A numerical study has been carried out to understand and highlight the effects of axial wall conduction in a conjugate heat transfer situation involving simultaneously developing laminar flow and heat transfer in a square microchannel with constant flux boundary condition imposed on bottom of the substrate wall. All the remaining walls of the substrate exposed to the surroundings are kept adiabatic. Simulations have been carried out for a wide range of substrate wall to fluid conductivity ratio (ksf ∼ 0.17–703), substrate thickness to channel depth (δsf ∼ 1–24), and flow rate (Re ∼ 100–1000). These parametric variations cover the typical range of applications encountered in microfluids/microscale heat transfer domains. The results show that the conductivity ratio, ksf is the key factor in affecting the extent of axial conduction on the heat transport characteristics at the fluid–solid interface. Higher ksf leads to severe axial back conduction, thus decreasing the average Nusselt number (Nu¯). Very low ksf leads to a situation which is qualitatively similar to the case of zero-thickness substrate with constant heat flux applied to only one side, all the three remaining sides being kept adiabatic; this again leads to lower the average Nusselt number (Nu¯). Between these two asymptotic limits of ksf, it is shown that, all other parameters remaining the same (δsf and Re), there exists an optimum value of ksf which maximizes the average Nusselt number (Nu¯). Such a phenomenon also exists for the case of circular microtubes.

Purpose This paper aims to emphasize on studying various geometrical modification performed in wavy and raccoon microchannel by manipulating parameters, i.e. waviness (γ), expansion factor (α), wall to fluid thermal conductivity ratio (ksf), substrate thickness to channel height ratio (dsf) and Reynolds number (Re) for obtaining optimum parameter(s) that leads to higher heat dissipation rate. Design/methodology/approach A three-dimensional solid-fluid conjugate heat transfer numerical model is designed to capture flow characteristics and heat transfer in single-phase laminar flow microchannels. The governing equations are solved using finite volume method. Findings The results are presented in terms of average base temperature, average Nusselt number, pressure drop, dimensionless local heat flux, dimensionless wall and bulk fluid temperature, local Nusselt number and performance factor including axial conduction number. Heat dissipation rate with raccoon microchannel configuration is found to be higher compared to straight and wavy microchannel. With waviness of γ = 0.167, and 0.267 in wavy and raccoon microchannel, respectively, performance factor attains maximum value compared to other waviness for all values of Reynolds number. It is also found that the effect of axial wall conduction in wavy and raccoon microchannel is negligible. Additionally, thermal performance of wavy and raccoon microchannel is compared with straight microchannel. Practical implications In recent past years, much complex design of microchannel has been proposed for heat transfer enhancement, but the feasibility of available manufacturing techniques to fabricate complex geometries is still questionable. However, fabrication of wavy and raccoon microchannel is easy, and their heat dissipation capability is higher. Originality/value This makes the difference in wall and bulk fluid temperature smaller. Thus, present work highlighted the dominance of axial wall conduction on thermal and hydrodynamic performance of wavy and raccoon microchannel under conjugate heat transfer situation.

No abstract

No abstract

No abstract