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A mare may be in heat for 4 to 10 days, followed by approximately 14 days in diestrus. Thus, a cycle may be short, totaling approximately 3 weeks. [21] Horses mate in spring and summer; autumn is a transition time, and anestrus occurs during winter.
Two primary classes of thermodynamic cycles are power cycles and heat pump cycles. Power cycles are cycles which convert some heat input into a mechanical work output, while heat pump cycles transfer heat from low to high temperatures by using mechanical work as the input. Cycles composed entirely of quasistatic processes can operate as power ...
Q H = W + Q C = heat exchanged with the hot reservoir. η = W / (Q C + Q H) = thermal efficiency of the cycle If the cycle moves in a clockwise sense, then it is a heat engine that outputs work; if the cycle moves in a counterclockwise sense, it is a heat pump that takes in work and moves heat Q H from the cold reservoir to the hot reservoir.
Thermodynamic heat pump cycles or refrigeration cycles are the conceptual and mathematical models for heat pump, air conditioning and refrigeration systems. [1] A heat pump is a mechanical system that transmits heat from one location (the "source") at a certain temperature to another location (the "sink" or "heat sink") at a higher temperature. [2]
A reversible heat engine with a low efficiency delivers more heat (energy) to the hot reservoir for a given amount of work (energy) to this engine when it is being driven as a heat pump. All these mean that heat can transfer from cold to hot places without external work, and such a heat transfer is impossible by the second law of thermodynamics.
Importantly, for a heat engine, including the Carnot cycle, the free-energy change after a full cycle is zero, =, while the engine produces nonzero work. It is important to note that for heat engines and other thermal systems, the free energies do not offer convenient characterizations; internal energy and enthalpy are the preferred potentials ...
Novikov engine showing irreversible heat transfer between and , coupled to a Carnot cycle operating between and . [ 8 ] Consider a semi-ideal heat engine , in which heat transfer takes time, according to Fourier's law of heat conduction : Q ˙ ∝ Δ T {\displaystyle {\dot {Q}}\propto \Delta T} , but other operations happen instantly.
The estrous cycle (also spelled oestrous) controls when a mare is sexually receptive toward a stallion, and helps to physically prepare the mare for conception. It generally occurs during the spring and summer months, although some mares may be sexually receptive into the late fall, and is controlled by the photoperiod (length of the day), the ...