Lecture+10.++Heat+Exchangers-Examples+and+Calculations -...

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UNIVERSITY OF CALIFORNIA Department of Viticulture and Enology VEN 135 WINE TECHNOLOGY AND WINERY SYSTEMS 10. HEAT EXCHANGERS-EXAMPLES AND CALCULATIONS TEMPERATURE CONTROL DURING FERMENTATION In order to control the temperature in a fermentation, all heat generated must be removed. Most of this heat will be removed via transfer to a coolant flowing through an external jacket on the tank. The heat flux from the fermenting juice/must to the coolant can be described as: LM TOT T U A Q = (1) where Q TOT is the total heat generation rate for the fermentor, A is the heat transfer area, U is the overall heat transfer coefficient, and T LM is the log mean difference between the coolant temperature and the fermentation temperature. To use this equation we must further define all of the terms. The maximum rate of heat generation during a wine fermentation coincides with the maximum sugar utilization rate. For white fermentations, this sugar utilization rate corresponds to 2-3 Brix/day, while for red wines, 4-6 Brix/day is more typical. From data in the Boulton et al. text, heat generation per unit volume at this point in the fermentation can be described by the relationship: [ ] s TOT R day Brix L W Q / / 10 5 . 77 3 - × = (2) where R S is the sugar utilization rate in Brix/day. The units of Q TOT are then W/L. To get heat generation rate for the whole fermentor, we then use the relationship: TOT w TOT Q V Q = (3) where V w is the working volume of the fermentor. The heat transfer area, A , can be calculated from the geometry of the tank: j t H D A π = (4) where D t is the diameter of the tank and H j is the height (i.e. length) of the jacket.
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The log mean temperature difference, T LM , can be calculated using the jacket inlet ( T i ) and outlet ( T o ) temperatures, along with the fermentation temperature, T f (see Figure 10A.1 for notation). The form of this mean temperature difference is: ( 29 )] /( ) ln[( i f o f o i LM T T T T T T T - - - = (5) Finally, the overall heat transfer coefficient, U , is a function of jacket geometry, coolant flows, fermentation mixing, materials of construction, and expected jacket fouling. It is a property of the fermentor design and the fermentation system. The vendor
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This note was uploaded on 09/29/2010 for the course VEN 91866 taught by Professor Davidblock during the Spring '09 term at UC Davis.

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Lecture+10.++Heat+Exchangers-Examples+and+Calculations -...

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