Heat transfer enhancement characteristic of twisted elliptical tube heat exchanger at high Re condition and its energy-saving application in mechanical vapor recompression system

Abstract

To understand the characteristc of the twisted elliptical tube heat exchanger at high Re conditions and the feasibility of its application in MVR system, the effect of geometric parameters on performance of twisted elliptical tubes was numerically studied. The results demonstrate that overall performance decreases rapidly as Re increases within the range of 13,000 < Re < 60,000. While at 60,000 < Re < 110,000, it stabilizes while still being better than that of circular tubes. A novel MVR evaporation crystallization system using a twisted elliptic tube evaporator is firstly developed. The industrial locale experiment indicates that the twisted elliptic tube evaporator enhances heat transfer, reduces the compression ratio and temperature rise of the vapor compressor and significantly reduces the energy consumption of the MVR system. The average specific energy consumption (SEC) and COP of the MVR system are 32.9 kWh·t⁻¹ and 19.0, respectively. These values are 45.2 % lower and 85.4 % higher than those of the conventional MVR system. The novel MVR system reduces standard coal consumption by approximately 76.6 % and 68.8 % compared to conventional three-effect and four-effect evaporation systems, respectively. These findings show significant energy savings can be achieved by using the twisted elliptic tube evaporator for MVR system.