Gaseous Slip Flow Mixed Convection in Vertical Microducts of Constant but Arbitrary Geometry

Sadeghi, Morteza | 2013

694 Viewed
  1. Type of Document: M.Sc. Thesis
  2. Language: Farsi
  3. Document No: 45405 (08)
  4. University: Sharif University of Technology
  5. Department: Mechanical Engineering
  6. Advisor(s): Saidi, Mohammad Hassan
  7. Abstract:
  8. In the study of heat transfer in micro-channels, free and force convections are two limit cases and these two methods of heat transfer are combined together generally, so to achieve the most accurate informations about the flow field they should be considered in combination. In the first part of the thesis the fully developed slip flow mixed convection in vertical micro-ducts of arbitrary shapes is investigated.Uniform axial heat flux and uniform peripheral wall temperature (H1) is considered. The method considered is analytical-numerical in which the governing equations and three of the boundary conditions are exactly satisfied but the remaining slip boundary condition on the duct wall would not be exactly satisfied analytically and is applied to the solution through the least squares matching method. As an application of the method, flow and heat transfer results are presented for the duct geometries of trapezoidal, double-trapezoidal, isosceles triangular, rhombic and elliptic cross sections. The results indicate that the Poiseuille number and the Nusselt number are decreasing functions of Knudsen number and increasing functions of mixed convection parameter. Also it is seen that for polygonal ducts, the point of minimum local wall heat flux to averaged wall heat flux and local wall shear stress to averaged wall shear stress ratios are in one of the corners duct. In the second part, the fully developed longitudinal slip flow mixed convection between a periodic bunch of vertical microcylinders arranged in regular arrays is being investigated with the same way except that the least square procedure which results in a more complex code, higher time execution and memory requirement is not necessary and only the point-matching method is used. The two axially constant heat flux boundary conditions of H1 and H2 are considered in the analysis. The results indicate that both the pressure drop and Nusselt number are not dependent on the type of the boundary conditions at small and moderate blockage ratios while at higher blockage ratios, the pressure drop parameter and Nusselt number are higher for H2 case and H1 case, respectively. Furthermore, it is seen that the pressure drop and Nusselt number are decreasing functions of Knudsen number. In the third part, consideration is given to the buoyancy effects on the fully developed gaseous slip flow in a vertical rectangular microduct, which is the most widely used geometry in industry such as heat exchangers. Two different cases of the thermal boundary conditions are considered, namely uniform temperature at two facing duct walls with different temperatures and adiabatic other walls (case A) and uniform heat flux at two walls and uniform temperature at other walls (case B). After nondimensionalizing equations, they are solved by means of finite Fourier transform method. The results show that the Poiseuille number of case A is an increasing function of the mixed convection parameter and a decreasing function of the channel aspect ratio, whereas its functionality on the Knudsen number is not monotonic and depends on the value of mixed convection parameter. For case B, the Poiseuille number is decreased by increasing each of the mixed convection parameter, the Knudsen number, and the channel aspect ratio
  9. Keywords:
  10. Microchannel ; Slip Flow ; Sliding Speed ; Knudsen Number ; Mixed Convection ; Temperature Jump

 Digital Object List