A nonstationary method for measuring heat fluxes

Improvement of free convection heat transfer from three finned cylinders arranged at a triangle shape fixed between two walls has been investigated in this study. Three mild steel finned cylinders fixed between two walls from Pyrex glass have been used as a test rig. It has been changed the spacing between the cylinders (X/D=1,2,3 & S/D=2,4,6) and the head orientation of a triangle to the top under constant heat flux values (38, 254, 660, 1268) W/m2 and compare with case of three finned cylinders arranged in vertical array in line fixed between two wall. The experiments are carried for Rayleigh number (Ra) from (15x103 to 14 x104 ) and Prandtl number from (0.706-0.714 ). The results indicated an increase in Nu with increasing Ra for all cylinders. Furthermore,hx and Nu increased proportionally with the increasing of cylinder spacings for all heat fluxes. Also the experimental results show the case of triangle arrangement is improvement the heat transfer more than case of vertical arrangement. Heat transfer dimensionless correlating equation is also proposed. Nomeclature: Ax: surface area(m2), T∞: surrounding temperature(k), D: the outer diameter of fin (m), Kf: the thermal conductivity for air at film temperature(W/m.k), hx: Local convection heat transfer(W/m2.k), Gravitational acceleration(m/s2), I: Electric current (Amp), Nu: Nusselt number, Pr: Prandtl number

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OBSERVATION ON HEAT FLUXES ABOVE THE TERRESTRIAL SURFACES IN THE CENTER OF URBAN AREA AND THE BAY IN TOKYO

Journal of Architecture and Planning (Transactions of AIJ) ◽

10.3130/aija.59.65_2 ◽

1994 ◽

Vol 59 (463) ◽

pp. 65-73 ◽

Cited By ~ 4

Author(s):

Hidetaka KOMIYA ◽

Tatsuo OKA ◽

Taizou SHIMOKAWA ◽

Hiroyuki AKAGAWA ◽

Junn SUGIYAMA

Keyword(s):

Urban Area ◽

Heat Fluxes

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Ecosystem modeling of methane and carbon dioxide fluxes for boreal forest sites

Canadian Journal of Forest Research ◽

10.1139/x00-164 ◽

2001 ◽

Vol 31 (2) ◽

pp. 208-223 ◽

Cited By ~ 11

Author(s):

Christopher Potter ◽

Jill Bubier ◽

Patrick Crill ◽

Peter Lafleur

Keyword(s):

Carbon Dioxide ◽

Boreal Forest ◽

Land Surface ◽

Net Primary Production ◽

Ground Cover ◽

Methane Flux ◽

Growing Season ◽

Ecosystem Model ◽

Heat Fluxes ◽

Water Levels

Predicted daily fluxes from an ecosystem model for water, carbon dioxide, and methane were compared with 1994 and 1996 Boreal EcosystemAtmosphere Study (BOREAS) field measurements at sites dominated by old black spruce (Picea mariana (Mill.) BSP) (OBS) and boreal fen vegetation near Thompson, Man. Model settings for simulating daily changes in water table depth (WTD) for both sites were designed to match observed water levels, including predictions for two microtopographic positions (hollow and hummock) within the fen study area. Water run-on to the soil profile from neighboring microtopographic units was calibrated on the basis of daily snowmelt and rainfall inputs to reproduce BOREAS site measurements for timing and magnitude of maximum daily WTD for the growing season. Model predictions for daily evapotranspiration rates closely track measured fluxes for stand water loss in patterns consistent with strong controls over latent heat fluxes by soil temperature during nongrowing season months and by variability in relative humidity and air temperature during the growing season. Predicted annual net primary production (NPP) for the OBS site was 158 g C·m2 during 1994 and 135 g C·m2 during 1996, with contributions of 75% from overstory canopy production and 25% from ground cover production. Annual NPP for the wetter fen site was 250 g C·m2 during 1994 and 270 g C·m2 during 1996. Predicted seasonal patterns for soil CO2 fluxes and net ecosystem production of carbon both match daily average estimates at the two sites. Model results for methane flux, which also closely match average measured flux levels of 0.5 mg CH4·m2·day1 for OBS and 2.8 mg CH4·m2·day1 for fen sites, suggest that spruce areas are net annual sinks of about 0.12 g CH4·m2, whereas fen areas generate net annual emissions on the order of 0.30.85 g CH4·m2, depending mainly on seasonal WTD and microtopographic position. Fen hollow areas are predicted to emit almost three times more methane during a given year than fen hummock areas. The validated model is structured for extrapolation to regional simulations of interannual trace gas fluxes over the entire North America boreal forest, with integration of satellite data to characterize properties of the land surface.

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Effects of Varying Geometrical Parameters on Boiling From Microfabricated Enhanced Structures

Journal of Heat Transfer ◽

10.1115/1.1513575 ◽

2003 ◽

Vol 125 (1) ◽

pp. 103-109 ◽

Cited By ~ 52

Author(s):

C. Ramaswamy ◽

Y. Joshi ◽

W. Nakayama ◽

W. B. Johnson

Keyword(s):

Heat Dissipation ◽

Layer Structure ◽

Single Layer ◽

Nucleate Boiling ◽

Heat Fluxes ◽

Working Fluid ◽

Geometrical Parameters ◽

Small Range ◽

Two Phase ◽

Wall Superheat

The current study involves two-phase cooling from enhanced structures whose dimensions have been changed systematically using microfabrication techniques. The aim is to optimize the dimensions to maximize the heat transfer. The enhanced structure used in this study consists of a stacked network of interconnecting channels making it highly porous. The effect of varying the pore size, pitch and height on the boiling performance was studied, with fluorocarbon FC-72 as the working fluid. While most of the previous studies on the mechanism of enhanced nucleate boiling have focused on a small range of wall superheats (0–4 K), the present study covers a wider range (as high as 30 K). A larger pore and smaller pitch resulted in higher heat dissipation at all heat fluxes. The effect of stacking multiple layers showed a proportional increase in heat dissipation (with additional layers) in a certain range of wall superheat values only. In the wall superheat range 8–13 K, no appreciable difference was observed between a single layer structure and a three layer structure. A fin effect combined with change in the boiling phenomenon within the sub-surface layers is proposed to explain this effect.

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