Heat exchanger capacity (condenser and evaporator)

In summary: A typical fan will give you much less.In summary, when conducting an experiment on a window-type air conditioner, it is best to measure changes in the refrigerant rather than the air. This eliminates the use of equations involving the specific heat and mass flow of the air. Instead, using the change in enthalpy of the refrigerant will provide more accurate results. Additionally, when considering the air, it is important to take into account the humidity and use a psychrometric chart for accurate calculations. The pressure increase caused by the fan blowing air is minimal and can be neglected.
  • #1
plucker_08
54
0
Window-type Aircon

how to get this in an actual experiment?

is it just (mass flow rate of the refrigerant X specific heat X Change in temp of the refrigerant)

or (mass flow rate of the air passing thru the heat exchanger X specific heat X Change in temp of the air)

or (mass flow rate of the refrigerant X change in enthalpy (outlet and inlet state of the refrigerant)

or (mass flow rate of the air X Change in enthalpy of the air)
 
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  • #2
First, think about what control volume you are doing the analysis on. Are you measuring the air or the refrigerant? Under ideal situations, the heat absorbed by the refrigerant is the same as the heat rejected in the room. But practically, you are much more likely to get good data measuring changes in the refrigerant.

This eliminates your second and fourth equations.

Your first equation assumes that the refrigerant is a perfect gas but because in a traditional vapor-compression refrigeration cycle the flow through a heat exchanger is typically two-phase this is a bad assumption, hence this equation does not apply.

Your third equation will allow you to properly calculate the amount of heat absorbed.
 
  • #3
The first response is fine, but just a quick fyi - if the air is dry, you can use the specific heat times delta-T times mass flow for the air, but if it is moist, you'll need to add the specific heat and mass flow of condensed water. But just using enthalpy instead covers that.

Btw, there is a recent thread about a window heat pump unit where I do this exact experiment. I'm trying to get a paper published.
 
  • #4
can i use the pyschrometric chart for 100KPa, even if the air is blown thru fan?

the air pressure increases when blown by fan, right?
 
  • #5
Yes, air pressure increases when blown through a fan, but not by much. A powerful air conditioning fan might give you 1kPa of pressure rise.
 

Related to Heat exchanger capacity (condenser and evaporator)

What is a heat exchanger capacity?

A heat exchanger capacity is the measure of how much heat can be transferred between two fluids in a given time period. It is typically measured in units of energy per unit time, such as BTU/hour or watts.

What is the difference between a condenser and an evaporator in a heat exchanger?

A condenser is a heat exchanger that is responsible for transferring heat from a hot fluid to a cooler fluid, while an evaporator is a heat exchanger that is responsible for transferring heat from a cool fluid to a warmer fluid.

How does the size of a heat exchanger affect its capacity?

The size of a heat exchanger, specifically the surface area of the heat transfer surfaces, directly affects its capacity. A larger heat exchanger will have a higher capacity due to the increased surface area available for heat transfer.

What factors can affect the capacity of a heat exchanger?

The capacity of a heat exchanger can be affected by several factors, including the type of fluids being used, the flow rate of the fluids, the temperature difference between the fluids, and the design and size of the heat exchanger.

How can the capacity of a heat exchanger be increased?

The capacity of a heat exchanger can be increased by increasing the surface area of the heat transfer surfaces, increasing the flow rate of the fluids, or increasing the temperature difference between the fluids. Additionally, using more efficient heat transfer materials or designs can also increase the capacity of a heat exchanger.

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