Axial Heat Conduction Research Articles

Heat and Mass Transfer in the Vicinity of the Vapor-Gas Front in a Gas-Loaded Heat Pipe

An analysis is presented of axially conducting gas-controlled heat pipes leading to a predictive capability for the heat and mass transfer along the heat pipe. In addition, experimental results are presented which verify the analysis, and computational results are presented which show the relative influence of various parameters which affect the system behavior. In particular it was found that axial heat conduction is of much greater importance than axial mass diffusion in establishing the wall temperature profiles and condenser heat-transfer characteristics of gas-loaded heat pipes. However, mass diffusion and, consequently, the choice of working fluid and control gas are of considerable importance in establishing the “diffusion freezeout rate” if the potential exists for freezing of vapor which penetrates the gas-blocked portion of the condenser. It is believed that the analysis and associated computer program are useful tools for designing gas-loaded heat pipes.

Thermal and economic analysis of the overlapped-glass plate solar-air heater

The heat transfer analysis of the overlapped-glass plate air heater was based on the quasi-steady state performance and was carried out in two steps. In the first step, the glass plates were assumed to absorb the short-wave solar radiation, but the long-wave emission from the plates was ignored. In the second step, the approximate glass temperatures obtained from the first-step solution were used in the exact determination of the long-wave radiation exchange between the glass plates; therefore, improved results were obtained. The computer programs in Fortran IV were run on IBM 7044 and 360 O/S computers; convective film coefficients, Reynolds numbers and boundary-layer thicknesses were determined along the glass plates throughout the whole collector. Further refinement was attained by considering axial heat conduction within the glass plates and the change in the kinematic viscosity of air along the glass plates, due to temperature variation. The air and glass plate temperatures were calculated by taking into account the uneven distribution of the incoming air stream between the glass plates, obtained from a water table analogy. The model was constructed and tested under clear-sky conditions at the Middle East Technical University, Ankara, Turkey. The air and glass temperatures were measured on each plate using copper-constantan thermocouples. The total air-flow rate was measured using a Venturi-Herschell tube. The solar radiation intensity was measured using a Kipp and Zonen actinometer and a silicon solar cell pyranometer. The cost analysis of the collector was carried out for various glass plate lengths, spacings, interest rates, three different levels of total sunshine hours, ten years of expected life, and cost figures based upon the local market prices and salary rates reported in Turkey.

Approximate determination of temperature field in heat-carrier flow with axial heat conduction and internal sources

The application is considered of the variational process to solve the axisymmetrical problem of convectlve heat exchange in which axial heat conduction and internal sources have been taken into account in laminar regime.

Heat transfer in a tube with forced convection, internal radiation exchange, axial wall heat conduction and arbitrary wall heat generation

Heat transfer in a tube with forced convection, internal radiation exchange, axial wall heat conduction and arbitrary wall heat generation

The Effect of Axial Heat Conduction on the Thermal Development of a Heat-Generating Fluid

The Effect of Axial Heat Conduction on the Thermal Development of a Heat-Generating Fluid

The effects of axial heat conduction on the freezing or melting of cylinders

NOMENCLATURE heat-transfer coefficient [Btujh ftx”F] ; dimensionle~ heat-transfer coelllcient, = H~~/k~; thermal conductivity [Btu/hft”F] ; conductivity ratio, = krJk,; dimensionless heat flux, = Q/2nk,T,; radial and axial coordinates [ft] ; outer radius [ft] ; dimensionless radial and axial coordinates, = (r ri)/ri and z/ri; length of cylinder [ft] ; temperature E”F] ; time [hr] ; dimensionless time, = T,k,t/pLrf ; material property, = L/CT,; fusion front position [ft] (see Fig. 1) : dimensionless fusion front position =(t r,)/ri; fusion front slope, [rad.] (see Fig. 1); dimensionless temperature, (T T&T,.

Heat Transfer in Magnetohydrodynamic Channel Flow

The general mathematical problem of magnetohydrodynamic thermal entrance regions is investigated for a parallel plate channel by including the Hall effect, axial heat conduction, Joule heating, and viscous dissipation. The associated eigenvalue problem is solved by the Galerkin method and the results are presented for the temperature development in a channel under uniform wall temperature conditions. It is concluded that the Hall current has considerable effect on the thermal problem and that the axial heat conduction cannot be neglected for low Peclet numbers.

Heat transfer by Hagen-Poiseuille flow in the thermal development region with axial conduction

The heat transfer in the region of circular pipes close to the beginning of the heating section is investigated for low-Peclet-number flows with fully developed laminar velocity profile. Axial heat conduction is included and its effect on the temperature distribution is studied not only for the region downstream of the start of heating but also for that upstream. The energy equation is solved numerically by a finite difference method. Results are presented graphically for various Peclet numbers between 1 and 50. The boundary conditions are uniform wall temperature and uniform wall heat flux with step change at a certain cross-section. For the latter case, also some results for the region near the end of the heating section are reported. The solutions are applicable for the corresponding mass transfer situations where axial diffusion is important if the temperature is replaced by the concentration andPe byReSc.

Axial Heat Conduction in Reactor Fuel Elements

Axial Heat Conduction in Reactor Fuel Elements

Combined Radiation and Convection in an Asymmetrically Heated Parallel Plate Flow Channel

An analysis is made of the effects of radiation exchanges upon the wall-temperature distributions in a parallel plate channel through which a gas transparent to thermal radiation is flowing. A uniform heat flux is applied at one wall, while the other wall has no imposed heat flux and only receives energy by radiation or convection from the heated wall. This situation approximates that found in the outer passage of a nuclear reactor fuel element where one channel wall is a fuel plate while the other is the support structure. Axial heat conduction is neglected in the channel walls and the gas, and constant fluid properties are assumed. The effects of a number of independent parameters, such as Stanton number, inlet gas temperature, and length-spacing ratio, are illustrated.

The Effect of Axial Heat Conduction in Fuel Plates on Maximum Heat Flow Rates and Temperatures

The standard analytical approaches to calculating the maximum temperature and surface -heat-flow rate in nuclear reactor fuel plates over-estimates both of these quantities due to the omission of c...

JPDRの重大事故時における燃料棒温度の検討

Calculations are made of JPDR fuel temperature at loss-of-coolant accident. At the accident, the reactor is scrammed either by a low-reactor-water-level signal or by a high-enclosure-pressure signal, and the core spray system is initiated.In analyses, a fuel rod and a clad is devided into six and two annulus sections, respectively. Various cases with and without control rods and a core spray system in operation are evaluated. In evaluation of a case without a core spray system in operation, axial heat conduction in UO2 is neglected before radial temperature distribution is flattened and after that, radial heat conduction is neglected to calculate axial temperature distribution.

Simplified Calculation on Thermal Transient of a UO2 Fuel Rod

A lumped parameter technique is described for simplifying the calculation of a thermal transient of a uranium dioxide fuel rod. The calculation is accomplished by evaluating the thermal resistances and capacitances of the pellet and the clad at their average condltions in time and space. Each quantlty is lumped at the middle of lts physical geometry and axial heat conduction is neglected. The equivalent thermal circuit is shown. The technique gives a fairly accurate solution in comparison with other exact methods. (N.W. R.)

The Effect of Electrodes in a Linear Pinched Discharge

A linear pinched discharge in fully ionized hydrogen or deuterium is examined theoretically under an idealized steady-state condition, when there is a pressure and an energy balance and no instabilities. Under this condition, the Joule heating caused by the axial current is balanced by bremsstrahlung radiation losses and by axial heat conduction and diffusion to the electrodes. A partial analytical solution is found assuming that the transport coefficients have the usual power dependencies on temperature throughout the plasma. It is shown that all the energy not radiated is carried to the anode, the cathode even having a negative total heat flux at its surface due to thermal effects of diffusion by the current-carrying electrons. The maximum temperature in the discharge is shown to vary directly with the voltage across the tube and only insensitively to other parameters. Further relations are derived involving the dimensions of the discharge, the current and the maximum temperature. The temperature, the line density and the electric field are plotted showing their variation along the axis. The relative importance of heat conduction and radiation losses is seen to depend only on the total axial current which is flowing. A typical example of a discharge shows that temperatures of 106 to 107 oK are quite feasible in the presence of heat losses to the electrodes.

Theoretical Temperature Distribution in Packed Bed

In a cylindrical packed tube heated under the uniform wall temperature, the partial differential equation for the temperature in the steady state is given by Eq. (1).However, when no chemical reaction takes place, Eq. (1)reduces to Eq. (1') with the assumption thatCp G is uniform over the cross section and ke, r and ke, z are uniform within the bed.The solutions can be obtained by applying the finite Hankel transform with respect to. In case of semi-infinite cylinder, Eq. (2) representing the boundary condition at the bed inlet and Eq. (3) representing the boundary condition at the inside wall surface, are applied to Eq. (1'). The solution is given by Eqs. (6) and (7), where ξi is the root of Eq. (4). On the other hand, in case of finite cylinder, Eq. (10) which stands for the bed outlet condition should be employed together with Eqs. (2) and (3), in solving Eq. (1'). The solution is shown by Eqs. (6) and (11).The temperature at the center axis of the packed tube tc and the mixed-mean temperature over the cross section tm are represented by Eqs. (8) and (9), respectively, which are modified forms of Eq. (6).However the solution for the temperature distribution in the finite cylinder will be valid for any value of δ, Eq. (11) is nearly equal to Eq. (7) when δ is less than 30 or so.The value of δ is smaller than 10 for the usual packed beds14), consequently, it may be concluded that Eqs. (6) and (7) are applicable enough, regarding the packed bed as the semi-infinite cylinder.In case the flow-rate is relatively high, k becomes small, and then Eqs. (6) and (7) are nearly equal to Eq. (13) obtained by Maeda et al4) and Marshall et al1), in which equation the axial heat conduction is neglected. But it should be pointed that Eqs. (6) and (7) serve as a good solution for the low flow-rate range, because k is not so small in this range.When chemical reaction approximated by q=q0·exp[-αl] takes place, the temperature distribution is reprerented by Eq. (14), assuming the packed bed as the semi-infinite cylinder.

Heat transfer by laminar flow in a cylindrical tube

In a recent paper1) a method for determining the discrete set of eigenvalues and the associated eigenfunctions of a certain Sturm-Liouville differential system has been developed and it has been pointed out that by this method the problem of heat transfer by laminar flow in cylindrical channels can be worked out withaxial heat conduction, viscous dissipation and any prescribedheat generation included. In the present paper an exact solution of this problem for a circular channel is presented and the first four eigenvalues and the corresponding eigenfunctions are found for Peclet numbers 100 and 1000 (hitherto worked out by assuming thatδ2T/δx2 ≪δ2T/δr2 + (1/r)δT/δr, and also neglecting the viscous dissipation). It is found that the effect of axial heat-conduction is almost negligible for higher Peclet numbers (Pe>100), and hence it can be definitely stated that the approximate solution is good enough under the usual experimental conditions. The heat transfer problem for plug flow is also solved exactly, and it is concluded that the effect of axial heat conduction is negligible forPe>100. The mean mixed temperature and the Nusselt numbers are tabulated and plotted against the Graetz number.

Unique air conditioning system serves new industrial building

Accurate modeling of solar heating or cooling with storage generally requires an accounting of the stratification within such storage tank, since overall system performance is significantly affected by the storage temperature distribution. In this study, a simple one-dimensional multi-node approach, taking into account of the axial heat conduction between nodes, has been used to theoretically analyze temperature stratification in the thermal storage tank. The results indicate that, for less collector area, the heat removal factor plays a major role in increasing the system performance, than the thermal stratification. Also, an optimum ratio of tank volume over collector area exists for a solar powered absorption air conditioning system. This paper also reviews the state of the art on different kinds of variable inlet design, and a simple new inlet design (partitioning the tank) has been introduced to effect better thermal stratification in storage tank.