Variation of Heat Transfer Coefficient with Length

Farber, E. A.; Rennat, Harry O.

doi:10.1021/ie51392a043

Cited by 11 publications

(5 citation statements)

References 0 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…Thus the position of the woody axis relative to the soil surface determines its lheat transfer properties. Farber and Rennat (8) showed that the conductance (1t) decreased in the first 15 cm of length when the position of an infinite cylinder was varied from 00 with the horizontal, to 900. The film coefficient of heat transfer showed a similar distribution, reaching the maximum decrease at about 750 with the horizontal.…”

Section: Methodsmentioning

confidence: 99%

Thermal Conductivity of Functional Citrus Tree Wood

Turrell¹,

Austin²,

McNee³

et al. 1967

Plant Physiol.

View full text Add to dashboard Cite

Sunmiary. Thermal conductivity coefficients have been determined for longitudinal and transverse flow in 4 varieties of fresh Citrus wood using steady state-method's.Equations were developed from which thermal conductivity could be rapidly estimated from moisture content or electrical conductivity. The heat balance of large and small tree trunks on a freezing night has been calculated on the basis of the coefficients. Thermal Conductivity of Fuinctional Citruts TreeWood. Heat transfer of the woody stems of trees is chiefly by radiation, convection and conduction. Radiation loss is minimized by the insulating effect of the leafy crown, and convection assumes the dominant role only during the day because the transpiration stream flows most actively then (4); at night thermal conduction, though relatively small, is the principal mode of heat transfer. Although thermal conduction was correctly considered bv Raschke (18) to plav a minor role in the heat transfer of the plant, under the stress of nocturnal advection freezes and radiation frosts, this is not the case in subtropical plants which bear leaves and fruit during winter. The magnitude of thermal conduction in the wood, relative to its mass, is important in preventing frost damage to citrus trees (24). Therefore, we have determined longitudinal and transverse thermal coniductivity coefficients for 4 species of citrus and used these coefficients to analy)se the effects of freezing temperatures on 2 cm and 20 cm diameter trees. For this analysis we have used the weather parameters which existed in Weslaco, Texas, fronm Januarv 9 to 12, 1962 (32).Thermal conductivity coefficients (K) have been determined on about /70 species of dry woods (10,13,14,20). Across grain K for nearly dry woods, having about 12 % moisture, ranges from 0.1 to 0.S

show abstract

Section: Methodsmentioning

confidence: 99%

Thermal Conductivity of Functional Citrus Tree Wood

Turrell¹,

Austin²,

McNee³

et al. 1967

Plant Physiol.

View full text Add to dashboard Cite

show abstract

“…Al-Arabi and Khamis 4 suggested the correlation Nu L = m (ϕ)Ra L n (ϕ) using the inclination angle φ and cylinder length L , and the variation of L and φ depends on the angle of inclination. Farber and Rennat 22 conducted an experiment with a stainless steel tube with a 6 ft (1.829 m) length and 0.125 in. (3.175 mm) OD, which was heated by inserting an electric current through it for producing a constant heat flux.…”

Section: Literature Reviewmentioning

confidence: 99%

Natural Convection from the Outside Surface of an Inclined Cylinder in Pure Liquids at Low Flux

et al. 2019

View full text Add to dashboard Cite

Many studies have investigated natural convection heat transfer from the outside surface of horizontal and vertical cylinders in both constant heat flux and temperature conditions. However, there are poor studies in natural convection from inclined cylinders. In this study, free convection heat transfer was examined experimentally from the outside surface of a cylinder for glycerol and water at various heat fluxes. The tests were performed at 10 different inclination angles of the cylinder, namely, φ = 0°, 10°, 20°, 30°, 40°, 50°, 60°, 70°, 80°, and 90°, measured from the horizon. Our results indicated that the average Nusselt number reduces with the growth in the inclination of the cylinder to the horizon at the same heat flux, and the average Nusselt number enhanced with the growth in heat flux at the same angle. Also, the average Nusselt number of water is greater than that of glycerol. A new experimental model for predicting the average Nusselt number is suggested, which has a satisfactory accuracy for experimental data.

show abstract

“…Linear scale-out models assume that all of the channels behave similarly without taking into account the effects due to exterior heat loss. , However, the reaction is quenched if loss of too much heat occurs, , and thus, the issue of extinction could not be addressed with the linear scale-out assumption. The heat loss coefficient is inversely proportional to the characteristic length scale, and thus large heat loss coefficients are inherent to microchannel reactors. , Accordingly, the total heat loss may be increased significantly, , which will cause the reaction to extinguish. , The critical heat loss coefficient is an effective means of assessing the importance of stack structure and heat loss in microreactor design, thus making it possible to obtain the optimum reaction conditions by controlling the complex physicochemical processes. The knowledge of critical heat loss coefficients is of vital importance to ensure effective reactor operation.…”

Section: Introductionmentioning

confidence: 99%

“…The heat loss coefficient is inversely proportional to the characteristic length scale, and thus large heat loss coefficients are inherent to microchannel reactors. 37,38 Accordingly, the total heat loss may be increased significantly, 39,40 which will cause the reaction to extinguish. 41,42 The critical heat loss coefficient is an effective means of assessing the importance of stack structure and heat loss in microreactor design, thus making it possible to obtain the optimum reaction conditions by controlling the complex physicochemical processes.…”

Section: Introductionmentioning

confidence: 99%

Effects of Stack Structure and Heat Loss on the Stability and Efficiency of Steam-Methanol Reforming Microreactors for Hydrogen Production

Chen

Miao

2023

Ind. Eng. Chem. Res.

View full text Add to dashboard Cite

The linear scale-out approximation ignores the influence of exterior heat loss and thus cannot address extinction issues. The present study is focused primarily upon the roles of stack structure and heat loss in the stability and efficiency of microreactors for hydrogen production by steam-methanol reforming. Computer simulations are performed to model the complex physicochemical processes in a variety of different heat loss situations. The effects of channel number, wall thermal conductivity, and surface-area-to-volume ratio are investigated to assess the importance of stack structure and heat loss in microreactor design. The results indicate that the total heat loss becomes increasingly significant for designing reactors with small stacks of channels. About half of heat released is lost if a global-type extinction occurs. The critical heat loss coefficient depends heavily upon the number of channels. The design with a large stack of channels more closely beneficially improves heat utilization and reduces heat loss. There is a significant linear relationship between energy efficiency and heat loss coefficient. Significant heat loss may cause extinction in edge channels while still permitting very high conversion in center channels. The wall thermal conductivity is of vital importance to ensure stability operation. Higher wall thermal conductivity provides stability benefits, but walls with very low thermal conductivity can be employed to reduce heat loss by sacrificing the thermal coupling capability.

show abstract

Variation of Heat Transfer Coefficient with Length

Cited by 11 publications

References 0 publications

Thermal Conductivity of Functional Citrus Tree Wood

Thermal Conductivity of Functional Citrus Tree Wood

Natural Convection from the Outside Surface of an Inclined Cylinder in Pure Liquids at Low Flux

Effects of Stack Structure and Heat Loss on the Stability and Efficiency of Steam-Methanol Reforming Microreactors for Hydrogen Production

Contact Info

Product

Resources

About