottom cycle are taken as the entry point in the combined cycle, using the method of system simulation, the influence of TEG/ORC bottom cycle ratio, evaporation pressure and flow rate of ORC working fluid flow on the key performance of system output power, system thermal efficiency, and waste heat utilization rate of main engine flue gas are studied. The results show that TEG‐ORC combined cycle can overcome the limitations of TEG or ORC, maximize the recovery amount of waste heat, improve the stability and safety of ORC bottom cycle, simulation results show that when the bottom cycle ratio (QTEG/QORC) is 0.52, the maximum output power and maximum thermal efficiency of the experimental system are 2933.7w and 24.68%, respectively. In this condition, the scale of TEG bottom cycle is 41 pieces, the ORC working fluid flow rate is 0.046 kg/s, and the ORC working medium evaporation pressure is 3 MPa.

Experimental investigation on the enhanced performance of a solar PVT system using micro-encapsulated PCMs

In a photovoltaic–thermal (PVT) solar collector, a small percentage of the absorbed solar radiation can be converted into electricity and the rest become heat. The heat could be collected through various working mediums. It is of great practical significance to study PVT system and improve its performance further. In this study, an experimental PVT system using MPCM (Microencapsulated Phase Change Material) slurry as the cooling medium was designed and established. The comprehensive performance of the PVT system was studied. The measured electrical and thermal efficiency of the PVT system using MPCM slurry or tap water under various conditions were compared. Moreover, the MPCM slurry was also used as the working fluid in an outdoor PVT system. The practical performance was compared with those of a traditional water-cooled PVT system and a similar system with PCM layer. The results showed that increasing the flow rates of the MPCM slurry could reduce the temperature of PV cell and improve the thermal and electrical efficiency. The performance of the present PVT system using MPCM slurry is better than that using pure tap water or water with a PCM layer. The average electrical efficiency and the maximum thermal efficiency of the system can effectively increase by 0.8% and 13.5% respectively. The slurry containing low concentration MPCM could enhance the performance, indicating the feasibility of the actual application in solar PVT system.

Energy Efficiency Analysis of Hot Oil Heater System with Waste Heat Recovery Device

In this paper, the energy efficiency analysis of a hot oil heater system with waste heat recovery device is carried out by using the counter balance method. The influence of different excess air coefficient and different flue gas recirculation percentage on the energy efficiency is studied. Through comparative analysis, it is concluded that: as excess air coefficient increases, the exhaust gas heat loss increases, the dissipation heat loss decreases, the overall heat loss increases, and the system thermal efficiency decreases; as flue gas recirculation percentage increases, the exhaust gas heat loss increases, the dissipation heat loss decreases, the overall heat loss increases, and the system thermal efficiency decreases. These conclusions provide some reference for improving the design and operation of hot oil heater system with waste heat recovery device.

Advanced waste heat harvesting strategy for marine dual-fuel engine considering gas-liquid two-phase flow of turbine

The depletion of fossil fuel reserves and deterioration of ecological environment have brought unprecedented challenges to marine manufacturers under the prevailing global trade. To alleviate the severe situation and comply with the concept of energy-conservation and emission-reduction, the development of green, efficient and sustainable waste heat recovery technology is imperative. Here, we propose an advanced waste heat harvesting strategy considering two-phase flow simulation and energy deployment for marine dual-fuel engine. Significantly, the mechanism of bubble formation and its effect on the system are discussed. Subsequently, the relationships between the working-fluid and sensitivity parameters to the subsystem performance are analyzed. Interestingly, a parallel system is designed to dynamically control and deploy energy in coping with the marine real-time energy demand. After the multi-objective optimization, the thermodynamic, economic and environmental performance of the multistage system are calculated. The results prove that (i) the multistage system can recover the investment cost in 10.71 years, the output-power, cooling-capacity and fresh-water are 278.87 kW, 28.96 kW and 0.24 kg/s, respectively; (ii) compared with the original engine system, the output-power and thermal-efficiency of the engine-multistage system are increased by 287.6 kW and 6.89%, showing excellent thermodynamic performance.

Investigation of an integrated solar thermochemical plant for hydrogen production using high-temperature molten salt

One of the most promising methods for producing hydrogen is the use of a water splitting process utilising the copper-chlorine (Cu-Cl) thermochemical cycle. The Cu-Cl cycle uses heat and electricity to produce hydrogen and oxygen from the decomposition of water molecules. In this paper, a new solar-powered integrated system is proposed which utilises (LiNaK)2CO3 high-temperature carbonate molten salt as both a heat transfer fluid and a thermal energy storage medium to provide the required heat for the Cu-Cl cycle reactors and heat exchangers. The system is integrated with a supercritical regenerative steam Rankine cycle (SRC) which produces the required electricity for the electrolyser unit. Thermodynamic and economic analyses were conducted to evaluate the proposed system in terms of hydrogen production cost and system performance. For the base case, the integrated system was found to be capable of producing 823.71 kg/h of hydrogen. The system is optimised for two objective parameters, overall system thermal efficiency and the levelized cost of hydrogen. The results of optimisation analysis indicated that, for the optimal Pareto solution, the overall system thermal efficiency and levelized cost of hydrogen were 29.17%, and $7.58/kg of H2, respectively.

Assessing the performance of the evacuated tube solar collector using smart curtain through (PSO based PID) controller and Nano fluids

This research revealed control on nanofluid temperature in the evacuated tube solar collector system, where nanofluid used in ETSC as working fluid to increase heating system thermal efficiency. Smart curtain was used to shadow the evacuated tube solar collector in heating or cooling conditions to control the temperature of the nanofluid. Moreover, (PSO based PID) controller which is an artificial intelligence method was ‎applied to control on the shadow the evacuated tube solar collector. Where the curtain's main idea is to control the polarization of the sun's radiation, the work of the curtain refers to the parameters: the first parameter is the nano fluid temperature and the second is the ambient temperature, and one output parameter is defined by (distance parameter).

Numerical investigation on the capacity and efficiency of a deep enhanced U-tube borehole heat exchanger system for building heating

Deep geothermal energy has become widely exploited in recent years through the use of closed loop systems for building heating. Intended to meet high heating demand in densely populated neighbourhoods, an enhanced U-tube borehole heat exchanger (EUBHE) system, in which a deviated deep borehole is connected with another vertical one to form a closed loop, is introduced in this work. For capacity and efficiency analysis of applying EUBHE systems to extract deep geothermal energy, a 3D numerical model is implemented and established based on the OpenGeoSys software. Through evaluation by thermal performance tests and thermal response tests on the EUBHE system, the maximum sustainable heat extraction rate is found to be 1.2 MW in a single heating season and 1.1 MW in 10 years, which can provide heating to more than 35,000 m2 of residential buildings located in northern China. Moreover, the 10-year system thermal performance and efficiency are evaluated when coupled with a ground source heat pump (GSHP), and compared with the two deep borehole heat exchanger (2-DBHE) array system that has the same total borehole length as the EUBHE system. Results show that GSHP-coupled EUBHE system is more efficient than the 2-DBHE array system, as it consumes 27% less electricity.