Janusz Wojtkowiak

Measurements of temperature distribution in ground

Temperature distributions in ground are important, for example, for calculations of heat losses of buildings to the ground, for design of thermal energy storage equipment and ground heat exchangers, and for analysis of biodegradation processes of organic substances and processes of nitrification. In this communication, the temperature distributions measured in ground since the summer of 1999 to the spring 2001 are presented. The investigation has been done in Poznan for two different ground surface covered locations (car park and lawn). Temperatures were measured with thermocouples distributed in ground at a depth from 0 to 7 m (car park) and from 0 to 17 m (lawn). It was found that the short-period temperature variations reached a depth of approximately 1 m. From July to the end of September from the surface region at ground depth (below about 1.5 m) a heat flux of density q = 3.6 W/m 2 was transferred. The measurements show also that during the summer period the temperature of ground under the bare surface (car park) below I m was about 4° higher in comparison with the temperature of ground covered with short grass (lawn). However, in winter, the temperature distributions were almost the same. A comparison of the Buggss formula for the ground temperature distribution adopted to the European region of the Poznan city shows a good agreement with the experimental data.

Simple Formulas for Thermophysical Properties of Liquid Water for Heat Transfer Calculations (from 0°C to 150°C)

Abstract In this communication, simple formulas (based on the latest experimental tabulated data) for 11 physical properties of liquid ordinary water substance at saturation state—saturation pressure, density, volumetric thermal expansion coefficient, specific volume of saturated vapor, specific enthalpy, specific heal, latent heal of vaporization, thermal conductivity, dynamic viscosity, Prandtl number, and surface tension as a function of temperature (from 0 to 150°C)—which are used in heat transfer calculations for heat exchangers in heating systems and also for many other technological applications, are presented. Also, the uncertainties of these formulas are given. In most practical cases the pressure of liquid water is within the range from 1 to 10 absolute bar, which makes it possible to neglect the effect of pressure. All properties of saturated liquid water calculated with the recommended formulas are tabulated with a temperature increment of 5°.

Efficiency of the Horizontal Single Pin Fin Subjected to Free Convection and Radiation Heat Transfer

In this communication, the results of numerical calculations of the heat transfer coefficient and temperature distribution along the horizontal single pin fin in still ambient air, as well as the fin efficiency, are presented and compared with classical analytical results in the case of the constant heat transfer coefficient fin theory. The measured temperature distributions along the two low carbon steel pin fins having a length-to-diameter ratio of 35—one covered with the polished nickel and the other painted mat black—agree very well with the numerical results and are higher than the classical results. The analytically calculated fin efficiency does not differ significantly from the results of the numerical calculations if they are compared for the same dimensionless fin parameter in which the heat transfer coefficient is determined for the fin base temperature. More extended numerical calculations showed that beyond the fin parameter of five, the analytical results of the fin efficiency are higher than the numerical results by no more than about 1%. The largest difference between the classical and numerical fin base efficiencies is about 3.5%, and it was observed at a fin parameter of about 1, where the length of the pin fin has the optimal value based on the classical theory.

Flow and heat transfer in a pipe containing a coaxially-rotating disk

A numerical investigation was made of steady laminar flow and convective heat transfer in a pipe constricted by a coaxially rotating disk. The analysis was executed by using the finite volume approach. Calculations were made for the through-flow Reynolds numbers (based on the pipe radius) of 10, 25, 50, 75, 100, 125, 150, the rotational Reynolds numbers of 0, 250, 500 and 1000, for the disk-to-pipe radius ratios of 0.9, 0.95 and 0.99, and for the Prandtl numbers of 0.7 and 7. The heat transfer rate, the pressure drop coefficient, and the temperature distributions are determined. The results show that the temperature and flow characteristics are substantially affected by the rotation of the disk. In the disk downstream-flow, the wall and disk recirculation zones are noticed. The swirl imparted to the flow measurably increases the heat transfer rate. The increase is especially noticeable when the wall recirculation region does not exist. Physical rationalizations are made of the computed flow features, and a brief description is given of the Nusselt number distribution.

Inherently Linear Annular-Duct-Type Laminar Flowmeter

where: C is a constant depends on a duct cross-section shape , A is the duct cross-sectional area, Dh is the hydraulic diameter of the duct, K is the incremental pressure drop number in a fully developed flow region depends both on the duct cross-section shape and on the inflow conditions , L is the distance between the flowmeter pressure taps, is fluid density, and is fluid kinematic viscosity. The first component on the right-hand side of Eq. 1 is the pressure drop in the fully developed flow. The second one describes some additional pressure drop due to momentum change and accumulated increment in wall shear between developing flow and developed flow 1 . It is seen that the relationship between produced differential pressure P and flow rate Q is not linear. As a result, in the majority of commercial laminar flowmeters, to obtain precise Q values software corrections are required. In some of the commercial “laminar flow elements” the entrance effect is ignored as a relatively low one. In order to eliminate the necessity of reading corrections and to achieve inherent linearity the second term of Eq. 1 must be removed. It can be done by locating the first pressure tap P1 at the beginning of the fully developed flow region. As the entrance length Le increases with the Reynolds number Re=DhQ / A , the distance between the duct entrance and the pressure tap P1 should not be shorter than the entrance length for the maximum flow rate, i.e., for the laminar-turbulent transition Reynolds number. The main aim of this work was to determine the design recommendation for the inherently linear laminar annular-duct flowmeter. The pressure distribution along the annular duct was measured. The entrance lengths for various inlet conditions and Reynolds numbers were investigated.

Viscosity Correction Factor for Rotameter

This paper describes how the developed formula for rotameter flow coefficient using the rotameter scale provided by a manufacturer and valid for a specific fluid and for design (or calibration) flow conditions allow them to determine the actual flow rate at measurement conditions and for different fluid having different viscosity or allow them to determine the viscosity correction factor. The developed theory has been verified experimentally using typical rotameter equipped with the plumb type float, for water of 15 C and having a flow rate range from 10 to 100 l/hr. A very good agreement between theoretical calculation and calibration results was obtained for water flow at 88 C. In this case the kinematic viscosity ratio was {nu}{sub 15}/{nu}{sub 88} = 3.46 and the density correction factor was F{sub dns} = 1.019 and the viscosity correction factor varied from F{sub visc} = 1.095 at 100 l/hr to F{sub visc} = 1.93 at 10 l/hr.