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This research is focused on the experimental measurement of the thermal conductivity of CF3I and the subsequent development of empirical models, which are integral to engineering system design calculations. CF3I is identified as a potential key component in the formulation of future refrigerant mixtures, owing to its non-explosive nature, low toxicity, and minimal contribution to ozone layer depletion and global warming. Its applicability is further reinforced by its advantageous thermodynamic properties, including a low boiling point and a high critical temperature, making it a vital constituent in refrigerant mixtures. The study employs the well-established transient hot-wire method to measure the thermal conductivity of CF3I in both its liquid and vapor phases. This method is characterized by the sequential arrangement of two platinum wires which are linked in parallel to nullify any impacts from axial heat conduction. Experimental data were methodically gathered across a range of temperatures, spanning from 311 K to 374 K for the liquid phase and from 312 K to 394 K for the vapor phase, under varying pressures from 1.5 MPa to 4.0 MPa and 0.5 MPa to 3.0 MPa, respectively. The combined uncertainties associated with these measurements were meticulously calculated, amounting to 1.8% for the liquid phase and 2.0% for the vapor phase. Furthermore, the research advanced to the development of thermal conductivity models for CF3I, employing both the Extended Corresponding States method and the modified Residual Entropy Scaling method. These models effectively encapsulate the empirical findings, fitting within the established uncertainty limits with reasonable extrapolating behavior. Critically, these models are expected to play a pivotal role in predicting the thermal conductivity of refrigerant mixtures that incorporate CF3I as a component, marking a significant contribution to the field of refrigerant technology. [ABSTRACT FROM AUTHOR]

This study explores the application of zigzag-shaped, finless tubes in enhancing heat transfer performance within heat exchangers. Using three-dimensional numerical simulations, we examined the heat transfer per unit area and the volume of the pressure drop, comparing these findings with a traditional parallel tube heat exchanger. This innovative design strategy involved arranging zigzag-shaped tubes at varying distances, and the thermal transfer and frictional characteristics were tested at different air speeds. This research suggests that the introduction of zigzag heat exchangers, as opposed to traditional fin-and-tube designs, led to a significant improvement in heat transfer. This enhancement is attributed to the swirling flow created around the zigzag tubes, which increased the total heat transfer area. Furthermore, we found that the heat transfer area increased by 14.2%, 32.1%, and 63.9% for tube zigzag angles of 30°, 45°, and 60°, respectively, when compared to a parallel tube heat exchanger. Consequently, the zigzag-shaped tube heat exchanger demonstrated not only superior heat transfer, but also a reduction in frictional pressure loss. [ABSTRACT FROM AUTHOR]

Due to its low global warming potential (GWP) and good environmental properties, CF3I can be a suitable component of refrigerant mixtures in the field of refrigeration and air conditioning. In this work, the local condensation heat transfer characteristics of CF3I were experimentally investigated in a plate heat exchanger (PHE). The condensation heat transfer experiments were carried out under conditions of vapor qualities from 1.0 to 0.0, at saturation temperatures of 25–30 °C, mass fluxes of 20–50 kg/m2s, and heat fluxes of 10.4–13.7 kW/m2. Local heat transfer coefficients were found to vary in both the horizontal and vertical directions of the plate heat exchanger showing similar trends in all mass fluxes. In addition, the characteristics of local heat flux and wall temperature distribution as a function of distance from the inlet to the outlet of the refrigerant channel were explored in detail. The comparison of the experimental data of CF3I with that of R1234yf in the same test facility showed that the heat transfer coefficients of CF3I were comparable to R1234yf at a low vapor quality and a mass flux of 20 kg/m2s. However, R1234yf exhibited a transfer coefficient about 1.5 times higher at all vapor qualities and a mass flux of 50 kg/m2s. The newly developed correlation predicts well the experimentally obtained data for both CF3I and R1234yf within ±30%. [ABSTRACT FROM AUTHOR]

In this paper, an experimental study on the condensation heat transfer coefficient of refrigerant R1234yf was obtained inside a 3.5 mm outside diameter (OD) horizontal microfin tube. Comparison of present work (3.5 mm OD) and previous research (2.5 mm OD) was reported to evaluate the effect of diameter to heat transfer coefficient. Data were obtained over a range of mass velocity from 50 to 200 kg m-2s-1, vapor quality 0 to 1, and saturation temperature from 20°C to 30°C. The effect of mass velocity, vapor quality, and saturation temperature on condensation heat transfer coefficient was clarified. The experimental results were compared with some existing correlations in the open literature. Hirose et al. (2018) correlation has good agreement with experimental data. [ABSTRACT FROM AUTHOR]