Numerical and experimental investigations of thermo-hydrodynamic characteristics of ice slurry in helical heat exchangers

Abstract

Mining industry has experienced a dramatic change over the past 20 years in terms of methods, equipment as well as human resource policies. These changes have had impacts on the design of mine ventilation systems. Despite all the advantages of surface Bulk Air Cooling (BAC) systems, implementing an underground solution for thermal pollution especially for ultra-deep mines becomes essential. In addition, with the increase in the mining depth and the pumping distance the operational cost of underground BAC also rises. The location and working fluid becomes important as the depth of working areas increases. The performance of the heat exchanger is a critical factor as it affects the energy consumption and thermal conditions of the underground environment. Ice slurry has been recently proposed as a new potential coolant for deep underground cooling as it is prone to no or slight increase in temperature when pumped to working areas. To investigate the feasibility of such systems for mine cooling, characterizing the heat exchanger behaviour operating with ice slurry is crucial. This study will explore the thermal and hydraulic performance of ice slurry used as coolant in a coil heat exchanger. Finite volume approach in Computational Fluid Dynamics (CFD) along with experiments will be implemented to characterize the heat transfer and flow within the heat exchanger.In the first part of the research, a detailed numerical investigation of the thermo-hydrodynamic performance of a helical coil heat exchanger operated with a laminar and non-Newtonian flow of ethyl-alcohol ice slurry subject to phase change is presented. The Bingham plastic model is used to reflect the non-Newtonian behaviour of ice slurry. The phase change of ice slurry is modelled using the enthalpy-porosity method. The pressure drop and heat transfer of ice slurry in a double-turn helical coil are determined in terms of ice mass fraction and Dean number.The second part of the research numerically examines the flow characteristics of monopropylene glycol ice slurry through a horizontal U-bend. An Eulerian two-phase model is used to investigate the effect of inlet flow velocity, particle diameter and ice volume fraction on the particle distribution and pressure drop throughout the U-bend. The flow is considered isothermal so the heat transfer and melting of solid particles are not taken into account.In the final stage of the study, the aim is to experimentally investigate the flow characteristics of an ice slurry through horizontal and vertical U-bends. The effects of flow rate (inlet velocity), ice volume fraction and pipe diameter on the pressure drop and loss coefficients of the U-bend for horizontal and vertical orientations are investigated. To get a clear picture the ice slurry structure, the flow is also visualized in both straight and bend sections.