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TRANSMISSIVITY is DEFINED as the ratio of RADIATION transmitted to the incident radiation.

Transmissivity, τ = Radiation transmitted / Incident radiation.

Transmissivity is defined as the ratio of radiation transmitted to the incident radiation.

Transmissivity, τ = Radiation transmitted / Incident radiation.

REFRIGERATION effect is the total heat REMOVED from the refrigerant in the evaporator.

COP = Refrigeration effect / Work DONE.
Refrigeration effect = COP x Work done.

Refrigeration effect is the total heat removed from the refrigerant in the evaporator.

COP = Refrigeration effect / Work done.
Refrigeration effect = COP x Work done.

Advantages:

• 1. The refrigerant used namely air is cheap and easily AVAILABLE.
• 2. There is no danger of fire or toxic effects due to leakages.
• 3. The weight to tonne of refrigeration ratio is LESS as compared to other systems.

Disadvantages:

• 1. The quantity of refrigerant used per tonne of refrigeration is HIGH as compared to other system.
• 2. The COP of the system is very LOW. Therefore running cost is high.
• 3. The danger of frosting at the expander valves is more as the air CONTAINS moisture content.

Advantages:

Disadvantages:

REFRIGERATION is the process of providing and maintaining the TEMPERATURE in space below atmospheric temperature. Air CONDITIONING is the process of supplying SUFFICIENT volume of clean aircontaining a specific amount of water vapour and maintaining the predeterminedatmospheric condition with in a SELECTED enclosure.

Refrigeration is the process of providing and maintaining the temperature in space below atmospheric temperature. Air conditioning is the process of supplying sufficient volume of clean aircontaining a specific amount of water vapour and maintaining the predeterminedatmospheric condition with in a selected enclosure.

The HEAT exchanger EFFECTIVENESS is DEFINED as the ratio of ACTUAL heat transfer to the maximum possible heat transfer.

Effectiveness ε = Actual heat transfer / Maximum possible heat transfer = Q / Qmax

The heat exchanger effectiveness is defined as the ratio of actual heat transfer to the maximum possible heat transfer.

Effectiveness ε = Actual heat transfer / Maximum possible heat transfer = Q / Qmax

We know that the temperature difference between the hot and COLD fluids in the heat exchanger VARIES from point to point. In addition various modes of heat transfer are involved. Therefore based on concept of appropriate mean temperature difference, ALSO called logarithmic mean temperature difference, the total heat transfer rate in the heat exchanger is expressed as

Q = U A [∆T]m

Where, U=Overall heat transfer co-coefficient [W/m2K], A=Area, M2
[∆T]m = Logarithmic mean temperature difference.

We know that the temperature difference between the hot and cold fluids in the heat exchanger varies from point to point. In addition various modes of heat transfer are involved. Therefore based on concept of appropriate mean temperature difference, also called logarithmic mean temperature difference, the total heat transfer rate in the heat exchanger is expressed as

Q = U A [∆T]m

Where, U=Overall heat transfer co-coefficient [W/m2K], A=Area, m2
[∆T]m = Logarithmic mean temperature difference.

In this TYPE of HEAT EXCHANGER, hot and cold FLUIDS move in the same direction.

In this type of heat exchanger, hot and cold fluids move in the same direction.

In this type of HEAT exchangers, the transfer of heat between TWO fluids COULD be carried out by TRANSMISSION through a WALL which separates the two fluids.

In this type of heat exchangers, the transfer of heat between two fluids could be carried out by transmission through a wall which separates the two fluids.

In DIRECT contact heat exchanger, the heat exchange TAKES PLACE by direct mixing of hot and COLD fluids.

In direct contact heat exchanger, the heat exchange takes place by direct mixing of hot and cold fluids.

Absorptivity is DEFINED as the RATIO between RADIATION ABSORBED and incident radiation. Absorptivity, α = Radiation absorbed / Incident radiation.

Absorptivity is defined as the ratio between radiation absorbed and incident radiation. Absorptivity, α = Radiation absorbed / Incident radiation.

σ = Stefan BOLTZMANN constant = 5.6697 X 10-8 W/ (m² K4).

σ = Stefan Boltzmann constant = 5.6697 x 10-8 W/ (m² K4).

HEAT transfer from the moving fluid to SOLID surface is given by the equation.

Q = h A = [TW – T∞]

This equation is REFERRED to as Newton’s law of cooling.
Where h = Local heat transfer coefficient in W/m2K.
A = Surface AREA in m2
Tw = Surface [or] Wall temperature in K.
T∞ = Temperature of fluid in K.

Heat transfer from the moving fluid to solid surface is given by the equation.

Q = h A = [Tw – T∞]

This equation is referred to as Newton’s law of cooling.
Where h = Local heat transfer coefficient in W/m2K.
A = Surface area in m2
Tw = Surface [or] Wall temperature in K.
T∞ = Temperature of fluid in K.

It is DEFINED as the RATIO of INERTIA FORCE to VISCOUS force.

Re = Inertia force / Viscous force

It is defined as the ratio of inertia force to viscous force.

Re = Inertia force / Viscous force

1. REYNOLDS number [Re].
2. NUSSELT number [Nu].
3. Prandtl number [PR].

LAMINAR flow: Laminar flow is sometimes called stream LINE flow. In this type of flow, the fluid moves in layers and each fluid PARTICLE follows a smooth continuous PATH. The fluid particles in each layer remain in an orderly sequence without mixing with each other.

Laminar flow: Laminar flow is sometimes called stream line flow. In this type of flow, the fluid moves in layers and each fluid particle follows a smooth continuous path. The fluid particles in each layer remain in an orderly sequence without mixing with each other.

The FLUIDS which obey the NEWTON’s LAW of viscosity are called Newtonian fluids and those which do not obey are called no-newtonian fluids.

The fluids which obey the Newton’s law of viscosity are called Newtonian fluids and those which do not obey are called no-newtonian fluids.

It is the ratio of Nusselt number to the PRODUCT of REYNOLDS number andPrandtl number.

St = NU / Re X Pr.

It is the ratio of Nusselt number to the product of Reynolds number andPrandtl number.

St = Nu / Re x Pr.

It is DEFINED as the ratio of PRODUCT of inertia FORCE and buoyancy force to the square of VISCOUS force.

GR = Inertia force x Buoyancy force / [Viscous force]2

It is defined as the ratio of product of inertia force and buoyancy force to the square of viscous force.

Gr = Inertia force x Buoyancy force / [Viscous force]2

It is FLUID motion is produced due to change in density resulting from TEMPERATURE GRADIENTS, the mode of heat TRANSFER is SAID to be free or natural convection.

It is fluid motion is produced due to change in density resulting from temperature gradients, the mode of heat transfer is said to be free or natural convection.

1. MOISTURE
2. Density of MATERIAL
3. Pressure
4. TEMPERATURE e. STRUCTURE of material.

Answer :THERMAL conductivity is defined as the ABILITY of a SUBSTANCE to CONDUCT HEAT.

Answer :The RATE of heat conduction is proportional to the area measured normal to the direction of heat FLOW and to the TEMPERATURE gradient in that direction. Q α – A dT / dx Q = -kA dT /dx Where, A – Area in m2 dT / dx – Temperature gradient, K/m k – Thermal CONDUCTIVITY, W/mK.

Answer :HEAT conduction is a MECHANISM of heat transfer from a region of high temperature to a region of low temperature within a medium [solid, liquid or GASES] or different medium in direct PHYSICAL contact.

1. CONDUCTION
2. CONVECTION
3. RADIATION.

Answer :Heat TRANSFER can be DEFINED as the transmission of energy from one REGION to another DUE to temperature DIFFERENCE.