Flat heaters

Large horizontal flat heater 0,149 Width or diameter... 

In the horizontal-tube box heater with side-mounted convection tube bank, the radiant-section tubes run horizontally along the walls and the flat roof of the box-shaped heater, but the convection section is placed in a box of its own beside the radiant sec tion. Firing is horizontal from the end walls. The design of this heater results in a relatively expensive unit justified mainly by its abihty to burn low-grade high-ash fuel oil. Duties are 53 to 210 GJ/h (50 to 200 10 Btu/h). 

A flat-bottomed cylindrical vessel, 2 m in diameter, containing boiling water at 373 K, is mounted on a cylindrical section of insulating material, l m deep and 2 m ID at the base of which is a radiant heater, also 2 m in diameter, with a surface temperature of 1500 K. If the vessel base and the heater surfaces may be regarded as black bodies and conduction though the insulation is negligible, what is the rate of radiant heat transfer to the vessel How would this be affected if the insulation were removed so that the system was open to the surroundings at 290 K ... 

Adiabatic Reactors. Like isothermal reactors, adiabatic reactors with a flat velocity profile will have no radial gradients in temperature or composition. There are axial gradients, and the axial dispersion model, including its extension to temperature in Section 9.4, can account for axial mixing. As a practical matter, it is difficult to build a small adiabatic reactor. Wall temperatures must be controlled to simulate the adiabatic temperature profile in the reactor, and guard heaters may be needed at the inlet and outlet to avoid losses by radiation. Even so, it is hkely that uncertainties in the temperature profile will mask the relatively small effects of axial dispersion. 

Figure 2.18 Vapor jet configuration f or boiling on a horizontal flat-plate heater, as postulated by Zuber (1959). Adapted from Leinhard and Dhir, 1973. Reprinted with permission of U.S. Department of Energy.)...

Effect of geometric factors As shown in Section 2.4.3.1, Lienhard and Dhir (1973b) expressed the minimum dimension, L, of a horizontal flat-plate heater in terms of the dimensionless ratio L/ d. For ordinary liquids they found that the CHF is constant as long as L/ d > 3 (Eq. 2-128a). Otherwise, the CHF depends on the actual number of vapor jets (Lienhard and Dhir, 1973b),... 

Kirby, G. J., R. Staniforth, and J. H. Kinneir, 1965, A Visual Study of Forced Convection Boiling Part I, Results fora Flat Vertical Heater, UK Rep. AEEW-R-281, UK AEEW, Winfrith, England. (5) Kirillov, P. L., 1968, A Generalized Functional Relationship between the CHF and Pressure in the Boiling of Metals in Large Quantities, Transl. Atomic Energy 24 143. (2)... 

Overcast morning, bite of cold. Her knee ached, her back ached. She worried about Shifty, wondered where she was, took out her phone to ring her as she neared home. No reception. She should have known this would happen, the bill hadn t been paid and her phone was now cut off. She went into the hock shop on the corner and sold the handset. Further down the street a block from her flat she found a small bar heater, took it home and plugged it in. It worked. 

Hot Plates. These devices have a metal (cast aluminum, stainless steel, or some alloy), ceramic, or pyroceramic top. Underneath the top is an electric resistance heater. Hot plates are used for heating flat-bottom containers such as beakers and Erlenmeyer flasks. Because hot plate tops are non-porous, there are fewer concerns for spills affecting the heating elements as there are with heating mantles. Magnetic stirring devices are commonly included with hot plates. 

Air at 5°C and 70 kPa flows over a flat plate at 6 m/s. A heater strip 2.5 cm long is placed on the plate at a distance of 5 cm from the leading edge. Calculate the heat lost from the strip per unit depth of plate for a heater surface temperature of 65°C. Use the appropriate integral equation result... 

Figure 3.18b shows the same streams plotted with a lower value of AT in- The amount of heat exchanged is increased and the utility requirements have been reduced. The temperature driving force for heat transfer has also been reduced, so the heat exchanger has both a larger duty and a smaller log-mean temperature difference. This leads to an increase in the heat transfer area required and in the capital cost of the exchanger. The capital cost increase is partially offset by capital cost savings in the heater and cooler, which both become smaller, as well as by savings in the costs of hot and cold utilities. In general, there will be an optimum value of ATmin, as illustrated in Figure 3.19. This optimum is usually rather flat over the range 10°C to 30°C.

Layers often require heating after applying the reagent in order to complete the reaction upon which detection is based and ensure optimum color development. Typical conditions are 10-15 min at 105-110°C. If a laboratory oven is used, the plate should be supported on a solid metal tray to help ensure uniform heat distribution. A plate heater (Fig. 2), which contains a 20 X 20-cm flat, evenly heated surface, a grid to facilitate proper positioning of TLC and high-performance TLC plates, programmable temperature between 25°C and... 

Each heating zone is 20 cm in height, and the power to each zone is controlled by a silicon-controlled rectifier circuit. An additional flat plate heater is located at the bottom of the vessel. Furnace and reactor temperatures are recorded on a 12-point Barber-Colman chart recorder. 

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