Following the hot vacuum forming of a paper-pulpmixture, the product, an egg carton, is transported on aconveyor for 18 s toward the entrance of a gas-firedoven where it is dried to a desired final water content.Very little water evaporates during the travel time.So, to increase the productivity of the line, it is proposed that a bank of infrared radiation heaters, whichprovide a uniform radiant flux of
The chief engineer of your plant will approve the purchase of the heaters if they can reduce the water contentby 10% of the total mass. Would you recommend thepurchase? Assume the heat of vaporization of water is
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Fundamentals of Heat and Mass Transfer
- Determine the power requirement of a soldering iron in which the tip is maintained at 400C. The tip is a cylinder 3 mm in diameter and 10 mm long. The surrounding air temperature is 20C, and the average convection heat transfer coefficient over the tip is 20W/m2K. The tip is highly polished initially, giving it a very low emittance.arrow_forward1.15 A thermocouple (0.8-mm-diameter wire) used to measure the temperature of the quiescent gas in a furnace gives a reading of . It is known, however, that the rate of radiant heat flow per meter length from the hotter furnace walls to the thermocouple wire is 1.1 W/m and the convection heat transfer coefficient between the wire and the gas is K. With this information, estimate the true gas temperature. State your assumptions and indicate the equations used.arrow_forwardA thin, disk-shaped silicon water of diameter 20cm on a production line must be maintained at a temperature of 100 degree celcius. The wafer loses heat to the room byconvection and radation from its upper surface, while heat is supplied at a constant flux from below. The surrounding air is at 20 degree C while all surrounding surfaces can be approximated to be isothermal at a temperature of 15 degree C. The wafer to air heat transfer coefficient is 30W/m^2-K and the emisivity of the wafer’s surface (approximate as graybodies) is 0.85. How much heat must be applied to the wafer at the unit of W?arrow_forward
- Trasient Cooling What are some of the factors and assumptions that would casue a different between the experimential convection coefficient, hexp, and the theorectical htheo?arrow_forwardWhat is the rate of rice husk consumption of a 2-ton grain dryer requiring to dry paddy from 22 to 14% in 8 hrs. The dryer overall thermal efficiency is 45%. Assume a heat of vaporization for paddy of 600 kCal/kg of moisture evaporated and heating value for rice husk of 3,000 kcal/kg.arrow_forwardAmmonia is to be removed from a 10 per cent ammonia-air mixture by countercurrent scrubbing with water in a packed tower at 293 K so that 99 per cent of the ammonia is removed when working at a total pressure of 101.3 kN/m². If the gas rate is 0.95 kg/m?s 155 of tower cross-section and the liquid rate is 0.65 kg/m²s, what is the necessary height of the tower if the absorption coefficient Kga = 0.001 kmol/m³s (kN/m²) partial pressure difference. The equilibrium data are: Concentration (kmol NH3/kmol water) Partial pressure NH3 (kN/m²) 0.021 0.031 0.042 0.053 0.079 0.106 0.150 1.6 2.4 3.3 4.2 6.7 9.3 15.2arrow_forward
- A manufacturing plant of 5500 square meters has 3.8 m high ceilings and changes its inside air three times per hour by maintaining a slightly positive air pressure (100kPa). The roomtemperature is maintained at 23°C. To assist in the sizing of a heating system it is assume in the design conditions that the outside temperature is -20°C. Basing the heating requirements on the indoor conditions, determine the heating required to compensate for the infiltration.A. 881.5 kwB. 188.5 kwC. 588.1 kwD. 511.8 kwarrow_forwardVacuum furnaces are used in manufacturing for metal heating in brazing and sintering processes, as well as for heat treatment of steel alloys. The vacuum, and absence of air/oxygen, facilitates a low contamination process and prevents detrimental surface oxidisation. Heat is often provided in these furnaces by electrical heating elements, and their thermal design is critical to the effective operation of the furnace. In one such case, this element is modelled as a long, cylindrical electrically heated rod, 20 mm in diameter installed in a vacuum furnace as shown. The surface of the heating rod has an emissivity of 0.9 and is maintained at 1000 K, while the interior walls of the furnace are black and are at 800 K. Calculate the net rate at which heat is lost from the rod per unit length.arrow_forwardA silicon wafer of diameter D -120 mm, and emissivity of 0.6 is at an initial temperature of Ti- 325oC and is allowed to cool in quiescent, ambient air and large surroundings for which Tair Tsur 35oC. What is the rate of cooling from the upper surface of the wafer? Properties of Air: k0.0373 W/m.C.v- 32.3910-6 m2 alpha 47.2106 m2/s Pr 0.686. B= 1/Tf = 0.0022 K-1. Select one: O a. 344 W O b. 53 W O . 627 W O d. 86 Warrow_forward
- 21. A facing operation is normally performed on which one of the following machine tools: O drill press O lathe Omilling machine Oplaner Oshaper ترك السؤال ارسال الاجابةarrow_forwardThe fuel assembly shown in the left figure consists of periodic arrays of annular bare fuel rods, which are cooled by passing water through the center of the rods as well as over the outer surface. We want to analyze the thermal performance of the fuel rods by dividing the assembly into a number of unit cells (control volumes) and evaluating the performance of a cell, as shown in the right figure.arrow_forwardQuestion : Studies show that the major energy consumption in Fijian villages is wood which is used for cooking over open fires. Typical consumption of wood is 1 kg person–1day–1. (a) Estimate the heat energy required to boil a 2-liter pot full of water. Assuming this to be the cooking requirement of each person, compare this with the heat content of the wood, and thus estimate the thermal efficiency of the open fire. (b) How much timber has to be felled each year to cook for a village of 200 people?Assuming systematic replanting, what area of crop must the village therefore set aside for fuel use if it is not to make a net deforestation? Hint: refer to Table 10.4. (c) Comment on the realism of the assumptions made, and revise your estimates accordingly. Answer: (a) mcDT ≈ 0.6 MJ (heat losses from pot imply actual requirement is higher). h ≈ 3%. (b) 70 tonnes; 7 ha.arrow_forward
- Principles of Heat Transfer (Activate Learning wi...Mechanical EngineeringISBN:9781305387102Author:Kreith, Frank; Manglik, Raj M.Publisher:Cengage Learning