Rate of heat absorption

We obtain from (11.9-11.11) the equations for small perturbations of velocity, pressure, temperature and enthalpy, as well as the specific volumetric rate of heat absorption. Assuming that hi = Cp. 7) we arrive at... 

The amount of charring or decomposition is often related to the maximum rate of heat absorption, which is given below as a factor of the average rate of heat absorption.58... 

What would be the corresponding effect of water vapor on the overall rate of heat production The rate of heat production must now be considered as the sum of the rates of heat evolution by deposition and burning plus the rate of heat absorption by distillation i.e., the overall rate of heat production must be smaller than the dry rate ... 

It is fundamental, therefore, to control the rate of heat absorption and temperature variations during the cure cycle [33,34]. The cure cycle depends on the part geometry, thermal... 

As indicated in Sec. IIB, ordinary nucleate boiling is a two-step process. First, nuclei must appear. Second, the nuclei must grow into bubbles large enough to move away from the nucleation sites. The rate of heat absorption by the liquid may be controlled by either one or both of these two processes. The growth of a nucleus (tiny bubble) into ordinary bubbles has received attention recently. The theoretical attack of Forster and Zuber was discussed in Sec. IIB2. Inasmuch as the theory of Zwick and Plesset (P3, P4, Zl, Z2) represents another attempt to obtain exact expressions for bubble growth, and since the theory fits well with the few data for steam bubbles in superheated water, their theoretical method is summarized below. 

Sometimes, deposits accumulate on the exterior of tubes. These deposits are unavoidable when heavy industrial fuel oil is fired.Such fuel oils contain high concentrations of vanadium, nickel, sodium, and iron (in that order of concentration). These metals deposit as an ash, on the exterior of both the radiant- and convective-section tubes. The ash will get very hot and will turn sections of tubes yellow, or even whitish silver. This is not an indication of tube overheating. If the deposits get thick enough, they will interfere with the rate of heat absorption by the tube. It is very difficult to distinguish between a real hot spot and glowing ash. Dirty fuel gas also leads to ash formation on the radiant surface of tubes. 

In a solar pond, the absorption of solar energy can be modeled as heat generation and can be approximated by = where cq is the rate of heat absorption at the top surface pec unit votume and I) is a constant. Obtain a relation for the total tateof heat generation in a water layer of surface area 4 and thickness L at tlie top of the pond. 

To design the evaporator, compressor, condenser,and auxiliary equipment one must know tire rate of circulation of refrigerant/w. This is determined from the rate of heat absorption in tire evaporator by the equation ... 

The process is limited by the rate of heat supply to the reactor rather than the rate of heat absorption by the pyrolysing biomass as in other reactors. 

A typical DSC plot of the rate of heat absorption versus temperature Is shown for poly(llmonene oxide) In Figure 6. An endothermic transition corresponding to an enthalpy change of 0.3 cal g was observed between 65.2 and 84.5 C, the peak being at 74.2 C. A similar plot was obtained for poly(a-plnene oxide), the peak occurring at 81.3 C with a AH of 0.13 cal g measured between 78.3 and 84.3°C. Ruckel et al. (14) have reported very similar softening ranges of 67-80 and 65-80 C for the catalytlcally-prepared poly(o-plnene oxide) and poly(B plnene oxide). 

Speil et al. (12) first pointed out that the actual peak temperature is the point at which the differential heat input equals the rate of heat absorption and therefore... 

Table 1-2. Effect of Tube Spacing on Average Rate of Heat Absorption Per Square Foot of Circumferential Area ...

Take as a basis one square foot of radiant absorbing surface in the heater. This should be a square foot of the equivalent plane surface. The rate of heat absorption on this surface will be the same as that on the most exposed element of the... 

RHA = rate of heat absorption = heat flux rate received by a furnace load, usually in Btu/ft hr. 

Bloom, F.S. Rate of heat Absorption of Steel, Iron and Steel Engineer, 1955. 

Improvements have been made to gain more efficiency and more capacity. Efforts have heen made to increase the rate of heat absorption by increased circulation of water in the tubes. However, such designs have added to some deposition and corrosion problems. 

Hot Tubes. The rate of heat absorption tends to be high at the entrance to the convection section because heat is delivered by both radiation and convection [black tubes in types (o), (c), (d), (e), and 0 )]. The feed, because it is cooler, is sometimes introduced through these tubes (a screen bank), and in some instances steam is superheated or water is heated in the screen bank. Likewise, the tubes situated closest to the flame receive the largest amount of heat [black tubes in (d), (/), (p), (A), and (i)l. 

Control of Rates. Stills (z) and (k) fure eminently suitable for precise control of the rate of heat input and for operation at exceedingly high (1000 to 1500 F) temperatures. Very low rates of heat absorption can be attained in the circular types (/), (g), and (A), mid in other types if enough radiant surface is provided. 

The advantages of a symmetrical arrangement of radiant-heat-absorbing surface are apparent in the stills of Fig. 18-1. The ideal still will be one in which the rate of heat absorption is the maximum (at all points) that can be transferred to the oil without causing coking, discoloration, or decomposition. If two coils are to be heated and properly controlled in a... 

In terms of 9, defined as the rate of heat absorption per squmre foot of projected tube area,... 

The rate of radiant absorption varies at different parts of the radiant section. In ordinary stills the exact distribution of radiation is not important but for (1) heating sensitive stocks such as treated lubricating oils, (2) heating to very high temperatures as in cracking stills, and (3) heating two different stocks in separate coils in the same radiant section, the rate of heat absorption in the different parts of the furnace box becomes very important. Data on several stills have been reported that indicate radian tion rates that varied by 400 per cent in different parts of the radiant section. Combustion space is not of direct importance in pipestills. 

The rate of heat absorption in the convection section can be approached with more assurance than for the radiant section. The only troublesome points are (1) the combination of radiation and convection heating that occurs through the first rows of the convection section and (2) the radiar-tion from the hot gas and the walls of the convection section. The first difficulty is often handled by counting these tubes twice i.e., the first two rows are counted as radiant tubes, and they are also counted as convection tubes. The second difficulty is discussed later. 

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