Thermodynamics equilibrium pdf

Ajibola2; S. Oni2 1 Department of Agricultural Engineering, University of Maiduguri, Maiduguri, Nigeria; e-mail of corresponding author: nddyaviara yahoo. The models were compared using the standard error of estimate, mean relative percent deviation and residual plots. The moisture sorption isotherms of soya bean were sigmoidal in shape, of the type II and were markedly affected by temperature.

The desorption equilibrium moisture content and water activity relationships as expressed by the moisture sorption isotherm models that best predicted the experimental data, were used to determine the thermodynamic characteristics of soya bean. All rights reserved Published by Elsevier Ltd 1. Proper modelling and optimisation of which functions both as an oil seed as well as a the drying process require a knowledge of the equili- proteineous seed. The by researchers Roman et al.

Labuza et al. However, the gravimetric et al. Moisture sorption isotherm models, Wolf et al. The GAB does not incorporate a equipment. They are needed in the analytical determina- temperature term; therefore, the determination of the tion of the thermodynamic functions related to moisture effect of temperature using the model usually involves sorption in biological materials Iglesias et al.

The properties involved, relate the presented a more comprehensive list. In a similar study, transport phenomena in drying and determine the end Aviara and Ajibola found differences in the point to which food must be dehydrated in order to values and trends of the thermodynamic properties of achieve a stable product with optimal moisture content.

Thermo- soya bean TGX E. Iglesias et al. Materials and methods Fish studied the thermodynamics of water in 2. Material preparation potato starch gel and noted that starch at very high moisture content is thermodynamically similar to pure The soya bean variety TGX E developed at the water. This involved the soaking of bulk and trends observed. The soya bean seeds at an calculating the isosteric heat at different temperatures. At the end of soaking, the seeds were spread out and gari, respectively, from their moisture sorption in thin layer to dry in natural air for about 8 h.

They isotherms. Aviara and Ajibola studied the were then sealed in polyethylene bags and stored in that thermodynamics of moisture sorption in plantain and condition for a further 24 h. The vapour pressure of allowed to equilibrate in the ambient condition for six moisture in the material can be determined using the hours. Equilibrium moisture content determination The values of water activity aw can be obtained with the moisture sorption isotherm model, which best describes The desorption equilibrium moisture contents of soya the equilibrium moisture content water activity relation- bean seed were determined at the temperatures of 40, 50, ships of the product.

Saturated solutions 2. Excess salt was maintained in each solution. The equilibrium moisture content was enthalpy from the slope of the straight line obtained. The calculated on dry basis from the weight change and dry surface potential, can be calculated using an analytical matter weight, and the average value at each tempera- procedure similar to the one described by Iglesias et al. Determination of thermodynamic properties A m 0 aw where the moisture ratio y is: 2.

The Clausius—Clapeyron equation as surface area of a water molecule in m2; and M is the stated by Rizvi and Kapsalis , after some moisture content, d. The monolayer moisture content mathematical manipulations Fasina et al.

The saturated water vapour pressure Ps at Entropy change plays an important role in the energy different temperatures can be obtained from Rogers and and exergy analysis of food processing systems. T where awm is the geometric mean water activity obtained 2.

Thermodynamic characteristics at constant surface potential. The thermodynamic characteristics of soya bean were analytically determined using the desorption equilibrium 2. Data and analysis moisture content data as expressed by the moisture sorption isotherm model that best described its equili- 2. Moisture sorption isotherms brium moisture content and water activity relationships. Saturated water vapour pressure was steps. All the models are three parameter equations, obtained at each of the above temperatures from Rogers which can be solved explicitly for equilibrium moisture and Mayhew , and the actual vapour pressure at content as a function of temperature and water activity each temperature was determined using Eqn 2.

The or for water activity as a function of temperature and natural log of actual vapour pressure was plotted equilibrium moisture content. The non-linear regression against the natural log of saturated water vapour procedure required that initial parameter estimates be pressure at the same temperature.

The ln Po was chosen close to the true values. The initial parameter regressed against ln Ps to establish the linear relation- estimates were obtained by linearisation of the models ship existing between them. Multiple regression analysis was performed to were used as the initial parameter estimates in the non- determine the relationship existing between ln Po , linear regression procedure. Model parameters were moisture content M and temperature T of the seeds.

This equation relates the moisture content of was evaluated using the standard error of estimate food and agricultural material to the ratio of the heat of calculated by the procedure; mean relative percent vaporisation of moisture in the product hpw to the latent deviation and residual plots. The monolayer moisture The residual plots are plots of residuals differences contents of soya bean at different temperatures were between measured and predicted values of EMC and aw obtained by applying Eqn 6 to the equilibrium against measured values.

The surface potentials of Desorption equilibrium moisture contents of soya bean moisture in the seed at different temperatures were TGXE at different water activities and temperatures calculated using Eqn 4. The data were used to estimate the parameters in both that the parameter estimates obtained for the EMC the EMC and aw models. Table 3 shows the parameter models were not the same as the corresponding estimates for the EMC models in which the EMC is parameter estimates for the aw models.

Several investi- taken as the dependent variable, while Table 4 shows the gators Duggal et al. These different ; Ajibola et al. According to Ajibola and Dairo model and associated parameter values that best suit the , the EMC models were obtained by logarithmic particular application.

The tables also show the indices transformation of the aw models and in the non-linear used in comparing the models namely the standard error regression analysis, the errors were assumed to be of estimate, mean relative percent deviation and nature normally and independently distributed.

This caused of residual plots. Pollio et al. For predicting the water activity, 0 0 0. Ratio of heat of vaporisation of moisture in soya bean to Fig. Log-log plot actual Po and saturated Ps water the latent heat of saturated water vapour as a function of vapour pressure for soya bean at various moisture contents moisture content compared with cowpea, sesame seed, melon d. For soya bean, saturated water vapour pressure ln Ps and moisture Eqn 10 therefore becomes content.

The the crops. Net integral enthalpy and entropy 6 The variation of net integral enthalpy with moisture content is shown in Fig. Net integral enthalpy of soya 5. Variation of the monolayer moisture content of soya root, its insoluble fraction and sucrose Iglesias et al. The surface tensional forces being weaker 0. Net integral entropy of soya 0 0. Variation of the net integral enthalpy of soya bean with The surface potential isotherms of soya bean are moisture content, compared with sesame seed, melon seed, and shown in Fig.

Variation of the net integral entropy of soya bean with predicting the water activity of soya bean. Rizvi and Benado also noted that in foods, there tend to be two opposing References entropic contributions upon moisture sorption, viz. Equilibrium moisture properties of entropy due to incipient solution formation, that is winged bean seed. The chemical composition will be the same throughout the system and this will not vary that system in chemical equilibrium. This is a reversible reaction.

A system is said to be mechanical equilibrium when there is no unbalanced force within the system or between system and surroundings. It deals with the force. The pressure in the system is the same at all points and does not change with respect to time.

Treadmill: This is a gym instrument on which we run but we don move forward because the force you trying to push forward the same force acting opposite to push backward. So this is one of the best examples of mechanical equilibrium. A system is said to be thermal equilibrium when there is no temperature difference present and the temperature remains equal at all point. A hot cup of tea has a higher temperature as compared to surrounding so this is not in thermal equilibrium.

But when you keep this in an open environment for some duration, the temperature starts emitting by radiation process to the environment and the surrounding temperature and a cup of tea temperature remains the same at that moment we can say this is in thermal equilibrium. Your email address will not be published.