Ratio heat transferred from 37oC to a colder body and from that body to – 11oC is 2, what is the temperature of colder body if surface areas are same for all bodies?

Fourier's law of heat conduction is (where Q = Amount of heat flow through the body in unit time, A = Surface area of heat flow, taken at right angles to the direction of heat flow, dT = Temperature difference on the two faces of the body, dx = Thickness of the body, through which the heat flows, taken along the direction of heat flow, and k = Thermal conductivity of the body)

A

k. A. (dT/dx)

B

k. A. (dx/dT)

C

k. (dT/dx)

D

k. (dx/dT)

Fourier's law of heat conduction is (where Q = Amount of heat flow through the body in unit time, A = Surface area of heat flow, taken at right angles to the direction of heat flow, dT = Temperature difference on the two faces of the body, dx = Thickness of the body, through which the heat flows, taken along the direction of heat flow and k = Thermal conductivity of the body)

A

$${\text{kA}}\frac{{{\text{dT}}}}{{{\text{dx}}}}$$

B

$${\text{kA}}\frac{{{\text{dx}}}}{{{\text{dT}}}}$$

C

$${\text{k}}\frac{{{\text{dT}}}}{{{\text{dx}}}}$$

D

$${\text{k}}\frac{{{\text{dx}}}}{{{\text{dT}}}}$$

Two refrigerators M and N operate in series. The refrigerator M absorbs energy at the rate of 1 kW from a body at temperature 400 K and rejects energy as heat to a body at a temperature T. The refrigerator N absorbs the same quantity of energy which is rejected by the refrigerator N from the body at temperature T, and rejects energy as heat to a body at temperature 800 K. If both the refrigerators have the same C.O.P., what is the value temperature T?

A

600 K

B

200 K

C

565.68 K

D

459.21 K

In a surface condenser, the water flowing through a series of tubes at the rate of 200 kg/hr is heated from 15 degree Celsius to 75 degree Celsius. The steam condenses on the outside surface of tubes at atmospheric pressure and the overall heat transfer coefficient is estimated at 860 k J/m2 hr degree. Find the effectiveness of the heat exchanger. At the condensing pressure, stream has a saturation temperature 0f 100 degree Celsius and the latent heat of vaporization is 2160 k J/kg. Further, the steam is initially just saturated and the condensate leaves the exchanger without sub-cooling i.e. only latent heat of condensing steam is transferred to the water. Take specific heat of water as 4 k J/kg K

A

0.224

B

0.706

C

2.224

D

3.224

In a surface condenser, the water flowing through a series of tubes at the rate of 200 kg/hr is heated from 15 degree Celsius to 75 degree Celsius. The steam condenses on the outside surface of tubes at atmospheric pressure and the overall heat transfer coefficient is estimated at 860 k J/m2 hr degree. Find the number of transfer units of the heat exchanger. At the condensing pressure, stream has saturation temperature 0f 100 degree Celsius and the latent heat of vaporization is 2160 k J/kg. Further, the steam is initially just saturated and the condensate leaves the exchanger without sub-cooling i.e. only latent heat of condensing steam is transferred to water. Take specific heat of water as 4 k J/kg K

A

3.224

B

2.224

C

1.224

D

0.224

Directions : In each of the following questions a statement is given, followed by two conclusions. Give answer :

Statements : The average number of persons per household is 5 in urban areas whereas it is 7 in rural areas. The national average is 6.

Conclusions :
I. The population per unit area in the rural areas is higher than in the urban areas.
II. More persons live in the same household in the rural areas as compared to those in the urban areas.

A

Only conclusion I follows

B

Only conclusion II follows

C

Either I or II follows

D

Neither I nor II follows

E

Both I and II follow

The figure shows two bodies P and Q. The body Q is placed on the ground and the body P is placed on top of it. The weights of P and Q are WP and WQ, respectively. The bodies are at rest and all the surfaces are assumed to be frictionless. R represents reaction force, if any, between the bodies. The correct free body diagram of the body P is

A

B

C

D

Consider an enclosure formed by three surfaces having the following values of shape factors, emissivities and temperatures Surface 1 i.e. curved cylindrical has an emissivity 0.75 and temperature 800 K Surface 2 i.e. closing disc has an emissivity 0.8 and temperature 700 K Surface 3 i.e. closing disc has an emissivity 0.8 and temperature 700 K The closing flat discs are 25 mm in diameter and they have interspacing distance equal to 100 mm. If the shape factor between these two identical discs is 0.05, calculate the net rate of radiant heat flow from the curve surface to each of the closing end surface

A

1.561 W

B

2.561 W

C

3.561 W

D

4.561 W

A finned surface consists of root or base area of 1m2 and fin surface area of 2m2. The average heat transfer coefficient for finned surface is 20W/m2K effectiveness of fins provided is 0.75. If finned surface with surface with root or base temperature of 50°C is transferring heat to fluid of 30°C, then the rate of heat transfer without using fin is _______

A

400W

B

800W

C

1000W

D

1200W

Extended heat transfer surface like fins are used to increase the heat transfer rate. Fin efficiency is defined as the ratio of heat transferred across the fin surface to the theoretical heat transfer across an equal area held at the

A

Surrounding temperature

B

Average temperature of the fin

C

Temperature of the fin end

D

Constant temperature equal to that of the base

Ratio heat transferred from 37oC to a colder body and from that body to – 11oC is 2, what is the temperature of colder body if surface areas are same for all bodies?

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