steam jet ejector design calculation spreadsheet

According to the Laplace equation, for a bubble in equilibrium the difference between the two pressures is determined by the equation ∆ p = p1-p = 2s/r, Where s = surface tension kg/m, r = curvature radius of bubble, m.Īfter their formation, the bubble grows rapidly and detach from the surface on attaining a certain size. The pressure inside a bubble p1 is greater than the surrounding liquid pressure p owing to surface tension. Surface tension is defined as the stress causing the free surface of the fluid to contact this stress is tangential to the surface. Essentially, this dependence is traced to the phenomenon of surface tension appearing at the liquid vapour interface. A rise in ∆t entails an increase in Z and boiling intensifies. on the temperature difference, ∆t = tw - ts. Adhesion is defined as the effort required detaching the liquid from unit area of the hard surface.įurther, experience shows that the number of starting points of bubble (Z) depends on the degree of superheat at the heating surface, i.e. The surface where the effect of adhesion is minimum may become evaporation starting points. It has been established by visual observation that vapour bubbles form only on the heated surface, where liquid superheat is maximum, and only at individual points of that surface called starting boiling. The temperature profile of liquid near heating surface is shown in following curve. The value of ∆t rises with an increase in the rate of heat transfer q (W/m2.K.).

Hence the temperature of the liquid on the heating surface is higher than the saturation temperature by ∆t=tw-ts. (feed temperature, tf is greater than ts).Įxperience shows that a sharp increase in the temperature is observed only in a layer 2-5mm thick over the heated surface.

Experience however shows that the boiling liquid is usually overheated. This temperature ts remains constant through out the process of boiling of any liquid at constant pressure. Heat transfer in boiling liquids and condensing vapour is accompanied by a change in the phase of liquid or vapour, the saturation temperature of the forming vapour (ts) is determined by the ambient pressure P. The proper calculation of heat transfer area and the water requirement will decide the energy requirement and the capacity of each system components.

While the vapour from the final effect enters in the vapour condenser where cooling water is circulated to condense the vapour and thereby maintains the vacuum. In the evaporation system, steam is used as a heating medium as well as vapour produced from the previous effect is used as a heating medium in next effect.

Steam jet ejector design calculation spreadsheet