Concept explainers
We go out to sunbathe on a warm summer day. If we soak up 100 British thermal units per hour [BTU/h] of energy, how much will the temperature of 132 pound-mass [lbm] person increase in 2 hours [h] in units of degrees Celsius [°C]? We assume that since our bodies are mostly water they have the same specific heat as water, 4.18 joules per gram degree Celsius [J/(g °C)].
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- The data from a series of flow experiments is given to you for analysis. Refrigerant-22 is flowing at a velocity of 0.043m/s and a bulk temperature of 370K over an isothermal plate at 290K. Some thermo-physical properties are shown in the table below. Thermal Conductivity [W/m/K] 0.06728 Kinematic Viscosity [m2/s] Prandtl Number [-] 1.235*10-7 3.28 If the transition from laminar to turbulent flow is determined to happen at the end of the plate: A. What is the length of the plate? B. What are the hydrodynamic and thermal boundary layer thicknesses at the end of the plate? C. What is the heat transfer rate per plate width for the entire plate? Given the plate length you determined in part A above is increased by 50%, at the end of the extended plate, what are D. Reynolds number? E. Hydrodynamic and thermal boundary layer thicknesses?arrow_forwardTo heat potatoes, you use a microwave with an output power of 780 watts [W]. The microwave has "pre-set" cook buttons. The "potato" button will cook a 0.625 pound-mass [lbm] potato by heating the potato from room temperature (assumed to be 68 degrees Fahrenheit [°F]) to 425 degrees Fahrenheit [°F]. The specific heat of a potato is 3.4 kilojoules per kilogram kelvin [kJ/(kg K)]. What is the length of time the "pre-set" button is programmed to operate in units of minutes [min]?arrow_forwardWhen not in use, the water in a pool is kept at a temperature of 60 degrees Fahrenheit [°F]. For synchronized swimming competitions, the water should be increased by 18 degrees Fahrenheit [°F]. The system that heats the water can raise the temperature of the water by 3.4 kelvin [K] every 13 minutes [min]. Determine the time it will take to heat the pool to the appropriate competition temperature in units of hours [h]. Click the icon to view the factors for temperature intervals conversion. The time is h. (Round your answer to two decimal places.)arrow_forward
- Water enters a boiler at 20 degrees Celsius [°C]. The boiler operates for 5 minutes [min] to heat 25 gallons [gal] of water. The boiler requires an input power of 15.5 kilowatts [kW] and is 85% efficient. The specific heat capacity of water is 4.18 kilojoules per kilogram kelvin [kJ /(kg K)]. What is the temperature of the water in degrees Celsius [°C] as it exits the boiler?arrow_forwardA robotic rover on Mars finds a spherical rock with a diameter of 8 centimeters [cm]. The rover picks up the rock and lifts it 25 centimeters [cm] straight up. The rock has a specific gravity of 4.75. The gravitational acceleration on Mars is 3.7 meters per second squared [m/s²]. If the robot's lifting arm has an efficiency of 35% and required 10 seconds [s] to raise the rock 25 centimeters [cm], how much power in units of watts [W] did the arm use?arrow_forwardA motor has circular cylinders with a 3.875 inch diameter. The height of the cylinder is 4.7 inches and has an ideal gas The piston moves up in the cylinder and compresses the ideal gas. At the end of compression, the cylinder has a volume of 7.37 cubic inches The amount of gas and the temperature of the gas stay the same during compression and the initial pressure in the cylinder is 1.2 atmosphere [atm]. Find the pressure after compression in units of pounds-force per square inch [psi].arrow_forward
- The size of your classroom is 80 ft wide, 40 ft deep, and 12 ft high. Assume that theair in the classroom is 25 oC and at 14.7 psia. Calculate(a) the mass of oxygen in the room in kilograms, and(b) the viscosity of the air, in pascal-seconds (Pa s) [kg/(m s)].arrow_forwardA robot is exploring Charon, the dwarf planet Pluto's largest moon. Gravity on Charon is 0.278 meters per second [m/s2]. During its investigations, the robot picks up a small spherical rock for inspection. The rock has a diameter of 6 centimeters [cm] and is lifted 16 centimeters [cm] above the surface. The specific gravity of the rock is 10.7. The mechanism lifting the rock is powered by a 9-volt [V] power supply and draws 1.09 milliamperes [mA] of current. It requires 13 seconds [s] to perform this lifting task. What is the efficiency of the robot?arrow_forwardIn a factory, 12 gallons [gal] of a liquid need to be raised 30 feet [ft] to be loaded into a piece of equipment. During this process, the electric motor loses 700 watts [W] to heat while operating in a circuit that requires 15 amperes [A] of current and 110 volts [V]. The liquid has a total mass of 5 slugs [slugs] and the mass of the container is negligible. Determine the time required to lift the liquid in seconds [s].arrow_forward
- One mole of an ideal gas, initially at 30 [°C] and 1 [bar], is changed to 130 [°C] and 10 [bar] by two different mechanically reversible processes: • The gas is first heated at constant volume until its temperature is 130 [°C], then it is compressed isothermallyuntil its pressure is 10 [bar].• The gas is first compressed adiabatically; then it is heated isobarically to 130 [°C] and 10 [bar]. Calculate Q, W, ΔU, and ΔH in [J] for each case. Take Cp = 5/2R and Cv = 3/2R.arrow_forwardA plastic bin with a volume of 1 gallon [gal] has a mass of 0.35 kilograms [kg] when empty and is sitting on a table in a warehouse. After the bin becomes partially filled, 1.3 pounds-force [lb] of force is applied to move the bin across the table, and the bin and its contents accelerate at a rate of 1.5 meters per second squared Ignore frictional losses. Determine the total weight of the bin and its contents in units of newtons [N].arrow_forwardA heat pump is used to heat a house. The heat loss of the house at a time when the outside temperature is A ° C is B kJ / h. The interior temperature of the house is C ° C. If the coefficient of action (COPIP) of the heat pumpis D under these conditions ,a) The power consumed by the heat pump [kW],b) The heat transferred from the cold outside air to the heat pump [kJ / h]c) If the heat pump is considered to work reversibly,calculate the COPIP.arrow_forward
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