Energy by convection

The thermocouple is made by welding together two wires of metals 1 and 2 in such a manner that a segment of metal 1 is connected to two terminal wires of metal 2. One junction between metals 1 and 2 is heated by the infrared beam, and the other junction is kept at constant temperature small changes in ambient temperature are thus minimised. To avoid losses of energy by convection, the couples are enclosed in an evacuated vessel with a window transparent to infrared radiation. The metallic junctions are also covered with a black deposit to decrease reflection of the incident beam... 

Input of energy by convective transport in the axial direction... 

The Damkohler III is obtained by dividing the dimensions representing generation per unit volume of chemical reaction by the dimensions representing the transport of energy by convection. This is defined by... 

The term e/(e — 1), which appears in equations 1 and 2, was first developed to account for the sensible heat transferred by the diffusing vapor (1). The quantity S represents the group ratio of total transported energy to convective heat transfer. Thus it may be thought of as the fractional... 

The use of wind as a renewable energy source involves the conversion of power contained in moving air masses to rotating shaft power. These air masses represent the complex circulation of winds near the surface of Earth caused by Earth s rotation and by convective heating from the sun. The actual conversion process utilizes basic aerodynamic forces, ie, lift or drag, to produce a net positive torque on a rotating shaft, resulting in the production of mechanical power, which can then be used directly or converted to electrical power. 

Radiation differs from conduction and convection not only in mathematical structure but in its much higher sensitivity to temperature. It is of dominating importance in furnaces because of their temperature, and in ciyogenic insulation because of the vacuum existing between particles. The temperature at which it accounts for roughly half of the total heat loss from a surface in air depends on such factors as surface emissivity and the convection coefficient. For pipes in free convection, this is room temperature for fine wires of low emissivity it is above red heat. Gases at combustion-chamber temperatures lose more than 90 percent of their energy by radiation from the carbon dioxide, water vapor, and particulate matter. 

Kinetic energy generated by convective heat source ( Wj-, ) ... 

The air temperature of a room at any given time is given hy a heat-balance equation which includes the heat flux exchanged by convection at each wall element (A q ), the heat flow exchanged by ventilation (4>j,), the convective part of heat flow due to internal heat gains the convective part of heat flow due to the HVAC system (< >[,(.), and the variation of energy in the room air(r M ... 

In the simulation, the time dependency of the energy release of such sources is defined in so-called schedules. The heat sources transfer energy to the room air by convection and to the surfaces by long-wave radiation. In principle, heat sources can be modeled by two kinds of parameterization ... 

The transfer of heat from a source to a receiver by radiant energy is radiation. The sun transfers its energy to the earth by radiation. A fire in a fireplace is another example of radiation. The fire in the fireplace heats the air in the room and by convection heats up the room. At the same time, when you stand within line of sight of the fireplace, the radiant energy coming from the flame of the fire itself makes you feel warmer than when you are shielded from the line of sight of the flame. Heat is being transferred both by convection and by radiation from the fireplace... 

A mechanism of heat transfer in which heat energy is transmitted by convection current motion through gases and liquids. Part of the heat-transfer process in a boiler is by convection whereby the circulation of water carries heat from the tube near the fire to the drum and surrounding areas. 

The heat loss to the melting polymer was assumed (for a first order approximation) to be negligible compared to the heat loss by convection. This is one area of the model which could profit from more study to determine the exact magnitude of energy exchange with the polymer. 

The transfer of heat by radiation in general can be said to occur simultaneously with heat transfer by convection and conduction. Transfer by radiation tends to become more important than that by the other two mechanisms as the temperature increases. It is useful to gain an appreciation of the basic definitions of the energy flux terms, the surface property terms and their relationships while discussing radiative heat transfer. With this objective, reference may be made to Table 3.4 in which these are presented. 

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