Thermal Efficiency Factor Research Articles

A Semi-Analytical Model for the Heat Generation during Hybrid Metal Extrusion and Bonding (HYB).

Hybrid Metal Extrusion and Bonding (HYB) is a novel solid-state welding method for metals and alloys that utilises continuous extrusion as a technique to enable aluminium filler metal additions. In the present study, a new semi-analytical model for the heat generation during aluminium butt welding is presented. As a starting point, the classical Rosenthal thin plate solution for the pseudo-steady-state temperature distribution around a fully penetrating line source is invoked. Then, the associated heat generation is calculated by considering the individual contributions from the tip of the rotating pin, the pin shoulder, and the filler metal additions on the net power input. In a calibrated form, the model yields thermal efficiency factors that are in close agreement with those obtained from more sophisticated finite element analyses but with considerably less computational effort.

Numerical investigation on flat plate collector with struts for drying of fruits and vegetables

The demand for quality food product is growing all around globe due to population explosion. Drying is one of the ancient technique to preserve the fruits and vegetables. Indirect solar drying system with flat plate collector is used in this experiment for drying operation. V-Shaped struts on top of the absorber plate to augment the thermal performance of the dryer. CFD study on the influence of V-shaped struts and its relative roughness pitch parameter on the thermal efficiency, Nusselt number and friction factor was performed. Providing V-shaped struts improved the thermal efficiency of the collector also increased the friction factor. Thermal efficiency improved by 47% while the Nusselt number increased by 2.1 times for plate with V-shaped strut of relative roughness pitch 10 compared to the plain tube.

Thermodynamic analysis and optimization of organic Rankine cycles based on radial-inflow turbine design

In recent years, high-temperature organic Rankine cycle (ORC) with a heat source temperature over 300 °C has attracted interests, which has wide range of applications from industrial point of view. However, few researchers have focused on the coupled design and optimization of the high-temperature ORC system and radial-inflow turbine (RIT). In this work, a coupled design of the ORC system and RIT with the heat source inlet temperatures of 300, 350 and 400 °C is developed using non-dominated sorting genetic algorithm. The ORC thermal efficiency and turbine performance factor (PF) are introduced as optimization objectives. Two mixtures of siloxanes, seven pure siloxanes and nine pure hydrocarbons are considered as working fluid candidates. In addition, the thermodynamic comparison between mixtures of siloxanes and pure working fluids is presented. Moreover, the influences of the turbine inlet total temperature, total-to-static expansion ratio, and specific speed on the ORC thermal efficiency, turbine performance, and turbine size are investigated. The results show that the turbine power output and cycle thermal efficiency are more sensitive to the expansion ratio while turbine size is more sensitive to the turbine inlet total temperature and specific speed. In addition, PF increases with the rise of the turbine inlet total temperature, expansion ratio and specific speed. Moreover, compared with pure working fluids, mixtures of siloxanes have higher efficiencies, but larger turbine and heat exchanger size. Cyclohexane, toluene, m-xylene and hexane with higher PF and smaller size of turbine and heat exchanger are promising working fluids in applications where the compact turbine and heat exchanger is preferred, such as vehicle waste heat recovery.

Heat transfer assessment of turbulent nanofluid flow in a circular pipe fitted with elliptical-cut twisted tape inserts

In the present work, a numerical study is conducted to improve the thermal performance of a circular pipe fitted with the elliptical-cut twisted tape (ECT) inserts in presence of a nanofluid as the working fluid. A comparison between the pipe with and without ECTs in different cases is implemented. This investigation is accomplished for a 3D periodically turbulent flow with constant heat flux on the walls. The effect of inserting the ECTs with different parameters, namely the ratio of short diameter to twisted tape width (WA = a/W = 0.7, 0.8, 0.9) as well as the ratio of long diameter to short diameter of the twisted tape (BA = b/a = 2, 2.5, 3) is examined. In the case of WA = 0.7 and BA = 2 for Reynolds number of 7000, the Nusselt number and thermal efficiency factor (TEF) are maximum with the values about 117.25 and 1.392, which show 6.18% and 6.6% improvement compared to the case with the square-cut twisted tape. Moreover, the Cupric Oxide nanoparticles-enhanced fluid with the nanoparticle concentration ranging from 1 to 4% is used to study the effects of the nanofluid on the heat transfer performance of the different configurations. Based on the results, the highest Nusselt number and TEF occur at the concentration of 4%, which are equal to 177.81 and 1.7637, respectively. Moreover, the TEF for the case with the elliptical-cut twisted tape and nanofluid is 21% higher than the same geometry with water as the working fluid, and 26% higher than the square-cut twisted tape in the presence of water.

Thermo-economic comparison of coal-fired boiler-based and groundwater-heat-pump based heating and cooling solution – A case study on a greenhouse in Hubei, China

Currently in China, the replacement of coal-fired boilers by clean and renewable energy sources is considered as an essential measure to alleviate air pollution. This paper investigates the thermo-economic performance of replacing a coal-fired boiler by a Groundwater Heat Pump (GWHP) system for a greenhouse, where the GWHP system was constructed to reduce emission and also to provide cooling. The operation of this system has been monitored over a one–year period. The results show that the thermal efficiency factor of the boiler varies in the range of 0.53–0.68 and the Coefficient of Performance (COP) of the GWHP system averages at 4.1 for cooling and at 3.3 for heating. Although the boiler has both lower capital costs and lower operating costs, the analysis of Average Energy Price (AEP) shows that the GWHP system has a higher economic performance, since it has a lower AEP of 0.040 USD /kWh in heating and 0.023 USD/kWh in cooling over an expecting lifetime of 20 years, in comparison to the boiler at 0.052 USD/kWh over a lifetime of 10 years. This indicates that GWHP system may be considered as an alternative over traditional boilers in terms of thermo-economic performance for applications in other places of the world with similar climate condition.

Investigation on influence of dimpled surfaces on heat transfer enhancement and friction factor in solar water heater

The solar water heating system efficiently converts available solar energy into useful thermal energy. The collector is the predominant unit of the solar water heating system. Using a heat transfer enhancer in the tube is pondered as one of the effective methods to improve the thermal efficiency of the system. Dimples are used as heat transfer enhancer and created using a punching machine. The primary objective of the research is to endow a numerical investigation on the influence of dimples and its various parameters on the thermal efficiency and friction factor of the solar collector. Simulation is performed by varying pitch-to-dimple diameter ratio (P/Dd), number of dimples and mass flow rate. For the result to be independent of mesh, the optimum number of control volumes is identified as 2.2 million. Numerical modeling is done in such a way that the experimental and CFD results are in good agreement with each other and the error percentage is below 10%. Dimples on the tube disturb the fluid flow and reduce the hydraulic diameter, thus enhancing the heat transfer rate and efficiency of the collector. A maximum of 2.5 times increment in the Nusselt number was observed for the dimpled tube with P/Dd ratio 3 and six dimples between two pitches than plain tube at a mass flow rate of 2.5 kg min−1. The friction factor due to the presence of dimples increased by 11.1% compared to that of the normal tube. The relative better enhancement in thermal efficiency with less friction factor makes dimples a superior heat transfer enhancer.

Technical analysis of an oven with coupled receiver for scheffler solar concentrator tested under cloudy weather conditions

Most of the solar collectors experiments are carried out under clear-sky conditions to evaluate the maximum performance of collectors, even though this condition is not critical for some uses, such as cooking. The optical and thermal performance of a solar oven heated by Scheffler concentrator is here analyzed in more adverse weather conditions. The receiver for conversion and heat transfer of the concentrated solar energy is coupled to an oven specially developed for this work. The Scheffler concentrator geometry is a lateral cut angled 43.23° of a paraboloid matrix, and it works in a two-axis tracking system, to always maintain its focal image at the stationary receiver with the progression of the Earth rotation and solar declination movements. A model for distributing the daily radiation over the hours is used to compare the results. The time-constant experimental method is considered. The heating and cooling tests were carried out at the official local time. The maximum temperature achieved by the absorber was 328°C, and the maximum average temperature in the oven was 150°C. The results for heat loss factor were evaluated, and the trends for thermal efficiency and optical efficiency factor were analyzed for the system considered

The Prediction of Electric Vehicles Load Profiles Considering Stochastic Charging and Discharging Behavior and Their Impact Assessment on a Real UK Distribution Network

Abstract Electric vehicle (EV) as one of the most promising solutions to reduce the greenhouse emission is developing faster than ever. With the increasing number of EVs, the additional load will cause technical issues on the existing distribution network. To cope with possible challenges, the reasonable prediction of EV load profile is fundamental to the evaluation of how the distribution network responds to the potential increasing EV penetration. This paper investigates the critical issues that EVs bring into the network at various penetration levels considering the uncertainties due to stochastic charging and discharging behaviour. To deal with these uncertainties, a Monte Carlo based simulation method is utilised to create EV charging and discharging profiles. Three scenarios are proposed and their impacts on a real UK distribution network are analysed by the simulation in OpenDSS and MATLAB. The simulation results imply that EV charging process has the negative effect in regard to thermal stress, voltage drop, system efficiency and power factor of the network. Conclusions are drawn to provide the guidance for the upgrading and reinforcement of the existing network assets.

Performance evaluation of Ge/SiGe-based thermoelectric generator

The performance of the Ge/SiGe-based Thermoelectric Generator (TEG), is significantly affected by the design and configuration of its Ge/SiGe superlattice structure. Superlattice structures in general play a significant role in the performance of the TEG - module. Experimental observations to design and fabricate an optimized Ge/SiGe based thermoelectric generator are conducted. The Ge element represents the 2D quantum well while Si1-xGex alloy forms the barriers required to reduce the lattice thermal conductivity of the material. The alternate combination of the Ge quantum wells and Si1-xGex barrier forms the superlattice structure. Experiments were conducted for both open and close circuit connections of the Ge/SiGe TEG-module. An estimated Seebeck coefficient of 471.9 μV/K was obtained for the open circuit connection while for the close circuit connections, an estimated power density of 0.111 μW/cm2 and thermal efficiency factor of 0.0035 μWcm−2 K−2 was obtained at a temperature difference of 5.6 K. The results obtained were compared with previous published works. Based on this comparison, it was recommended that the contact resistance should be reduced significantly for improved performance. Also, the TEG module should be extended to multiple legs in order to yield better performances.

Studying thermodynamic efficiency of thermal power plants heat schemes by the exergy method

In this paper the technology for providing peak thermal power of combined heat and power plants using a peak network heater and an additional water-to-water heat exchanger fed by the condensate of this peak heater is proposed. A comparative analysis between the thermodynamic efficiency of traditional thermal power plant heating system diagram with the peak water-heating boilers and the proposed diagram with the peak network heater and the additional water-to-water heat exchanger has been conducted. The analysis was carried out using the exergy method, which allows taking into account different types of energy generated at the thermal power plant. For traditional and proposed technologies to operate the thermal power plant exergy flows, exergy losses, and exergy efficiency factor have been calculated.

Performance enhancement of a curved solar air heater using CFD

In this paper, we report the investigation of various curved solar air heater designs that shows significant enhancement of heat transfer. We have taken the initial design proposed in the reference: Mahboub, C., Moummi, N., Brima, A., Moummi, A., 2015. Experimental study of new solar air heater design. International Journal of Green Energy 13, 521–529, and incorporated promising design modifications to further look for the avenues for thermal efficiency enhancement features. The Computational Fluid Dynamic (CFD) model was first validated by the results reported by Mahboub et al. It was observed that secondary vortex formation near the absorber wall increases the Nusselt number significantly. New correlations for friction factor and Nusselt number has been developed as a function of Reynolds number and various geometric parameters such as relative groove height and pitch ratios for different design of air heaters. It is hoped that data of parameters i.e. Nusselt number (Nu), outlet air temperature (To), thermal efficiency (ηth) and friction factor (f) presented in this paper would help researchers and industry in developing efficient designs of solar collectors.

Optimization of multiple arcs protrusion obstacle parameters using AHP-TOPSIS approach in an impingement jet solar air passage

Present investigation studied the influence of flow and geometric factors on the behavior of solar air passage (SAP) offered among the circular impingement air jets. The experimentation is performed for the variant criterion which is relevant to establish the best design of SAP. The experimental examination shows that the air impingement jet improves the thermal efficiency of a collector but at concurrent period friction factor rate also increases which reduces the whole functioning of arrangement. To overcome this analytical hierarchy process and order of preference by similarity to ideal solution (AHP-TOPSIS) technique is adopted using different performance condition in order to find out the best set of geometric parameters which provides the highest thermal efficiency and lowest friction factor within the SAP. The superlative set of geometric parameters achieved as a response of considered process is relative width ratio of 3, the relative height ratio of 1.0, relative pitch ratio of 9.5, the angle of arc 550 and tream Reynolds number of 19,000 respectively.

Heat transfer enhancement by asymmetrically clamped flexible flags in a channel flow

Two flexible flags clamped in a heated channel were numerically modeled to investigate the dynamics of the flexible flags and their effects on heat transfer enhancement. The penalty immersed boundary method was adopted to analyze the fluid–structure–thermal interaction between the surrounding fluid and the flexible flags. A system comprising the thermally conductive flags in an asymmetric configuration (FAC) with respect to the channel centerline is described for the first time in the present study. The effect of the resulting vortices on heat transfer enhancement was investigated. The FAC generated a reverse Kármán vortex street that encouraged a greater degree of thermal mixing in the wake compared to the vortical structures generated by the flags in a symmetric configuration (FSC). The ratio of FAC occupying a cross-section to the channel height decreased, resulting in a decrease in the pressure drop compared to FSC. The FAC significantly improved the thermal efficiency compared to the FSC. The effects of the gap distance between FAC (G/L) and the ratio of the channel height to the flag length (H/L) on the thermal enhancement were characterized to identify the parameters that optimized the thermal efficiency. The relationship between the flapping dynamics and the heat transfer properties was examined in detail. The presence of the FAC with the optimal parameters increased convective heat transfer by 207% and the thermal efficiency factor by 135% compared to the baseline (open channel) flow. The thermal efficiency factor obtained in the present study was compared with that obtained in the previous studies.

Heat transfer enhancement in solar air heater duct with conical protrusion roughness ribs

Application of protrusion rib roughnesses on the absorber plate of solar air heater (SAH) duct can effectively enhance the heat transfer rate irrespective of pressure drop penalty. This paper presents the numerical investigation of SAH duct, roughened with conical protrusion ribs. Effect of relative ribs pitch (6≤p/e≤12) and relative ribs height (0.020≤e/D≤0.044) on Nusselt number and friction factor have been studied for the range of Reynolds number from 4000 to 16,000. Thermal efficiency of roughened duct have been determined using useful energy gain to air and heat losses to environment. The maximum thermal efficiency (η) and efficiency enhancement factor (EEF) are found as 69.8% and 1.346%, respectively. Correlations of friction factor and Nusselt number have also been developed as function of Reynolds number and roughness parameters of conical ribs.

Performance monitoring: A study on ISO 14001 certified power plant in Malaysia

ISO 14001 has been widely applied by various power plant sectors to manage their plants’ performance. This paper aims to conduct monitoring on the environmental and operational performances of an ISO 14001 certified coal power plant in Malaysia. This work suggests some area for improvements for those performance parameters which show inconsistency and downtrend, statistically. Relevant environmental and operational performance parameters were selected as the indicators for air quality, generating efficiency, power availability and reliability. The environmental parameters are the air quality parameters which include Total Suspended Particulate, Particulate Matter up to 10 μm in size and Sulfur Oxides. Thermal Efficiency and Equivalent Availability Factor were selected as parameters for generating efficiency and availability. For reliability, the parameters are Equivalent Unplanned Outage Factor and Equivalent Planned Outage Factor. Overall findings showed that better performance was recorded on environmental aspect, suggesting more focuses were put on regulatory concerns to ensure high environmental compliances. The present work provides some of the approaches in achieving more effective ISO 14001 implementation in power plant industry, in tandem with the policy of Malaysia government towards a more self-regulating manner. It demonstrates some relevant evidences toward treating operational improvement as equally significant and beneficial efforts for economic gain and environmental enhancement. Furthermore, this study provides a useful structure method for future research on performance monitoring as well as for the reference of other certified and non-certified ISO 14001 power plants.

Методика определения режимов послойной электронно-лучевой наплавки проволоки для аддитивных технологий

Electron beam wire feed deposition is a process that uses an electron beam as a power source and wire as raw material to fabricate metallic items in a vacuum chamber. This technology can be widely used for industrial applications due to its ability of using metal in a very efficient manner, making parts within a short period of time, and ensuring good quality of the produced items. The article presents elaboration of the calculation method for determining the operation modes of the electron beam technology for depositing the metal of wire made of Grade AISI 316L corrosion-resistant austenitic steel on a substrate made of the same material. The calculation method correlates the main process parameters, including the electronic beam current, the additive wire feed rate, and the electron beam gun translation speed, and the effects these parameters have on the geometry, microstructure, and mechanical properties of the obtained beads. The method assumes that the electron beam power is spent for heating and melting the wire and the substrate material. The production process thermal efficiency factor was introduced for taking into account the thermal losses. The item’s macrostructure was analyzed, as a result of which the thermal efficiency was estimated together with the effect the main process parameters have on its value. It was noted in an analysis of the weld beads’ microstructure that columnar crystals (dendrites) appear in the course of metal solidification. It has been found that the electron beam gun displacement speed (the deposition rate), a parameter affecting the molten metal cooling rate, is the key factor influencing the size of columnar grains. The hardness of the obtained beads was investigated, and the following conclusions have been drawn from those investigations. The deposited metal hardness decreases with increasing the bead height. The hardness of beads increases with the deposition rate, which is attributed to a higher melt crystallization rate and the formation of a more fine-grained structure. The growth of hardness toward the bead root is attributed to the fact that the temperature gradient in the root zone is higher than that at the bead top. It has also been found that the hardness value depends on the heat source parameters, the heat source traveling speed (the deposition rate), and the thermophysical properties of the material.

Heat transfer enhancement by flexible flags clamped vertically in a Poiseuille channel flow

A pair of flexible flags clamped vertically in a heated channel was numerically modeled to investigate the dynamics of the flexible flags and their effects on heat transfer enhancement. The penalty immersed boundary method was adopted to analyze the fluid–structure–thermal interaction between the surrounding fluid and the flexible flags. The flexible flags displayed three distinct movement modes: a flapping mode, a fully deflected mode, and an irregular mode that depended on the relationship between the hydrodynamic force and the restoring force. In the flapping mode, vortices shed from flexible flags merged and increased in magnitude. The merged vortical structures swept out the thermal boundary layer and enhanced thermal mixing between the fluid near the heated wall and the channel core flow. Compared to rigid flags, the flexible flags significantly improved the thermal efficiency. The effects of the bending rigidity, channel height, and Reynolds number on the thermal efficiency were observed, and an optimal parameter set was obtained. The presence of the flexible flags with the optimal parameter set resulted in an increase of up to 185% in the net heat flux and 106% in the thermal efficiency factor, compared to the baseline flow. The correlation between the vorticity and the temperature field was examined in detail using the dynamic mode decomposition (DMD) method.

Forced convective heat transfer and thermal efficiency assessment in square channel equipped with 10° wavy thin rib

Forced convective heat transfer and thermo-hydraulic efficiency in the heat exchanger square channel (HESC) inserted with 10° wavy thin rib (WTR) are reported numerically. The effects of rib height, pitch distance and flow velocity on flow and heat transfer profiles are considered. The rib height to the channel height; e/H or HR, is varied in the range 0.05–0.30, while the rib pitch to the channel height; P/H or PR, is varied in the range 0.50–1.25. The air velocity in the HESC inserted with the WTR is considered in terms of Reynolds number. The Reynolds numbers (Re = 100–2000) for the present investigation is analyzed at the inlet condition. The finite volume method (commercial code) with SIMPLE algorithm is picked to solve the present problem. The numerical model of the HESC inserted with the WTR is validated for both grid independence and verification of the smooth HESC. The numerical results of the HESC inserted with the WTR are printed in terms of flow and heat transfer profiles. The values of Nusselt number, friction factor and thermal efficiency factor in the HESC inserted with the WTR are also plotted. As the numerical result, it is found that the WTR in the HESC can produce the vortex flow that the reason for the enhancements of heat transfer and efficiency. The increment of the heat transfer ability in the HESC is detected when increasing rib height and Reynolds number. In addition, the greatest thermal efficiency factor in the HESC inserted with the WTR is around 3.43 at HR = 0.20, PR = 1, and Re = 2000.

Calculation of t8/5 by response surface methodology for electric arc welding applications

One of the greatest difficulties traditionally found in stainless steel constructions has been the execution of welding parts in them. At the present time, the available technology allows us to use arc welding processes for that application without any disadvantage. Response surface methodology is used to optimise a process in which the variables that take part in it are not related to each other by a mathematical law. Therefore, an empiric model must be formulated. With this methodology the optimisation of one selected variable may be done. In this work, the cooling time that takes place from 800 to 500?C, t8/5, after TIG welding operation, is modelled by the response surface method. The arc power, the welding velocity and the thermal efficiency factor are considered as the variables that have influence on the t8/5 value. Different cooling times,t8/5, for different combinations of values for the variables are previously determined by a numerical method. The input values for the variables have been experimentally established. The results indicate that response surface methodology may be considered as a valid technique for these purposes.

Heat input in full penetration welds in gas metal arc welding (GMAW)

Weld bead characteristics are metallurgically controlled by heat input, which depends on the welding parameters. However, for numerous welding specialists, an accurate measurement of the current, voltage, and welding speed is enough for preventing unambiguous process specifications. But a comprehensive knowledge of the effect of others parameters, such as plate thickness and the type of pass to be performed (full penetration, root pass, or filler pass), is also required if a less conservative welding procedure is aimed. The goal of the present paper is to increase the ability to control the quality of the welding processes used in production by considering the effect of heat losses through the back side of the weld by radiation for full penetration welding, when developing welding procedure specifications. It is concluded that the thermal efficiency factor and, consequently, the heat input need to be differentiated in the welding specifications for full penetration welding.