6.1. Water shower

In plate exchangers U = 2900–4800 w/m2�C [10], at 3500–6500 w/m2�C [8], from 2400 to 2600 w/

In spiral exchangers U = 1700 w/m2�C [10], of 2000–2100 w/m2�C [8], from 760 to 1060 w/

In direct refrigeration system, two fluids that exchange energy are physically in contact. In oenology, the inert gases N2 and CO2 are used as refrigerating fluids, since when vaporizing at

Of the two inert gases mentioned above, CO2 in solid and liquid forms is the most used in oenology, due to its low sublimation temperature at atmospheric pressure –72.4�C, added contribution of inert atmosphere of conservation, possibility of partial freezing of the must

The cooling capacity provided by CO2 in solid form is defined by the following expression

If ice is produced due to the freezing of the water from the must to this expression (Eq. (19)),

QH2O ¼ m � λH2O, resultado : dQ ¼ m � λH2O þ ρ � V � Ce � ðT1–T2Þ ¼ M � ðλFS þ λVPÞ

).

To form 1 kg of ice in the must mass, it is necessary to add 0.58 kg of CO2 to the freezing temperature of the must (–2.5 to 3.0�C). In the refrigeration of musts, wines and crushed-

dQ ¼ ρ � V � Ce � ðT1–T2Þ ¼ M � ðλFS þ λVPÞ (18)

(19)

low temperatures they absorb heat from the must/crushed-grapes.

we must add the energy due to the sublimation heat of CO2:

λH2O is the latent heat of water fusion (0.108 kJ/kg).

Ce is the specific heat of must/crushed-grapes (kJ/kg �C). T<sup>1</sup> is the initial temperature of must/crushed-grapes (�C). T<sup>2</sup> is the final temperature of must/crushed-grapes (�C).

λFS is the latent heat of fusion of solid CO2 (573 kJ/kg).

M is the mass of CO2 in solid form required for refrigeration (kg).

λVP is the latent heat of vaporization of liquid CO2 (393 kJ/kg).

ρ: is the must/crushed-grapes density (�C). V is the must/crushed-grapes volume (m<sup>3</sup>

with the consequent sugar concentration, ease of handling and no residues.

m2�C [10, 13], of 2000 w/m2�C [3].

5.2. Direct refrigeration systems

m2�C [10, 13, 36].

86 Refrigeration

(Eq. (18)) [4, 8–10, 13]:

m is the formed ice mass (kg).

where

It consists on spraying the walls of the fermentation tank with water from an upper ring connected to a general feed system. A very fine and homogeneous layer of laminar water is generated, which descends through the walls and is normally collected in channels arranged in the lower part of the tank. An automatic control allows the opening and closing of solenoid 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 vaporization of the circulation system water.

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 applied in any case for rose and white wine vinifications.

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 (Eq. (22)):

$$Q\mathbf{s} = \mathcal{U} \times \mathcal{S} \times \left( T\_{\text{inside tank}} - T\_{\text{curtain water}} \right) \tag{22}$$

where

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].

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

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

$$Q\_1 = H \times \mathcal{S} \times \left( T\_{air} - T\_{wet\ air\ bulb} \right) \tag{23}$$

where

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 conditions subjected to wind action.

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

The wet bulb temperature of the air can be determined on a psychometric diagram and depends on the room temperature and the relative humidity of the air.

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 air humidity occurs on the tank.
