Heat Transfer Coefficient In Minichannel Research Articles

Flow and heat transfer behaviour of nucleating agent-enhanced nanofluids through manifold mini-channels

Improving the thermal performance of mini-channels is crucial. The nature of working nanofluids and the mini-channel structure can have a significant impact on the thermal efficiency of mini-channels. This study investigated the flow and heat transfer characteristics of a manifold mini-channel heat sink (MCHS) structure. The working fluids were composite nano-phase change emulsions (NPCE), which were prepared from eicosane, eicosanol, and metal oxide particles (nano-MgO). They possess low supercooling, high thermal conductivity, and high stability. Using these NPCEs, convective heat transfer studies were conducted in the two mini-channels. The impacts of the channel type, NPCEs, and Re on the heat transfer characteristics, flow characteristics, and overall performance were investigated. The results showed that the prepared NPCE can improve the heat transfer coefficient in mini-channels compared to water. The incorporation of nano-MgO particles effectively enhanced the heat transfer capacity with the highest enhancement (17.7%) in the heat transfer coefficient compared to water. The addition of alcohol further enhanced the heat transfer performance. A mixture of 6 wt% eicosane + 1 wt% nano-MgO + 0.6 wt% eicosanol yielded the highest enhancement in the heat transfer coefficient of 29.7%. In addition, a manifold mini-channel was found to have a better comprehensive performance than a rectangular mini-channel. The maximum reductions in pressure drop and thermal resistance of the manifold MCHS were 51.2% and 53.9%, respectively, compared to the rectangular mini-channel. Overall, the evaluated performance indicators of the manifold MCHS with composite nanofluid were 17.9% higher than those of the rectangular MCHS.

Review of the calculation of the boiling heat transfer coefficient in mini-channels and micro-channels

The need to dissipate high heat flux densities has led researchers and designers to employ phase change as a mechanism to achieve this goal and thereby achieve more compact heat exchanger equipment. In the present work, a study of the literature on boiling in mini-channels and microchannels was carried out. For this purpose, bibliographies dating from the 1990s to the present were consulted, which revealed the main parameters or topics that characterize this process in mini-channels and microchannels. Thus, the terms mini-channels and microchannels, forced flow boiling and flow regimes (map) are addressed. In addition, a summary of the equations for the determination of the heat transfer coefficient in two-phase regime (hdf) is presented.

The application of the Beck`s method combined with the FEM and Trefftz functions to determine the heat transfer coefficient in minichannel

The aim of this study is to determine the heat transfer coefficient between the heated surface and the boiling fluid flowing in a minichannel on the basis of experimental data. The calculation model is based on Beck’s method coupled with the FEM and Trefftz functions. The Trefftz functions used in the Hermite interpolation are employed to construct the shape functions in the FEM. The unknown local values of the heat transfer coefficient at the foil- -fluid contact surface are calculated from Newton’s law. The temperature of the heated foil and the heat flux on the foil surface are determined by solving a two-dimensional inverse heat conduction problem. The study is focused on the identification of the heat transfer coefficients in the subcooled boiling region and the saturated nucleate boiling region. The results are compared with the data obtained through the one-dimensional method. The investigations also reveal how the smoothing of measurement data affects calculation results.

Direct estimation of local convective boiling heat transfer coefficient in mini-channel by using conjugated gradient method with adjoint equation

The purpose of this paper was to present an inverse heat conduction method used for determining the local convective boiling heat transfer coefficient in mini-channel for pure water, copper nanofluid by using three different concentrations of nanoparticles: 5mg/L, 10mg/L and 50mg/L. Conjugated gradient method with adjoint equation is used to solve the IHCP and estimate directly the space-variable convective heat transfer coefficient. Direct estimation local convective boiling heat transfer coefficient is a nonlinear inverse heat problem. The uncertainties in the estimated in heat transfer coefficient are calculated using bias and variance errors. This method is able to estimate local convective boiling heat transfer coefficient very well.