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Psychrometrics
Published in Samuel C. Sugarman, HVAC Fundamentals, 2020
Dew point temperature is the temperature at which moisture will start to condense from the air. The scale (shown from 0F to 85F) for dew point temperatures is along the right side of the chart (#7, Figure 3-1). The dew point temperature lines run horizontally, at right angles to the dry bulb temperature lines (#4 in Figure 3-1); in fact, they are the same lines as the specific humidity (also known as humidity ratio) lines (#6, Figure 3-1). For some charts, dew point temperature is along the curved line on the left side of the chart (#8, Figure 3-1). This curved line is the 100 percent saturation line. The dew point is where the humidity ratio line intersects the 100 percent saturation curve.
Applications in the Civil Engineering Domain
Published in Paresh Chra Deka, A Primer on Machine Learning Applications in Civil Engineering, 2019
The dew point temperature is the temperature at which the moisture in the air begins to condense into dew or water droplets. The accurate estimation of the dew point temperature is very important as it controls the heat stress on humans and detects fluctuations in evaporation rates and humidity trends. The dew point temperature is a significant parameter required in various hydrological, climatological, and agronomical related research. This study proposes SVM and ELM models for the estimation of daily dew point temperature. The daily measured weather data (wet-bulb temperature, relative humidity, vapor pressure, and dew point temperature) of humid and semi-arid regions of India were used for model development. The statistical indices, namely mean absolute error (MAE), root mean square error (RMSE), Nash–Sutcliffe efficiency (NSE) were adopted to evaluate the performances of these two models. The merit of the extreme learning machine (ELM) model is evaluated against support vector machine (SVM) technique in the estimation of dew point temperature. The proposed ELM models demonstrated much greater capability than the SVM models in the estimation of daily dew point temperature.
(i) Precipitation
Published in Richard J. Chorley, Introduction to Physical Hydrology, 2019
Important contributions to the total precipitation are sometimes made by dew and fog. Dew forms on the ground and vegetation surfaces as a result of deposition from the atmosphere when the air is cooled to its dew-point temperature by contact with the radiatively cooling surface. However, in very still air most of the dew originates from vapour derived by evaporation from the soil. The rate of deposition is limited by the rate of removal of latent heat of condensation from the surface. Average dew deposition measured on lysimeters at Coshocton, Ohio, during the snow-free period 1944–55 was between 0.38 and 0.75 mm (0.015 and 0.030 in.) per day.
Numerical simulations of frost growth using mixture model on surfaces with different wettability
Published in Numerical Heat Transfer, Part A: Applications, 2023
Shantanu Shahane, Yuchen Shen, Sophie Wang
Frost, as a composition of ice crystal and air in a porous structure, has variable thermal properties (density, thermal conductivity, etc.) depending on the conditions it subjects to and the history it goes through [1, 2]. When the surrounding air temperature is below the dew point and the surface temperature is subzero, water vapor in the air first condenses on the cold surfaces and then becomes solidified, which is called condensation-frosting. Under extremely low air temperatures, desublimation frosting can occur. As frost grows, the local temperature of frost, humidity of the trapped air varies, and ultimately affects the following frost growth. So frosting is a highly transient coupled heat-mass transfer process, and multiple factors including surface temperature, wettability, roughness [3–10], air temperature, humidity, and velocity [11–14] can affect the process.
Experimental and Artificial Neural Network Evaluation of Frost Formation on Square Finned Tube under Natural Convection
Published in Heat Transfer Engineering, 2023
Soroush Abadi Iranagh, Ali Reza Tahavvor, Mahmood Yaghoubi, Mohammad Mehdi Tavakol
Fins are utilized for various purposes such as air conditioning operations, heating systems, refrigeration, finned-heat exchangers, ventilation, solar processes, electric cooling, electrical systems, etc. The frost layer forming on the tubes and fins causes heat and performance loss by impacting variables such as air properties, wall temperature, and air humidity. Frost forms when the surface temperature is lower than the freezing point of water and the dew point of the air. This exchanging phenomenon limits the airflow area by obstructing the flow channel, raising thermal resistance, and subsequently lowering the heat transfer rate of the system. Fins are widely used in various heating, ventilation, and air conditioning applications due to their geometrical properties such as evaporators in cooling systems, oil coolers, refrigerators, and heat exchangers. Also, fins are available in a wide range of shapes. The square-finned tube is specially used in incinerating devices, economizing systems, and air conditioners.
Drying and Atterberg limits of Cochin marine clay
Published in International Journal of Geotechnical Engineering, 2020
Amal Azad Sahib, Retnamony G. Robinson
To verify the role of shrinkage stresses upon drying, suction values were measured in Cochin marine clay specimens using Dew point Potentiameter (WP4) that employs the chilled mirror hygrometer. The device is used as a rapid means of determining the total suction of unsaturated soils (Leong, Tripathy, and Rahardjo 2003; Vikas and Singh 2005). The specimens were filled in slurry state (about 1.5 times liquid limit) in a mould of 35 mm diameter and 7 mm height. The soil sample was placed in a sealed chamber containing a mirror with a detector of condensation. The dew-point is the temperature to which the air must be cooled so that the water vapour in the air condenses to liquid water. At the dew-point, the water vapour present in the air is just sufficient to saturate it. When equilibrium prevails, the relative humidity of the air in the chamber is equal to the relative humidity of the soil sample. Relative humidity is calculated as the ratio of the saturated vapour pressure of water at the dew-point to the saturated vapour pressure of water at the air temperature. This ratio can be substituted in the following thermodynamic equation to calculate the total suction pressure.