Thus, if adequate pressure drop is available, it may be possible to reduce baffle spacing to obtain increased heat transfer rates. High vapor velocities can reduce resistance to heat transfer through the shear effect on the condensate film. The resistance to heat transfer due to the presence of noncondensing gases is inversely proportional to the vapor velocity. Pressure drop depends on vapor velocity, and hence on baffle spacing The tubes must be supported to avoid tube vibration This is a simple method of condensing a vapor, but there are practical problems associated with generating a good distribution of bubbles of small size, which are required for efficient heat transfer. The sparge pipe consists of a pipe with holes for injecting bubbles of vapor into a pool of liquid. The liquid is usually injected in counterflow to the vapor. A jet of liquid is injected into a pipeline carrying vapor via a small bore pipe and a nozzle located at the center line. This is a device in which a jet of liquid is directed into a vapor stream, usually with the objective of desuperheating the vapor. The disadvantage of this type of condenser is that the pressure drop is higher than in other types of direct-contact condenser. Liquid is supplied to the top of the column and vapor is supplied to the bottom. A packed column may consist of tightly-packed metal rings to increase the interfacial area for heat transfer. (Flooding is an unstable condition when the vapor flow is such that the downward flow of condensate is interrupted and held up.) It has the advantage of countercurrent flow of vapor and coolant, though care must be taken to avoid flooding. The vapor is supplied to the bottom of the column.
#Heat transfer rate series
This is similar to the spray condenser, except that the coolant is directed to flow over a series of trays in a column (see Figure 2). It is important that the spray nozzles and vessel are designed to produce a fine spray of liquid (to give a large interfacial area for heat transfer), and a long enough residence time of liquid droplets in the vessel. The coolant is sprayed, using nozzles, into a vessel to which the vapor is supplied. Low specific heat and low thermal conductivityĭ.The Spray Condenser. High specific heat and high thermal conductivityĬ. High specific heat and low thermal conductivityī.
Question 1: For cooking the food, which of the following type of utensil is most suitableĪ.
An electric heater is used in a room of total wall area 137 m 2 ( IIT JEE 1986).
A double pane window used for insulating a room thermally from outside (IIT JEE 1997).A point source of heat of power P kept at the centre of a spherical shell (IIT JEE 1991).MCQ on a composite block is made of slabs A, B, C, D, and E (IIT JEE 2011).Evaporation of water and melting of ice kepts at two ends of a metal rod AB of length 10x (IIT JEE 2009).Effective thermal conductivity of two concentric cylinders (IIT JEE 1988).Temperature at the vertex? (IIT JEE 1995) Three rods forms an isosceles triangle.Temperature at the junction of the three identical rods (IIT JEE 2001).Two conducting cylinders of equal length but different radii connected in series (IIT JEE 2018).Two rods connected in series and parallel (IIT JEE 2014).Two blocks connected in series and parallel ( IIT JEE 2013).The end Q and R of two thin wires, PQ and RS, are soldered (IIT JEE 2016).Solved Problems on Conduction Heat Transfer from IIT JEE At a given temperature T, the ratio of thermal conductivity (K) to the electrical conductivity (σ) is constant i.e., K/σT= L (a constant). In general, a substance that is a good conductor of heat is also a good conductor of electricity. If rods is parrallel are of same physical dimensions but thermal conductivities $K_1$ and $K_2$ then effective thermal conductivity of the system is The effective thermal resistance of a system of two rods connected in parallel is given by If these rods are of same physical dimensions and of thermal conductivities $K_1$ and $K_2$ then effective thermal conductivity of the system is The effective thermal resistance of a system of two rods connected in series is given by In electrical circuits, equivalents of heat current, temperature difference and thermal resistance is electric current, potential difference and electrical resistance, respectively.Ĭonsider two rods of thermal resistances $R_1$ and $R_2$. The rate of heat transfer through a rod of length x and cross-section area A whose two ends are maintained at a temperature T 1 and T 2 is given by
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