Pick out the wrong statement.

(A) Reciprocal of the resistance to heat flow is called thermal conductance

(B) Unit of thermal conductance is W/°K

(C) Thermal conductance of a wall of thickness 'L', thermal conductivity 'k'

and heat flow area 'A' is kL/A

(D) None of these

1 Answer

Answer :

(C) Thermal conductance of a wall of thickness 'L', thermal conductivity 'k'

and heat flow area 'A' is kL/A

Related questions

Description : The heat flux (from outside to inside) across an insulating wall with thermal conductivity, K = 0.04 W/m.°K and thickness 0.16m is 10 W/m2 . The temperature of the inside wall is - 5°C. The outside wall temperature is (A) 25°C (B) 30°C (C) 35°C (D) 40°C

Last Answer : (C) 35°C

Description : A furnace is made of a refractory brick wall of thickness 0.5 metre and thermal conductivity 0.7 W/m.°K For the same temperature drop and heat loss, this refractory wall can be replaced by a layer of diatomaceous earth of ... and thickness __________ metre. (A) 0.01 (B) 0.1 (C) 0.25 (D) 0.5

Last Answer : (B) 0.1

Description : Conductance is given by (where, x = thickness, A = heat flow area, K = thermal conductivity.) (A) x/KA (B) KA/x (C) K/Ax (D) A/Kx

Last Answer : (B) KA/x

Description : Walls of a cubical oven are of thickness l, and they are made of material of thermal conductivity k. The temperature inside the oven is 100°C and the inside heat transfer co-efficient is 3k/l'. If the wall temperature ... wall temperature in degree centigrade? (A) 35.5 (B) 43.75 (C) 81.25 (D) 48.25

Last Answer : (C) 81.25

Description : A composite flat wall of a furnace is made of two materials 'A' and 'B'. The thermal conductivity of 'A' is twice of that of material 'B', while the thickness of layer of 'A' is half that of B. If the temperature ... drop (in °K) across the layer of material 'A' is (A) 125 (B) 133 (C) 150 (D) 160

Last Answer : (D) 160

Description : One face of a furnace wall is at 1030°C and the other face is exposed to room temperature (30°C). If the thermal conductivity of furnace wall is 3 W. m-1. k-1 and the wall thickness is 0.3 m, the maximum heat loss (in W/m) is (A) 100 (B) 900 (C) 9000 (D) 10000

Last Answer : (D) 10000

Description : The variation of thermal conductivity of a metal with temperature is often correlated using an expression of the form K = K0 + at, where, K is the thermal conductivity and T is the temperature (in °K). The units of 'a' in SI system will be (A) W/m.k (B) W/m (C) W/m.k

Last Answer : (C) W/m.k

Description : Pick out the wrong statement. (A) Superheated steam is preferably not used for process heating because of its low heat transfer film co-efficient (B) In a shell and tube heat exchanger ... surface heat exchangers, when the direction of fluid flow is parallel to the axis of the tube

Last Answer : (C) S.I. unit of fouling factor is Watt/m2 .°K

Description : What is the critical radius of insulation (cms) for a metallic cylinder, if the convective heat transfer co-efficient with the ambient atmosphere is 5 W/m2. °K? Thermal conductivity of metal and insulation material are 40 and 0.1 W/m.°K respectively. (A) 2 (B) 8 (C) 10 (D) 40

Last Answer : (A) 2

Description : The left face of a one dimensional slab of thickness 0.2 m is maintained at 80°C and the right face is exposed to air at 30°C. The thermal conductivity of the slab is 1.2 W/m.K and the heat transfer co-efficient from the ... temperature of the right face in °C is (A) 77.2 (B) 71.2 (C) 63.8 (D) 48.7

Last Answer : (D) 48.7

Description : The unit of conductance in SI unit is (A) W/m (B) W/m2 (C) W/°K (D) W/m°K

Last Answer : (C) W/°K

Description : Pick out the wrong statement. (A) The shear stress at the pipe (dia = D, length = L) wall in case of laminar flow of Newtonian fluids is (D/4L). ∆p (B) In the equation, T. gc = k. ... to motion (D) With increase in the Mach number >0.6, the drag co-efficient decreases in case of compressible fluids

Last Answer : (D) With increase in the Mach number >0.6, the drag co-efficient decreases in case of compressible fluids

Description : reduction in thermal resistance during heat transfer does not occur in the (A) Convection heat transfer by stirring the fluid and cleaning the heating surface (B) Conduction heat transfer by ... Radiation heat transfer by increasing the temperature and reducing the emissivity (D) None of these

Last Answer : Option C

Description : Pick out the wrong statement. (A) In the McCabe-Thiele diagram for binary distillation, vertical feed line represents saturated liquid feed and horizontal feed line represents saturated vapour feed (B) In ... layers over a flat plate are of equal thickness, if Schmidt number is equal to unity

Last Answer : (C) For Laminar flow over a plate of length L, the local mass transfer co￾efficient at a distance L from the leading edge is 1.5 × 10 -2m/s. Then the average mass transfer co-efficient for the plate is 2 × 10 -2m/s

Description : Heat transfer rate described by Fourier's law will decrease, if the __________ increases. (A) Thermal conductivity (B) Thickness (C) Temperature difference (D) Heat transfer area

Last Answer : (B) Thickness

Description : In SI units, thermal conductivity is expressed in (A) Watt/m.°K (B) Watt/m2 . °K (C) Watt/m2 . °K (D) Watt/m4 . °K

Last Answer : (A) Watt/m.°K

Description : The ratio of thermal & electrical conductivity is same for all the metals at the same temperature; and at around room temperature, this ratio is proportional to(where, T = absolute temperature, °K) (A) T (B) 1/T (C) T2 (D) 1/T2

Last Answer : A) T

Description : A wall has two layers of materials A and B; each made of a different material. Both the layers have the same thickness. The thermal conductivity of material A is twice that of B. Under the equilibrium, the temperature ... difference across the layer A is __________ °C. (A) 6 (B) 12 (C) 18 (D) 24

Last Answer : (B) 12

Description : Choose the most important factor on which the heat conducted through a wall in a unit time will depend on? (A) Thickness of the wall (B) Area of the wall perpendicular to heat flow (C) Material of the wall (D) Temperature difference between the two surfaces of the wall

Last Answer : (D) Temperature difference between the two surfaces of the wall

Description : A metal wire of 0.01 m dia and thermal conductivity 200 W/m.K is exposed to a fluid stream with a convective heat transfer coefficient of 100 W/m2 .K. The Biot number is (A) 5.6 (B) 0.025 (C) 3.5 (D) 0.0035

Last Answer : (B) 0.025

Description : What happens to thermal conductivity of a wall if its thickness double?

Last Answer : Need answer

Description : Pick out the wrong statement. (A) Pure rubber is as useless as pure gold as a material of construction (B) Thermal conductivity of aluminium is higher than that of copper; henceit is ... has poor weldability (D) Reinforced plastics are made from both thermoplastic as well as thermosetting plastics

Last Answer : (B) Thermal conductivity of aluminium is higher than that of copper; henceit is increasingly used for utensil making

Description : Pick out the wrong statement. (A) Bubble size increases with the dynamic viscosity of the liquid in case of nucleate pool boiling (B) Thermal conductivity of a dry material is more than ... in kg/hr in an evaporator (D) Vaporisation of organic substances in evaporator mostly causes foam formation

Last Answer : (B) Thermal conductivity of a dry material is more than that of the damp material

Description : Pick out the wrong statement. (A) With decrease in feed temperature, the number of plates required for binary distillation decreases for a given L/V' ratio (B) The extraction per unit ... and its cross￾section is wider at the bottom (D) Vander wall adsorption is also called chemisorption

Last Answer : (D) Vander wall adsorption is also called chemisorption

Description : Conductance is reciprocal of a. permeability b. action potential c. resistance d. depolarization

Last Answer : resistance

Description : Finned tube heat exchangers (A) Give larger area per tube (B) Use metal fins of low thermal conductivity (C) Facilitate very large temperature drop through tube wall (D) Are used for smaller heat load

Last Answer : (A) Give larger area per tube

Description : Which of the following is the formula for thermal resistance?  A. Thickness of material/ thermal conductivity of material  B. 2(thickness of material)/thermal conductivity of material  C. ... / 2(thermal conductivity of material)  D. Thickness of material x thermal conductivity of material

Last Answer : Thickness of material/ thermal conductivity of material

Description : Pick out the correct statement. (A) 1 kcal/hr.m.°C is equal to 1 BTU/hr. ft.°F (B) In steady state heat conduction, the only property of the substance which determines the ... in the direction of temperature rise (D) In heat transfer by forced convection, Grashoff number is very important

Last Answer : (B) In steady state heat conduction, the only property of the substance which determines the temperature distribution, is the thermal conductivity

Description : Heat transfer rate per unit area is called (A) Thermal conductivity (B) Heat flux (C) Heat transfer co-efficient (D) Thermal diffusivity

Last Answer : (B) Heat flux

Description : Pick out the wrong statement. (A) Seam welding, projection welding & spot welding are the classification of electrical resistance welding (B) Electrode tip in spot welding is of copper and the ... joined are overlapped and placed between two electrodes (D) Mild steel sheet cannot be spot welded

Last Answer : (D) Mild steel sheet cannot be spot welded

Description : Pick out the wrong statement: (A) Greater is the kinematic viscosity of the liquid, greater is the thickness of the boundary layer (B) Blowers develop a maximum pressure of 2 atmospheres ( ... factor in case of turbulent flow of liquids in pipe depends upon relative roughness & Reynolds number

Last Answer : (C) Friction losses in pipe fittings are generally expressed in terms of velocity heads

Description : Thermal diffusivity of a material (A) Has the unit m2 /sec (B) Is defined as K/ρ . Cp (C) Is the ratio of thermal conductivity to thermal capacity (D) All (A), (B) and (C)

Last Answer : (D) All (A), (B) and (C)

Description : The critical radius of insulation for a spherical shell is (where, K = thermal conductivity of insulating material h0 = heat transfer coefficient at the outer surface) (A) K/h0 (B) 2K/h0 (C) h0 /K (D) h0 /2K

Last Answer : (B) 2K/h0

Description : Pick out the wrong statement. (A) The controlling resistance in case of heating of air by condensing steam is in the air film (B) The log mean temperature difference (LMTD) for ... a pure fluid at a given pressure from liquid to vapor or vice-versa occurs at saturation temperature

Last Answer : (C) In case of a 1 - 2 shell and tube heat exchanger, the LMTD correction factor value increases sharply, when a temperature cross occurs

Description : Reciprocal of resistivity is called a. Resistance b. Inductance c. Conductivity d. Flexibility

Last Answer : c. Conductivity

Description : Three materials A, B and C of equal thickness and of thermal conductivity of 20, 40 & 60 kcal/hr. m. °C respectively are joined together. The temperature outside of A and C are 30°C and 100°C respectively. The interface ... C will be at a temperature of __________ °C. (A) 40 (B) 95 (C) 70 (D) 50

Last Answer : (C) 70

Description : Thickness of stock does not affect the fuel economy of furnaces, if thematerial to be heated is of (A) Low emissivity (B) High thermal conductivity (C) Both (A) and (B) (D) Neither (A) nor (B)

Last Answer : (C) Both (A) and (B)

Description : Which of the following variables affects the furnace capacity? (A) Temperature of flue gas (B) Thermal conductivity of stock (C) Thickness of heating stock (D) All (A), (B) and (C)

Last Answer : (D) All (A), (B) and (C)

Description : From Arrhenius law, a plot of loge K versus 1/T gives a straight line with a slope of (-E/R). The unit of E/R is (A) k cal (B) k cal/°K (C) °K (D) k cal. °K

Last Answer : (C) °K

Description : Pick up the item of work not included in the plinth area estimate (A) Wall thickness (B) Room area (C) W.C. area (D) Courtyard are

Last Answer : (D) Courtyard area

Description : Reciprocal of permeability is (a) reluctivity (b) susceptibility (c) permittivity (d) conductance

Last Answer : (a) reluctivity

Description : Conductance is reciprocal of?

Last Answer : Conductance is reciprocal of resistance.

Description : Resistance to heat flow by conduction is proportional to (where, t & ρ are thickness & density of the material respectively and A = area normal tothe direction of heat flow.) (A) t (B) 1/ρ (C) 1/A (D) All (A), (B) & (C)

Last Answer : (D) All (A), (B) & (C)

Description : How is the rate of a cooling of a building affected by the thickness and the thermal conductivity of its walls?

Last Answer : Generally thicker walls slow down the transfer of heat, and if the material is a good thermal conductor that will increase the rate of transfer.

Description : Pick out the wrong statement. (A) Higher specific gravity of petroleum products means higher C/H ratio (B) Aromatics have lower specific gravity than corresponding paraffins (C) Hydrocarbons of low ... of high specific gravity (e.g., aromatics) possess the maximum thermal energy per unit weight

Last Answer : (B) Aromatics have lower specific gravity than corresponding paraffins

Description : Pick out the wrong statement. (A) Longer tubes are less expensive per unit heat transfer area as compared to shorter tubes (B) A cost index is merely a number for a given year ... butt welded joints are less expensive compared to lap welded joints, because squaring of plates is not necessary

Last Answer : (D) Plates with butt welded joints are less expensive compared to lap welded joints, because squaring of plates is not necessary

Description : Pick out the wrong statement: (A) The capacity of an evaporator is reduced by the boiling point elevation (B) Corrosive liquid is normally passed through the tubes in a ... recompression evaporator (D) Heat sensitive materials should be concentrated in high pressure evaporators

Last Answer : (D) Heat sensitive materials should be concentrated in high pressure evaporators