Under conditions for which the same room temperatureis maintained by a heating or cooling system, it is not uncommonfor a person to feel chilled in the winter but comfortable in the summer. Provide a plausible explanation for this situation (with supporting calculations)by considering a room whose air temperature is maintained at 20°C throughout the year, while the walls ofthe room are nominally at 27°C and 14°C in the summer and winter, respectively. The exposed surface of aperson in the room may be assumed to be at a temperature of 32°C throughout the year and to have an emissivity of 0.90. The coefficient associated with heattransfer by natural convection between the person andthe room air is approximately
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Fundamentals of Heat and Mass Transfer
- The air-conditioning system in a Chevrolet van for use in desert climates is to be sized. The system is to maintain an interior temperature of 20C when the van travels at 100 km/h through dry air at 30C at night. If the top of the van is idealized as a flat plate 6 m long and 2 m wide and the sides as flat plates 3 m tall and 6 m long, estimate the rate at which heat must be removed from the interior to maintain the specifiedarrow_forward1.29 A spherical interplanetary probe with a 30-cm diameter contains electronic equipment that dissipates 100 W. If the probe surface has an emissivity of 0.8, what is its surface temperature in outer space? State your assumptions in the calculations.arrow_forwardUnder conditions for which the same room temperature is maintained by a heating or cooling system, it is not uncommon for a person to feel chilled in the winter but comfortable in the summer. Consider a room whose air temperature is maintained at 22°C throughout the year, while the walls of the room are nominally at 24°C and 12°C in the summer and winter, respectively. The exposed surface of a person in the room may be assumed to be at a temperature of 32°C throughout the year and to have an emissivity of 0.90. The coefficient associated with heat transfer by natural convection between the person and the room air is approximately 2 W/m2-K. Calculate the following. Heat flux due to convection: qbonv W/m? Heat flux due to radiation in the summer: Trad i W/m? Heat flux due to radiation in the winter: gad W/m? i Physical Properties Mathematical Functionsarrow_forward
- A concrete wall, which has a surface area of 20 m2 and is 0.30 m thick, separates conditioned room air from ambient air. The temperature of the inner surface of the wall is maintained at 25°C, and the thermal conductivity of the concrete is 1 W/mK.(a) Determine the rate of heat loss through the wall for outer surface temperatures ranging from −15°C to 38°C, which correspond to winter and summer extremes, respectively. Display your results graphically.(b) On your graph, also plot the rate of heat loss as a function of the outer surface temperature for wall materials having thermal conductivities of 0.75 and 1.25 W/m⋅K. Explain the family of curves you have obtainedarrow_forwardIt is designed in such a way that the internal temperature of a commercial heat treatment furnace can reach up to 165 oC. All surfaces of the furnace consist of firebrick (10 cm), insulation material and sheet metal (3mm) from the inside out. Given that the outdoor temperature is 22 oC, the outer sheet will be allowed to go up to 35 oC, which is a temperature that will not disturb in contact with hands. In this case, determine the insulation material thickness to be used. The thermal conductivity coefficient of the insulation material is insulation 0.066 W / m oC, 60 W / m oC for sheet metal and 115 W / m oC for firebrick. Indoor heat transfer coefficient will be accepted as 25 W / m2 oC and 12 W / m2 oC for outdoor environment.arrow_forwardDuring hot summer weather, many people put “koozies” around their beverages to keep the drinks cold. In addition to preventing a warm hand from heating the container through conduction, what other mechanisms slow the process of warming beverages?arrow_forward
- The upper and lower compartments of a well-insulated container are separated by two parallel sheets of glass with an air space between them. One of the compartments is to be filled with a hot fluid and the other with a cold fluid. If it is desired that heat transfer between the two compartments be minimal, would you recommend putting the hot fluid into the upper or the lower compartment of the container? Why?arrow_forwardRequired information Consider an electrically heated brick house (k = 0.40 Btu/h-ft-°F) whose walls are 9 ft high and 1 ft thick. Two of the walls of the house are 50 ft long and the others are 35 ft long. The house is maintained at 70°F at all times while the temperature of the outdoors varles. On a certain day, the temperature of the Inner surface of the walls is measured to be at 64°F while the average temperature of the outer surface is observed to remain at 45°F during the day for 10 h and at 35°F at night for 14 h. 35 ft 50 ft 9 ft Determine the amount of heat lost from the house that day. (You must provide an answer before moving on to the next part.) The amount of heat lost from the house that day is [ 18526 Btu.arrow_forwardIt is designed in such a way that the internal temperature of a commercial heat treatment furnace can reach up to 165 oC. All surfaces of the furnace consist of firebrick (10 cm), insulation material and sheet metal (3mm) from the inside out. Given that the outdoor temperature is 22 oC, the outer sheet will be allowed to go up to 35 oC, which is a temperature that will not be disturbed by hand contact. In this case, determine the insulation material thickness to be used. Insulation material thermal conductivity coefficient is 0.066 insulation W / m oC, 60 W / m oC for sheet metal and 115 W / m oC for firebrick. Indoor heat transfer coefficient will be accepted as 25 W / m2 oC and 12 W / m2 oC for outdoor environment.arrow_forward
- Estimate the rate of heat transfer (J/s) from a 50.6°C sphere which has an emissivity of 0.2 if it is suspended in a cold volume maintained at -10.7°C. The sphere has a diameter of 0.2m. Reduce your answer in to two decimal point.arrow_forward[2] Consider a 1.2-m-high and 2-m-wide double-pane window consisting of two 3-mm-thick layers of glass (k = 0.78 W/m °C) separated by a 12-mm-wide stagnant air space (k = 0.026 W/m- °C). Determine the steady rate of heat transfer through this double-pane window and the temperature of its inner surface for a day during which the room is maintained at 24°C while the temperature of the outdoors is -5°C. Take the convection heat transfer coefficients on the inner and outer surfaces of the window to be h1 = 10 W/m2.°C and h2 = 25 W/m2.°C, and disregard any heat transfer by radiation. Glass 3 12 3 mm Frame a.) Steady rate of heat transfer. А. 318 W B. 214 W C. 114 W D. 321 W b.) Temperature of its inner surface. A. 25°C B. 17.5°C С. 15°С D. 19.2°Carrow_forwardTo control the aeration and the temperature, a composting plant stores compost in tall 1-m diameter cylindrical heaps. These compost cylinders are exposed to air at 20°C. The thermal conductivity of the compost heap is 1.12 W/m-K. The air around the compost has an average convection coefficient of 8 W/m2.K. The compost generates heat uniformly at 400 W/m³. Neglect any heat transfer from the top and bottom surfaces of the heap and neglect radiation. what is the surface temperature of the compost heap under steady conditions? 32.5 Carrow_forward
- Principles of Heat Transfer (Activate Learning wi...Mechanical EngineeringISBN:9781305387102Author:Kreith, Frank; Manglik, Raj M.Publisher:Cengage Learning