# How Do I Calculate Internal Heat Transfer Rates in a Plate Chiller System?

• johnp909
In summary, a person is working on a design project for school involving a plate chiller that cools hot liquid. They have researched and calculated various factors, but are struggling with determining the heat transfer rate inside the plate due to changing temperatures and fluid flow. They are considering using the LMTD method, but are unsure if it is applicable in this situation. They are seeking advice or guidance.
johnp909
Hi There.

I'm currently working on a design project for school. Basically its a plate chiller which is lowered into a pot of hot liquid. The plates have channels in them thru which water will flow, the result being cooling of the hot liquid in the pot.

I've done a lot of research and reading in my fluid science book and I can't figure out the direction to go in my calcuations.

Here's what I know so far...

I have the specifics for the hot liquid. Thermal properties, mass volume, intended starting temperature and final temperature for the liquid etc. As well as a goal for the time that this process will take.

I know the total heat to be removed. Calculated that.

I know the heat transfer rate on the outside of the plates by convection. I calculated that using lumped system analysis and calculating coefficient of convection for a vertical plates. etc.

The thing that's got me crossed up is figuring out how to calculate the heat transfer rate inside the plate. I know the dimensions of the channels. At least as a starting point.

I understand that...

Heat Transfer Rate = mass flow rate x Cp x Difference in Temperature

and

Heat Transfer Rate = convection coefficient x cooling area x Difference in Temperature

The Thing that confuses me is that in this system the temperature of the hot liquid is changing over time as it's cooled this will slow the heat transfer rate. In addition the cooling fluid is raising temperature as it flows thru, therefore removing less heat at the end then at the begining.

It seems like LMTD only deals with constant inlet and outlet temperature situations. This seems different to me.

If the fluid residence time is short in the heat exchange is short, you can still assume quasi steady state and employ the LMTD.

## 1. What is heat transfer and why is it important?

Heat transfer is the movement of thermal energy from one object to another. It is important because it helps regulate temperature and allows for the transfer of energy in various systems, such as in the human body, in buildings, and in industrial processes.

## 2. What are the three modes of heat transfer?

The three modes of heat transfer are conduction, convection, and radiation. Conduction is the transfer of heat through direct contact between two objects, convection is the movement of heat through a fluid or gas, and radiation is the transfer of heat through electromagnetic waves.

## 3. How is heat transfer calculated?

The rate of heat transfer can be calculated using the equation Q=mcΔT, where Q is the heat transferred, m is the mass of the object, c is the specific heat capacity of the object, and ΔT is the change in temperature.

## 4. What factors affect heat transfer?

The rate of heat transfer is affected by several factors, including the temperature difference between the objects, the thermal conductivity of the materials, the surface area of the objects, and the distance between them.

## 5. How can heat transfer be controlled or manipulated?

Heat transfer can be controlled or manipulated by using insulating materials to reduce the rate of heat transfer, by increasing or decreasing the surface area of the objects, and by adjusting the temperature difference between the objects. Additionally, heat transfer can be enhanced by using materials with high thermal conductivity and by increasing the surface area or temperature difference.

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