Second law analysis of a mixture of ethylene glycol/water flow in modified heat exchanger tube by passive heat transfer enhancement technique

This experimental study presents the entropy generation analysis of diverging, converging-diverging and converging conically coiled wire inserts in a heat exchanger tube using ethylene glycol and water mixtures as a working fluid. The experiments are performed with three different volumetric ratios of ethylene glycol and water mixtures and two different pitch ratios of diverging, converging-diverging and converging conically coiled wire inserts. The effects of conically coiled wire inserts on the dimensionless entropy generation number and Bejan number are discussed for the Reynolds number ranging from 4627 to 25,099. The results indicated that the converging conically coiled wire inserts generate higher entropy rates than the other insert types. It is pointed out that the entropy generation numbers for the diverging conically coiled wire inserts used tube reach the lowest value for each fluid type. The experimental results revealed that because the friction forces increase with the use of ethylene glycol, the Bejan number is lower for the fluids with 20 and 40% ethylene glycol than pure water. The highest Bejan number of 0.968 is determined for the smooth tube with pure water at the lowest Reynolds number. The lowest Entropy generation number of 0.42 is obtained for a pure water as a working fluid and diverging conically coiled wire insert with pitch ratio of 2 at the Reynolds number 6882, and the highest entropy generation number of 0.94 is observed while the converging conically coiled wire insert with pitch ratio of 3 is used in tube flow at Reynolds number of 22,230 for fluid type with 60% water and 40% ethylene glycol.