Investigation of Condensation Mass Transfer Time Relaxation Parameter in Thermosyphons

Heat pipes and thermosyphons are widely used in various industries for their efficient heat transfer capabilities and reliability. Thermosyphons consist of three sections: the evaporator, adiabatic section, and condenser. The working fluid absorbs heat and vaporizes in the evaporator, travels through the adiabatic section, and condenses in the condenser, releasing the heat. Gravity helps return the liquid to the evaporator, completing the heat transfer cycle. To study thermosyphon flow distribution and heat transfer, researchers have conducted experiments and numerical simulations, often using computational fluid dynamics (CFD). In CFD simulations, the mass transfer time relaxation parameter plays a crucial role in determining evaporation and condensation rates, as well as temperature and pressure distribution. However, determining the correct value for this parameter is challenging, with no standardized criterion in thermosyphons.

Addressing this issue, a recent study published in the peer-reviewed International Journal of Heat and Mass Transfer by Mr. Wandong Min, Dr. Wei Zhong, Ms. Yuting Zhang, Dr. Xiaoling Cao, Porf. Yanping Yuan from the Southwest Jiaotong University in China investigated the condensation mass transfer time relaxation parameter in thermosyphons. They conducted elegant experiments and developed a CFD model using ANSYS FLUENT 2021 software to predict the behavior of a two-phase closed thermosyphon under different conditions. The researchers employed the Volume of Fluid method and made assumptions about gas-liquid balance, bubble shape, and incompressibility. The CFD model considered symmetry and incorporated clear boundary conditions. The solution utilized the SIMPLE algorithm, upwind scheme, and interpolation schemes, while scaled residuals were monitored to ensure convergence. The study’s importance lies in its contributions to the optimization of thermosyphon performance, advancement in computational fluid dynamics simulations, practical guidelines for determining the condensation mass transfer time relaxation parameter, and the overall promotion of energy efficiency and sustainability in heat transfer processes.

To validate their findings, the research team constructed an experimental setup and monitored the thermosyphon’s performance using temperature and pressure sensors along with a data acquisition instrument. They conducted experiments with different working fluids (methanol, ethanol, and water), filling ratios, and heating inputs. Before supplying heating power, they followed a specific experimental procedure and adjusted the cooling water flow rate and temperature. After analyzing the temperature distribution on the condenser wall’s surface for 15 seconds, they confirmed reaching equilibrium. By establishing the relationship between the average condenser wall temperature and condensation mass transfer time relaxation parameter, they observed that higher parameter values led to a rise in the average condenser wall temperature, which eventually converged on a constant value. The entire progression of wall temperature showed excellent agreement, with simulations providing more consistent and uniform results due to fewer experimental factors. The researchers derived an empirical equation for the condensation mass transfer time relaxation parameter based on key parameters and performed nonlinear fitting in MATLAB. The resulting scaling equation considered fluid properties, filling ratio, and saturation temperature. The temperature differences between experimental and simulated results for various fluids and filling ratios remained within a 2% error margin, confirming the accuracy and applicability of their method for determining the condensation mass transfer time relaxation parameter.

In summary, the authors successfully investigated the condensation mass transfer time relaxation parameter in thermosyphons through a combination of experiments and CFD simulations. The researchers established empirical relationships between the parameter and working fluid properties, filling ratio, and saturation temperature, validating their determination method through close agreement between experimental and simulated results. The findings of the authors contribute to energy efficiency and sustainability. Improving heat transfer processes is crucial in various industries, including power generation, electronics cooling, and thermal management systems. By optimizing thermosyphons through a better understanding of the condensation mass transfer time relaxation parameter, it becomes possible to enhance energy efficiency, reduce energy consumption, and minimize environmental impacts.