The addition of nanoparticles in the base fluid (e.g water) affects several different properties including thermal conductivity, viscosity, density, and specific heat. One way to find the effectiveness of the nanofluids is to draw a Figure of Merit (FOM) for example by using the Mouromtseff number (Mo) (mainly used in turbulent flow regimes). I wanted to ask what are some other FOMs we can use to evaluate the performance of nanofluids, especially in the laminar flow regime.
The figure of merit (FoM) is used to measure the thermal performance of equipment and find the optimum thermal condition.
As you indicated, one of the earliest FOM definitions is the Mouromtseff number (Mo) that has been used to compare the heat transfer capabilities of HTFs (Heat Transfer Fluids) in laminar and turbulent flow conditions. However, another FOM is defined as the ratio of viscosity enhancement and thermal conductivity enhancement coefficients, valid in the case of fully developed laminar flow. Sekrani et al. suggested two different types of FOMs to compare the heat transfer capability of nanofluids as the performance evaluation criterion, i.e., PEC, and overall energetic efficiency.
The addition of nanoparticles will change the thermal properties of the cooling fluid, by calculation with the performance evaluation criterion (PEC). If PEC < 1, then the heat transfer performance is less than the pumping power, so the system is not feasible for use in increasing heat transfer. If PEC = 1, then the heat transfer performance is smaller equal to the pumping power so that the system does not have an impact on increasing heat transfer. If PEC > 1, then the heat transfer performance is higher than the energy used to drive the fluid or pumping power, and then it can be accepted as a solution to the problem of increasing heat transfer so that the system is feasible for use in practical applications.
Regards
Please find the following study "Thermo-economic performance and sensitivity analysis of ternary hybrid nanofluids" and check out the equations (10-11).
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