Heat transfer enhancement in a corrugated tube heat exchanger

Introduction. The use of corrugated tubes is an effective method of intensification of heat transfer in tubular heat exchangers, but there is currently no universal method of calculation and design of such heat exchangers. Materials and methods. The heat transfer characteristics of flexible corrugated stainless steel tubes with different corrugation profile were studied. The laboratory stand is a "tube in tube" type heat exchanger with outer smooth tube and inner corrugated tube, equipped with sensors for measuring temperature and hydraulic flow parameters. Results and discussion. The research of heat transfer and hydrodynamics in the "tube in tube" type heat exchanger with a corrugated inner tube found considerable intensification of heat transfer compared with traditional smooth tube heat exchanger in the range of Reynolds numbers from 4000 to 40000. The increasing of heat transfer coefficient was from 2.0 to 2.6 times during the increase of the hydraulic resistance in 1,9...2,0 times. It was found that the tubes with the small corrugation height and the big corrugating pitch (height/pitch ratio - 1.9/4.0 mm) have 15...20% higher convective component of the heat transfer coefficient in comparison with tubes with the higher corrugation height and the small corrugation pitch (height/pitch ratio - 2.4/3.2 mm) under identical flow conditions. Two-dimensional axially symmetric computer model of the unit cell of the heat exchanger was developed to estimate the effect of the tube geometry on the intensity of the heat transfer process. Numerical simulation of hydrodynamics and heat transfer in the unit cell channel showed that mathematical calculations are quite close to the experimental studies. The heat exchanger with capacity of 350 kW for the administrative building heating is designed and engineered using criterial dependences. The experimental operation of the heat exchanger confirmed the effectiveness of the proposed technical solutions. Conclusions. The using of corrugating tubes allowed to increase the heat transfer coefficient. The received criterial dependences allow to calculate and optimize the process of heat transfer in a tubular heat exchanger with flexible corrugated pipes.