Basis Of Temperature Measurements Research Articles

Estimation of Time-Varying Inlet Temperature and Heat Flux in Turbulent Circular Pipe Flow

Abstract This study addresses the conjugate heat transfer problem of hydrodynamically developed turbulent flow in a circular pipe. An inverse method is used to estimate the time-varying inlet temperature and the outer-wall heat flux simultaneously on the basis of temperature measurements taken at two different locations within the pipe flow. The present approach rearranges the matrix forms of the governing differential equations and then applies a whole domain estimation with the function specification method and the linear least-squares-error method to determine the two boundary conditions of the pipe flow. The dimensionless temperature data obtained from the direct problem are used to simulate the temperature measurements. The influence of temperature measurement errors upon the precision of the estimated results is investigated. The proposed method provides several advantages compared to traditional methods: (1) it yields a solution within a single computational iteration, (2) no prior information is required regarding the functional form of the quantities of interest, (3) no initial guesses of the unknown parameter values are required, and (4) the inverse problem can be solved in a linear domain. This study also considers the influence of the location of the temperature measurement sensors upon the accuracy of the calculated results. The numerical results confirm that the proposed method provides an efficient, robust, and accurate means of estimating the inlet temperature and outer-wall heat flux simultaneously in turbulent pipe flow.

Experimental evaluation of flow boiling incipience of subcooled fluid in a narrow channel

Experimental investigations dealt with heat transfer of R123 flowing through a narrow vertical channel of 1 mm height with one wall heated uniformly and others approximately adiabatic. Particular attention was paid to boiling incipience conditions and nucleate hysteresis phenomena. An inverse problem was dealt with as, on the basis of temperature measurement on external side of the heating foil (with thermography technique) and the measurement of the electric power supplied to this foil, it was possible to determine local heat transfer coefficients on the contact surface of the heating wall and the fluid flowing along the narrow channel. Two models of heat transfer through the heating foil and the isolating glass into the boiling liquid were proposed and discussed: one- and two-dimensional. In order to solve the two-dimensional inverse heat conduction problem the method of thermal polynomials was used with application of the least square and Trefftz computational techniques. Some exemplary results of numerical calculations on the basis of experimental data were presented for both models. The correlations concerning Nusselt number determination for R123 boiling incipience in vertical narrow channel were developed.

Investigation of the Internal Aerodynamics of the Chimney-Type Evaporative Cooling Tower

We propose a technique for determining the hydrodynamic drag of the chimney-type evaporative cooling tower on the basis of temperature measurements and the mathematical model developed by us. The presence of return vortex flows in the upper part of the subsprinkling compartment of the cooling tower is shown. The air velocity in the sprinkler and the radius of the stagnant zone in the central part have been estimated.

Field study and simulation of diurnal temperature effects on infiltration and variably saturated flow beneath an ephemeral stream

Two experiments were performed to investigate flow beneath an ephemeral stream and to estimate streambed infiltration rates. Discharge and stream‐area measurements were used to determine infiltration rates. Stream and subsurface temperatures were used to interpret subsurface flow through variably saturated sediments beneath the stream. Spatial variations in subsurface temperatures suggest that flow beneath the streambed is dependent on the orientation of the stream in the canyon and the layering of the sediments. Streamflow and infiltration rates vary diurnally: Streamflow is lowest in late afternoon when stream temperature is greatest and highest in early morning when stream temperature is least. The lower afternoon Streamflow is attributed to increased infiltration rates; evapotranspiration is insufficient to account for the decreased Streamflow. The increased infiltration rates are attributed to viscosity effects on hydraulic conductivity from increased stream temperatures. The first set of field data was used to calibrate a two‐dimensional variably saturated flow model that includes heat transport. The model was calibrated to (1) temperature fluctuations in the subsurface and (2) infiltration rates determined from measured Streamflow losses. The second set of field data was to evaluate the ability to predict infiltration rates on the basis of temperature measurements alone. Results indicate that the variably saturated subsurface flow depends on downcanyon layering of the sediments. They also support the field observations in indicating that diurnal changes in infiltration can be explained by temperature dependence of hydraulic conductivity. Over the range of temperatures and flows monitored, diurnal stream temperature changes can be used to estimate streambed infiltration rates. It is often impractical to maintain equipment for determining infiltration rates by traditional means; however, once a model is calibrated using both infiltration and temperature data, only relatively inexpensive temperature monitoring can later yield infiltration rates that are within the correct order of magnitude.

Subsurface temperature field of the Bohemian Massif

On the basis of temperature measurements in 190 boreholes we constructed a map of temperature distribution at a depth of 100 m below the terrain level and maps of temperature gradients in different depth intervals below the Earth's surface in the territory of the Bohemian Massif. Investigations were made into the effects of hydrogeological, geomorphological, structure geological and microclimatic factors on the subsurface temperature field in the Bohemian Massif together with an assessment of effects of these factors on heat flow determinations in shallow boreholes 100 – 200 m deep.

The Basis of Temperature Measurement

Measurement activity in the UK is estimated to cost about £18,000 million per annum, and yet the principles which underlie measurement processes are frequently ignored or misunderstood. In the case of temperature, one of the four or five most important parameters in industrial process control, the difficulties are compounded by the obscure nature of the quantity that is being measured. Starting with the definition of the unit, this article outlines how the temperature scale is built up and how the standards are established which form the basis of temperature measurement in the UK and internationally. Progress with improvements for the future, including the revision of the International Practical Temperature Scale, are discussed.

Determination of average heat-transfer coefficients by means of built-in?-calorimeters

The article describes an approximate method for determining the average heat-transfer coefficient on a surface upstream from a built-inα-calorimeter, on the basis of temperature measurements on the wall, as well as measurements of the local heat-transfer coefficient and the local flow velocity at the point of installation of theα-calorimeter.

Temperature-frequency dependence of the elastic constants of certain resins

The authors present the results of an experimental investigation of the elastic constants of certain crosslinked and linear polymers in the temperature range from −50 to +110° C and the frequency range from 101 to 105 Hz. The elastic constants were determined by both quasi-static and dynamic methods. The range of application of the different methods are characterized with respect to a time scale. It is shown that when certain experimental conditions are observed (strain rate, frequency), the values of the constants obtained by the different methods almost coincide. On the basis of temperature measurements it is postulated that rigid epoxies have a secondary low-temperature dispersion region.

On the law of approach to saturation in manganese-magnesium ferrite

The law of approach to saturation is studied for three differently porous samples of polycrystalline sintered Mn-Mg ferrite. Such an internal fieldH is sought that the dependenceI=I s(1−a/H 2) might be satisfied. The changes which occu rin such a dependence, if the fieldH is changed by a certain multiple of the magnetization, ere investigated by calculation. Relations are derived for this case, which are satisfied very well by the experimental values. The properties of the effective anisotropy constants ara dealt with and, on the basis of temperature measurements, these constants are ascribed with very great probability to the internal form anisotropy.

Immersion Pyrometry and Open Hearth Furnace Productivity

The use of platinum thermocouples to measure molten steel temperatures has been well established for many years, and normal steelmaking practice involves the control of tapping temperatures by this means. But in the new melting shop at the Ravenscraig works of Colvilles Limited the author has developed a method of controlling the whole open hearth process on the basis of temperature measurement at fixed intervals of time. The procedure he describes here results in a significant increase in productivity and reduction in cost per ton of steel.