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.

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Purpose This study aims to capture the heat transfer and entropy generation characteristics of temperature-dependent nano-encapsulated phase change material (NEPCM) slurry in a hybrid wavy microchannel. In addition, the effect of substrate material combined with NEPCM slurry on conjugate heat transfer condition is captured for different microchannel heat sinks. Design/methodology/approach A novel “hybrid wavy microchannel” is proposed to enhance the overall heat transfer and reduce the pressure drop by combining wavy and raccoon geometry. NEPCM–water slurry is implied in the hybrid wavy, conventional wavy and raccoon microchannel. A user-defined function (UDF) is used to observe the effect of phase-change of paraffin material in thermophysical properties of NEPCM–water nanofluid. All three (hybrid, wavy, raccoon) microchannels are engraved on a rectangular substrate of 1.8 mm width (ωs) and 30 mm length (L), respectively. For hybrid, wavy and raccoon microchannel, waviness (γ) of 0.067 is selected for the investigation. Findings The result shows that NEPCM particle presence reduces the fluid domain temperature. The thermal performance of proposed Heat sink 2 is found better than the Heat sink 1. The effect of the geometrical modification, wall thermal conductivity, different volumetric concentrations of nanoparticles (ϕ ∼ 1 – 5%) and Reynolds number (Re ∼ 100 – 500) on thermodynamic irreversibility is also observed. Additionally, the effect of thermal and frictional entropy generation is reduced with a combination of NEPCM slurry and higher conductive material for all heat sinks. Practical implications A combination of NEPCM slurry with laminar flow microchannel cooling system emerged as a better alternative over other cooling techniques for higher power density devices such as microprocessors, electronic radar systems, aerospace applications, semiconductors, power electronics in modern electronic vehicles, high power lasers, etc. Originality/value The phase-change process of the NEPCM slurry is tracked under conjugate heat transfer in a hybrid wavy microchannel. Furthermore, the phase-change process of NEPCM slurry is captured with different heat sink materials (SS316, silicon and copper) under conjugate heat transfer situation for different heat sinks and concentrations (ϕ ∼ 1–5) of NEPCM.

A three-dimensional numerical study has been carried out to understand the effect of axial wall conduction in a conjugate heat transfer situation in a wavy wall square cross section microchannel engraved on solid substrate whose thickness varying between 1.2–3.6 mm. The bottom of the substrate (1.8 × 30 mm2) is subjected to constant wall heat flux while remaining faces exposed to ambient are assumed to be adiabatic. The vertical parallel walls are considered wavy such that the channel cross section at any axial location will be a square (0.6 × 0.6 mm2) and length of the channel is 30 mm. Wavelength (λ) and amplitude (A) of the wavy channel wall are 12 mm and 0.2 mm respectively. Simulations has been carried out for substrate thickness to channel depth ratio (δsf ∼ 1–5), substrate wall to fluid thermal conductivity ratio (ksf ∼ 0.34–646) and flow rate (Re ∼ 100 to 500). The results show that with increase in flow rate (Re), the hydrodynamic and thermal boundary layers are thinned due to wavy passage and they shifted from the centerline towards the peak which improves the local heat transfer coefficient at the solid-fluid interface. It is also found that after attaining maximum Nuavg at optimum ksf, the slope goes downward with increasing ksf for all set of δsf and flow rate (Re) considered in this study.

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Heat transfer in laminar flow microtube is numerically explored with an objective of discriminating conjugate heat transfer process experienced in a microtube under two different thermal conditions. Two classical thermal conditions-constant heat flux and constant wall temperature-are imposed separately on the outer surface of a microtube. Wide parametric variations are considered in this study, for the two thermal conditions, albeit the problem under consideration being very classical from both geometry and thermal condition point of view. The parametric variations considered in this work include wall thickness, wall conductivity and coolant flow rate. An expression for Nusselt number in terms of radial (or transverse) and axial conduction number is presented and validated against existing theoretical correlation as well as reported experimental data for both circular and non-circular channels. Dominance of axial conduction over radial (or transverse) conduction is explored and it is found that the effect of wall material on conjugate heat transfer plays an important role. Additionally, it is also observed that with the increase in coolant flow rate, the ratio of radial to axial conduction number increases for both thermal boundary conditions.