Read Chapter 1 from the Text hook What is the difference bet
Read Chapter 1 from the Text hook. What is the difference between evaporation and boding? What is the difference between subcooled and saturated boiling? How does film boiling differ from nucleate boiling? What is condensation & how does it occur. What is the difference between film and dropwise condensation? A 50 cm long. 2 cm diameter brass heating element is to be used to boil water at 120 degree C. If the surface temperature of the heating element is not to exceed 125 degree C, determine the highest rate of steam production in the boiler, in kg/h. In a gas fired boiler, water is boiled at 150 degree C by Hot gases flowing through a 50 m long, S cm outer diameter mechanically polished stainless steel pipes submerged in water. If the outer surface temperature of the pipes is 165 degree C, determine (a) the rate of heat transfer from the hot gases to water, (b) the rate of evaporation, (c) the ratio of critical heat flux to the present heat flux, and (d) the surface temperature of the pipe at which critical heat flux occurs. Saturated steam at 1 atm condenses on a 3m high and 4 m wide vertical plate that is maintained at 90 degree C by circulating cooling water through the other side. Determine (a) the rate of heat transfer by condensation to the plate and (b) the rate at which condensate drips off the plate at the bottom. Saturated steam at 270.1 kPa condenses inside a horizontal, 4m long, 3cm internal diameter pipe whose surface is maintained at 110 degree C. Assuming low vapor velocity, determine the average heat transfer coefficient and the rate of condensation of the steam inside the pipe.
Solution
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| Evaporation | Boiling |
| It is a process in which a substance changes its state from liquid to vapour while increasing temperature | It is a process in which a substance changes its state from liquid to vapour at constant temperature |
| It occurs only on the surface of the liquid | It occurs throughout the liquid. |
| It is a slow process | It is a fast process |
| It can occur in wide range of temperatures | it will occur at a definite temperature |
| It takes the heat of vapourisation from surrounding atmosphere. | A heat source is needed to supply the energy. |
