1-8] Kirkwood, J. a. F. Buff: Statistical Mechanical Theory of Surface Tension. J. Chem. Phys. Vol. 17 (1948) p. 338. I-9] Konorski, A.: Wet Steam Processes in Turbines; Ther- modynamics of Saturated Vapour (in Polish). Zeszt Nauk. IMP PAN (Report of the Institute of Fluid Flow Machinery). No. 247/1130/87, Gdafisk 1987. 1,10] Kotake, S. a. I. Glass: Survey of Flows with Nucleation and Condensation. Toronto: Inst. Aerospace Stud. 1978. [11] Ono, S. a. S. Kondo: Molecular Theory of Surface Ten- sion in Liquids. In: Fliigge: Encyklopedia of Physics. Vol. X. Berlin: Springer 1960. [12] Rusanov, A.: Thermodynamics of Surface Phenomena (in Russian). Leningrad: Izdat. Univ. 1960. [-13] Skripov, 14(.: Metastable Liquids (in Russian). Izd. "Nauka", Red. Mat-Fiz, Moskva 1972. 1-14] Straub, J., N. Rosner a. U. Grigull: Oberfl~ichenspan- nung von leichtem und schwerem Wasser. W/irme- und Stoffiibertragung (Thermo and Fluid Dynamics) 1980, p. 241/52. [15] Tolman, R.: Considerations of the Gibbs Theory of Sur- face Tension. J. Chem. Phys. Vol. 16 (1948) p. 758. [16] Tolman, R.: Effect of Droplet Size on Surface Tension. J. Chem. Phys. Vol. 17 (1949) p. 333. 1,17] Vogelsberger, W.., a. G. Marx: Zur Kriimmungsabh/in- gigkeit der Oberfl/ichenspannung kleiner Tr6pfchen. Z. Phys. Chemic (Leipzig) Vol. 257 (1976) p. 580/86. Received November 9, 1989 F 4022 The Effect of Hall Currents on the Magneto Hydro Dynamic (MHD) Boundary Layer Flow over a Flat Plate V.G. Naidu, S.R. Koneru, H.R. Nataraja and B.N. Rao*) Studies are made on laminar compressible magneto hydro dynamic ( MHD ) boundary layer flow over a flat-plate with Hall and ionslip currents. Viscous drag, magnetic drag and heat transfer coefficients are determined for the values of interaction parameter, electromagnetic load parameter, Hall parameter and ionslip current parameter. It is found that the overall drag (magnetic plus viscous) coefficient increases and the heat transfer coefficient decreases with interaction parameter. 1. Introduction One of the important applications of magneto hydro dy- namics is towards a strong magnetic field which noticeably influences the electromagnetic force and towards a low den- sity of the gas such as in space flight and in nuclear fusion research. In a gas, which is sufficiently dense, the electron- atom collision frequency vc is large enough so that the ten- dency for free electrons to spiral around the magnetic field lines is suppressed. If the applied field is large or the gas density is low so that the cyclotron frequency, ~o=elBl/m, exceeds the collision frequency vc, the electron can make a number of cyclotron orbits between collisions and will drift in a direction perpendicular to the direction of the magnetic (/~) and electric (/~) fields. This drift produces a current (the Hall current), and the gyromotion decreases the electric con- ductivity of the gas. By lowering the conductivity, the Hall effect thus reduces the current in the direction of electric field and causes a current to flow normal to both /~ and B. The current will interact with the applied magnetic field to induce a transverse motion of the field. When the ratio og/vc becomes very large, the electromagnetic field can force both the ions and electrons to produce a relative drift between them and the neutrals. This drift is called "ionslip" and is of course negligible for highly ionized gases. Since both the Hall effect and ionslip will occur in low pressure, moderately high tem- *) EG. Naidu, Prof. S.R.Koneru, Departmentof Mathematics,IndianInstitute of Technology Powai, Bombay,Dr. H.R. Nataraja, CompressorDivision, Gas Turbine Research Establishment, Bangalore, and Dr. B. Nageswara Rao, Structural Engineering Group,VikramSarabhaiSpaceCentre,Trivan- drum/India. perature environments, they will affect the heat transfer in a boundary layer. Wilcox [1] has derived the equations for a steady two- dimensional laminar compressible MHD boundary layer and solved for velocity and temperature profiles, along the wedges and fiat plates, using similarity principles. It is found that the heat transfer rate decreases and the overall drag (magnetic plus viscous) increases with the magnetic interaction parame- ter. These results indicate the possibility of controlling the heat transfer through magneto gas flow by increasing the strength of the applied magnetic field. It is very important to consider the contribution of the Hall and the ionslip cur- rents in the formulation when the strength of the applied fields are large. Naidu et al. [2] have recently studied the problem of a two-dimensional boundary layer flow over an electrode plate with a uniform magnetic field and Hall cur- rents. The equations governing the boundary layer flow are found to be nonsimilar due to the presence of a uniform magnetic field. It is noted previously in [3] that the Hall effect renders the insulator boundary layer three dimensional, since the Lorentz force due to the axial current induces a cross flow. A general formulation of the problem and its solution is discussed here by considering the Hall alid the ionslip cur- rents. The nonsimilar boundary layer equations are solved following the numerical method as suggested in 14]. A para- metric study has been made to examine the effect of the Hall and the ionslip currents, on the growth of the boundary layer. The coefficient of viscous drag, magnetic drag and the heat transfer rate are determined and are presented for different values of the Hall and the ionslip currents. Forschung im Ingenieurwesen Bd. 56 (1990) Nr. 4 129