Edward Kolbe

Recommended design parameters for thermal conductivity probes for nonfrozen food materials

Abstract This paper analyzes the various design parameters of the thermal conductivity (k) probe and makes design recommendations for applications for nonfrozen food materials. The k probe is a simplified application of the line-heat source theory, but this simplification contributes to the instrument error which can be minimized by paying particular attention to the size of the k probes and materials of construction. As the diameter of the k probe decreases, its accuracy increases; however, small k probes are difficult to make. Therefore, it is recommended that users design their k probes using the highest acceptable error for their intended applications.

Analysis of various design and operating parameters of the thermal conductivity probe

Abstract The thermal conductivity ( k ) probe is derived from an idealized transient heat transfer model; therefore, there are inevitable differences between the real probe and the theoretical model. However, the k probe is still an accurate and practical measurement device with wide-ranging applications if designed and used properly. Users of a thermal conductivity probe must be aware of its limitations and the possible errors that can develop in its application. This paper includes a theoretical derivation of the k probe equation and some experimental and theoretical simulations of parameters that can cause errors in the application of the k probe. An explanation is given of the significance of certain design and operating parameters. Some of the findings in the study are that the time-correction factor is not required and contact resistance does not affect accuracy. The calibration factor is necessary since it compensates for the difference in the thermal masses of the probe and the sample. Errors due to edge effects and convection can be avoided by limiting data analysis to the linear section of the time-temperature plot. The truncation error is minimized by making β as small as possible.

Thermophysical properties of surimi paste at cooking temperature

Thermal conductivity, specific heat and density of Pacific whiting surimi paste with 74, 78, 80 and 84% moisture content were measured and modelled over the cooking temperature range. Thermal conductivity and specific heat were measured using a linear heat source probe and differential scanning calorimetry (DSC), respectively. Both thermal conductivity and specific heat were found to increase with increasing moisture content and temperature. Surimi density was found to decrease with increasing moisture content and temperature. Empirical models, based on quadratic functions of temperature and moisture content, were fitted to the experimental data for each property.

Analysis of food block freezing using a PC-based finite element package

Abstract Variable boundary condition problems characteristic of food block freezing in plate freezers present complications in computer simulations. This paper explores the application of a commercial PC-based finite element package as an alternative to programming complete heat-transfer models. Results of the package gave reasonable agreement with measured data. The sensitivity of freezing-time calculation to important model parameters was also investigated. The parameters in decreasing order of influence were apparent specific heat, geometric dimension, overall heat transfer coefficient, ambient temperature, thermal conductivity, and density.

Analysis of Heat Transfer in Surimi Paste Heated by Conventional and Ohmic Means

Abstract Heating of surimi paste was studied to determine the effects of conventional (water-bath) cooking vs. ohmic (electrical resistance) cooking. Results of both experiments and models were observed over the cooking temperature range for Pacific whiting surimi paste having a salt content of 2% and moisture contents of 74% and 80%. A good correlation between model and experiment resulted using a finite element analysis. Ohmic heating under a high voltage gradient (1200 V/m) resulted in a heating rate 11 times higher than that of conventional (90°C water bath) heating for a cylindrical sample of 19 mm diameter. Results also showed the significant effects of the two heating mechanisms upon the time during which the sample center dwells within the critical enzyme activity range. The effects of voltage gradient across the sample, moisture content, heat exchange with the surrounding ambients, and electrode design were also investigated. Heat leakage to the sample holder and surroundings caused a significantly lower heating rate in the outer edges of the sample compared to the center.

A round robin evaluation of differential scanning calorimetry to measure transition enthalpy and temperatures

Twelve laboratories participated in a thermal analysis study to determine onset and peak transition temperatures and enthalpy, for both starch gelatinization and tristearin melting and crystallization. The reproducibility of these results was compared for three types of Differential Scanning Calorimeters (DSC). The transition temperatures and enthalpy results for starch were similar between labs, as were the melting and crystallization temperatures for tristearin. Enthalpy values for tristearin were consistent among most labs, however significant differences existed between DSC types. From this data it appears that some differences between laboratories do exist, but reliable comparisons can usually be made when the DSC is used to evaluate the thermal properties of foods.

Refrigeration Energy Prediction for Flooded Tanks on Fishing Vessels

Calculations combined with documented experience predict and compare direct energy consumption for the two onboard flooded-tank refrigeration systems in current use. These are RSW (refrigerated seawater) which uses mechanical refrigeration, and CSW (chilled seawater) which uses ice brought from shore. RSW is found to consume energy at roughly half the rate predicted for CSW; seawater temperature has a major influence on results.

Measurement and prediction of freezing times of vacuum canned Pacific shrimp

Abstract Freshly cooked Pacific shrimp, vacuum packed in cans fitted with monitoring instruments, were frozen under industrial conditions. Surface heat transfer coefficients were determined experimentally using aluminium cyclinders. Freezing times were measured and also calculated using Planks equation and the formulae of Cleland and Earle. The investigation indicated that the vacuum level had little effect on the freezing time and that freezing time essentially doubled when cans were enclosed in a commercial carton. For the prediction of freezing times, Cleland and Earles method was found to be more accurate than Planks for the tests performed, with predicted values within ± 10% of measured values.

ESTIMATING ENERGY CONSUMPTION IN SURIMI PROCESSING

Documented power consumption rates for individual food processing operations are applied to surimi processing, freezing, and cold storage. Electrical power consumption is predicted to be 314 and 272 kWh/t (285 and 247 kWh/ton) for representative surimi plants in Oregon and Alaska, respectively, during summer operation. The influencing factors for each operation are identified.

Frozen Stabilized Mince as a Source of Pacific Whiting Surimi

Pacific whiting is available off the U.S. West Coast for about six months each year. A plan to extend the period of shore-based surimi production from whiting was investigated. Headed/gutted fish, and mince stabilized with cryoprotectants, were frozen, stored for up to six months, then processed into surimi. Measurements of texture and color were compared with those for a surimi control sample. Frozen mince stabilized with 6% sucrose and stored at -20 ° C resulted in production of good quality surimi. Pilot scale yield and freezing rate studies indicated the potential feasibility of commercial-scale production.