ENERGY, WORK, AND HEAT ThermodynamicsAs with work, the amount of heat transferred depends upon the path and not simply on the initialand final conditions of the system. Also, as with work, it is important to distinguish betweenheat added to a system from its surroundings and heat removed from a system to itssurroundings. A positive value for heat indicates that heat is added to the system by itssurroundings. This is in contrast to work that is positive when energy is transferred from thesystem and negative when transferred to the system. The symbol q is sometimes used to indicatethe heat added to or removed from a system per unit mass. It equals the total heat (Q) addedor removed divided by the mass (m). The term "specific heat" is not used for q since specificheat is used for another parameter. The quantity represented by q is referred to simply as theheat transferred per unit mass.(1-16)qQmwhere:q = heat transferred per unit mass (Btu/lbm)Q = heat transferred (Btu)m = mass (lbm)Example:Determine the heat transferred per unit mass if 1500 Btu’s are transferred to 40 lbm ofwater.Solution:Using Equation 1-16qQmq1500 Btu40 lbmq37.5 Btu/lbmThe best way to quantify the definition of heat is to consider the relationship between the amountof heat added to or removed from a system and the change in the temperature of the system.Everyone is familiar with the physical phenomena that when a substance is heated, itstemperature increases, and when it is cooled, its temperature decreases. The heat added to orremoved from a substance to produce a change in its temperature is called sensible heat. Theunits of heat are often defined in terms of the changes in temperature it produces.HT-01 Page 20 Rev. 0
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