Analysis of the problems in the temperature contro

Analysis of problems in temperature control of beer conical fermentation tank (Part I)

in the first issue of "beer science and technology" in 2000, an article entitled "several problems in temperature control of beer conical fermentation tank" was published. Later, some articles in relevant magazines also talked about this aspect, and felt it necessary to discuss it again. This paper is going to discuss the following aspects:

1 Definition of temperature and basic criteria for temperature measurement

2 Temperature and heat

3 In the process of beer fermentation by accurately controlling tiny ceramic fibers, the role of temperature and the essence of control

4 Temperature control in beer fermentation process

5 Several opinions on the evaluation of temperature control system

I. The definition of temperature and the basic criteria for temperature measurement

temperature is one of the physical quantities that are most closely related to human daily life and production practice, and it is closely related to temperature around us and everywhere. But not everyone understands the definition of temperature and temperature measurement very well, even some technicians engaged in temperature measurement and control engineering are no exception. This is mainly because people are easy to confuse the concepts of temperature and heat, sometimes related to people's subjective intuition. Among all the basic physical quantities, temperature is the most difficult to understand and measure

the most popular concept of temperature refers to temperature as a physical quantity that represents the degree of cold and heat of an object. But this kind of expression is not rigorous, which is easy to produce illusion. For example, when we touch wood blocks, foamed plastics and metal rods at the same temperature indoors, we will feel a slight difference. Obviously, we cannot judge that their temperatures are different from this. The reason is not simple. It is not only related to the nature of objects, body temperature and room temperature, but also related to the way people produce thermal sensation. Therefore, to correctly understand the meaning of object temperature, we must make a scientific definition of the concept of temperature

the scientific definition of temperature comes from the zeroth law of thermodynamics, which is not expressed one by one here. It can be popularly considered that temperature is the state parameter representing the thermal equilibrium state of an object. When two objects in thermal equilibrium contact without heat exchange, the two objects have the same temperature; When two objects in thermal equilibrium contact and exchange heat, the two objects have different temperatures, and the heat flows from the object with higher temperature to the object with lower temperature. There are two things that must be explained here: first, the thermal equilibrium state of an object refers to the thermal equilibrium state in which there is no heat exchange inside the object; Second, when there is no heat exchange between objects, the heat balance between the two objects. On the contrary, the purpose of thermal balance is to deepen the impression that an absolutely ideal thermal balance does not exist in fact, and can only be close to the thermal balance, which is the reason why the physical quantity of temperature is the most difficult to understand and the most difficult to measure

when we use a thermometer to measure the temperature of an object, we don't just touch the temperature sensing part of the thermometer with the measured object. The displayed value of the thermometer is the real temperature of the measured object. The thermometer actually shows the temperature of the temperature sensing part of the thermometer. Only when there is no heat exchange between the temperature sensing part of the thermometer and the measured object, that is, heat balance, is the temperature of the measured object. Therefore, when using a thermometer to measure the temperature of an object, it is the basic principle of temperature measurement to minimize the heat flow between the temperature sensing part of the thermometer and the measured object and control it within the allowable range. The greater the heat flow passing through the temperature sensing part in unit time, the greater the error of temperature measurement; On the contrary, the error is smaller. Therefore, when using the thermometer to measure the temperature, there should be a certain insertion depth, so that the heat flow from the outside through the thermometer rod can be divided before reaching the temperature sensing part, so that the heat flow through the temperature sensing part can be reduced to the allowable range. If you want to further reduce the error, you can also wrap the whole thermometer with insulating materials to block the influence of the surrounding ambient temperature changes on the temperature measurement

another point must be emphasized: the temperature of the measured object cannot be absolutely uniform in fact, and the temperature of the temperature measurement point only represents the temperature of this part of the object

second, temperature and heat

temperature is a state parameter that represents the macro thermal state of an object. From a microscopic point of view, temperature is a representation of the intensity of molecular thermal motion in an object. The input or output of heat can aggravate or slow down the intensity of molecular thermal motion in an object, and the temperature of the object will also increase or decrease. It can be seen that temperature describes the thermal state of an object, and heat is a form of exchanging energy with the outside world during the change of the state of an object. Temperature is related to the thermal state of the object, while heat is related to the process of changing the state of the object. There are connections between the two, but they are two concepts. Temperature is a basic physical quantity, and heat is a form of energy, which can be connected by the first law of thermodynamics

it is specific to the temperature control of the object, rather than discussing thermal machinery, without considering the exchange of mechanical energy between the object and the outside world. For a certain mass object, the increase or decrease of the temperature of the object completely depends on the direction and size of the heat flow of heat exchange with the outside world. In order to greatly improve the current situation of manufacturing industry in California, heat is input when the temperature is increased, and heat is output when the temperature is reduced. To keep the temperature unchanged, complete insulation or balance of input and output heat is required. To control the temperature is actually to choose a controllable heat transfer channel to balance the input or output heat of the controlled object with the output or input heat of the controllable heat transfer channel. Therefore, controlling temperature is essentially controlling the heat exchange capacity of controllable heat transfer channels. The so-called controllable heat transfer channels are what we call heat exchangers, heaters, coolers, etc. the cooling jacket on the outer wall of the fermentation tank, namely the cold belt, is a kind of heat exchanger. The outer diameter of the outer wall of the fermentation tank must also be φ 6- φ The thermometer installed on 11 uses the introduction of China Xinda today to control the heat taken away by the refrigerant in the cooling jacket. It shows the temperature of the fermentation broth at the measuring point. The temperature distribution in the whole tank is related to many factors, and it is also different in different stages of the whole fermentation process. We will discuss this problem specifically below

(to be continued)