Single Pass Exchanger

The mean temperature difference (A T)m depends on the terminal temperatures, the thermal properties of the two fluids and on the flow pattern through the exchanger. 

This is called the logarithmic mean temperature difference. The temperature profiles are straight when the heat capacities are 

Medium Trade Name Phase F atm, gage Remarks 

Diphenyl-diphenyl oxide eutectic Dowtherm A liquid or vapor 450-750 0-9 nontoxic, carbonizes at high temp 

Di + triaryl cpds Dowtherm G liquid 20-700 0-3 sensitive to oxygen 

Ethylene glycol, inhibited Dow SR-1 liquid -40--250 0 acceptable in food industry 

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Ft is unity for a single-pass exchanger. UQ is given by the values of ha, and the foul- ing coefficient ht as follows ... 

Mean Temperature Difference 172 Single Pass Exchanger 172 Multipass Exchangers 173 F-Method 173... 

Parallel flow is rarely used in a single-pass exchanger such as that shown in Fig. 11.3 because, as inspection of Fig. 11,4a and b will show, it is not possible with this method of flow to bring the exit temperature of one fluid nearly to the entrance temperature of the other and the heat that can be transferred is less than that possible in countercurrent flow. In the multipass exchangers, described on pages 430 and 431, parallel flow is used in some passes, largely for mechanical reasons, and the capadty and approaches obtainable are thereby affected. Parallel flow is used in special situations where it is necessary to limit the maximum temperature of the cooler fluid or where it is important to change the temperature of at least one fluid rapidly. 

Only limited information about the electrochemical properties of astatine is available. The formation of a singly positively charged cation, At+, in aqueous and other solvent environments has been observed. A study in a nitric acid environment investigated the adsorption into ion exchange materials of this cation [206]. In a similar study in aqueous perchloric acid, the mobility of At+ was found to change with pH and the presence of a strongly water bound species, At(H20)2", with a pA of ca. 1.5 was proposed [207]. 

The tracer diffusion coefficient of oxide ions in single crystals was measured by using the gas-solid isotopic exchange technique with 1 0 tracer. Least-squares analysis of tracer diffusion coefficients under an oxygen pressure of 4.5 x lO Pa gave ... 

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