Incoming Heat Flux Research Articles

Comment on “application of the Canadian regional climate model to the Laurentian Great Lakes region: Implementation of a lake model”

A recently published slab model formulation of lake thermodynamics (Goyette et al., 2000), including an empirical factor to adjust the incoming heat flux so that the modelled lake surface temperature agrees with observed climatology, leads to a distinct lack of energy conservation. The empirical adjustment conceptually represents an exchange of heat between the mixed‐layer water (the slab that is explicitly simulated in the model) and deeper layers of water. It ensures a realistic temporal progression of temperature in the mixed layer, but the thermodynamic balance of the deeper water is not considered. When the deeper water is considered, it is found that the empirical adjustment accounts for the entire heat input to the deeper water, and on an annual mean basis, it is considerably unbalanced. This reveals a flaw in this model concept and, although not entirely invalidating the model, it needs to be included as a caveat in its use.

Meteorological pre-processing of incoming solar radiation and heat flux over a sparse boreal forest at a northern site during winter conditions

Measurements from Northern Finland on radiation and turbulent fluxes over a sparse boreal forest with snow-covered ground were analysed. The measurements represent harsh winter conditions characterised by low sun angles. The absorption of incoming solar radiation in clear skies (turbidity) was found to be a strong function of the solar elevation. At low solar elevation angles, commonly used expressions for turbidity did not fit the measurements well. A simple energy balance type met-processor performed well during daytime, but it was not satisfactory during night time. Simplifications and possible improvements in the energy balance model are discussed.

Generalized Finite Element-Harmonic Analysis for Nonlinear Heat Transfer

A numerical method is devised for the solution of nonlinear problems in bodies whose boundaries can be uniquely described in cylindrical coordinates. It provides a generalization of standard finite element (FE) Fourier analysis to nonlinear problems with asymmetric geometry and material properties. One class of problems in this category is that involving nonlinear steady-state heat transfer in a body with asymmetric geometry, thermal loading, and thermal properties. The proposed method combines FE discretization in a plane or interval and a symbolically implemented Fourier decomposition in the circumferential direction. Applications include space structures or structural members in space structures exposed to incoming solar heat flux and emitting thermal radiation

The anisotropic overall thermal conductivity induced by preferentially oriented pores

The differential formulation employing a self-consistent concept is extended to study the directional response of overall thermal conductivity in a porous medium containing anisometric pores. The anisometric pores distribute in a special direction relative to the incoming heat flux vector, rendering an anisotropic overall thermal conductivity tensor when discharging the heat flow in the porous medium. Cylindrical cavities with insulated surfaces are exemplified in the numerical example, demonstrating the directional response. Effects of the preferential orientation and the aspect ratio of the cylindrical cavities on the anisotropy of the overall thermal conductivity tensor are studied.

Amalgamation of traditional and modern cooling techniques in a passive solar house: A design analysis

In this presentation, different roof and wall designs/treatments have been proposed, incorporating modern and ancient features together, for passive cooling. On the basis of their thermal analysis (by solving energy balances of different components of roof and walls, etc.), the variation of living room temperature in different cases has been computed numerically for Jodhpur (India). The climatic conditions of Jodhpur are characterized as hot and dry. It is inferred that (a) evaporative cooling with an air cavity in the roof is the best option to reduce the incoming heat flux through the roof if water is easily available and (b) a thin layer of cow dung slurry inside the wall cavity reduces the incoming heat flux through the walls. It is better than solid walls and air cavity walls.

A comparison of passive cooling techniques

A comparison of passive cooling techniques of a non-airconditioned apartment for Delhi climate condition has been presented. The various cooling techniques namely, evaporative cooling, movable canvas, roof gardens, shading effect and air cavity in walls etc. have been incorporated in the thermal analysis. Numerical computations were carried out for Delhi climatic conditions and it is inferred that 1. (i) the evaporative cooling is the best option to reduce the incoming heat flux through the roof if the water is easily available, and 2. (ii) the air cavity also reduces the incoming flux entering through walls.

Experimental characterization of the heat transfer in a free-falling-particle receiver

This paper describes the measurements performed on a Free Falling curtain of spherical beads being irradiated in a high-flux solar furnace. The curtain of spherical beads is part of a direct absorption solar receiver concept, which replaces the conventional water and steam receiver (DAR) and is potentially more efficient and less expensive than a conventional receiver. To adequately describe a DAR a series of experiments have been designed and implemented to measure radiative heat flux and particle temperatures. The extinction coefficient for the DAR bead curtain has also been measured. These data and results along with a new method for measuring bulk bead temperature will be discussed. A method is also described which uses the angular distribution of incoming radiative heat flux to estimate the incoming intensity field.

Evaporation and heat exchanges between the sea and the atmosphere in the Gulf of Trieste during 1988

Daily mean values of meteo-oceanographic parameters are used to compute evaporation and heat fluxes between the sea and the atmosphere in the Gulf of Trieste during 1988. Incoming solar radiation, long-wave radiation, latent and sensible heat fluxes are considered in the total heat budget. The contribution of the single parameters entering each formula is examined and a comparison between the results from different evaporative formulae is performed. The total heat budget for the year considered gives a net loss of energy of 21 W/m2 which must be supplied by the heat transported by marine currents. The balance is positive for the sea surface from April to July, negative for the remaining period. Long-wave radiation accounts for the 45% of the total heat loss, latent heat for 53% and sensible heat for 2%. Computed annual mean evaporation is 1058 mm, with high peaks of more than 15 mm/day during strong Bora wind events. Evaporation slightly prevails on precipitation giving a net water loss of 30 cm. A comparison with what is found in the literature shows these results representative of the entire North Adriatic Sea. They confirm that this basin represents a sink of heat whose role in the general Mediterranean circulation consists in trasforming surface warmer waters coming from South in denser ones.

Variability of the sea surface temperature in the eastern equatorial Pacific during 1986–1988

Time series of surface wind and upper ocean temperature and velocity, obtained from equatorial moorings along 110°W, are used to assess the importance of various oceanic and atmospheric processes in the variation of the mixed layer temperature for the period January 1986 to June 1988. This period coincides with the onset and development of the 1986–1987 El Niño‐Southern Oscillation warm event and a subsequent cold event in 1988. Results of the temperature equation analyses indicate that seasonal and interannual variability of sea surface temperature (SST) in the eastern Pacific cannot be accounted for by observed surface heat flux; oceanic processes play an important role in the heating of the surface water. Although no single process dominated SST change, the most important processes in the mean balance were the net incoming surface heat flux, the penetrative solar radiation, and the vertical turbulent flux out the bottom of the mixed layer. The mean vertical entrainment could not be estimated with the available data. On the seasonal time scales, both the vertical turbulent heat flux and the vertical entrainment variations were well correlated with SST change. Zonal advection was a significant contribution to the heat flux variability, but its fluctuations were poorly correlated with the mixed layer heating. In particular, it was found that zonal advective heat flux tended to be out of phase with the spring warming. At higher frequencies, little zonal advective heat was found to be associated with the passage of a Kelvin event in January 1987. Surprisingly, meridional heat advection appeared more important than the zonal heat advection in modifying the local SST as this event passed the mooring location.

In-situ Heat Release Measurement Of Smoldering Combustion Of Wood Sawdust

To evaluate in-situ heat release rate of the smoldering combustion, temperature histories in a wood sawdust layer were measured. There were three distinct region in a measured temperature history. They were attributed to the preheat region, the charring region, and the decaying region. Boundaries between those regions were identified on the temperature history as points of inflection. The smoldering front was considered to be the boundary between the preheat and the charring regions. The fact that the temperature history has a point of inflection at the smoldering front means heat release at the front. The heat release rate at the front if incoming and outgoing heat fluxes at the front were evaluated. To evaluate these fluxes, temperature profile in the layer was derived from the temperature histories at several heights and spread rate of the smoldering front, which was constant during a test run. Heat release rate at the smoldering front was estimated from the difference between the incoming and outgoing heat fluxes at the smoldering front. The evaluated heat release rate showed no dependence on the atmospheric oxygen concentration. From the result, the reaction occurred at the smoldering front was considered to be a pyrolysis reaction. However, the activation energy evaluated from the heat release rate was 13.7 kJ/mol whicH is much smaller than usually referred activation energy for wood pyrolysis. Oxygen in atmosphere is considered to work, at least, as a catalyst of the reaction.

Periodic heat flux through extended structures and projections of buildings

An explicit expression for periodic heat flux through extended structures and projections has been obtained in terms of Fourier series. Numerical results show that it is imperative to include hourly variation of solair and ambient temperatures for realistic thermal load calculation of buildings with projections. It is interesting to note that projections may enhance or reduce thermal fluctuations in the incoming heat flux depending upon their transverse dimensions.

Numerical analyses of plasma and neutral particle behavior and design criteria for poloidal divertor in fusion experimental reactor

Divertor performance is investigated using a numerical model for various incoming ion and heat fluxes and geometrical configurations. It is shown that the solution is double-valued over a part of the range of the input fluxes, and that helium exhaust and cold and dense plasma formation will be attained even in open geometry for the expected range of the incoming ion flux.

Freshwater contents and heat budgets of James Bay and Hudson Bay

The freshwater and heat budgets of James Bay and Hudson Bay showed that for a yearly cycle the annual ice cover and runoff are major and equal components of the freshwater budgets. James Bay has a baywide freshwater layer thickness of 6.25 m, while Hudson Bay has a 4.7 m layer; these represent summer residence times of 10 months and 4.1 years, respectively. The heat budget results indicated that the incoming surface heat flux is mainly balanced by the heat required to melt the seasonal ice cover and bring the water temperature up to the observed summer values. Thus, an assessment of hydroelectric developments in the surrounding watersheds should not only investigate the changes that will occur in the marine environment, but also in the seasonal ice cover, as they together determine the oceanic climate pattern of the two bays.