A metal ball of radius 0.1 m at a uniform temperature of 90°C is left in air at 30°C. The density and the specific heat of the metal arekg/m³ and 0.4 kJ/kg.K respectively. The heat transfer co-efficient isW/m².K Neglecting the temperature gradients inside the ball, the time taken (in hours) for the ball to cool to 60°C is

What is the unit of thermal conductivity ?

Heat transfer by __________ may not necessarily require the presence of a medium.

For flow over a flat plate, the ratio of thermal boundary layer thickness, 'xt' and hydrodynamic boundary layer thickness 'x' is equal to (where, N_Pr = Prandtl number)

A perfect black body is a perfect __________ of radiation.

Which one gives the monochromatic emissive power for black body radiation ?

For the same heat load and mass flow rate in the tube side of a shell and tube heat exchanger, one may use multipass on the tube side, because it

The thermal radiation emitted by a body is proportional to Tⁿ, where T is its absolute temperature. The value of 'n' is exactly 4 for

Which of the following is unimportant in forced convection ?

__________ chart is known as transient heat conduction chart.

Pick out the correct statement.

In a shell and tube type heat exchanger, the floating tube bundle heat arrangement is used

The range of electromagnetic spectrum important in heat transfer by radiation is __________ microns.

In case of parallel flow heat exchanger, the lowest temperature theoretically attainable by the hot fluid is __________ the outlet temperature of the cold fluid.

An equipment which converts the latent or sensible heat of one fluid into the latent heat of vaporisation of another, is called a

For what value of Prandtl number, St = f/2?

When vaporisation takes place through a blanketting film of gas, the phenomenon is termed as __________ boiling.

Minimum recommended baffle spacing in a shell and tube heat exchanger is about (where, D = shell diameter)

It is not preferable to use superheated steam in evaporators, because of its very

Steam is to be condensed in a shell and tube heat exchanger, 5 m long with a shell diameter of 1 m. Cooling water is to be used for removing the heat. Heat transfer co-efficient for the cooling water, whether on shell side or tube side is the same. The best arrangement is

Film boiling occurs at __________ pressure.

Which of the following is correct ?

In a multipass shell and tube heat exchanger, tube side return pressure loss is equal to __________ the velocity head.

Nusselt number (for forced convection heat transfer) is a function of the __________ number.

Stefan-Boltzman law applies to __________ body.

Use of transverse baffles in a shell and tube heat exchanger is done to increase the

Which of the following is directly concerned with the heat transfer ?

In a shell and tube heat exchanger,

Dietus-Boelter equation used for the determination of heat transfer co-efficient is valid

Stefan-Boltzman law which describes the radiation heat transfer states that, it is proportional to (where, t = temperature in °C T = absolute temperature in ° K )

The Nusselt number for fully developed (both thermally and hydrodynamically) laminar flow through a circular pipe, where the wall heat flux is constant, is

It is desired to concentrate asalt solution (kg of salt inkg of solution) to asalt solution in an evaporator. Consider a feed ofkg/min at 30°C. The boiling point of the solution is 110°C, the latent heat of vaporisation iskJ/kg and the specific heat of the solution is 4 kJ/kg.K. The rate at which the heat has to be supplied in (kJ/min) to the evaporator is

LMTD for counterflow and prallel flow heat exchanger will be the same, when the

In a multiple effect evaporator, the effect of boiling point elevation is to

Steam traps are provided in steam carrying pipelines to

Heat flux through several resistances in series in analogous to the current flowing through several

Convective heat transfer, in which heat is transferred by movement of warmed matter is described by

As the difference between the wall temperature and bulk temperature increases, the boiling heat transfer co-efficient

For a given ambient air temperature with increase in the thickness of insulation of a hot cylinderical pipe, the rate of heat loss from the surface would

Pick out the wrong statement.

Which type of heat exchanger is preferred for heavy heat loads ?

The film co-efficient is decreased due to the presence of non-condensing gases in the vapors. The film co-efficient of superheated vapor as compared to that of saturated vapor is

For specified tube outside diameter, higher BWG means higher

The actual temperature drop across the heating surface of an evaporator depends on the

Economy of a multiple effect evaporator depends upon the

If Prandtl number is greater than the Schmidt number, then the

Pick out the wrong statement:

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

Vacuum is generally maintained in the vapour space of an evaporator mainly to

Heat transfer efficiency leading of energy conservation in a heat exchanger can be achieved by