Thermal Efficiency Factor Research Articles

Prediction of thermal efficiency of double pass solar air heater having discrete multi V and staggered ribs

AbstractThis manuscript endeavors to elucidate a comprehensive analysis for the assessment of thermal efficiency in double pass solar air collectors augmented with fabricated roughness, instrumental in the generation of heated air for applications in heating and drying. The analytical procedure delineates comparisons between a smooth and a double‐sided, roughened absorber, characterized by discrete, multi V and staggered configurations of roughness. The analysis was performed for different roughness parameters including relative roughness width (W/w) from 4 to 8 and relative staggered rib size (r/e) from 1 to 4 and relative rib pitch (p′/p) from 0.2 to 0.8 while other parameters were kept constant. The research scrutinizes the impact of a constellation of parameters: the temperature rise coefficient (ΔT/I, varying between 0.002 and 0.02 K‐m²/W), Reynolds number (Re, spanning 2000–20,000), solar irradiance (I, ranging from 600 to 1000 W/m²), and the geometric variables of the artificial roughness, on both the thermal efficiency and efficiency enhancement factor of the collector. The study revealed that the roughened collector exhibits higher thermal efficiency compared to smooth collector for a similar condition. The extreme enhancement in thermal efficiency of the collector with roughness has been found to be 56.75% more than nonroughened collector for Re = 2000. A further observation was made that thermal efficiency has increased sharply for lower flow rate (Re < 10,000) whereas for higher flow rates (Re > 10,000), this increase becomes nearly asymptotic. In addition, the efficiency enhancement factor has also been found to increase with an increase in ΔT/I. A peak value of 2.321 has been found to be obtained for the efficiency enhancement factor for ΔT/I = 0.02 K‐m2/W and I = 1000 W/m2 as a result of the studies conducted.

An experimental study on fuel reforming waste heat recovery engine system fueled with methane

The effects of various operating parameters on a fuel reforming waste heat recovery engine system fueled with methane were experimentally investigated. Steam methane reforming was employed in the system because it is endothermic. Experiments were conducted on the parameters of methane flow rate to reformer and steam-to-carbon ratio to study their effects on the conversion of methane and resulting the overall thermal efficiency of the system. The components of the reformed gas were analyzed, and their effects on the combustion characteristics and thermal efficiency factors of a spark-ignition gas engine were discussed. The effects of engine operating parameters such as spark timing and excess air ratio on the exhaust gas heat recovery effect by fuel reforming and the improvement of system thermal efficiency were also investigated through experiments.

Rice husk reuse as a sustainable energy alternative in Tolima, Colombia

Colombia has great potential to produce clean energy through the use of residual biomass from the agricultural sector, such as residues obtained from the life cycle of rice production. This document presents a mixed approach methodology study to examine the combustion of rice husks as a possible energy alternative in the Tolima department of Colombia. First, the physicochemical characteristics of the rice husk were analyzed to characterize the raw material. Next, System Advisor Model (SAM) software was used to model a bioenergy plant to obtain biochar, bio-oil, and biogas from the combustion of rice husks and generate performance matrices, such as thermal efficiency, heat rate, and capacity factor. Then, the project was evaluated for financial feasibility using a mathematical model of net present value (NPV) with a planning horizon of 5 years. Finally, a subset of the local population was surveyed to assess perspectives on the project in the region. The results of the rice husk physicochemical analysis were the following: nitrogen content (0.74%), organic carbon (38.04%), silica (18.39%), humidity determination (7.68%), ash (19.4%), presence of carbonates (< 0.01%), and pH (6.41). These properties are adequate for the combustion process. The SAM simulation showed that the heat transferred in the boiler was 3180 kW, maintaining an efficiency between 50 and 52% throughout the 12 months of the year, meaning that the rice husk can generate electricity and thermal energy. The financial analysis showed that the internal rate of return (IRR) was 6% higher than the opportunity interest rate (OIR), demonstrating economic feasibility of the project. The design and creation of a rice husk processing plant is socially and environmentally viable and has the potential to contribute to the economic development of the Tolima community and reduce greenhouse gases. Likewise, this activity has the potential to promote energy security for consumers and environmental sustainability while at the same time being economically competitive.

Enhancing heat transfer in laminar channel flow by tuning the mass distribution of a flexible reed

Recent studies have leveraged wall-mounted flexible reeds to augment heat transfer efficiency in channel flows. In this study, we demonstrate that tuning the reed's mass distribution can substantially elevate this heat transfer enhancement. Numerical simulations incorporating the fluid–structure–thermal interaction are performed to investigate the impact of mass distribution on the reed dynamics and the associated heat transfer augmentation. The results indicate that the mass distribution of the reed significantly affects its motion mode, which, in turn, critically modulates the heat transfer characteristics. The maximum thermal efficiency factor is obtained when the reed's mass is concentrated at its distal end. Furthermore, the enhancement effect of tuning reed's mass distribution on heat transfer efficiency is closely related to the bending stiffness γ. Within the range of bending stiffness considered in this study (0.02–0.14), the effect of tuning the reed's mass distribution on the thermal efficiency factor exhibits a trend of increase–decrease–increase as the bending stiffness increases. At high bending stiffness, simply tuning the reed's mass distribution can increase the channel heat flux and reduce energy loss, thereby achieving the goal of enhancing the thermal efficiency factor. At γ = 0.14, allocating the reed's mass at its distal end resulted in a notable enhancement, with a thermal efficiency factor surge of 11.1%.

Innovative cinque rib-roughened stimulators on performance improvement in triangular channel solar air heater

Abstract Present study investigates application of cinque-faced rib roughening to improve the efficiency of solar air heaters (SAHs). Research focuses on a novel design, the cinque-faced rib-roughened triangular channel SAH (CFRTCSAH), which incorporates five-faced wire ribs on the absorber plate’s underside. By breaking down the laminar sublayer and enhancing flow separation and reattachment, - ribs significantly enhance heat transfer. It establishes a comprehensive theoretical model to analyze the thermal and hydraulic performance of the CFRTCSAH. The study considers the influence of parameters such as relative roughness pitch (P/e) and relative roughness height (e/Dh) on thermal efficiency and heat removal factor. The results demonstrate that the CFRTCSAH achieves remarkable thermal efficiency, reaching up to 80.7% under optimal roughness parameters (P/e = 12, e/Dh = 0.05). It is found that an increase in mass flow rates positively impacts thermal efficiency but should not exceed 0.09 kg/s for maximum effective efficiency. Additionally, it has observed that the CFRTCSAH performs most effectively when the relative roughness pitch ratio (P/e) is set to 12. A higher relative roughness height (e/Dh) promotes convective heat transfer, enhancing thermal performance, especially at lower mass flow rates. Conclusion presents a novel approach to improving the thermal performance of SAHs by introducing cinque-faced rib roughening. The CFRTCSAH design exhibits significant potential for achieving high thermal efficiency and can contribute to more efficient solar energy utilization in various applications. These findings offer valuable insights for the development of SAHs, promoting sustainable and energy-efficient technologies.

Heat Transfer Enhancement of a Mini Channel Heatsink by Utilizing Flexible Beams Placed Downstream of a Cylindrical Obstacle

Several studies have demonstrated that flexible vortex generators exhibit higher hydrothermal efficiency than their rigid counterparts. The present study focuses on the implementation of a cylindrical rigid obstacle located in the vicinity of the inlet of a mini channel. Downstream, several flexible beams are attached to the channel walls, oscillating due to the forces exerted by the Von-Karmann vortex street generated by the cylinder. The Reynolds number is sufficiently low to maintain a laminar regime throughout the mini channel. A parametric analysis is conducted to explore the performance of various configurations of flexible beams with differing numbers, heights, and inter-distances. The hydrodynamic, thermal, and hydrothermal performance of the mini channel is evaluated using the time average friction factor, Nusselt number, and thermal efficiency factor. Results indicate that the presence of flexible beams significantly enhances heat transfer. The best configuration increases the overall thermal efficiency by 45%, while elevating the heat transfer and mechanical loss by 3.05 and 8.52 times, respectively, in comparison with an empty mini channel.

BUILDING HEAT SUPPLY SYSTEM BASED ON HYBRID SOLAR COLLECTORS

Increasing the efficiency of solar heat supply systems is one of the important problems of solar energy. The research presented in this article is aimed at improving the efficiency of hybrid solar collectors without a transparent coating for building heating systems. One of the key challenges in the field of solar energy is the development of new technologies to ensure high collection of solar energy and to integrate it into traditional heating and hot water systems. The study shows that hybrid solar collectors with the placement of heat carrier circulation circuit tubes above the heat absorber can increase the thermal efficiency factor with a certain change in the angle of inclination and the density of solar radiation. A nomogram was also developed that determines the dependence of this coefficient on the angles of arrival of solar radiation and its density.

Performance Assessment of Malaysian Fossil Fuel Power Plants: A Data Envelopment Analysis (DEA) Approach

This paper investigated the performance of Malaysian power plants from the year 2015 to 2017 using Malmquist Total Factor Productivity (TFP) index, which is based on Data Envelopment Analysis (DEA). This approach offers substantial advantages as compared to other existing methods as it can measure productivity changes over time for a variety of inputs and outputs. Moreover, it comprises two primary components: the technical efficiency change and the technological change indexes that provide clearer insight into the factors that are responsible for shifts in total factor productivity. This study uses a single input, installed generation capacity (MW), and two outputs, average thermal efficiency (%) and average equivalent availability factor (%). These output-input data included ten main power plants: TNB Natural Gas, SESB Natural Gas, SESB Diesel, SEB Natural Gas, SEB Coal, SEB Diesel, IPP Semenanjung Natural Gas, IPP Semenanjung Coal, IPP Sabah Natural Gas, and IPP Sabah Diesel. The results have two significant implications for fossil fuel power plants in Malaysia. First, technological change was the primary factor in boosting the TFP performance of the fossil fuel power plants in Malaysia. Meanwhile, the decline in TFP performance in Malaysian fossil fuel power plants may be attributed, in part, to a lack of innovation in technical components as the results found that the average technical efficiency changes in 2015 – 2016 were at 146% and then dropped significantly to 2% in 2016 – 2017. Second, the average scale efficiency changes rose dramatically from -53% to 3% providing a significant contribution to the improvement of technical efficiency changes. The fossil fuel power plants become efficient as the power plants’ size increases. This indicates that the size of a power plant positively impacts the performance of the TFP.

Performance improvement of shell and tube heat exchanger by using Fe3O4/water nanofluid

The objective of this paper is to study the effect of nanofluid on the performance of the heat exchanger, as well as the heat transfer rate, coefficient of total heat transfer, friction influence and average Nusselt number, and thermal efficiency factor and has been investigated and discussed. In this work, the output heat transfer of Fe3O4/water nanofluid through shell and tube heat exchanger has been numerically investigated under laminar flow. CFD simulations with ANSYS FLUENT 2020R1 were used adopting finite volume approach to solve the governing equations. Numerical calculations were carried out for Reynolds numbers ranging from 200 to 1400, with nanoparticles as the volume fraction (0.2% and 0.35%). The results show that the augmentation in increase Nusselt number and amount of heat transfer rate and the efficiency of nanofluid at the concentration of 0.35% are approximately 19%, 25% and 12% respectively. It was observed through the results that the friction decreases as the Reynolds number increase.

Effect of triangular cross-sectional transverse wedge on the performance of an inline tube bundle heat exchanger

ABSTRACT In order to have a heat transfer per volume, heat exchangers have to have high overall heat coefficient. The effects of a transverse wedge on the heat transfer, the pressure drop, and the thermal efficiency factor (TEF) of air flow through a tube bundle heat exchanger was investigated. TEF increases continuously with the wedge aspect ratio (α). Form α = 0.275, 0.550, 0.758 to 1, TEF increases continuously from 1.157 to 1.84, 1.11 to 1.72, 1.05 to 1.42, and 1.02 to 1.39 for x/L = 1/3, 2/3, 1, and 0, respectively.

Дослідження впливу основних режимних параметрів на ексергетичний ККД конвективної сушильної установки

Mathematical model is proposed for the numerical study of exergy losses in a chamber convective drying unit and the determination of the Impact of the main mode parameters during convective drying on the exergy coefficient of the useful effect of the convective drying unit. The mathematical model is implemented in the MathCad environment. The SKRR-400 intermittent chamber dryer for drying agricultural products with a one-time load of 400 kg was chosen as the object of the study. The components of exergy losses, which have the greatest influence on the thermodynamic perfection of the drying plant, are determined, and the ways of reducing their specific weight in the exergy balance are indicated. Numerical studies of the effect on the exergetic efficiency coefficient of the dryer of such parameters as the ambient temperature, the temperature of the coolant at the entrance to the drying installation, the temperature of the coolant at the outlet of the drying installation — spent coolant, the temperature of the steam condensate in the heater have been carried out. A numerical experiment showed that with the increase in the initial air temperature, the useful specific exergy consumption for moisture evaporation decreases and the change the prominence of the dryer performance does not affect the total exergy losses. It is established that the energy or exergetic and thermal efficiency factors of the dryer differ significantly . According to the calculations, the exergetic.efficiency of the chamber dryer, which reflects its thermodynamic perfection, does not exceed 14.5 %. Comparison of exergetic.efficiency with the energy or thermal efficiency of SKRR-400 type dryer showed that the thermal efficiency of dryers is significantly higher (50,4 % versus 14,5 %). It is hypothesized that this is due to the fact that thermal efficiency does not take into account the phenomena of irreversibility of heat and mass transfer processes. It was established that losses with waste coolant in the exergy balance make up 8 %, and in the thermal balance — 33,2 %. According to the results of the numerical experiment, it is shown that increasing the efficiency of drying units can be achieved by improving their heating devices and reducing their losses.

Experimental Performance Investigation of a Nanofluid Based Parabolic Trough Concentrator in Malaysia

Abstract— Concentrating solar energy system is a potential solar thermal technology, wherein parabolic trough concentrators (PTC) are becoming growingly popular. In this research, both analytical and experiment analyses have been done. The experiment has compared with analytical results. to examine the effect of different operating parameters. Water and water-carbon nanotube (w-CNT) are used to explore the performance of PTC system. Optimum receiver diameter is found 51.80 mm for the maximum efficiency of the collector. During optimization, mass flow rate and concentration ratio are found to be influencing on the thermal efficiency and heat removal factor. Investigations show improvement in heat transfer for added nanoparticles. Heat transfer rate is better in laminar flow than in turbulent flow. After analytical analyses, an experiment has been done using water and carbon nanotube and compared with analytical results. Results show that for every 1oC increase in outlet temperature heat gain and thermal efficiency with water increase at the rate of 0.02 kJ/s and 1.6% respectively. On the other hand, for w-CNT as HTF, for every 100 W/m2 increase in irradiance, heat gain augments at a rate of 0.23 kJ/s and thermal efficiency upsurges by around 7%. Flow rate of working fluids and solar irradiance are found to have respective negative and positive impact on thermal efficiency of the parabolic trough collector.

Influences of latent heat storage heat sink integrated with solar dryer to enhance drying period

Drying is an important procedure and is popular among farmers to dry agricultural produce. However, farmers cannot dry their crops due to the limited availability of sun rays during the daytime. Because of the above issue, a solar-operated heat sink unit was designed and developed to store 40 kg of phase change material (PCM) for latent heat storage, enabling the desired drying temperature for continuous drying operation. Barium Hydroxide Octahydrate [Ba(OH)2. 8H2O] was used as a PCM which can store the energy in the daytime and release it during off-sunshine hours. The performance of PCM integrated with a solar dryer was investigated with a drying of potato chips in terms of thermal efficiency, drying rate, drying efficiency, and heat utilization factor. In the PCM-enabled dryer, the product was dried in a single day, maintaining the average drying temperature between 58 °C to 66 °C throughout the drying. In contrast, the same product was dried in next day in case of open sun drying. The developed drying system is positioned to operate effectively 4-5 hours after sunset and found a viable option for Agri industries and domestic purposes as it is nonpolluting to the environment and does not contain many more conventional energy sources. Moreover, the developed system saved 5604 kWh of electrical energy and 555.06 liters of diesel fuel each year, as well as reduced 5.49 t CO2 emissions.

Thermal Performance Evaluation of a Tubular Heat Exchanger Fitted with Combined Basket–Twisted Tape Inserts

Features of the tubular type of heat exchanger were examined experimentally in the current study. A rig is fitted with a novel insert as a negative heat transfer increase technique. The core fluid used is air under steady heat flux and a turbulent discharge state (6000 ≤ Re ≤ 19,500) conditions. Two heat transfer augmentation inserts are employed; one is the basket turbulators utilized as a turbulator and placed inside the heat exchanger with a constant pitch ratio (PR = 150 mm), and the other is the basket turbulators together with twisted tape that are installed at the core of the basket turbulators. The measurements illustrated that the Nusselt number (Nu) was found to be higher by about 131.8%, 169.5%, 187.7%, and 206.5% in comparison with the plain heat exchanger for basket turbulators and the combined basket–twisted tape inserts with y/w = 6, 3, and 2, respectively. The highest thermal efficiency factor of the increased tubular heat exchanger is 1.63 times more elevated than that of the simple heat exchanger on average, due to a binary basket-quirky strip for a twisting percentage y/w equal to 2 under steady pumping energy. Further, practical correlations for the Nusselt number, as well as friction characteristics, were established and presented.

Investigation of double-layered wavy microchannel heatsinks utilizing porous ribs with artificial neural networks

Microchannel heatsinks with porous media, wavy and multi-layered configurations introduce compact designs and high efficiencies in cooling applications. Current Computational Fluid Dynamics (CFD) based study bridges the concept by introducing a novel double layered microchannel heatsink with wavy up-down and porous ribs alongside each other. Since Artificial Neural Network (ANN) trained by CFD results reveals designs with better thermal and hydraulic performance with an insignificant computational time, ANN is employed for finding the best performers and effects of waviness on Nusselt number, pressure drop, and maximum temperature difference at the bottom of the microchannel for a Reynold number range of 100 < Re < 800 by defining a thermal efficiency factor. Even though the pressure drop increases in the wavy design, the thermal performance is affected positively. Nusselt number increases more than 55% for Re = 800. The thermal performance increases with the introduction of Dean vortices, especially at higher Re. The best design provides maximum bottom temperature difference of 1.2 °C, with a Thermal Efficiency Factor of 1.34. However, it is observed that better thermal efficiency factors are attained by using a wavy channel at the top layer and keeping the bottom layer straight for the final design.

Examining the Effects of Installed Capacity Mix and Capacity Factor on Aggregate Carbon Intensity for Electricity Generation in China.

Promoting technological advancements and energy transitions in electricity generation are crucial for achieving carbon reduction goals. Some studies have examined the effectiveness of these measures by analysing the driving forces of “aggregate carbon intensity” (ACI) change. However, only a few studies have considered the effect of the installed capacity mix and capacity factor. Moreover, such analysis has never been applied at China’s provincial level after 2015. To alleviate this gap, our study applied a temporal and multi-regional spatial IDA-LMDI model to analyse the driving factors of ACI changes and disparities among the provinces of China from 2005 to 2019. The model notably includes the effects of the installed capacity mix, thermal capacity factor, and overall capacity factor. The analysis revealed that the decline in China’s ACI was diminished after 2015, while an ACI rebound was identified in five provinces. The changes in the ACI from 2015 to 2019 were mainly driven by the effect of the installed capacity mix rather than by the thermal efficiency and thermal capacity factor. The overall capacity factor was the only factor with a negative impact on the ACI change. We also found that its combined effect with the thermal capacity factor on increasing ACI can offset the effect of the installed capacity mix by reducing the ACI in provinces with significant additions of renewable energy installed capacity. The analysis of the influencing factors on the provincial ACI differences revealed that the share of hydropower installed capacity was significant. Moreover, the thermal efficiency and thermal capacity factor both played key roles in the ACI disparities in northeast, northwest, and central China. Overall, this study paves the way for data-driven measures of China’s carbon peak and carbon neutrality goals by improving the capacity factor of wind and solar power, leveraging the critical impact of hydropower, and narrowing the differences in the thermal power sector among provinces.

Wood-Cement Composite and its Reinforcement with Wooden Bars

The task of reducing the negative environmental impact of industrial production and human economic activity is a prerequisite for the development of energy-saving technologies and materials based on industrial and household waste. The technology for the production of wood-cement composite materials is of great importance from an engineering point of view, as well as the technology for wood waste disposal, which has environmental attractiveness. Wood-cement composites are used as heat-insulating and structural materials. At the same time, one of the factors limiting their wide distribution is insufficient bearing capacity. In the course of the research, the strength indicators of building blocks made of wood-cement composite were determined, provided they were reinforced with wooden bars. The authors also concentrated on the thermal efficiency factors influenced by the presence of a block of reinforcing elements in the massif. The study was carried out by means of a physical experiment using Elcut software package. The resulting increase in strength during reinforcement amounted to 27 ... 31% or 3.1 ... 3.22 MPa with the initial strength indicators of the unreinforced block - 2.44 MPa. The volume of the resistance to heat transfer of the block made of a wood-cement composite during its reinforcement practically does not change. The results obtained can be used in the design and operation of building structures.

Heat transfer and pressure drop through mono and hybrid nanofluid‐based photovoltaic‐thermal systems

AbstractUsing nanofluids in photovoltaic‐thermal systems enhances the overall efficiency; however, increasing the pressure drop and pumping power, because of the higher viscosity of nanofluids, is a challenging factor for the nanofluid‐based systems. In the present study, the thermohydraulic performance of the photovoltaic‐thermal system is compared using two water‐based nanofluids including hybrid Ag‐MgO and carbon nanotubes (CNT) nanofluids, as the working fluids. The effect of type and flow rate of the working fluid, nanoparticle concentration, and channel height on the friction factor and Nusselt number is studied using the numerical model. The model is validated using the experimental and numerical results and found that the relative errors of the results are less than 3.8% and 5.2%, respectively, which confirmed the model accuracy. The results showed that at a flow rate of 8 L/h, the volume fraction of 2%, and channel height of 10 mm, the system electrical efficiency, thermal efficiency, and friction factor using CNT nanofluid are, respectively, 0.04%, 1.31%, and 62% higher than those using base fluid and 0.03%, 0.89%, and 53% higher than those using Ag‐MgO nanofluid. It is also found that although increasing the nanoparticle concentration and decreasing the channel height improves the system efficiency, it increases the friction factor and pressure drop. Comparing the results using the mono and hybrid nanofluids showed that the thermal performance of the photovoltaic‐thermal system using CNT nanofluid is slightly better; however, the hydraulic system performance using hybrid Ag‐MgO nanofluid is improved.

Prospects for reducing energy consumption in zinc oxide technology

The heat-technological scheme for the production of zinc oxide from metallic zinc is considered. It is shown that the thermal efficiency factor of the existing industrial process is very low and is equal to 5%. The technological process thermodynamics analysis showed that the zinc vapor combustion exothermic reaction heat is sufficient to provide heat for all endothermic technology stages. The conditions and design of the installation, which make it possible to use this heat for all stages of the technological process, are considered. This provides an increase efficiency factor up to 44%.

Thermal Efficiency, Heat Transfer, and Friction Factor Analyses of MWCNT + Fe3O4/Water Hybrid Nanofluids in a Solar Flat Plate Collector under Thermosyphon Condition

The heat transfer, friction factor, and collector efficiency are estimated experimentally for multi-walled carbon nanotubes+Fe3O4 hybrid nanofluid flows in a solar flat plate collector under thermosyphon circulation. The combined technique of in-situ growth and chemical coprecipitation was utilized to synthesize the multi-walled carbon nanotubes+Fe3O4 hybrid nanoparticles. The experiments were carried out at volume flow rates from 0.1 to 0.75 L/min and various concentrations from 0.05% to 0.3%. The viscosity and thermal conductivity of the hybrid nanofluids were experimentally measured at different temperatures and concentrations. Due to the improved thermophysical properties of the hybrid nanofluids, the collector achieved better thermal efficiency. Results show that the maximum thermal conductivity and viscosity enhancements are 28.46% and 50.4% at 0.3% volume concentration and 60 °C compared to water data. The Nusselt number, heat transfer coefficient, and friction factor are augmented by 18.68%, 39.22%, and 18.91% at 0.3% volume concentration and 60 °C over water data at the maximum solar radiation. The collector thermal efficiency improved by 28.09% at 0.3 vol. % at 13:00 h daytime and a Reynolds number of 1413 over water data. Empirical correlations were developed for friction factor and Nusselt number.