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ilovemoney518
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Thermal Energy Problem HELP PLEASE!
Hi guys I have these 2 thermal energy problems that I keep getting wrong answer, I really want to know the answer and the way to solve it. Thank u very much!
1. The average thermal conductivity of the walls (including windows) and roof of a house in Figure P11.32 is 4.8 10-4 kW/m°C, and their average thickness is 20.0 cm. The house is heated with natural gas, with a heat of combustion (energy given off per cubic meter of gas burned) of 9300 kcal/m3. How many cubic meters of gas must be burned each day to maintain an inside temperature of 24.5°C if the outside temperature is 0.0°C? Disregard radiation and loss by heat through the ground.
2. When you jog, most of the food energy you burn above your basal metabolic rate (BMR) ends up as internal energy that would raise your body temperature if it were not eliminated. The evaporation of perspiration is the primary mechanism for eliminating this energy. Determine the amount of water you lose to evaporation when running for 30 minutes at a rate that uses 400 kcal/h above your BMR. (That amount is often considered to by the "maximum fat-burning" energy output.) The metabolism of 1 gram of fat generates approximately 8.5 kcal of energy and produces approximately 1 gram of water. (The hydrogen atoms in the fat molecule are transferred to oxygen to form water.) What fraction of your need for water will be provided by fat metabolism? (The latent heat of vaporization of water at room temperature is 2.5 106 J/kg.)
For the first problem the answer I got is 119.96. But it was wrong. I can't afford to try more because I only have 3 chances and I am totally lost. The second problem I have no clue, could anyone guide me a little?
Hi guys I have these 2 thermal energy problems that I keep getting wrong answer, I really want to know the answer and the way to solve it. Thank u very much!1. The average thermal conductivity of the walls (including windows) and roof of a house in Figure P11.32 is 4.8 10-4 kW/m°C, and their average thickness is 20.0 cm. The house is heated with natural gas, with a heat of combustion (energy given off per cubic meter of gas burned) of 9300 kcal/m3. How many cubic meters of gas must be burned each day to maintain an inside temperature of 24.5°C if the outside temperature is 0.0°C? Disregard radiation and loss by heat through the ground.
2. When you jog, most of the food energy you burn above your basal metabolic rate (BMR) ends up as internal energy that would raise your body temperature if it were not eliminated. The evaporation of perspiration is the primary mechanism for eliminating this energy. Determine the amount of water you lose to evaporation when running for 30 minutes at a rate that uses 400 kcal/h above your BMR. (That amount is often considered to by the "maximum fat-burning" energy output.) The metabolism of 1 gram of fat generates approximately 8.5 kcal of energy and produces approximately 1 gram of water. (The hydrogen atoms in the fat molecule are transferred to oxygen to form water.) What fraction of your need for water will be provided by fat metabolism? (The latent heat of vaporization of water at room temperature is 2.5 106 J/kg.)
For the first problem the answer I got is 119.96. But it was wrong. I can't afford to try more because I only have 3 chances and I am totally lost. The second problem I have no clue, could anyone guide me a little?
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