Also note that qmax is proportional to hfg and large

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Unformatted text preview: eases with pressure up to about one-third of the critical pressure, and then starts to de· crease and becomes zero at the critical pressure. Also note that qmax is proportional to hfg, and large maximum heat fluxes can be obtained using fluids with a large enthalpy of vaporization, such as water. · q kg J m · s kg m kg s2 m3 N m W1 m m2 W/m2 1/23 J °C kg · °C J kg 3 1/2 (1)3 FIGURE 10–10 Equation 10–2 gives the boiling heat flux in W/m2 when the quantities are expressed in the units specified in their descriptions. TABLE 10–1 Surface tension of liquid–vapor interface for water T, °C , N/m* 0 20 40 60 80 100 120 140 160 180 200 220 240 260 280 300 320 340 360 374 0.0757 0.0727 0.0696 0.0662 0.0627 0.0589 0.0550 0.0509 0.0466 0.0422 0,0377 0.0331 0.0284 0.0237 0.0190 0.0144 0.0099 0.0056 0.0019 0.0 *Multiply by 0.06852 to convert to lbf/ft or by 2.2046 to convert to lbm/s2. cen58933_ch10.qxd 9/4/2002 12:38 PM Page 524 524 HEAT TRANSFER TABLE 10–2 TABLE 10–3 Surface tension of some fluids (from Suryanarayana, Ref. 26; originally based on data from Jasper, Ref. 14) Values of the coefficient Csf and n for various fluid–surface combinations Substance and Temp. Range Water–copper (polished) Water–copper (scored) Water–stainless steel (mechanically polished) Water–stainless steel (ground and polished) Water–stainless steel (teflon pitted) Water–stainless steel (chemically etched) Water–brass Water–nickel Water–platinum n-Pentane–copper (polished) n-Pentane–chromium Benzene–chromium Ethyl alcohol–chromium Carbon tetrachloride–copper Isopropanol–copper Fluid-Heating Surface Combination Surface Tension, , N/m* (T in °C) Ammonia, 75 to 40°C: 0.0264 0.000223T Benzene, 10 to 80°C: 0.0315 0.000129T Butane, 70 to 20°C: 0.0149 0.000121T Carbon dioxide, 30 to 20°C: 0.0043 0.000160T Ethyl alcohol, 10 to 70°C: 0.0241 0.000083T Mercury, 5 to 200°C: 0.4906 0.000205T Methyl alcohol, 10 to 60°C: 0.0240 0.000077T Pentane, 10 to 30°C: 0.0...
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