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J.s. Saini – One of the best experts on this subject based on the ideXlab platform.

  • A review of thermohydraulic performance of artificially roughened solar Air Heaters
    Renewable and Sustainable Energy Reviews, 2014
    Co-Authors: Anil Kumar, R.p. Saini, J.s. Saini
    Abstract:

    Abstract Solar Air Heaters form the major component of solar enerenergy 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.

  • a comprehensive review on roughness geometries and investigation techniques used in artificially roughened solar Air Heaters
    International Journal of Renewable Energy Research, 2012
    Co-Authors: Anil Kumar Patil, J.s. Saini, K Kumar
    Abstract:

    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.

  • thermal and effective efficiency based analysis of discrete v down rib roughened solar Air Heaters
    Journal of Renewable and Sustainable Energy, 2011
    Co-Authors: Sukhmeet Singh, Subhash Chander, J.s. Saini
    Abstract:

    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.

Ho-ming Yeh – One of the best experts on this subject based on the ideXlab platform.

  • 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, 2012
    Co-Authors: Ho-ming Yeh
    Abstract:

    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.

  • heat transfer enhancement of double pass solar Air Heaters with external recycle
    Journal of The Taiwan Institute of Chemical Engineers, 2011
    Co-Authors: Ho-ming Yeh
    Abstract:

    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.

  • downward type solar Air Heaters with internal recycle
    Journal of The Taiwan Institute of Chemical Engineers, 2011
    Co-Authors: Ho-ming Yeh
    Abstract:

    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.

R.p. Saini – One of the best experts on this subject based on the ideXlab platform.

  • a review on different techniques used for performance enhancement of double pass solar Air Heaters
    Renewable & Sustainable Energy Reviews, 2016
    Co-Authors: Ravi Kant Ravi, R.p. Saini
    Abstract:

    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.

  • A review of thermohydraulic performance of artificially roughened solar Air Heaters
    Renewable and Sustainable Energy Reviews, 2014
    Co-Authors: Anil Kumar, R.p. Saini, J.s. Saini
    Abstract:

    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.

  • performance of artificially roughened solar Air Heaters a review
    Renewable & Sustainable Energy Reviews, 2009
    Co-Authors: Vishavjeet Singh Hans, R.p. Saini, J.s. Saini
    Abstract:

    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.

  • optimization of thermo hydraulic performance in three sides artificially roughened solar Air Heaters
    Solar Energy, 2015
    Co-Authors: B.n. Prasad, Ashwini Kumar, K P Singh
    Abstract:

    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.

  • Thermal performance of artificially roughened solar Air Heaters
    Solar Energy, 2013
    Co-Authors: B.n. Prasad
    Abstract:

    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.

  • Investigation for the optimal thermohydraulic performance of artificially roughened solar Air Heaters
    Renewable Energy, 2000
    Co-Authors: Sanjay Verma, B.n. Prasad
    Abstract:

    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.

Laljee Prasad – One of the best experts on this subject based on the ideXlab platform.

  • Thermal performance investigation of three sides concave dimple roughened solar Air Heaters
    Solar Energy, 2019
    Co-Authors: Vikash Kumar, Laljee Prasad
    Abstract:

    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.

  • heat transfer friction factor and thermal performance of three sides artificially roughened solar Air Heaters
    Solar Energy, 2016
    Co-Authors: Aru K Ehura, N Prasad, Laljee Prasad
    Abstract:

    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.