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second law optimization of a solar air heater having chamfered rib groove roughness on absorber plate

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. The entropy generation in the duct of solar air heater having repeated transverse chamfered rib–groove roughness on one broad wall is studied numerically. Roughness parameters, viz., relative roughness pitch P/e, relative roughness height e/Dh relative groove position g/P, chamfer angle φ and Flow Reynolds Number Re have a combined effect on the heat transfer as well as fluid friction. The entropy generation is minimized and reasonably optimized designs of roughness are found.

analysis of heat transfer augmentation and Flow characteristics due to rib roughness over absorber plate of a solar air heater

A computational analysis of heat transfer augmentation and Flow characteristics due to artificial roughness in the form of ribs on a broad, heated wall of a rectangular duct for turbulent Flow (Reynolds Number range 3000–20,000, which is relevant in solar air heater) has been carried out. Shear stress transport k−ω turbulence model is selected by comparing the predictions of different turbulence models with experimental results available in the literature. A detailed analysis of heat transfer variation within inter rib region is done by using the selected turbulence model. The analysis shows that peak in local heat transfer coefficient occurs at the point of reattachment of the separated Flow as observed experimentally. The results predict a significant enhancement of heat transfer in comparison to that for a smooth surface. There is a good matching between the predictions by SST k−ω and experimental results. In this work, nine different shapes of rib are examined using SST k−ω model and compared on the basis of heat transfer enhancement, friction characteristics and performance index considering heat transfer enhancement with the same pumping power.

heat transfer coefficient and friction factor correlations for rectangular solar air heater duct having transverse wedge shaped rib roughness on the absorber plate

As is well known, the heat transfer coefficient of a solar air heater duct can be increased by providing artificial roughness on the heated wall (i.e. the absorber plate). Experiments were performed to collect heat transfer and friction data for forced convection Flow of air in solar air heater rectangular duct with one broad wall roughened by wedge shaped transverse integral ribs. The experiment encompassed the Reynolds Number range from 3000 to 18000; relative roughness height 0.015 to 0.033; the relative roughness pitch 60.17φ−1.0264

transfer coefficient and friction factor are compared with the result of smooth duct under similar Flow conditions. Statistical correlations for the Nusselt Number and friction factor have been developed in terms of geometrical parameters of the roughness elements and the Flow Reynolds Number.

heat and fluid Flow in rectangular solar air heater ducts having transverse rib roughness on absorber plates

An experimental investigation has been carried out to determine the effect of transverse wire roughness on heat and fluid Flow characteristics in transitionally rough Flow region (5 < e+ < 70) for rectangular solar air heater ducts with an absorbec plate having transverse wire roughness on its underside. The investigation covered a Reynolds Number range of 3000–18000 for a duct aspect ratio of 6.8–11.5, relative roughness height of 0.018–0.052 at a relative roughness pitch of 10 encompassing a range of roughness Reynolds Number between 5–70. Simple correlations for a Nusselt Number and friction factor have been developed in terms of geometrical parameters of roughness, duct cross section, and the Flow Reynolds Number.

nusselt Number and friction factor correlations for solar air heater duct with broken v down ribs combined with staggered rib roughness

Artificial roughening of a broad wall of solar air heater leads to significant enhancement in heat transfer besides comparable rise in friction losses. This paper presents the outcome of experimental study on heat transfer and fluid friction characteristics of solar air heater duct roughened with broken V-down rib combined with staggered rib piece. Experimental data were collected on a high aspect ratio rectangular duct by varying the Reynolds Number from 3000 to 17 000, relative gap position (s′/s) 0.2–0.8, relative staggered rib position (p′/p) 0.2–0.8, relative staggered rib size (r/e) 1–2.5, for the fixed values of relative roughness pitch (p/e) of 10, relative roughness height (e/Dh) of 0.043, relative gap size (g/e) of 1, and angle of attack (α) of 60°. The effect of Flow Reynolds Number and roughness parameters on Nusselt Number and friction factor has been explored and the results are compared with continuous V-down rib roughened duct and smooth duct under similar Flow conditions. Correlations for...

exergy based analysis of solar air heater having discrete v down rib roughness on absorber plate

Abstract The artificially rib roughened solar air heaters perform thermally better than the conventional flat-plate solar air heater under same operating conditions. However, the artificial rib roughness leads to higher friction factor thereby increasing pumping power. The second law based exergy analysis is suitable for design of rib roughened solar air heaters as it incorporates quality of useful energy output and pumping power. The exergetic efficiency of a solar air heater having discrete V-down rib roughness is studied analytically and the results obtained are compared with that of a conventional flat-plate solar air heater. Flow Reynolds Number and rib-roughness parameters, viz., relative roughness pitch, relative gap position, relative gap width, angle of attack and relative roughness height have combined effect on heat transfer as well as fluid friction. The exergy based criterion suggests use of the discrete V-down rib roughened solar air heater for the Reynolds Number range normally used in solar air heaters. It was found that there exist optimum roughness parameters of the discrete V-down rib for a given Reynolds Number (or temperature rise parameter) at which the exergetic efficiency is highest. Curves of optimum rib-roughness parameters are also plotted.

investigation of heat transfer and friction characteristics of packed bed solar air heater using wire mesh as packing material

Abstract An experimental investigation has been carried out on a packed bed solar air heater using wire mesh as packing material. Data pertaining to heat transfer and friction characteristics were collected for air Flow rates ranging from 0.0159 to 0.0347 kg/s-m 2 for eight sets of matrices with varying geometrical parameters. The thermal efficiency of a packed bed solar air heater was compared with that of a conventional solar air heater to determine the enhancement which was found to be strong function of system and operating parameters of the bed. It was found that an enhancement of the order of 76.9–89.5% can be obtained. Experimental data were utilised to develop correlations for Colburn J h factor and friction factor as function of geometrical parameters of the bed and the Flow Reynolds Number. These correlations were found to predict the experimental results with reasonable accuracy. It has also been found that the present correlations show much better agreement as compared to the values predicted by earlier correlations for such systems.

second law optimization of a solar air heater having chamfered rib groove roughness on absorber plate

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. The entropy generation in the duct of solar air heater having repeated transverse chamfered rib–groove roughness on one broad wall is studied numerically. Roughness parameters, viz., relative roughness pitch P/e, relative roughness height e/Dh relative groove position g/P, chamfer angle φ and Flow Reynolds Number Re have a combined effect on the heat transfer as well as fluid friction. The entropy generation is minimized and reasonably optimized designs of roughness are found.

heat transfer coefficient and friction factor correlations for rectangular solar air heater duct having transverse wedge shaped rib roughness on the absorber plate

As is well known, the heat transfer coefficient of a solar air heater duct can be increased by providing artificial roughness on the heated wall (i.e. the absorber plate). Experiments were performed to collect heat transfer and friction data for forced convection Flow of air in solar air heater rectangular duct with one broad wall roughened by wedge shaped transverse integral ribs. The experiment encompassed the Reynolds Number range from 3000 to 18000; relative roughness height 0.015 to 0.033; the relative roughness pitch 60.17φ−1.0264

transfer coefficient and friction factor are compared with the result of smooth duct under similar Flow conditions. Statistical correlations for the Nusselt Number and friction factor have been developed in terms of geometrical parameters of the roughness elements and the Flow Reynolds Number.

investigation of twisted tape inserted solar water heaters heat transfer friction factor and thermal performance results

Abstract Heat transfer in a solar water heater could be enhanced by means of twisted tapes, inserted inside the fluid Flow tubes, which induce swirl Flow and act as turbulence promoters. Experimental investigations for a solar water heater with twisted tape inserts having twist pitch to tube diameter ratio ranging from 3–12 have been carried out for varying mass Flow rates. The results on heat transfer and friction data have been found to compare well with available results. Within the range of investigated parameters, the heat transfer in the twisted tape insert collectors has been found to increase by 18–70%, whereas the pressure drop increased by 87–132%, as compared to plane collectors. An expression correlating the Nusselt Numbers in twisted tape and plane collectors, the twist pitch ratio has been developed in the form of Nus/Nu=1.3+2.88/y, which predicts the heat transfer within the range of the present investigation. Results conclude that such collectors would be preferable for higher grade energy collection as it is also at higher rate. Solar water heaters having twisted tape inserts inside the Flow tubes perform better than the plane ones. It has been observed that heat losses are reduced (due to the lower value of the plate temperature) consequently increasing the thermal performance by about 30% over the plane solar water heaters under the same operating conditions. The effect of twisted-tape geometry, Flow Reynolds Number and intensity of solar radiation on the thermal performance of the solar water heater has been presented. It has been found that the twisted-tape collectors perform remarkably better in the lower range of Flow Reynolds Number (Re≈12,000), beyond which the increase in thermal performance is monotonous. It has also been found that such collectors might perform even better at higher values of intensity of solar radiation.

Investigation for the optimal thermohydraulic performance of artificially roughened solar air heaters

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.

heat transfer and friction factor correlations for impinging jet solar air heater

Abstract Experimental investigation has been carried out to study heat transfer and friction factor characteristics using impinging jets in solar air heater duct. The effect of Flow and geometrical parameters, especially the jet diameter, streamwise and spanwise pitch has been studied. The experiments encompassed the Flow Reynolds Number in the range 3800–16,000. The jet diameter, streamwise pitch and spanwise pitch each normalized by hydraulic diameter of the duct are in the range: 0.043–0.109; 0.435–1.739; 0.435–0.869 respectively. The air through the jets is impinged normally onto the absorber surface which was heated with uniform heat flux of 1000 W/m 2 . The heat transfer and friction factor data obtained is compared with that of parallel Flow solar air heater under similar geometrical and Flow conditions. The results show that there is considerable enhancement in heat transfer and friction factor by 2.67 and 3.5 times respectively. Correlations for Nusselt Number and friction factor have been developed in terms of above parameters which reasonably correlate the experimental data.

IHTC14-22399 NUMERICAL STUDY OF LAMINAR Flow AND MASS TRANSFER FOR IN-LINE SPACER-FILLED PASSAGES

ABSTRACT Performance calculations for laminar fluid Flow and mass transfer are presented for a spacer-filled passage containing cylindrical spacers configured in an inline-square arrangement, typical of those employed in the process industries. Numerical calculations are performed for fully-developed Flow, based on stream-wise periodic conditions for a 'unit cell' and compared with those obtained for developing regime in a row of 10 such units. The method is validated for an empty passage (i.e. a plane duct). Results are presented for the normalized mass transfer coefficient and driving force, as function of mean Flow Reynolds Number, and also the wall mass flux, or blowing parameter. Both constant and variable wall velocities were considered, the latter being typical of those found in many practical membrane assemblies

investigation of twisted tape inserted solar water heaters heat transfer friction factor and thermal performance results

Abstract Heat transfer in a solar water heater could be enhanced by means of twisted tapes, inserted inside the fluid Flow tubes, which induce swirl Flow and act as turbulence promoters. Experimental investigations for a solar water heater with twisted tape inserts having twist pitch to tube diameter ratio ranging from 3–12 have been carried out for varying mass Flow rates. The results on heat transfer and friction data have been found to compare well with available results. Within the range of investigated parameters, the heat transfer in the twisted tape insert collectors has been found to increase by 18–70%, whereas the pressure drop increased by 87–132%, as compared to plane collectors. An expression correlating the Nusselt Numbers in twisted tape and plane collectors, the twist pitch ratio has been developed in the form of Nus/Nu=1.3+2.88/y, which predicts the heat transfer within the range of the present investigation. Results conclude that such collectors would be preferable for higher grade energy collection as it is also at higher rate. Solar water heaters having twisted tape inserts inside the Flow tubes perform better than the plane ones. It has been observed that heat losses are reduced (due to the lower value of the plate temperature) consequently increasing the thermal performance by about 30% over the plane solar water heaters under the same operating conditions. The effect of twisted-tape geometry, Flow Reynolds Number and intensity of solar radiation on the thermal performance of the solar water heater has been presented. It has been found that the twisted-tape collectors perform remarkably better in the lower range of Flow Reynolds Number (Re≈12,000), beyond which the increase in thermal performance is monotonous. It has also been found that such collectors might perform even better at higher values of intensity of solar radiation.