Maximum Effective Efficiency Research Articles

Performance analysis and optimization of solar air heater with double-pass configuration using perforated blocks and semi-circular tubes as artificial roughness

The low heat transfer and thermal efficiency of the solar air heater are primarily caused by the formation of a thermal boundary layer along the absorber plate, which contributes to the low convective heat transfer coefficient between the absorber and air. The use of different artificial roughness geometries enhanced the turbulence that help to supress region of hot spot on the absorber plate more effectively and reduce the thermal boundary layer on the absorber for improved heat transfer. In light of this, the present study explores the double-pass configuration of solar air heater equipped with perforated blocks and semi-circular tubes together as artificial roughness on the performance metrics. The mathematical modeling is performed to evaluate the effect of design parameters: tube amplitude ratio (at/Hd), open area ratio (β) and blockage height ratio (eb/Hd), on thermal and effective efficiency at different Reynolds numbers (Re) and solar irradiation (I). Among the parameters studied, the maximum thermal efficiency is found to be 85.36 %, at eb/Hd of 0.8, at/Hd of 0.3, β of 30 %, Re of 19,000 and I of 1000 W/m2. The maximum effective efficiency has been evaluated, which is found to be 81.89 %, at at/Hd of 0.3, eb/Hd of 0.4, β of 30 %, Re of 11,000 and I of 1000 W/m2. In addition, novel correlations have been established for thermal and effective efficiency, showing absolute percentage errors of 0.2 % and 2.2 % respectively. The results indicate enhanced performance in terms of both thermal and effective efficiency, outperforming earlier designs.

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.

Inertial capture of aerosol particles using liquid bridges in cross flow

We investigate the inertial capture of aerosol particles, suspended in a laminar cross flow between parallel plates, by stationary cylindrical liquid bridges. We track the motion and fate of individual aerosol droplets (3–9 μm diameter) suspended in a flow moving across a single liquid bridge or two-bridge systems, using high-speed imaging under a microscope. First, we measure the capture efficiency by inertial impaction of an isolated liquid bridge collector as a function of the aerosol particles Stokes number and show that it agrees with the efficiency calculated for rigid particles moving in a potential flow past a solid cylinder. We then consider two-bridge systems, that is two parallel cylindrical collectors oriented perpendicular to the flow, but offset from each other. We investigate the effect that the upstream collector has on the effective capture efficiency of the downstream test collector, depending on the transverse offset and Stokes number. The offset is the relative displacement of the downstream collector normal to its axis and in the direction perpendicular to the freestream flow. For small values of the transverse offset, smaller than the radius of the collector, small (zero) effective efficiencies are measured for the test collector, due to a partial (complete) shielding effect by the upstream collector. The effective efficiency thus increases from zero with increasing transverse offset, above a threshold value for complete shielding. As the transverse offset increases further, effective efficiencies larger than the efficiency of an isolated bridge are measured for the test collector, showing enhanced capture due to the redistribution of particles moving past the upstream collector. The relative increase in the inertial capture efficiency is significant for Stokes numbers around (but below) unity, 0.45≲St≲0.9, with relative gains as large as approximately 50%. There is an optimum offset displaying maximum effective efficiency and larger offset values lead to a slight decrease in measured efficiencies. These results demonstrate the importance of the relative arrangement of individual collectors on the overall inertial capture efficiency of aerosol particles and suggest that an array of bridges in a slanted configuration (with optimal transverse offsets) could be used as a high-performance filtration system for aerosol particles.

Performance based investigation of inclined spherical ball roughened solar air heater

Heat transfer augmentation for inclined spherical ball roughened solar air heaters has been investigated and reported in this work. The roughness geometry investigated has advantages of both protruded shape and inclined pattern. This investigation covers the determination of all performance parameters viz., thermal, thermohydraulic and exergetic efficiency and its variations as these parameters are essential to justify the practical utility of the roughened system. The impact of roughness on performance is determined and compared to smooth plate air heater at identical flow conditions. Experimental study on spherical ball roughness aligned inclined to flow direction has not been performed to the best of author’s knowledge. The key outcomes were inline with literature as the maximum thermal efficiency for roughened ducts obtained was 81 % compared to 38 % for smooth duct at flow rate of 0.0319 kg/s. With varying roughness configuration, maximum effective efficiency was found 0.67, 0.748, 0.725 and 0.739 respectively at flow rate 0.0372, 0.0391, 0.04 and 0.0418 kg/s. The determination of exergetic efficiency along with thermal and effective efficiency is something that makes present work different from other works since most of the work performed on roughened solar duct system only deals with thermal and effective efficiency determination. The variation in exergetic efficiency with Reynolds number and temperature rise parameter at different roughness geometrical orientations revealed that as Reynolds number changed, both smooth and rough absorber showed maximum exergetic efficiency at same Reynolds number but rough absorber showed maximum exergetic efficiency at temperature rise parameter of 0.0295, 0.0274, 0.031 and 0.045 with maximum exergetic efficiency being 0.0246, 0.037, 0.0262 and 0.0349 respectively.

Thermal Performance of Double Pass Solar Air Heater With Tubular Solar Absorber

In this investigation, the effect of replacing the conventional solar absorber with a new solar absorber on the thermal performance of a double-pass solar air heater has been studied experimentally and numerically. Three configurations have been introduced, the first configuration is a double pass solar air heater with a flat plate solar absorber (DPSAHWFP) for the aim of comparison, and the second configuration is a double pass solar air heater with a tubular absorber that includes a set of tubes which are fitted perpendicularly to the direction of airflow (DPSAHWT-1), and the third configuration is double-pass solar air heater with a tubular absorber that involves set of tubes which are fitted in parallel to the direction of airflow (DPSAHWT-2). The experiments have been carried out under indoor conditions at a constant heat flux equal to 1000 W/m2 and different air mass flow rates (0.01– 0.03 kg/s). The results revealed that the air mass flow rate has a substantial impact compared to the rise in air temperature, hence, the thermal performance of solar air heater is directly proportional to increase air mass flow rate. In addition, the experimental and numerical outcomes indicated that for all air flow rates. The (DPSAHWT-2) offers higher thermal performance as compared to other models, where the maximum effective efficiency has been obtained at 0.03 kg/s equal to 80.9 %. Moreover, (DPSAHWT-2) is more efficient than DPSAHWFP and DPSAHWT-1 by 4.2 % and 9.8 % respectively.

Study of the working process of a dual-fuel hydrogen engine

The relevance of the article is due to the need to replace petroleum fuels with motor fuels obtained from alternative raw materials. Hydrogen is considered as a promising alternative fuel. The use of hydrogen as a motor fuel makes it possible to solve the problem of a cardinal reduction in carbon dioxide emissions into the atmosphere. Using the DIESEL-RK software package, computational studies of the effect of hydrogen supply on the working process of the gas-diesel engine D-245 were carried out. The diesel cycle of the engine and its gas-diesel cycle were calculated with hydrogen supplies equal to 5, 10, 20, 40, 60 and 80% (taking into account the difference in the heat of combustion of the studied fuels). The maximum effective efficiency of a diesel engine is achieved when 40% hydrogen is supplied to the combustion chamber. In this case, compared to operation only on petroleum diesel fuel, the effective efficiency of the diesel engine increased by 7%.

Theoretical Prediction of Quadruple-Pass Solar Air Heater with Longitudinal Fins by a One-Dimensional Approach

Multi-pass solar air heater is attributed to the increase in efficiency due to reduce top heat loss. In this paper, a quadruple-pass solar air heater equipped with longitudinal fins on both sides of an absorber plate was investigated for efficiencies and axial temperature distribution. A mathematical model is formulated in form of ordinary differential equation (ODE) from eight heat transfer equations to solve for four local temperatures of airflow and four local temperatures of surfaces (two glass covers and two absorber plates). ODEs are solved by numerical integration and validated by the comparison with the published data. The current approach is conducted since an analytical model and parametric study on quadruple-pass solar air heater has not been found in the open literature. Among the fin parameters including thickness, quantity, and height, the fin height has a great influence on thermal efficiency. Thermal efficiency can reach 65.7% at maximum fin height. Reynolds number of 5500 achieves maximum effective efficiency of 63.5%. When the Reynolds number is large, heat transfer in the fourth pass is poor due to the sharp drop in surface temperature at high airflow rate.

Experimental investigation of thermo-hydraulic efficiency and performance characteristics of an impinging jet-finned type solar air heater

The current experimental study aimed to assess the overall performance of a sustainable design solar air heater (SAH). The investigated design comprise of mutual combination of jet impingement technique and application of fins. The array of longitudinal and continuos fins extends the rear side of the absorber and just below to it a jet plate is also encapsulated which consist of inline pattern of holes. For experimentation and testing natural climatic conditions were considered under specific range of design parameters enlisted in Table.1. The influence of the listed parameters is investigated on effective efficiency, outlet air temperature and friction factor respectively. The results are compared with the similar literature available. The outlet air temperature is enhanced while increasing the solar intensity values in comparison to the smooth duct. The maximum effective efficiency obtained is 82.5% for X/Dh = 0.46 respectively. With an increase in the values of Re friction factor decreases and the maximum friction factor has been observed at stream wise pitch ratio of 0.46, jet diameter ratio of 0.046 and least fin spacing of 0.23 yields low values of friction factor. The maximum efficiency in case of impinging jet with fins type design (IJWFSAH) obtained is 84% with 6% and 16% enhancement as compared to simple impinging (IJSAH) and smooth configuration. On the basis of comparative analysis between the theoretical and experimental results of thermal efficiency for IJSAH and IJWFSAH. An average deviation of ± 2% for (Re < 9000) and ± 2.2–3% for (Re > 9000) has been reported for IJWFSAH. The average deviation noted for IJSAH is ± 1.5% for (Re < 9000) and ± 2–3% for (Re > 9000) respectively. The data of comparative analysis shows a good agreement between the experimentally evaluated and theoretically calculated values.

CFD based performance analysis of solar air heater provided with artificial roughness in the form of V – Shaped ribs

The current study comprises of computational fluid dynamics (CFD) analysis of solar air heater integrated with V-shaped ribs on the absorber plate with artificial roughness. The investigation of various fluid flow properties namely flow behaviour, temperature distribution and velocity distribution are performed using Renormalization group (RNG) k-ɛ turbulent model. The turbulence intensity of 5% is considered to investigate the mentioned fluid flow properties by considering the relative roughness height (e/D) range between 0.02 and 0.04, relative roughness pitch (P/e) as 10 and angle of attack (α) from 30° to 90°. The working parameters namely Reynolds number (Re) and intensity of solar radiations ranges from 2500 to 18,000 and 1000 W/m2 respectively. The direction and intensity of solar radiations are monitored by using Discrete Ordination (DO) model. The effective efficiency (ηeff) for different values of relative roughness height is analysed theoretically using the heat energy balance equation keeping relative roughness pitch as constant. The results indicated maximum effective efficiency as 74% for Reynolds number and relative roughness height values of 14,000 and 0.034 respectively.

Effect of variable blockage height ratio on performance for solar air heater roughened with 45° Z-shaped baffles

Solar air heater performance can be augmented using turbulators on the absorber plate. Turbulators like ribs, baffles, vortex generator, etc. has been used. In present work, the absorber plate has been roughened with z-shaped baffles. Various performance parameters have been estimated using MATLAB code. The effect of blockage height ratio (rib height/Channel height) has been studied for configuration having relative pitch ratio of 1.5 and attack angle of 45° under operating condition i.e., insolation of 1100 W/m2 and for attack angle of angle of 45°. It can be concluded that maximum effective efficiency of present configuration is found for Reynold number ranging from 5000 to 10000. Moreover, the blockage ratio of 0.3 has yielded optimum performance.

Effective efficiency assessment of a solar air heater having baffles spaced with different successive ratios

The baffle in the air collector duct increases heat transfer, while also significantly increasing the pressure loss penalty. Pressure loss reduction can be achieved using the unequal baffle pitch which is proposed in this study. In the current paper, a numerical investigation of an air collector duct with inclined baffles is presented. Inclined baffles spaced with successive ratio (r) from 1 to 1.4 and Reynolds number (Re) of air from 2370 to 13250 were varied to evaluate Nusselt number, friction factor and effective efficiency of the collector. 2D numerical simulations with the standard k-ε turbulence model were performed to clarify the flow mechanism through baffles. The results show that pressure loss in case of r > 1 significantly reduces compared to that of r = 1. Therefore, the maximum effective efficiency of the baffled collector duct with successive ratios from 1 to 1.3 is the same and equals to 0.6. It is better to install dense baffles near the inlet than dense baffles near the outlet because many baffles concentrated on the inlet create high turbulence in the rest of the air collector duct.

Performance Evaluation of a Solar Air Heater Roughened with Conic-Curve Profile Ribs Based on Efficiencies and Entropy Generation

First and second laws of thermodynamics are well-established benchmarks to assess a thermal system. The literature revealed that efficiencies of a solar air heater are still low because the transport properties and heat transfer coefficient of the air are not superior. In the previous study, the heat and fluid flow characteristics and thermohydraulic performance of the solar air heater roughened conic-curve profile ribs were numerically examined. In the present extended work, the thermal efficiency, effective efficiency, and exergy efficiency were analytically evaluated. The entropy generation in the vicinity of the rib and the Bejan number along the length of the absorber plate were numerically analysed. These considerations aimed to provide a comprehensive evaluation and subsequent minimization of entropy generation. The impacts of the conic constant and Reynolds number on the above parameters were considered. The results indicated that decreasing the conic constant induced an increase in all efficiencies and a decrease in the entropy generation number. The maximum effective efficiency of 0.6719 occurred at a Reynolds number of 20,122, whereas the exergy efficiency of 0.01527 was obtained at a Reynolds number of 2786. The highest entropy generation due to heat transfer was found at the upstream and downstream corners of a rib and at the position just behind the detachment point. The largest entropy generation due to viscous dissipation was identified at the position in front of the rib tip. The entropy generation due to heat transfer was much higher than the entropy generation due to viscous dissipation.

Thermohydraulic performance enhancement of a new hybrid duct solar air heater with inclined rib roughness

In this work, a new hybrid duct configuration of solar air heater is analytically investigated to improve the thermal performance of the system. The proposed design consists of parallel pass air flow paths with rectangular and triangular cross sections at upper and lower sides of the absorber plate. Both the sides of the absorber plates are roughened with inclined shape ribs. The roughness parameters are configured with relative roughness pitch at the bottom of the plate (Pb/eb) of 4–16, relative roughness height of e/Dh ranges from 0.021 to 0.050 and relative angle of arc of (α/60) 0.5–1. Based on the analytical results it is concluded that the maximum effective efficiency is 80.1% for roughness pitch of 8, relative roughness height of 0.021 and relative angle of arc of (α/60) 0.5, at the mass flow rate of 0.045 kg/s at the upper and lower duct. The effect of the mass flow fraction (i) on the thermal performance of the solar air heater is also analyzed. The system improves the thermal and effective efficiency by 22.4% and 18.1% when compared to conventional rectangular duct parallel pass SAH. The design plots are developed to find the optimum values of roughness parameters with respect to ambient conditions.

Thermal and thermo-hydraulic analysis of arc shaped rib roughened solar air heater integrated with fins and baffles

Present study deals with thermo hydraulic performance enhancement of solar air heater (SAH) with various design configurations. Analytical modeling is carried out to study the effect of absorber plate integrated with arc shaped rib roughened barrier with fins and baffles on thermal and effective efficiency of SAH. Variations of flow factors such as Reynolds number and temperature rise parameter with reference to baffle design parameters are presented. The proposed SAH improves the energy and effective efficiency by 28.3% and 27.1% compared with arc shape rib roughened solar air heater. From the results, it is also concluded that lower baffle width and length values provide maximum effective efficiency at higher mass flow rates. Further, the correlations as a function of Reynolds number, baffle width, length and number of fins is developed for predicting the values of effective efficiency. Thereafter, a plot is developed for comparing analytical effective efficiency with predicted effective efficiency and it is found that the averaged deviation of 13%. This present mathematical model for proposed SAH is validated with models available in the literature.

The effects of engine design and operating parameters on the performance of a diesel engine fueled with diesel-biodiesel blends

This paper reports the effects of engine design and operating parameters such as stroke length, ratio of bore to stroke length, compression ratio, equivalence ratio, engine load, biodiesel percentage, friction coefficient, engine speed and mean piston speed on engine performance and energy losses by experiments and a theoretical model based on the finite-time thermodynamics. In this study, the performance of a single cylinder, four-stroke, direct injection diesel engine fueled with diesel-biodiesel mixtures has been experimentally and theoretically investigated. The simulation results agree with the experimental data. After model verification, parametrical studies have been conducted for various conditions. The results showed that the biodiesel percentage and the cycle pressure ratio affect positively the engine performance. The friction coefficient has negative influence on the engine performance. The effective efficiency decreases with the increasing of the engine load, stroke length, and engine speed but effective power increases with increasing them. The effective power always increases with the increasing mean piston speed. However, the effective efficiency decreases at the constant stroke length condition, as it increases at the constant engine speed condition. The effective power and the effective efficiency increase with increasing equivalence ratio to a specified value and then begin to decrease for constant bore/stroke length conditions. The effective efficiency increases with decreasing equivalence ratio as effective power has an optimum value for constant compression ratio condition. The effects of bore/stroke length change at different conditions. At the constant compression ratio condition, the engine performance increases with increasing ratio of bore to stroke length. They are the optimum values which provide the maximum effective efficiency and maximum effective power at the other conditions. This study also reports the energy losses as the ratio of fuel energy and they are classified as friction losses, incomplete combustion losses, heat transfer losses, and exhaust losses. They are defined with respect to compression ratio. With the increasing compression ratio, the friction losses are constant for constant cycle temperature ratio and equivalence ratio, whereas the incomplete combustion losses increase at a constant cycle temperature ratio condition and are constant at constant equivalence ratio condition. The heat transfer losses increase and the exhaust losses decrease for both the conditions. The presented model could be used to optimize the performance of diesel engines fueled with biodiesel and it can be developed for all kinds of engines running at different conditions with various fuels.

Parametric investigation on thermo-hydraulic performance of wire screen matrix packed solar air heater

This paper presents performance results of a wire screen matrix packed solar air heater based on a mathematical model developed to investigate the effect of various system and operating parameters on the thermo-hydraulic performance. A computer programme is developed in C++ to estimate the temperature rise of the entering air for evaluation of effective efficiency by solving the governing equations numerically using relevant correlations for heat transfer coefficient for packed bed systems. The mathematical model developed is compared with the experimental results as well as previous model and the results are found fairly in agreement. Further, a correlation is developed for determination of extinction coefficient based on the geometrical parameter of matrix. Comparative study of thermo-hydraulic performance of high and low porosity matrices indicate the superiority of high porosity matrices as maximum effective efficiency for high porosity matrix is 76% while for low porosity it is found to be 50%, showing an overall enhancement of about 26%. The effective efficiency value clearly indicates that there exists an optimum duct depth (0.015–0.035m), duct length (2–5m) and width (0.2–0.6m) which results in best thermo-hydraulic performance for various mass flow rates and the maximum effective efficiency is obtained for duct depth of 0.015m, length 5m and width 0.5m.

Investigation of the thermohydraulic performance of impinging jet solar air heater

Jet impingement is an established method of convective heat transfer from the heated surface to the carrier fluid. High heat transfer rates are achieved using impinging jets in solar air heater duct but at the cost of increased friction power penalty. This paper presents thermohydraulic performance of impinging jet solar air heater in the form of effective efficiency and compared the same with that of conventional solar air heater. The study has been carried out to study the effect of Reynolds number, diameter of the jet, streamwise and spanwise pitch on effective efficiency. Based upon the study, it has been concluded that impinging jet solar air heater performs better than the conventional solar air heater for specified range of Reynolds number. The effective efficiency has been computed based upon the correlations developed by the investigators and maximum effective efficiency of 70% has been achieved for impinging jet solar air heater in the range of investigated system and operating parameters. Also, based upon the study, the design plots have been prepared for each jet parameter with temperature rise parameter in order to obtain optimum effective efficiency for desired value of temperature rise.

Second law analysis of a solar air heater having 60° inclined discrete rib roughness on absorber plate

Artificially roughened solar air heaters perform better than the smooth ones under the same operating conditions. However, artificial roughness leads to even more fluid pressure thereby increasing the pumping power. The entropy generation in the duct of solar air heater having 60° inclined discrete rib roughness on one broad wall is studied numerically. The effect of system parameters such as relative roughness height (e/D), relative roughness pitch (P/e) and relative gap position (d/W) have been studied on the heat transfer and entropy generation as well as fluid friction with relative gap width (g/e) 1 and temperature rise parameter () varied from 0.002 to 0.02. For the range of parameters considers in this study, it is seen that for optimum conditions, the entropy and entropy generation number are minimum with maximum effective efficiency. Key words: Solar air heater, 60° inclined discrete roughness, entropy generation, effective efficiency.