Divided flow heat exchanger

A numerical study of the effect of area ratio on the flow distribution in parallel flow manifolds used in a Hquid cooling module for electronic packaging demonstrate the useflilness of such a computational fluid dynamic code. The manifolds have rectangular headers and channels divided with thin baffles, as shown in Figure 12. Because the flow is laminar in small heat exchangers designed for electronic packaging or biochemical process, the inlet Reynolds numbers of 5, 50, and 250 were used for three different area ratio cases, ie, AR = 4, 8, and 16. 

Moving-Bed Type This concept uses a single-pass tube bundle in a vertical shell with the dividea solids flowing by gravity in the tubes. It is little used for sohds. A major difficulty in divided-sohds apphcations is the problem of charging and discharging with uniformity. A second is poor heat-transfer rates. Because of these hmita-tions, this tube-bundle type is not the workhorse for solids that it is for liquid and gas-phase heat exchange. 

Pressure drop during condensation results essentially from the vapor flow. As condensation proceeds, the vapor flowrate decreases. The equations described previously for pressure drop in shell-and-tube heat exchangers are only applicable under constant flow conditions. Again the exchanger can be divided into zones. However, in preliminary design, a reasonable estimate of the pressure drop can usually be obtained by basing the calculation on the mean of the inlet and outlet vapor flowrates. 

The dead time of a heat exchanger equals its volume divided by the flow rate through it. As process flow increases, the process dead time is reduced and the loop gain is also decreased. If the controlled variable (Th2 in Figure 2.105) is differentiated with respect to the coolant flow (manipulated variable Fc), the steady-state gain of the process is given by ... 

The heat-transfer coefficient is a function of all chain, where heat flow passes, and for one-dimensional (plane model) heat exchange between liquid and hydride bed divided by heat-conducting wall can be expressed by ... 

Other types of heat-exchanger configurations not illustrated here are sometimes used. Curves for determining the value of F for these are presented in Ref. 11. These configurations include divided-flow and split-flow exchangers. 

The heat exchanger is divided into 3 computational cells in parallel-flow and counterflow types, and into 9 cells in crossflow type. The mass and heat balances of the cells are calculated by means of heat balance of a single plate [3,4]. The procedure of the calculation is similar to the case of the flue gas heat exchanger. The surface temperatures and air temperatures leaving the different types of heat exchangers are shown in Fig. 10. The pressure drop of the heat exchanger is calculated according to [5]. 

Spang et al. [22] and Xuan et al. [23] have analyzed 1-N TEMA G (split flow) and 1-N TEMA J (divided flow) shell-and-tube exchangers, respectively, with an arbitrary number of passes N, arbitrary surface area (NTU,) in each pass, and arbitrary locations of inlet and outlet shellside nozzles in the exchangers. Baclic et al. [24] have analyzed two-pass crosscounterflow heat exchanger effectiveness deterioration caused by unequal distribution of NTU between passes. 

Y. Xuan, B. Spang, and W. Roetzel, Thermal Analysis of Shell and Tube Exchangers with Divided-Flow Pattern, Int. J. Heat Mass Trans., Vol. 34, pp. 853-861,1991. 

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