Condensers temperature profile

Figure 10-78. Typical condenser temperature profiles for 43% propane-57% n-butane mixture at 176 psi abs.—up-flow. (Used by permission Clements, L. D., and Colver, C. P. AlChE Heat Transfer Symposium, V. 131, No. 69, 1973. American Institute of Chemical Engineers. All rights reserved.)...

Rohsenow [13] showed that if the condensate temperature profile was allowed to be nonlinear to account for convection effects in the condensate film, an improved correction term, i tg = itg + 0.68c,f( Ts - TJ) results. Another correction pertains to the variation of viscosity with temperature. For the assumed linear temperature profile in the condensate, Drew [14] showed that if l/pf is linear in temperature, then the condensate viscosity should be calculated at a reference temperature equal to T, - Yt(T, - Tw). 

Today, a modern freeze-dryer relies mostly on indirect parameters to ensure repeatability in product treatment. Those indirect parameters have been clearly identified as being shelf temperature profile and pressure profile (vacuum), but, to be consistent, have to be completed with condenser temperature profile which is today an uncontrolled important parameter in sublimation cinematic. 

The condenser temperature profile is the third of the indirect, product-related, most important parameters for cycle validation. 

Using a freeze-dryer fitted with an integral HTF system drastically extends the field of validation related to the indirect parameters of a freeze-drying cycle by being able to validate on top of the usual shelf temperature profile and pressure (vacuum) profile the third main parameter of the freeze drying cycle, namely, the condenser temperature profile. ... 

Using integral HTF system technology, in steady conditions, the shelf temperature profile is usually validated within the range of 1°C, and the condenser temperature profile is usually validated within a range of 2°C resulting in almost perfect control of the sublimation rate and thus increased uniformity of the product process from batch to batch. 

A temperature profile of vapor condensing in the presence of a noncondensable gas on a tube wall, as shown in Figure 16 indicates the resistance to heat flow. Heat is transferred in two ways from the vapor to the interface. The sensible heat is removed in cooling the vapor from t to t, at the convection gas cooling rate. The latent heat is removed only after the condensable vapor has been able to diffuse through the noncondensable part to reach the tube wall. This means the latent heat transfer is governed by mass transfer laws. 

Figure 16. Temperature profile showing effect of vapor condensation on a tube wall in the presence of a noncondensable gas.

Figure 10-81. Illustration for Example 10-11. (A) Temperature profile for fluid desuperheating and condensing. (B) Baffle and tube support layout.

Figure 26.7 Temperature profile during condensation of steam...

When the vapour entering the condenser is superheated, and the condensate leaving the condenser is cooled below its boiling point (sub-cooled), the temperature profile will be as shown in Figure 12.46. 

If the degree of superheat is large, it will be necessary to divide the temperature profile into sections and determine the mean temperature difference and heat-transfer coefficient separately for each section. If the tube wall temperature is below the dew point of the vapour, liquid will condense directly from the vapour on to the tubes. In these circumstances it has been found that the heat-transfer coefficient in the superheating section is close to the value for condensation and can be taken as the same. So, where the amount of superheating is not too excessive, say less than 25 per cent of the latent heat load, and the outlet coolant temperature is well below the vapour dew point, the sensible heat load for desuperheating can be lumped with the latent heat load. The total heat-transfer area required can then be calculated using a mean temperature difference based on the saturation temperature (not the superheat temperature) and the estimated condensate film heat-transfer coefficient. 

To evaluate the true temperature difference (driving force) in a mixed vapour condenser a condensation curve (temperature vs. enthalpy diagram) must be calculated showing the change in vapour temperature versus heat transferred throughout the condenser, Figure 12.48. The temperature profile will depend on the liquid-flow pattern in the condenser. There are two limiting conditions of condensate-vapour flow ... 

An alternative method, which can also be used to estimate the pressure drop in a partial condenser, is given by Gloyer (1970). The pressure drop is calculated using an average vapour flow-rate in the shell (or tubes) estimated as a function of the ratio of the vapour flow-rate in and out of the shell (or tubes), and the temperature profile. 

From the design viewpoint, Eq. (78) could be coupled with Eq. (71) to obtain an approximation of the system performance and if the liquid temperature profile can be estimated, the same procedure can be followed with Eq. (80). However, in general the design engineer needs to use analytical expressions for the absolute rates of vaporization and condensation, so that with a knowledge of the rate terms and the other parameters, Eqs. (71) and (72) could be solved for the temperature and mass flow-rate profiles. 

Anomolous pressure-temperature profiles in a pipeline can cause unusual behavior of the water condensation profile in the line. If this happens, the methanol requirements predicted on the basis of terminal pipeline conditions could be low. 

Fig. 3.12 Temperature profile in the condensed phase of an energetic material.

The temperature in the condensed phase increases from the initial propellant temperature, Tq, to the burning surface temperature, Tj, through conductive heat feedback from the burning surface. Then, the temperature increases in the gas phase because of the exothermic reaction above the burning surface and reaches the final combustion temperature, Tg. Since the physical structure of AP composite propellants is highly heterogeneous, the temperature fluctuates from time to time and also from location to location. The temperature profile shown in Fig. 7.2 thus illustrates a time-averaged profile. This is in a clear contrast to the combustion wave... 

Fig. 7.8 shows the temperature profiles [temperature (K) versus burning time (s)] in the combustion waves of this propellant at 0.0355 MPa and at 0.0862 MPa. The temperature is seen to increase relatively smoothly in the condensed phase, but then increases with large fluctuations in the gas phase at both pressures. However, the rate of temperature increase is clearly much higher at 0.0862 MPa than at 0.0355 MPa. 

A conventional flow apparatus shown in Figure 1 was used. It consisted of gas-flow controlling devices, tubular reactor in an electric furnace, Liebig condenser, liquid trap, etc. The temperature profile along the longitudinal axis of the reactor was measured by a thermocouple. The reaction zone is defined here as the part of the reactor above 350°C. The reaction temperature means the highest temperature in the reaction zone. 

The chromatogram obtained for the extract of the cumene-deactivated parent H-mordenite is shown in Figure 9. The temperature profile-product distribution of the chromatogram is similar to that obtained by Venuto et al. (8, 4) in their studies on REX catalyst deactivation. They established the presence of condensed polynuclear aromatics in the REX adsorbate. 

Translate the heat-transfer area determined above into corresponding tube bundle dimensions. If different from those assumed in step (2), repeat steps (2) through (8) until satisfactory agreement is reached. The s-IVm method cannot be appHed to cases in which U varies along the tube length or the stream temperature profile is not smooth, ie, boiling or condensation is included. 

The usual temperature of flue gas entering the shield section is 1300-1650°F and should be 200-300°F above the process temperature at this point. The proportions of heat transferred in the radiant and convection zones can be regulated by recirculation of hot flue gases into the radiant zone, as sketched on Figure 8.19(b). Such an operation is desirable in the thermal cracking of hydrocarbons, for instance, to maintain a proper temperature profile a negative gradient may cause condensation of polymeric products that make coke on the tubes. Multiple chambers as in... 

FIGURE 1 Typical temperature profiles for several process heat exchanger applications (a) product cooler (b) feed heater with condensing stream (c) multicomponent feed heater with vaporization and superheating (d) pure-component product condenser (e) multicomponent product condenser (f) typical feed-effluent heat exchanger. 

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