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J.s. Saini - One of the best experts on this subject based on the ideXlab platform.
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A review of thermohydraulic performance of artificially roughened solar Air Heaters
Renewable and Sustainable Energy Reviews, 2014Co-Authors: Anil Kumar, R.p. Saini, J.s. SainiAbstract:Abstract Solar Air Heaters form the major component of solar energy utilization system which absorbs the incoming solar radiation, converting it into thermal energy at the absorbing surface, and transferring the energy to a fluid flowing through the collector. The efficiency of flat plate solar Air heater has been found to be low because of low convective heat transfer coefficient between absorber plate and the flowing Air which increases the absorber plate temperature, leading to higher heat losses to the environment resulting in low thermal efficiency of such collectors. Artificial roughness in the form of repeated ribs is the most effective and economic way of improving the thermal performance of solar Air heater. This paper presents an extensive review on the research carried out on artificial roughened solar Air heater ducts. The objective of this paper is to review various studies, carried out on thermal as well as hydraulic performance of artificial roughened solar Air heater ducts. The review presented in this paper will be useful for the researchers working in this area.
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a comprehensive review on roughness geometries and investigation techniques used in artificially roughened solar Air Heaters
International Journal of Renewable Energy Research, 2012Co-Authors: Anil Kumar Patil, J.s. Saini, K KumarAbstract:Artificial roughness applied on the absorber plate is the most acclaimed method to improve thermal performance of solar Air Heaters at the cost of low to moderate friction penalty. Experimental investigations pertinent to distinct roughness geometries unfolds that the enhancement in heat transfer is accompanied by considerable rise in pumping power. In view of the fact, a designer needs to carefully examine shape and orientation of roughness elements in order to choose the best fit roughness geometry for intended application. Moreover it is required to understand how flow field is affected by particular roughness geometry so that direction of future researches could be conceived. So as to elucidate the useful findings an attempt has been made to review roughness geometries employed in solar Air Heaters. Some distinguished roughness geometries have been compared on the basis of heat transfer enhancements and thermohaydraulic performance to draw attention towards their usefulness for specific applications. Furthermore, light is thrown on different investigation techniques adopted for prediction of heat transfer and friction characteristics of artificially roughened solar Air Heaters to recognize features and limitations of each technique.
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thermal and effective efficiency based analysis of discrete v down rib roughened solar Air Heaters
Journal of Renewable and Sustainable Energy, 2011Co-Authors: Sukhmeet Singh, Subhash Chander, J.s. SainiAbstract:A parametric investigation of discrete V-down rib-roughness geometry in the absorber plate of solar Air heater has been carried out and results obtained are compared with those of conventional flat plate solar Air heater. The thermal and thermohydraulic performance evaluation has been carried out for various values of Reynolds number and roughness parameters of discrete V-down rib-roughness geometry in the absorber plate of solar Air heater duct. The performance curves are plotted in terms of Reynolds number and temperature rise parameter. The discrete V-down rib-roughened solar Air heater performs better as per thermal efficiency or heat energy gain criteria for the investigated range of Reynolds number and rib-roughness parameters. The thermal efficiency is high for discrete V-down rib-roughened solar Air heater due to higher turbulence; however, the pumping power required for Air flow also increases. The thermohydraulic performance on the basis of effective efficiency is a more suitable criterion as it takes into account both the heat collected and the pump work required. For Reynolds number range (or temperature rise parameter) generally employed in solar Air Heaters, the discrete V-down rib-roughened solar Air heater gives higher effective efficiency. It was found that there exist optimum roughness parameters of discrete V-down rib for a given Reynolds number (or temperature rise parameter) at which the effective efficiency is the highest. Curves of optimum roughness parameters based on effective efficiency criterion are also plotted.
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performance of artificially roughened solar Air Heaters a review
Renewable & Sustainable Energy Reviews, 2009Co-Authors: Vishavjeet Singh Hans, R.p. Saini, J.s. SainiAbstract:The conversion, utilization and recovery of energy invariably involve a heat exchange process, which makes it imperative to design more efficient heat exchanger. The use of artificial roughness in different forms, shapes and sizes is the most common and effective way to improve the performance of a solar Air heater. Several studies have been carried out to determine the effect of different roughness element geometries on heat transfer and friction in solar Air Heaters. This study reviews various roughness element geometries employed in solar Air Heaters for performance enhancement. Based on the correlations of heat transfer and friction factor developed by various investigators, an attempt has been made to compare the thermohydraulic performance of roughened solar Air Heaters.
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models for predicting thermal performance of packed bed energy storage system for solar Air Heaters a review
The Open Fuels & Energy Science Journal, 2009Co-Authors: Ranjit Singh, R.p. Saini, J.s. SainiAbstract:Packed bed is generally recommended for attaching with solar Air heater in order to store thermal energy of hot Air. For designing such a system under the given system and operating parameters, it is required to predict performance of the system by using mathematical models. In the present paper an attempt has been made to discuss mathematical models reported in the literature for predicting thermal performance of packed bed energy storage system for solar Air Heaters. The designer may be benefited from the consolidated information reported in the present paper. The continuous use of fossil fuels resulted energy crisis and environmental threat. It is felt that renewable energy sources are quite capable of meeting energy demand of today's world. The use of renewable energy sources for meeting energy needs can conserve the conventional energy sources for more number of decades. Among renewable energy sources solar energy is considered to be one of the most dominating energy source. It has many advantages like large potential, free of cost, available everywhere, environment friendly etc. However time dependent nature is the major disadvantage of solar energy. In order to overcome this disadvantage it is required to attach an energy storage system with the solar energy utilization system. With such a provision the stored energy can be utilized in the absence of solar radiation or under peak load conditions. In case of solar Air Heaters it is required to store thermal energy of flowing hot Air. Packed bed is generally recommended for such an application. Packed bed consists of a container in which solid material elements having good heat capacity remain packed. The hot Air flows from top to bottom of the bed to transfer heat energy. The rise in temperature of solid material takes place and energy can be retained by having properly insulated packed bed. The stored energy can be retrieved by making flow of cold Air from bottom to top of the bed. The schematic of packed bed energy storage system for solar Air Heaters is shown in Fig. (1). The working of such a system is described in detail by Duffie and Beckman (1).
Ho-ming Yeh - One of the best experts on this subject based on the ideXlab platform.
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upward type flat plate solar Air Heaters attached with fins and operated by an internal recycling for improved performance
Journal of The Taiwan Institute of Chemical Engineers, 2012Co-Authors: Ho-ming YehAbstract:Abstract The effect of internal recycle on the collector efficiency in upward-type flat-plate solar Air Heaters attached with fins has been investigated theoretically. The equations for predicting the outlet Air temperature and the collector efficiency were derived from the energy balances on the absorbing plate and flow Air. Considerable improvement in collector efficiency is obtainable if collector is attached with fins to extend the heat-transfer area, and if the operation is carried out with an internal recycle to increase the fluid velocity, leading to improved heat transfer coefficient. The enhancement in collector efficiency increases with increasing reflux ratio, especially for operating at lower Air flow rate with higher inlet Air temperature. It is found that more than 100% of improvement in collector efficiency is obtained by recycling operation. Furthermore, the performance in the device operated with internal recycle overcomes that in the same-size device operated with external recycle.
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heat transfer enhancement of double pass solar Air Heaters with external recycle
Journal of The Taiwan Institute of Chemical Engineers, 2011Co-Authors: Ho-ming YehAbstract:Abstract The effects of double-pass and external-recycle operations on the collector efficiency in solar Air Heaters have been investigated theoretically. It is found that considerable improvement in collector efficiency is obtainable if the operation is carried out with an external recycle, where the desirable effect of increasing fluid velocity to decrease the heat transfer resistance compensates for the undesirable effect of decreasing the driving force (temperature difference) of heat transfer, due to the remixing at the inlet by recycle operation. The enhancement increases with increasing reflux ratio, especially for operating at lower Air flow rate. Moreover, performance of double-pass solar Air heater with recycling device is better in comparison to single-pass solar Air heater of the same size.
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downward type solar Air Heaters with internal recycle
Journal of The Taiwan Institute of Chemical Engineers, 2011Co-Authors: Ho-ming YehAbstract:Abstract The effect of internal-recycle operation on the collector efficiency in flat-plate solar Air Heaters has been investigated theoretically. It is found that considerable improvement in collector efficiency is obtainable if the operation is carried out with an internal recycle, where the desirable effect of increasing fluid velocity to decrease the heat transfer resistance compensates for the undesirable effect of decreasing the driving force (temperature difference) of heat transfer, due to the remixing effect at the inlet by recycle operation. The enhancement increases with increasing reflux ratio, especially for operating at lower Air flow rate, as well as with higher solar radiation incident and inlet Air temperature. Further, the performance in a solar Air heater operated with internal recycle overcomes that in the same-size device operated with external recycle.
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collector efficiency of upward type double pass solar Air Heaters with fins attached
International Communications in Heat and Mass Transfer, 2011Co-Authors: Ho-ming Yeh, Tsungching ChenAbstract:The collector efficiency of upward-type double-pass flat plate solar Air Heaters with fins attached and external recycle is investigated theoretically. The double-pass device was constructed by inserting the absorbing plate into the Air conduit to divide it into two channels (the upper and lower channels). The double-pass device introduced here was designed for creating a solar collector with heat transfer area double as well as the extended area of fins between the absorbing plate and heated Air. Moreover, the advantage of external recycle application to solar Air Heaters is the enhancement of forced heat convection strength, resulting in considerable device heat transfer performance improvement. This advantage may compensate for the remixing at the inlet which decreases the heat transfer transfer-driving force decrement (temperature difference).
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the influences of recycle on performance of baffled double pass flat plate solar Air Heaters with internal fins attached
Applied Energy, 2009Co-Authors: Ho-ming Yeh, Tsungching Chen, Tungwen Cheng, R C WangAbstract:A new device for inserting an absorber plate to divide a flat-plate channel into two parts with fins attached by baffles and external recycling at the ends is presented. The proposed device substantially improves the heat-transfer efficiency. Experimental and theoretical investigations into the device efficiency are presented. The theoretical prediction agreement with the measured values from the experimental results is good. The experimental and theoretical results are represented graphically and compared with data from the downward-type single-pass solar Air Heaters of the same size without recycling. Considerable heat-transfer improvement is obtained by employing baffled double-pass operations with external recycling and fin attached over and under the absorber plate. The recycle ratio and absorber plate location influences on the heat-transfer efficiency and on the power consumption increment are also discussed.
R.p. Saini - One of the best experts on this subject based on the ideXlab platform.
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a review on different techniques used for performance enhancement of double pass solar Air Heaters
Renewable & Sustainable Energy Reviews, 2016Co-Authors: Ravi Kant Ravi, R.p. SainiAbstract:Abstract The performance of a conventional solar Air heater (SAH) can be effectively improved by reducing the losses from the collector surface by providing the proper insulation and increasing the convective coefficient between heat collecting surface and working fluid by enhancing the heat transfer area which can be increased by double pass design. Various experimental and theoretical investigations have been considered to enhance the performance of double pass solar Air Heaters (DPSAHs) provided with performance enhancement techniques i.e. using packed bed materials (PBMs), extended surfaces and corrugated/grooved absorbing surfaces. These studies include the cost analysis, thermohydraulic characteristics and design of DPSAH. The objective of present study is to review the various investigations conducted on performance enhancement of double pass system. Based on the review, it is found that the most of the investigations were performed on double pass system having PBM and integrated with extended surfaces. Few studies were conducted on corrugated or grooved absorbing surface and very few studies have been presented on double pass systems having artificial roughness. Further, in order to compare the thermal performance of different designs of DPSAHs, an attempt has been made to generate the performance results using correlations developed by various investigators.
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A review of thermohydraulic performance of artificially roughened solar Air Heaters
Renewable and Sustainable Energy Reviews, 2014Co-Authors: Anil Kumar, R.p. Saini, J.s. SainiAbstract:Abstract Solar Air Heaters form the major component of solar energy utilization system which absorbs the incoming solar radiation, converting it into thermal energy at the absorbing surface, and transferring the energy to a fluid flowing through the collector. The efficiency of flat plate solar Air heater has been found to be low because of low convective heat transfer coefficient between absorber plate and the flowing Air which increases the absorber plate temperature, leading to higher heat losses to the environment resulting in low thermal efficiency of such collectors. Artificial roughness in the form of repeated ribs is the most effective and economic way of improving the thermal performance of solar Air heater. This paper presents an extensive review on the research carried out on artificial roughened solar Air heater ducts. The objective of this paper is to review various studies, carried out on thermal as well as hydraulic performance of artificial roughened solar Air heater ducts. The review presented in this paper will be useful for the researchers working in this area.
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performance of artificially roughened solar Air Heaters a review
Renewable & Sustainable Energy Reviews, 2009Co-Authors: Vishavjeet Singh Hans, R.p. Saini, J.s. SainiAbstract:The conversion, utilization and recovery of energy invariably involve a heat exchange process, which makes it imperative to design more efficient heat exchanger. The use of artificial roughness in different forms, shapes and sizes is the most common and effective way to improve the performance of a solar Air heater. Several studies have been carried out to determine the effect of different roughness element geometries on heat transfer and friction in solar Air Heaters. This study reviews various roughness element geometries employed in solar Air Heaters for performance enhancement. Based on the correlations of heat transfer and friction factor developed by various investigators, an attempt has been made to compare the thermohydraulic performance of roughened solar Air Heaters.
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models for predicting thermal performance of packed bed energy storage system for solar Air Heaters a review
The Open Fuels & Energy Science Journal, 2009Co-Authors: Ranjit Singh, R.p. Saini, J.s. SainiAbstract:Packed bed is generally recommended for attaching with solar Air heater in order to store thermal energy of hot Air. For designing such a system under the given system and operating parameters, it is required to predict performance of the system by using mathematical models. In the present paper an attempt has been made to discuss mathematical models reported in the literature for predicting thermal performance of packed bed energy storage system for solar Air Heaters. The designer may be benefited from the consolidated information reported in the present paper. The continuous use of fossil fuels resulted energy crisis and environmental threat. It is felt that renewable energy sources are quite capable of meeting energy demand of today's world. The use of renewable energy sources for meeting energy needs can conserve the conventional energy sources for more number of decades. Among renewable energy sources solar energy is considered to be one of the most dominating energy source. It has many advantages like large potential, free of cost, available everywhere, environment friendly etc. However time dependent nature is the major disadvantage of solar energy. In order to overcome this disadvantage it is required to attach an energy storage system with the solar energy utilization system. With such a provision the stored energy can be utilized in the absence of solar radiation or under peak load conditions. In case of solar Air Heaters it is required to store thermal energy of flowing hot Air. Packed bed is generally recommended for such an application. Packed bed consists of a container in which solid material elements having good heat capacity remain packed. The hot Air flows from top to bottom of the bed to transfer heat energy. The rise in temperature of solid material takes place and energy can be retained by having properly insulated packed bed. The stored energy can be retrieved by making flow of cold Air from bottom to top of the bed. The schematic of packed bed energy storage system for solar Air Heaters is shown in Fig. (1). The working of such a system is described in detail by Duffie and Beckman (1).
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Performance of artificially roughened solar Air Heaters—A review
Renewable and Sustainable Energy Reviews, 2009Co-Authors: Vishavjeet Singh Hans, R.p. Saini, J.s. SainiAbstract:The conversion, utilization and recovery of energy invariably involve a heat exchange process, which makes it imperative to design more efficient heat exchanger. The use of artificial roughness in different forms, shapes and sizes is the most common and effective way to improve the performance of a solar Air heater. Several studies have been carried out to determine the effect of different roughness element geometries on heat transfer and friction in solar Air Heaters. This study reviews various roughness element geometries employed in solar Air Heaters for performance enhancement. Based on the correlations of heat transfer and friction factor developed by various investigators, an attempt has been made to compare the thermohydraulic performance of roughened solar Air Heaters.
B.n. Prasad - One of the best experts on this subject based on the ideXlab platform.
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optimization of thermo hydraulic performance in three sides artificially roughened solar Air Heaters
Solar Energy, 2015Co-Authors: B.n. Prasad, Ashwini Kumar, K P SinghAbstract:Abstract Providing artificial roughness on the Air flow side is an effective technique to enhance rate of heat transfer in solar Air Heaters, which results in associated higher value of friction factor, and more power required. A novel solar Air heater duct with three artificially roughened sides has been analyzed (Prasad et al., 2014), for more increase in heat transfer than that in only one side roughened solar Air Heaters. Artificially roughened solar Air Heaters have been analyzed (Prasad and Saini, 1991) and investigated (Verma and Prasad, 2000), for optimal thermo hydraulic performance. The present analysis deals with optimization of thermo hydraulic performance in three sides artificially roughened solar Air Heaters, and arrives at the conclusion that the equation given by e opt + = e / D f ¯ r 2 Re = 23 , always corresponds to the optimal thermo hydraulic performance, when every set of the values of the roughness and flow parameters p/e, e/D and Re, separately or combined, results in the optimal thermo hydraulic performance. Optimal thermo hydraulic performance of such solar Air heater is both quantitatively and qualitatively better than one side roughened solar Air Heaters.
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Thermal performance of artificially roughened solar Air Heaters
Solar Energy, 2013Co-Authors: B.n. PrasadAbstract:Artificially roughened solar Air Heaters have been analysed (Prasad and Saini, 1988) for fully developed turbulent flow and found to perform better both quantitatively and qualitatively compared to the smooth ones under the same operating conditions. Optimal thermo-hydraulic performance of such solar Air Heaters has been analysed (Prasad and Saini, 1991) and investigated (Prasad and Verma, 2000) for the maximum heat transfer and minimum pressure drop. This paper represents the experimental results on heat transfer and thereby thermal performance of artificially roughened solar Air Heaters for fully developed turbulent flow data collected under actual outdoor conditions. Such solar Air Heaters have been found to give considerably high value of collector heat removal factor (FR), collector efficiency factor (F′) and thermal efficiency (ηth) as compared to the corresponding values of those of smooth collectors. In the range of the operating parameters investigated, the ratio of the respective values of the parameters FR, F′ and ηth for the roughened collectors to the smooth collectors have been found to be 1.786, 1.806 and 1.842 respectively.
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Investigation for the optimal thermohydraulic performance of artificially roughened solar Air Heaters
Renewable Energy, 2000Co-Authors: Sanjay Verma, B.n. PrasadAbstract:Artificially roughened solar Air Heaters perform better than the plane ones under the same operating conditions. However, artificial roughness leads to even more fluid pressure thereby increasing the pumping power. Roughness and flow parameters viz. relative roughness pitch p/e, relative roughness height e/D and flow Reynolds number Re have a combined effect on the heat transfer as well as fluid pressure (friction factor). Investigation for the optimal thermohydraulic performance (i.e. maximum heat transfer for minimum friction loss) of artificially roughened solar Air Heaters has been carried out. An optimisation parameter known as roughness Reynolds number which combines the roughness and flow effect and is expressed as e+=e/Dfr/2 Re has been considered. Thermohydraulic performance has been defined by the equation ηthermo=(Str/Sts)3/(fr/fs). It has been found that e+opt≃24 gives the optimal thermohydraulic performance in such collectors and therefore the optimal thermohydraulic performance curves [3], for designing such collectors for practical applications are suitable. The value of optimal thermohydraulic performance has been found to be about 71% corresponding to e+opt=24.
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optimal thermohydraulic performance of artificially roughened solar Air Heaters
Solar Energy, 1991Co-Authors: B.n. Prasad, J.s. SainiAbstract:Abstract The heat transfer coefficient of solar Air Heaters can be increased by provinding artificial roughness on the bottom of the absorber plate, leading to higher collection efficiency. Inclusion of artificial roughness, however, results in a higher friction factor and consequently a higher pumping power is required. Results show that both the Nusselt number and friction factor increase with increasing relative roughness height and decrease with increasing relative roughness pitch, but not in direct proportions. Optimization of the roughness and flow parameters ( p e , e D , Re) to maximize heat transfer while keeping friction losses minimum was attempted. It has been found that a particular value of roughness Reynolds number ( e + = e D f 2 Re ), always corresponds to optimum thermohydraulic conditions in the range of parameters investigated. On this basis design curves have been developed that give the optimal thermohydraulic performance combination of these parameters.
Laljee Prasad - One of the best experts on this subject based on the ideXlab platform.
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Thermal performance investigation of three sides concave dimple roughened solar Air Heaters
Solar Energy, 2019Co-Authors: Vikash Kumar, Laljee PrasadAbstract:Abstract A novel work conducted upon three sides concave dimple roughened SAHs is presented here. Exhaustive experimental investigations were carried out in Feb-May 2017 upon one and three sides roughened solar Air Heaters on test setup installed at terrace of Mechanical Engineering Dept., NIT Jamshedpur and results are presented as rise in heat transfer and thermal performance of three sides over one side roughened duct against corresponding frictional losses. The experimental setup was validated using Nusselt number and friction factor correlation derived by Saini and Verma (2008) using one side roughened similar duct model. The geometrical parameters were used as dimensionless ratio as relative dimple pitch (p/e), relative dimple height (e/Dh) and relative dimple depth (e/d) in the range of 8–15, 0.018–0.045 and 1–2 respectively. The range of Reynolds number covered during experimentation was 2000–13500. Heat transfer augmentation for three sides over one side roughened ducts was appreciable considering rise in frictional losses. The thermal efficiency was measured in terms of collector heat removal factor (FR) and collector efficiency factor (F') and the collector’s performance parameters were given as F R τ α and ( F R U L ). The optimum roughness parameter was found to be p/e = 12, ‘e/Dh’ = 0.036 and ‘e/d’ = 1.5. For m = 0.0293 kg/s and Cp = 1.005 kJ/kg K, F R τ α and F R U L comes out equal to 0.7346 and 8.85 W/m2 K, respectively. Three sides roughened SAHs have high thermal efficiency of the order of 44–67% more than that of one side roughened SAH for the range of flow and roughness parameters investigated.
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heat transfer friction factor and thermal performance of three sides artificially roughened solar Air Heaters
Solar Energy, 2016Co-Authors: Aru K Ehura, N Prasad, Laljee PrasadAbstract:This paper presents the experimental results on heat transfer, friction factor and thermal performance of a novel type of three sides artificially roughened and glass covered solar Air heater under fully developed turbulent flow conditions. The results on heat transfer and friction factor compare well with analytical values (Prasad et al., 2014), for the range of the values of operating parameters. Such solar Air Heaters have higher value of heat transfer coefficient than those of one side artificially roughened solar Air Heaters in the range of 21–78% for the same values of operating parameters. The values of performance parameters, FRUL and FR(τα) and consequently those of FR and F′, have been found to be superior to those of one side roughened solar Air Heaters. Thermal performance equations in terms of the performance parameters have been derived. Enhancement of about 40–48% in thermal performance over those of one side artificially roughened solar Air Heaters has been achieved.
