The rates of convection and evaporation at the interface between the human body and the surrounding air are expressed by the parameters convective heat transfer coefficient hc, in W m-2 degrees C-1 and evaporative heat transfer coefficient h(e), W m-2 hPa-1. These parameters are determined by heat transfer equations, which also depend on the velocity of the airstream around the body, that is still air (free convection) and moving air (forced convection). The altitude dependence of the parameters is represented as an exponential function of the atmospheric pressure p: hc approximately pn and h(e) approximately p1-n, where n is the exponent in the heat transfer equation. The numerical values of n are related to airspeed: n = 0.5 for free convection, n = 0.618 when airspeed is below 2.0 ms-1 and n = 0.805 when airspeed is above 2.0 ms-1. This study considers the coefficients hc and h(e) with respect to the similarity of the two processes, convection and evaporation. A framework to explain the basis of established relationships is proposed. It is shown that the thickness of the boundary layer over the body surface increases with altitude. As a medium of the transfer processes, the boundary layer is assumed to be a layer of still air with fixed insulation which causes a reduction in the intensity of heat and mass flux propagating from the human body surface to its surroundings. The degree of reduction is more significant at a higher altitude because of the greater thickness of the boundary layer there. The rate of convective and evaporative heat losses from the human body surface at various altitudes in otherwise identical conditions depends on the following factors: (1) during convection--the thickness of the boundary layer, plus the decrease in air density, (2) during evaporation (mass transfer)--the thickness of the boundary layer, plus the increase with altitude in the diffusion coefficient of water vapour in the air. The warming rate of the air volume due to convection and evaporation is also considered. Expressions for the calculation of altitude dependences hc (p) and h(e) (p) are suggested.

An ejector system is to be designed in order to pump out the gasses from low pressure to ambient conditions. Ejectors mainly use the principles of fluid dynamics for pumping. They do not consist of any mechanical parts and hence no wear and tear. But consequently the design of the ejectors should be very much precise for the proper and reliable function. In this part of the work, the configuration of a nozzle is calculated from a predefined rocket air ejector configuration. Models are developed and analyzed using numerical simulation software's. Taking the predefined input and boundary conditions, pressure, temperature, Mach number and velocity contours are developed for the analysis to identify the convergence for a flow through nozzle for cold and hot air. Further, Parametric analysis is also carried out by plotting various graphs to understand the corresponding effect.

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I report here a theoretical study of the dependence on ambient pressure of heat and mass (water vapour) rate transfer processes between the human body and its gaseous surroundings, for monocomponent gases (N2, O2, He) and/or diatomic gas mixtures (He-O2, N2-O2). Heat and water vapour rate transport are described by the following rate transfer parameters: the convective heat transfer coefficient (hc), the evaporative heat transfer coefficient (he) and the Lewis relationship (LR). It is shown that the thermal stability of the human body under hyperbaric conditions is proportional to the evaporative resistance. It is also shown that in a He atmosphere the change in the thermal state caused by a heat load of 1 W x m(-2) at sea level is equivalent to the effect of a heat flow of 0.186 W x m(-2) at 30 atmospheres absolute. This indicates that the thermal state of the body is more prone to instability at increasing ambient pressures.