Channel Blockage and Flow Maldistribution during Unsteady Flow in a Model Microchannel Plate heat Exchanger

Abstract

This paper describes the problem of channel blockage as a result of flow maldistribution between the channels of a model mini channel plate heat exchanger consisting of one pass on each leg. Each leg of the heat exchanger contains 51 parallel and rectangular minichannels of four hydraulic diameters namely 461 µm, 571 µm, 750 µm and 823 µm. In addition, a more complex geometry has been investigated where for the sake of breaking the development length the inclined transverse cuts have been incorporated. The moment of liquid phase transition through the exchanger (the working medium: water) was recorded for the mass fluxes ranging from 18.67 to 277.76 kg/m2s in 51 parallel channels with the use of a fast speed camera. The Reynolds numbers Re in the individual channels were from 10.76 to 90.04. The relationship between the mass flux and the size of the minichannels in the presence of the maldistribution is discussed here. The existence of the threshold in the mass flux below which the phenomenon occurs has been shown. Two mechanisms of channel blocking have been recorded and described in detail. A miniscale variation of one of them containing the extended geometry was created as well.

Fluid Flow and Heat Transfer Characteristics Investigation in the Shell Side of the Branch Baffle Heat Exchanger

“…In summary, the research on improving the heat transfer efficiency of STHXs has been making progress for many years. On this basis, the development of baffles and the improvement of baffles structure to overcome the defects of high flow resistance and high energy consumption of heat exchangers remain a key research direction (Dabrowski et al 2019) and are completely consistent with the requirements of recent academic progress (Klemes et al 2020). Depending on the different flow modes of the shell-side operating fluid in the STHX, the flow behavior can be roughly classified into four categories: the crossflow, the longitudinal flow, the helical flow, and oblique flow.…”

Image Analysis of Flow Maldistribution during Boiling in Parallel Minichannels

“…During flow boiling in minichannels flow maldistribution has been observed [4,5]. The effect of heat exchanger configurations (geometry), occurring flow patterns, geometrical characteristics of the channels, flow rate, and channel diameter on flow distribution was investigated [5][6][7][8].…”

“…The dynamic instabilities are characterized as oscillations between different states (flow patterns). Examples of such oscillations are pressure drop oscillations, density wave oscillations, acoustic oscillations, thermal oscillations, and channel blocking [8,9,11,12]. Channel blocking in minichannels connected with the occurrence of bubbles expanding into slugs which push the liquid away was observed in [13].…”

Mitigation of Flow Maldistribution in Minichannel and Minigap Heat Exchangers by Introducing Threshold in Manifolds

“…The maldistribution is not examined well enough and there are inconsistencies in reports about reasons, predictions and methods of reduction. Moreover, there are a lot of works that are dealing with a maldistribution phenomenon in parallel minichannels (Dąbrowski et al 2019;García-Cascales et al 2017;Najim & Feddaoui, 2018;Dąbrowski et al 2017;Sakamatapan & Wongwises, 2014;Yang et al 2017;Zhou et al 2014) but few that mentioned about flow non-uniformity and non-uniform temperature field in minigaps (Alam et al 2013;Mathew et al 2019;Tamanna & Lee, 2015).…”