tailieunhanh - ENERGY MANAGEMENT HANDBOOKS phần 10

Trong điều kiện vật lý, đó là nhiệt độ hỗn hợp hơi nước bắt đầu ngưng tụ làm lạnh ở áp suất không đổi. Nếu độ ẩm tương đối là 100% điểm sương và bóng khô nhiệt độ giống hệt nhau. Trong không khí không khí có độ ẩm tương đối ít hơn 100%, hơi nước tồn tại ở áp suất thấp hơn áp suất bão hòa. Do đó, nếu không được đặt tiếp xúc với nước ở dạng lỏng, một số nước sẽ được. | Thermal Sciences Review 823 Fig. Behavior of water in air ộ P1 P3 T2 dew point. A convenient way of describing the condition of atmospheric air is to define four temperatures dry-bulb wet-bulb dew-point and adiabatic saturation temperatures. The dry-bulb temperature is simply that temperature which would be measured by any of several types of ordinary thermometers placed in atmospheric air. The dew-point temperature point 2 on Figure is the saturation temperature of the water vapor at its existing partial pressure. in physical terms it is the mixture temperature where water vapor would begin to condense if cooled at constant pressure. if the relative humidity is 100 the dew-point and dry-bulb temperatures are identical. in atmospheric air with relative humidity less than 100 the water vapor exists at a pressure lower than saturation pressure. Therefore if the air is placed in contact with liquid water some of the water would be evaporated into the mixture and the vapor pressure would be increased. if this evaporation were done in an insulated container the air temperature would decrease since part of the energy to vaporize the water must come from the sensible energy in the air. if the air is brought to the saturated condition it is at the adiabatic saturation temperature. A psychrometric chart is a plot of the properties of atmospheric air at a fixed total pressure usually psia. The chart can be used to quickly determine the properties of atmospheric air in terms of two independent properties for example dry-bulb temperature and relative humidity. Also certain types of processes can be described on the chart. Appendix ii contains a psychrometric chart for atmospheric air. Psychrometric charts can also be constructed for pressures other than psia. HEAT TRANSFER Heat transfer is the branch of engineering science that deals with the prediction of energy transport caused by temperature differences. Generally the field is broken down .