Abstract
Given its configuration and operation conditions, the performance of a counter-flow microchannel heat exchanger (MCHX) is evaluated through detailed calculations. The fluids, both liquid water and air, are considered as continuum flow flowing in microchannels. The MCHX has 59 sheets, and each sheet has 48 microchannels. The microchannels for both fluids have the same cross section of 0.8mm×1mm and same length of 200mm. Log mean temperature difference method is adopted for this evaluation. Using appropriate equations, the properties of air-water vapor mixture are calculated based on that of the two components. Given the inlet temperature for liquid water(35℃) and air (170℃),the calculated outlet temperature for both fluids are 55.5℃ and 43.3℃, respectively. The results also show that the air at the outlet is saturated. The overall heat transfer coefficient reaches 100W/m2ꞏK, which is much higher than that of conventional heat exchanger with similar fluid combinations.
Highlights
Microchannel heat exchangers (MCHXs) have been increasingly attractive in many applications such as energy system, electronic cooling, fuel cell automobiles, etc
The MCHX was fabricated by photochemical etching and diffusion brazing processes
The outlet temperature for both liquid water and air, as well as the heat load of the MCHX are obtained through the iteration process
Summary
Microchannel heat exchangers (MCHXs) have been increasingly attractive in many applications such as energy system, electronic cooling, fuel cell automobiles, etc. They have advantages of small size, light in weight, less materials, and high heat transfer coefficients. The photochemical etching and diffusion bonding processes were used to fabricate the MCHXs. For high temperature gasgas heat exchanging, a ceramic counter-counter flow MCHX was designed, fabricated and evaluated [3]. Given inlet temperature for both fluids, the heat load is calculated through an iteration process It is found water vapor in the air starts to condense at somewhere along the flow passage and the air at the outlet is saturated.
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