Page 383 - Introduction to Marine Engineering

Appendix 353

Readings of pressure are considered to be absolute unless followed by
the word 'gauge' indicating a pressure gauge value. The actual value of
atmospheric pressure is usually read from a barometer in millimetres of
mercury:
atmospheric pressure = mm of mercury X 13.6 x 9.81 Pa

A standard value of 1 atmosphere is often used where the actual value
is unknown,
1 atmosphere = 10 1300 Pa
= 1.013 bar

Volume
The amount of physical space occupied by a body is called volume. The
unit of volume is the cubic metre (m ). Other units are also in use, such as
3
litre (1) and cubic centimetre (cm ), i.e.
1m 3 = 10001 = 10000000cm 3

Temperature
The degree of hotness or coldness of a body related to some zero value is
known as temperature. The Celsius scale measure in °C simply relates to
the freezing and boiling points of water dividing the distance shown on a
thermometer into 100 equal divisions. An absolute scale has been
devised based on a point 273. 16 kelvin (0.0 1°C) which is the triple point
of water. At the triple point the three phases of water can exist, i.e. ice,
water and water vapour. The unit of the absolute scale is the kelvin. The
unit values in the kelvin and Celsius scales are equal and the
measurements of temperature are related, as follows:

x°C = (x°C + 273)K
= yK- 273)°C
(

Heat
Heat is energy in motion between a system and its surroundings as a
consequence of a temperature difference between them. The unit, as
with other forms of energy, is the joule (J).

The burning of fuel in an engine cylinder will result in the production of
power at the output shaft. Some of the power produced in the cylinder