Experimental Validation for Heat Transfer Enhancement by Using Square Cut Circular Ring Insert

An experimental investigation is carried for heat transfer enhancement with the help of Square cut circular ring insert for heat exchanger application. Experimental investigation is for measuring tube side heat transfer co-efficient, friction factor, thermal performance factor of air for turbulent flow in a circular tube fitted with square cut circular ring insert. An experimental setup consist of Blower, flow control valve to maintain measured quantity of flow, Orifice meter is used for flow measurement, Pressure drop is measure along test section and orifice meter with 2 U-tube manometer. A stainless steel tube of (SS304) material having 34mm of inner diameter & 38mm outer diameter & 1000mm test length is used. A mild steel of 0.5mm thickness square cut circular ring insert with 3 different cut area & 3 different pitch inserted into the smooth tube. The square cut circular ring have: (1). 8.5mm depth & 10mm width. (40% area remove) (2).6.5mm depth & 10mm width(30% area remove) (3).3.5mm depth & 10mm width (16% area remove) In each case (1). 6 insert with distance between insert is16cm. (2) 5 insert with distance between insert is 20cm. (3). 4 insert with distance between insert is 27cm.A uniform heat flux condition is created by Band type nichrome wire heater (9 heater 70w each at length of 100mm each) around the test section & asbestos insulation of 3mm thickness over the band type heater. Outer surface temperature of tube is measured at 8 different points of test section by K-type thermocouple. 2 Thermocouple is used for calculating heat loss to surrounding. Another 2 thermocouple is used for measuring the bulk temp (inlet & outlet temperature of air). The Reynolds number is varied in the range of 4000 to 16000 with constant heat flux supplied by heater is 1.25 kw/m2 for smooth tube & tube with insert. Nusselt number obtained from smooth is compared with Dittus- Boelter correlation & errors are found to be in the range of ±7.0758 % .Friction factor is compared with Blasius corelation.Experimental setup is validate with the help of Dittus-Boelter equation and Blasius co-relation. At comparable Reynolds number, Nusselt number in the tube with square cut circular ring insert is enhanced by 2.3 to 2.9 times at cost of increase of friction factor by compared to smooth tube & also at cost of increase of pressure drop as compared to that of smooth tube. Thermal performance factor are found to be higher than unity up to 14000 Reynolds number and also heat transfer enhancement is increases with increased of Reynolds number.