Heat transfer - conduction, convection, radiation -pharmaceutical engineering

B.Pharmacy second year
third semester

1. Heat Transfer B. Pharmacy Second Year By: Shalini Keshvrao Dhawale Assistant Professor D. K. Patil Institute Of Pharmacy sayal road Loha .

2. Introduction Heat transfer is the process of transfer of heat from high temperature system to a low temperature system. Heat transfer is a movement of heat due to temperature difference at various points inside the system. The process in which there is no transfer of heat between the system and surrounding is called as Adiabatic process. There are there modes of heat transfer: Conduction Convection Radiation 2 DKPIOP

3. Conduction when heat flows through a body by the transference of the momentum of individual atoms or molecules without mixing. Conduction is transfer of heat through solids or stationary fluids. Example – the flow of heat through the brick wall of furnace or the metal shell. 3 DKPIOP

4. Convection When heat flows by actual mixing of warmer portion with cooler portion of the same material the mechanism is known as convection.Convection is restricted to flow of heat in fluids. Forced Convection: uses external mean of producing fluid movement. Example: the heating of a room by means of steam heater Hearting water by a hot surface . 4 DKPIOP

5. Radiation Radiation is a term given to the transfer of energy through space by means of electromagnetic waves. If radiation passes through empty space, if matter appears in the path the radiation will be Transmitted, Reflected or Absorbed. Only absorbed energy appears as heat. Example: Solar radiation, microwave oven, solar cooker. 5 DKPIOP

6. Black body DKPIOP 6 Imagine a surface or a black body, where all the radiant energy striking on a surface is absorbed and none is reflected or transmitted, such receiver is known as black body. Thus black body is defined as a body that radiates maximum possible amount of energy at a given temperature. No physical substance is perfectly black body.

7. Fourier’s Law Fourier’s law state that the rate of heat flow through a uniform material is proportional to the area , temperature drop and inversely proportional to length of the path flow. The mechanism of conduction is most easily understood by study of conduction through solid. Rate of heat flow = Driving force Resistance dQ = - kAdt dø dL 7 DKPIOP

8. Fourier’s Law DKPIOP 8 Heat can flow then there is temp. gradients Fourier’s law mathematically expressed as Rate of heat flow = area × temp. diffrence Thickness dQ = - kAdt dø dL dQ / dø = rate of heat transfer K = thermal conductivity of material (- sign indicate decrese in temp.) A = cross sectional area dt / dL = the rate of change of temp. with respect to length at path of heat flow.

9. Heat Exchanger Heat exchanger are the device used for transferring heat from one fluid to another fluid through metal wall. Heat interchanger: these are devices used for transferring heat from one liquid to another or from one gas to another through a metal wall. Examples: Shell and tube Heat exchanger Double pipe heat exchanger U- Tube heat exchanger 9 DKPIOP

10. Shell and tube Heat exchanger Most widely used vehicle for transfer of heat in industrial application. Construction: Shell and tube exchanger is a pressure vessel with many tube inside of it. Fluid flows through the tube of exchanger while other fluid flow outside of the tubes within shell. The tube side and shell side fluids are separated by tube sheet. 10 DKPIOP

11. Shell and tube Heat exchanger 11 DKPIOP Working: shell and tube heat exchangers are used for liquid liquid , gas liquid, condensing or vaporizing heat transfer. A shell and tube exchanger consist of number of tubes mounted inside cylindrical shell. Two fluids can exchange heat ,one fluid flows over the outside of tube while second fluid flows through the tubes. The fluid can flow in parallel or counter flow arrangement. Uses: used in industries for over 150 years Advantages: available in many size, designed for high pressure without excessive cost.

12. Double pipe heat exchanger DKPIOP 12 Double pipe heat exchanger are the simplest of all type They are fabricated from two pieces of pipe one inside the other. One fluid flow through inner pipe while other fluid flows through the annulus between the pipe. When the hot fluid and cold fluid enter at the same end of apparatus and flow parallel to each other through it this arrangement is known as parallel or co- current flow. The alternative method in which hot water enter at one end and cold fluid at other end, fluid pass by each other in opposite direction such flow is counter-current flow. Flow inside the double pipe heat exchanger can be co- current or counter-current.

13. Double pipe heat exchanger DKPIOP 13 Advantages of Double pipe heat exchanger it is not expensive Easily designed for high pressure service. Disadvantages of Double pipe heat exchanger difficult to clean on shell side. Only suitable for small size.

14. U- Tube heat exchanger DKPIOP 14 The internal tube bundle has a U-shape for U-tube heat exchangers, hence its name. A U-tube heat exchanger is used mostly according to the counter flow principle. For heat transport according to the counter flow principle, hot and cold medium flow in opposing directions. As a result, heat recovery of almost 100% is achieved. Counter flow heat exchangers therefore have a very high efficiency level. Due to the bent individual tubes, a heat exchanger with U-tube bundles require significantly less space than a straight tube heat exchanger with the same design. U-tube heat exchangers also only generate a low pressure loss during operation.

15. Advantages of U- tube heat exchanger DKPIOP 15 Low pressure loss, Compact design, high efficiency Compensation of heat stresses, Large differences of the input temperature of both media possible Tube bundle replaceable, Media : Water, gases, oils, vapour , all common liquids and gases

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