Study of Heat Transfer Characteristics on Sharp Turn Channels for Solar Collectors

Abstract

Heat transfer characteristics in sharp turn channel influenced by some of fluid flow characteristics in the channel. Fluid flow in rectangular cross section with sharp turns has its own characteristic due to changes in flow direction when through sharp turns. The flow pattern in the channel has a complex three-dimensional structure caused by centrifugal force. Local convection heat transfer rates for small surface area are expected to change significantly, for that reason why sharp bend techniques are often used on thermal equipment. In this study we have examined the heat transfer in sharp turn channels for solar collector applications. The size of the collector under study was 305 cm x 80 cm. To absorb the heat of solar radiation, in this test used iron sand as thick as 3 cm as an absorber. The iron sandbox is made of wood with a thickness of 15 mm and as a transparent cover is used 5 mm glass. The position of the air heater box is made tilted 15 degree with the aim that the airflow process can take place with the difference of input and output elevation. The barrier used is nine pieces. Arrangement of obstacles shape consists 3 types sharp multi-turns channel (angles 90-degree, 105-degree and 130-degree) and without obstacle channel as a comparison. Temperature measurements were made as much as 20 points on the flow path. The results showed that the distribution of absorber temperature for the four solar collector types tends to be the same. The highest temperature distribution can be achieved by collector with a sharp turn with a resistance angle of 130 and 105 degree, i.e. a maximum temperature of 85 degree Celsius occurs at 1-2 pm. The sharp turn of the solar collector type with the 90-degree resistance angle has slightly lower highest temperature distribution that can be achieved at 81 degree Celsius.