Consider temperature measurement in a gas stream using the thermocouple junction described in Problem 7.86
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Fundamentals of Heat and Mass Transfer
- A 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_forwardFully developed conditions are known to exist for water flowing through a 50-mm ID tube at 0.02 kg/s and 27°C. What is the maximum velocity of the water in the tube? What is the pressure gradient associated with the flow?arrow_forwardMerrill 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_forward
- Provide schematic diagram and solutions.arrow_forwardA square isothermal chip is of width 5mm on a side mounted in a substrate such that its side and back surfaces are well insulated, while the front surface is exposed to the flow of coolant at 15C. From reliability considerations, the chip temperature must not exceed 85C. If air is used as a coolant, h = 200W/m2. If a dielectric liquid is used as coolant, h = 3000W/m2. What is the difference in maximum allowable power through the chip between the two coolants? (answer in W) *arrow_forward8.25 Engine oil flows at a rate of 1 kg/s through a 5-mm-diameter straight tube. The oil has an inlet temperature of 45°C and it is desired to heat the oil to a mean temperature of 80°C at the exit of the tube. The surface of the tube is maintained at 150°C. Determine the required length of the tube. Hint: Calculate the Reynolds numbers at the entrance and exit of the tube before proceeding with your analysis.arrow_forward
- Question c d and e pleasearrow_forwardConsider two cases involving parallel flow of dry air at V = 5 m/s, T = 45°C, and atmospheric pressure over an isothermal plate at T = 20°C. In the first case, Rex, = 5 x 105, while in the second case the flow is tripped to a turbulent state at x = 0 m. At what x-location, in m, are the thermal boundary layer thicknesses of the two cases equal? What are the local heat fluxes, in W/m², at this location for the two cases? x = d'am = qturb = Mc i m W/m² W/m²arrow_forward! Required information The local atmospheric pressure in Denver, Colorado (elevation 1610 m), is 83.4 kPa. Air at this pressure and at 30°C flows with a velocity of 6.00 m/s over a 2.50-m × 8.00-m flat plate whose temperature is 120°C. The properties of air at 0.823 atm and at the film temperature of (120 + 30)/2 = 75°C are k = 0.02971 W/m.°C, v = 2.486 × 10-5 m²/s, and Pr = 0.7166. Determine the rate of heat transfer from the plate if the air flows parallel to the 8.00-m-long side. The rate of heat transfer from the plate if the air flows parallel to the 8.00-m-long side is kW.arrow_forward
- A vehicle carrying refrigeration box is moving with a speed of 24 m/s on a road withambient temperature of 323 K. The dimensions of box are 3 m(H) × 4 m (W) × 10 m (L).Assume a wall temperature of 283 K and air flow is parallel to the longest side of the box.Neglecting the heat loss from the front side and backside of the box, calculate heat lossfrom four surfaces. For flow over flat surfaces useNu = 0.036(Re)0.8(Pr)1/3The properties of air at bulk mean temperature are : = 1.165 kg/m3, Pr = 0.701, cp = 1005 J/kg – K, = 16 × 10–6m2/sarrow_forwardConsider two cases involving parallel flow of dry air at V = 3 m/s, T = 45°C, and atmospheric pressure over an isothermal plate at T = 20°C. In the first case, Rex = 5 x 105, while in the second case the flow is tripped to a turbulent state at x = 0 m. At what x-location, in m, are the thermal boundary layer thicknesses of the two cases equal? What are the local heat fluxes, in W/m², at this location for the two cases? x = 91am = qurb = i i m W/m² W/m²arrow_forwardPLEASE ANSWER COMPLETELY AND CLEAN FOR AN UPVOTE!!arrow_forward
- Principles of Heat Transfer (Activate Learning wi...Mechanical EngineeringISBN:9781305387102Author:Kreith, Frank; Manglik, Raj M.Publisher:Cengage Learning