There  are  a  number  of  technical  terms  used  in connection   with   steam   generation.   Some   of   these commonly used terms you should know are as follows: "Degree" is defined as a measure of heat intensity. "Temperature"   is  defined  as  a  measure  in degrees of sensible heat. The term sensible heat refers  to  heat  that  can  be  measured  with  a thermometer. "HEAT" is a form of energy measured in British thermal units (Btu). One Btu is the amount of heat required  to  raise  1  pound  of  water  1  degree Fahrenheit  at  sea  level. "Steam"  means  water  in  a  vapor  state.  DRY SATURATED STEAM is steam at the saturation temperature  corresponding  to  pressure,  and  it contains   no   water   in   suspension. WET SATURATED STEAM is steam at the saturation temperature  corresponding  to  pressure,  and  it contains  water  particles  in  suspension. The "QUALITY" of steam is expressed in terms of percent. For instance, if a quantity of wet steam consists  of  90  percent  steam  and  10  percent moisture, the quality of the   mixture is 90 percent. "SUPERHEATED  STEAM"  is  steam  at  a temperature  higher  than  the  saturation  temperature corresponding to pressure. For example, a boiler may operate at 415 psig (pounds per square inch gauge).  The  corresponding  saturation  temperature for this pressure is 483°F, and this will be the temperature of the water in the boiler and the steam in the drum. (Charts and graphs are available for computing this pressure-temperature relationship.) This steam can be passed through a superheater where the pressure remains about the same, but the temperature will be increased to some  higher  figure. Q4. Q5. Q1.  When  heat  is  applied  to  water,  what  physical change  occurs? Q2. How is a "degree" of heat defined? Q3.  As  long  as  the  pressure  in  a  boiler  is  held constant, what factor remains the same in the boiler? BOILER DESIGN REQUIREMENTS Learning   Objective:   Describe the design requirements for boilers. A boiler must meet certain requirements before it is considered satisfactory for operation. Three important requirements for a boiler are as follows: 1. The boiler must be safe to operate. 2. The boiler must be able to generate steam at the desired  rate  and  pressure. 3. The boiler must be economical to operate. NOTE Make  it  a  point  to  familiarize  yourself w i t h   t h e   b o i l e r   c o d e   a n d   o t h e r requirements  applicable  to  the  area  in which you are located. Design rules for boilers are established by the ASME (American  Society  of  Mechanical  Engineers).  These rules  are  general  guidelines  used  by  engineers  when designing  boilers.  These  rules  require  that  for  economy of operation and to generate steam at the desired rate and pressure, a boiler must have the following attributes: Adequate water and steam capacity Rapid and positive water circulation A large steam generating surface Heating surfaces that are easy to clean on both water  and  gas  sides Parts  accessible  for  inspection A  correct  amount  and  proper  arrangement  of heating  surface A  firebox  for  efficient  combustion  of  fuel What three requirements must a boiler meet before being  considered  satisfactory  for  operation? What organization has established guidelines for designing   boilers? TYPES OF BOILERS Learning  Objective: Identify  the  different  types  of boilers  and  describe  the  operation  of  each. The Utilitiesman is concerned primarily with the FIRE-TUBE type of boiler, since it is the type generally used in Seabee operations. However,  the  WATER- TUBE type of boiler may occasionally be used at some activities. The  information  in  this  chapter  primarily concerns the different designs and construction feature: of fire-tube boilers. 1-2