Flat plates heat transfer coefficient

We see that the heat transfer coefficient is inversely proportional to the square root of the wire diameter, which is the reason for the development of fine wire heat exchangers after all. With an air velocity v of 0.5 m/s and a wire of 100 m, we have a=226 W/m K, which is around ten times the typical value of flat plate heat exchangers to air. 

Shakerin, S. (1987). Wind-Related Heat Transfer Coefficient for Flat-Plate Solar Collectors. Journal of Solar Energy Engineering 109 108-110. 

A candle bums at a steady rate (see the drawing below). The melted wax along the wick has a diameter D — 0.5 mm and pyrolysis occurs over a length of /p = 1 mm. Treat the wick as a flat plate of width ttD and a height of Ip which has a convective heat transfer coefficient h — 3 W/m2K. Ignore all radiative effects. 

In a practical still a stack of annular flat plates with a large diameter central channel for the compressed steam would replace a single complete flat plate (Figure 10 shows the No. 4 still modified to take multiple rotors), and here a multiplicity of feed nozzles for each surface becomes less important. Figure 11 illustrates calculations of film thickness and heat transfer coefficient for a central feed on a flat rotor without a center hole. Adding a center hole would amount to removing the region of lowest... 

Heat Conduction across a Flat Solid Slab Solve the problem of heat transfer across an infinitely large flat plate of thickness H, for the following three physical situations (a) the two surfaces are kept at T and T2, respectively (b) one surface is kept at T while the other is exposed to a fluid of temperature Tb, which causes a heat flux q,, h = 2( 2 — Tb),h2 being the heat-transfer coefficient (W/m2-K) (c) both surfaces are exposed to two different fluids of temperatures Ta and Tb with heat-transfer coefficients h and hi, respectively. 

Compare the heat-transfer coefficients for laminar forced and free convection over vertical flat plates. Develop an approximate relation between the Reynolds and Grashof numbers such that the heat-transfer coefficients for pure forced convection and pure free convection are equal. 

Equation (5-56), called the Reynolds-Colburn analogy, expresses the relation between fluid friction and heat transfer for laminar flow on a flat plate. The heat-transfer coefficient thus could be determined by making measurements of the frictional drag on a plate under conditions in which no heat transfer is involved. 

Using the linear-velocity profile in Prob. 5-2 and a cubic-parabola temperature distribution [Eq. (5-30)], obtain an expression for heat-transfer coefficient as a function of the Reynolds number for a laminar boundary layer on a flat plate. 

Assuming that the local heat-transfer coefficient for flow on a flat plate can be represented by Eq. (5-81) and that the boundary layer starts at the leading edge of the plate, determine an expression for the average heat-transfer coefficient. 

An experiment is to be designed to demonstrate measurement of heat loss for water flowing over a flat plate. The plate is 30 cm square and it will be maintained nearly constant in temperature at 50°C while the water temperature will be about 10°C. (a) Calculate the flow velocities necessary to study a range of Reynolds numbers from 104 to 107. (b) Estimate the heat-transfer coefficients and heat-transfer rates for several points in the specified range. 

Plot hj versus x for air at 1 atm and 300 K flowing at a velocity of 30 m/s across a flat plate. Take Reonl = 5 x 10s and use semilog plotting paper. Extend the plot to an x value equivalent to Re 10. Also plot the average heat-transfer coefficient over this same range. 

Air flows over an isothermal flat plate maintained at a constant temperature of 65°C. The velocity of the air is 600 m/s at static properties of 15°C and 7 kPa. Calculate the average heat-transfer coefficient for a plate 1 m long. 

Glycerin at 30°C flows past a 30-cm-square flat plate at a velocity of 1.5 m/s. The drag force is measured as 8.9 N (both sides of the plate). Calculate the heat-transfer coefficient for such a flow system. 

The average heat-transfer coefficient from horizontal flat plates is calculated with Eq. (7-25) and the constants given in Table 7-1. The characteristic dimension for use with these relations has traditionally [4] been taken as the length of a side for a square, the mean of the two dimensions for a rectangular surface, and 0.9d for a circular disk. References 52 and 53 indicate that better agreement with experimental data can be achieved by calculating the characteristic dimension with... 

Conduction with Heat Source Application of the law of conservation of energy to a one-dimensional solid, with the heat flux given by (5-1) and volumetric source term S (W/m3), results in the following equations for steady-state conduction in a flat plate of thickness 2R (b = 1), a cylinder of diameter 2R (b = 2), and a sphere of diameter 2R (b = 3). The parameter b is a measure of the curvature. The thermal conductivity is constant, and there is convection at the surface, with heat-transfer coefficient h and fluid temperature I. ... 

Friction Coefficient 400 Heat Transfer Coefficient 401 Flat Plate with Unhealed Starting I engih 403 Uniform Heat Flux 403... 

Consider a flat-plate solar collector placed on the roof of a hoifse. The temperatures at the inner and outer surfaces of the glass pover are measured to be 28°C and 25°C, respectively. I he glass bover has a surface area of 2,5 mF, a thickness of 0.6 cm, and a themial conductivity ofO.7 W/ni °C, Heat is lost from the outer surface of the cover by convection and radiation with a Convection heat transfer coefficient of lOW/m Ctuid anaiflbienljtemperature of 15°C, Determine the fraction of heal lo.st from the glass cover by radiation. 

Note that /i, is proportional to Re and thus to. v- - for laminar flow. Therefore, is infinite at the leading edge (jc = 0) and decreases by a factor of.r in the flow direction. The variation of the boundary layer thickness 5 and the friction and heat transfer coefficients along an isothermal flat plate are shown in Fig. 7-9. The local friction and heat transfer coefficients are higher in... 

The variation of the local friction and heat transfer coefficients for flow over a flat plate. 

Consider a 50-cm-diameter and 95-cm-long hot water tank. The tank is placed on the roof of a house. The water inside the tank is heated to 80°C by a flat-plate solar collector during the day. The tank is then exposed to windy air at 18°C with an average velocity of 40 km/h during the night. Estimate the temperature of the lank after a 45-min period. Assume the lank surface to be at the same temperature as the water inside, and the heat transfer coefficient on the top and bottom surfaces to be the same as that on the side surface. 

Knowledge of the temperature field in the fluid is a prerequisite for the calculation of the heat transfer coefficient using (1.25). This, in turn, can only be determined when the velocity field is known. Only in relatively simple cases, exact values for the heat transfer coefficient can be found by solving the fundamental partial differential equations for the temperature and velocity. Examples of this include heat transfer in fully developed, laminar flow in tubes and parallel flow over a flat plate with a laminar boundary layer. Simplified models are required for turbulent... 

As a result, the overall heat transfer through the composite refractory wall is known. The hot face and cold face heat transfer coefficients can be calculated from known expressions for forced and free convection near a flat plate. These expressions have the same structure but different empirical constants and can be found in, for example, Reference 20. 

A thin horizontal flat plate receives 1,200 W/m2 of radiant heat from the sun. The upward and downward heat transfer coefficients are 10 and 2.5 W/m2 -K. Determine the steady temperature of the plate if placed in ambient air at a temperature of 25 C... 

Reconsider Prob. 1.9. The heat loss will now be eliminated by attaching a flat-plate heater to the cold surface of the wall. The heat transfer coefficient between the heater and the cold ambient is also 10 W/m2 -K. Evaluate the power need in W/m2. Sketch the temperature distribution. 

Evaluate the heat loss by natural convection, forced convection, and radiation from a flat plate at a uniform temperature Tm to ambient air or water at a temperature Tm. The temperature difference between the wall and ambient is 100 K. The heat transfer coefficients for natural and forced convection in air are 10 and 200 W/mz-K, and in water are 500 and 10,000 W/m2 -K, respectively. Plot the various heat losses from the plate as a function of Tm/ TW - Tm) for To, = 0,400,800, and 1200 K. Note the effect of convection relative to radiation as a function of temperature. 

Let the rate of energy per unit volume u " x) be generated in a flat plate and let the thickness and the thermal conductivity of the plate be 2i and k(T), respectively. Under steady conditions, the total energy generated in the plate is transferred, with a heat transfer coefficient h, to an ambient at temperature Too This plate could be one of the fuel plates of a nuclear reactor core or one of the elements of an electric heater.4... 

A flat plate of thickness i separates two ambients at temperatures 7" and T0(< Tt). The heat transfer coefficient on both sides is h. We wish to eliminate the heat loss from the warm ambient. 

The core of a pool reactor is composed of flat fuel plates of thickness 71. Both sides of each plate are covered with fiat clads, each of thickness L. Assume that the gap between the fuel plates and the clads is negligible. Nuclear energy is generated only in the fuel plates (Fig. 2.20). Under steady conditions, this energy is transferred, with a heat transfer coefficient h, from the clads to an ambient at temperature %0. We wish to know the maximum temperature in the fuel plates. 

Consider a flat plate of thickness S (Fig. 3.16), Let the temperature distribution in the plate be time dependent. The upward and downward heat transfer coefficients respectively are h and h2, and the Biot numbers based on these coefficients allow a transversally lumped formulation. 

Rectangular Isothermal Fins on Vertical Surfaces. Vertical rectangular fins, such as shown in Fig. 4.23a, are often used as heat sinks. If WIS > 5, Aihara [1] has shown that the heat transfer coefficient is essentially the same as for the parallel-plate channel (see the section on parallel isothermal plates). Also, as WIS - 0, the heat transfer should approach that for a vertical flat plate. Van De Pol and Tierney [270] proposed the following modification to the Elenbaas equation [88, 89] to fit the data of Welling and Wooldridge [283] in the range 0.6 < Ra < 100, Pr = 0.71,0.33 < WIS < 4.0, and 42 < HIS < 10.6 ... 

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