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• Application of the Euler-Euler method to CFD modelling of the flow of ice slurry. • Low slip velocity of solid particles. • Highest slip velocities are observed near the channel sidewalls. • Homogeneous flow, lower border velocities for downward compared to upward flow. • Flow map of ice slurry for vertical flow in slit channel. In this article, the Euler-Euler method was applied to CFD modelling of adiabatic ice slurry flow, for different flow directions in a vertical slit channel. The mean relative accuracy of determining pressure drops compared to experimental studies was 5.6%. Calculations showed that the relative slip velocity and the effect of flow direction on slip velocity increase with decreasing carrier fluid concentration, decreasing mean flow velocity, and decreasing mean solid particles volume fraction. The mean particle slip velocity does not exceed 4%, and local slip velocity values can be 58% of the mean suspended solids flow velocity. For heterogeneous flow, the highest slip velocities occur at a distance of 15% of the channel width from the channel sidewalls. The shape of the solid particles distribution profile is determined by the mean flow velocity and the mean solid particles volume fraction. Excluding the area at a distance of 8% of the channel width from the sidewall where local maximum (for low velocities) and minimum (for higher velocities) values may occur, the profile is stabilised in the central part of the channel. In this study, the boundary curves between heterogeneous and homogeneous flow were determined for ice slurry flow in a vertical slit channel. [ABSTRACT FROM AUTHOR]

• New correlations for Nu number of ethanol ice slurry in a vertical slit channel. • The effect of flow direction on the values of α coefficients was investigated. • For laminar flow, the melting process has a greater effect of on α coefficient. • For turbulent flow, the convection process has a greater effect on α coefficient. • The upward flow, high ice mass fraction increase the αcoefficients. The article concerns the heat transfer process of ethanol ice slurry during downward and upward flow in a vertical slit channel (3x35.8x700 mm) under constant heat flux density conditions. Experimental studies were conducted for three initial concentrations of ethanol (X vai = 10.5 %, 13.2 %, 15.8 %) and mass fractions of ice of 0 ≤ x s ≤ 30 %. For upward flow, heat transfer coefficients were 6–14 % higher than for downward flow. For laminar flow, a greater effect of the melting process was observed, and for turbulent flow, the convection process had a greater effect on heat transfer coefficients. For laminar flow, the heat transfer coefficients of the ice slurry can be 200 % higher than the corresponding values for the carrier fluid. In turbulent flow, the corresponding increase in heat transfer coefficients did not exceed 15 %. For generalised non-Newtonian flow of ice slurry, criterion relationships were proposed for calculating heat transfer coefficients, taking into account the effect of the concentration of the carrier fluid, mass fractions of ice, its melting process, as well as the nature and direction of the flow. [ABSTRACT FROM AUTHOR]

• Flow resistances of ethanol ice slurry in a vertical slotted channel. • Determination of dynamic plastic viscosity and shear stress of ethanol ice slurry. • Impact of flow direction, settling velocity on flow resistance. • Dimensionless relationships for the determination of Fanning friction factors. • Generalized non-Newtonian fluid flow through a vertical slit channel. The paper presents the results of experimental flow investigations of an ethanol-based ice slurry flowing up and down a vertical slit channel. The impact of flow direction, carrier fluid concentration, ice mass fraction and mean velocity on pressure drop values has been investigated. Stronger mutual interaction between the phases on flow resistances was observed for low carrier fluid concentrations and in the laminar range of ice slurry flow. The measured resistance values for downward flow in the laminar area were 6–10% higher than the pressure drops for upward flow, while in the turbulent flow area they were 1–8% higher. Using the generalized non-Newtonian fluid model, the authors have proposed equations for calculating the friction factors for a vertical slit channel and various flow directions. [ABSTRACT FROM AUTHOR]

The paper presents thermal and flow analyses of the boiling process of R507, R410 and R407 C refrigerants inside vertical tubes (21 mm) with coiled-wire inserts and various coil diameters (20; 20.5 mm), coil pitches (26; 44 mm) and wire diameters (1.5; 2 mm). The study differs from other publications as regards the conditions under which the experiment was conducted. It focuses on the boiling process in two long vertical tube sections (2 m), paired in an in-line arrangement. The study was conducted within a moderate range of mass flux densities 80–240 kgm−2s−1 and at low heat flux densities 5–11 kWm−2, corresponding to the operating conditions of air coolers. The study examined the influence of vapour quality, mass flux density, geometrical parameters of the inserts and the impact of temperature glide on heat transfer coefficient and flow resistance increases as compared with a plain tube. The obtained increase ratios of heat transfer coefficients amounted to 1.1-1.7 for an azeotropic agent and to 1.1-1.3 for zeotropic agents, with the relative increase in flow resistances amounting to 1.8-4.5. New equations are proposed in the paper for the calculation of heat transfer coefficient and flow resistance values for boiling inside vertical tubes with spiral inserts. [ABSTRACT FROM AUTHOR]

The paper presents the phenomena accompanying the processes of non-adiabatic transport of ice slurry with ice mass fraction values below 20% in the transport sections of the system, assuming the conditions of significant changes in hydrostatic pressure. The subject of the analysis presented herein was to indicate the influence of hydrostatic pressure values on melting and secondary recrystallisation phenomena in the case of medium expansion in a vertical shaft pipeline and a three-chamber PES distributor. The paper proposes a computational model to determine the mass fraction of ice in the downstream section of the supply system: upstream and downstream of the PES distributor. The presented calculation results indicate that a reduction in the mass fraction of ice in the range of 0.004% per 1 m of the pipeline could be observed in vertical shaft pipelines. Maximising the enthalpy flux of the slurry at the inlet to the secondary circuit and minimising the temperature of the return water to the chiller favours mixing rates in the PES three-chamber distributor below 7%, which increase as the mass fraction of ice decreases. • Ice slurry applications in central air-conditioning systems of mining plants. • Ice slurry flow and heat transfer in shaft pipelines and PES distributors. • Ice slurry melting and recrystallisation in primary and secondary circuits. [ABSTRACT FROM AUTHOR]

The paper presents the results of thermal and flow analyses of the boiling process in vertical tubes with heat transfer enhancing inserts. Tests were performed for three different geometrical shapes of the inserts: a spiral tape with a core rod, a rib insert and a spring insert. Experimental measurements were performed for R507, R410A and R407C refrigerants at low heat flux. The obtained results indicate the increase ratio of heat transfer and flow resistance coefficients in tubes with inserts, as opposed to a plain one. Finally, the paper presents the dimensionless relationships which enable the calculation of heat transfer coefficients and pressure drops during boiling in vertical tubes with the studied heat transfer enhancing inserts. [ABSTRACT FROM AUTHOR]

The paper presents the results of experimental research of pressure drop and heat transfer coefficients of ice slurry during its flow through tubes of rectangular and slit cross-sections. Moreover, the work discusses the influence of solid particles, type of motion and cross-section on the changes in the pressure drop and heat transfer coefficient. The analysis presented in the paper allows for identification of the criterial relations used to calculate the Fanning factor and the Nusselt number for laminar and turbulent flow, taking into account elements such as phase change, which accompanies the heat transfer process. Ice slurry flow is treated as a generalized flow of a non-Newtonian fluid. [ABSTRACT FROM AUTHOR]

The paper presents the results of experimental studies of the heat transfer process on the outer surface of longitudinally finned tubes. Experimental values of heat transfer coefficients under free and forced convection conditions were calculated for low air flow velocities. Two air flow patterns were analysed, i.e. airflow parallel and perpendicular to the axis of the pipe. The mean values of heat transfer coefficients obtained during the study amounted to 2-8.5 (W m-2 K-1) under free convection conditions, 4.5-19 (W m-2 K-1) for forced transverse flow and 4-11 (W m-2 K-1) for forced convection along the axis of the tube. Experimental values of heat transfer coefficients for transverse flow around the tube were 22% higher than heat transfer coefficients for airflow along the axis of the tube. The paper lists the dimensionless relationships which can be used to calculate the values of the heat transfer coefficient under free and mixed convection conditions, with transverse and longitudinal air flow around the outer surface of vertical longitudinally finned tubes. [ABSTRACT FROM AUTHOR]

Abstract: The paper presents the results of experimental research on heat transfer of ice slurry during its flow through tubes of circular, rectangular and slit cross-sections. Moreover, the work discusses the influence of solid particles, type of motion and cross-section on the changes in the heat transfer coefficient. The analysis presented in the paper allows for an identification of the criterial relations used to calculate the Nusselt number for laminar and turbulent flow, taking into account elements such as phase change, which accompanies the heat transfer process. Ice slurry flow is treated as a generalized flow of a non-Newtonian fluid. [Copyright &y& Elsevier]

Abstract: In this paper, we present results of the studies of pressure drops during laminar and turbulent flows of ice slurry produced on the basis of 10.6% ethanol solution. The results, obtained at various ice mass fractions, include pressure drops determined in horizontal ducts of circular, rectangular, and slit cross-sections. The critical Reynolds numbers were also determined. By introducing the Kozicki''s generalized definition of the Reynolds number, it was possible to verify the Fanning, Blasius and Dodge–Metzner–Kozicki relations used for determining ice slurry pressure drops during its flow through channels of various cross-sections. [Copyright &y& Elsevier]

Abstract: In this paper we present results of the studies of ice slurry flow in horizontal tubes. The possibility of treating the rheological parameters of ice slurry as being those of Bingham fluid was confirmed. The values of parameters (mass fraction, flow velocity) corresponding to the laminar, intermediate and turbulent flow were determined which permits to optimize the flow in the systems working with this cooling agent. Critical flow velocity and mass fraction of ice values were determined thereby; they correspond to a change in character of an ice slurry flow from a laminar to turbulent motion. Experimental results were compared to the analytical results, based on the Hedström and Tomita algorithms (the laminar and turbulent flow, respectively). The comparison showed a very good agreement between these data. [Copyright &y& Elsevier]

Abstract: In this paper, we analyzed the possibility of the simulations of ice slurry flow based on the known CFD procedures, for both Bingham fluids and mulitiphase flow models (the mixture and Eulerian models). It was shown that in the laminar region, the models selected (the Bingham and mixture model) gave a correct description of momentum transfer. In the turbulent range, corresponding to low values of the Reynolds number, the best agreement between experimental and simulation results (for the single-phase as well as for the multiphase Eulerian model) was obtained when the RNG k–ε turbulence model with the enhanced wall treatment algorithm was selected. [Copyright &y& Elsevier]

Abstract: This paper presents results of studies on heat transfer in ice slurry flows through horizontal tubes. On the basis of the energy equation and experimental results, the authors developed their own dimensionless relationships to determine local values of heat transfer coefficients for turbulent and laminar flows. Appropriate parameters were introduced to these expressions, in order to account for the effects of the following: the rheological properties of ice slurry, phase change, and the multiphase flow character. The second part of this paper discusses the possibility of modeling heat transfer in ice slurry tube flows using the CFD (fluent) methods. Correct description of heat transfer in ice slurry flows in tubes was made possible by assuming a single-phase model for Bingham fluid, and the enthalpy-porosity method for the analysis of melting, as well as by taking into account variations of the heat conductivity in a moving suspension. [Copyright &y& Elsevier]

This paper looks at entropy generation during ice slurry flow in straight pipes and typical heat exchanger structures used in refrigeration and air-conditioning technology. A dimensionless relationship was proposed to determine the interdependency between flow velocity and the volume fraction of ice, for which the entropy generation rates were at the minimum level in the case of non-adiabatic ice slurry flow. For pipe flow, the correlation between the minimum entropy generation rate and the overall enhancement efficiency was analyzed. As regards heat exchange processes in heat exchangers, the authors analyzed the relationship between the minimum entropy generation rate and the heat exchange surface area and exchanger efficiency. [ABSTRACT FROM AUTHOR]

The article contains the results of research on transient heat and mass transfer processes occurring in a honey dehydrator with the capacity of 30 kg of honey with closed air circulation with volumetric flow rates Va = 0.01–0.03 m³s−1. The research was carried out different rotational speeds of the honey mixer ns = 120-270 rpm, without and with preheating of the honey. The article presents heat and mass balance equations for the considered process of honey dehydration, the values of heat transfer and mass transfer coefficients between honey and air were determined. The values obtained are respectively α = 5-25 Wm−2 K−1, β = 0.001–0.035 kg m−2s−1. The reduction of mixer speed from ns = 270 rpm tons = 120 rpm was accompanied by an increase in average heat and mass transfer coefficients of approx. 30% and 52%, respectively. The tripled volumetric flow rate of air(Va1/Va2 = 3) resulted in an increase in heat and mass transfer coefficients – on average by 80% and 140%, respectively. Preheating the honey allows to increase the amount of removed water by 30%. The paper presents the general dimensionless expressions allowing for the calculation of heat and mass transfer coefficients. [ABSTRACT FROM AUTHOR]

This paper presents a mathematical model of the heat and mass transfer processes for a rotary-spray honey dehydrator with a heat pump and a closed air circuit. An analytical calculation model, based on the energy balance equations of the dehydrator and heat pump, was used to model the transient dehydration process of honey in a dehydrator. The presented article includes a different approach to modelling both the dryer and the heat pump assisting the drying process. The novel quality of this study lies in the use of original equations to determine the heat and mass transfer coefficients between honey and air and using an actual model of a cooling unit to model the honey dehydration process. The experimentally verified calculation algorithm enables an analysis of the effects of air flow rate, mixer rotation speed, and cooling unit power on the efficiency of the drying process. The dehydrator calculation model was used to minimize the drying time by selecting the optimal evaporative temperature values of the cooling unit. For fixed mixer speed and air flow rates, optimal values of evaporation temperatures allow for 8–13% reduction in honey drying time and an increase in the specific moisture extraction rate (SMER) by 4–32%. [ABSTRACT FROM AUTHOR]