A common procedure for measuring the velocity of anairstream involves the insertion of an electrically heatedwire (called a hot-wire anemometer) into the airflow,with the axis of the wire oriented perpendicular to the flow direction. The electrical energy dissipated inthe wire is assumed to be transferred to the air by forcedconvection. Hence, for a prescribed electrical power, thetemperature of the wire depends on the convection coefficient, which, in turn, depends on the velocity of the air.Consider a wire of length
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Fundamentals of Heat and Mass Transfer
- Mass flow rate of hot fluid is 0.007 kg/s. Convection heat transfer coefficient of hot fluid stream is 1000 W/m?.°C. Thermophysical properties are given as follows. Hot fluid; c, = 5000 J/kg.°C Water; dynamic viscosity, µ = 0.001 Pa.s; Prandti number, Pr = 6.14; thermal conductivity, k = 0.607 W/m.°C; density, p = 1000 kg/m³; specific heat c, = 4200 J/kg.°C. Neglecting conduction resistance of the pipe, calculate heat exchanger effectiveness (ɛ), heat transfer rate (Q in J/s), outlet temperatures of the hot fluid (Thout) and water (Tw.out) for varying mass flow rate values of water provided below. Mass flow rate of water, m (kg/s) 0.0025 0.01 0.025 0.05 0.075 0.1 Plot heat exchanger effectiveness (ɛ), heat transfer rate (Q in J/s), outlet temperatures of the hot fluid (Thout) and water (Tw.out) as a function of water mass flow rate (m .). Comment on the results. Hot fluid in (65 °C) Water Water in (25 °C) out d = 0.5 cm Hot fluid out L= 5 marrow_forwardA thermocouple junction is in the form of 8 mm diameter sphere. Properties of materialare: Cp = 420 J/kg-K; ρ = 8000 kg/m3 ; k = 40 W/m-K; h = 40 W/m2 -K. This junction isinitially at 40 oC and inserted in a stream of hot air at 300 oC. Find the following:a. Time constant of the thermocouple.b. The thermocouple is taken out from the hot air after 10 seconds and kept in still airat 30 oC. Assuming the heat transfer coefficient in air is 10 W/m2-oC, find thetemperature attained by the junction 20 seconds after removal from hot air.arrow_forwardA certain liquid flow inside a 4 cm diameter pipe, 6 meter long with an entering temperature of 350 C. the wal temperature is maintained at 575 C, and the mass flow rate of the metal is 60 kg/min. p=6000 kg/m, Npr = 0.003, m = 0.003 N-s/m, k = 6.2 w/m-k, Cp = 0.41 kj/kg-k. what is the convection coefficient of the liquid (w/m-k)arrow_forward
- Merrill et al. (1965) in a series of classic experiments studied the flow of blood in capillary tubes of various diameters. The blood had a hematocrit of 39.3 and the temperature was 20°C. They measured the pressure drop as a function of the flow rate for five tube diameters ranging from 288 to 850 μm. When they expressed the measured pressure drops in terms of the wall shear stress, and the volumetric flow rates in terms of the reduced average velocity, all of the data for the various tube sizes formed, within the experimental accuracy, a single line as predicted by the Rabinowitsch equation expressed in terms of reduced average velocity. From their results they provide the following values of the Casson parameters at 20°C: τy = 0.0289 dynes cm−2 and s = 0.229 (dynes s cm−2)1/2. Using these values for τy and s, show that the equation below for reduced average velocity provides an excellent fit to their data summarized in the following table. (Wall shear stress) τw , dynes cm-2…arrow_forwardAn electric resistance heater is embedded in a long cylinder ofdiameter 30mm. When water with a temperature of 25 C and velocityof 1m/s flows crosswise over the cylinder, the power per unit lengthrequired to maintain the surface at a uniform temperature of 90 C is28kW/m. When air, also at 25 C, but with a velocity of 10m/s isflowing, the power per unit length required to maintain the samesurface temperature is 400W/m. Calculate and compare the convectioncoefficients for the flows of water and air.arrow_forwardTopic: Heat transfer Completely solve and box the final answer. 1. A 20degC water flows to 50cmx60cm flat plate with velocity of 5.2m/s . The flat plate surface temperature is maintained at 40deg C. The air flows parallel to the 50cm side of the plate. If the kinematic viscosity of water is 78x10-8 m2/s, at what length the flow become turbulent?arrow_forward
- Example(1-14): mixture gas and liquid flow through 0.02 m inside diameter pipe at total flow rate of 0.2 kg/s. if the gas weight fraction is 0.149 what is the pressure drop per unit length of pipe. Where the pipe roughness 0.00015 mm, liquid and gas viscosities are 2x103 pa.s and 1x10-5 pa.s respectively. finaly the liquid and gas densities are 1000 kg/m³ and 60 kg/m³ pa.s respectively.arrow_forwardMass flow rate of hot fluid is 0.007 kg/s. Convection heat transfer coefficient of hot fluid stream is 1000 W/m?.°C. Thermophysical properties are given as follows. Hot fluid; c, = 5000 J/kg.°C Water; dynamic viscosity, u = 0.001 Pa.s; Prandti number, Pr = 6.14; thermal conductivity, k = 0.607 W/m.°C; density, p = 1000 kg/m?; specific heat c, = 4200 J/kg.°C. Neglecting conduction resistance of the pipe, calculate heat exchanger effectiveness (ɛ), heat transfer rate (Q in J/s), outlet temperatures of the hot fluid (Th,out) and water (Tw,out) for varying mass flow rate values of water provided below. Mass flow rate of water, m„ (kg/s) 0.0025 0.01 0.025 0.05 0.075 0.1 Plot heat exchanger effectiveness (8), heat transfer rate (Q in Jis), outlet temperatures of the hot fluid (Th,out) and water (Tw,.cut) as a function of water mass flow rate (m„.). Comment on the results. Hot fluid in (65 °C) Water Water in (25 °C) out d = 0.5 cm Hot fluid out L= 5 marrow_forwardQ2/ An aluminum sphere weighting 7kg and initially at a temperature of 533K is suddenly immersed in a fluid at 283K. if heat transfer coefficient between the sphere and fluid is 50W/m?.°C. Take density=2707kg/m3, specific heat=0.9KJ/kg.ºC and thermal conductivity= 204W/m°C. Determine th Bi number and And determine the time required to cool sphere to 263karrow_forward
- A composite plane wall consisting of materials, 1.5-in steel (k = 312 BTU-in/HR.ft2.0F) and 2-in aluminum (k = 1400 BTU-in/HR.ft2.0F), separates a hot gas at Ti = 2000F, hi = 2 BTU/HR.ft2.0F, from cold gas at To = 80 deg F, ho = 5. If the hot fluid is on the aluminum side, find: a) Transmittance, U; b) The heat through 100 sq. ft of the surface under steady state condition and c) The interface temperature at the junction of the metals.arrow_forwardEstimate the natural convection heat transfer coefficient of the horizontal pipe. The temperature of the outer surface of the pipe is 120 ° C. The ambient air temperature is 40 ° C. The outer diameter of the pipe is 18 cm. Convection coefficient = ..... W / m² ° C.arrow_forwardMass flow rate of hot fluid is 0.007 kg/s. Convection heat transfer coefficient of hot fluid stream is 1000 W/m? °C. Thermophysical properties are given as follows. Hot fluid; c, = 5000 J/kg.°C Water; dynamic viscosity, u = 0.001 Pa.s; Prandtl number, Pr = 6.14; thermal conductivity, k = 0.607 W/m.°C; density, p = 1000 kg/m2; specific heat c, = 4200 J/kg.°C. Neglecting conduction resistance of the pipe, calculate heat exchanger effectiveness (ɛ), heat transfer rate (Q in J/s), outlet temperatures of the hot fluid (Th,out) and water (Tw.out) for varying mass flow rate values of water provided below. Mass flow rate of water, m (kg/s) 0.0025 0.01 0.025 0.05 0.075 0.1 Plot heat exchanger effectiveness (:), heat transfer rate (Q in J/s), outlet temperatures of the hot fluid (Thout) and water (Tw.out) as a function of water mass flow rate (m). Comment on the results. Hot fluid in (65 °C) Water Water in (25 °C) out d = 0.5 cm Hot fluid out L = 5 marrow_forward
- Principles of Heat Transfer (Activate Learning wi...Mechanical EngineeringISBN:9781305387102Author:Kreith, Frank; Manglik, Raj M.Publisher:Cengage Learning