An analysis is made of problems associated with prediction of and correction for temperature disturbance created by thermocouples placed beneath a surface of a heat sink (or calorimeter) exposed to heat flux during re-entry. Two of the important factors affecting temperature measurement are discussed: (a) The disturbance created by the thermocouple itself, “hot spot.” (b) The fact that the thermocouple has to be placed at some distance from the heat flux surface and thus not measuring the surface temperature. The magnitude of the surface hot spot caused by the presence of the thermocouple is determined, and optimum location of the thermocouple is found where the undisturbed surface temperature may be read with least over-all error.

R. G. TISCHERbThe Quartermaster Food and Container Institide for the Armed Forces, Chicago, IlEinois ANDThe modern trend in evaluation of lethality of canning processes (1, 2, 8) is founded on the basis of thermal history of the whole can volume rather than on that of the geometrical center of the container only, and necessitates a study of temperature distribution in the container during the canning process. With the exception of the paper by Hurwicz and Tischer (5), no such data pertaining to the foodstuffs are available in the literature.The experimental temperature distributions and their analyses presented here are a part of a larger study to determine thermal, thermobacteriological, and other physical characteristics of round of beef processed at higher than conventional retort temperatures and for short processing times. The containers used were 300 x 308 cans, retort temperature range was 225-315°F. The experimental procedure was similar to that used by Hurwicz and Tischer in Part I1 of this series ( 5 ) and has been fully described in ( 3 ) and (6).The objective of this work was to determine the temperature distributions in the can during processing and to analyze the experimental deviations from the theoretical expectations. EXPERIMENTAL TEMPERATURE DISTRIBUTIONThe temperature distributions observed and mapped during this experiment did not meet the theoretical expectations. The expected isothermal distribution for a homogeneous isotropic body heating by conduction would be symmetrical about the vertical and horizontal axes; it would change from a cylindrical distribution on the outside of the can through an ellipsoidal form to end in a point at the center of the container or, all these forms would be taken by one isothermal surface moving from the outside toward the center of the container as the heating progressed in time. Approximately such a distribution was observed by Hurwicz and Tischer (5) in No. 2 cans of beef, even though some of the constants of the heating equations had to be multiplied by a correction factor applied to all locations in the container.Mapping procedure. The locations investigated have been shown in Figure I , aiid have been assumed to be located on any half-plane of the central vertical cross-section. The diagrams of the isotherms were prepared in two steps. First, 72 interpolation diagrams were prepared for each cut of round (e.g. Fig. 2). For this purpose temperatures obtained from 3 heating curves were plotted against the points located along one of the 4 vertical axes in the can. Five-minute intervals were used from the beginning t o the end of the heating phase for each retort temperature (RT). Next, the temperatures were determined from the interpolation diagram (for heating periods increasing in length by 5-minute intervals) a t the intersection of the horizontal tema Journal Paper J-2745 of the Iowa Agricultural Experiment Station, Ames, Iowa.

No abstract

The effect of heat in the destruction of microorganisms important in the preservation of foods has been under investigation practically since the first concepts of bacteriology were enunciated. TZ 6''d (In t) = K I , d T f5? a Journal Paper KO. J2317 of the Iowa Agricultural Experiment Station, Ames, Iowa. Project No. 1123. Present address, Quartermaster Food I % Container Institute, Chicago, Illinois.Present address, The Trane Co., La Crosae, Wis.