Exergy Characteristics Research Articles

Thermodynamic Comparative Analysis of Cascade Refrigeration System Pairing R744 with R404A, R448A and R449A with Internal Heat Exchanger: Part 2—Exergy Characteristics

The cascade refrigeration systems (CRS) used in hypermarkets and supermarkets, which are used by many people, have been employing R744 for the low-temperature cycle (LTC) and R404A for the high-temperature cycle (HTC) due to environmental and public safety issues. However, the use of R404A is limited due to its high GWP, and therefore research on alternative refrigerants is necessary. Nevertheless, there is no detailed study in the literature that compares and analyzes the three refrigerants for practical design by applying R744 for LTC and R404A, R448A, and R449A for HTC in CRS. Therefore, this study aims to provide data for the practical detailed design of an alternative system to R744/R404A CRS. Under standard conditions, we analyzed how the exergy destruction rate (EDR) and exergy efficiency (EE) of the system and the EDR of each component change when the important factors affecting CRS (degree of superheating (DSH), degree of subcooling (DSC), and internal heat exchanger (IHX) efficiency of HTC, DSH of LTC, condensation temperature (CT), evaporation temperature (ET), cascade evaporation temperature (CET), and temperature difference of CHX) are varied over a wide range. The main conclusions are as follows. (1) Under the given constant conditions, the smallest change in system EDR based on R448A is DSH of HTC (decreased by 0.07–0.1 kW), followed by IHX of HTC (decreased by 0.12–0.3 kW), DSH of LTC (increased by 0.19–0.25 kW), DSC of HTC (decreased by 0.59–0.69 kW), temperature difference of CHX (increased by 1.57–1.83 kW), CET (decreased and then increased by 0.67–4.43 kW), CT (increased by 1.49–3.9 kW), ET (decreased by 2.39–4.61 kW). (2) The highest change rate of system EE based on R448A is CET (increased and then decreased by 1.38–8.28%), followed by temperature difference of CHX (decreased by 2.96–3.16%), ET (increased and then decreased by 0.63–2.75%), DSC of HTC (increased by 1.26–1.34%), CT (increased and then decreased by 0.24–1.12%), IHX of HTC (increased by 0.11–1.02%), DSH of LTC (decreased by 0.35–0.49%), and DSH of HTC (increased by 0.14–0.19%).

Enhancement of the energy and exergy analysis capabilities of the yoghurt process: a case study of the dairy industry

This study provides a comprehensive analysis of the thermal and exergy characteristics of a dairy plant that produces yoghurt. This study aims to perform a comprehensive analysis of the thermal and exergy aspects of a dairy facility that produces yoghurt. This study also seeks to improve the accuracy of the results by evaluating the reliability of the energy and production data. A comprehensive analysis of energy and exergy is utilized to enhance the yoghurt production process. Moreover, the Grassmann-Sankey diagram is employed to produce a map of energy density. The process’s energy and exergy efficiencies were assessed by taking into account the enhancements and alterations made in addition to the existing implementations. Analysis of the yoghurt production process revealed that the total energy input was 113.9 [kW], the total energy output was 72.05 kW as well and the energy efficiency was 63.3%. The exergy input and output for the yoghurt production process were calculated to be 48.95 [kW] and 29.77 [kW], and the exergy efficiency was determined to be 60.8%. This study is expected to promote the growth of livestock and agriculture in the energy sector, and is forecasted to act as a catalyst for future research. This study, which is the first of its kind in the region and is expected to stimulate further research, reveals that improving energy efficiency and conservation in the production of yoghurt products enhances the factory’s overall energy efficiency.

Experimental Investigation of R404A Indirect Refrigeration System Applied Internal Heat Exchanger: Part 2—Exergy Characteristics

Although the R404A indirect refrigeration system (IRS) with an internal heat exchanger (IHX) and R744 as the secondary fluid has potential applications in supermarkets and hypermarkets, the exergy characteristics of this IRS have not been extensively investigated. In this study, the factors affecting the R744 exergy characteristics (degree of subcooling (DSB) and degree of superheating (DSP) of the R404A cycle, DSP of the R744 cycle, condensation temperature (CT) and cascade evaporation temperature (CET), and IHX efficiency) were experimentally evaluated to obtain basic data for the design of R404A IRS with R744 as the optimal secondary fluid. The main results can be summarized as follows: (1) Under given conditions, the smallest change in the system exergy destruction rate (EDR) according to the change in each parameter is the DSP of the R744 cycle (0.3–1%), followed by the DSB of the R404A cycle (6.1–8.8%), the IHX efficiency of the R404A cycle (3.8–14.3%), the DSP of the R404A cycle (11.7–15.9%), the CET (29.4–41.9%), and the CT (35–47%). (2) Also, in terms of the exergy efficiency of system (EES), the largest value was obtained for the DSP of the R404A cycle (2.4–12.7%), followed by the IHX efficiency of the R404A cycle (3–10.2%), the CET (2.2–8.7%), the CT (4–6.9%), the DSB of the R404A cycle (2.7–6.2%), and the DSP of the R744 cycle (0.04–1.2%). (3) In order to lower the system EDR, DSP, DSB, and IHX efficiency of the R404A cycle, the CET must be increased to the maximum, and to lower the DSP of the R744 cycle, the CT must be reduced to the minimum.

Exergy analysis of thermodynamic performance of a gas turbine unit

BACKGROUND: Gas turbine units are the most widespread type of power plants used in almost all industries. Such a wide distribution in combination with a high level of energy characteristics, high specific power and flexibility determine the relevance of research in the field of assessing their operating parameters.
 AIM: Determining the exergy characteristics (exergy efficiency and exergy dissipation factor) of a gas turbine plant and evaluation the efficiency of energy use in a gas turbine plant, as well as analysis of the influence of ambient temperature on the selected parameters.
 METHODS: The paper presents the results of an exergy analysis of the gas turbine plant as part of the Jandar Thermal Power Plant, Syria. To evaluate the described parameters, the method of exergy analysis of the thermodynamic characteristics of a gas turbine plant based on the first and second laws of thermodynamics in conjunction with the laws of conservation of mass and energy was used. An important feature of the study, which also emphasizes its novelty, is taking into account the chemical exergy of combustion gases during the exergy analysis.
 RESULTS: Based on the results of the study, it was found that the maximum exergy efficiency was 92.8% and was typical for a turbine as part of a gas turbine, while the highest exergy dissipation was observed in the process of fuel combustion in the combustion chamber and was equal to 80% (117.3 MW). The lowest exergy values corresponded to the compressor — 6.0% (9 MW). For the gas turbine unit as a whole, the total exergy dissipation was 147.3 MW and the exergy efficiency was 53.3%. In this case, the main sources of irreversibility in the gas turbine unit are the combustion chamber and combustion gases.
 CONCLUSION: Exergy analysis is a convenient method for evaluating the thermodynamic perfection of gas turbine units. As a further line of the study, it is necessary to evaluate the effects of various conditions, such as air humidity or compressor pressure ratio, on the exergy characteristics of the gas turbine fuller.

Preliminary study of a dual channel solar photocatalytic ventilation wall system for year-round air purification and building energy savings

With the aim of meeting the weak adaptability to different seasons and low solar energy utilization efficiency for solar ventilation wall system. In the present work, a novel dual-channel solar photocatalytic ventilation wall (DSPVW) integrated with a photovoltaic (PV) panel and phase change materials (PCM) has been numerically proposed and simulated in winter and summer in subtropical climate zone. A range of performance indicators, such as outlet temperature, air heating gain, and clean air delivery rate (CADR), is evaluated. Furthermore, a comparative analysis is performed to assess the energy and exergy characteristics, distribution, comfortable temperature range percentage (CTRP), energy consumption and savings rate of three different systems: typical solar photocatalytic ventilation wall (SPVW), dual-channel solar photocatalytic ventilation wall (DSPVW), and DSPVW-PV/PCM. Results show that melting temperature of 313.15 K and 323.15 K respectively shows a good performance in winter and summer. The rate of temperature change and peak temperature to the outlet air slow down and decrease with the increase of PCM thickness, resulting in a cooling effect of 1.27 % and 2.83 % in winter and summer. In addition, the simulations with small channels exhibit poor thermal performance but better air purification effect, reaching total CADR as high as 69.46 m3 and 67.33 m3 respectively in winter and summer. Meanwhile, the energy consumption and energy saving rate of the DSPVW-PV/PCM is −3.09 kW and 75.7 %, respectively, compared to the SPVW system. This study could contribute to the widespread adoption and application of solar ventilation walls in regions with hot summers and warm winters.

Experimental Study of the Influences of Operating Parameters on the Performance, Energy and Exergy Characteristics of a Turbocharged Marine Low-Speed Engine

With appropriate strategy of EVC timing and fuel injection, the engine NOx emission could be reduced with acceptable deterioration of fuel consumption. However, for the mechanism of these favorable results, few studies focus on improving the fuel economy from the perspective of energy and exergy analysis, which could be helpful for providing a deeper comprehensive to researchers. Therefore, an experimental study for the combination of EVC timing and fuel injection strategy is conducted based on a marine low-speed engine with 340 mm bore, then the energy and the exergy analysis are separately carried out according to the obtained experimental results. The experimental results show that delaying the exhaust valve closing (EVC), complemented with an appropriate injection strategy, could improve the marine low-speed diesel engine brake specific fuel consumption (BSFC) with the NOx emission almost kept constant. The following energy balance analysis demonstrates that the losses from exhaust gas and heat transfer account for about 50% of total energy. However, from the perspective of exergy analysis, an opposite conclusion could be obtained; the proportion of exhaust gas and heat transfer exergy could reach about 15%, and the ratio of heat transfer could be higher relatively. The losses caused by irreversibility is the biggest source of all, and the irreversibility from combustion could takes about 70% of the total irreversibility. Finally, the reduction of total irreversibility could reach about 4% by optimizing the parameters of marine low-speed engines.

Experimental investigations of particle sizes effects on exergy and entropy characteristics of AL2O3 - MWCNT hybrid nanofluid along the transitional flow regime

Experimental investigation on particle size effect on entropy and exergy characteristics of AL2O3 - MWCNT hybrid nanofluid in transitional flow Regime was carried out with four different particle sizes (i.e., for Aluminum oxide (AL2O3), 20 nm, and 5 nm used while Multiwalled Carbon Nanotubes (MWCNT) <7 nm and 30–50 nm particles). 0.3 vol concentrations of three hybrid nanofluids with different particle size combinations (i.e., Al2O3(20 nm) – MWCNT(20–30 nm), Al2O3(20 nm) – MWCNT(<7 nm), and then Al2O3(5 nm) – MWCNT(<7 nm)) are prepared using a two-step method, at a percentage weight composition (PWC) of 60:40. Results shows that Nanofluid with Al2O3 (20 nm) and MWCNT (<7 nm) have shown the best performance. It has an exergy efficiency of 54.12% at turbulent Reynold number of 4500, while in the transitional flow regime, it records an exergy efficiency of 47.85%. Frictional entropy and thermal entropy in the transitional regime were reduced with hybrid nanofluid of Al2O3 (20 nm) and MWCNT (<7 nm) by 6.78% and 13.53%, respectively, as compared to Al2O3 (5)- MWCNT (<7) nanofluid. Both thermal and frictional entropy effects were better minimized in the turbulent regime than in the lamina and transitional regime, as they were reduced by 16.66 and 24.7%, respectively. The study also recommends that for further investigations, more samples need to be taken to reach a clearer conclusion the effect of particle size, and since this is a hybrid nanofluid the samples should be of different sizes from both nanoparticles.

Energy and exergy analysis of VCR engine fueled with rubber-seed oil methyl ester using response surface methodology

This study presents a comprehensive analysis of the thermodynamic performance of a variable compression ratio engine fueled with rubber-seed oil methyl ester blended with diesel. The objective is to evaluate the energy and exergy characteristics according to the first and second laws of thermodynamics for various compression ratios and supercharging pressures. A 3.5 kW engine with compression ratios values ranging from 18:1 to 22:1 and SC pressures of 0, 0.25, and 0.5 bar (g) at 80% load was considered. The inlet manifold pressure was controlled using a centrifugal-type blower (1.5 m3/min, 350 W, 240 V AC) with an adjustable valve. Key fuel energy parameters including shaft energy, cylinder pressure, brake specific energy consumption, thermal efficiency, heat release rate, absorbed energy by cooling water, exhaust gas temperature, exergy efficiency, exergy destruction, exhaust energy, and emissions were analyzed. Results showed significant improvements in shaft energy (35.51%), thermal efficiency (35.37%), and heat release rate (25.17 J/°CA) for compression ratios 20 and supercharging pressure of 0.25 bar, with a reduction in brake specific energy consumption of 2.912 kJ/s kW. The second law efficiency and irreversibility were observed to be 60.31% and 0.0118 kW/K, respectively. Experimental findings demonstrated a reduction in carbon monoxide (25.12%) and hydrocarbon (40%) under the aforementioned conditions. Response surface methodology was employed to predict optimal operating conditions, and the equations were validated using analysis of variance and p-test. The D-optimality test facilitated the determination of optimal operating parameters for different responses through multi-objective optimization techniques. Individual desirability values were combined to obtain a composite desirability of 0.9054. The study identified compression ratios 18 with a supercharging pressure of 1.78 bar as the optimum operating condition for 20% fuel blends in a low-speed agricultural diesel engine, resulting in a remarkable improvement of 41.24% in energy efficiency and 68.45% in exergy efficiency, with minimal emissions.

Energy and exergy characteristics of an ethanol-fueled heavy-duty SI engine at high-load operation using lean-burn combustion

Ethanol, as the most produced renewable biofuel, is considered a promising low-carbon alternative to petroleum-based fuels in the transport sector due to its high energy density and auto-ignition resistance. The lean-burn combustion in spark-ignition (SI) engines has the potential to further improve thermal efficiency in regard to knock mitigation and the reduction of combustion temperature. However, the characteristics of lean-burn combustion in an ethanol-fueled engine in relation to the combustion losses and the gas-exchange process remain unclear, especially for high-load operation. This study contributes with a deeper understanding of the high-load performance of an ethanol-fueled heavy-duty SI engine using lean-burn combustion. Based on the experimental results from a single-cylinder engine test, a 6-cylinder engine model is built by integrating a validated predictive combustion model to characterize the lean-burn combustion process. The engine’s thermal efficiency and combustion phasing are evaluated for knock limited operation and then compared to the theoretical optimum which is regardless of knock. The energy and exergy balances are applied to evaluate the effect of dilution with excess air ratios up to 1.8. Losses through heat transfer, exhaust flow, and incomplete combustion are quantified. In addition, entropy generated through combustion is discussed to identify the relationship between exergy destruction and different operating conditions. In the context of lean-burn combustion, the thermal efficiency at high-load operation incrementally increases from 40.4% at stoichiometric condition to 47.3% at an excess air ratio of 1.8. At the same time, the exergy destruction through combustion increases by 3.3 percentage points across the selected dilution range. Furthermore, the challenging requirements to realize lean-burn combustion with lower exhaust gas temperatures and higher intake boost pressures is assessed through an exergy analysis of the turbocharging system.

COMPARATIVE ANALYSIS OF EXERGETIC LOSSES IN HEAT RECOVERIES OF GLASS FURNACES

The paper presents the results of a comparative analysis of the exergy losses of heat recovery units of various types included in the waste gas heat recovery systems of glass melting furnaces. Based on the principles of universality and additivity of exergy characteristics, as well as design features of heat recoveries, a comprehensive methodology for studying exergy losses in heat recoveries has been developed. With the help of the developed technique, exergy losses in hot water and hot air heat recoveries, as well as in individual heat exchanger modules, were calculated. A comparative analysis of exergy losses and technological features of heat recovery units included in various schemes for the utilization of waste gases from glass melting furnaces has been carried out. For water-heating heat recoveries, the value of energy losses is less than the value of losses for air-heating heat recoveries. When using water-heating heat recovery units in heat recovery schemes, the coefficient of heat using of the furnace fuel increases, on average, by 20%. Despite the higher level of exergy losses in hot air heat recoveries, taking into account a number of important technological factors determined their competitiveness in heat recovery technologies of glass melting furnaces. At the same time, the heat utilization factor of the furnace fuel increases, on average, by 12.5%.

Performance analysis of a novel mode using solar energy to recycle and reuse water vapor from flue gas of coal-fired power station

Coal-fired power stations need to use massive quantities of coal and discharge substantial amounts of pollutants every year. Coupling solar energy with traditional coal-fired power stations can solve these problems. Most studies focus on using solar energy to heat boiler inlets, feedwater and high-temperature steam. However, areas with more solar energy are often water-deficient areas and saving water resources is particularly important. In this study, a 600 MWe coal-fired power station and solar energy are combined into a solar-aided coal-fired power generation (SACPG) system. Five SACPG systems are studied. There are parallel steam heating, reheating, double reheating, heating feedwater before pump and recycle and reuse water vapor from flue gas. For the first time propose using solar energy to recycle and reuse water vapor from the flue gas of coal-fired power stations in power-boosting (PB) and fuel-saving (FS) modes to analyze its thermal characteristics, exergy characteristics and energy savings. The research shows that feedwater recycle mode has the largest total thermal efficiency, which is 42.47 % and boiler thermal efficiency of 95.02 %. Three operation modes of saving water scheme including feedwater recovery, reheat steam recovery and FS mode are considered in this paper. Among three modes, FS has the smallest exergy loss of all parts, except fans. The FS mode coal saving rate is 10.79 g/kWh and the water saving rate is 3.87 × 105 t per year. The PB mode water saving rate is 4.04 × 105 t per year. Feedwater recycling output is larger than that of reheated steam recycling. The mode with the highest total thermal efficiency, largest solar field exergy efficiency and coal saving rate is using solar energy to heat feedwater parts and parallel steam generation employing thermal solar energy, which are 42.76 %, 27.70 % and 15.53 g/kWh, respectively. Using thermal solar energy to heat feedwater prior to the feedwater pump offers the highest boiler thermal efficiency (94.44 %) and the lowest exergy loss of all parts except fans. Using solar energy to heat high-temperature parts, the reheated steam mode has the largest boiler thermal efficiency, total thermal efficiency and solar field exergy efficiency, which are 94.16 %, 43.68 % and 33.61 % respectively and the smallest exergy loss of all parts, except fans. Meanwhile, the double reheated steam mode has the largest coal saving rate, which is 9.60 g/kWh.

Performance, emissions and exergy analyses of adding CNTs to various biodiesel feedstocks

Extraction of biodiesel from waste cooking oil, jatropha, and corn oils is done by transesterification. Diesel and biodiesel were blended at 20% volume ratio to make methyl ester. At doses of 25, 50, and 100 mg/l, carbon nanotubes (CNTs) was mixed with biodiesel blend. The objective of the present research is to examine experimentally a diesel engine performance, combustion characteristics, exergy and emissions analyses with inclusion of nano additive to various methyl ester feedstocks. Methyl ester blend is enriched with CNTs as JB20C100, WB20C100 and CB20C100 where the improvements in thermal efficiency are raised about biodiesel mixture by 9%, 13% and 15%, respectively. Addition of 100 ppm of CNTs to biodiesel blends achieves the greatest reductions in CO (14%, 22% and 30%), HC (16%, 20% and 25%), and smoke emissions (15%, 19% and 23%) for JB20C100, WB20C100 and CB20C100, respectively. By comparing with B20, blending 100 ppm CNTs with JB20, CB20, and WB20 obtained the highest increases in cylinder pressure of 3%, 5%, and 10%, as well as the highest increases in heat release of 4%, 7%, and 11%, respectively. The downside of CNTs addition achieves a rise in NOx emissions by 10%, 17%, and 22% for JB20C100, WB20C100, and CB20C100, respectively. Exergetic efficiency increases by 8%, 19%, and 24% for B20T100, B20A100, and B20C100, respectively. Sustainability index improvements achieve 1.5%, 5% and 6.5%, for B20T100, B20A100, and B20C100, respectively. WB20 with CNTs of 100 ppm is highly recommended for improving engine performance, combustion, and exergy characteristics with considerable emissions reduction.

Exergy analysis of the Mexican energy sector

This paper proposes a step-by-step, replicable methodology for analyzing the exergy characteristics of a country’s energy system. It introduces a set of indicators comparable to those commonly used to describe national energy systems: (1) exergy intensity (2) exergy destruction per capita, (3) exergy destruction per gross domestic product (GDP), (4) exergy efficiency, and (5) exergetic cost. The energy efficiency of the energy sector in Mexico was roughly 20% lower than energy efficiency, with substantially less improvement over the 15 years from 2013 to 2018. This difference arises from a strong dependency on fossil fuels and associated exergy destruction, which is not immediately apparent when taking only an energy perspective. The economic value of exergy destruction could represent 2.9 % of GDP in Mexico. A decreasing trend in the final exergy consumption is not necessarily reflected in lower exergy destruction. Those indicators provide information about the Jevons’ paradox. And it points to substantial room for efficiency improvements in the energy sector, with important implications for greenhouse gas emissions. Applying the exergy perspective will allow policymakers to understand better opportunities to unlock new efficiencies and improve the sustainability of Mexico’s energy system and those of other countries.

Energy and exergy analysis of a trapezoidal absorber plate‐based solar air collector

AbstractThis study presents energy and exergy characteristics of solar air collectors (SACs) having two different absorber plates, namely flat (Model‐I) and trapezoidal (Model‐II) plates. Experiments were conducted at different tilt angles of 15º, 30º, and 45º and varying mass flow rates (MFR) from 0.0039 kg/s to 0.0156 kg/s in an open environment. Results indicated that with an increment in MFR, the outlet temperature decreases while the heat extraction rate improves. Quantitatively, increasing MFR threefold improves thermal efficiency by 60% and reduces exergy efficiency by 39%. Furthermore, its efficiency increased by 38%–66% when the inclination angle is increased from 15º to 45º. The energy and exergy efficiencies of Model‐II were increased by 8.5% and 8.4%, respectively, more than that of Model‐I. Results indicated that the trapezoidal plate‐based collector offers better heat extraction characteristics and performs better in terms of energy, exergy, effective efficiency, and temperature rise than its flat counterpart.

Experimental Analysis of the R744/R404A Cascade Refrigeration System with Internal Heat Exchanger. Part 2: Exergy Characteristics

This paper examines the exergy efficiency and exergy destruction rate of the R744/R404A cascade refrigeration system (CRS) using an internal heat exchanger in supermarkets according to various conditions affecting the system. A refrigerant of a low-temperature cycle uses R744 and a refrigerant of a high-temperature cycle in the CRS uses R404A. Experiments were conducted by changing various conditions on the high- and low-temperature side, and exergy analysis was performed accordingly. The main results are summarized as follows: (1) the lower the total exergy destruction rate of the CRS, the higher the exergy efficiency of the system, and accordingly the coefficient of performance (COP) of the system is also improved. (2) In the CRS, since the optimum cascade evaporation temperature exists (about −16 °C), it can be said that the limit point, that is, the cascade evaporation temperature with the maximum COP of the system, is the optimum point at about −16 °C. Therefore, at this optimum point, the exergy destruction rate of the cascade heat exchanger becomes the minimum. In other words, it should be noted that when the cascade evaporation temperature is the optimum point, the exergy destruction rate of the R744 compressor and the cascade heat exchanger is minimal. The purpose of this study is to provide basic design data by analyzing the exergy characteristics according to various conditions on the high- and low-temperature side for optimal design of a CRS to which R744 is applied.

ANALYSIS OF EXERGY LOSSES IN HEAT RECOVERY SYSTEMS OF BOILER PLANTS WHEN IMPLEMENTING THE BYPASS METHOD TO PROTECT CHIMNEYS

The results of the analysis of exergy losses in the heat recovery systems of boiler plants during the implementation of one of the thermal methods of anticorrosion protection of gas exhaust ducts - the bypass method - are presented. Gas-consuming boiler plants with a heat recovery system for heating heat supply water are considered. The choice of a complex technique for the analysis of exergy losses in a heat recovery system with gas bypass is substantiated. The technique includes structural-variant and integral balance methods of exergy analysis and is effective due to the small number of parameters required for the calculation, the simplicity of the calculation and analytical methods for obtaining exergy characteristics, and the high accuracy of the results obtained. The principal and structural diagram of the heat recovery system in the implementation of the bypass method is given. In the block diagram, the input and output exergy flows between the individual elements of the heat recovery system are identified. According to the block diagram, an exergy balance equation was compiled, on the basis of which the exergy losses and the heat exergy efficiency criterion were determined. The exergy characteristics of the heat recovery system are given with an increase in the amount of bypassed gases and different values of the heat load of the heat recovery system. It is shown that the nature and extent of the impact of these parameters depend on the specified load. It has been established that an increase in the amount of bypassed gases at all values of the heat load of the heat recovery system leads to a decrease in exergy losses and the heat power criterion. The value of the heat load of the heat recovery system is determined, at which its exergy efficiency in the implementation of the bypass method is the highest.

Energy and Exergy Characteristics of an Ethanol-Fueled Heavy-Duty Si Engine at High-Load Operation Using Lean-Burn Combustion

Energy and Exergy Characteristics of an Ethanol-Fueled Heavy-Duty Si Engine at High-Load Operation Using Lean-Burn Combustion

OPTIMIZATION OF THE TECHNOLOGICAL PARAMETERS OF THE HEAT RECOVERY SYSTEM OF A BOILER PLANT WITH THE AIR PROTECTION METHOD OF GAS WATER TRACTS

The results of a study of the efficiency and optimization of technological parameters of the heat recovery system of a boiler plant, in which the method of mixing part of the heated air into the flue gases after the heat recovery unit, is implemented. The essence of the air method is to increase the temperature and decrease the relative humidity of the resulting mixture, which reduces the amount of condensate on the walls of the exhaust ducts. A gas-consuming boiler plant with a heat recovery system for heating heat supply water is considered. To optimize the technological parameters of the system in the implementation of this method, a complex technique based on exergy analysis was used. The technique combines structural-variant methods and balance integral methods of exergy analysis. This allows you to determine the exergy, heat engineering and technological characteristics that are included in the criteria for evaluating the efficiency of heat recovery systems. Due to the small number of parameters required for the calculation, and the simplicity of the calculation and analytical methods for obtaining exergy characteristics, the technique is convenient for research. The accuracy of the results obtained is 0.3-0.5%. A block diagram of a boiler plant with a heat recovery system in the implementation of the mixing method is given. In the block diagram, input and output excretory flows between individual elements are identified. The criteria for evaluating the efficiency of heat recovery and the main technological optimization parameters have been selected. Based on the general system of exergy, thermal and material balance equations in accordance with the structural scheme, an exergy balance equation was compiled, from which exergy losses and heat-exergy efficiency criteria were determined. The optimal values in the heat exchanger heat output and the amount of mixed air, which correspond to the high efficiency of the system, are determined.

Energy and exergy analyses of a helicoidal water to air geothermal heat exchanger for arid regions

ABSTRACT Helicoidal water-air geothermal heat exchanger (HWAGHE) uses the water well as a heat source/sink for air refreshing purposes in space. It has been exploited as a passive technique to minimize the energy uses in buildings. This work goals to estimate the energy and exergy characteristics of HWAGHE for arid zone weather condition of Algeria. The helicoidally geometry enhancing the heat exchange with the soil is chosen to decrease the operating cost and the needed area. The studied HWAGHE was constructed from a flexible PVC pipe with 30 m length and 0.6 m diameter. It was immersed into a drilled borehole with 1 m diameter and 5 m depth. The heat exchange rate with the ground and exergy and energy efficiencies of HWAGHE is evaluated. Experimental findings revealed that the inlet ambient temperature has a considerable impact on the HWAGHE performances mainly when the change in temperature between the ambient and the water well increments. Maximal exergy and energetic efficiencies of the HWAGHE, reaching 89% and 92%, respectively, are obtained at 0.035 kg s−1 mass flow rate.

Spectral radiation characteristics in semi-coke jet flame for energy utilization

To provide a reference for research and design of the photo-thermal energy cascaded utilization system of fuel combustion, this paper studies the spectral radiation characteristics of the semi-coke jet flame from the perspective of radiative energy utilization. Based on a self-built Hencken flat-flame burner, the spectral radiation characteristics of the semi-coke flame are measured under O2/N2 and O2/CO2 atmospheres using an optical fiber spectrometer. In particular, the spectral radiative exergy characteristics are analyzed based on the second law of thermodynamics. It is found that the intensity of radiative energy and exergy increase, as does the proportion of spectral radiation below the wavelength of 3 μm, with the oxygen ratio and temperature under the experimental conditions. There is little difference between O2/CO2 and O2/N2 atmospheres in the effect on the spectral radiation characteristics. The spectral proportion in the waveband below 1.1 μm is about 7%, while that is over 60% in the waveband of 1.1–3 μm, showing considerable utilization potential. The proportion characteristics of spectral radiation exergy are similar to that of spectral radiation energy in the total spectrum. The spectral radiation in the waveband below 3 μm has higher energy quality because its exergy-to-energy ratio could reach between 76% and 85%. The main factor affecting the radiation exergy is temperature, whereas the influence of the waveband is not obvious. One-dimensional calculation cases of radiation transfer constructed according to the combustion characteristics can well simulate the proportion of spectral radiation. Further studies could adopt numerical simulation as a reasonable supplementary.