FLOW AND HEAT TRANSFER IN A SIMPLE MINICHANNEL SYSTEM INVOLVING TWO STRAIGHT SECTIONS SEPARATED BY A 180° BEND

摘要

Steady, incompressible flow through a basic minichan-nel system has been considered. Slip at the wall has been assumed to be negligible. The channel has a rectangular cross-section. The flow enters the channel with a uniform velocity and temperature and passes through a straight channel section that has a length that is 30 times the width of the channel. The How then passes around a 180° bend. Following the bend, the flow passes down another straight channel which also has a length of 30 limes the size of the channel. A uniform heat flux is applied over the entire surface of the duct. The How geometry does not represent any that is likely to occur in minichannel system applications but is adequate for the evaluation of the assumptions often adopted regarding pressure losses, flow development lengths and heat transfer rates in the preliminary design real such systems. The governing equations have been writ ten in dimension-less form and solutions to these equations have obtained using a commercial finite-element software package, FI-DAP. The solution has the following parameters: the Reynolds number, Re, the Prandtl number, Pr, the di-mensionless height-to-width ratio of the channel H = h / w, and the dimensionlcss radius of the bend R_i = r_i / w. Here w is the width of the channel, h is the height of the channel and r_i is the radius of the inside surface of the bend. Results are only presented for P r = 0.7 and R_i = 1. Re values between 10 and 500 and H values between 0.5 and 2 have been considered.