Heat loss constants

The above Eq. 6.4 has two heat loss constants that can be converted into single heat loss constant by using the thermal mass relationship between the copper and composite. For a body of uniform composition, thermal mass, C , can be approximated by Cfh = m Cp, where m is the mass of the body and Cp is the isobaric specific heat capacity of the material averaged over temperature range in question. Thus, the equivalent thermal mass for a copper plate to aerogel composite for a constant cross-sectional area (Axz) will be as follows ... 

U18P3 (Calculated transient response fiM various reactivity stqis and heat loss constants (R) m U-235 systems 5k(t) = 6ko - B, Jo E(f le" dt ... 

The conveyor and collector parts are thoroughly insulated to reduce heat losses in diying and other heating operations. Operating control is maintained usually by control of the exit-gas temperature, with the inlet-gas temperature varied to compensate for changing feed conditions. A constant solids feed rate must be maintained. 

To determine the exact Si02 content of the residue, moisten it with 1 mL water, add two or three drops of concentrated sulphuric acid and about 5 mL of the purest available hydrofluoric acid. (CARE ) Place the crucible in an air bath (Section 3.21) and evaporate the hydrofluoric acid in a fume cupboard (hood) with a small flame until the acid is completely expelled the liquid should not be boiled. (The crucible may also be directly heated with a small non-luminous flame.) Then increase the heat to volatilise the sulphuric acid, and finally heat with a Meker-type burner for 15 minutes. Allow to cool in a desiccator and weigh. Re-heat to constant weight. The loss in weight represents the weight of the silica (Note 2). 

A stirred reactor contains a batch of 700 kg reactants of specific heat 3.8 kJ/kg K initially at 290 K, which is heated by dry saturated steam at 170 kN/m2 fed to a helical coil. During the heating period the steam supply rate is constant at 0.1 kg/s and condensate leaves at the temperature of the steam. If heat losses arc neglected, calculate the true temperature of the reactants when a thermometer immersed in the material reads 360 K. The bulb of the thermometer is approximately cylindrical and is 100 mm long by 10 mm diameter with a water equivalent of 15 g, and the overall heat transfer coefficient to the thermometer is 300 W/m2 K. What would a thermometer with a similar bulb of half the length and half the heat capacity indicate under these conditions ... 

A longitudinal tin on the outside of a circular pipe is 75 mm deep and 3 mm thick. If tire pipe surface is at 400 K. calculate the heat dissipated per metre length from the fin to the atmosphere at 290 K if the coefficient of heat transfer from its surface may be assumed constant at 5 W/m2 K, The thermal conductivity of the material of the fin is 50 W/m K and the heat loss from the extreme edge of the fin may be neglected. It should be assumed that the temperature is uniformly 400 K at the base of the fin. 

Liquid is heated in a vessel by means of steam which is supplied to an internal coil in the vessel. When the vessel contains 1000 kg of liquid it takes half an hour to heat the contents from 293 to 368 K if the coil is supplied with steam at 373 K. The process is modified so that liquid at 293 K is continuously fed to the vessel at the rate of 0.28 kg/s. The total contents of the vessel are always being maintained at 1000 kg. What is the equilibrium temperature which the contents of the vessel will reach, if heat losses to the surroundings are neglected and the overall heat transfer coefficient remains constant ... 

Unlike at adiabatic conditions, the height of the liquid level in a heated capillary tube depends not only on cr, r, pl and 6, but also on the viscosities and thermal conductivities of the two phases, the wall heat flux and the heat loss at the inlet. The latter affects the rate of liquid evaporation and hydraulic resistance of the capillary tube. The process becomes much more complicated when the flow undergoes small perturbations triggering unsteady flow of both phases. The rising velocity, pressure and temperature fluctuations are the cause for oscillations of the position of the meniscus, its shape and, accordingly, the fluctuations of the capillary pressure. Under constant wall temperature, the velocity and temperature fluctuations promote oscillations of the wall heat flux. 

The above relation is obtained if the constant a obtained from the work of Zel dovich [7] is assumed to be a = Nu.U (which was not suggested in the work of Zel dovich [7]), where k is the thermal dif-fusivity and d is the characteristic length. However, Nu/Pe is a parameter in the solution of energy equation for flames with heat losses above certain value for which no solution of the energy equation exist (see, e.g., Ref. [8], p. 108)... 

The system is ideal, with equilibrium described by a constant relative volatility, the liquid components have equal molar latent heats of evaporation and there are no heat losses or heat of mixing effects on the plates. Hence the concept of constant molar overflow (excluding dynamic effects) and the use of mole fraction compositions are allowable. 

It is assumed that there are no heat losses from the column and that there is zero heat exchange between the gas and liquid phases. Consequently the gas phase temperature will remain constant throughout the column. A liquid phase heat balance, for element of volume dV is given by... 

The temperature in the gas phase is assumed constant with no heat losses, and zero heat exchange between gas and liquid. 

A metal rod is in contact with a constant temperature source at each end. At steady state the heat conducted towards the center is balanced by the heat loss by radiation. This leads to a symmetrical temperature profile in the rod, as shown. 

The equation is the same for co-current flow, but the terminal temperature differences will be (T — fi) and (T 2 — t2). Strictly, equation 12.4 will only apply when there is no change in the specific heats, the overall heat-transfer coefficient is constant, and there are no heat losses. In design, these conditions can be assumed to be satisfied providing the temperature change in each fluid stream is not large. 

In these gages, a wire inside the gas whose pressure is to be measured, is electrically heated by a constant power (see Fig. 1.29). As the gas density decreases, the heat loss from the filament to the envelope walls decreases and hence the filament temperature increases (not linearly). The temperature (200-300°C) is read by a thermocouple in thermal contact with the wire. 

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