Heat exchangers plane surfaces

In the case where fluid flows in the shell side space of a shell-and-tube-type heat exchanger, with transverse baffles, in directions that are transverse, diagonal, and partly parallel to the tubes, very approximate values of the heat transfer coefficients at the tube outside surfaces can be estimated using Equation 5.12a, if is calculated as the transverse velocity across the plane, including the shell axis [1]. 

Calculate the radiation heat exchange in 1 day between two black planes having the area of the surface of a 2-ft-diameter sphere when the planes are maintained at -320 and 70°F. What does this calculation indicate in regard to Prob. 1-5 ... 

One way of reducing radiant heat transfer betwen two particular surfaces is to use materials which are highly reflective. An alternative method is to use radiation shields between the heat-exchange surfaces. These shields do not deliver or remove any heat from the overall system they only place another resistance in the heat-flow path so that the overall heat transfer is retarded. Consider the two parallel infinite planes shown in Fig. 8-30a. We have shown that the heat exchange between these surfaces may be calculated with Eq. (8-42). Now consider the same two planes, but with a radiation shield placed between them, as in Fig. 8-306. The heat transfer will be calculated for this latter case and compared with the heat transfer without the shield. 

Two parallel black plates are separated by a distance of 50 cm and maintained at temperatures of 250 and 600°C. Between the planes is a gas mixture of 15 percent C02, 20 percent water vapor, and 65 percent N2 by volume at a total pressure of 2.5 atm. The gas temperature is 1400 K. Calculate the heat exchange with each plate per unit surface area. What would the heat transfer be if the gas were not present ... 

Here A is the heat or mass exchanging outer surface face of the particle and lc the circumference of the projection plane in the direction of the flow. For a sphere with diameter dpL=ndp / ndp = dp and for a cylinder with diameter dp and height H, if the direction of flow is perpendicular to the cylinder axis,... 

An integral procedure similar to that adopted previously for momentum boundary layers will be used here to obtain the expression for the rate of heat exchange between the fluid and the plane surface. A heat balance will be made over a control voliune (Figure 7.4) which extends beyond the limits of both the momentum and thermal boimdaiy layers. 

All channel elements had an emissivity Sj = e = 0.6, j = 1, N, while examples of the calculated factors Fk-j are presented in Fig. 8.2 for two channel wall elements and the inlet channel enclosure. The inlet and outlet planes of the enclosure had emissivities equal to those of the channel wall surfaces, jj,j = squt — — 0.6, while the inlet and outlet exchange temperatures were set equal to the inlet mixture and outlet mixing cup temperatures, respectively. This arrangement mimics the tight space in microreactor systems, wherein the entry and outlet sections cannot usually be of large enough size to allow for a black body enclosure treatment. The outer horizontal wall of the microreactor channel was treated as adiabatic (see Fig. 8.1) nevertheless, the reactor itself was non-adiabatic due to radiation heat losses, primarily from the channel wall inner surface as well as from the vertical front solid wall face towards the colder inlet enclosure. 

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