First Law of Thermodynamics

First Law of Thermodynamics
The first law of thermodynamics states that in any closed system, energy is conserved. Which means that energy cannot be created nor destroyed, but it can only
change forms. Meaning:
ΔEsys = 0 and ΔEproducts = -ΔEreactants

QUESTION.....?

Q: Which of the following can be called as a refrigeration process?
a) Cooling of hot ingot from 1000oC to room temperature
b) Cooling of a pot of water by mixing it with a large block of ice
c) Cooling of human beings using a ceiling fan
d) Cooling of a hot cup of coffee by leaving it on a table
e) Cooling of hot water by mixing it with tap water
f) Cooling of water by creating vacuum over it
Ans: b) and f)

NATURAL REFRIGERATION

Natural Refrigeration
In olden days refrigeration was achieved by natural means such as the use of ice or evaporative cooling. In earlier times, ice was either:
1. Transported from colder regions,
2. Harvested in winter and stored in ice houses for summer use or,
3. Made during night by cooling of water by radiation to stratosphere.

REFRIGERATION

Refrigeration may be defined as the process of achieving and maintaining a temperature below that of the surroundings, the aim being to cool some product or space to the required temperature.

SUBCOOLING

Subcooling
Let us now consider a single component refrigerant at a fixed pressure in a liquid state.
If we pass the liquid through a cooler its temperature will fall. The difference in temperature between the saturation temperature and the measured temperature is called the subcooling effect which is expressed in temperature units°C or °F. As an example of this let us consider water from the cold tap. The temperature of this water is usually about 5°C. The normal boiling point or saturation point of water at atmospheric pressure is 100°C so our tap water is said to be subcooled by 95°C. Hot water will still be subcooled by whatever the difference between is temperature and the boiling point is.
Subcooling is important in the expansion and evaporating parts of the refrigeration cycle.
Two phase

LATENT HEAT

Heat is added to the liquid (which in this case is water) causing it’s temperature to rise until it reaches its boiling point. When the liquid reaches its boiling point it begins to change into steam.
In order to change into steam the water requires additional energy from the heater element.The water temperature will not rise above the boiling point until all the liquid has been evaporated.This additional energy is known as latent heat.
Fig.3 shows the type of evaporator which we manufacture

Chain drive

Chain drive

Chain drive is a way of transmitting mechanical power from one place to another. It is often used to convey power to the wheels of a vehicle, particularly bicycles and motorcycles. It is also used in a wide variety of machines besides vehicles.Most often, the power is conveyed by a roller chain, known as the drive chain or transmission chain,passing over a sprocket gear, with the teeth of the gear meshing with the holes in the links of the chain. The gear is turned, and this pulls the chain putting mechanical force into the system.

Chains versus belts

Roller chain and sprockets is a very efficient method of power transmission compared to belts, with far less frictional loss.

Although chains can be made stronger than belts, their greater mass increases drive train inertia.


Drive chains are most often made of metal, while belts are often rubber, plastic, or other substances. Drive belts can slip unless they have teeth which means that the output side may not rotate at a precise speed, and some work gets lost to the friction of the belt against its rollers. Teeth on toothed drive belts generally wear faster than links on chains, but wear on rubber or plastic belts and their teeth is often easier to observe.