A solid copper ball of mass 500 gram, when quenched in a water bath at 30⁰C, cools from 530⁰C to 430⁰C in 10 seconds. What will be the temperature of the ball after the next 10 seconds?

Analyze the following statements

1. The heat loss from an insulated pipe reaches maximum when outside radius of insulation is equal to ratio of thermal conductivity to the surface heat transfer coefficient.

2. On increasing thickness of insulation, heat loss decreases.

3. On increasing thickness of insulation heat loss 1^st increases reaches maximum and then decreases.

Which of the following statements are correct.

Heisler charts are used to determine transient heat flow rate and temperature distribution when:

6.0 kJ of conduction heat transfer has to take place in 10 minutes from one end to other   end of a metallic cylinder. It has cross sectional area of  10 cm², length 1 meter and thermal conductivity as 100 W/mK. What is the temperature difference between the two ends of the cylindrical bar?

A 0.5 m thick plane wall has its two surfaces kept at 300⁰C and 200⁰C. Thermal conductivity of the wall varies linearly with temperature and its values at 300⁰C and 200⁰C are 25 W/mK and 15 W/mK, respectively. Then the steady heat flux through the wall is

A hollow pipe of 1 cm outer diameter is to be insulated by thick cylindrical insulation having thermal conductivity 1 W/mK. The surface heat transfer coefficient on the insulation surface is 5 W/m²K. what is the minimum effective thickness of insulation for causing the reduction in heat leakage from the insulated pipe?

The Poisson’s equation of general conduction heat transfer applies to

Which of the following expressions gives the thermal resistance for heat conduction through a hollow sphere of radii r₁ and r₂?

Surface defined by lambert law is

Which of the following is correct  according to lambert law?

If the surface is both Gray and diffuse then?

Shape factor is

According to Kirchoff’s law for diffuse surface

Which of the following is the expression for Stephen boltzmans law?

The temperature distribution curve for a heat exchanger is shown in the figure below (with usual notations) refers to which one of the following?

If the temperature of a sold surface changes from 27⁰C to 627⁰C, then the ratio of  its emissive power  is.......?

The equation of effectiveness $\in =1-e^{-NTU}$for a heat exchanger is valid in the case of

After expansion from a gas turbine, the hot exhaust gases are used to heat the compressed air from a compressor with the help of a cross flow compact heat exchanger of 0.8 effectiveness. What is the number of transfer units of the heat exchanger?

Which one of the following heat exchangers gives parallel straight line pattern of temperature distribution for both cold and hot fluid?

In a counter-flow heat exchanger, the hot fluid is cooled from 110⁰C to 80⁰C by a cold fluid which gets heated from 30⁰C to 60⁰C, LMTD for the heat exchanger is

In a counter flow heat exchanger, the product of specific heat and mass flow rate is same for the hot and cold fluids. If NTU is equal to 0.5 then the effectiveness of the heat exchanger is

Consider the following statements:

The effect of fouling in a water cooled steam condenser is that it

1. Reduces the heat transfer coefficient of water

2. Reduces the overall heat transfer coefficient

3. Reduces the area available for heat transfer

4. Increases the pressure drop of water

Which of these statements are correct?

The effectiveness of a fin will be maximum in an environment with

On heat transfer surface, fins are provided

Fins are made as thin as possible to

Which one among the following will have highest thermal conductivity?

A fin will be necessary and effective only when

[Where k = thermal conductivity of fin material, h = convective heat transfer coefficient between the fin surface and environment temperature.

Three fins of equal length and diameter but made of aluminium, brass and cast-iron are heated to 200^oC at one end. If the fins dissipate heat to the surrounding air at 25^oC the temperature at the free end will be least in case of

In the case of turbulent flow through a horizontal isothermal cylinder of diameter ‘D’ free convection heat transfer coefficient for the cylinder will

Given that

Pr = Prandtl number

Nu = Nusselt number

Sh = Sherwood number

Re = Reynolds number

Sc = Schmidt number and

Gr = Grashoff number

the functional relationship for free convective mass transfer is given as:

Heat is lost from a 100 mm diameter steam pipe placed horizontally in ambient at 30^oC. If the Nusselt number is 25 and thermal conductivity of air is 0.03 W/mK, then the heat transfer coefficient will be

For laminar flow over a flat plate, the local heat transfer coefficient h_x varies as x^–1/2, where x is the distance from the leading edge (x = 0) of the plate. The ratio of the average coefficient h_a between the leading edge and some location A at x = x on the plate to the local heat transfer coefficient h_x at A is

For the fully developed laminar flow and heat transfer in a uniformly heated long circular tube, if the flow velocity is doubled and the tube diameter is halved, the heat transfer coefficient will be

In respect of free convection over a vertical flat plate the Nusselt number varies with Grashoff number ‘Gr’ as

The Nusselt number is related to Reynolds number in laminar and turbulent flows respectively as

If heat and mass transfer take place simultaneously, the ratio of heat transfer coefficient to the mass transfer coefficient is a function of the ratio of

Match List-I with List-II and select the correct answer using the codes given below the lists (h_m : mass transfer coefficient, D : molecular diffusion coefficient, L : characteristics length dimension, k : thermal conductivity, $\rho$: density, C_p : specific heat at constant pressure, µ : dynamic viscosity)

Which of the following is an effective way of producing forced convection in liquid bath?

The ratio of thermal conductivity to electrical conductivity is?

The critical radius of insulation for a sphere is?