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ADVANCED THERMODYNAMICS ENGINEERING phần 2

Bây giờ xem xét việc chuyển giao năng lượng do nhiệt (tức là do chênh lệch nhiệt độ) thông qua các bức tường vững chắc vào một loại khí đang được rắn ở nhiệt độ cao hơn. Các phân tử trong một nhóm của các phân tử khí tác động đến trên tường nhận năng lượng ngẫu nhiên và chúng có thể được đặt ở mức năng lượng khác nhau như thể hiện trong hình 32c. | component of the molecular velocity V that increases the te . The energy level of this group of molecules is raised as shown in Figure 32e. Thus the total number of states do not change even though the energy level for each group has increased due to work input. Now consider the energy transfer due to heat i.e. due to temperature difference through solid walls into a gas with the solid being at a higher temperature. The molecules within a group of gas molecules impinging on the wall pick up the energy randomly and these can be placed at different energy levels as shown in Figure 32c. The energy transfer through heat results in an entropy increase while energy transfer through work does not. In Chapter 3 we will see that dS ỗQrev T but not ỖWrev T or PdV T . The entropy increases as two different species are mixed. This can be illustrated through the example of two adjacent adiabatic containers of volumes V1 and V2 at the same temperature that respectively contain nitrogen and oxygen. If the partition between them is removed then N2 and O2 gases have a new set of quantum states due to extension of volume from V1 and V2 to V1 V2 . This increases the entropy of each species. Hence mixing causes an increase in entropy and consequently the system entropy. In this instance mixing causes the entropy to increase even though total energy of nitrogen and oxygen is unchanged due to mixing. 11. Properties in Mixtures - Partial Molal Property A kmole of any substance at standard conditions contains 6.023x1026 molecules known as Avogadro number. The molecular energy is in the form of vibrational rotational and translational energy and the molecules are influenced by the intermolecular potential energy ipe . At the standard state the energy of pure water u is 1892 kJ kmole the bar at the top indicates pure property on a kmole basis . If a kmole of water is mixed at the molecular level at standard conditions with 2 kmoles of ethanol each H2O molecule is now surrounded by 2 .