Experimental Study of the Double-Pass Solar Air Collector With Staggered Fins

Transcription

1 Experimental tudy of the Double-Pass olar Air Collector With taggered Fins A. FUDHOLI, M.H. RULAN, M.Y. OTHMAN, M. YAHYA, UPRANTO, A.ZAHARIM AND K. OPIAN olar Energy Research Institute Universiti Kebangsaan Malaysia 43 Bangi elangor MALAYIA Abstract:- The purpose of this study is to evaluate the thermal performance of a forced-convective double-pass solar air collector with staggered fins. The efficiency of the solar collector has been examined by changing the intensity of solar radiation and the mass flow rate. Beside, several important relationships between the design and operating conditions have been obtained. The results of this study suggest firstly, the double-pass solar collector with staggered fins has efficiency of more than 75% at a mass flow rate.83 kg/s and solar radiation at 788 W/m 2. econdly, the efficiency of solar collector is significant depending on the mass flow rate and solar radiation. The efficiency is increased proportional to mass flow rate and solar radiation. At the solar radiation at 423W/m 2 to 788W/m 2 increase efficiency is about 25%. At a mass flow rate varies from.4 kg/s to.83 kg/s, the efficiency increase is about %. Key-Words: Double-pass solar air collector,, taggered fins absorber 1 Introduction Depleting of fossil and gas reserves, combined with the growing concerns of global warming, has necessitated an urgent search for alternative energy sources to cater to the present day demands. An alternative energy resource such as solar energy is becoming increasingly attractive. olar energy is a permanent and environmentally friendly source of renewable energy. The use of non-renewable fuels, such as fossil fuel has many side effects. Their combustion products produce pollution, acid rain and global warning. Various types of solar energy systems for agricultural and marine products have been reviewed [1]. One of the most important components of a solar energy system is the solar collector. Various applications of the solar air collector are well documented [2]. olar collectors can be used for drying, space heating, solar desalination, etc. Conventional solar air collectors have inherent disadvantages is lower thermal efficiency. Ekechukwu and Norton [3] reviews have shown typical conventional style solar air collector to have efficiencies between -%. Various designs of solar air collectors have been proposed including multi-pass collectors and extended heat transfer area. Fudholi et al [4] concluded that multi-pass solar air collectors with heat transfer surface enhancement to have efficiencies between -%. The use of doublepass solar air collector with heat transfer surface enhancement has better performance than the conventional single-pass collector. Choudhury et al. [5] reported that the performance of double pass solar air collector with a single cover is found to be most cost-effective, as compared to the other design. Wijeysundera et al. [6] concluded that double-pass designs perform better than the singlepass solar air collector and reported an increase of 1-15 % in collector efficiency. One way to achieve considerable improvement in collector efficiency is to use an extended heat transfer area by using corrugated surfaces [7-9], matrix type absorber [1], compound honeycomb collector [11], box-type absorber [12], porous media [13] and finned absorber [14-16]. In the present study, the main concern is to study experimentally on the efficiency of the double-pass solar air collector with staggered fins. 2 Material and Methodology Fig. 1 shows the cross section of the collector with the aluminium plate fins. The collector consists of the glass cover, the insulated container and the black painted aluminium absorber. The size of the IN: X 41 IBN:

2 collector is 12 cm wide and 2 cm long. In this type of collector, the air initially enters through the first channel formed by the glass covering the absorber plate and then through the second channel formed by the back plate and the finned absorber plate. The size of the fins is 6 cm wide and 2 cm long. The fins have area of m 2. (a) Glass cover Absorber plate of the first pass, outlet, room, glass cover, absorber plate, and back-plate). Halogen lamps Glass cover Air flow in Air flow in (b) Air flow out Insulation Fins upport frame Vane anemometer probe Blower Data acquisition Air flow out Fig. 2 Test facility of solar air collector Fig. 1 (a) The schematic of a double-pass solar collector with fins absorber in the second channel and (b) top view of the staggered finned absorber. Fig. 2 shows the schematic of the indoor testing facility and the experimental setup of the doublepass solar collector. The simulator uses halogen lamps, each with rated power of W. The maximum average radiation of 788 W/m 2 can be reached. Dimmers are used to control the amount of radiation that the test collector received. A Data acquisition recorder is used to record the required parameters such as the temperatures (inlet, outlet, absorber, glass cover, and ambient) and intensity of the solar simulator. A type-t thermocouple is used in this experiment. A pyranometer is used to measure the solar intensities. This system is a forced air convection solar collector, so a blower is needed to force the air. The amount of air delivered by the blower is controlled by rheostat. A vane anemometer probe is used to measure linear velocity of air flow. The lighting control of the simulator has been adjusted to obtain the required radiation levels. The solar collector has been operated at varying inlet temperature, air flow rate, and radiation conditions. Air is circulated for thirty minutes prior to the period in which data are taken. Data include radiation, and temperatures (inlet, end 3 Results and Discussion The useful gain by the solar collector to solar radiation with measured values of fluid inlet (T i ) and outlet temperature (T o ) and the fluid mass flow rate (m) is given as follows Q u p ( T T) = mc (1) o i where C p is the specific heat of the fluid. The physical properties of air are assumed to vary linearly with temperature ( o C) by Ong [17] specific heat C p = T 27 (2) density ρ = T 27 (3) The efficiency of the collector is given by Qu η = (4) A c ( T T ) i a η = FR τα FRU L (5) IN: X 411 IBN:

3 ( T T ) o a η = Fo τα FoU L (6) where A c is the area of collector, is the solar radiation incident on the collector, F R is heat removal factor referred to inlet temperature of solar collector, F o is heat removal factor referred to outlet temperature of solar collector and U L is collector total loss coefficient. Fig. 3 shows the variation of temperature with experiment time is about 75 minutes for solar radiation of 788 W/m 2 and mass flow rate at.39 kg/s. Generally, temperatures increased constantly up to minutes and then tended to approach a constant value. Temperature ( o C) Time (minutes) Fig. 3 Temperatures data Tg ave Tp ave Tb ave Tfn ave Ti ave To ave The effect of solar radiation on the efficiency of the solar collector is shown in Fig. 4 and 5. At the solar radiation at 423W/m 2 to 788W/m 2 increase efficiency is about 2-25%. Fig 5 shows the effect mass of flow rate on the efficiency of the doublepass solar air collector with staggered fins absorber. The efficiency of the collector is strongly dependent on the flow rate. The collector efficiencies increase with flow rate, efficiency increase is about % at mass flow rate of.4 kg/s to.84 kg/s. Fig. 5 The effect of solar radiation and mass flow rate on efficiency To determine the physical characteristics of the collector, one represents effectiveness with efficiency curve, i.e. efficiency versus the reduced temperature parameters (T o -T a )/ in Fig As seen in the figure shows the efficiency curve decrease with increase of the reduced temperature parameters. The curve obtained is a straight line. It will results where the slope is equal to F o U L and the y-intercept is equal to F o (τα). The respective efficiency equation and the physical characteristic of the collector are presented in Table y = -7.7x R² = (To-Ta)/ Fig. 6 versus (To-Ta)/ for =788 W/m 2 75 y = -5.8x R² = (To-Ta)/ Fig. 7 versus (To-Ta)/ for =572 W/m 2 Fig. 4 The effect of solar radiation on efficiency at different mass flow rate IN: X 412 IBN:

4 y = -5.6x + 66 R² =.977 rate for =788 W/m2, =572 W/m 2 and =423 W/m 2, respectively. As seen in the figures, as efficiency increased with flow rate, increase temperature (T o -T i ) decreased correspondingly (To-Ta)/ Fig. 8 versus (To-Ta)/ for =423 W/m 2 Table 1, loss factor and efficiency equation of double-pass solar air collector with staggered fins (W/m2) F o (τα) F o U L equations y=-7.7x y=-5.8x y=-5.6x The efficiency and collector outlet temperature were an important parameter for a wide variety of applications, such as solar industrial process heat and solar drying of agricultural produce. Outlet temperature was investigated for mass flow rates from about.3 to.9 kg/s. Fig. 9 shows the optimum operating condition with respect to efficiency and outlet temperature were determined for =788 W/m 2. The optimum efficiency (-8%) lies between the mass flow rates.7-.9 kg/s. A mass flow rate of about.63 kg/s is considered for solar drying of agricultural produce. Minimal increase in the efficiencies occurs as the mass flow rate is increased, therefore, operating at these conditions will only increase the blower power. R 2 Fig. 1 Variation of T o -T i and η with mass flow rate at =788 W/m 2 Fig. 11 Variation of T o -T i and η with mass flow rate at =572 W/m 2 Temperature rise, To-Ti ( o C) Mass flow rate (kg/s) To-Ti Eff Fig. 12 Variation of T o -T i and η with mass flow rate at =423 W/m 2 Fig. 9 Variation of T o and η with mass flow rate at =788 W/m 2 Fig show the variation of increase temperature (T o -T i ) and efficiency with mass flow 4 Conclusions Performance curves of double-pass solar air collector with staggered fins absorber in lower channel have been obtained. These include the effects of mass flow rate and solar radiation on efficiency of the solar collector. The efficiency of the collector is strongly dependent on the flow rate. It increases with flow rate. The solar collector with IN: X 413 IBN:

5 staggered rows fins absorber has efficiency of more than 75 % at a mass flow rate of over.8 kg/s. References: [1] Fudholi A. opian K, Ruslan MH, Alghoul MA, ulaiman MY. Reviev of solar dryers for agricultural and marine products. Renewable & ustainable Energy Review 21;14:1-3. [2] Grupp M, Bergler H, Bertrand JP, Kromer B and Cieslok J. Convective flat plate collectors and their applications. olar Energy 1995; (3): [3] Ekechekwu OV, Norton B. Review of solar energy drying systems III: low temperature air-heating solar collectors for crop drying applications. Energy Conver Manage 1999;:7-67. [4] Fudholi A,, Ruslan MH, opian K, upranto. tudies of advanced multi-pass solar air collectors with heat transfer surface enhancement. In: Proceedings of eminar on Progress of olar Energy Research and Development 28. p [5] Choudhury C, Chauhan PM and Garg HP. Performance and cost analysis of two-pass solar air heater. Heat Recovery ystem & CHP 1995;15(8):7-73. [6] Wijeysundera LL, Ah and Ek Tjioe L. Thermal performance study of two-pass solar air heaters. olar Energy 1982;28 (5): [7] Fudholi A, opian K, Othman MY, Ruslan MH, AlGhoul MA, Zaharim A and Zulkifly. Heat transfer correlation for the v-groove solar collector. Proceedings of the 8 th WEA International Conference on IMULATION, MODELING and optimization (MO 8) 28., p [8] Ruslan MH, Othman MY, alleh MM, opian K. Design and indoor testing of the V-groove back pass solar collector. Renewable Energy 1999;16: [9] Gao W. et al. Analytical and experimental studies on the thermal performance of crosscorrugated and flat-plate solar air heaters. Applied Energy 27;84: [1] Kolb A, Winter ERF and Viskanta R. Experimental studies on solar air collector with metal matrix absorber. olar Energy 1999; (2): [11] Abdullah AH, A-Ziyan HZ, and. Ghoneim AA. Thermal performance of flat plate solar collector using various arrangements of compound honeycomb. Energy Conversion & Management 23;44: [12] Matrawy KK. Theoretical analysis for an air heater with a box-type absorber. olar Energy 1998;63 (3): [13] opian K, Alghoul MA, Alfegi EM, ulaiman MY and Musa EA., Evaluation of thermal efficiency of double-pass solar collector with porous-nonporous media, Renewable Energy 29;34: 6-. [14] Ali Y. tudy and optimization of the thermal performances of the offset rectangular plate fin absorber plates, with various glazing. Renewable Energy 25;31: [15] Karim MA, Hawlader MNA. Performance investigation of flat plate, v-groove and finned air collectors. Energy 26;31:2-. [16] Naphon P. On the performance and entropy generation of the double-pass solar air heater with longitudinal fins. Renewable Energy 25;3: [17] Ong K. Thermal performance of solar air heaters: mathematical model and solution procedure. olar Energy 1995;(2): IN: X 414 IBN: