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The energy consumption associated with a home water heater has two components: (i) the energy that must be supplied to bring the temperature of groundwater to the heater storage temperature, as it is introduced to replace hot water that has been used; (ii) the energy needed to compensate for heat losses incurred while the water is stored at the prescribed temperature. In this problem, we will evaluate the first of these components for a family of four, whose daily hot water consumption is approximately 100 gal. If groundwater is available at
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Chapter 1 Solutions
Introduction to Heat Transfer
- 2.2 A small dam, which is idealized by a large slab 1.2 m thick, is to be completely poured in a short Period of time. The hydration of the concrete results in the equivalent of a distributed source of constant strength of 100 W/m3. If both dam surfaces are at 16°C, determine the maximum temperature to which the concrete will be subjected, assuming steady-state conditions. The thermal conductivity of the wet concrete can be taken as 0.84 W/m K.arrow_forward1.67 In beauty salons and in homes, a ubiquitous device is the hairdryer. The front end of a typical hairdryer is idealized as a thin-walled cylindrical duct with a 6-cm diameter with a fan at the inlet that blows air over an electric heating coil as schematically shown in the figure. The design of this appliance requires two power settings, with which the air blown over the electric heating coil is heated from the ambient temperature of to an outlet temperature of and with exit air velocities of 1.0 m/s and 1.5 m/s. Estimate the electric power required for the heating coil to meet these conditions, assuming that heat loss from the outside of the dryer duct is neglected.arrow_forwardModel the following heat transfer situations. Specify heat flows and storages. Try to write down the mathematical expressions. (i) Solar heating of the road surface (ii) A steam pipe passing through an open space between two buildings (iii) Heat transfer from a person in a warm room in the cold season (iv) Pressure cooker-warming up-cooling down (v) Pressure cooker-steady conditions (vi) A rod with one end in a furnace and the remaining surface in atmosphere (vii) A wire carrying current, exposed to air (viii) A water heater (electrical) with hot water being drawn out with cold water admission. (ix) Cake being baked in an oven or a fruit placed in a refrigeration (x) A frying pan placed on a stove. 1.2 Choose the correct statement in each question. (i) A pipe carrying steam at about 300°C traverses a room, the air being still at 30°C. The major fraction of the heat loss will be by (a) conduction to the still air (b) convection to the air (c) radiation to the surroundings…arrow_forward
- Determine the quantity (volume) of saline water in a steam generator. The heat energy of 1631 kJ is supplied to saline water in the steam generator to heat from 23ºC to 115ºC for the generation of water vapor, Take the density & specific heat of the solution as 1010 kg/m3 & 3.8 J/kgºK respectively. Solution: Change in Temperature (in K) Mass of the saltwater (in kg) Quantity (Volume) of saltwater (in m3)arrow_forwardWe have a system made up of a glass container (glass) whose bottom and top have been insulated. A mass of liquid (m) is introduced inside it at a temperature T. As this mass of water transmits heat, its temperature TI decreases, without changing the ambient temperature TA. Measurements of temperature are made with water and with saline water at different times. How would you calculate the convective heat transfer coefficient (h)?arrow_forwardSuppose that the 10 cm thick concrete wall of a commercial building measures 30 mby 4 m. The energy impinging on the surface is 700 Wm-2. Under these conditionsthe external air temperature is 25ºC, and the internal and external surfacetemperatures of the concrete wall are 17ºC and 40ºC, respectively.(a) State and briefly describe the three heat transfer mechanisms.[30%](b) Calculate the net amount of thermal energy radiated by the wall.[40%](c) State your assumptions and briefly discuss their effect on the relativesizes of the heat transfer mechanisms.[30%]Data for Question A3.Heat transfer coefficient of air at 25ºC = 5 Wm-2K-1Thermal conductivity of concrete = 1.2 Wm-1K-1Emissivity of concrete = 0.85Stefan’s constant = 5.7 x 10-8 Wm-2K-4arrow_forward
- List and describe three methods of heat transfer. Give an example of each. (1) Method? Example? (2) Method? Example? (3) Method? Example?arrow_forwardRadioactive wastes are packarrow_forwardQuestion 2 Steam at 320ºC flows in a stainless steel pipe, whose inner and outer diameters are D₁ = 5 cm and Do 5.5 cm. The pipe is insulated with insulating material - glass fiber (organic bonded) at a thickness of 3 cm. Heat is lost to surroundings at 5°C via convection and radiation with a combined heat transfer coefficient of h₂ = 18 W/m²K. If the heat transfer coefficient inside the pipe is h₁ = 60 W/m²K, determine: a) the heat loss from the steam per unit length of pipe b) temperature drop across the pipe thicknessarrow_forward
- Q2) A central processing unit (CPU), also called a central processor or main processor, is the t important processor in each computer. Thermal design of CPUs is vital for its stable ration. Consider the design problem described below. w = 5 cm. N-1 H L=5 cm w=5 cm. L=5 cm. K-200 W/mK Kar 0.025 W/mK T= 100 C Tair= 25 C Vair=1.0 m/s Vair1.3 x 10-5 m²/s Pr=0.72arrow_forwardAs shown in the figure below, a jacketed container is used to cool the process stream. Some information is given for this process;(i) The volume of liquid inside the tank, V and the volume of refrigerant in the jacket, VJ, are constant. The volumetric flow rate qF is constant. But qJ changes over time.(ii) the heat transfer coefficients through the jacketed container are negligible.(iii) the tank contents and jacket contents are well mixed and have significant heat capacitances.(iv) the thermal capacitances of the tank wall and jacket wall are negligible.(v) The overall heat transfer coefficient used for heat conduction between the tank liquid and the coolant varies with the coolant flow rate:U = K.qJ0,8Here, U (Btu / hr.ft2.0F), qJ (ft3 / hr), K (constant)Derive the dynamic model for this system. Perform a degree of freedom analysis. Do not forget to write down any additional assumptions!arrow_forwardQ2 FigureQ2showsaHeatingRoom,whichpartlyisolated.Thereisathermalsystemconsisting of an electric heater in a room. Heat input by the heater is Q1and heat loss from room is Q2. Air in the room is at uniform temperature, ?, and surrounding temperature is ?o. Thermal capacity of the room is C, and wall thermal resistance is R. (a) Determine a mathematical model of temperature of the room. (b) DeterminetheTransferFunctionoftheheatingroom. (c) Determine the output response of the system when a step input 25°? is given.arrow_forward
- Principles of Heat Transfer (Activate Learning wi...Mechanical EngineeringISBN:9781305387102Author:Kreith, Frank; Manglik, Raj M.Publisher:Cengage Learning
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