Thermodynamic analysis of low-grade solar heat source-powered modified organic Rankine cycle using zeotropic mixture (Butane/R1234yf)

This paper communicates detailed energy and exergy analysis of low-grade energy resource of solar-powered organic Rankine cycle (ORC) integrated with both the internal heat exchanger and open feed water heater, ORC incorporated with the internal heat exchanger, with open feed water heater and basic ORC, respectively. Results indicate that highest first law efficiency (11.9%), exergetic efficiency (51.88%) and lowest exergy destruction (1749?kW) are obtained for ORC integrated with both internal heat exchanger and open feed water heater among other considered ORCs. Moreover, zeotropic mixture (butane/R1234yf) shows better first law and exergetic efficiency and lower exergy destruction than pure fluid.     

Theoretical simulation and experimental research on the system of air source energy independence driven by internal-combustion engine

Presents a new system of air source energy independence driven by internal-combustion engine (EIICE), which used natural gas or other fuels as an independent input energy, and could provide the heating, cooling and hot water for the buildings efficiently. It also could provide electricity for electric equipments of the system. The performance of air source EIICE system was investigated theoretically and experimentally. The experimental and simulation results indicated that the heat capacity of plate heat exchanger (P-HE), heat recovered from exhaust gas heat exchanger (EG-HE), input power of compressor, output power of engine and fuel consumption increased with the increase of the rotary speed, water flow rate of the P-HE and evaporation temperature. Heat recovered from the cylinder jacket heat exchanger (CJ-HE) increased with the increase of the rotary speed and evaporation temperature, but decreased with the increase of the water flow rate of P-HE. The coefficient of performance (COP_t) and primary energy ratio (PER_t) of air source EIICE system also increased with the increase of the water flow rate of P-HE and evaporation temperature, but decreased with the increase of the rotary speed.     

Exergetic cost analysis of a space heating system

In order to evaluate and improve the design of space heating systems with groundwater source heat pumps (GWHP), common design practices should be examined. In this paper, a GWHP system with common design is studied. The COP of the heat pump is 3.5 at design condition. The system is divided into five subsystems, and exergetic cost analysis is performed on it based on structural theory of thermoeconomics. The results show that the three largest relative exergy destructions and lowest exergy efficiencies occur in power generation and distribution, heat pump, and terminal unit subsystems with relative exergy destructions of 71.2%, 17.1% and 7.02% and exergy efficiencies of 32.8%, 54.8% and 65.6% respectively. The three subsystems also have the largest increases of unit exergetic costs of 2.04 W/W, 2.15 W/W, and 2.73 W/W respectively. Therefore, designers of GWHP space heating systems should pay close attention to heat pump and terminal unit subsystems, especially to the latter one because of its larger increase of unit exergetic cost. The unit exergetic cost of the system final exergetic product is 7.92 W/W. This value can be used to evaluate the system and compare it with others from the viewpoint of energy conservation.     

Energy and exergy analysis of a ground-coupled heat pump system with two horizontal ground heat exchangers

In this paper we investigate of energetic and exergetic efficiencies of ground-coupled heat pump (GCHP) system as a function of depth trenches for heating season. The horizontal ground heat exchangers (HGHEs) were used and it were buried with in 1 m (HGHE1) and 2 m (HGHE2) depth trenches. The energy efficiency of GCHP systems are obtained to 2.5 and 2.8, respectively, while the exergetic efficiencies of the overall system are found to be 53.1% and 56.3%, respectively, for HGHE1 and HGHE2. The irreversibility of HGHE2 is less than of the HGHE1 as about 2.0%. The results show that the energetic and exergetic efficiencies of the system increase when increasing the heat source (ground) temperature for heating season. And the end of this study, we deal with the effects of varying reference environment temperature on the exergy efficiencies of HGHE1 and HGHE2. The results show that increasing reference environment temperature decreases the exergy efficiency in both HGHE1 and HGHE2.     

Optimisation of the thermodynamic performance of the Stirling engine

In this communication, the thermodynamic performance of an ideal Stirling cycle engine has been investigated. In this regard, the first law of thermodynamics has been employed to determine state of total heat addition, network output, and thermal efficiency with changes in dead volume percentage and regenerator effectiveness. Second law analysis is applied to obtain the trends for the total entropy generation of the cycle. Moreover, the entropy generation of each element involving the Stirling cycle processes is measured. Three objective functions including the output power per rate of mass of the ideal gas working fluid (w_net) and the thermal efficiency (η_t) have been considered simultaneously for maximisation, and the ratio of total entropy generation to rate of mass of the ideal gas working fluid of the Stirling engine is minimised at the same time. Multi-objective evolutionary algorithms based on the NSGA-II algorithm have been employed, while effectiveness of the regenerator, effectiveness of low- and high-temperature heat exchangers, effectiveness of high-temperature heat exchanger, temperatures of the hot side and cold side, and dead volume ratio are considered as decision variables. After the definition of the Pareto optimal frontier, the final optimal solution has been selected using different decision-making methods such as the fuzzy Bellman–Zadeh, LINMAP and TOPSIS.     

Modeling and performance evaluation of ground source (geothermal) heat pump systems

This study deals with the energetic and exergetic modeling of ground source heat pump (GSHP) systems for the system analysis and performance assessment. The analysis covers two various GSHPs, namely a solar assisted vertical GSHP and horizontal GSHP. The performances of both GSHP systems are evaluated using energy and exergy analysis method based on the experimental data. Energy and exergy specifications are also presented in tables. Some thermodynamic parameters, such as fuel depletion ratio, relative irreversibility, productivity lack and exergetic factor, are investigated for both systems. The results obtained are discussed in terms of energetic and exergetic aspects. The values for COP_HP ranged from 3.12 to 3.64, while those for COP_sys varied between 2.72 and 3.43. The exergy efficiency peak values for both whole systems on a product/fuel basis were in the range of 80.7% and 86.13%. It is expected that the model presented here would be beneficial to everyone dealing with the design, simulation and testing of GSHP systems.     

Experimental investigation on heat transfer characteristics of heat exchanger with bubble fin assistance

ABSTRACT

Heat transfer area per unit volume (m²/m³) of heat exchangers decides the size of the heat exchangers, over the period of years heat exchangers have undergone numerous development in this aspect. One such attractive design is plate heat exchanger which is very compact and has high thermal effectiveness, whereas the flow nature of fluid through this type of heat exchangers is complex. The most common type of plate heat exchanger is chevron type which suffers from large pressure drop (Δp) at higher heat transfer rates, to overcome this problem bubble finned heat exchangers are designed. In this paper the performance of bubble finned heat exchanger is studied with single phase fluid flow condition. The comparative study of finned and no fin configuration shows that the former has 1.8 times higher rate of heat transfer at lower value of Reynold’s number, further the flow remains laminar hence the Δp is minimum.     

CFD analysis of natural convection heat transfer augmentation from square conductive horizontal and inclined pin fin arrays

Numerical investigations on natural convection heat transfer from a vertical isothermal plate with pin fins have been made by solving the Navier–Stokes equation along with the energy equation. Average Nusselt number for the plate with different configurations of pin fins have been obtained. It was observed that the maximum increase of the average Nusselt number occurs at S_v/L?=?0.2 for θ?=?45° with fin height of 24?mm (H/t?=?8). The average Nusselt number increases with fin aspect ratio and decreases with angle of inclination. There is not much difference between the average Nusselt number for in-line and staggered arrangement of fins for the range of parameters studied in the present work. A correlation is developed to predict the average Nusselt number of the plate as a function of fin spacing in stream- and span-wise direction, aspect ratio of fins and its angle of inclination.     

Comparison of natural gas driven heat pumps and electrically driven heat pumps with conventional systems for building heating purposes

Electrically driven heat pumps achieve good efficiencies for space heating. If heat pumps are driven directly by a combustion engine instead of an electric motor, losses attributed to the production and transport of electricity are eliminated. Additionally, the use of the combustion engine's heat leads to a reduced temperature difference across the heat pump. This article presents annual efficiencies of these systems and compares internal combustion engine and electrically driven heat pumps in terms of primary energy consumption and CO₂ emissions. Because heat pump performance depends strongly on the heating circuit's flow temperature level, the comparison is performed for air-to-water and geothermal heat pump systems in two cases of maximum flow temperatures (40 °C and 60 °C). These temperature levels represent typical modern buildings with large heating surfaces and older buildings with high-temperature radiators, respectively. In addition to the different heat pump setups, conventional space heating systems are included in the comparison. The calculations show that natural gas-driven heat pumps achieve about the same efficiency and CO₂ emissions as electrically driven heat pumps powered with electricity from the most modern natural gas-fired combined cycle power plants. The efficiency of such systems is about twice that of conventional boiler technologies.     

Optimisation of electronic device coupled LiBr–H2O absorption heat pump system working at ambient temperature using Taguchi approach

The study attempts to optimise the parameters of a lithium bromide–water (LiBr–H₂O) miniature absorption refrigeration system using Taguchi approach for electronic cooling working at ambient conditions. Thermodynamic optimisation was performed to obtain the optimum coefficient of performance (COP) for heat removal of 100?W by using the Taguchi approach. Three factors were considered: generator temperature (T_g), condenser temperature (T_c) and absorber temperature (T_a), at three different levels. The result showed that the percentage contribution of generator temperature is more on COP. Optimisation of three significant heat exchangers: evaporator, condenser and absorber, was performed by using the Taguchi approach. The study was carried out individually for all the components by varying the hydraulic diameter and aspect ratio at three different levels. The results showed that the hydraulic diameter contributes more than the aspect ratio.     

Energetic and exergetic analysis and assessment of a thermal energy storage (TES) unit for building applications

The main objective of this study is to investigate the energetic and exergetic performances of a latent energy storage system in both charging (solidification) and discharging (melting) processes. A shell-and-tube TES unit was designed, constructed and tested in Dokuz Eylul University, Izmir, Turkey. This experimental unit basically consisted of a heat exchanger section, a measurement system and flow control systems. For the charging mode, the inlet temperatures varied to be −5 °C, −10 °C and −15 °C, while the volumetric flow rates changed to be 2 l/min, 4 l/min and 8 l/min. The experiments were performed for three different tube materials, copper, steel and PE32 and two various shell diameters of 114 mm and 190 mm to investigate the tube material and shell diameter effects on energetic and exergetic efficiencies. It may be concluded that for the charging period, the exergetic efficiency increased with the increase in the inlet temperature and flow rate. For discharging period, irreversibility increased as the temperature difference between the melting temperature of the PCM and the inlet temperature of the heat transfer fluid (HTF) increased and hence the exergy efficiency increased.     

Performance optimisation for an irreversible variable-temperature heat reservoir air refrigerator

The performance analysis and optimisation of an irreversible air refrigerator with variable-temperature heat reservoirs is carried out by taking the cooling load density, i.e., the ratio of cooling load to the maximum specific volume in the cycle, as the optimisation objective using finite-time thermodynamics (FTT) or entropy generation minimisation (EGM) in this paper. The analytical formulae for the relationships between cooling load density and pressure ratio, as well as between coefficient of performance (COP) and pressure ratio are derived with the heat resistance losses in the hot- and cold-side heat exchangers, and the irreversible compression and expansion losses in the compressor and expander. The influences of the effectiveness of the heat exchangers, the inlet temperature ratio of the reservoirs, and the efficiencies of the compressor and expander on the cooling load density versus and pressure ratio are provided by numerical examples. The cooling load density optimisation is performed by finding the optimum pressure ratio of the compressor, the optimum distribution of heat conductance of the hot- and cold-side heat exchangers for a fixed total heat exchanger inventory, and the optimum heat capacity rate matching between the working fluid and the heat reservoirs. The influences of some design parameters, including the effectiveness of the heat exchangers between the working fluid and heat reservoirs, the efficiencies of compressor and expander, the inlet temperature ratio of heat reservoirs, the heat conductance distribution and the heat capacity rate matching between the working fluid and the heat reservoirs on the maximum cooling load density are provided by numerical examples. Optimisation of refrigeration plant design leads to a reduction in size of the compressor, expander, and the hot- and cold-side heat exchangers.     

Thermodynamic investigation of an integrated DI diesel engine with waste heat operated rankine cycle

ABSTRACT

A DI Diesel Engine has been integrated with a Rankine Cycle for making a proposed ‘integrated power generation cycle’. The heat of engine’s exhaust gases and jacket’s water is as a single heat source to produce additional output power through the Rankine Cycle. In exergy analysis, destruction of input exergy is nearly 64.13% due to irreversibilities. The useful exergy output is about 30.3%. The exhaust exergy lost to atmosphere is 5.39%, which is smaller than 20.83% of exhaust energy loss of its input, whereas the useful energy output is almost 38.02%. Moreover, there is the reduction in the BSFC due to the recovery of the exergy from the waste heat. The average reduction in the BSFC is about 18.42%. The results of this proposed cycle also show that the integration of the Diesel Engine with the Rankine Cycle has drastic effect on the efficiencies based on exergy and energy.     

Enhancing heat transfer rate in a car radiator by using Al2O3 nanofluid as a coolant

Conventional fluids such as water, ethylene glycol and mineral oils are normally used as heat transfer fluids. Various techniques are applied to enhance the heat transfer. Heat exchange of the coolant moving through the vehicle radiators is of incredible significance for the advancement of fuel utilisation. In this experiment, the heat transfer performance of the automobile radiator is evaluated experimentally. For this we have taken two different combinations of nanoparticles. Aluminium oxide (Al₂O₃) and magnesium oxide (MgO) nanoparticles are added to the base fluid (80% water?+?20% ethylene glycol) at two concentrations 0.12% and 0.4% volume concentration considering the best pH for longer stability. Similarly, another combination with aluminium oxide (Al₂O₃) and titanium oxide (TiO₂) at the same volume concentrations of 0.12% and 0.4% in the base fluid is also prepared. Furthermore, this increases nanoparticle concentration, air velocity and nanofluid velocity and enhances the overall heat transfer coefficient.     

带膨胀机CO2跨临界热泵系统运行特性

建立了带膨胀机CO2跨临界热泵系统的数学模型,将模拟计算结果与实验测量结果进行了比较,验证了模型的准确性。利用数学模型分析了冷却水进口温度和质量流量、冷冻水进口温度和质量流量对带膨胀机CO2跨临界热泵系统的制冷性能系数及最佳高压侧压力的影响。降低冷却水进口温度和提高其质量流量不仅有利于提高制冷性能系数,而且能降低最佳高压侧压力。提高冷冻水进口温度及质量流量有利于提高制冷性能系数,对最佳高压侧压力影响不大。     

Experimental investigation of heat transfer characteristics of the LED module using passive heat sinks

ABSTRACT

Light-emitting diode (LED) has several advantages and applications due to energy efficiency, versatility, performance, and long life. LED converts only 20–30% of the power input into light, converting the remaining 70–80% of the energy into heat that must be conducted from the LED die to the underlying circuit board, heat sinks, and housings. Improper thermal management will lead to an increase in the junction temperature above the safe limit, thus leading to premature failure of the LED. The present investigation aims to study the variation of case and junction temperature for three types of heat sinks, namely, diagonal, cylindrical, and spiral using 16?W LED. Light output in terms of lux is measured. Experiments were conducted by varying currents from 100 to 300?mA. It was observed that the spiral heat sink has the least junction temperature and thermal resistance among the three heat sinks at all current ratings.     

Thermodynamic performance of HCFC22 alternative refrigerants for residential air-conditioning applications

In this study, thermodynamic performance of two pure hydrocarbons and seven mixtures composed of propylene (R1270), propane (R290), HFC152a, and dimethylether (RE170, DME) was measured in an attempt to substitute HCFC22 in residential air-conditioners. The pure and mixed refrigerants tested have greenhouse warming potentials (GWPs) of 3–58 as compared to that of CO₂ and the mixtures are all near-azeotropic having the gliding temperature difference (GTD) of less than 0.6 °C. Thermodynamic cycle analysis was carried out to determine the optimum compositions before testing and actual tests were performed in a breadboard type laboratory heat pump/air-conditioner at the evaporation and condensation temperatures of 7 and 45 °C, respectively. Test results show that the coefficient of performance (COP) of these mixtures is up to 5.7% higher than that of HCFC22. While propane showed 11.5% reduction in capacity, most of the fluids had the similar capacity to that of HCFC22. Compressor discharge temperatures were reduced by 11–17 °C with these fluids. There was no problem found with mineral oil since the mixtures were mainly composed of hydrocarbons. The amount of charge was reduced up to 55% as compared to HCFC22. Overall, these fluids provide good thermodynamic performance with reasonable energy savings without any environmental problem and thus can be used as long term alternatives for residential air-conditioning and heat pumping applications.     

Boundary layer flow of nanofluids to analyse the heat absorption/generation over a stretching sheet with variable suction/injection in the presence of viscous dissipation

ABSTRACT

In this investigation, the heat and mass transfer characteristics in boundary layer flow about a stretching sheet in a porous medium filled with TiO₂ – water and Al₂O₃ – water-based nanofluids, in the presence of internal heat generation or absorption and viscous dissipation with variable suction or injection effects is numerically studied. The similarity transformations are used to transform the governing boundary layer equations for momentum, energy and species transfer into a set of non-linear ordinary differential equations which are solved numerically by Keller-box method. The obtained numerical results are validated against results computed by using MATLAB bvp4c routine, and excellent agreement is observed. The impact of various pertinent parameters on velocity, temperature and concentration as well as the friction factor coefficient, local heat and mass transfer rates are derived and discussed through graphs and tables for TiO₂ and Al₂O₃ water-based nanofluids. The present study reveals that an increase in Eckert number (Ec) and heat generation/absorption parameter (Q) significantly decreases local heat transfer rate.     

A parametric study on the effects of displacer-cylinder-circumferential-wall thermal conditions on the performance of a γ-type LTD Stirling engine

ABSTRACT

Regarding a Stirling engine’s heat source and heat sink, most of the studies in the literature focus only on the magnitude of temperature difference between them. However, different Stirling engines adopt very different heat-source and heat-sink configurations. This study is aimed at understanding the effects of different displacer-cylinder-wall thermal conditions on engine performance using computational fluid dynamics (CFD). Results include p–V diagrams, heat flux distributions, temperature variations, and effects of three displacer-cylinder-wall parameters on indicated power and efficiency. It is found that the thermal conditions on the displacer-cylinder-circumferential wall (DCCW) impose significant effects on engine performance. Within the ranges of parameters investigated in this study, extending the coverage of heat source and heat sink on this wall improves up to 28% in indicated power at the cost of losing about 10% in efficiency, proving the significance of DCCW conditions on engine performance.