In this numerical study, an entropy generation analysis is performed to optimize the geometry of a stepped solar still through minimization of irreversibilities. The moist air model is used for the simulation of the double diffusive free convection heat transfer inside the stepped solar still. The governing equations are solved by employing a finite volume technique. The influences of some geometrical and operating parameters, including the number and height of the steps and the temperatures of glass ceiling and water surface, on the flow structure, concentration and temperature fields, and different types of irreversibilities inside the solar still are studied. The computational results show that the active sites for generating the irreversibilities are regions near the evaporation and condensation surfaces inside the solar still. The fluid friction and concentration terms have negligible contributions to the irreversibility generation, and the thermal irreversibility is the dominant term in the solar still. All types of irreversibility are intensified by increasing the number or height of the steps. From the view point of irreversibility minimization, the usage of a stepped solar still with lower operating temperatures is recommended. In a solar still with four steps, the viscous, thermal, and concentration irreversibilities increase about 41.55%, 316.43%, and 316.6%, respectively, as the step height increases in the range of 2–5 cm. The viscous, concentration, and thermal irreversibilities increase about 8.2%, 53.5%, and 1.57%, respectively, by increasing the temperatures of the glass ceiling and water surface from T_g = 44 °C and T_w = 49 °C to T_g = 54 °C and T_w = 59 °C.

中文翻译：

---

基于熵产生最小化的阶梯式太阳能蒸馏器的设计改进

在此数值研究中，进行了熵生成分析，以通过最小化不可逆性来优化阶梯式太阳能蒸馏器的几何形状。湿空气模型用于模拟阶梯式太阳能蒸馏器内部的双扩散自由对流传热。控制方程通过采用有限体积技术求解。研究了某些几何和操作参数（包括台阶的数量和高度以及玻璃天花板和水表面的温度）对流结构，浓度和温度场以及太阳能内部不同类型的不可逆性的影响。计算结果表明，产生不可逆性的活性部位是太阳蒸馏器内蒸发和凝结面附近的区域。流体摩擦和浓度项对不可逆性的贡献可忽略不计，而热不可逆性是太阳蒸馏器中的主要项。通过增加台阶的数量或高度，可加剧所有类型的不可逆性。从最小化不可逆性的角度出发，建议使用工作温度较低的阶梯式太阳能蒸馏器。在具有四个台阶的太阳能蒸馏器中，随着台阶高度在2–5 cm范围内增加，粘性，热和浓度不可逆性分别增加约41.55％，316.43％和316.6％。通过提高玻璃天花板和水表面的温度，粘性，浓度和热不可逆性分别增加了约8.2％，53.5％和1.57％。T _g  = 44°C和T _w  = 49°C至T _g  = 54°C和T _w  = 59°C。