6.2. Refrigerating shirts

The use of refrigeration shirts is currently the most widespread fermentation control system in both white and red winemaking. Traditionally, they have been constructed in stainless steel and are fixedly arranged in the upper part of the tank, occupying between 15 and 30% of the surface. In the recent years, some manufacturers are using new polymers of medium rigidity and high resistance that makes possible their installation on the tank according to the needs of the campaign. As to their disposition, and in agreement with the results of several investigations that advise for vinifications in red wine the use of fermentation tanks of equal height and base diameter, the shirts are installed covering the greatest part of the side surface of the deposit, reaching in some cases 90% of it. This new system allows a homogeneous control of fermentation, avoiding the problem of the thermal stratification that takes place with large diameters.

Similar to the tubular and plaque exchangers, the exchanged energy is defined by the general energy transfer equation (Eq. (24)) [8, 10, 13, 38]:

$$\mathbf{dQ/dt} = \rho \times V \times \mathbf{d}T/\mathbf{dt} = F\_T \times \mathbf{U} \times \mathbf{S} \times (\Delta T)\_{\text{ml}} = W \times \mathbb{C}\_t \times (t\_1 - t\_2) = W' \times \lambda \tag{24}$$

dQ/dt is the dissipated energy per unit of time (kJ/h).

ρ: is the must density (kg/m3 ).

V is the tank volume (m<sup>3</sup> ).

valves according to the temperature inside the tank and the preset. The refrigeration mechanism by conduction and convection is based on the removal of energy from the tank by partial

Thermodynamically, it is the most unfavorable refrigeration system and the one that uses the greater volume of water, which supposes a greater environmental cost. These cases are recommended where no refrigerated water is available (below 20�C). For this reason, it is used with efficiency in the control of fermentation in red wine vinifications, not being able to be

The refrigeration power of the water curtain is defined by the heat of vaporization of the water at room temperature. The heat of its vaporization is the sum of its sensible heat in liquid state and the latent heat of vaporization corresponding to the change in water-vapor station. For calculation purposes, the refrigeration power of the water due to sensible heat is defined by

K is the thermal transfer coefficient. For stainless steel tanks and water circulation in a thin layer laminar regime on the surface, the value of U is of the order of 100 w/m2�C [3, 7, 8, 35].

H is the coefficient of thermal transmission by convection between the water curtain and the tank surface. According to McCabe et al. [8] and Geankoplis [9], Lamúa [37] takes values between 10 w/m2�C for closed rooms without air circulation and 40 w/m2�C for exterior

The wet bulb temperature of the air can be determined on a psychometric diagram and

Only if the water temperature exceeds the humid bulb temperature of the air, vaporization has place and therefore a dissipation of energy of the tank, since if it is lower a condensation of the

The use of refrigeration shirts is currently the most widespread fermentation control system in both white and red winemaking. Traditionally, they have been constructed in stainless steel

The refrigeration power due to the latent heat of water vaporization is (Eq. (23)):

Qs ¼ U � S � ðTinside tank–Tcurtain waterÞ (22)

Q<sup>1</sup> ¼ H � S � ðTair–Twet air bulbÞ (23)

vaporization of the circulation system water.

(Eq. (22)):

88 Refrigeration

where

where

conditions subjected to wind action.

air humidity occurs on the tank.

6.2. Refrigerating shirts

applied in any case for rose and white wine vinifications.

S is the surface of the tank in contact with the water curtain.

S is the surface of the tank in contact with the water curtain.

depends on the room temperature and the relative humidity of the air.

dT/dt is the must temperature variation per unit of time (�C/h).

FT is the correction factor depending on the ratio of the must and coolant velocities. It is a measure of the thermal efficiency of the exchange.

U is the global coefficient of heat transfer (w/m2�C). The coefficient depends on the type of refrigeration jacket, vinification and exterior environment conditions. Based on empirical data, mean values of 12–60 x/m2�C are stablished [10, 13]. Other authors raise the value of U to 200–600 w/m2�C [3] or 600–1000 [39].

S is the shirt surface (m<sup>2</sup> ).

(ΔT)ml is the logarithmic mean temperature difference between glycol water and must (Eq. (25))

$$\left(\left(\Delta T\right)\_{\text{ml}} = \frac{\left(t\_{\text{em}} - t\_{\text{sa}}\right) - \left(t\_{\text{sm}} - t\_{\text{ea}}\right)}{\ln \frac{\left(t\_{\text{em}} - t\_{\text{sa}}\right)}{\left(t\_{\text{sm}} - t\_{\text{sa}}\right)}}\tag{25}$$

W is the mass flow of refrigerant (kg/h).

Ce is the specific heat of refrigerant (kJ/kg �C).

tem is the must initial temperature (�C).

tsm is the must final temperature (�C).

W' is the vaporization rate of refrigerant (kg/h).

λ is the vaporization latent heat of refrigerant (kJ/kg).

Two of the cases that take place, the refrigerating fluid changes of state for example R-717 evaporated to 5–7�C (in that case the fluid temperature is constant) or there is no change of state (glycol water), producing a heating throughout the cooling process. As approximate data, it is considered that water enters between 5 and 7�C and exits between 10 and 12�C.

For the purpose of calculating the equipment of the cold production facility, a simplified equation of the above is used (Eq. (26)):

$$Q\_c = \mathcal{U} \times \mathcal{S} \times \left( T\_{\text{inside tank}} - T\_{\text{circular water}} \right)\_{\text{ml}} \tag{26}$$

Since the must/wine inside the tank is in steady state and this heat exchange equation is applied for counter current flowing fluids, the term (ΔT)ml is simplified to (Tinside tank�Tcirculating water).

It should be noted that 50% of the refrigerating protein produced by the shirt dissipates in the environment surrounding the tank if it is not well heat-insulated. In case no insulation is available, the required shirt surface must be doubled, or, if appropriate, the cooling capacity is reduced by half for calculation purposes.

The cooling jackets have very low heat transfer coefficients due to the steady state in which the must/wine is located inside the tank. The effectiveness of the refrigeration decreases proportionally with the diameter of the tank, being considered that for normal temperatures of circulation water limiting diameters of more than 4 m, due to the vertical thermal stratification that occurs [10, 13, 35]. If only large diameter tanks are available, the effectiveness decreases in a high percentage, so to maintain it in appropriate values, very low temperatures are required in the glycolic water, close to 1–2�C. According to Bouton et al. [10, 13], if the diameter doubles the surface of the jacket, it is multiplied by four and the volume of the must/wine is refrigerated by eight, maintaining the ratio surface/volume. As an approximate value and only for approximate calculations, 2 m2 of cooling jacket per 100 hl of must in fermentation is recommended.

The cooling jackets are used in the tartaric stabilization process of the wines by the system of planting nuclei of crystallization, circulating glycolic water at �7�C to reach temperatures of �1�C.
