Heat exchangers minimum flow

As a minimum, record the following the mole fracs of the two products and the two bottom streams the heat duties of the two condensers, the two reboilers and the heat exchanger the flow rates of all the streams in the process L7D in each column N and feed locations in each column and the tenperatures... 

Nominal RHR Pumps (per pump) Minimtun flow required for shutdown cooling (gpm) Minimum flow required for low pressure makeup (gpm) Design flow (gpm) Design head (ft) Normal RHR Heat Exchangers Minimum UA required for shutdown cooling (BTU/h-°F) Design heat removal capacity (BTU/h) 1425 1100 1500 360 2.2xl(y 23xl0 Tube Side Shell Side... 

The minimum value of the Nusselt Number for which equation 9.216 applies is 3.5. Reynolds Numbers in the range 2000-10,000 should be avoided in designing heat exchangers as the flow is then unstable and coefficients cannot be predicted with any degree of accuracy. If this cannot be avoided, the lesser of the values predicted by Equations 9.214 and 9.216 should be used. 

In a countercurrent-flow heat exchanger, 1.25 kg/s of benzene (specific heat 1.9 kJ/kg K and specific gravity 0.88) is to be cooled front 350 to 300 K with water at 290 K. In the heat exchanger, tubes of 25 mm external and 22 mm internal diameter are employed and the water passes through the tubes. If the film coefficients for the water and benzene are 0.85 and 1.70 kW/nr K respectively and the scale resistance can be neglected, what total length of tube will be required if the minimum quantity of water is to be used and its temperature is not to be allowed to rise above 320 K ... 

Nozzles. minimum area of flow 1M. pressure drop, heat exchanger 528... 

While the shell-and-tube heat exchanger is the most commonly used in the process industries, it has the disadvantages that the flow is not truly countercurrent, which limits the minimum temperature difference that can be accommodated, and the area density is relatively low. Commonly used alternatives for shell-and-tube heat exchangers are ... 

In some situations it is very important to be able to increase the flow rate above the design conditions (for example, the cooling water to an exothermic reactor may have to be doubled or tripled to handle dynamic upsets). In other cases this is not as important (for example, the feed flow rate to a unit). Therefore it is logical to base the design of the control valve and the pump on having a process that can attain both the maximum and the minimum flow conditions. The design flow conditions are only used to get the pressure drop over the heat exchanger (or fixed resistance part of the process). 

Fig. 1. There is no oscillatory behavior if the system are either separately operated or uncontrolled. Indeed, trajectories converge to an equilibrium point belonging to physically realizable domain. Above Vector field of the heat exchanger under no recycle and for (a) minimum and (b) maximum flow rates. Below (c) 2-dimensional projection of the bioreactor trajectories for several initial conditions.

Heat exchanger network resilience analysis can become nonlinear and nonconvex in the cases of phase change and temperature-dependent heat capacities, varying stream split fractions, or uncertain flow rates or heat transfer coefficients. This section presents resilience tests developed by Saboo et al. (1987a,b) for (1) minimum unit HENs with piecewise constant heat capacities (but no stream splits or flow rate uncertainties), (2) minimum unit HENs with stream splits (but constant heat capacities and no flow rate uncertainties), and (3) minimum unit HENs with flow rate and temperature uncertainties (but constant heat capacities and no stream splits). 

The solution of this optimization problem provides the HEN shown in Fig. 20, where flow rates and temperatures are listed for the three operating periods. The areas of the heat exchangers are given in Table XII. Notice that there is splitting of cold stream Sc2 into two branches. Bypasses are also involved in stream Scl (match Shj—Sc]), stream Shl (match Shl-SC2), and stream Sh2 (match Sh2-Sc2). This network, which is feasible for the three operating periods that are considered, features a minimum investment cost of 196,900 and a minimum utility cost of 1.078/hour for operating period 1, 1.999/hour for period 2, and 0.9943/hour for period 3. 

These are based on the minimum temperature drop between the inlet and outlet of each heat exchanger. Such a minimum temperature drop can be calculated if all input flow rate goes through the exchanger ... 

Frigid-Flow Co. has received final test results on the company s new heat exchanger. The values given below are overall heat-transfer coefficients 60 63 60 68 70 72 65 61 69 67 BTU/h ft2 °F. At the 99% confidence level, what minimum value for the exchanger s overall heat-transfer coefficient can the company suggest ... 

The heat transfer and friction factor for two typical compact exchangers are shown in Figs. 10-19 and 10-20. The Stanton and Reynolds numbers are based on the mass velocities in the minimum flow cross-sectional area and a hydraulic diameter stated in the figure. 

For the low-temperature distillation process shown in the flow diagram in Fig. 7.18, calculate the minimum hot-utility requirement and the location of the heat recovery pinch. Assume that the minimum acceptable temperature difference, ATrma, equals 5°C. The specifics of the process streams passing through the seven heat exchangers appear in the first five columns of Table 7.8, the mass flowrates of the streams being represented within the enthalpy (AH) values. 

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