THERMAL PROPERTIES OF CHEDDAR CHEESE: EXPERIMENTAL AND MODELING

Thermal properties (thermal conductivity, thermal diffusivity and heat capacity) of Cheddar cheese were measured as a function of cheese age and composition. The composition ranged from 30–60% moisture, 8–37% fat, and 22–36% protein (wet basis). The thermal conductivity and heat capacity ranged from 0.354–0.481 W/m °C and from 2.444–3.096 kJ/kg °C. Both thermal conductivity and heat capacity increased with moisture and protein content and decreased with fat content. The thermal diffusivity ranged from 1.07×10^?7 ? 1.53 × 10^?7 m²/s. There was no significant relationship between thermal diffusivity and moisture, fat and protein content of cheese. No statistically significant effect (at the 10% level) of age (0 to 28 wk) on thermal properties was observed. Models predicting thermal properties as a function of cheese composition were developed and their predictive ability was compared with that of empirical models available in the literature. In addition, several theoretical thermal conductivity models were evaluated for their usefulness with Cheddar cheese. Published thermal conductivity models cannot accurately predict (mean error was from 3.4 to 42%) the thermal conductivity of Cheddar cheese.     

Thermal properties of wood-gypsum boards

Transient simultaneous measurements of thermal conductivity, volume heat capacity and thermal diffusivity of laboratory wood-gypsum boards have been performed with ISOMET 2104 at room temperature. The influences of wood particle content, density and moisture content on thermal properties were investigated. The measurements were performed in a direction perpendicular to the board plane. The effect of density and wood particle content on the thermal properties may be related to the presence of voids both between and inside particles. It seems, that the dominant mechanism of heat transfer across the board is the heat conduction through the voids. Wood-gypsum boards with a density of 850–1300 kg/m³, a moisture content of 2–11% and a wood particle content of 0–35% have the following thermal conductivity of 0.189–0.753 W m^-1 K^-1, volume heat capacity of 0.683–1.43×10⁶ J m^-3 K^-1 and thermal diffusivity of 0.171–0.367×10^-6 m² s^-1; their magnitudes are higher than those ones of OSB, MDF, particleboard and plywood.     

Thermal properties of wood-gypsum boards

Transient simultaneous measurements of thermal conductivity, volume heat capacity and thermal diffusivity of laboratory wood-gypsum boards have been performed with ISOMET 2104 at room temperature. The influences of wood particle content, density and moisture content on thermal properties were investigated. The measurements were performed in a direction perpendicular to the board plane. The effect of density and wood particle content on the thermal properties may be related to the presence of voids both between and inside particles. It seems, that the dominant mechanism of heat transfer across the board is the heat conduction through the voids. Wood-gypsum boards with a density of 850–1300 kg/m³, a moisture content of 2–11% and a wood particle content of 0–35% have the following thermal conductivity of 0.189–0.753 W m^-1 K^-1, volume heat capacity of 0.683–1.43×10⁶ J m^-3 K^-1 and thermal diffusivity of 0.171–0.367×10^-6 m² s^-1; their magnitudes are higher than those ones of OSB, MDF, particleboard and plywood.     

BULK THERMAL CONDUCTIVITY AND DIFFUSIVITY OF SOYBEAN

Bulk thermal conductivity of soybean, determined by the transient heat flow method, exhibited positive linear correlation with moisture content. The bulk thermal conductivity values increased from 0.1157 to 0.1756 W/m-K in the moisture range of 8.1 to 25% d.b. Further, thermal diffusivity of soybean, computed from the values of thermal conductivity, specific heat and bulk density showed linear increase from 2.94 × 10⁻⁴ to 3.07 × 10⁻⁴ m²/h in the specified range of 8.1 to 25% d.b. moisture content.     

THERMAL CONDUCTIVITY AND DIFFUSIVITY OF SHELLED CORN AND GRAIN

Increasing energy costs have stressed the importance of calculation of heat and mass transfer in a grain bulk in order to be able to optimize drying facilities. Therefore values for the thermal conductivity and diffusivity of grain and especially shelled corn were determined. The investigations were carried out for single kernels as well as for grain and corn in bulk. Thermal conductivity and diffusivity were found to be mainly dependent on moisture content. Regression analyses showed a good correlation between moisture content and thermal conductivity or diffusivity, respectively.     

Thermo‐physical properties of composite bread dough with maize and cassava flours

Composite wheat–cassava and wheat–maize flours were produced in ratio 100:0. 60:40, 50:50, 40:60 and 0:100 respectively. Thermo‐physical properties of bread dough were determined. For wheat –cassava composite bread dough, moisture content ranged between 44.02 ± 2.04 to 51.31 ± 2.99% dry basis (db), density (1035.2 ± 20.4 to 975.6 ± 12.6 kg m^?3), specific heat capacity (2.51 ± 0.61 to 3.01 ± 0.42 kJ kg^?1 K) and thermal conductivity (0.362 ± 0.13 to 0.473 ± 0.12 W mK^?1). While wheat–maize mixture gave 44.14 ± 1.94 to 45.09 ± 1.26%(db) of moisture content, 981.4 ± 16.3–960.4 ± 22.5 kg m^?3 density, 1.77 ± 0.17–2.61 ± 0.63 kJ kg^?1 K specific heat capacity and 0.36 ± 0.07–0.39 ± 0.02 W mK^?1 thermal conductivity. Effects of substitutions was significant on moisture content and thermal conductivity of dough while non significant influence was recorded on density and specific heat capacity at P < 0.05.     

Thermophysical Properties of Sugarcane,Palmyra Palm,and Date-palm Granular Jaggery

Effect of moisture content on thermo-physical properties of sugarcane, palmyra palm, and date-palm granular jaggery were investigated. Thermal conductivity and diffusivity were determined by line-heat-source transient heat-transfer methodology, while specific heat was calculated from additional data on bulk density of the samples. Thermal conductivity, diffusivity, specific heat, and bulk density was found to vary from 0.08 to 0.39 W m^?1 K^?1, 0.10 to 0.13 × 10^?6 m² s^?1, 1.19 to 2.97 kJ kg^?1 K^?1, and 510 to 1310 kg m^?3, respectively, for a moisture range of 2.0–14.3 (%d.b.); all at an average temperature of 30°C. All these properties except—thermal diffusivity—followed an increasing trend; with the increase in moisture content, each showed a high correlation coefficients. The variation of thermal diffusivity was found to be insignificant.     

THERMOPHYSICAL PROPERTIES OF FRESH AND ROASTED COFFEE POWDERS1

The present work deals with experimental determination of bulk specific heat, bulk thermal conductivity, bulk and true density and moisture content of Columbian and Mexican coffee bean powders. Specific heat was determined by DSC, thermal conductivity by modified Fitch apparatus, density by stereopycnometer and moisture contents by standard vacuum oven method. Specific heat values showed marginal rise over the temperature range (45 to 150C) studied. Thermal conductivity values, determined in the temperature range of 20–60C were not found to have any definite trend with rise in moisture in the experimental range of 4.8 to 9.8% moisture (dry basis). Bulk density of powders varied appreciably (1.298 to 0.882 g.cm^?3), while the change was negligible for true density (1.361 to 1.092 g.cm^?3) with the degree of roasting. Statistical analysis of the data shows the reliability of the experimental determinations. Suitable correlations were developed to determine bulk specific heat and bulk density.     

Effect of Moisture Content on Density, Heat Capacity and Conductivity of Restructured Pork/Soy Hull Mixtures

Sixteen restructured pork/soy hull mixtures were studied. Incorporation of unprocessed and processed and two particle sizes of hydrated soy hulls in the mixture resulted in moisture contents ranging from 74% to 85%. Standard laboratory procedures were used to measure density, heat capacity and thermal conductivity. Thermal diffusivity was calculated as a mathematical function of these three properties. Thermal diffusivity values were affected the most (1.14–2.01 × 10^-7 m²/sec) by moisture, followed by heat capacity (2.75–4.18 J/g°C), and thermal conductivity (4.80–5.72 x 10^-3W/cm°C). No significant changes in density occurred (1.02–1.06 g/cm³).     

Influence of Moisture Content and Temperature on Thermal Conductivity and Thermal Diffusivity of Rice Flours

The thermal conductivity and thermal diffusivity for four types of rice flours and one type of rice protein were determined at temperatures ranging from 4.8 to 36.8?°C, bulk densities 535 to 875.8 kg m^?3, and moisture contents 2.6 to 16.7% (w.b.), using a KD2 Thermal Properties Analyzer. The thermal conductivity of rice flours and rice protein increased with the increase in temperature, moisture content as well as with increase in bulk density. Thermal diffusivity decreased with increase in moisture content, increase in temperature and bulk density. The thermal conductivities values obtained were within the range of 0.045 to 0.124 W m^?1 K^?1 whereas the thermal diffusivity values were in the range of 0.094 to 0.138 mm² s^?1.     

Thermal Properties of Kerstingiella geocarpa Seeds as Influenced by Moisture Content

The specific heat capacity, thermal conductivity and thermal diffusivity of Kerstingiella geocarpa seeds were determined as a function of moisture content. The initial moisture content of the seeds determined using the ASAE standard test was 10.0 % (d.b). The specific heat capacity of Kerstingiella geocarpa seed increased from 155.83 to 204.45 Jkg^?1k?1, as the moisture content increased from 10 to 30 % (d.b). The thermal conductivity of the seed increased from 5.13 × 10^?2 to 4.87 × 10^?1 Wm^?1k^?1, as the moisture content increased. The thermal diffusivity of the seed increased from 2.35 × 10^?4 to 3.66 × 10^?3 m²s^?1, as the moisture content increased. These values indicate the ability of the Kerstingiella geocarpa seed to retain heat when processed. The regression models that could be used to adequately express the relationships existing between the thermal properties of the Kerstingiella geocarpa seed and moisture content were established.     

Heat transfer properties of chicken-drum muscle

Thermal properties namely bulk density, specific heat capacity and thermal conductivity of chicken-drum muscle were measured over a wide range of muscle moisture content and temperature. Variation of muscle density was quadratic with respect to moisture content. Specific heat capacity and thermal conductivity also showed quadratic variation with moisture content. The effect of temperature on specific heat capacity was related to the state of thermal denaturation of the chicken muscle protein. Regression equations of density, specific heat capacity and thermal conductivity are presented. © 1998 Society of Chemical Industry.     

Thermophysical Properties of Extruded Beef/Corn Flour Blends

Thermal properties, specific heat, and thermal conductivity of three beef/corn meal blends extruded to reach end product temperatures of = 91°C and 109°C were analyzed. Density was also measured and used to calculate thermal diffusivity. The extruded products had densities of 1,054 to 1,091 kg/m³; specific heat was 2.944 to 3.055 kJ/ kgK; and thermal conductivity, 0.26 to 0.39 W/mK. Calculated values of thermal diffusivity were 0.831 to 1.200 (xl0^-7m7sec). With the exception of specific heat, extrusion conditions and formulation affected some of the products physical characteristics and thermal properties.     

Wheat Gluten and Glutenin Thermal Conductivity and Diffusivity at Extruder Temperatures

Thermal properties (thermal conductivity and diffusivity) of gluten and glutenin were measured in the temperature range 60-175°typically used in extrusion processing. Thermal conductivity and diffusivity of gluten decreased with increasing temperature and increased with increasing moisture content. Thermal conductivity and diffusivity of glutenin increased with temperature and moisture content. Thermal conductivity of gluten was 0.06-0.35 W/m-C and glutenin was 0.29-0.49 W/m-C for the temperature range 60-175°and moisture content range of 0-30%.     

PHYSICAL and THERMAL PROPERTIES of GORGON NUT

Bulk density, true density, angle of repose, coefficient of friction on metal surfaces, specific heat, thermal diffusivity and conductivity of gorgon nut were determined using standard techniques for different sizes of nuts at moisture contents and temperatures ranging from 15 to 60% (dry basis) and 25 to 55C, respectively. the physical properties varied quadratically with moisture content. Specific heat increased with moisture and temperature but decreased with the size of the nut; whereas, the thermal diffusivity showed a reverse trend. Thermal conductivity increased with moisture content but did not follow any trend with temperature within the range of the study. the physical and thermal properties data at various moisture contents and temperatures were used to develop equations for different sizes of gorgon nuts.     

Thermo-physical Properties of Cooked Ham

Experimental studies were carried out to determine thermal conductivity (k), thermal diffusivity (α), specific heat at constant pressure (c_p), and density (ρ) of cooked ham as functions of both sample moisture content (M) and temperature (T). Thermal conductivity was measured using the heat-line-source probe, thermal diffusivity by Dickerson method, specific heat by differential scanning calorimeter, and density by pycnometer assembly. Temperature ranged from 3.08 °C to 74.08 °C, corresponding to the cooking process, and moisture ranged from 40.0 to 73.0% (w.b.). Equations are provided for α as a function of M, c_p as a function of T, and ρ as a function of both M and T. Results for thermal conductivity are compatible with those published in the literature.     

Increasing the moisture content of imitation cheese: effects on texture, rheology and microstructure

Increasing moisture content may be a practical and cost-effective means to control the functional properties of imitation cheese. Imitation cheeses with moisture contents of 46, 50, 52 and 54 g/100 g were manufactured. An increase in the moisture content of the imitation cheese resulted in significantly increased meltability, tan values and decreased hardness (all P<0.05). The relationship between moisture content (x) and meltability (y) was described by the model (r²=0.99). A linear relationship emerged between moisture content (x) and hardness (y), where (r²=0.95) but cohesiveness was unaffected by moisture content. Increasing the moisture content to 52 or 54 g/100 g led to pockets of free water within the cheese and larger but fewer fat globules. The maximum level of moisture that the cheese matrix can retain appears to be 54 g/100 g.     

Rapid Inverse Method to Measure Thermal Diffusivity of Low‐Moisture Foods

Thermal diffusivity is an important transport property needed in modeling and computations of transient heat transfer in basic food processing operations. In addition, the prediction of nutritional and microbial changes occurring in food during thermal processing requires knowledge of thermal diffusivity of foods. The objectives of this study were to develop a new nonisothermal and nonlinear determination method of thermal diffusivity and to measure the thermal diffusivity of low‐moisture foods using that new method. Thermal diffusivities of 5 kinds of low‐moisture foods (almond meal, corn meal, wheat flour, chocolate fudge, and peanut butter) were estimated using an inverse technique. Samples were canned and heated at the surface in a water bath at about 70 °C. The 1‐dimensional transient heat conduction problem for radial coordinates was solved with a finite‐difference model. The thermal diffusivity of each of the 5 samples was determined by the ordinary least squares and sequential estimation methods, respectively. Predicted and observed temperature matched well, with maximum residuals of 0.9 °C. The thermal diffusivity values of the samples ranged from 9.8 × 10⁻⁸ to 1.3 × 10⁻⁷ m²/s. The advantages of this method are that the device and the estimation method are simple, inexpensive, rapid, and can handle large spatial temperature gradients, such as those experienced during heating of low‐moisture foods. The results obtained in this study will be useful in the design of equipment and in calculations for the thermal processing of low‐moisture foods.     

Moisture loss and oil uptake during deep fat frying of “Kroštula” dough

The mechanism of moisture transfer by diffusion and uptake of frying oil was studied during deep fat frying of Krotula dough with an initial moisture content of 0.4358 kg/kg (db). The experimental data were found to fit well to a first-order exponential model for moisture transfer (with a regression coefficient of 0.99). The effective moisture diffusivity of Krotula dough was determined for two periods of moisture loss (intensive in first 60 s and constant after 60 s of frying). In the frying range 0–60 s at temperatures of 160, 170, 180 and 190±1 °C, the effective moisture diffusivity values were 5.837, 6.607, 8.472 and 9.728×10^–9 m²/s, from which the activation energy (30 kJ/mol) was calculated by using an Arrhenius-type equation. The effective oil diffusivity values of Krotula dough in the frying time range 0–210 s at temperatures of 160, 170, 180 and 190±1 °C were 0.932, 1.135, 1.094 and 1.054×10^–9 m²/s, from which the activation energy (5.5 kJ/mol) was calculated by using an Arrhenius-type equation.     

Thermo-Physical Properties of Distillers’ Spent Grain Pellets at Different Moisture Contents and Condensed Distillers’ Soluble Concentrations

The thermo-physical properties of distillers’ spent grain (DSG) pellets are the key input parameters for the heat and mass transfer modeling of the drying process and for the design of the suitable drying and storage systems. The main thermo-physical properties like particle density, thermal conductivity, and specific heat capacity of DSG pellets were determined using standard laboratory methods. The effects of moisture content, percentage of condensed distillers’ solubles (also called solubles), and temperature on these selected properties were determined. The average particle density of the DSG pellets with 0, 10, 30, and 50 % solubles was found to be in the range of 898.8–1136.7 kg/m³. It was observed that the particle density of DSG pellets increased with an increase in condensed distillers’ soluble concentration and decreased with an increase in moisture content. Thermal conductivity (0.17–0.42 W/(mK)) and specific heat (1.76–3.47 kJ/(kgK)) of the DSG pellets increase linearly with an increase in moisture content, soluble concentration of the sample, and temperature of the drying medium. Three multiple linear regression equations were developed for predicting these properties as a function of moisture content, soluble concentration, and temperature with R ² value ≥0.86.