# Complete Plumbing and Central Heating Guide by Jacson, Day

By Jacson, Day

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Flow work. This is the energy transferred into or out of a system by the ﬂuid ﬂowing into or out of it. Heat is a form of energy, speciﬁcally thermal energy. Heat transfer requires a temperature diﬀerence, and the higher the temperature diﬀerence, the greater the heat transfer rate. Thermal energy ﬂows only from a higher temperature level to a lower temperature unless external energy is added to force the opposite to occur. If there is no heat transfer involved in a process, it is called adiabatic.

All real processes are irreversible, because there always exist irreversibilities in the real world. 3). In an actual electrical generating plant, the actual electricity generated is always less than the reversible electricity generation rate, which is higher and which represents an ideal or maximum. The diﬀerence between the ideal and actual electricity generation rates is directly related to the irreversibility of the process. 4). Similarly, for an electrical heat pump, the actual electricity required to operate the device is always greater than the reversible electricity input rate, which is lower and represents an ideal or minimum.

30) where ΣRt = Rt,t = 1∕HA and denotes the thermal resistance, while H denotes the overall heat transfer coeﬃcient, which can be expressed as follows: H= 1 Rt,t A = 1 (1∕h1 + L1 ∕k1 + ..... , a pipe). 4 Fluid Mechanics A good grounding of ﬂuid mechanics helps in understanding geothermal energy systems, as ﬂuid ﬂow problems often arise. Facets of ﬂuid mechanics relevant to geothermal energy systems and their applications are introduced in this section to assist the reader. 1 Fluid Flow Fluid ﬂow is the movement of a ﬂuid.