heattransfer

1. HEAT TRANSFER
” It is the process of heat from high temperature reservoir to low temperature is reservoir. It occurs due
to temperature different between system & surrounding.”
It can also take place due to temperature different at various points inside the system.
The different between temperature & heat is that temperature may be defined as amount of energy
passed by molecules of a system.
Its symbol is ‘T’ & SI units of temperature is ‘C’ & ‘K’.
On the other hand, heat may be defined as the process by which heat energy flow hotter body to cold
one.
Its symbol ‘Q’ & SI units are ‘Joule’ (J) & ‘Calorie’.
Different stage of heat transfer involved in unit
operation in the pharmaceutical industries, so it is
very necessary to know about the heat transfer to the involved person for minimizing the
energy loss in the form of heat.
 Temperature, wherein the temperature of a region is required to maintained close to a specific
value. Requiring both insulator’s & enhancement to operate at various steps of operational
sequence of a device kept in a region of interest.
APPLICATIONS OF HEAT TRANSFER
01]. Evaporation:
Heat is supplied in order to convert a liquid into vapour which is substituent remove this process is used
for preparating vegetable extracts. The heat flow of the evaporator can be quantifying so as to estimate
the efficiency of the process.
02]. Distillation:
Heat is supplied to a liquid mixture for converting the liquid into vapour, so that the individual vapour
components are condensed at another place.
OBJECTION OF HEAT TRANSFER

2. 03]. Drying =
In the production of tablet heat is passed through a carrier gas over a bed of wet solid mass for
achieving drying.
In case of spray dryer heat is supply to solution & suspensions.
04]. Sterilization:
Autoclave are used with steam as a heating medium for sterilization of
pharmaceuticals. Dry heat used for sterilization of glass apparatus & another container.
05]. Crystallization:
Saturated solution is heated to bring about super-saturation which promotes crystallization of the drug.
On the other hand, removal of heat (cooling) also promote crystallization.
In case of purification of drugs.
05]. Sterilization =
Auto clave are used with stream as a heating medium for heating of pharmaceuticals. Dry heat is used
for sterilization of glass apparatus & other containers.

3. MECHANISMS OF HEAT TRANSFER (FLOW)
Heat flow from a region of high temperature region to low temperature region. The mechanism involved
for heat transfer are:
CONDUCTION
It is a process in which heat flow in a body is achieved by transfer of momentum of individual atom or
molecule without mixing. It can be evaluated in terms of Fourier’s low of heat conduction.
Example: Flow heat through the metal shell of a boiler takes place by conduction. No k=mixing is
involved, conduction is limited to the substance whose movements is restricted. Flow of heat depends
on transfer of vibrational energy from one molecule to another as in case of metals.
CONVECTION
It is the process in which heat flow is achieved by actual mixing of warmer
portion with cooler portion of the same material.
Example:
Heating of water by hot surface is mainly due to convection. It is restricted to fluid & gases.
RADIATION
Radiation is an energy transfer process in which heat flow by means of electro-magnetic waves.
Example: A black surface absorbs most of the radiation received by it. Solar water heater, solar cooker
etc.
Utilize radiation for production of heat.

4. HEAT EXCHANGERS & HEAT INTER-CHANGERS
Heat exchangers are the device used for transferring heat from one fluid (stream) to another fluid
(liquid) through a metal wall.
HEAT INTER-CHANGERS
These are the device used for transferring heat from liquid to
another or from one gas to another through a metal wall.
HEAT EXCHANGERS
TUBULAR HEATER OR SHELL TUBES HEATER
PRINCIPLE
In heat exchangers the heat transfer coefficient of the stream site is usually much larger than the heat
transfer coefficient on cold liquid site. Therefore, overall heat transfer coefficient will be nearer to cold
liquid site hence heat transfer become less.
The efficiency can be improved by passing the liquid at high velocity as a result resistance of liquid
decreases.
CONSTRUCTION

5. WORKING
Stream is introduced through the stream inlet (F) into the space surrounding the
tubes. The stream flow down the tubes in this process the tubes get heated due to high value of stream
film coefficients.
The condense vapour drains through outlet at (G) & non-condense gases escape from vent (K) at the
top.
The fluid to be heated is pump through the cold fluid inlet (H) in to the distributing chamber (D2). The
stream & fluid are physically separated but are in thermal contact through the thin tube wall.
The fluid gets heated due to heat transfer by conduction through the metal wall followed by convection.
The heated fluid reaches the distributing chamber (D1) & leaves through the hot fluid outlet (I).
ADVANTAGES
It provides large heating surface into small volume.
DISADVANTAGES
The velocity of the fluid is low because of large cross section area or larger surface.
APPLICATIONS
➢ It is used for cooling & heating, sweaming pool water.
➢ Cooling of engine oil also.

6. HEAT INTER-CHANGERS
These are the device used for transferring heat from one liquid to another or from one gas to another
through a metal wall.
PRINCIPLE
In heat inter-changers the heating medium I hot liquid, the liquid to be heated is
the cold liquid in the case the film coefficient both outside & inside the tubes are nearly the same.
CONSTRUCTION
Tow pipe are used the inside pipe 7 tube is use to pumping the cold liquid to be heated. The outer pipe
act as a jacket for circulation of hot liquid.
All the jacketed section is inter connected. Glass tube, iron pipes are used for construction.
DOUBLE PIPE HEAT INTER-CHANGERS

7. WORKING
The hot liquid is pump into the jacketed section, the liquid to be heated is
pumped through the inlet provided at right side.
The liquid gets heated up & flow through the vent into the next section of the pipe. The liquid further
gest heated. The same liquid continues to flow & finally leaves the inter changer through the exit point
on the right side.
USES
Heat inter-changers are used for transferring heat from water or oil or could be moving air.
ADVANTAGES
Double pipe heat inter-changers are useful when not more than 0.9 to 1.4 square surface required.
DISADVANTAGES
The equipment is quite expensive & require more maintenance cost.