To measure the specific heat in the liquid phase of a newly developed cryoprotectant, you place a sample of the new cryoprotectant in contact with a cold plate until the solution’s temperature drops from room temperature to its freezing point. Then you measure the heat transferred to the cold plate. If the system isn’t sufficiently isolated from its room-temperature surroundings, what will be the effect on the measurement of the specific heat? (a) The measured specific heat will be greater than the actual specific heat; (b) the measured specific heat will be less than the actual specific heat; (c) there will be no effect because the thermal conductivity of the cryoprotectant is so low; (d) there will be no effect on the specific heat, but the temperature of the freezing point will change.
To measure the specific heat in the liquid phase of a newly developed cryoprotectant, you place a sample of the new cryoprotectant in contact with a cold plate until the solution’s temperature drops from room temperature to its freezing point. Then you measure the heat transferred to the cold plate. If the system isn’t sufficiently isolated from its room-temperature surroundings, what will be the effect on the measurement of the specific heat? (a) The measured specific heat will be greater than the actual specific heat; (b) the measured specific heat will be less than the actual specific heat; (c) there will be no effect because the thermal conductivity of the cryoprotectant is so low; (d) there will be no effect on the specific heat, but the temperature of the freezing point will change.
To measure the specific heat in the liquid phase of a newly developed cryoprotectant, you place a sample of the new cryoprotectant in contact with a cold plate until the solution’s temperature drops from room temperature to its freezing point. Then you measure the heat transferred to the cold plate. If the system isn’t sufficiently isolated from its room-temperature surroundings, what will be the effect on the measurement of the specific heat? (a) The measured specific heat will be greater than the actual specific heat; (b) the measured specific heat will be less than the actual specific heat; (c) there will be no effect because the thermal conductivity of the cryoprotectant is so low; (d) there will be no effect on the specific heat, but the temperature of the freezing point will change.
Consider a flat-plate solar collector placed on the roof of a house. The temperatures at the inner and outer surfaces of the glass cover are measured to be 33°C and 31°C, respectively. The glass cover has a surface area of 2.5 m2, a thickness of 0.6 cm, and a thermal conductivity of 0.7 W/m·K. Heat is lost from the outer surface of the cover by convection and radiation with a convection heat transfer coefficient of 10 W/m2·K and an ambient temperature of 15°C. Determine the fraction of heat lost from the glass cover by radiation.
A hot solid substance with mass 3.44kg and temperature 81.5 oC, is taken out of the oven and placed in cool liquid water of mass 2.04kg and temperature 20 oC. Heat flows from the hot substance to the water until they are both at the equilibrium temperature of 31.8 oC. Assuming no heat transfer between the environment and the water/substance system, find the specific heat of the substance. Take the specific heat of water as 4190 Jkg -1C -1. Express your answer to at least 3 significant figures in Jkg -1C -1.
Consider an opaque plate that is well insulated on the edges and it is heated at the bottom with an electric heater. The plate has an emissivity of 0.67, and is situated in an ambient surrounding temperature of 7°C where the natural convection heat transfer coefficient is 7 W/m2?K. To maintain a surface temperature of 80°C, the electric heater supplies 1000 W/m2 of uniform heat flux to the plate. Determine the radiosity of the plate under these conditions.
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