Methodology for calculating the pipe-in-pipe heat exchanger characteristics Bulletin of the Tomsk Polytechnic University. Geo Assets Engineering Vol. 328, № 8
Relevance of the discussed issue is caused by inaccuracy of calculation methods for pipe-in-pipe heat exchangers using various simplifications. The heat exchangers are used in various industries: chemical, food, geothermal power systems, hot water supply systems. The main aim of the study is to develop the improved methodology for calculating thermal and geometric characteristics of pipe-in-pipe heat exchangers without using simplifications and to estimate errors. The methods used in the study: the calculation using the criterion equation for the flow in circular pipe, logarithmic mean temperature difference, the heat transfer coefficient for cylindrical wall, an iterative method for determining correction for nonisothermicity. The results. The authors have calculated the pipe-in-pipe heat exchanger with specified parameters and analyzed the calculation results is comparison with other methods using various simplifications, their errors was estimated. Conclusions. It was found the replacement of the cylindrical wall by a flat one, the use of the arithmetic mean temperature difference instead of the logarithmic one and calculating the heat transfer coefficient from the heated wall to the heating liquid without gap thickness correction result in underestimated values of the surface area by 30-47 %. The proposed method allows calculating the heat transfer coefficient more accurately in the cylindrical section, the temperature difference between primary and secondary water, taking into account the curvature of the pipe walls and the casing. The automation of the methodology by implementing on Turbo Pascal facilitates the calculation. The use of the implemented methodology for operation of the pipe-in-pipe heat exchangers at the design stage will reduce material costs.
heat exchanger, heat calculation, criterial equation, heat transfer, heat flow, cylindrical wall, flat wall, logarithmic mean temperature difference