Calculation of Steam Consumption and Vaporization Capacity using OPEN PAN EVAPORATOR

How to calculate the true cost of steam

Open Pan Evaporator:

AIM: Evaluation of Heat transfer coefficient and vaporization efficiency in an open pan evaporator

OBJECTIVES: To calculate the vaporization efficiency of an open pan evaporator and to calculate the heat transfer coefficient.

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Evaporation is a unit operation wherein the solution is concentrated by removal of solvent, namely water. It differs from drying in that the end product is a solid rather than a liquid. It differs from distillation in that the end product is concentrated solution rather than a vapor. When a liquid surface is open to atmosphere, a concentration gradient is set in between the liquid surface and atmospheric air. At the liquid surface, the partial pressure of vapor will be equal to vapor pressure of the liquid at the surface temperature; the partial pressure of the vapor away from the liquid surface is determined by water vapor present in the atmosphere. The performance of any evaporator is governed by two factors,

Capacity and Economy
1. Capacity is defined as the amount of water evaporated /hr.
2. The economy is the amount of water evaporated /kg of steam. 
Steam consumption is defined as Capacity / Economy.

Vaporization efficiency is defined as:

Heat supplied per evaporating a fixed amount of water /Theoretical amount of heat required.

Steam heated boiler, Water Cylinder, pan, and temperature indicators.

MATERIALS USED: Water / Milk can any liquid for study

OPEN PAN EVAPORATOR experimental set up
1. The diameter of the vessel is measured.
2. The steam boiler is started and pressure is developed.
3. 0. 5 litres of milk is measured and poured into the pan.
4. Steam is allowed by opening the valve and steam pressure is adjusted to (0.5 to 1. kg/cm2) and stop clock is started.
5. The evaporation is continued until 80% of the liquid is evaporated and milk gets concentrated.
6. The boiling temperature of milk is noted down.
7. Steam supply is started and the boiler is switched off.
8. The concentrated milk is collected and weighed.


Diameter of pan = …… cm
Height from center =……
Initial weight of milk = W1 Kg
Final weight of milk = W2 kg
Pressure gauge reading = , 
Surface temperature, TS = 0C 
Initial temperature of milk = Tm1 0C
Final temperature of milk = Tm2 0C
Time of evaporation = t, min
Mass of steam condensate collected, m = kg


Amount of water evaporated V = W1-W2
Rate of evaporation V1 = V/t Kg/min
The rate of heat transfer = V1*l J/min, where l = Latent heat of vaporization at atm pressure
Steam rate = m/t 
Vaporization efficiency = (V1/m) *100
Diameter of pan = d = cm
Height from center = h = cm
Heat transfer area = p * (1.2d)2/4 m2
Average milk boiling temperature = (Tm1+Tm2)/2 =Tm
U = Q/(A* Ts-Tm) W/m2Deg.C

The procedure is a sample calculation method used with prototype pan evaporator. Dimensions will vary with the model of the equipment used in the experiment in determining steam economy and efficiency of the steam evaporator. Studies on the efficiency of the evaporator for particular feed material will differ from the properties.To find out the data of that specific feed material number of consistent trail runs are done on open pan evaporator. 

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