F-method, heat transfer

F-method, heat transfer, 173, 175-177 example, 180 formulas. 179 Fans, 143... 

In the field of heat transfer, a good example of this category of shortcut design method is the famous F correction factor to correct the log mean temperature difference of shell and tube heat exchangers for deviations from true countercurrent flow. For multipass heat exchangers, the assumptions are ... 

Lin Q, Jiang F, Wang X-Q, Han Z, Tai Y-C, Lew J, Ho C-M (2000) MEMS Thermal Shear-Stress Sensors Experiments, Theory and Modehng, Technical Digest, Solid State Sensors and Actuators Workshop, Hilton Head, SC, 4—8 June 2000, pp 304-307 Lin TY, Yang CY (2007) An experimental investigation of forced convection heat transfer performance in micro-tubes by the method of hquid crystal thermography. Int. J. Heat Mass Transfer 50 4736-4742... 

In the model equations, A represents the cross sectional area of reactor, a is the mole fraction of combustor fuel gas, C is the molar concentration of component gas, Cp the heat capacity of insulation and F is the molar flow rate of feed. The AH denotes the heat of reaction, L is the reactor length, P is the reactor pressure, R is the gas constant, T represents the temperature of gas, U is the overall heat transfer coefficient, v represents velocity of gas, W is the reactor width, and z denotes the reactor distance from the inlet. The Greek letters, e is the void fraction of catalyst bed, p the molar density of gas, and rj is the stoichiometric coefficient of reaction. The subscript, c, cat, r, b and a represent the combustor, catalyst, reformer, the insulation, and ambient, respectively. The obtained PDE model is solved using Finite Difference Method (FDM). 

A plasma centrifugal furnace uses thermal heat transferred from arc plasma to create a molten bath that detoxifies the feed material. Organic contaminants are vaporized at temperatures of 2000 to 2500°F (1093 to 1371°C) to form innocuous products. Solids melt and are vitrified in the molten bath at 2800 to 3000°F (1540 to 1650°C). Metals are retained in this phase, which is a nonleachable, glassy residue. This method is applicable to soils contaminated with organic compounds and metals. 

Hewitt, G. F., 1964, A Method of Representing Burnout Data in Two-Phase Heat Transfer for Uniformly Heated Round Tubes, Rep. AEEW-R-4613, UK Atomic Energy Authority, Winfrith, England. (5)... 

New York (1933) 7) R.R. Wenner Thermochemical Calculations , McGraw Hill, New York (1941) 8) J.M. Cork Heat , J. Wiley, New York (1942) 9) J. Reilly W.N. Rae Physicochemical Methods , Van Nostrand, New York (1943) 10) H.S. Carslaw J.C. Jaeger Conduction of Heat in Solids , Clarendon Press, Oxford (1947) 11) M. Jacob, Heat Transfer , J. Wiley Sons, New York, V. 1 (1949) 12) D.Q. Kern Process Heat Transfer , McGraw Hill, New York (1951) 13) F. Reif... 

Figure 3.14. The lower ends of fractionators, (a) Kettle reboiler. The heat source may be on TC of either of the two locations shown or on flow control, or on difference of pressure between key locations in the tower. Because of the built-in weir, no LC is needed. Less head room is needed than with the thermosiphon reboiler, (b) Thermosiphon reboiler. Compared with the kettle, the heat transfer coefficient is greater, the shorter residence time may prevent overheating of thermally sensitive materials, surface fouling will be less, and the smaller holdup of hot liquid is a safety precaution, (c) Forced circulation reboiler. High rate of heat transfer and a short residence time which is desirable with thermally sensitive materials are achieved, (d) Rate of supply of heat transfer medium is controlled by the difference in pressure between two key locations in the tower, (e) With the control valve in the condensate line, the rate of heat transfer is controlled by the amount of unflooded heat transfer surface present at any time, (f) Withdrawal on TC ensures that the product has the correct boiling point and presumably the correct composition. The LC on the steam supply ensures that the specified heat input is being maintained, (g) Cascade control The set point of the FC on the steam supply is adjusted by the TC to ensure constant temperature in the column, (h) Steam flow rate is controlled to ensure specified composition of the PF effluent. The composition may be measured directly or indirectly by measurement of some physical property such as vapor pressure, (i) The three-way valve in the hot oil heating supply prevents buildup of excessive pressure in case the flow to the reboiier is throttled substantially, (j) The three-way valve of case (i) is replaced by a two-way valve and a differential pressure controller. This method is more expensive but avoids use of the possibly troublesome three-way valve.

This method is especially easy to apply when the terminal temperatures are all known, because then F and (A7 )logmean are immediately determinable for a particular flow pattern. Then in the heat transfer equation... 

Thonon B, Chopard F. Condensation in plate heat exchangers assessment of a general design method. Eurotherm 47, Heat Transfer in Condensation. Elsevier, 1996 10-18. 

ASTM F 955 Standard Test Method for Evaluating Heat Transfer through Materials for Protective Clothing upon Contact with Molten Substances... 

ASTM F 2700 Standard Test Method for Unsteady-State Heat Transfer Evaluation of Flame Resistant Materials for Clothing with Continuous Heating... 

Kayan, C. F. Heat Transfer Temperature Patterns of a Multicomponent Structure by Comparative Methods," Trans. ASME, vol. 71, p. 9, 1949. 

Because of the higher heat-transfer rates, dropwise condensation would be preferred to Him condensation, but it is extremely difficult to maintain since most surfaces become wetted after exposure to a condensing vapor over an extended period of time. Various surface coatings and vapor additives have been used in attempts to maintain dropwise condensation, but these methods have not met with general success to date. Some of the pioneer work on drop condensation was conducted by Schmidt [26] and a good summary of the overall problem is presented in Ref. 27. Measurements of Ref. 35 indicate that the drop conduction is the main resistance to heat flow for atmospheric pressure and above. Nucleation site density on smooth surfaces can be of the order of 10 sites per square centimeter, and heat-transfer coefficients in the range of 170 to 290 kW/m2 °C [30,000 to 50,000 Btu/h ft2 °F] have been reported by a number of investigators. 

Consider a large uranium plate of thickness L = 4 cm, thermal conductivity k -- 28 W/m °C, and thermal diffusivity a = 12.5 X 10 m /s that is initially at a uniform temperature of 2C0 C. Heat is generated uniformly in the plate at a constant rate of e = 5 x 10 W/m. At lime t = 0, one side of llie plate is brought into contact with iced water and is maintained at 0°C at all times, while the other side is subjected to convection to an environment at f, = 30°C with a heat transfer coefficient of / = 45 W/m °C, as shov/n in Fig. 5 44. Considering a total of three equally spaced nodes in the medium, two at the boundaries and one at the middle, estimate the exposed surface temperature of the plate 2.5 min after the start of cooling using (a) the explicit method and (6) the implicit metliod. 

Considep two-dimensional transient heat transfer in an L-shaped solid body that is initially at a uniform temperalure of 90°C and whose cross section is given in Fig. 5-51. The thermal conductivity and diffusivity of the body are k = 15 W/m C and a - 3.2 x 10 rriVs, respectively, and heat is generated in Ihe body at a rate of e = 2 x 10 W/m. The left sutface of the body is insulated, and the bottom surface is maintained at a uniform temperalure of 90°C at all times. A1 time f = 0, the entire top surface is subjected to convection to ambient air at = 25°C with a convection coefficient of h = 80 W/m C, and the right surface is subjected to heat flux at a uniform rate of r/p -5000 W/m. The nodal network of the problem consists of 15 equally spaced nodes vrith Ax = Ay = 1.2 cm, as shown in the figure, Five of the nodes are at the bottom surface, and thus their temperatures are known. Using the explicit method, determine the temperature at the top corner (node 3) of the body after 1,3, 5, 10, and 60 min. 

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