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• 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]

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 ice slurry heat transfer process in flow can be described as forced convection heat transfer of a non-Newtonian fluid subject to phase change (melting of ice crystals). This paper looks at the application of the enthalpy-porosity method to the modelling of the melting process occurring during homogenous tube flow of ice slurry. It will discuss experimentally verified results of thermal calculations, including the distribution of temperature values, heat transfer coefficients and changes to the content of solid particles. The results of the calculations apply to the laminar and turbulent flow areas, various initial mass fractions of ice and various tube cross-section shapes. [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]

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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]

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: 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]

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]