Miyatake Osamu

The liquid flow in multi-stage flash evaporators

Abstract In an attempt to reach a quantitative understanding of the interaction between the fluid mechanics and flash evaporation in a stage of a multi-stage flash (MSF) evaporator, and in horizontal free-surface streams in general, a numerical analysis is performed, as a first step, of two-dimensional turbulent isothermal flow of a liquid in a flash chamber (stage) with and without a baffle (sill) placed downstream of the inlet orifice. Experiments are also performed, and validate the model successfully in the range of flows of 4.3 × 10 5 −8.7 × 10 5 kg h −1 (m width) −1 and liquid level of 0.4 m, conditions typical to MSF evaporators. The baffle plate is found to serve well in propelling the entering liquid to the free surface and in generating low-pressure regions, primarily near the stream line rising from the top edge of the baffle, both effects promoting evaporation rates. The interstage orifice coefficient is found to be practically independent of the liquid superheat, temperature, and mass flow rate.

Natural convective heat transfer from a vertical isothermal surface to a non-Newtonian Sutterby fluid

This paper deals with the laminar natural convection of a non-Newtonian fluid along a vertical isothermal surface. The boundary-layer equations for a Sutterby fluid are solved numerically, and several characteristics of the non-similarity solution are represented graphically. An approximate expression of local Nusselt number Nux is proposed as Nux = 0·.50(Gr0xPr0)0·.25(1+m) , where m= 0−04 Pr00.23 A3·7 Pr0−0.34 Z00·63A0.66 Gr0x and Pr0 are Grashof number and Prandtl number based on zero viscosity respectively, and A and Z0 are non-Newtonian parameters. Local heat-transfer coefficients are obtained by experiments with aqueous solutions of polyethyleneoxide (PEO) and carboxymethylcellulose (CMC). The experimental results are in excellent agreement with the theoretical ones.

Natural convective heat-transfer from a vertical surface of uniform heat flux to a non-newtonian sutterby fluid

Abstract This paper deals with the laminar natural convection of a non-Newtonian fluid along a vertical surface with uniform heat flux. The boundary layer equations for a Sutterby fluid are solved numerically, and the typical results for the local Nusselt number Nux, are represented graphically. From the results an approximate expression of Nux, is proposed as Nu x = 0.62(Gr ∗ ox Pr o ) 0.2(1+m ∗ where m ∗ = 0.06Pr o −0.28 A 3.7 pr o -0.34 Z ∗ o 0.35A0.66 , Gr∗0x and Pr0 are Grashof and Prandtl numbers based on zero viscosity respectively, and A and Z ∗ 0 are non-Newtonian parameters. Local heat-transfer coefficients are obtained by experiments with aqueous solutions ofpolyethyleneoxide (PEO) and carboxymethylcellulose (CMC). The experimental results are in excellent agreement with the theoretical predictions.