Thermal design

Basic Thermal Design Methods for Heat Exchangers... 

Effect of Uncertainties in Thermal Design Parameters. The parameters that are used ia the basic siting calculations of a heat exchanger iaclude heat-transfer coefficients tube dimensions, eg, tube diameter and wall thickness and physical properties, eg, thermal conductivity, density, viscosity, and specific heat. Nominal or mean values of these parameters are used ia the basic siting calculations. In reaUty, there are uncertainties ia these nominal values. For example, heat-transfer correlations from which one computes convective heat-transfer coefficients have data spreads around the mean values. Because heat-transfer tubes caimot be produced ia precise dimensions, tube wall thickness varies over a range of the mean value. In addition, the thermal conductivity of tube wall material cannot be measured exactiy, a dding to the uncertainty ia the design and performance calculations. 

Entrance andExit SpanXireas. The thermal design methods presented assume that the temperature of the sheUside fluid at the entrance end of aU tubes is uniform and the same as the inlet temperature, except for cross-flow heat exchangers. This phenomenon results from the one-dimensional analysis method used in the development of the design equations. In reaUty, the temperature of the sheUside fluid away from the bundle entrance is different from the inlet temperature because heat transfer takes place between the sheUside and tubeside fluids, as the sheUside fluid flows over the tubes to reach the region away from the bundle entrance in the entrance span of the tube bundle. A similar effect takes place in the exit span of the tube bundle (12). 

The thermal design of cooling towers follows the same general procedures already presented. Integration of equation 35 is usually done numerically using the appropriate software, mass-transfer coefficients, saturation enthalpies, etc. In mechanical-draft towers the air and water dows are both suppHed by machines, and hence dow rates are fixed. Under these conditions the design procedure is straightforward. 

Fig. 3. Solar thermal designs (a) parabohc trough (b) central receiver and (c) parabohc dish.

Kenneth J. Bell/ Ph.D./ P.E./ Regents Professor Emeritus, School of Chemical Engineering, Oklahoma State University Member American Institute of Chemical Engineers. (Thermal Design of Heat Exchangers, Conden.ser Reboilers)... 

F. C. Standiford/ M.S./ P.E./ Member American In stitute of Chemical Engineers, American Chemical Society. (Thermal Design of Evaporators, Evapor ators)... 

Thermal Design for Single-Phase Heat Transfer. 11-5... 

THERMAL DESIGN FOR SINGLE-PHASE HEAT TRANSFER... 

Thermal Design If the controUing resistance for heat and mass transfer in the vapor is sensible-heat removal from the cooling vapor, the following design equation is obtained ... 

This method may also be used for the thermal design of horizontal thermosiphon rehoilers. The recirculation rate and pressure profile of the thermosiphon loop can be calculated by the methods of Fair [Pet Refiner, 39(2), I05-I23 (I960)]. 

The thermal design of tank coils involves the determination of the area of heat-transfer surface required to maintain the contents of the tank at a constant temperature or to raise or lower the temperature of the contents by a specified magnitude over a fixed time. 

Thermal design concerns itself with sizing the equipment to effect the heat transfer necessaiy to cany on the process. The design equation is the familiar one basic to all modes of heat transfer, namely,... 

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