A concrete wall, which has a surface area of
(a) Determine the heat loss through the wall for outersurface temperatures ranging from
(b) On your graph, also plot the heat loss as a function ofthe outer surface temperature for wall materials having thermal conductivities of 0.75 and
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Chapter 1 Solutions
Fundamentals of Heat and Mass Transfer
- 1.19 A cryogenic fluid is stored in a 0.3-m-diameter spherical container is still air. If the convection heat transfer coefficient between the outer surface of the container and the air is 6.8 , the temperature of the air is 27°C, and the temperature of the surface of the sphere is –183°C, determine the rate of heat transfer by convection.arrow_forwardA pipe carrying superheated steam in a basement at 10C has a surface temperature of 150C. Heat loss from the pipe occurs by radiation (=0.6) and natural convection (hc=25W/m2K). Determine the percentage of the total heat loss by these two mechanisms.arrow_forward1.60 Two electric resistance heaters with a 20 cm length and a 2 cm diameter are inserted into a well-insulated 40-L tank of water that is initially at 300 K. If each heater dissipates 500 W, what is the time required for bringing the water temperature in the tank to 340 K? State your assumption for your analysis.arrow_forward
- 2.38 The addition of aluminum fins has been suggested to increase the rate of heat dissipation from one side of an electronic device 1 m wide and 1 m tall. The fins are to be rectangular in cross section, 2.5 cm long and 0.25 cm thick, as shown in the figure. There are to be 100 fins per meter. The convection heat transfer coefficient, both for the wall and the fins, is estimated to be K. With this information determine the percent increase in the rate of heat transfer of the finned wall compared to the bare wall.arrow_forward700 W/m3 electrical heat is generated in a large plane wall whose one side is insulated while the other side is subjected to convection. The thermal conductivity of the wall is (k W/m.K) and the convection heat transfer coefficient is (h = 17 W/m?K). Determine the location and the value for the maximum temperature and the minimum temperature in the plate for steady one-dimensional heat transfer. Assume T. = 25°C. A=1 m?; L= 25 cm). = 20arrow_forward1. A 1000-W iron is left on the iron board with its base exposed to the air at 20°C. The convection heat transfer coefficient between the base surface and the surrounding air is 35 W/m². °C. If the base has an emissivity of 0.6 and a surface area of 0.02 m², determine the temperature of the base of the iron. 2. The inner and outer surfaces of a 5-m x 6-m brick wall of thickness 30 cm and thermal conductivity 0.69 W/m °C are maintained at temperatures of 20°C and 5°C, respectively. Determine the rate of heat transfer through the wall, in W.arrow_forward
- An isolating wall (made up of 2-10mm thick plywood with 5mm woven silica sheet in between) encloses a steam-room to prevent the outside area from having the same temperature as the inside of the room. If the total area of the wall is 100 sq.m. and coefficient of thermal conductivity (k) for plywood and silica sheets are 0.12 and 0.015 W/mK respectively, what is the rate of heat transfer if the inside temperature is 800 °C while the outside is 42°C? answer must be in Wattsarrow_forward4. A box with total wall area of 0.6m² and wall thickness 3cm is used to cool drinks. The inner and outer surface of the box are 0°C and 50°C respectively. Determine: (i) The rate of heat flow into the box (ii) The total heat flow in one day (iii) The mass of ice melted Take: Thermal conductivity of the box material to be 0.010 W / (m. K) Heat of fusion of ice to be Lf = 3.34 × 105 J /kg 86,400 seconds are in a day. 3. 4500J of heat was absorbed from a Carnot engine from a reservoir at 65OK. The engine did some work, and discards some heat to a sink at 350K. Evaluate: ) The heat that is discarded (ii) The work the engine did (iii) The efficiency of the systemarrow_forwardThe rate of heat flow through a hallow sphere of inner radius 0.25 m and outer radius 0.35m, whose thermal conductivity is 5 W/mK, maintained at temperatures of 400°C and 300°C respectively equal toarrow_forward
- Q1) Consider the base plate of a 800-W household iron having a thickness of L=0.6 cm, base area of A=160 cm2, and thermal conductivity of k3120 W/m-°C. The inner surface of the base plate is subjected to uniform heat flux generated by the resistance heaters inside. When steady operating conditions are reached, the outer surface temperature of the plate is measured to be 85°C. Disregarding any heat loss through the upper part of the iron and taking the nodal spacing to be 0.2 cm, (a) obtain the finite difference formulation for the nodes and (b) determine the inner surface temperature of the plate by solving those equations. Insulation Resistance heater, 800 W 85°C Base plate Ar= 0.2 cm 160 cm? 11111111111I D00000000000000000000000arrow_forwardRock has often been suggested as a medium for the thermal storage of energy.A cylindrical piece of rock with diameter 10 m and height 20 m is used for thestorage of thermal energy. The rock is insulated and has an average heattransfer coefficient, U = 0.28 kW/m2 K. The density of the rock material is2,650 kg/m3 and its specific heat capacity is 0.72 kJ/kgK. The temperature ofthe rock is raised to 500C and the ambient temperature is 25C. Determine:a) The total energy stored in the rock in MWh.b) The temperature of the rock 12 h after the heating process stops.c) The heat that has escaped from the rock during this 12 h period.d) The loss of exergy of the rock during this 12 h period.arrow_forwardAnswerCalculate the total resistance (in K/W ) through the vertical walls of a boiler furnace 20 m in area. The walls are constructed from aninner fire brick wall 30 cm thick of thermal conductivity 0.4 W/mK, a 5 mm thick steel protective layer of thermal conductivity 0.055kW/mK and a layer of ceramic blanket insulation of thermal conductivity 0.2 W/mK at 8 cm thickness. The inside temperature of thefire bricklayer was measured at 600 C and the temperature of the outside of the insulation 60 C.arrow_forward
- Principles of Heat Transfer (Activate Learning wi...Mechanical EngineeringISBN:9781305387102Author:Kreith, Frank; Manglik, Raj M.Publisher:Cengage Learning