Design of the condenser
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When designing a condenser, the heat transfer coefficient for the shell side is calculated. Could you explain the parameters in the formula for this heat transfer coefficient? For example, density, viscosity, and thermal conductivity – should we refer to the physical properties of the steam on the shell side or those of the condensed steam? I need help understanding this. Also, I saw an example today stating that if the temperature difference between the hot and cold fluids is greater than 60 degrees, then a floating-head heat exchanger should be used Where in the literature is it mentioned? There are also conditions for installing expansion joints. . .
1. Steam. 2, 3: Those are things from old practices. 4. Calculating based on the strength of the tube sheet – the idea that a certain temperature difference must be considered is unscientific.
This post was last edited by cl6119 on 2012-7-19 at 17:26. Regarding the calculation of the condensation heat transfer coefficient for the shell side in a condenser, if the condenser is horizontal, it involves condensation heat transfer outside the horizontal tube bundle; one can refer to the section on convective heat transfer during film condensation of vapor in the chapter on phase-change convective heat transfer in \"Principles of Chemical Engineering\" for the calculation method of such coefficients. The thermal resistance of this process should be concentrated on the liquid film formed during the condensation process; therefore, the properties of the liquid phase should be used in the general calculation formulas. For quasi-empirical correlation equations, since they are semi-empirical formulas, one should follow the requirements of those formulas and use whatever is specified; otherwise, it will be incorrect. As for whether to use a floating-head type heat exchanger and whether to include compensation rings, it is now commonly determined through stress calculations of the tube bundle; the era of relying on temperature differences is over.
I’m reading books on heat exchangers and chemical engineering design; in them, the symbols used for formulas refer to the viscosity of the condensate and its density. But the following sentence states that 【except for the latent heat of vaporization, for which the value at the condensation temperature is used, all other relevant property parameters in the formula are taken as the film temperature (the arithmetic average of the steam temperature and the wall temperature）.】 As a beginner in design, I’m really confused by all this. . . Yesterday I saw an example problem on the forum that used the property parameters of steam again.
As you said, in most cases, it should be calculated based on the properties of the condensate. However, it is not ruled out that some correlations are fitted using gas-phase properties, so gas-phase parameters are required. In short, whatever formula is chosen, one must follow the requirements of that formula.