The calorimeter as an object with a heat source

A calorimeter can be treated as a physical object with active heat sources inside it. An analysis of the thermal processes occurring inside the calorimeter, and those between the calorimeter and its environment, requires utilization of the laws and relations defined by heat transfer theory [1-5]. 

The relations arising from heat transfer theory are applied to design the mathematical models of calorimeters, which express the dependence of the change in temperature measured directly as a function of the heat effect produced. There is an understandable tendency to attempt to express these models in the simplest way. In practice, this is achieved by applying simplifications to the original formulas. To make use of them wisely, one has to understand precisely the assumptions made. This chapter will present a detailed consideration of this topic. 

Selected problems from heat transfer theory are also presented. Special attention is paid to a discussion of the processes occurring in a non-stationary heat transfer state. An understanding of these processes is of importance for a proper interpretation of calorimetric measurements. The general heat balance equation is introduced into the considerations. Particular forms of this equation will be applied to consider problems that form the subject of this book. 

Heat transfer by conduction in a homogenous, isotropic body is mathematically described by the Fourier law [1]  

Quantity Tin Eq. (1.1) is a function of the coordinates x, y, z and time t. For any time t the value of T determines the scalar temperature field. At every point upon it, the temperature at this instant is the same. Such a surface is called the isothermal surface for temperature T. 

---

Various methods are used to construct the mathematical model of a calorimeter. The theory of calorimetry presented below is based on the assumption of the calorimeter as an object with a heat source, and as a dynamic object with well-defined parameters. A consequence of this assumption is that the calorimeter is described in terms of the relationships and notions applied in heat transfer theory and control theory. With the aim of a description and analysis of the courses of heat effects, the method of analogy is applied, so as to interrelate the thermal and the... 

A furniture calorimeter consists of a weighing platform that is located on the floor of the laboratory, beneath a hood connected to an instrumented exhaust duct (see Figure 14.13). The object is placed on the platform and ignited with the specified ignition source. The products of combustion are collected in the hood and extracted through the exhaust duct. Measurements of oxygen concentration, flow rate, and light transmission in the exhaust duct are used to determine the heat release rate and smoke production rate from the object as a function of time. 

---