Process Heat Transfer

Explain Buckingam's   theorem.

A 50 mm inside diameter iron pipe at 423 K passes through a room in which the surroundings area at temperature of 300 K. If the emissivity of the pipe metal is 0.8, what is the net interchange of radiation energy per meter length of the pipe? The outside diameter of the pipe is 60 mm.

Obtain a relation to find the net radiation heat transfer between two large parallel plates of different emissivities.

A light lubricating oil (specific heat, C_p - 2090 J/kg-K) is cooled by allowing it to exchange energy with water in a small heat exchanger. The oil enters and leaves the heat exchanger at 375 K and 350 K, respectively and flows at a rate of 0.5 kg/s Water (C_p=44177 J/kg-K) at 280 K is available in sufficient quantity to allow 0.201 kg/s to be used for cooling purposes. Determine the required heat transfer area for counter Dow operation. The overall heat transfer coefficient way be taken as 250 W/ m² K . 

Explain the step-by-step procedure followed for the design of a double pipe heat exchanger.

Define concurrent and counter-current flow with neat sketches.

With a neat labeled diagram, explain the basic construction and important components of a shell-and-tube heat exchanger. 

Explain different types of condensation mechanism.

Explain the concept of nucleate pool boiling and film boiling.

Derive an expression for rate of heat conduction through a composite solid/multi-layered wall.

Give the Dittus and Boelter equation and Sieder-Tate equation for turbulent flow through a circular pipe and also mention the conditions for applicability of these correlations. 

List the important dimensionless numbers in convective heat transfer and mention their physical significances. 

A thermocouple is formed by soldering end-to-end wires of 0.5 mm diameter. The thermal diffusivity of the material is 5.3 x 10^-6 m/s. The probe initially at 30°C is placed in a fluid at 600°C to measure the temperature of the fluid. If the convective heat transfer coefficient between the wire and the fluid is 85 W/m²K, determine the time constant for the probe and also time taken for it to read 598°C. Take thermal conductivity of material as 19.1 W/m-K. 

Taking an example of double pipe heat exchanger in co current or counter current flow,derive an expression to determine the log mean temperature difference (LMTD).

An aluminium rod (fin) 25 om is diameter and 100 mm long protrudes from a wall which is maintained at 525K into the environment maintained at 288K. Estimate the heat lost by rod assuming that the rod and is insulated. Also estimate the fin efficiency of temperature at the end of the fin. Thermal conductivity of aluminium is 200 W/mK of heat transfer coefficient between the rod surface of environment is 15 W/ m²K. 

What do you mean by critical insulation thickness? Show that the critical outer radius (r_o) of an insulated pipe is k/he. Where k_e is thermal conductivity of insulating material and h_e is the convective heat transfer co-efficient outside the insulation. Take the inner radius of the insulation and the corresponding temperature as r_i rand T_i, respectively. Also, the insulated pipe is exposed to an ambient temperature, T_o 

A cylindrical hot gas duct, 0.5m inside radius, has an inner layer of fireclay brick (Thermal conductivity, K=1.3 W/m°C) of 0.27m thickness. The outer layer, 0.1 4m thick, is made of a special brick (K = 0.92 W/m°C). The brick work is enclosed by an outor steel cover which has a temperature of 65°C. The inside temperature of the composite cylindrical wall of the duct is 400°C. Neglecting the thermal resistance of the steel cover, calculate the rate of heat loss per meter of the duct and also the interface temperature between the layers.