Recent questions in Heat Transfer

Ratio of momentum diffusivity to thermal diffusivity isReynolds numberPrandtl numberNusselt numberPeclet number

Leidenfrost phenomenon refers tothe condensation of vapour on a cold surfacethe exchange of heat between two solidsthe melting of frostfilm boiling and evaporation of liq...

Prandtl number signifies the ratio of$\frac{Momentum \: Diffusivity}{Thermal \: Diffusivity}$$\frac{Mass \: Diffusivity}{Thermal \: Diffusivity}$$\frac{Thermal \: Diffusi...

Pool boiling equipment operating above ambient temperature is usually designed to operatefar above the critical heat fluxnear the critical heat fluxfar above the Leidenfr...

Consider the two countercurrent heat exchanger designs for heating a cold stream from $t_{in}$ to $t_{out}$ as shown in figure. The hot process stream is available at $T_...

A solid sphere of radius $1$ $cm$ and initial temperature of $25^{\circ}\:C$ is exposed to a gas stream at $100^{\circ}\:C$. For the solid sphere, the density is $10^{4}$...

Stream $A$ with specific heat capacity $C_{PA}=2000\:J/\left ( kg\:K \right )$ is cooled from $90^{\circ}C$ to $45^{\circ}C$ in a concentric double pipe counter current...

A $20$ $cm$ diameter cylindrical solid pellet of a nuclear fuel with density $6000\: kg/m^{3}$ and conductivity of $300\:W/\left ( m\:K \right )$ generates heat by nucle...

The one-dimensional unsteady heat conduction equation is $$\rho C_{p}\frac{\partial T}{\partial t}=\frac{1}{r^{n}}\frac{\partial }{\partial r}\left ( r^{n}k\frac{\partial...

In a heat exchanger, the inner diameter of a tube is $25\:mm$ and its outer diameter is $30\:mm$. The overall heat transfer coefficient based on the inner area is $360\:W...

A fluid flows over a heated horizontal plate maintain at temperature $T_{W}$. The bulk temperature of the fluid is $T_{\infty }$ . The temperature profile in the thermal...

In nucleate boiling, the pressure inside a bubble is higher than the pressure of the surrounding liquid. Assuming that both the liquid and vapour are saturated, the tempe...

A composite wall is made of four different materials of construction in the fashion shown below. The resistance (in $K/W$) of each sections of the wall is indicated in th...

Steam at $100^{\circ}C$ is condensing on a vertical steel plate. The condensate flow is laminar. The average Nusselt numbers are $Nu_{1}$ and $Nu_{2}$, When the plate tem...

Match the dimensionless numbers in $Group–I$ with the ratios in $Group–2$.$\begin{array}{cc}\\&\text{Group-1} & \text{Group-2} \\ &\text{P. Biot number} & \text{ I. $\fr...

In a $1-1$ pass shell and tube exchanger, steam is condensing in the shell at a temperature $(T_{s})$ of $135^{\circ}C$ and the cold fluid is heated from a temperature $(...

In an experiment setup, mineral oil is filled in between the narrow gap of two horizontal smooth plates. The setup has arrangements to maintain the plates at desired unif...

The space between two hollow concentric spheres of radii $0.1\:m$ and $0.2\:m$ is under vacuum. Exchange of radiation (uniform in all directions) occurs only between the ...

Two infinitely large parallel plates ($I$ and $II$) are held at temperatures $T_{I}$ and $T_{II}$ $(T_{I}>T_{II})$ respectively, and placed at a distance $2d$ apart in va...

In the figure below, the temperature profiles of cold and hot fluids in counter double pipe heat exchangers (in different modes of operation) are shown on the left. For e...

A heated solid copper sphere (of surface area $A$ and volume $V$) is immersed in a large body of cold fluid. Assume the resistance to heat transfer inside the sphere to b...

Air is flowing at a velocity of $3\:m/s$ perpendicular to a long pipe as shown in the figure below. The outer diameter of the pipe is $d=6\:cm$ and temperature at the out...

Consider a solid block of unit thickness for which the thermal conductivity decreases with an increase in temperature. The opposite faces of the block are maintained at c...

The bottom face of a horizontal slab of thickness $6 \:mm$ is maintained at $300^{\circ}C$. The top face is exposed to a flowing gas at $30^{\circ}C$. The thermal conduct...

An oil with a flow rate of $1000\:kg/h$ is to be cooled using water in a double-pipe counter-flow heat exchanger from a temperature of $70^{\circ}C$ to $40^{\circ}C$. Wat...

A brick wall of $20\:cm$ thickness has thermal conductivity of $0.7\:W\:m^{-1}\:K^{-1}$. An insulation of thermal conductivity $0.2\:W\:m^{-1}\:K^{-1}$ is to be applied o...

In a completely opaque medium, if $50\%$ of the incident monochromatic radiation is absorbed, then which of the following statements are $CORRECT$$50\%$ of the incident r...

In a double pipe counter-current heat exchanger, the temperature profiles shown in the figure were observed. During operation, due to fouling inside the pipe, the heat tr...

Calculate the heat required (in kJ, up to 1 digit after the decimal point) to raise the temperature of 1 mole of a solid material from 100 $^{o}$C to 1000 $^{o}$C. The sp...

A hole of area 1 cm$^{2}$ is opened on the surface of a large spherical cavity whose inside temperature is maintained at 727 $^{o}$C. The value of stefan-Boltzmann consta...

In a pool boiling experiment, the following phenomena were observed.P.Natural convectionQ.Film boilingR.Transition boilingS.Nucleate boilingWhat was the CORRECT sequence ...

The effectiveness of a heat exchanger in the $\varepsilon$-NTU method is defined as$\frac{increase\ in temperature\ of\ the\ cold\ fluid}{decrease\ in\ temperature\ of\ t...

For the enclosure formed between two concentric spheres as shown ($R_2 = 2R_1$), the fraction of radiation leaving the surface area $A_2$ that strikes itself is ...

Heat generated at a steady rate of $100\: W$ due to resistance heating in a long wire (length = $5\:\text{m}$, diameter = $2\:\text{mm}$). This wire is wrapped with an in...

In a counter-flow double pipe heat exchanger, oil ($\dot m = 2 \text{ kg/s}, C_p= 2.1 \text{ kJ/kg}.\:^{\circ} C$) is cooled from $90^{\circ}C$ to $40^{\circ} C$ by water...

The one-dimensional unsteady state heat conduction equation in a hollow cylinder with a constant heat source $q$ is$$ \frac{\partial T}{\partial t}=\frac{1}{r}\frac{\part...

If the Nusselt number $(\text{Nu})$ for heat transfer in a pipe varies with Reynolds number $(Re)$ as $\text{Nu}$ $ {\displaystyle \propto }\; Re^{0.8}$, then for constan...

A solid sphere with an initial temperature $T{_1}$ is immersed in a large thermal reservoir of temperature $T{_0}$. The sphere reaches a steady temperature after a certai...

For heat transfer across a solid-fluid interface, which one of the following statements is $\text{NOT}$ true when the Biot number is very small compared to $1$?Conduction...