KNOWN: Saturated ethylene glycol at 1 atm heated by a chromium-plated heater of 200 mm diameter and maintained at 480 K. FIND: Heater power, rate of evaporation, and ratio of required power to maximum power for critical heat flux. ASSUMPTIONS: (1) Nucleate pool boiling, (2) Fluid-surface,
KNOWN: Chips on a ceramic substrate operating at power levels corresponding to 50% of the critical heat flux. FIND: (a) Chip power level and temperature rise of the chip surface, and (b) Compute and plot the chip temperature Ts as a function of heat flux for the range 0.25 ≤ q″s/q″max ≤ 0.90.
KNOWN: Nickel-coated heater element exposed to saturated water at atmospheric pressure; thermocouple attached to the insulated, backside surface indicates a temperature To = 266.4°C when the electrical power dissipation in the heater element is 6.950 × 10^7 W/m³. FIND: (a) From the foregoing data,
KNOWN: Copper pan, 150 mm diameter and filled with water at 1 atm, is maintained at 115°C. FIND: Power required to boil water and the evaporation rate; ratio of heat flux to critical heat flux; pan temperature required to achieve critical heat flux. ASSUMPTIONS: (1) Nucleate pool boiling, (2)
KNOWN: Fluids at 1 atm: mercury, ethanol, R-12. FIND: Critical heat flux; compare with value for water also at 1 atm. ASSUMPTIONS: (1) Steady-state conditions, (2) Nucleate pool boiling. PROPERTIES: Table A-5 and Table A-6 at 1 atm,
KNOWN: Diameter of copper pan. Initial temperature of water and saturation temperature of boiling water. Range of heat rates (1 ≤ q ≤ 100 kW). FIND: (a) Variation of pan temperature with heat rate for boiling water, (b) Pan temperature shortly after start of heating with q = 8 kW. ASSUMPTIONS: (1)
KNOWN: Simple expression to account for the effect of pressure on the nucleate boiling convection coefficient in water. FIND: Compare predictions of this expression with the Rohsenow correlation for specified Δ Te and pressures (2 and 5 bar) applied to a horizontal plate. ASSUMPTIONS: (1)