The stability analysis of tri-hybrid nanofluid is examined theoretically in the presence of three types of gravity modulation. Normal mode techniques have been carried out for linear stability analysis, and the truncated Fourier series method is used for non-linear analysis. We observe both stationary and oscillatory convection is possible in the bottom-heavy case, and the onset of convection gets delayed in stationary in comparison to oscillatory. We also observe the onset of convection is earlier in the case of top-heavy with respect to bottom-heavy. Heat and mass transport start earlier in the day–night profile in comparison to other profiles of gravity modulation. In the graph of nusselt number, mass transfer of the first particle increases with an increase in Rn1 value while other two concentration Rayleigh numbers (Rn2, Rn3) does not have any effect on first concentration nusselt number. If we generalize the problem for n-different types of nanoparticles, then two cases may be possible (1) Top-heavy-ordinary nanofluids will be the most stabilizing case. (2) Bottom-heavy-nanofluids with n-type particles will be the most stabilizing case. The most stabilizing case is possible with the same ratio of Rn in the top-heavy, whereas the opposite result is found in the bottom-heavy.

In the present paper an effect of gravity modulation in a horizontal parallel flat plate having micropolar nanofluid saturated by a porous medium is examined. Local thermal nonequilibrium (LTNE) has been observed for the problem, i.e., the fluid, particle, and solid matrix are at different temperatures. Onset of convection and heat and mass transfer for both the cases, i.e., linear stability and nonlinear stability, is analyzed. We conclude that rate of convection in the LTNE case is faster than in the LTE case. Effect of porosity is observed in the LTNE region, which is opposite to the effect observed in the LTE region. Increase in value of A, K₁, and δ delay the rate of convection. Small value of frequency of gravity modulation forms a greater number of small periods which delay the rate of convection. On increasing the value, heat transfer increases. At higher frequency of modulation we obtain the case similar to unmodulated case.