Creating a Heat Exchanger for an Aesthetic/Medical Laser System

Creating a Heat Exchanger for an Aesthetic/Medical Laser System.

Several characteristics must be considered while constructing a heat exchanger for an aesthetic/medical laser system (laser, IPL, RF, and ultrasound). In this piece, we will go over some of the most important parameters.

Determine how much heat will be removed from the heat source, which could be a laser, IPL, RF, or ultrasonic. The next step is to add the heat created by the pump and fan while they are running, as well as some safety overhead, to the heat from our heat source. This is crucial because if the heat exchanger is designed below that total heat capacity, our system will not have stable working conditions for a lengthy period of time and will finally shut down due to overheating.

The liquid used in the cooling system and heat exchanger is also significant. The type of liquid effects both the materials used to make the heat exchanger and the system's actual thermal performance.

If deionized water is used, the heat exchanger must be built using medical-grade stainless-steel tubing (such as 316 stainless-steel). If deionized water is used with non-stainless-steel tubing, it will pollute the system and cause leaks.

If the liquid is not corrosive, the heat exchanger can be built with non-stainless-steel tubes. It is crucial to realize that adding inhibitors to corrosive liquids (such as deionized water) does not totally eliminate the corrosiveness issue, and so using non-stainless-steel tubing will offer the same issues mentioned above, albeit at a slower rate.

The available area for the heat exchanger is critical. It is critical to study and obtain the right size while considering the thermodynamic characteristics as well as the cost-benefit analysis when designing the proper heat exchanger. Surface ratio, air flow speed, heat exchange area, and other parameters will assist us in determining the appropriate size.

The ambient temperature has a considerable impact on the performance of the cooling system. When the system is in a stable working state, any change in ambient temperature or the temperature of the air passing through the heat exchanger will cause the total system temperature to rise or fall. Another key consideration is that the closer the ambient temperature is to the temperature of the liquid entering the heat source, the more difficult it will be to remove that heat. Trying to remove 600 watts of heat with an ambient temperature of 24° C is not the same as attempting to remove the same amount of heat with an ambient temperature of 30° C. Working in an air-conditioned facility at around 24° C is common in many Western countries, but in countries such as India, China, and others, this is not the norm, and the ambient temperature can approach 32° C. We propose that the cooling system be designed for an ambient temperature of 30° C - 32° C.

We can proceed with the actual heat exchanger design once we have the general requirements:

Heat exchanger size - With the available liquid and the set ambient temperature, the heat exchanger size must be able to remove the needed amount of heat. The correct flow of air and liquid, as well as the pressure drop for both, should be considered in the design.

Pump choice - A few things must be considered when choosing a pump. One of the most significant requirements is that the pump supply the flow rate required by the heat source (diode, lamp, RF or ultrasound). Also, the pump must be made of materials that are compatible with the liquid we are utilizing. Another critical aspect to consider is the pump's ability to handle the pressure drop induced by the heat exchanger when operating at the required flow rate, as well as the aggregate pressure drop caused by other sections of the cooling system, such as pipes, connectors, and so on. We must confirm and verify, using the pump manufacturer's data, that we will be able to utilize the pump and achieve the requisite flow rate while dealing with the overall aggregated pressure drop we predicted for our system. The heat exchanger must be tuned to get the highest flow rate with the least amount of pressure drop. It is usual for heat exchangers to be designed with a pressure drop range of 0.2 kPa - 0.3 kPa. Dealing with pressure drops outside of this range can have a severe impact on the thermal performance of the heat exchanger and lower the pump's life expectancy. The pressure drop created by the heat exchanger is determined by the length and radius of the pipework in the heat exchanger, which were chosen to remove the necessary quantity of heat at the set flow rate. This problem can be solved by designing the heat exchanger with several circuits.

Fan selection - While choosing a fan, numerous factors must be addressed.

The volume of air required is determined by the total amount of heat to be evacuated and the cooling system's required performance.

Maximum pressure drop permitted - We must locate the point on the fan's graph where we will receive adequate airflow vs. the pressure drop caused on the heat exchanger's surface. When analyzing the air flow, we must consider the air speed across the surface of the heat exchanger. The pressure drop is controlled by both the air speed across the surface of the heat exchanger and the actual surface size, depth, and distances between the fins.

Noise level required

Working liquid temperature - If we are constructing a system with a liquid temperature above 50° C, we must ensure that the fan is built to work in these conditions.

It is critical to remember that while still in the design stage, we must work to achieve the optimal point that takes into account the surface area for heat transfer, heat exchanger surface area, air flow speed, and minimal pressure drop. Our system can be optimized by adjusting the heat transfer area and the distances between the fins. Furthermore, if we already know the pump specifications, we can proceed with the thermal calculations for our chosen working point and choose a specific fan based on the thermal calculation results for air flow and pressure drop.

Heat exchanger design and installation best practices:

After considering all working and thermal parameters, it is critical to ensure that all components are synchronized with the heat exchanger and that the cooling system is at the proper working point.

In the case of deionized water with stainless steel heat exchanger tubing, a certain standard of welding is required, which is done with Argon (inert gas) to protect the welding environment.

If the heat exchanger is stainless steel, it must be cleaned correctly at the end of the manufacturing process. This involves the elimination of any oil deposits (by melting) as well as any other welding process leftovers. Eventually, a passivation process must be completed to seal all heat exchanger surfaces. The longer and more extensive the passivation process, the higher the working temperature of the heat exchanger.

It is strongly advised to install the fan in a sealed-off enclosure to enhance air flow and ensure uniform flow across the heat exchanger. It is advised that the fan be installed at a minimum distance of 25 millimeters from the heat exchanger's edge. With this distance, the air coming out of the fan has time to "straighten," resulting in a more uniform flow. Another thing to keep in mind is that the fan should be placed for air suction. This method has several key advantages:

The heat exchanger performs better because a larger volume of air passes through it.

The noise level will be significantly reduced.

Assured air flow by using air from outside the system that is at the ambient temperature for which the system was designed, rather than air from inside the system that is warmer than the ambient temperature. If we use the air inside the system and have it flow through our heat exchanger, we must evaluate the difference in temperature between the inside and outside air to ensure that we can still remove the appropriate quantity of heat. If we must use air from within the system, we must ensure that there are enough ventilation apertures to allow maximum fresh air, at the ambient temperature, to enter the system. Furthermore, we must ensure that the airflow to and from the heat exchanger is not impeded at any point.

Heat exchanger installation is similarly important: we recommend installing the heat exchanger at the system's edge and the fan in suction mode inside so that the suction of outside air through the heat exchanger is maximized.

It is critical that the heat exchanger be installed with the fluid ports (both in and out) towards the bottom, so that we may totally empty the heat exchanger of ALL fluids if necessary. During transit, the system may be extremely cold (as low as -20° C). If the system is exposed to such high temperatures for an extended period of time and any fluid is left inside the heat exchanger, the fluid may freeze and may shatter the tubing, resulting in a leak when the system is turned on.

It is advised that the thermal calculation be performed first. To achieve the best results, we recommend running numerous working situations, even extreme ones. Utilizing the best thermal calculation first, and then the mechanical calculation, we will be able to construct the optimal heat exchanger with the best (gold) cost-benefit ratio.

The design of a heat exchanger is a complex procedure that has a direct impact on the overall system performance. Many elements and variables must be considered, and if all of them are, we will end up with an effective and reliable system that uses the ideal heat exchanger while considering the cost-benefit analysis (while retaining the system's dependability and effectiveness).

Our professionals at Vrcoolertech are prepared to assist you with any of your heat exchanger requirements. Our website contains additional information.