9.82 The front door of a dishwasher of width 580 mm has a vertical air vent that is 500 mm in height with a 20-mm spacing between the inner tub operating at 52°C and an outer plate that is thermally insulated. Tub- T,= 52°C- -Insulated surface Air (a) Determine the heat loss from the tub surface when the ambient air is 27°C. (b) A change in the design of the door provides the opportunity to increase or decrease the 20-mm spacing by 10 mm. What recommendations would you offer with regard to how the change in spacing

9.82 The front door of a dishwasher of width 580 mm has a vertical air vent that is 500 mm in height with a 20-mm spacing between the inner tub operating at 52°C and an outer plate that is thermally insulated. Tub- T,= 52°C- -Insulated surface Air (a) Determine the heat loss from the tub surface when the ambient air is 27°C. (b) A change in the design of the door provides the opportunity to increase or decrease the 20-mm spacing by 10 mm. What recommendations would you offer with regard to how the change in spacing

Principles of Heat Transfer (Activate Learning with these NEW titles from Engineering!)

8th Edition

ISBN:9781305387102

Author:Kreith, Frank; Manglik, Raj M.

Publisher:Kreith, Frank; Manglik, Raj M.

Chapter9: Heat Transfer With Phase Change

Section: Chapter Questions

Problem 9.34P

See similar textbooks

Similar questions

1. A composite furnace wall is made up of a 12-in. lining of magnesite refractory brick, a 5-in.thickness of 85% magnesia, and a steel casing 0.10-in. thick. Flue gas temperature is 2200 F andthe boiler room is at 80 F. Gas side film coefficient is 15 Btu/hr-sq.ft-F and air side is 4.0.Determine:a. The thermal current Q/Ab. Interface temperaturesc. Effect on thermal current and inside refractory wall temperature if the magnesia insulation weredoubled.
c) A steel pipe of 100 mm bore, and 10 mm bore thickness, carrying dry saturated steam at 28 bars, is insulated with a 40 mm layer of moulded insulation. This insulation in turn is insulated with a 60 mm layer of felt. The atmospheric temperature is 15 °C. Calculate: (i) the rate of heat loss by the steam per metre pipe length. (ii) the temperature of the outside Dimensions in mm surface.zzzzzzz h₂-15 W/m²K Steel k₁=50 W/mK AVALEHT Ø100 1₂ " Steam 28 bar h-550 W/m²K, Inner heat transfer coefficient = 550 W/m² K Outer heat transfer coefficient = 15 W/m² K Thermal conductivity of steel = 50 W/m K Thermal conductivity of felt = 0.07 W/m K Moulded insulation Felt Moulded insulation K₂=0.09 W/mK Thermal conductivity of moulded insulation = 0.09 W/m 40 10. A 60 15°C Felt K₁=0.07 W/mK zzzzzzzz
3. A 3 in O.D. aluminum tube (k=133 BTU/h ft°F) has 16 longitudinal fins spaced around its outside surface as shown below. The fins are .06 in thick and extend 2 in from the outside surface of the tube. If the outside surface of the tube wall is at 200F, the surrounding air is at 70°F and the convective heat transfer coefficient is 15 BTU/h ft°F, determine the percent increase in heat transfer for the finned pipe over that for the unfinned pipe. Note: longitudinal fins are rectangular fins that extend along the length of the tube. Figure shows view looking down the tube
VI.2 A coolant is transported in a pipe with external wall temperature of -30 °C and with outer diameter of 10 cm. The tube is thermally isolated by two layers: 1) an internal layer of foamed polypropylene with thermal conductivity of 0.08 W.m.K and thickness of 10 cm, and 2) an external felt layer with thermal conductivity of 0.05 W.m.K and thickness of 5 cm. Temperature of the outer surface is 25 °C. Calculate the heat flow from the surroundings to the tube with length of 100 m. What is the temperature on the boundary between polypropylene and felt layers? Result: The heat flow from the surroundings is approx. 1.77 kW. Temperature between layers of isolation is 8.8 °C.
2. A steam line is covered with two successive layers of insulation. The 1.6 in thick layer in contact with the pipe is asbestos which is covered with a 1.4 inch thickness of magnesia insulation. The internal pipe diameter is 3 in, the pipewall thickness is 0.40 in made from common brick. The steam temperature is 850ºF, and the internal surface film coefficient is 50 Btu/hr.ft².F, while the ambient outer temperature is 105°F and the outer surface film coefficient is 3.0 Btu/hr.ft².F. Calculate the following: a. value of U based upon the external area of the magnesia covering, Btu/hr.ft2.F b. heat loss from the steam for a length of 190 feet of pipe, Btu/hr
QUESTION 1 A domestic refrigerator with Inner dimensions of 0.7 m by 0.7 m at the base and height 1 m was designed to malntaln a set temperature of 6 "C. The bodies consist of two 10-mm-thick layers of Aluminium (k - 225 WmK) separated by a 30 mm polyurethane Insulation (k-0.028 WimK). If the average convection heat transter coefficient at the Inner and outer surfaces are 11.6 W/m2k and 14.5 W/m2K respectively, calculate: the resistance(R) for the Aluminium near the inner thermal layer in K/W to 8 decimal places. QUESTION 2 A domestic refrigerator with Inner dimensions of 0.7 m by 0.7 m at the base and helght 1 m was designed to malntaln a set temperature of 6 "C. The bodies consist of two 10-mm-thick layers of Aluminium (k - 225 W/mK) separated by a 30 mm polyurethane Insulation (k-0.028 WimK). If the average convection heat transfer coefficlent at the Inner and outer surfaces are 11.6 W/m2K and 14.5 W/mK respectively, calculate: the resistance(R) for the Aluminium near the outer…
T = 310 K The thickness of a wall is 0.07 m. right side of the wall 8. air and 300 K exposed to the ambient air. External surface temperature of the sur wall (right side) 500 K and heat transfer coefficient h=3OW /m² K k=0,86 W/mK emissivity rate of 0.78 and heat transfer coefficient of the wall What is the temperature of the inner wall?
A camera used for monitoring marine life is placed in water where T.. -5°C and the convection heat transfer coefficient h=1420 W/m²K. The camera is operating, but its battery is experiencing thermal runaway, causing the camera to become very hot, and there is volumetric heat generation, qe inside it. There is no heat generation within the waterproof, protective enclosure surrounding it. 00:08 The camera is already compromised; however, its owner hopes to save the protective case. Each interface (between layers A and B and between layers B and C) must not exceed a temperature of 185°C, or these plastic, protective layers will begin to melt. Approximate the camera and its casing as a composite, rectangular object with flat surfaces. The device's total thickness, L=LA + 2LB +Lc, is much smaller than its area (into the page); therefore, 1-D conduction can be approximated through the layers. On the left surface of layer A, the temperature is measured to be T₁ = 8.0°C, and the temperature on…
Example 29.10. (S.I. Units). 4 25 om nteam main, 225 matres long is covered with 5 orm of high temperature insrulation (K=0'095 W/m°K) and 4 om of low temperature inmudation (K-6-085 W/m K). The inner and outer surface temperaturen as measured are 400°C and 50°0 svapselively. Conspute : (a) the lotal hoat loss per hour (b) the total hent loes per aq. m. of outer eurface (c) the heat loss per aq. m. of pipe aurfuce (d) the temperalure between the two layere of inoulation. Negled hent conduetion through pipe material.
One vessel having a carbon-steel wall of thickness 5 mm carrying saturated steam and water at 423K. The vessel is insulated with magnesia of thickness 50 mm. If the ambient air temperature is 321 K, determine the heat loss from the vessel. Given: i. thermal conductivity of carbon steel is 52 W/m.K ii. thermal conductivity of magnesia is 0.5 W/m.K iii. surface coefficient of insulation surface is 3 W/m2.K
c) The heat transfer rate into the salmon fillet is governed by its surface thermal resistance, R °K/W, and the temperature difference across its surface, T; - T °K. (T, -r) Watts ...(1) R Also, the rate of temperature rise is dependent on the heat flow rate and thermal capacity of the salmon fillet. † = 4 K/s mC ..(2) In Equation (1), identify the 'through' variable and the 'across' variable. Is Equation (1) an equilibrium, compatibility or constitutive relationship?
3. Compute for the Nusselt value of a natural convection in a small holding tank with a heating element at the bottom. The calculated Ra number is 2.37 x 10º.