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ELECTRIC WATER HEATER

Water heater is an equipment used to produce hot water. In an electric water heater wemake use of electrical energy to heat up the water content.The main component in a waterheater is a heating element. It also consists of all the pipe lines or pockets required toaccommodate the water inlet & outlet line, safety features etc. These pipes have to be fixed

with a base component by any convenient matal joining processes.

The major components required in a standard water heater are,

SI NO COMPONENTS REQUIRED MATERIAL PROPERTY PURPOSE

1 Container Good thermal resistivity To cotain the water

2 Heating element Good electrical resistivity To generate heat energy

3 Inlet Pipe Good Stability water intake

4 Outlet Pipe Good Stability Hot water outlet

5 Safety devices Good electrical conductivity To sense the temperatureand to keep it at therequired level.

The detailed description of an electric water heater which is given below,

1. HEATING ELEMENTThe prime genereator of heat energy. Here it makes use of its high electrical

resistivity property to produce heat. This heat generated is transmitted to water by convectionheat transfer.

Convection heat transfer is that mode of heat transfer in which the heat is transmitted

by the movement or circulation of molecules within the fluids(ie. Liquids and gases). It can'ttake place in solids since there is no significant diffusion happens in solids.

There 2 types of convectiona) Natural Convection b) Forced Convection

a) Natural ConvectionHere heat itself causes fluid motion via expansion and buoyancy while at the same timecausing heat to be transmitted by this bulk motion of the fluid.The onset of natural convection is determined by the Rayleigh's number,Ra and is given byRa=gL^3/D

Where, difference in densities between two parcels of material that aremixing

g local gravitational accelerationL characteristic length scale of convectionD diffusivity of the fluid dynamic viscosity of the fluid

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But we have the density variations due to thermal expansion as,

= 0Twhere,

0 reference density or average density

- co-efficient of thermal expansionT temperature difference across the medium

The general diffusivity 'D' is redefined as thermal diffusivity 'k'.

Inserting these substitutions produces a Rayleigh's no. that can be used to predictthe thermal convection as,

Ra=0TgL^3/k

b) Forced ConvectionIn forced heat convection, transfer of heat is due to the movements of fluid which isa result of some external forces such as a fan or a pump.

2. WATER INLET PIPEa) Inner Part

To supply water into the tank without disturbing the free flow of hot water through theoutlet pipe.The pipe hole size is deterministic in the time for complete filling of the waterinside.

b) Outer PartIt must have enough strength to withstand all the loads coming on it.

3. WATER OUTLET PIPEa) Inner Part

To deliver hot water outside the tank. The hot water taken out should not be mixedup with the cold water entring at the inlet.It must posses minimum value of mixingfactor. The pipe hole size is deterministic in the discharge of the water outside.b) Outer Part

It must have enough strength to withstand all the loads coming on it.

4. SAFETY FEATURESIn order to control the heating process, we would be introducing some safety devices thatwould be working with the help of the heat energy. Device will be having a sensing elementwhich responds to the heat changes which in turn actuates some mechanisms that finally cutsthe power supply. This mechanism comes to its initial state when the temperature inside thetank comes down. Thus it is able to control the heating process.