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The vapor compression refrigeration cycle is a common method for transferring heat from a low temperature to a high temperature. The above figure shows the objectives of refrigerators and heat pumps. The purpose of a refrigerator is the removal of heat, called the cooling load, from a low-temperature medium. The purpose of a heat pump is the trans...

20 trang | Chia sẻ: nguyenlinh90 | Ngày: 25/07/2019 | Lượt xem: 715 | Lượt tải: 0

We consider power cycles where the working fluid undergoes a phase change. The best example of this cycle is the steam power cycle where water (steam) is the working fluid. Carnot Vapor Cycle

41 trang | Chia sẻ: nguyenlinh90 | Ngày: 25/07/2019 | Lượt xem: 749 | Lượt tải: 0

Our study of gas power cycles will involve the study of those heat engines in which the working fluid remains in the gaseous state throughout the cycle. We often study the ideal cycle in which internal irreversibilities and complexities (the actual intake of air and fuel, the actual combustion process, and the exhaust of products of combustion amon...

71 trang | Chia sẻ: nguyenlinh90 | Ngày: 25/07/2019 | Lượt xem: 954 | Lượt tải: 0

The energy content of the universe is constant, just as its mass content is. Yet at times of crisis we are bombarded with speeches and articles on how to “conserve” energy. As engineers, we know that energy is already conserved. What is not conserved is exergy, which is the useful work potential of the energy. Once the exergy is wasted, it can neve...

29 trang | Chia sẻ: nguyenlinh90 | Ngày: 25/07/2019 | Lượt xem: 719 | Lượt tải: 0

Entropy and the Clausius Inequality The second law of thermodynamics leads to the definition of a new property called entropy, a quantitative measure of microscopic disorder for a system. Entropy is a measure of energy that is no longer available to perform useful work within the current environment. To obtain the working definition of entropy an...

52 trang | Chia sẻ: nguyenlinh90 | Ngày: 25/07/2019 | Lượt xem: 920 | Lượt tải: 0

The second law of thermodynamics states that processes occur in a certain direction, not in just any direction. Physical processes in nature can proceed toward equilibrium spontaneously: Water flows down a waterfall. Gases expand from a high pressure to a low pressure. Heat flows from a high temperature to a low temperature.

34 trang | Chia sẻ: nguyenlinh90 | Ngày: 25/07/2019 | Lượt xem: 740 | Lượt tải: 0

If we neglect the changes in kinetic and potential energies as fluid flows through an adiabatic turbine having one entrance and one exit, the conservation of mass and the steady-state, steady-flow first law becomes

43 trang | Chia sẻ: nguyenlinh90 | Ngày: 25/07/2019 | Lượt xem: 907 | Lượt tải: 0

Conservation of Energy for Control volumes The conservation of mass and the conservation of energy principles for open systems or control volumes apply to systems having mass crossing the system boundary or control surface. In addition to the heat transfer and work crossing the system boundaries, mass carries energy with it as it crosses the syste...

25 trang | Chia sẻ: nguyenlinh90 | Ngày: 25/07/2019 | Lượt xem: 857 | Lượt tải: 0

The first law of thermodynamics is an expression of the conservation of energy principle. Energy can cross the boundaries of a closed system in the form of heat or work. Energy transfer across a system boundary due solely to the temperature difference between a system and its surroundings is called heat. Work energy can be thought of as the energ...

67 trang | Chia sẻ: nguyenlinh90 | Ngày: 25/07/2019 | Lượt xem: 727 | Lượt tải: 0

We now turn our attention to the concept of pure substances and the presentation of their data. Simple System A simple system is one in which the effects of motion, viscosity, fluid shear, capillarity, anisotropic stress, and external force fields are absent. Homogeneous Substance A substance that has uniform thermodynamic properties throughout...

61 trang | Chia sẻ: nguyenlinh90 | Ngày: 25/07/2019 | Lượt xem: 746 | Lượt tải: 0