Constant heating rale

Drying Rates. Drying a frozen material proceeds initially at a constant rate with rapid evolution of water vapor. As Ihe sublimation interface recedes within the product, water-vapor evolution decreases. This is the start of the falling-rate period. When only bound water remains within the cellular structure of the product, the desorption period begins. During the constant-rate period, the sublimation rate can be expressed in terms of the heat of sublimation of ice and the heat-rale equation ... 

A distillation tower s reflux rate must correspond to the tower s heat input. The heat input is the sum of the feed enthalpy and the reboiler duty. For a tower run at constant reflux rale, the reboiler duty will decline as the tower feed enthalpy rises. This relationship is summarized as follows ... 

At the beginning of the batch cycle, both the reactor liquid and the jacket water are at 203°F. At this point in lime, catalyst is added to the reactor and a reaction occurs which generates heat at a constant rate of 15,300 Btu/min. At this same moment in time, makeup cooling water at 68°F is fed into the jacket at a constant 832 lb ,/min flow rale. 

An air-cooled engine generates heat at a constant rale = 8530 Btu/min. 

Consider a plane wall of thickness L whose thermal conductivity varies in a specified temperature range as k(T) = bo(l + PT ) where kg and p are two specified constants. The wall surface at x = 0 is maintained at a constant temperature of Ti, while the surface at x = Ms maintained at Tj. Assuming steady one-dimensional heat transfer, obtain a relation for the heat transfer rale ihrough the wall. 

C Consider a pipe at a constant temperature whose ra- dius is greater than the critical radius of insulation. Someone claims that the rale of heat loss from the ] pe has increased when some insulation is added to the pipe. Is this claim valid ... 

A room is lo be heated by a coal-burning stove, which is a c indrical cavity with an outer diameter of 32 cm and a height of 70 cm. The rale of heal loss from the room is estimated to be 1.5 kW when the air temperature in the room is maintained constant at 24°C. The emi.ssiviiy of the stove surface is 0.8S and the average temperature of the surrounding wall surfaces is 14°C. Delermine the surface temperature of the stove. Neglect the transfer from the bottom surface and lake Ihe beat transfer coefficient at the top surface to be Ihc same as that on the side surface. 

A spherical vessel, wilh 30.0-cra outside diameter, is used as a reactor for a slow endothcnnic reaction. The vessel is completely submerged iu a large water-filled rank, held at a constant temperature of 30°C. The outside surface temperature of the vessel is 20°C. Calculate the rale of heat transfer in steady operation for the following cases (n) the water in the tank is still, (6) the water in the tank is still (as in a part a), however, the buoyancy force caused by the difference in water density is assumed to be negligible, and (c) the water in the tank is circulated at an average velocity of 20 cni/s. 

Cold water enters a counter-flov heat exchanger at lO C at a rate of 8 kg/s, where itjs heated by a hot-water stream that enters the heat exchanger at 70 C at a rale of 2 kg/s. Assuming the specific heal of water to remain constant at Cp = 4.1SkJ/kg °C, determine the maximum heat transfer rate and the outlet... 

After an initial rapid period the rate of dissolution, expressed as moles SiO m hr", becomes constant and is characteristic of the particular kind of silica. When BDH silica was first heated to 800 C for 36 hr, the characteristic rale decreased by 50% and approached that reported by StSber (139, 144) for vitreous silica. The original BDH probably contained some internal uncondensed OH groups. 

We have, in other words, shown that if we assume latent heat to be the predominant thermal quantity in distillation and that this property comes close to being identical for fhe two components, the vapor and liquid flow can, for practical purposes, be considered constant in the rectifying section. A similar procedure applied fo the stripping section leads to the conclusion that here also the flow rales will remain practically constant although different in value from those of the enriching section because of the intervening flow of feed. 

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