E FFECTS OF WIRE COIL INSERTS ON THERMAL EFFICIENCY OF SOLAR FLAT PLATE LIQUID COLLECTOR S

The efficiency of a solar liquid collector can be improved by augmenting heat transfer from the tube to the working fluid. Va rious types of heat transfer techniques has been used in heat exchangers which are mainly classified in active and passive types of techniques. Solar liquid collectors can also be enhanced by these active and passive devices. The passive devices do not requ ire any external source of power and they do not harm structure of the tube or weaken the strength of tube material. For the same reasons passive devices are most widely used heat transfer augmentation techniques. Initially twisted tape inserts and conical insert s were popular devices used in enhanced solar liquid collectors mainly because of availability of established corr elations of design parameters. Wire coil inserts are relatively less used and less experimented passive technique. Presence of well established correlation of design parameters does not mean that twisted tapes are the best heat transfer augmentation device . These passive devices enhance the heat transfer, but due to increased friction, pumping power requirement of the heat exchanger is also increased. The pres ent study is therefore focused on coiled wire inserts as heat transfer enhancement device in solar liquid collectors. The effect of dimensionless parameters such as pitch of coil to tube diameter and coil wire diameter to tube diameter on thermal efficiency of the solar collector was studied under changing flow rates in the study.