Heat exchangers cross-flow

Entrance andExit SpanXireas. The thermal design methods presented assume that the temperature of the sheUside fluid at the entrance end of aU tubes is uniform and the same as the inlet temperature, except for cross-flow heat exchangers. This phenomenon results from the one-dimensional analysis method used in the development of the design equations. In reaUty, the temperature of the sheUside fluid away from the bundle entrance is different from the inlet temperature because heat transfer takes place between the sheUside and tubeside fluids, as the sheUside fluid flows over the tubes to reach the region away from the bundle entrance in the entrance span of the tube bundle. A similar effect takes place in the exit span of the tube bundle (12). 

Fig. 15. Low hydrocarbon emission control system utilising a cross-flow heat exchanger TWC catalyst, A, and a 2eohte-based hydrocarbon absorber system. Cold start HCs are absorbed by the hydrocarbon trap, B, until the cross-flow heat exchanger catalyst is hot enough to destroy the HCs that...

The three commonly used recuperative flow-type heat exchangers in the power and refrigeration industry are parallel-flow, counter-flow, and cross-flow heat exchangers. Consider the case where a fluid is flowing... 

Figure 8.5. Correction [actor F, effectiveness and number of transfer units in multipass and cross flow heat exchangers (Bowman et al., Trans ASME 283, 1940 Kays and London, 1984) ...

Further experiments were carried out by Janicke et al. [66] applying cooling oil. Surprisingly for a cross-flow heat exchanger, an exit temperature of 207 °C was determined for the heat carrier, whereas the product gas exited at 70 °C. This phenomenon was attributed to the fact, that most of the energy was transferred to the oil at the feed inlet. Subsequently the product was then cooled by the cold oil, which had heated up not yet. 

Figure 2.66 Preparation of a ceramic monolith to obtain a cross-flow heat exchanger (left) and different options of monolith preparation (right) [102].

Figure 2.90 Cross-flow heat exchanger design applying punching technology developed by IMM (source IMM).

Figure 2.93 Stack of cross-flow heat exchangers developed by Karlsruhe Research Center [144],...

The temperature of each module can be adjusted by an integrated cross-flow heat exchanger. A temperature profile can be obtained by the combination of differently tempered modules. 

Taking into account typical numbers for a and D, this underlines that the channel width should be considerably smaller than 1 mm (1000 pm) in order to achieve short residence times. Actually, heat exchangers of such small dimensions are not completely new, because liquid cooled microchannel heat sinks for electronic applications allowing heat fluxes of 790 watts/cm2 were already known in 1981 [46]. About 9 years later a 1 cm3 cross flow heat exchanger with a high aspect ratio and channel widths between 80 and 100 pm was fabricated by KFK [10, 47]. The overall heat transport for this system was reported to be 20 kW. This concept of multiple, parallel channels of short length to obtain small pressure drops has also been realized by other workers, e.g. by PNNL and IMM. IMM has reported a counter-current flow heat exchanger with heat transfer coefficients of up to 2.4 kW/m2 K [45] (see Fig. 3). 

Flfl. 10-4 Cross-flow heat exchanger. one fluid mixed and one unmixed. 

Fig. 10-6 Typical temperature profile for cross-flow heat exchanger ot Fig. 10-5...

Hot exhaust gases are used in a finned-tube cross-flow heat exchanger to heat 2.5 kg/s of water from 35 to 85°C. The gases [cp = 1.09 kJ/kg °C] enter at 200 and leave at 93°C. The overall heat-transfer coefficient is 180 W/m2 °C. Calculate the area of the heat exchanger using (a) the LMTD approach and (b) the effectiveness-NTU method. 

Saturated steam at 100 lb/in2 abs is to be used to heat carbon dioxide in a cross-flow heat exchanger consisting of four hundred 1-in-OD brass tubes in a square in-line array. The distance between tube centers is j in, in both the normal- and parallel-flow directions. The carbon dioxide flows across the tube bank, while the steam is condensed on the inside of the tubes. A flow rate of I lb ,/s of CO at 15 lb/in2 abs and 70°F is to be heated to 200°F. Estimate the length of the tubes to accomplish this heating. Assume that the steam-side heat-transfer coefficient is 1000 Btu/h ft2 °F, and neglect the thermal resistance of the tube wall. 

An air preheater for a power plant consists of a cross-flow heat exchanger with hot exhaust gases used to heat incoming air at I atm and 300 K. The gases enter at 375°C with a flow rate of 5 kg/s. The air flow rate is 5.0 kg/s, and the heat exchanger has A = 110 nr and U = 50 W/m- °C. Calculate the heat-transfer rate and exit temperatures for two cases, both fluids unmixed and one fluid mixed. Assume the hot gases have the properties of air. 

Hot water at I80°F is used to heat air from 45°F to 115°F in a finned tube cross-flow heat exchanger. The water exit temperature is 125°F. Calculate the effectiveness of this heat exchanger. 

Use the correction factor for a 1-1 cross flow. The mean temperature difference for a 1 -1 cross-flow heat exchanger can be calculated by using the correction factor determined from Fig. 7.12. The mean temperature difference will be the product of this factor and the log mean temperature difference for countercurrent flow. To obtain the correction factor F, calculate the value of two parameters P and R ... 

Despite the geometric similarities, the problem analyzed here is fundamentally different from that of cross-flow heat exchangers or catalytic reactors in that the solid is not only used as a heat-exchange medium or as a catalyst support but also as the electrolyte across which oxygen ion transport occurs. This introduces an integral electron conservation balance which results in an integro-differential problem. 

Different flow configurations in cross-flow heat exchangers. 

Correction factor F charts for common shell -and-tube and cross-flow heat exchangers. 

C How does a cross-flow heat exchanger differ from a counter-flow one What is the difference between mixed and unmixed fluids in cross-flow ... 

The radiator in an automobile is a cross-flow heat exchanger ( M, = 10 kW/K) that uses air (c = 1.00 kJ/kg K) to cool the engine-coolant fluid (c = 4.00 kl/kg K). The engine fan draws 30°C air through this radiator at a rate of 10 kg/s while the coolant pump circulates the engine coolant at a rate of 5 kg/s. The coolant enters this radiator at 80°C. Under these conditions, the effectiveness of the radiator is 0.4. Determine (a) the outlet temperature of the air and (i) the rale of heat transfer between the two fluids. 

Air(cp 1005 J/kg °C) enters a cross-flow heat exchanger at 20°C at a rate of 3 kg/s. where it is healed by a lioi water stream (c = 4190 J/kg C) that enters the heai exchanger at 70°C at a rate of 1 kg/s. Delermine the maximum heal transfer rate and the outlet temperatures of both fluids for that case. ... 

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