Heat transfer methods

Industrial dryers may be broadly classified by heat-transfer method as being either direct or indirect heat. Dryers evolved from material handling equipment and thus most types of industrial dryers are specially suited for certain forms of material. Dryers are also classified as being batch or continuous. 

Mode of operation Generic type Feed condition Specific dryer types Jack- eted Suitable for heat-sensitive materials Suitable for vacuum service Retention or cycle time Heat transfer method Capacity Typical evaporation capacity... 

The heat transfer path through the surface area, A, can be represented as an equivalent electric circuit as shown in Figure 11.8. The thermal resistances, or their inverses, the conductances, can be computed using standard heat transfer methods. Some will be illustrated here. 

The heat release <57 is a function of pressure through the density term and qt is a less sensitive function of pressure through h, which, according to the heat transfer method by which the vessel walls are maintained at T0, can be a function of the Reynolds number. 

Probably the most important aspect of reactor design and control for a substantial number of industrial processes involves heat transfer, that is, maintaining stable and safe temperature control. Temperature is the dominant variable in many chemical reactors. By dominant variable, we mean it plays a significant role in determining the economics, quality, safety, and operability of the reactor. The various heat transfer methods for chemical reactors are discussed in a qualitative way in this chapter, while subsequent chapters deal with these issues in detail with several illustrative quantitative examples. 

There are three heat transfer mechanisms used to dry textiles. Conduction methods involve direct contact of the wet textile with heated surfaces. These are the most efficient heat transfer methods, but do not allow for control of fabric width during drying. Steam heated cylinders are examples of conduction drying methods... 

Tlie physical properties appearing in the dimensionless numbers Nu, Re, Pr, and Or all are evaluated at the bulk fluid temperature T. The values of the empirical con.slanls a, b, and c in Eq. 8-83 depend on the inlet configuration and are given in Table 8-7. The viscosity ratio accounts for the temperature effect on the process. Tlte range of application of the heat transfer method based on their database of 1290 points (441 points for re-entrant... 

The heat-transfer method using Eqs. (23.41) and (23.45) is equivalent to the mass-transfer method using Eqs. (23.42) to (23,44), The two methods give the same result. 

For heat dissipation only through the container wall, the exact solution of the design problem is complicated since there is heat release from the T rays in logarithmic attenuation identical with their absorption in the shielding material. To avoid this complication, it is conservatively assumed that all of the y power is released within the inner wall of the container and travels by conduction to the outside of the shield. The usual heat-transfer methods can then be employed. 

The external heating technique relies on heating working fluids in a microchannel with separated heating elements. This is also divided into two types by heat transfer methods contact and noncontact. 

From Equation (18-1), note that convection C can be positive or negative and add or remove heat fi om the body. Convection will remove heat (see Equation (18-2)) when the air temperature is lower than that of skin. Convection will add heat when the air temperature is greater than that of the skin. If convection adds heat, other heat transfer methods must remove heat to maintain a constant body temperature and prevent heat-related injury or illness. 

Heat transfer methods—friction, hot plate, compression, oxidation bomb... 

There are various different methods used in the determination of thermal properties of textile fabrics, including both steady state heat transfer method and nonsteady state (or transient) heat transfer methods. The typical steady state heat transfer methods include guarded hotplate method, Togmeter, and SGHP the typical... 

A detailed analysis of the steady-state heat transfer between the blood vessel wall and the mixed mean temperature of the blood can be done using standard heat transfer methods... 

This heat transfer method is mainly used to enhance the drying capacity in coaters when the web is wet Infrared heaters are usually gas fired. The gas heats a mesh to a temperature of about 900 to 1100 °C. The low thermal inertia of the mesh allows fast control of the mesh temperature and the heating rate as well as preventing fires in the case of sheet breaks. In some cases electrical heaters are in use with temperatures up to about 700 °C, exhibiting a fast cool down of the emitter plates. Infrared drying units need sufficient air flow in order to carry off the evaporated water and to prevent coat quality problems. 

The heat transfer method selected must be engineered to promote uniform temperatures within the mold-residence area to ensure that the mold heats up... 

As stated earlier, the calculation of the bulk or average surface temperature between two mating surfaces is performed by classic heat transfer methods. In fact the only unique aspect to this problem is the heat generation term Q comes from frictional heat and is assumed to occur at the interface. In order to begin a thermal analysis, we calculate the total heat ... 

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