Marcet Boiler

TITLE

Marcet Boiler

OBJECTIVE

The purposes of this experiment are:

1. To study the relationship between the pressure and the temperature of saturated steam in equilibrium with water.
2. To obtain the saturated pressure curve.

INTRODUCTION

This experiment was conducted to determine the relationship between the pressure and the temperature of saturated steam in equilibrium with water and to obtain the saturated pressure curve. Even if it took a long time to measure the temperature, the Marcet Boiler experiment was a very simple experiment. The temperature was measured until the pressure indicated 10 bar (maximum).

[pic 1]

Figure 1: Unit construction for Marcet Boiler (Model: HE169)

Table 1: Part Identifications List

        Steam is the gas formed when water passes from the liquid to the gaseous state. At the molecular level, this is when H2O molecules manage to break free from the bonds (i.e. hydrogen bonds) keeping them together (“What is Steam?”). If water is heated over the its boiling point, it vaporizes into steam, or water in the gaseous state. But, not all steam is the same. The properties of steam may vary significantly depending on the pressure and temperature to which it is subject. Saturated steam has many assets that make it a brilliant heat source, particularly at temperatures of 100 °C (373.2K) and higher.

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Figure 2: Pressure-temperature relationship of water and steam

Table 2: Advantages of using saturated steam for heating

        Saturated steam cannot be treated as ideal gas. Ideal gas is a gas in which the molecules have no interaction and they occupy negligible space while saturated steam is obtained when the boiling point of water is reached and then water start vaporizing.

Theory:

In this experiment, the Ideal Gas Law equation was used. The concept of an ideal gas as an indicator that helps us model and predict the behavior of real gases since it was hard to exactly describe real gas. The pressure P, volume V, and temperature T of an ideal gas are related by a simple formula called the ideal gas law. The molecules in the water that is increasing will enable the molecules to escape from the surface until it is in equilibrium (boiling point) when the energy is increased in the water. The state of equilibrium is depending on the pressure in the surface of the water. It will be easier for the molecules to leave the water with less energy when the pressure is low.

The Ideal Gas Law equation can be expressed as below:

PV = nRT

where,

P is the pressure in Pa (Pascal) or N m-2,        

V is the volume in m3,

n is the number of mole in mol,

R is the gas constant, R = 8.31441 J K-1 mol-1,

T is the temperature in K.

Table 3: Values for the gas constant R

Note: 0 °C and 1 atm pressure are referred to as the standard temperature and pressure (STP).

If the volume of the gas in constant, The Clausius-Clapeyron equation takes the form:

[pic 3]

where,

hg is the enthalpy of saturated vapor,

hf is the enthalpy saturated liquid,

hfg is the enthalpy of vaporization,

vg is the specific volume of saturated vapor,

vf is the specific volume of saturated liquid.

During the phase transition of pure substance, the process is isobaric and its temperature remains constant. This state indicates that under the equilibrium of phase changing (two coexisting phases), pressure and temperature are dependent properties.

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Figure 3: Phase transition in a p-T phase diagram

For saturated gas,

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Since vg ≥ vf, the Clausius-Clapeyron equation can be written as

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MATERIAL AND METHODS

Materials and Apparatus:

1. Distilled water / Water supply
2. Marcet Boiler (Model: HE169)

Methods:

Part 1: Start-up Procedure[pic 7]

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Part 2: Measurement

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DATA COLLECTION

Table 4: Tabulated Data of Experiment