A new calorimeter system is described, in which the rate of reaction is determined simultaneously with the heat of reaction. The system operates near ambient temperature and is particularly suitable for measurement of air/coal interactions which are responsible for self-heating and spontaneous combustion. These interactions are characterised by an extremely slow evolution of heat of the order of about 5*10-6 W per g of coal which changes with time requiring the instrument to remain stable over a period of several weeks. The instrument may also be suitable for investigations of self-heating of other materials which are commonly stockpiled.

This study confirms that the distribution of free gaseous oxygen in a coal stockpile agrees with a previously published model for self-heating within the stockpile. The simplified, isothermal model of the study predicts a hyperbolic cosine distribution which is characterized by a single parameter, the Thiele modulus. This depends on the stockpile properties of size, intraparticle porosity, oxygen diffusivity and the coal properties of density and reactivity towards oxygen. The Thiele modulus can be determined from two measurements of oxygen concentration at different depths in the pile. Changes in coal reactivity (weathering) on prolonged exposure to atmospheric oxygen are reflected in the magnitude of the Thiele modulus and thus can be measured in situ at storage temperatures.

Heat of wetting with water has been measured for samples of an Australian low-rank bituminous coal with different initial moisture contents. Although dry coal showed a substantial heat of wetting (≈6 kJ kg−1), values decreased rapidly with increasing moisture content and it is calculated that for a normal moist coal (65% relative humidity) heat of wetting could cause a temperature rise of only ≈2 °C, which would be unlikely to contribute significantly to self-heating in stored coal.

This paper is the second in a series of three on the self-heating of char in bulk. It reports measurements of the diffusivity of oxygen in a bulk of char, the specific heat capacity of dry and moist char as a function of temperature, the diffusivity of heat; the equilibrium water content of char is examined and the rates of moisture sorption and desorption. The roles which these properties play in the self-heating reaction is discussed briefly. A full analytical treatment of their roles is reserved for Paper III3 of this series.

As part of a study of self-heating tendencies of Australian coals and chars, the rates of oxidation of fresh and weathered chars and a weathered coal have been measured in dry (fresh char only) and moist air over the temperature range 45 to 94 °C. The oxidation of the weathered materials has an apparent activation energy lying between 63.9 and 69.0 kJ/mol which is independent of their moisture content. However, the rate of oxidation of char increases with increasing moisture content and decreases with increasing carbonization temperature of the parent coal, and with the extent of the char's weathering. Indeed, under adiabatic conditions it is shown that weathering or progressive oxidation, which conforms to the Elovich relation, may largely offset any substantial self-heating of char (or coal) caused by the accelerating effect of temperature.

A mathematical model of the self-heating reaction of coal or char in bulk has been developed. The model takes into account a local oxidation reaction which depends on temperature and the concentrations of unreacted and reacted oxygen. The transport processes of diffusion and convection take the mobile reactant, oxygen, from the boundary to the distributed reaction where heat energy is released, and then convey the latter back to the boundary. The equations of the model are evaluated numerically and results are in general agreement with those predicted by the Theory of Thermal Explosions appropriate to the assumptions of the model. Various situations arise in the heating regime, depending on whether the conversion reaction is controlled by thermal conduction, reactant diffusion, reactant convection, or thermal convection where no distinct separation exists between the various cases. Some guidelines emerge for evaluating safe storage conditions for coal or char where the criterion of safety has to be specified for different materials, probably as a maximum safe temperature and maximum time of storage.

The relationship between heat and mass transfer in textile beds is examined by the use of wires of similar dimensions to those of textile fibres. Some qualitative experiments validate this procedure, and hence a general law between the transport and the velocity of fluid passing through the bed is established. At this stage, however, the connexion between structural factors of the bed and the measured transport properties could only be treated in a most elementary manner.

Cassie's theory of propagation of heat and moisture changes in beds of wool fibres is re-examined by means of the method of characteristics. Substantial differences result in the predictions of the theory by treating the coefficients of the pertinent differential equations as functions of the dependent variables rather than as constants.

The thickness of the diffusional boundary layer has been shown to be too small to control the rate of uptake of dye under conditions similar to those used in package dyeing.

An account is given of an investigation of the effectiveness of steaming on the longitudinal stabilization of wool yarn. Specially prepared worsted yarns were used to study the effects of initial regain and of time and temperature of steaming. Of the several different mechanisms proposed for the longitudinal stabilization of yarn by steaming, only permanent setting is demonstrated directly, and the effects of temperature, initial regain, and time of treatment are established. Two threshold values were observed below which no permanent setting took place—an Initial-regain threshold of 7–8% and a temperature threshold of about 88°C. It is considered possible that the threshold temperature is a function of the particular release treatment used and that it would increase with increasing severity of the conditions of release. The contribution of permanent setting to the over-all longitudinal stabilization was apparently small, but this may have been a result of using a rather severe release treatment.

The predictions from a previously developed mathematical model for coupled heat and moisture diffusion in beds of hygroscopic fibers have been tested against experimental observations on wool bales and wool fabrics. The experiments on wool bales were concerned with the changes in regain and temperature consequent upon changes in the relative humidity and temperature of the surrounding air. The experiments on fabrics included measurements of temperature and regain during Hoffman pressing and measurements of heat flow through the fabric during changes in regain. Satisfactory agreement was found between the predictions from the model and the experimental observations.

Wool dry‐chlorinated in the laboratory plant described in Part I of this study was subjected to three tests. Degradation of the treated wool was assessed by load‐extension measurements on single fibres. Batches of treated wool were converted into knitted fabrics and handle and washing shrinkage tests were carried out on the fabrics. The treatment only slightly affected the elastic behaviour of single wool fibres, indicating insignificant degradation of the fibre. The best shrink resistance was obtained under conditions that also caused greatest deterioration in handle.

Click to increase image sizeClick to decrease image sizeKEY WORDS: WOOLREGAINVACUUM-STEAMINGTEMPERATURESPECIFIC HEATDIFFERENTIAL ENTHALPY OF WETTING

Some of the physical principles of the steaming of wool yarn packages are discussed. Experimental results are reported for the penetration of moisture and heat into packages during vacuum and open steaming. The influence of residual air in vacuum steaming has been investigated. Finally, recommendations are made for carrying out effective vacuum steaming.

A laboratory study is reported of the gas‐phase chlorination of wool at atmospheric pressure. The influence of chlorine concentration in chlorine—air mixtures, regain of wool, and temperature on the extent of the reaction has been measured. Two small‐scale pilot plants for the chlorination of top are described, one for batchwise and one for continuous operation. The washing performance of samples of wool chlorinated in these plants was tested; the results are given in Part II of this paper.

A finite difference solution, based on the “double sweep” method, has been found for solving the non-linear differential equations which describe coupled diffusion of heat and mass (moisture) in hygroscopic textile materials. In addition to the diffusion equations, a rate equation has been introduced describing the rate of exchange of moisture between the solid (textile fibres) and the gas phase (pore space). A numerical application of the theory has been made using wool as an example for the hygroscopic material and it is shown that, similar to forced convective transfer, transfer of moisture from air to the wool and from the wool to air are not symmetrical processes. The magnitude of the error caused by neglecting the rate of transfer of moisture between the solid and gaseous phases as compared to the time scale of the diffusional processes is discussed and shown to depend on the physical dimensions of the slab. Examples are also given of positive and negative temperature and concentration fronts which may be set up in the slab.