Thermal performance of thermoplastic natural rubber solar collector K. Sopian a,* , R. Zulki¯i a , J. Sahari a , M.Y. Othman b a Department of Mechanical and Materials Engineering, Universiti Kebangsaan Malaysia, 43600 Bangi, Selangor, Malaysia b Department of Physics, Universiti Kebangsaan Malaysia, 43600 Bangi, Selangor, Malaysia Accepted 25 January 2002 Abstract The paper presents the thermal performance of a solar collector with TPNR thermoplastic natural rubber) tubing as the absorber plate. A commercial blend of TPNR dynamically vulcanised natural rubberÐDVNR 9011) was used as the absorber plate which was of the parallel type and satis®es the test conditions indicated by the standard GB 4271-84. The values of the thermal performance parameters F R ta) and F R U L were 0.72 and 9.67, respectively. A domestic hot water thermosyphon solar collector system with a vertical tank was used for performance monitoring. The thermosyphon hot water system is capable of producing temperature output up to 65 8C for a typical day of 550 W/m 2 . For monitoring purposes, two methods were used. In the ®rst method, the storage tank was ®lled up with water the night before the test and the temperature readings were recorded for the next day's test. The end-of-the-day temperature rise in the storage tank and the accumulated total solar radiationvalues were also noted over the same period. The test were repeated under varied environmental conditions that covers low and high radiation intensities. A temperature rise of 15 8C in the storage tank was obtained for this system at an accumulated solar radiation of 4.5 kW h/m 2 . In the second method, the temperature readings without draw-off or draining of the hot water from the storage tankwererecordedfor6daysandatemperatureofmorethan60 8Ccanbeachievedbythestoragetank.Hence,thissystemhasthepotentialto be used as domestic thermosyphon hot water system. # 2002 Published by Elsevier Science B.V. Keywords: Thermoplastic natural rubber TPNR); Thermosyphon solar hot water systems; Solar collector performance parameters; Performance monitoring 1. Introduction The absorber in a collector system is an important com- ponent because its function is to absorb solar radiation and transfer heat to a circulating ¯uid. Copper, stainless steel, and mild steel are common materials for absorber for domestic solar water heaters because of its high thermal conductivity, mechanical strength, and resistance against corrosion. However, metal absorbers are prone to scaling in areas with hard water, and in many designs, damage by freezing, and may be rather heavy depended on the design itself. To maintain its performance, an absorber must be resistant to both external and internal corrosion. External corrosion may occur because of the humid conditions in the collector box, because of leaking in the enclosure allowing ingress of rainwater especially in the tropics, or because of drops of condensation falling on the glazing. In addition, metallic solar collectors are particularly susceptible to external corrosion, even when coated. Moreover, internal corrosion occurs when dissimilar metals and attack by the heat transfer ¯uid. The heat transfer ¯uid may contain high levels of dissolved oxygen and this may cause degradation of the less corrosive resistant metals. The presence of chlorine ions in solutions can also cause attack of some metals such as copper and certain grades of stainless steel [1]. Hence, the use of polymer-based materials for absorber plate as well as tubes has increased since it is cheaper, non- corrosive, and easy to fabricate. Initially, polymers were not used because of degradation and embrittlement on the exposure to sunlight. Furthermore, this is the most serious disadvantage of polymer absorbers inside glazed insulated collector boxes. However, recent advances in polymer tech- nology have resulted in the development of suitable materi- als, which can withstand long exposure to sunlight. Such material is EPDM ethylene propylene diene monomer), a petroleum-based product [2]. The common applications of polymer-based solar absor- bers are in applications involving lower temperature such as heating of swimming pools and heat pump applications. Polymer absorbers are not prone to scaling compared to metal absorbers. The reasons are due to large difference in the thermal expansion coef®cient of scale and polymers, and Journal of Materials Processing Technology 123 2002) 179±184 * Corresponding author. Tel.: 60-03-8929-6515; fax: 60-03-8929-6145. E-mail address: ksopian@vlsi.eng.ukm.my K. Sopian). 0924-0136/02/$ ± see front matter # 2002 Published by Elsevier Science B.V. PII:S0924-013602)00093-6