This work analyses the effects of three different Prandtl number fluids (Pr = 0.025, 5.83 and 151) on convective heat transfer inside a closed square cavity with an adiabatic left wall and three other cold walls. A centrally positioned square hot block with respective blockage ratios of 0.25 and 0.5 heats the cavity, which induces natural convection inside it for Grashof numbers Gr = 10⁴, 10⁵ and 10⁶. Besides, two different cases of mixed convection based on the direction of moving right wall are investigated for varying Richardson numbers (0.01 $\le$ Ri $\le$ 100) at Gr = 10⁴. We implement multiple-relaxation-time based thermal lattice Boltzmann model to study these flow configurations. The comprehensive analysis of the results suggests that the block size and Pr have a considerable influence on the flow and heat transfer behaviour. The average Nusselt number over the block surface $\overline{N{u}_h}$ and total entropy generation throughout the cavity $\overline{S_{tot}}$ increase with an increase in Pr and Gr due to the augmentation of convective heat transfer. For all three cases, $\overline{N{u}_h}$ at BR = 0.25 is higher compared to BR = 0.5. In mixed convection, the heat transfer irreversibility mostly dominates the entropy generation at all Pr irrespective of Ri values as indicated by large average Bejan number. The present code is carefully validated with the well-established results obtained through conventional numerical techniques.

这项工作分析了三种不同的Prandtl数种流体（Pr  = 0.025、5.83和151）对带有绝热左壁和其他三个冷壁的封闭方腔内部对流传热的影响。具有0.25和0.5各个阻塞比位于中央的方形热块加热空腔，其诱导在它里面的自然对流为格拉斯霍夫号码的Gr  = 10 ⁴，10 ⁵和10 ⁶。此外，研究了两种基于移动右壁方向的混合对流情况下的变化的Richardson数（0.01$\le$ 日 $\le$100）在Gr  = 10 ^4处。我们实施基于多重松弛时间的热晶格玻尔兹曼模型来研究这些流动配置。对结果的综合分析表明，块尺寸和Pr对流动和传热行为有很大影响。块体表面的平均努塞尔数$\stackrel{〜}{ñ{ü}_H}$ 和整个腔体的总熵产生 $\stackrel{〜}{{\mathrm{小号}}_{ŤØŤ}}$由于对流传热的增加，Pr和Gr的增加而增加。对于这三种情况，$\stackrel{〜}{ñ{ü}_H}$ 与BR  = 0.5相比，BR = 0.25时更高。在混合对流中，无论由大的平均Bejan数表示的Ri值如何，在所有Pr处，传热不可逆性都占主导地位。本代码已通过通过常规数值技术获得的公认结果进行了仔细验证。