Heat balance technique

M. Greenfeld described unique laboratory experiments designed to stimulate and understand the complex chemistry of in-situ coal gasification. Developed at the Alberta Research Council, the gasification simulator was heavily instrumented with calorimeters and gas chromatographs to determine the enthalpy, composition, and kinetics of formation of the product gases. Computer techniques were used to calculate mass and heat balances and to test kinetic models. 

For leaner sulfur streams, several techniques have been suggested to provide the heat balance. Among them are 1) use of oxygen rather than air for combustion, 2) addition of hydrocarbon or other fuel species to the sulfur burner section to provide heat,... 

A special section then deals with the use of time-scales for the heat balance, which provides a simple to use assessment technique. The third section is devoted to the heat balance with purely conductive heat removal. The chapter closes on practical aspects for the assessment of industrial heat confinement situations. 

With these properties and values the finite difference technique was used to model the curing process in sheet molding compound (SMC) plates using a heat balance with an exothermic reaction as... 

The Lewis and Matheson technique makes tray-to-tray calculations starting at the bottom and calculating up the column. Material and heat balances are made on each tray, the number of trays is determined in the calculations. 

The problem of a porous catalyst pellet, which had been addressed in the paper of Ray and Hastings, was later treated extensively by Jensen and Ray (242,297). They used surface coverage equations and mass and heat balances for the whole pellet, all of which, except for the heat balance, were solved for the nonlumped case. The solutions of the resultant partial differential equation set were obtained by collocation techniques. The surface reaction was assumed to be unimolecular and slightly more complex than the mechanism analyzed by Ray and Hastings in that the adsorption step was permitted to be reversible ... 

Using this technique and after some manipulation, the bulk phase mass and heat balance equations can be written in terms of the variables at the N intraparticle collocation points as follows ... 

The technique requires sufficient temperature measurements so that the inlet and outlet temperatures of the fluid stream entering and leaving the heat exchanger can be measured, or calculated from a suitable heat balance. 

It is sometimes possible to estimate those properties of a polymerization reactor which are not measurable. The most common application of these techniques is the use of a heat balance to estimate the rate of reaction. If the coolant duty necessary to remove the heat of polymerization is carefully monitored, the rate of polymerization can be calculated if the heat of reaction (propagation) is known. Unlike most situations where scale-up is detrimental, this is one case where the use of a large reactor is beneficial. A large reactor has a low surface-to-volume ratio, and therefore heat losses tend to be smaller (relatively) and more constant (and hence, characterizable) than in a smaller kettle. If the rate of polymerization is known as a function of time, monomer conversion can be calculated by integrating the rate of polymerization over time. This technique is inexpensive to implement and is applied in many latex reactors with surprisingly good results. Heat balance estimates of conversion can be combined with other, less frequent conversion measurements within the framework of a state estimator. 

The heat effects accompanying a crystallization operation may be determined by making heat balances over the system, although many calculations may be necessary, involving knowledge of specific heat capacities, heats of crystallization, heats of dilution, heats of vaporization, and so on. Much of the calculation burden can be eased, however, by the use of a graphical technique in which enthalpy data, solubilities and phase equilibria are represented on an enthalpy-composition H x) diagram, sometimes known as a Merkel chart. 

As an illustration of the application of approximate analytical techniques, we derive the asymptotic forms of the efiectiveness factor and average solid concentration/temperature for a non-isothermal reaction in a catalyst particle with external heat/mass gradients. Adopting the normalization in Equations 3.16-3.20 for a solid porous particle ( o = 0) with characteristic dimension in the direction of diffusion Rp, the mass and heat balances become... 

The heat production of animals can be measured physically using a procedure known as direct calorimetry. Alternatively, heat production can be estimated from the respiratory exchange of the animal. For this, a respiration chamber is normally used and the approach is one of indirect calorimetry. Respiration chambers can also be used to estimate energy retention rather than heat production, by a procedure known as the carbon and nitrogen balance technique. 

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