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The experimental studies of fin-tube type internally-cooled dehumidifiers are still limited until now. In the present paper, the performance of a cross-flow internally-cooled dehumidifier is studied by both of experiment and simulation. The dehumidifier is made up of fin-tube heat exchangers with high corrosion resistance. Compared with the dehumidifier of the literature, it is found that the dehumidifier of this work performs well in terms of the dehumidification efficiency. Meanwhile, the heat transfer coefficient is correlated on the basis of the experimental data. By applying the correlated coefficient, the theoretical model can predicate the performance of the dehumidifier with an acceptable accuracy. Then the validated model is employed to give suggestions for optimizing the geometry design and operating conditions of the dehumidifier. Through calculation, it is discovered that the best length of the air flow direction for the present dehumidifier is about 0.3 m. In addition, the ratio of solution to air flow rate can be decided by the simulation as well. [ABSTRACT FROM AUTHOR]

Building integrated photovoltaic (BIPV) applications are key to increase the share of renewable energy in the built environment. A large potential for BIPV deployment is related to building facades. The assessment of BIPV facades depends on the accurate modelling of exterior convective heat transfer coefficients (eCHTC). However, eCHTC models commonly used in BIPV modelling tend to be simplified. This paper proposes a simulation framework that combines detailed computational fluid dynamics with a multi-physics BIPV model to investigate the influence of eCHTC on the performance of BIPV facades (cell temperature and power). The evaluation is performed for different building geometries, wind speeds, wind directions, solar irradiations, and ambient temperatures. The results show that local variations in eCHTC can cause variations in cell temperature up to 42 ° C between the BIPV modules across the facade. These temperature differences are associated with differences in power up to 17% across the BIPV facade. In general, lower temperatures (and higher power output) occur near the edges of the facade while higher temperatures (and lower power output) occur at the middle and at the bottom of the facade. Therefore, a detailed assessment of wind effects is recommended in order to verify the local operating conditions of the BIPV modules. The framework and findings presented in this work are relevant for applications in which the knowledge of the local behaviour is important, such as degradation studies. • Impact of convective heat transfer on building-integrated photovoltaic facades. • A detailed analysis of the impact of building geometry, wind speed and direction. • Numerical analyses using a multi-physics model & computational fluid dynamics. • The local convective heat transfer significantly affects cell temperature and power. • Variations in cell temperature and power can go up to 42 °C and 17%, respectively. [ABSTRACT FROM AUTHOR]

• Condensation sequences of HFO1234yf in straight and convergent tubes are explored. • We simulate condensate films to resolve thermal and frictional characteristics. • Convergent design realizes heat transfer coefficient of 12.3 kW/m2 K at 800 kg/m2 s. • Empirical correlations of heat transfer coefficient and pressure drop are tested. • Dobson-Chato, Huang, Freidel correlations suitably estimate thermo-friction factors. This paper applies the computational fluid dynamics (CFD) simulation to study the condensate two-phase thermofluid characteristics of refrigerant HFO-1234yf flowing through horizontal straight and convergent passages for guiding the design of minitube heat exchangers. The theoretical analysis employs the volume-of-fluid (VOF) method to model the progression of film condensation process for determining the distributions of velocity, pressure, temperature, vapor volume fraction and film thickness for liquid-vapor interfacial flows. The Lee model is formulated as a user defined function to treat the phase change effect at the interface. The predictions of heat transfer coefficients and pressure drops agree reasonably well with the measured data from the referencing literature at the mass and heat fluxes of 200–800 kg/m2 s and 9.9–24.3 kW/m2 for validation of the computational model. The simulated results are presented to capture the complex two-phase flow behaviors during the film condensation progression, including the formation of interfacial ripples of annular films, wave-shaped films with elongated necking regions, shedding of liquid ligaments and breakup of these ligaments entrained into the vapor core. The VOF calculations also estimate the average heat transfer coefficient and pressure drop up to 11.3 kW/m2 K and 55.1 kPa at a mass flux of 800 kg/m2 s for the straight tube, showing similar thermal performance to refrigerant HFC-134a reported by open literature. The convergent passage essentially raises the average heat transfer coefficient and pressure drop because of more severe shear stresses over the film surface. The correlations of heat transfer coefficient and pressure drop are compared with CFD predictions for straight and convergent tubes. The performance assessment is thus conducted using the validated correlations to guide the redesign of minitube heat exchangers with HFO1234yf as an alternative refrigerant in various energy systems. Two design changes are presented using HFO1234yf refrigerant to enlarge the total surface area up to 13.49% in straight tubes or broaden the cooling surface area of only 6.4% in convergent tubes for matching the performance of R134a. [ABSTRACT FROM AUTHOR]

• Finned metal foam tube maximizes the heat transfer effect among the four tubes. • Metal foam improves the temperature field uniformity of phase change materials. • Metal foam in phase change materials severely limits the natural convection. • The flow rate has the strongest influence on finned metal foam tube. • The finned metal foam structure outperforms other heat transfer techniques. This paper introduced a further heat transfer enhancement technique by inserting porous metal foam into the fin interstitials for a shell-and-tube thermal energy storage unit. The energy charging/discharging were evaluated by means of indicators including complete melting/solidification time, heat transfer coefficient, temperature response and energy storage density. To squarely justify the contribution of fin and metal foam to phase change improvement, smooth tube, finned tube and metal foam tube were examined for comparison, as well. The thermal performance of the four thermal energy storage units were evaluated by numerical models that was validated by comparison with experimental results. Based on the smooth tube, the complete melting/solidification time significantly decreased by 85.83% and 95.83%, and the average heat flux increased by 655.09% and 1834.61%, and the mean Nusselt number greatly increased by 795.93% and 4731.99%, at an inlet velocity of 0.15 m/s for heat transfer fluid. In addition, the charging/discharging capacity of the four thermal energy storage units can be significantly enhanced by increasing the flow rate. The proposed novel finned shell-and-tube thermal energy storage unit filled with metal foam outperformed other competing heat transfer structures, favoring the potentials for further advances in thermal energy storage applications. [ABSTRACT FROM AUTHOR]

• New ISO 52016-1:2017 standard compared to the dynamic simulation model in TRNSYS. • Analysis done for a wide range of building conditions/characteristics. • Differences between the two methods up to 40% for heating and up to 18% for cooling. • Relatively large differences due to heat transfer through multi-pane windows. • Certain discrepancy due to the calculation of heat transfer through opaque elements. In 2017, the ISO 52016-1:2017 standard introduced a new methodology for the assessment of the building energy performance as a replacement for the simplified method used in the ISO 13790:2008 standard. The capabilities of the new standard have been considerably improved with respect to those of the old standard, but currently there is a lack of analyses that assess the accuracy and limitations of the new standard applied to realistic multi-zone buildings of various types and in various climates. This paper presents a comprehensive analysis of the model accuracy for a wide range of building uses, envelope properties, climates, and heating/cooling needs, ranging from 5 kWh/m2 to 216 kWh/m2 for heating and from 23 kWh/m2 to 170 kWh/m2 for cooling. The analysis was done by comparing the results from the ISO 52016-1:2017 standard with the dynamic simulation model in TRNSYS. The differences between the two methods in the annual energy needs are up to 40% for heating and up to 18% for cooling. Furthermore, it is shown that the use of constant values of solar energy transmittance and the overall heat transfer coefficient for windows can cause substantial errors in the calculation of building energy needs, more so for buildings with high-performance windows. Although a certain level of discrepancy between the ISO 52016-1:2017 standard and TRNSYS also occurs in the calculation of heat transfer through opaque elements, the differences seem to be less pronounced than for windows. [ABSTRACT FROM AUTHOR]