31. A uniformly heated square plate of 2 ft x 2 ft is exposed to cold air at 80 F. The heater output remains at a constant value of 1 kW. Air, at atmospheric pres- sure, flows over the plate at a velocity of 16.5 ft/s. Find the average temperature of this plate. [Ans.: ~ 513 F].

300960 W (e) Water is entering a heated tube at mass flow rate of 1.2 kg/s. The temperature at the inlet is 20°C and at the outlet is 80°C. Assume the surface temperature of the tube is 100°C. The convection coefficient of the water flow is 28 W/m².°c. The specific heat and density of water can be assumed to be 4180 J/kg.°C and 990 kg/m³. What is the rate of heat transfer to water during this process?

9) If the temperature of the sun were to suddenly double, by what multiplicative factor would the thermal radiation change ? Show Work

A solar energy storage compartment contains 1,778 rocks that can approximate 3-inch-diameter spheres. The properties of the rocks are k = 2.2 Btu / h ∙ ft ∙ ºF, α = 0.07 ft2 / h, cp = 0.2 Btu / lbm ° F, and the density is 160 lbm / ft3. How long (in hours) would it take for solar energy to saturate the compartment using 200 ° F air from a solar collector? How much energy (in Btu) is stored in the compartment under these conditions if it is initially at 79 ° F and h = 5 Btu / h ∙ ft2 ∙ ºF?

Apply the first law of thermodynamics to flow system with two inlets and one outlet. Assume that heat is supplied to the system. Draw the neat sketch and lable inlet and outlet properties

3. A food-processing plant requires that two large process areas A and B be kept at constant temperature TA 12°C. The refrigeration load of area A is 175 kW. The heating load of area B is 210 kW. Conditioning of the two spaces is achieved by an (cyclic) electrical air-conditioning and heating unit (CM) that also interacts with the environment at To = 5°C, as shown in the В., 12°С 8°C and TB Work R 5°C figure. А, —8°С a. What is the least amount of electrical power required to operate the air- conditioning and heating unit? b. Determine the rate of energy exchange between the unit (CM) and the environment in case a.

You are asked to assess the validity of a power-generating device. The device supposedly operates steadily by receiving 256 kW via heat transfer at 4.5 °C, receiving 370 kW via heat transfer at 115 °C, and rejecting 200 kW via heat transfer at -180 °C. The device generates electrical power in response to these various heat transfers. a. determine its electrical power output, in kW. b. Is the device feasible? Does it violate 1st and/or 2nd law of thermodynamics?

Air at 20◦C blows over a hot plate 50 by 75 cm maintained at 250◦C.The convection heat-transfer coefficient is 25 W/m2◦C. Calculate the heat transfer.Assuming that the plate is made of carbon steel (1%) 2 cm thick andthat 300 W is lost from the plate surface by radiation, calculate theinside plate temperature.

Illustrating the relationships between system constants for the chosenperfect gas system(refrigeration systems).   Discuss the relevance of the ideal gas law constants and explain how changes in one variable affectthe others under the condition of a perfect gas. Include molar mass, gas constant, and specific heatcapacities of gases, including the associated equations.

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