Concept explainers
On-Demand Water Heaters. Conventional hot-water heaters consist of a tank of water maintained at a fixed temperature. The hot water is to be used when needed. The drawbacks are that energy is wasted because the tank loses heat when it is not in use and that you can run out of hot water if you use too much. Some utility companies are encouraging the use of on-demand water heaters (also known as flash heaters), which consist of heating units to heat the water as you use it. No water tank is involved, so no heat is wasted. A typical household shower flow rate is 2.5 gal/min (9.46 L/min) with the tap water being heated from 50°F (10°C) to 120°F (49°C) by the on-demand heater. What rate of heat input (either electrical or from gas) is required to operate such a unit, assuming that all the heat goes into the water?
Learn your wayIncludes step-by-step video
Chapter 17 Solutions
University Physics with Modern Physics (14th Edition)
Additional Science Textbook Solutions
Cosmic Perspective Fundamentals
University Physics Volume 2
Conceptual Integrated Science
Essential University Physics: Volume 2 (3rd Edition)
University Physics (14th Edition)
College Physics: A Strategic Approach (3rd Edition)
- A power plant has been proposed that would make use of the temperature gradient in the ocean. The system is to operate between 20.0C (surface water temperature) and 5.00C (water temperature at a depth of about 1 km). (a) What is the maximum efficiency of such a system? (b) If the useful power output of the plant is 75.0 MW, how much energy is absorbed per hour? (c) In view of your answer to part (a), do you think such a system is worthwhile (considering that there is no charge for fuel)?arrow_forwardThe Bodø NATO base in northern Norway uses a heat pump to extract heat from ocean water. 7.0°C ocean water is continuously drawn into the system, heat is extracted, and the water is returned to the ocean at 3.0°C. When the system is working at full capacity, 2000 kW of heat is delivered to the building at the cost of 600 kW of electric energy.a. How much energy is removed from the water (the cold reservoir) each second?b. How much water moves through the system each second?arrow_forwardA refrigerator’s freezer compartment is set at –10°C; the kitchen is 24°C. What is the theoretical minimum amount of electric energy necessary to pump 1.0 J of energy out of the freezer compartment?A. 0.89 J B. 0.87 J C. 0.13 J D. 0.11 Jarrow_forward
- A 32% efficient electric power plant produces 900 MJ of electric energy per second and discharges waste heat into 20°C ocean water. Suppose the waste heat could be used to heat homes during the winter instead of being discharged into the ocean. A typical American house requires an average 20 kW for heating. How many homes could be heated with the waste heat of this one power plant?arrow_forwardIf you mix food in a blender, the electric motor does work on the system, which consists of the food inside the container. This work can noticeably warm up the food. Suppose the blender motor runs at a power of 250 W for 40 s. During this time, 2000 J of heat flow from the now-warmer food to its cooler surroundings. By how much does the thermal energy of the food increase?arrow_forwardAn automobile engine converts heat into work via a cycle. The cycle must finish exactly where it started, so the energy at the start of the cycle must be exactly the same as the energy at the end of the cycle. If the engine absorbs 226 J of heat per cycle, how much work can it do per cycle?arrow_forward
- A technician measures the specific heat of an unidentified liquid by immersing an electrical resistor in it. Electrical energy is converted to heat, which is then transferred to the liquid for 125 s at a constant rate of 67.9 W. The mass of the liquid is 0.770 kg, and its temperature increases from 18.58°C to 22.57° C. For related problem-solving tips and strategies, you may want to view a Video Tutor Solution of Circuit meltdown. Part A Find the average specific heat of the liquid in this temperature range. Assume that negligible heat is transferred to the container that holds the liquid and that no heat is lost to the surroundings. Express your answer in joules per kilogram per kelvin. V AZO ? C = J/(kg K) Submit Request Answer Part B Suppose that in this experiment heat transfer from the liquid to the container or its surroundings cannot be ignored. Is the result calculated in part (a) an overestimate or an underestimate of the average specific heat? underestimate O overestimatearrow_forwardIf you mix food in a blender, the electric motor does work on the system, which consists of the food inside the container. This work can noticeably warm up the food. Suppose the blender motor runs at a power of 250 W for 40 s. During this time, 2000 J of heat flow from the now-warmer food to its cooler surroundings. Match the answers with questions. (Hint: Example 11.12) v W- work done on the system (food) A. 2000 J v Q- Heat into or out of the system (food) B. 8000 J v AEth - Change in thermal energy of the system (food) C. OJ D. -10,000 J E. -8000 J F. -2000 J G. 10,000 Jarrow_forwardA heat engine has a solar collector receiving 600 Btu/h per square foot, inside which a transfer medium is heated to 800 R. The collected energy powers a heat engine that rejects heat at 100 F. If the heat engine should deliver 8500 Btu/h, what is the minimum size (area) of the solar collector?arrow_forward
- m = 0.593 kg of methanol in atmospheric pressure is heated with an electric heater from T₁ = 30.2 °C to its boiling point. After the heating my methanol is vaporized. Heating and vaporizing takes t = 450.41 s with n=0.59 heater's efficiency. What is the volume of methanol? V = What is the energy required for heating? E₁ = 1 kJ m³ Your last answer was interpreted as follows: 1 What is the energy required for vaporizing? Ev = 1 kJ Your last answer was interpreted as follows: 1 What is the power of the heater? P = 1 с Your last answer was interpreted as follows: 1 Your last answer was interpreted as follows: 1 What is the electr. energy needed for heating and vaporizing? Eε = 1 kJ Your last answer was interpreted as follows: 1 h Do not leave any fields blank. If you don't know the answer, insert 1 for example. Insert the answer with 3 significant digits without rounding the answer. Constant P Tb Value Unit 2.53 1165 786.3 64.7 °C umges Quantity heat capacity kg K kJ kW kg kg LAN Symbol h…arrow_forwardAn insulated 40-ft3 rigid tank contains air at 50 psia and 120°F. A valve connected to the tank is now opened, and air is allowed to escape until the pressure inside drops to 25 psia. The air temperature during this process is maintained constant by an electric resistance heater placed in the tank. Determine the electrical work done during this process.arrow_forwardA steam engine has a boiler that operates at 500 K. The energy from the burning fuel changes water to steam, and this steam then drives a piston. The cold reservoir’s temperature is that of the outside air, approximately 300 K. What is the maximum thermal efficiency of this steam engine?arrow_forward
- Principles of Physics: A Calculus-Based TextPhysicsISBN:9781133104261Author:Raymond A. Serway, John W. JewettPublisher:Cengage LearningCollege PhysicsPhysicsISBN:9781285737027Author:Raymond A. Serway, Chris VuillePublisher:Cengage LearningCollege PhysicsPhysicsISBN:9781305952300Author:Raymond A. Serway, Chris VuillePublisher:Cengage Learning
- Physics for Scientists and Engineers with Modern ...PhysicsISBN:9781337553292Author:Raymond A. Serway, John W. JewettPublisher:Cengage LearningCollege PhysicsPhysicsISBN:9781938168000Author:Paul Peter Urone, Roger HinrichsPublisher:OpenStax CollegePhysics for Scientists and EngineersPhysicsISBN:9781337553278Author:Raymond A. Serway, John W. JewettPublisher:Cengage Learning